Errymath

Radars On Track To See Through Stealth Fighter

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F-35B Lightning II aircraft takes off from the amphibious assault ship USS Wasp (LHD-1)</div>
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<img alt="In this July 7, 2006 photo, the Lockheed Martin F-35 Joint Strike Fighter is shown after it was unveiled in a ceremony in Fort Worth, Texas. " height="292" src="http://cdn.defenseone.com/media/img/upload/2015/11/11/AP_200691809359/defense-large.jpg" title="In this July 7, 2006 photo, the Lockheed Martin F-35 Joint Strike Fighter is shown after it was unveiled in a ceremony in Fort Worth, Texas. " width="640" /><br />
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A former senior U.S. Navy official told USNI 
News that</div>
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U.S. fighters — like the Lockheed Martin F-22 Raptor and F-35 
Lighting II Joint Strike Fighter (JSF) — are protected by stealth 
technology optimized for higher frequency targeting radars but not for 
lower frequency radars.<br />
Until now a focus on higher frequencies have not been a problem 
because low frequency radars have traditionally been unable to generate 
“weapons quality tracks.”<br />
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JSF and the F-22 are protected from higher frequencies in the Ku, X, C
 and parts of the S bands. But both jets can be seen on enemy radars 
operating in the longer wavelengths like L, UHF and VHF.<br />
In other words, Russian and Chinese radars can generally detect a 
stealth aircraft but not clearly enough to give an accurate location to a
 missile<br />
But that is starting to change.<br />
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“Acquisition and fire control radars are starting to creep down the 
frequency spectrum,” a former senior U.S. Navy official told USNI News.<br />
With improved computing power, low frequency radars are getting better and better at discerning targets more precisely.<br />
“I don’t see how you long survive in the world of 2020 or 2030 when 
dealing with these systems if you don’t have the lower frequency 
coverage,” the former official said.<br />
Further, new foreign rival warships are increasingly being built with both high and low frequency radars.<br />
“Prospective adversaries are putting low frequency radars on their 
surface combatants along with the higher frequency systems,” the former 
official said.<br />
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“If you don’t have the signature appropriate to that [radar], you’re not going to be very survivable,” he said.<br />
“The lower frequency radars can cue the higher frequency radars and now you’re going to get wacked.” <br />
Nor will the Navy’s <a href="http://news.usni.org/2014/01/23/navys-next-air-war">vaunted Naval Integrated Fire Control-Counter Air (NIFC-CA)</a>
 do much to help the situation. Firstly, given the proliferation of low 
frequency radars, there are serious questions about the ability of the 
F-35C’s survivability against the toughest of air defenses, the former 
official said.<br />
“All-aspect is highly desirable against this sort of networked [anti-air] environment,” he said.<br />
Secondly, the Chinese and Russians are almost certain to use cyber and 
electronic attack capabilities to disrupt NIFC-CA, which is almost 
totally reliant on data links.<br />
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“I question how well all these data links are going to work in a 
heavily contested [radio frequency] environment where you have lots and 
lots of jamming going on,” the former official said.<br />
Moreover, in certain parts of the world potential adversaries —China 
and Russia— are developing long-range anti-radiation missiles that could
 target the central node of the NIFC-CA network—the Northrop Grumman 
E-2D Advanced Hawkeye.<br />
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“I think the anti-radiation homing weapons that are passive and go 
long-range are very, very difficult for the NIFC-CA concept to contend 
with,” the former official said.<br />
Fundamentally, the Navy’s lack of an all-aspect broadband stealth jet
 on the carrier flight deck is giving fuel to advocates of a high-end 
Unmanned Carrier Launched Airborne Surveillance and Strike (UCLASS) 
aircraft that can tackle the toughest enemy air defenses.<br />
Without such capability, the Navy’s carrier fleet will fade into irrelevance, the former official said.<br />
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<h1 class="d1-post-title">
<span style="font-size: x-large;">Scientists Unveil New Stealth Material Breakthrough</span></h1>
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<b>A group of scientists from China may </b>have created a 
stealth material that could make future fighter jets very difficult to 
detect by some of today’s most cutting-edge anti-stealth radar.<br />
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<aside class="d1-author-bio-container"><br /><div class="d1-author-bio with-image">
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Patrick Tucker is technology editor for Defense One. He’s also 
the author of The Naked Future: What Happens in a World That Anticipates
 Your Every Move? (Current, 2014). Previously, Tucker was deputy editor 
for The Futurist for nine years. Tucker has written about emerging 
technology in Slate, </div>
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The researchers developed a new material they say can defeat microwave radar at ultrahigh frequencies, or <span class="caps">UHF</span>. 
 Such material is usually too thick to be applied to aircraft like 
fighter jets, but this new material is thin enough for military 
aircraft, ships, and other equipment.<br />
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Today’s synthetic aperture radar use arrays of antennas directing 
microwave energy to essentially see through clouds and fog and provide 
an approximate sense of the object’s size, the so-called radar cross 
section. With radar absorbent material not all of the signal bounces 
back to the receiver. A plane can look like a bird.<br />
<br />
“Our proposed absorber is almost ten times thinner than conventional 
ones,” said Wenhua Xu, one of the team members from China’s Huazhong 
University of Science and Technology, in a statement.<br />
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In their paper, published today in the<a href="http://scitation.aip.org/content/aip/journal/jap/118/18/10.1063/1.4934683"> Journal of Applied Physics</a>,
 the team describes a material composed of semi-conducting diodes 
(varactors) and capacitors that have been soldered onto a printed 
circuit board. That layer is sitting under a layer of copper resistors 
and capacitors just .04 mm thick, which they called an “active frequency
 selective surface material” or <span class="caps">AFSS</span>. The <span class="caps">AFSS</span>
 layer can effectively be stretched to provide a lot of absorption but 
is thin enough to go onto an aircraft. The next layer is a thin metal 
honeycomb and final is a metal slab.<br />
The good news: the material isn’t locked away in a lab but published openly, so it’s not going to surprise anyone.<br />
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<a href="http://scitation.aip.org/content/aip/journal/jap/118/18/10.1063/1.4934683" target="_blank">An ultra-thin broadband active frequency selective surface absorber for ultrahigh-frequency applications</a></h2>
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<u><span style="color: blue;"><span style="font-weight: normal;">Abstract</span></span></u></h3>
At frequencies below 2 GHz, conventional <span class="named-content">microwave</span>
 absorbers are limited in application by their thickness or narrow 
absorption bandwidth. In this paper, we propose and fabricate an 
ultra-thin broadband active frequency selective surface (AFSS) absorber 
with a stretching transformation (ST) pattern for use in the 
ultrahigh-frequency (UHF) band. This absorber is loaded with <span class="named-content">resistors</span> and varactors to produce its tunability. To expand the tunable bandwidth, we applied the ST with various coefficients <span class="jp-italic">x</span> and <span class="jp-italic">y</span> to the unit cell pattern. With ST coefficients of <span class="jp-italic">x</span> = <span class="jp-italic">y</span> 
= 1, the tunability and strong absorption are concisely demonstrated, 
based on a discussion of impedance matching. On analyzing the patterns 
with various ST coefficients, we found that a small <span class="jp-italic">x</span>/<span class="jp-italic">y</span> effectively expands the tunable bandwidth. After this analysis, we fabricated an AFSS absorber with ST coefficients of <span class="jp-italic">x</span> = 0.7 and <span class="jp-italic">y</span> = 1. Its measured <span class="named-content">reflectivity</span>
 covered a broad band of 0.7–1.9 GHz below −10 dB at bias voltages of 
10–48 V. The total thickness of this absorber, 7.8 mm, was only ∼λ/54 of
 the lower limit frequency, ∼λ/29 of the center frequency, and ∼λ/20 of 
the higher limit frequency. Our measurements and simulated results 
indicate that this AFSS absorber can be thin and achieve a broad 
bandwidth simultaneously.</div>
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<a href="https://www.blogger.com/null" id="s1" name="s1">I. INTRODUCTION</a></div>
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Microwave absorbers can effectively reduce the radar cross sections 
of aircraft, and so they are commonly used in stealth missions. However,
 as radar detection equipment that is developed that can extend to the 
near-meter microwave wavelength regime, high-performance absorbers are 
required, especially in the ultrahigh-frequency (UHF) band below 2 GHz. 
Unfortunately, absorbers are usually thick and have relatively narrow 
absorption bandwidth.<br />
Conventional λ/4 Salisbury screen absorbers are widely used for high 
frequencies, but absorbers of microwaves with near-meter wavelengths can
 be very thick.<span class="xref"><a href="http://scitation.aip.org/content/aip/journal/jap/118/18/10.1063/1.4934683#c1"><sup>1–3</sup></a></span>
 Fortunately, work on metamaterials has shown that a resonant metallic 
structure printed on a dielectric substrate acts as a strong resonant 
absorber, and such a metamaterial absorber is significantly thinner than
 the wavelengths absorbed.<span class="xref"><a href="http://scitation.aip.org/content/aip/journal/jap/118/18/10.1063/1.4934683#c4"><sup>4–6</sup></a></span> For example, Costa <span class="jp-italic">et al</span>.
 designed an electromagnetic (EM) absorber for a radio frequency 
identification device (RFID) system made of a painted patch array; this 
absorber had a narrow working bandwidth (865–868 MHz), but its thickness
 was only λ/44 of the resonance frequency.<span class="xref"><a href="http://scitation.aip.org/content/aip/journal/jap/118/18/10.1063/1.4934683#c7"><sup>7</sup></a></span><br />
Ideal absorbers exhibit broadband performance. Research on active 
frequency selective surfaces (AFSSs) shows that a frequency selective 
surface (FSS) loaded with lumped elements, such as varactors<span class="xref"><a href="http://scitation.aip.org/content/aip/journal/jap/118/18/10.1063/1.4934683#c8"><sup>8–11</sup></a></span> and PIN diodes,<span class="xref"><a href="http://scitation.aip.org/content/aip/journal/jap/118/18/10.1063/1.4934683#c12"><sup>12–15</sup></a></span>
 can exhibit a tunable absorption bandwidth. For instance, an FSS 
absorber loaded with PIN diodes has a tunable bandwidth of 5.3–13 GHz 
below −10 dB,<span class="xref"><a href="http://scitation.aip.org/content/aip/journal/jap/118/18/10.1063/1.4934683#c8"><sup>8</sup></a></span> and using varactors in a three-layer FSS absorber can produce a tunable bandwidth of 1.8–2.4 GHz.<span class="xref"><a href="http://scitation.aip.org/content/aip/journal/jap/118/18/10.1063/1.4934683#c14"><sup>14</sup></a></span> Specifically, Kong <span class="jp-italic">et al</span>. presented a tunable FSS absorber loaded with both PIN diodes and varactors for broadband application.<span class="xref"><a href="http://scitation.aip.org/content/aip/journal/jap/118/18/10.1063/1.4934683#c16"><sup>16</sup></a></span>
 These studies show that the resistance of the PIN diode and the 
capacitance of the varactor contribute to the input impedance of the 
absorber. At different bias voltages, the absorber impedance matches 
with free space at different frequencies, and thus the envelope of 
reflectivity curves measured at various bias voltages covers a broad 
absorption bandwidth. This result suggests that AFSS absorbers are 
practical candidates for broadband applications. As such, we believe it 
is possible to design an absorber that is both thin and that exhibits a 
broad bandwidth for near-meter microwave applications.<br />
In this paper, we present an ultra-thin broadband AFSS absorber with a
 stretching transformation (ST) pattern for use in UHF applications. 
Using the transmission line (TL) model, we give the resonance frequency 
and the real part of the input impedance as functions of loaded and 
distributed parameters. The device's ST coefficients of <span class="jp-italic">x</span> = <span class="jp-italic">y</span> 
= 1 demonstrate its tunability and strong absorption. Then, to expand 
the tunable bandwidth, we apply various ST coefficients to the unit cell
 pattern. We also fabricated the proposed ultra-thin absorber, finding 
that its measured reflectivity covered a broad bandwidth in the UHF band
 below 2 GHz.<br />
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<a href="https://www.blogger.com/null" id="s2" name="s2">II. AFSS ABSORBER WITH VARIOUS ST COEFFICIENTS FOR ITS UNIT CELL PATTERN</a></div>
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<span class="label">A. 
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<span class="tl-lowest-section">Unit cell structure</span>

Figure <span class="xref"><a href="http://scitation.aip.org/content/aip/journal/jap/118/18/10.1063/1.4934683#f1">1</a></span>
 shows the structure of the proposed absorber. The top layer is FR4 with
 a thickness of 0.8 mm, which has a sufficient mechanical strength to 
hold up all the units. The next layer is the AFSS loaded with resistors 
and capacitors, and the thickness of the copper is 0.04 mm. The third 
layer, used as a separation layer, is a 7.0-mm honeycomb with very low 
dielectric loss (<span class="jp-italic">ε</span> = 1.07(1 − <span class="jp-italic">i</span>0.0024) and <span class="jp-italic">μ</span> = 1) in the frequency range studied here. The bottom layer is a metallic slab. Figure <span class="xref"><a href="http://scitation.aip.org/content/aip/journal/jap/118/18/10.1063/1.4934683#f1">1(b)</a></span> shows the unit cell pattern, which is based on a bow-tie dipole.<span class="xref"><a href="http://scitation.aip.org/content/aip/journal/jap/118/18/10.1063/1.4934683#c11"><sup>11,17</sup></a></span> It is composed of a triangle, a semicircle with a radius of <span class="jp-italic">r</span>, and two rectangles each with the dimensions 2<span class="jp-italic">r</span> × <span class="jp-italic">b</span>.
 The width of the bias line is 1 mm. At the center of the pattern, there
 is a gap of 1 mm for lumped elements. A varactor with variable 
capacitance <span class="jp-italic">C<span class="jp-sub">variable</span></span> is connected in parallel to a resistor <span class="jp-italic">R</span>. <span class="jp-italic">L<span class="jp-sub">d</span></span> and <span class="jp-italic">C<span class="jp-sub">d</span></span> are the distributed parameters generated by the topological structure of the unit cell pattern.<br />
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<span class="captionLabel"><span class="label">FIG. 1.</span></span><span class="captionText">Model of the absorber. (a) Structure of the absorber. (b) The unit cell pattern with ST coefficients <span class="jp-italic">x</span> and <span class="jp-italic">y</span>.</span><br />
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With High-Frequency Structure Simulator (HFSS) electromagnetic 
simulation software, one can accurately simulate and optimize absorption
 performance. Figure <span class="xref"><a href="http://scitation.aip.org/content/aip/journal/jap/118/18/10.1063/1.4934683#f2">2</a></span>
 shows our model built in HFSS. The Floquet port is assigned to the top 
boundary along the k direction, and the bottom boundary is grounded by a
 plate made of a perfect electric conductor. The periodical boundary 
condition (master-slave boundary) is adopted in the air layer. The 
incident wave is modeled as a normal incident wave with the electric 
field polarized along the E axis. Finally, the resistor and varactor are
 simulated using a lumped LRC model.<br />
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<span class="captionLabel"><span class="label">FIG. 2.</span></span><span class="captionText">Three-dimensional model built in HFSS.</span><br />
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To meet the needs of applications in the UHF band below 2 GHz, we 
consider both the resonance frequency as well as the absorption 
bandwidth. Setting <span class="jp-italic">C<span class="jp-sub">variable</span></span> = 1 pF, we optimize the dimensions of the unit cell pattern by using a genetic algorithm.<span class="xref"><a href="http://scitation.aip.org/content/aip/journal/jap/118/18/10.1063/1.4934683#c18"><sup>18</sup></a></span> In this optimization, the resonance frequency <span class="jp-italic">f<span class="jp-sub">0</span></span> must be smaller than 2 GHz and ideally as low as possible. (2 − <span class="jp-italic">f<span class="jp-sub">0</span></span>) is the deviation of <span class="jp-italic">f<span class="jp-sub">0</span></span> from 2 GHz. The relative bandwidth is written as <span class="jp-italic">BW</span>/<span class="jp-italic">f<span class="jp-sub">0</span></span>, where <span class="jp-italic">BW</span> is the bandwidth with the reflectivity below −10 dB. Overall, the goal function is
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<span class="label">(1) 
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where <span class="jp-italic">m</span> and <span class="jp-italic">n</span>
 are the weighting factors of relative bandwidth and resonance 
frequency. Such a treatment is helpful in achieving better absorption at
 lower frequency. The optimized parameters of the unit cell are <span class="jp-italic">r</span> = 20 mm and <span class="jp-italic">b</span> = 2 mm.

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<span class="label">B. 
    </span>

<span class="tl-lowest-section">Transmission line model of the absorber</span>

Absorptivity can be described by <span class="jp-italic">A</span>(ω) = 1 − <span class="jp-italic">R</span>(ω)− <span class="jp-italic">T</span>(ω), where <span class="jp-italic">R</span>(ω) is the power reflection coefficient and <span class="jp-italic">T</span>(ω) is the power transmission coefficient. When the reflection coefficient and transmission coefficient are calculated by <span class="jp-italic">R</span>(ω) = s11<sup>2</sup> and <span class="jp-italic">T</span>(ω) = s21<sup>2</sup>, the absorptivity is described as <span class="jp-italic">A</span>(ω) = 1 − s11<sup>2 </sup>− s21<sup>2</sup>. For an absorber grounded with metal slab, the transmission coefficient <span class="jp-italic">T</span>(ω)
 equals zero. To minimize reflection of the incident wave, the intrinsic
 impedance of the material must be matched to that of free space. In 
effective medium theory, effective permittivity (<span class="jp-italic">ε = ε′ + iε′′</span>) and effective permeability (<span class="jp-italic">μ = μ′ + iμ′′</span>) are generally used to analyze absorptivity, because the characteristic impedance of a material can be defined as <span class="capture-id">
</span>. In previous work on metamaterials and ferrite-based absorbers,<span class="xref"><a href="http://scitation.aip.org/content/aip/journal/jap/118/18/10.1063/1.4934683#c19"><sup>19–22</sup></a></span>
 the effective permittivity and effective permeability are easily 
measured or calculated. However, in some cases, the EM parameters cannot
 be obtained. In such a case, the TL model is a powerful tool to 
characterize and interpret this novel structure.<br />
The unit cell of the proposed AFSS absorber is recognized as a 
microstrip line resonator loaded with a varactor and a resistor in the 
center. The electromagnetic wave is perpendicularly incident to the 
AFSS, with the electric field polarized along the E axis and the 
magnetic field polarized along the H axis. When the unit cell resonates,
 it exhibits pure resistance, and its total input reactance is zero. If 
the resonator is modeled by a capacitor <span class="jp-italic">C<span class="jp-sub">s</span></span> cascaded with an inductor <span class="jp-italic">L<span class="jp-sub">s</span></span>, the resonance frequency of the absorber will be <span class="capture-id">
</span>. Figure <span class="xref"><a href="http://scitation.aip.org/content/aip/journal/jap/118/18/10.1063/1.4934683#f3">3(a)</a></span> gives a rough equivalent circuit model of the absorber. <span class="jp-italic">C<span class="jp-sub">variable</span></span>
 is the capacitance of the varactor. As the bias voltage decreases, the 
capacitance of varactor increases, thus shifting the resonant point to a
 lower frequency. The simulated results in Figures <span class="xref"><a href="http://scitation.aip.org/content/aip/journal/jap/118/18/10.1063/1.4934683#f3">3(b)</a></span> and <span class="xref"><a href="http://scitation.aip.org/content/aip/journal/jap/118/18/10.1063/1.4934683#f3">3(d)</a></span> agree well with the rough equivalent circuit model. As shown in Figure <span class="xref"><a href="http://scitation.aip.org/content/aip/journal/jap/118/18/10.1063/1.4934683#f3">3(d)</a></span>, the value of the resistor <span class="jp-italic">R</span> is not equal to <span class="jp-italic">R</span><span class="jp-sub">s</span>. <span class="jp-italic">R</span> is the resistance of the lumped resistor while <span class="jp-italic">R<span class="jp-sub">s</span></span> is the equivalent resistance of the distributed and lumped resistance. Figure <span class="xref"><a href="http://scitation.aip.org/content/aip/journal/jap/118/18/10.1063/1.4934683#f3">3(c)</a></span> shows the electric field distribution for the AFSS absorber, with <span class="jp-italic">R</span> = 700 Ω and <span class="jp-italic">C<span class="jp-sub">variable</span></span> = 1 pF, revealing that the resonance state exists and may be important for deep absorption.<br />
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<div class="caption">
<span class="captionLabel"><span class="label">FIG. 3.</span></span><span class="captionText">Working mechanism of the absorber. (a) Rough equivalent circuit model of the presented absorber. (b) Reflectivity varying with <span class="jp-italic">C<span class="jp-sub">variable</span></span>. (c) Electric field distribution from the HFSS. (d) Reflectivity varying with <span class="jp-italic">R</span>.</span><br />
<span class="captionText"><br />

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To numerically study the absorption performance, we establish an accurate model for the AFSS absorber. Figure <span class="xref"><a href="http://scitation.aip.org/content/aip/journal/jap/118/18/10.1063/1.4934683#f4">4(a)</a></span> gives the equivalent circuit model of our absorber based on TL theory.<span class="xref"><a href="http://scitation.aip.org/content/aip/journal/jap/118/18/10.1063/1.4934683#c23"><sup>23–25</sup></a></span> By separating the imaginary and real parts, the impedance of the AFSS layer can be described as
<br />
<div class="capture-id" id="d2">
<span class="label">(2) 
    </span></div>
which is equivalent to a resistor connected with a capacitor. The real part of <span class="jp-italic">Z</span><span class="jp-sub">AFSS</span> is a resistor <span class="jp-italic">R<span class="jp-sub">equ</span></span>, and the imaginary part of <span class="jp-italic">Z</span><span class="jp-sub">AFSS</span> is a capacitor <span class="jp-italic">C<span class="jp-sub">equ</span></span>. ω is the angular frequency of the electromagnetic wave. <span class="jp-italic">R<span class="jp-sub">equ</span></span> and <span class="jp-italic">C<span class="jp-sub">equ</span></span> are described by
<br />
<div class="capture-id" id="d3">
<span class="label">(3) 
    </span></div>
<div class="capture-id" id="d4">
<span class="label">(4) 
    </span></div>
The equivalent impedance of the honeycomb along with a metallic slab is described as an inductor with an inductance <span class="jp-italic">L<span class="jp-sub">equ</span></span>
<br />
<div class="capture-id" id="d5">
<span class="label">(5) 
    </span></div>
where <span class="jp-italic">β</span> is the propagation constant and <span class="jp-italic">d</span> is the thickness of the honeycomb. <span class="jp-italic">Z<span class="jp-sub">c</span></span> is the characteristic impedance of free space. The FR4 layer is thin enough to be ignored, simplifying the analysis. Figure <span class="xref"><a href="http://scitation.aip.org/content/aip/journal/jap/118/18/10.1063/1.4934683#f4">4(b)</a></span> shows the simplified equivalent circuit model. The resonance frequency <span class="jp-italic">f<span class="jp-sub">resonance</span></span> of the simplified circuit is described as
<br />
<div class="capture-id" id="d6">
<span class="label">(6) 
    </span></div>
The real part of the input impedance at the resonance frequency is described as
<br />
<div class="capture-id" id="d7">
<span class="label">(7) 
    </span></div>
where <span class="jp-italic">R<span class="jp-sub">equ</span></span>, <span class="jp-italic">C<span class="jp-sub">equ</span></span>, and <span class="jp-italic">L<span class="jp-sub">equ</span></span> all are functions of <span class="jp-italic">R</span>, <span class="jp-italic">C<span class="jp-sub">variable</span></span>, <span class="jp-italic">L<span class="jp-sub">d</span></span>, and <span class="jp-italic">C<span class="jp-sub">d</span></span>.
<br />
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<div class="caption">
<span class="captionLabel"><span class="label">FIG. 4.</span></span><span class="captionText">Equivalent circuit of our absorber. (a) Equivalent circuit model. (b) Simplified equivalent circuit model.</span><br />
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ST is applied to the unit cell pattern. The size of the unit cell is (<span class="jp-italic">x</span> × <span class="jp-italic">a</span>) × (<span class="jp-italic">y</span> × <span class="jp-italic">a</span>), where <span class="jp-italic">a</span> is the basic size before ST and <span class="jp-italic">x</span> and <span class="jp-italic">y</span>
 are the ST coefficients on each side. The topological structure of the 
AFSS pattern significantly affects the resonant point of the absorber. 
For example, consider the dipole antenna: if resonance happens, the 
dipole length must be an integer multiple of λ/2, where λ is the 
wavelength of the resonance frequency. Thus, a larger unit cell will 
have a lower resonance frequency. <span class="jp-italic">L<span class="jp-sub">d</span></span> and <span class="jp-italic">C<span class="jp-sub">d</span></span>
 represent the distributed parameters, including inductance and 
capacitance. On one hand, they are determined by the pattern of the unit
 cell and on the other, <span class="jp-italic">L<span class="jp-sub">d</span></span> and <span class="jp-italic">C<span class="jp-sub">d</span></span>
 can also be adjusted by applying the ST to the chosen pattern. To 
obtain the parameters ideal for broadband absorption, we applied various
 ST coefficients to the unit cell pattern. Based on Wen <span class="jp-italic">et al</span>.<span class="xref"><a href="http://scitation.aip.org/content/aip/journal/jap/118/18/10.1063/1.4934683#c26"><sup>26</sup></a></span> extraction of distributed parameters by applying the ABCD matrix method to an electric split-ring resonator,<span class="xref"><a href="http://scitation.aip.org/content/aip/journal/jap/118/18/10.1063/1.4934683#c4"><sup>4</sup></a></span> we calculated <span class="jp-italic">L<span class="jp-sub">d</span></span> and <span class="jp-italic">C<span class="jp-sub">d</span></span> by simulating the AFSS layer. Figure <span class="xref"><a href="http://scitation.aip.org/content/aip/journal/jap/118/18/10.1063/1.4934683#f5">5</a></span> shows the S parameters calculated by using the TL model (short dashed lines), with <span class="jp-italic">R</span> = 700 Ω, <span class="jp-italic">C<span class="jp-sub">variable</span></span> = 1 pF, and <span class="jp-italic">x</span> = 1, <span class="jp-italic">y</span> 
= 1. For comparison, the results of HFSS simulations (solid lines) are 
also shown. These results agree well with each other over the whole 
frequency range studied. This agreement shows that the equivalent 
circuit model and the extracted parameters are reliable. The calculated 
distributed parameters are <span class="jp-italic">L<span class="jp-sub">d</span></span> = 3.76 nH and <span class="jp-italic">C<span class="jp-sub">d</span></span> = 0.63 pF.<br />
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<div class="caption">
<span class="captionLabel"><span class="label">FIG. 5.</span></span><span class="captionText">S
 parameters of the AFSS layer. The “Sim” S parameters are the results 
from the HFSS, while the “Cal” parameters are the results from the TL 
model calculation.</span><br />
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<div class="tl-main-part title">
<a href="https://www.blogger.com/null" id="s3" name="s3">III. NUMERICAL ANALYSIS OF PATTERN WITH ST COEFFICIENTS <span class="jp-italic">x</span> = <span class="jp-italic">y</span> = 1</a></div>
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If the input impedance of the absorber matches with that of free 
space, the real part will be 377 Ω and the imaginary part will be 0. 
According to Eqs. <span class="xref"><a href="http://scitation.aip.org/content/aip/journal/jap/118/18/10.1063/1.4934683#d6">(6)</a></span> and <span class="xref"><a href="http://scitation.aip.org/content/aip/journal/jap/118/18/10.1063/1.4934683#d7">(7)</a></span>, the resonance frequency <span class="jp-italic">f<span class="jp-sub">resonance</span></span> and real part at resonance <span class="jp-italic">Z<span class="jp-sub">re,resonance</span></span> are functions of <span class="jp-italic">C<span class="jp-sub">d</span></span>, <span class="jp-italic">L<span class="jp-sub">d</span></span>, <span class="jp-italic">C<span class="jp-sub">variable</span></span>, and <span class="jp-italic">R</span>. With <span class="jp-italic">x</span> = <span class="jp-italic">y</span> = 1, the calculated distributed parameters are <span class="jp-italic">L<span class="jp-sub">d</span></span> = 3.76 nH and <span class="jp-italic">C<span class="jp-sub">d</span></span> = 0.63 pF. In this case, <span class="jp-italic">f<span class="jp-sub">resonance</span></span> and <span class="jp-italic">Z<span class="jp-sub">re,resonance</span></span> depends only on the lumped elements <span class="jp-italic">C<span class="jp-sub">variable</span></span> and <span class="jp-italic">R</span>.<br />
Figure <span class="xref"><a href="http://scitation.aip.org/content/aip/journal/jap/118/18/10.1063/1.4934683#f6">6</a></span> shows how <span class="jp-italic">f<span class="jp-sub">resonance</span></span> varies with the capacitance of the varactor <span class="jp-italic">C<span class="jp-sub">variable</span></span>, when compared with the simulated results calculated by the HFSS. The <span class="jp-italic">f<span class="jp-sub">resonance</span></span>–<span class="jp-italic">C<span class="jp-sub">variable</span></span> curve shown in Figure <span class="xref"><a href="http://scitation.aip.org/content/aip/journal/jap/118/18/10.1063/1.4934683#f6">6(a)</a></span> was calculated according to Eq. <span class="xref"><a href="http://scitation.aip.org/content/aip/journal/jap/118/18/10.1063/1.4934683#d6">(6)</a></span>, which indicates that the resonant point is a descending function of <span class="jp-italic">C<span class="jp-sub">variable</span></span>. Figure <span class="xref"><a href="http://scitation.aip.org/content/aip/journal/jap/118/18/10.1063/1.4934683#f6">6(b)</a></span> shows the simulated results with various <span class="jp-italic">C<span class="jp-sub">variable</span></span>,
 which agree well with the calculated curve. However, there is still a 
small discrepancy between these two results. For instance, the simulated
 resonance frequency is ∼1.19 GHz at <span class="jp-italic">C<span class="jp-sub">variable</span></span> 
= 1 pF, while the calculated resonance frequency is ∼1.21 GHz. This 
difference is mainly caused by the simplification of the TL model.<br />
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<a class="media-link" href="http://scitation.aip.org/content/figure/aip/journal/jap/118/18/10.1063/1.4934683.f6" id="/content/figure/aip/journal/jap/118/18/10.1063/1.4934683.f6"><br />
<img alt="" border="0" src="http://scitation.aip.org/docserver/ahah/fulltext/aip/journal/jap/118/18/1.4934683.figures.online.f6_thmb.gif" /><br />Click to view</a></div>
<div class="caption">
<span class="captionLabel"><span class="label">FIG. 6.</span></span><span class="captionText"><span class="jp-italic">f<span class="jp-sub">resonance</span></span> varying with the capacitance of varactor <span class="jp-italic">C<span class="jp-sub">variable</span></span>. (a) <span class="jp-italic">f<span class="jp-sub">resonance</span></span>–<span class="jp-italic">C<span class="jp-sub">variable</span></span> curve calculated by using the TL model. (b) Simulated results calculated by the HFSS.</span><br />
<span class="captionText"><br />

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While <span class="jp-italic">f<span class="jp-sub">resonance</span></span> is a descending function of <span class="jp-italic">C<span class="jp-sub">variable</span></span>, the resistance of the lumped resistor contributes little to <span class="jp-italic">f<span class="jp-sub">resonance</span></span>. The relationship between <span class="jp-italic">R</span> and <span class="jp-italic">f<span class="jp-sub">resonance</span></span> is described in Figure <span class="xref"><a href="http://scitation.aip.org/content/aip/journal/jap/118/18/10.1063/1.4934683#f7">7(a)</a></span>, where we set <span class="jp-italic">C<span class="jp-sub">variable</span></span> = 1 pF. When <span class="jp-italic">R</span> varies from 400 to 2000 Ω, <span class="jp-italic">f<span class="jp-sub">resonance</span></span> remains unchanged. Figure <span class="xref"><a href="http://scitation.aip.org/content/aip/journal/jap/118/18/10.1063/1.4934683#f7">7(b)</a></span> shows the simulated results for various <span class="jp-italic">R</span>. The simulated results and calculated curve indicate that changing <span class="jp-italic">R</span> affects <span class="jp-italic">f<span class="jp-sub">resonance</span></span> only slightly.<br />
<div class="figure" id="f7">
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<img alt="" border="0" src="http://scitation.aip.org/docserver/ahah/fulltext/aip/journal/jap/118/18/1.4934683.figures.online.f7_thmb.gif" /><br />Click to view</a></div>
<div class="caption">
<span class="captionLabel"><span class="label">FIG. 7.</span></span><span class="captionText"><span class="jp-italic">f<span class="jp-sub">resonance</span></span> varying with resistance of resistor <span class="jp-italic">R</span>. (a) <span class="jp-italic">f<span class="jp-sub">resonance</span></span>–<span class="jp-italic">R</span> curve calculated by using the TL model. (b) Simulated results calculated by the HFSS.</span><br />
<span class="captionText"><br />

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Figure <span class="xref"><a href="http://scitation.aip.org/content/aip/journal/jap/118/18/10.1063/1.4934683#f8">8</a></span> shows the relationship between <span class="jp-italic">Z<span class="jp-sub">re,resonance</span></span> and the lumped elements at various <span class="jp-italic">C<span class="jp-sub">variable</span></span>. At each <span class="jp-italic">C<span class="jp-sub">variable</span></span>, <span class="jp-italic">Z<span class="jp-sub">re,resonance</span></span> increases with increasing <span class="jp-italic">R</span>, and there is a clearly ideal <span class="jp-italic">R</span> for impedance matching, named <span class="jp-italic">R</span><span class="jp-sub">0</span>. As <span class="jp-italic">C<span class="jp-sub">variable</span></span> varies from 1 to 10 pF, <span class="jp-italic">R</span><span class="jp-sub">0</span> varies slightly from 750 to 800 Ω. As such, an <span class="jp-italic">R</span><span class="jp-sub">0</span> calculated for one <span class="jp-italic">C<span class="jp-sub">variable</span></span> is close to ideal for all other <span class="jp-italic">C<span class="jp-sub">variable</span></span>, and <span class="jp-italic">Z<span class="jp-sub">re,resonance</span></span> will not change much with changes in <span class="jp-italic">C<span class="jp-sub">variable</span></span>.<br />
<div class="figure" id="f8">
<div class="image">
<a class="media-link" href="http://scitation.aip.org/content/figure/aip/journal/jap/118/18/10.1063/1.4934683.f8" id="/content/figure/aip/journal/jap/118/18/10.1063/1.4934683.f8"><br />
<img alt="" border="0" src="http://scitation.aip.org/docserver/ahah/fulltext/aip/journal/jap/118/18/1.4934683.figures.online.f8_thmb.gif" /><br />Click to view</a></div>
<div class="caption">
<span class="captionLabel"><span class="label">FIG. 8.</span></span><span class="captionText"><span class="jp-italic">Z<span class="jp-sub">re,resonance</span></span> varying with resistor <span class="jp-italic">R</span> and varactor <span class="jp-italic">C<span class="jp-sub">variable</span></span>. (a) <span class="jp-italic">Z<span class="jp-sub">re,resonance</span></span>–<span class="jp-italic">R</span> curves calculated by using the TL model. (b) Magnified region from (a).</span><br />
<span class="captionText"><br />

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Overall, the resonance frequency <span class="jp-italic">f<span class="jp-sub">resonance</span></span> is mainly related to <span class="jp-italic">C<span class="jp-sub">variable</span></span>, while the real part of the resonance frequency <span class="jp-italic">Z<span class="jp-sub">re,resonance</span></span> mainly depends on <span class="jp-italic">R</span>.
 AFSS loaded with a resistor and varactor is practical as a design of a 
broadband tunable absorber. Adopting the varactor, which supplies a 
variable <span class="jp-italic">C<span class="jp-sub">variable</span></span> at varying bias voltages, produces the device's tunability. <span class="jp-italic">R</span><span class="jp-sub">0</span>
 reliably produces strong absorption at the resonance frequency, which 
is realized by using a lumped resistor with constant resistance.<br />
The resonance peaks combine the effects of interference and absorption. Figure <span class="xref"><a href="http://scitation.aip.org/content/aip/journal/jap/118/18/10.1063/1.4934683#f9">9</a></span> shows the volume loss density distribution of the designed AFSS absorber, where <span class="jp-italic">C</span> = 1 pF and the resonance frequency is 1.19 GHz. Figure <span class="xref"><a href="http://scitation.aip.org/content/aip/journal/jap/118/18/10.1063/1.4934683#f9">9</a></span>
 also shows that both interference and absorption on the AFSS exist and 
contribute to the total energy loss. The loss on the AFSS is mainly 
produced by absorption from the resistive elements. Resonance happens at
 1.19 GHz, where the equivalent circuit yields a strong electric field. 
The varactor guides the generated current through the narrow band-gap 
between the triangle and the semicircle. Then, with the help of a 
resistor, electric-field energy gets converted into thermal energy. The 
loss between the AFSS and the metal slab is mainly produced by 
destructive interference of the wave reflected from the surface and from
 the back.<span class="xref"><a href="http://scitation.aip.org/content/aip/journal/jap/118/18/10.1063/1.4934683#c27"><sup>27–29</sup></a></span>
 In this case, destructive interference exists but contributes little to
 the total energy loss. Most of the energy losses comes from absorption 
of the lumped resistive element.<br />
<div class="figure" id="f9">
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<a class="media-link" href="http://scitation.aip.org/content/figure/aip/journal/jap/118/18/10.1063/1.4934683.f9" id="/content/figure/aip/journal/jap/118/18/10.1063/1.4934683.f9"><br />
<img alt="" border="0" src="http://scitation.aip.org/docserver/ahah/fulltext/aip/journal/jap/118/18/1.4934683.figures.online.f9_thmb.gif" /><br />Click to view</a></div>
<div class="caption">
<span class="captionLabel"><span class="label">FIG. 9.</span></span><span class="captionText">Volume loss density distribution of the AFSS absorber.</span><br />
<span class="captionText"><br />

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<a href="https://www.blogger.com/null" id="s4" name="s4">IV. TUNABLE BANDWIDTH FOR PATTERNS WITH DIFFERENT ST COEFFICIENTS</a> </div>
</div>
</div>
Based on our qualitative analysis of tunability, it is appealing to 
expand the tunable bandwidth of our proposed absorber. Aside from the 
lumped impedances of the loaded elements, the distributed parameters 
will also contribute to the absorption performance. Thus, we apply 
various ST coefficients to the unit cell pattern to obtain the available
 parameters to expand the tunable bandwidth.<br />
Figure <span class="xref"><a href="http://scitation.aip.org/content/aip/journal/jap/118/18/10.1063/1.4934683#f10">10(a)</a></span> shows the results of the HFSS simulations, showing the resonance frequency <span class="jp-italic">f<span class="jp-sub">resonance</span></span> varying with the ST coefficients <span class="jp-italic">x</span> and <span class="jp-italic">y</span>, where <span class="jp-italic">C<span class="jp-sub">variable</span></span> = 1 pF, <span class="jp-italic">R</span> = 700 Ω, and <span class="jp-italic">d</span> = 7 mm. The resonance frequency moves regularly from 0.8 to 1.64 GHz, with ST coefficients from 1.5 to 0.5 for <span class="jp-italic">x</span>, and 0.5 to 1.5 for <span class="jp-italic">y</span>. Figure <span class="xref"><a href="http://scitation.aip.org/content/aip/journal/jap/118/18/10.1063/1.4934683#f10">10(b)</a></span> shows the tunable bandwidth varying with <span class="jp-italic">x</span> and <span class="jp-italic">y</span>, where the bandwidth is calculated with <span class="jp-italic">C<span class="jp-sub">variable</span></span> varying from 1 to 14 pF. The tunable bandwidth moves regularly from 0.53 to 1.10 GHz, with ST coefficients from 1.5 to 0.5 for <span class="jp-italic">x</span> and 0.5 to 1.5 for <span class="jp-italic">y</span>. This result suggests that a pattern with a small ST coefficient ratio <span class="jp-italic">x</span>/<span class="jp-italic">y</span> leads to a high resonance frequency and also produces a wider tunable bandwidth.<br />
<div class="figure" id="f10">
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<a class="media-link" href="http://scitation.aip.org/content/figure/aip/journal/jap/118/18/10.1063/1.4934683.f10" id="/content/figure/aip/journal/jap/118/18/10.1063/1.4934683.f10"><br />
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<div class="caption">
<span class="captionLabel"><span class="label">FIG. 10.</span></span><span class="captionText">Effect of ST on the unit cell pattern. (a) Resonance frequency <span class="jp-italic">f<span class="jp-sub">resonance</span></span> varying with ST coefficients <span class="jp-italic">x</span> and <span class="jp-italic">y</span>. (b) Tunable bandwidth varying with ST coefficients <span class="jp-italic">x</span> and <span class="jp-italic">y</span>.</span><br />
<span class="captionText"><br />

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</div>
</div>
To gain insight into the mechanism of the ST coefficients affecting resonance frequency <span class="jp-italic">f<span class="jp-sub">resonance</span></span> and the tunable bandwidth, we now focus on the three patterns in Figure <span class="xref"><a href="http://scitation.aip.org/content/aip/journal/jap/118/18/10.1063/1.4934683#f11">11</a></span>. These patterns are conversions of the pattern shown in Fig. <span class="xref"><a href="http://scitation.aip.org/content/aip/journal/jap/118/18/10.1063/1.4934683#f1">1(b)</a></span>. The ST coefficients are <span class="jp-italic">x</span> = 0.7, <span class="jp-italic">y</span> = 1 for Pattern (1); <span class="jp-italic">x</span> = 1, <span class="jp-italic">y</span> = 1 for Pattern (2); and <span class="jp-italic">x</span> = 1.3, <span class="jp-italic">y</span> = 1 for Pattern (3). Table <span class="xref"><a href="http://scitation.aip.org/content/aip/journal/jap/118/18/10.1063/1.4934683#t1">I</a></span> shows the calculations for the distributed parameters by using the discussed TL model. Figure <span class="xref"><a href="http://scitation.aip.org/content/aip/journal/jap/118/18/10.1063/1.4934683#f11">11</a></span> plots <span class="jp-italic">f<span class="jp-sub">resonance</span>–C<span class="jp-sub">variable</span></span> curves for the three patterns. These curves agree well with the simulated results in Figure <span class="xref"><a href="http://scitation.aip.org/content/aip/journal/jap/118/18/10.1063/1.4934683#f10">10</a></span>. When <span class="jp-italic">C<span class="jp-sub">variable</span></span> = 1 pF, the curve for Pattern (1) with a smaller <span class="jp-italic">x</span>/<span class="jp-italic">y</span> has a higher resonant point at 1.55 GHz, while Pattern (3) with a greater <span class="jp-italic">x</span>/<span class="jp-italic">y</span> has a lower resonant point at 1.05 GHz. With <span class="jp-italic">C<span class="jp-sub">variable</span></span> varying from 1 to 14 pF, the tunable bandwidth for Pattern (1) is 1.15 GHz, while that for Pattern (3) is 0.65 GHz.<br />
<div class="figure" id="f11">
<div class="image">
<a class="media-link" href="http://scitation.aip.org/content/figure/aip/journal/jap/118/18/10.1063/1.4934683.f11" id="/content/figure/aip/journal/jap/118/18/10.1063/1.4934683.f11"><br />
<img alt="" border="0" src="http://scitation.aip.org/docserver/ahah/fulltext/aip/journal/jap/118/18/1.4934683.figures.online.f11_thmb.gif" /><br />Click to view</a></div>
<div class="caption">
<span class="captionLabel"><span class="label">FIG. 11.</span></span><span class="captionText"><span class="jp-italic">f<span class="jp-sub">resonance</span></span>–<span class="jp-italic">C<span class="jp-sub">variable</span></span> curves for three patterns.<br />

</span></div>
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</div>
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<div class="figure" id="t1">
<div class="image">
<a class="media-link" href="http://scitation.aip.org/content/table/aip/journal/jap/118/18/10.1063/1.4934683.t1" id="/content/table/aip/journal/jap/118/18/10.1063/1.4934683.t1"><br />
<img alt="TABLE I." border="0" src="http://scitation.aip.org/images/jp/table_thmb.gif" /><span class="label">TABLE I.</span><br />Click to view</a></div>
<div class="caption">
<span class="captionLabel"><span class="label">TABLE I.</span></span><span class="captionText">Distributed parameters calculated by using TL model.</span><br />
<span class="captionText"><br />

</span></div>
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</div>
</div>
Providing more numerical calculations, Figure <span class="xref"><a href="http://scitation.aip.org/content/aip/journal/jap/118/18/10.1063/1.4934683#f12">12</a></span> shows the distributed capacitance <span class="jp-italic">C<span class="jp-sub">d</span></span> varying with the ST coefficient ratio <span class="jp-italic">x</span>/<span class="jp-italic">y</span>. Generally, a pattern with greater <span class="jp-italic">x</span>/<span class="jp-italic">y</span> has a larger distributed capacitance <span class="jp-italic">C<span class="jp-sub">d</span></span>, while <span class="jp-italic">x</span>/<span class="jp-italic">y</span> more weakly affects the distributed inductance <span class="jp-italic">L<span class="jp-sub">d</span></span>. According to the TL model described in Figure <span class="xref"><a href="http://scitation.aip.org/content/aip/journal/jap/118/18/10.1063/1.4934683#f4">4(a)</a></span>, where two <span class="jp-italic">C<span class="jp-sub">d</span></span> are connected in parallel to <span class="jp-italic">C<span class="jp-sub">variable</span></span>, the distributed capacitance <span class="jp-italic">C<span class="jp-sub">d</span></span> affects <span class="jp-italic">f<span class="jp-sub">resonance</span></span> the same as <span class="jp-italic">C<span class="jp-sub">variable</span></span>. In this case, a small (<span class="jp-italic">C<span class="jp-sub">variable</span></span> + <span class="jp-italic">C<span class="jp-sub">d</span></span>) leads to high-frequency resonance, while a high (<span class="jp-italic">C<span class="jp-sub">variable</span></span> + <span class="jp-italic">C<span class="jp-sub">d</span></span>) leads to low-frequency resonance. When <span class="jp-italic">C<span class="jp-sub">variable</span></span> = 0.5 pF, the decrease in <span class="jp-italic">C<span class="jp-sub">d</span></span> greatly affects (<span class="jp-italic">C<span class="jp-sub">variable</span></span> + <span class="jp-italic">C<span class="jp-sub">d</span></span>), increasing the resonance frequency. When <span class="jp-italic">C<span class="jp-sub">variable</span></span> = 14 pF, the decrease in <span class="jp-italic">C<span class="jp-sub">d</span></span> slightly affects (<span class="jp-italic">C<span class="jp-sub">variable</span></span> + <span class="jp-italic">C<span class="jp-sub">d</span></span>),
 leaving the resonance frequency unchanged. Thus, the tunable bandwidth 
is markedly wider for Pattern (1) than for Patterns (2) and (3). This 
result shows that the ST coefficients greatly affect the design of a 
broadband tunable absorber. A pattern with a small ST coefficient ratio <span class="jp-italic">x</span>/<span class="jp-italic">y</span> will effectively expand the tunable bandwidth.<br />
<div class="figure" id="f12">
<div class="image">
<a class="media-link" href="http://scitation.aip.org/content/figure/aip/journal/jap/118/18/10.1063/1.4934683.f12" id="/content/figure/aip/journal/jap/118/18/10.1063/1.4934683.f12"><br />
<img alt="" border="0" src="http://scitation.aip.org/docserver/ahah/fulltext/aip/journal/jap/118/18/1.4934683.figures.online.f12_thmb.gif" /><br />
Click to view</a></div>
<div class="caption">
<span class="captionLabel"><span class="label">FIG. 12.</span></span><span class="captionText"><span class="jp-italic">C<span class="jp-sub">d</span></span> varying with ST coefficient ratio <span class="jp-italic">x</span>/<span class="jp-italic">y</span>.</span><br />
<span class="captionText"><br />

</span></div>
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<a href="https://www.blogger.com/null" id="s5" name="s5">V. RESULTS AND DISCUSSION</a> </div>
</div>
</div>
Based on our analyses, we designed and fabricated a broadband AFSS 
absorber with an ST pattern for use in UHF applications. Figure <span class="xref"><a href="http://scitation.aip.org/content/aip/journal/jap/118/18/10.1063/1.4934683#f13">13(a)</a></span>
 shows the fabricated sample, which had overall dimensions of 
500 × 500 × 7.8 mm. The AFSS was fabricated on a printed circuit board, 
and the resistors and varactors (BB131, NXP) were soldered between each 
of the two AFSS units. The AFSS substrate is FR4 with a thickness of 
0.8 mm (<span class="jp-italic">ε</span> = 4.4(1 − <span class="jp-italic">i</span>0.02) and <span class="jp-italic">μ</span> = 1). Figure <span class="xref"><a href="http://scitation.aip.org/content/aip/journal/jap/118/18/10.1063/1.4934683#f13">13(b)</a></span> shows the topological structure of the unit cell, where the ST coefficients are <span class="jp-italic">x</span> = 0.7, <span class="jp-italic">y</span> = 1. All the varactors worked in reverse bias. Figure <span class="xref"><a href="http://scitation.aip.org/content/aip/journal/jap/118/18/10.1063/1.4934683#f13">13(c)</a></span>
 shows a schematic representation of the power issue. The bias lines 
with the same polarity are connected together. All the devices are in 
parallel and biased at the same voltage. The reflectivity calculated by 
HFSS, shown in Figure <span class="xref"><a href="http://scitation.aip.org/content/aip/journal/jap/118/18/10.1063/1.4934683#f13">13(d)</a></span>,
 agrees well with the discussed theory. As capacitance increases, the 
resonant point moves to a lower frequency, covering a band below −10 dB 
from 0.7 to 2 GHz.<br />
<div class="figure" id="f13">
<div class="image">
<a class="media-link" href="http://scitation.aip.org/content/figure/aip/journal/jap/118/18/10.1063/1.4934683.f13" id="/content/figure/aip/journal/jap/118/18/10.1063/1.4934683.f13"><br />
<img alt="" border="0" src="http://scitation.aip.org/docserver/ahah/fulltext/aip/journal/jap/118/18/1.4934683.figures.online.f13_thmb.gif" /><br />
Click to view</a></div>
<div class="caption">
<span class="captionLabel"><span class="label">FIG. 13.</span></span><span class="captionText">Fabricated
 broadband AFSS absorber. (a) Photo of 500 × 500 mm sample. (b) 
Magnified picture of the unit cell. (c) Schematic showing the power 
issue. (d) Simulated reflectivity.</span><br />
<span class="captionText"><br />

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The reflectivity was measured with a free space setup,<span class="xref"><a href="http://scitation.aip.org/content/aip/journal/jap/118/18/10.1063/1.4934683#c30"><sup>30</sup></a></span> as shown in Figure <span class="xref"><a href="http://scitation.aip.org/content/aip/journal/jap/118/18/10.1063/1.4934683#f14">14</a></span>.
 The measurement setup comprised a vector network analyzer (Agilent 
8753ES), a double-ridged horn antenna (measurement range of 0.4–2 GHz), a
 power source, a pyramidal absorber, and a 500 × 500 mm metal slab. The 
frequency range measured was 0.4–2 GHz. To eliminate multiple scattering
 between the sample and the horns, time-domain gating was applied.<br />
<div class="figure" id="f14">
<div class="image">
<a class="media-link" href="http://scitation.aip.org/content/figure/aip/journal/jap/118/18/10.1063/1.4934683.f14" id="/content/figure/aip/journal/jap/118/18/10.1063/1.4934683.f14"><br />
<img alt="" border="0" src="http://scitation.aip.org/docserver/ahah/fulltext/aip/journal/jap/118/18/1.4934683.figures.online.f14_thmb.gif" /><br />
Click to view</a></div>
<div class="caption">
<span class="captionLabel"><span class="label">FIG. 14.</span></span><span class="captionText">Free space setup for measuring the tunable reflectivity.</span><br />
<span class="captionText"><br />

</span></div>
<div class="clearer">
</div>
</div>
Figure <span class="xref"><a href="http://scitation.aip.org/content/aip/journal/jap/118/18/10.1063/1.4934683#f15">15</a></span>
 shows the experimental results. As we varied the bias voltage from 10 
to 48 V with the power control system, the resonant point moved to a 
higher frequency and covered a frequency band of 0.7–1.9 GHz below 
−10 dB. The total specific mass of the sample was 0.189 g/cm<sup>2</sup>.
 The total thickness was only ∼λ/54 of the lower limit frequency, ∼λ/29 
of the center frequency, and ∼λ/20 of the higher limit frequency. As the
 bias voltage changed from 10 V to 48 V, the power consumption of each 
unit varied from 0.07 W to 1.65 W.<br />
<div class="figure" id="f15">
<div class="image">
<a class="media-link" href="http://scitation.aip.org/content/figure/aip/journal/jap/118/18/10.1063/1.4934683.f15" id="/content/figure/aip/journal/jap/118/18/10.1063/1.4934683.f15"><br />
<img alt="" border="0" src="http://scitation.aip.org/docserver/ahah/fulltext/aip/journal/jap/118/18/1.4934683.figures.online.f15_thmb.gif" /><br />
Click to view</a></div>
<div class="clearer">
<span class="captionLabel"><span class="label">FIG. 15.</span></span><span class="captionText">Measured reflectivity of the broadband tunable AFSS absorber.</span><br />
<span class="captionText"><br />
</span> </div>
</div>
The measured reflectivity does not perfectly agree with the simulated
 result: there are small discrepancies such as the depth of the peak and
 the bandwidth of each absorption beam. There are likely three reasons 
for these differences. First, the resistor and varactor have distributed
 impendence so, they are not exactly ideal. Second, the fabricated 
absorber is finite, while the device modeled in HFSS is infinite. 
Finally, there is a tolerated error for both the HFSS and the 
measurement system. Despite these discrepancies, both the measurements 
and simulated results indicate that our AFSS absorber with an ST pattern
 can be thin and achieve broad bandwidth simultaneously.<br />
<br />
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<div class="articleSection">
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<div class="sectionDivider">
<div class="clearer">
<a href="https://www.blogger.com/null" id="s6" name="s6">VI. CONCLUSION</a> </div>
</div>
</div>
We proposed and fabricated an ultra-thin broadband AFSS absorber with
 an ST pattern for UHF applications. Based on the TL model, the 
resonance frequency and real part of input impedance are given as 
functions of loaded and distributed parameters. With ST coefficients of <span class="jp-italic">x</span> = <span class="jp-italic">y</span> 
= 1, the tunability and strong absorption are concisely demonstrated. 
The calculated results suggest that the varactor modulates the imaginary
 part of the input impendence, producing the tunability, while the 
resistor mainly adjusts real part, producing the strong absorption. 
Applying various ST coefficients to the unit cell pattern, we found that
 a small <span class="jp-italic">x</span>/<span class="jp-italic">y</span>
 effectively expands the tunable bandwidth. The measured reflectivity of
 the proposed absorber covers a broad band of 0.7–1.9 GHz below −10 dB, 
and the total thickness 7.8 mm is only ∼λ/29 of the center frequency. As
 radar detection equipment continues to improve, our thin absorbers with
 broad bandwidth and working in the UHF band will be widely useful.<br />
<br />
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</div>
<div id="article-level-0-back">
<div class="articleSection">
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<div class="sectionDivider">
<div class="tl-main-part title">
<a href="https://www.blogger.com/null" id="acknowledgments-1" name="acknowledgments-1">ACKNOWLEDGMENTS</a></div>
<div class="clearer">
</div>
</div>
</div>
This work was supported in part by the National Natural Science Foundation of China under Grant No. 61172003.<br />
  <br />
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<a class="nonDisambigAuthorLink" href="http://scitation.aip.org/search?value1=Wenhua+Xu&option1=author&option912=resultCategory&value912=ResearchPublicationContent">Wenhua Xu</a><sup>1</sup>,
<a class="nonDisambigAuthorLink" href="http://scitation.aip.org/search?value1=Yun+He&option1=author&option912=resultCategory&value912=ResearchPublicationContent">Yun He</a><sup>1</sup>,
<a class="nonDisambigAuthorLink" href="http://scitation.aip.org/search?value1=Peng+Kong&option1=author&option912=resultCategory&value912=ResearchPublicationContent">Peng Kong</a><sup>1</sup>,
<a class="nonDisambigAuthorLink" href="http://scitation.aip.org/search?value1=Jialin+Li&option1=author&option912=resultCategory&value912=ResearchPublicationContent">Jialin Li</a><sup>1</sup>,
<a class="nonDisambigAuthorLink" href="http://scitation.aip.org/search?value1=Haibing+Xu&option1=author&option912=resultCategory&value912=ResearchPublicationContent">Haibing Xu</a><sup>1</sup>,
<a class="nonDisambigAuthorLink" href="http://scitation.aip.org/search?value1=Ling+Miao&option1=author&option912=resultCategory&value912=ResearchPublicationContent">Ling Miao</a><sup>1</sup>,
<a class="nonDisambigAuthorLink" href="http://scitation.aip.org/search?value1=Shaowei+Bie&option1=author&option912=resultCategory&value912=ResearchPublicationContent">Shaowei Bie</a><sup>1</sup> and
<a class="nonDisambigAuthorLink" href="http://scitation.aip.org/search?value1=Jianjun+Jiang&option1=author&option912=resultCategory&value912=ResearchPublicationContent">Jianjun Jiang</a><sup>1,a)</sup><br />
<br />
</div>
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<div class="articleSection">
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Radars On Track To See Through Stealth Fighter

F-35B Lightning II aircraft takes off from the amphibious assault ship USS Wasp (LHD-1) A former senior U.S. Navy official told USNI News that U.S. fighters — like the Lockheed Martin F-22 Raptor an…

The 'world's sexiest robot' revealed

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<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjbMepY0IPkEZuNZuSqAAZheir43XgeqvY6sLqshTEJYcQcyphrZDTO5bIv5boySr8TPQHBSjcK7URRVK_xzazE2Cg8cmEOtaYeNm6Zbb1SfO8DfGQ_xbEpjeYME_NSNyrUc4pPd7-hs-c/s1600/The+%2527world%2527s+sexiest+robot%2527+revealed.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img alt="The 'world's sexiest robot' revealed" border="0" height="510" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjbMepY0IPkEZuNZuSqAAZheir43XgeqvY6sLqshTEJYcQcyphrZDTO5bIv5boySr8TPQHBSjcK7URRVK_xzazE2Cg8cmEOtaYeNm6Zbb1SfO8DfGQ_xbEpjeYME_NSNyrUc4pPd7-hs-c/s640/The+%2527world%2527s+sexiest+robot%2527+revealed.jpg" title="The 'world's sexiest robot' revealed" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><span style="font-size: small;">The 'world's sexiest robot' revealed. </span><div class="imageCaption">
<span style="font-size: small;">An eerily life-like robot has been 
turning heads at the World Robot Exhibition in Beijing this week. Named 
Android Geminoid F, the robot has a legion of fans, with some even 
describing her as 'sexy'</span></div>
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<span id="ext-gen137" style="font-size: 1.2em;">An eerily life-like robot has been turning heads at the World Robot Exhibition in Beijing this week.</span></div>
<div class="mol-para-with-font">
<span style="font-size: 1.2em;">Named Geminoid F, the robot has amassed a legion of fans, with some even describing her as 'the world's sexiest robot'.</span></div>
<div class="mol-para-with-font">
<span style="font-size: 1.2em;">The 5ft 6 inch android is capable of eye movements, response to eye-to-eye contact and can recognise body language.</span></div>
<div class="imageCaption">
<br /></div>
</div>
<div class="mol-para-with-font">
<span style="font-size: 1.2em;">She is designed act like a human with rubber 'skin' and a woman's face - but can't walk and has to be wheeled around.</span></div>
<div class="mol-para-with-font">
<span style="font-size: 1.2em;">The robot was created by Hiroshi Ishiguro Laboratory at Osaka University who plan on creating a better model in the future.</span></div>
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<span style="font-size: 1.2em;">'Our final goal is creating some artificial intelligence by using this robot,' Kohei Ogawa, assistant professor said. </span></div>
<div class="mol-para-with-font">
<span style="font-size: 1.2em;">'Most voice recognition systems do not work, especially in this kind of noisy environment.</span></div>
<div class="mol-para-with-font">
<span style="font-size: 1.2em;">'In the future we're going to create some perfect AI system by using this robot.'</span></div>
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<img alt="The five-foot six-inch android is capable of eye movements, response to eye-to-eye contact and can recognise body language. She is designed act like a human with rubber 'skin' and a woman's face - but it is unable to walk and has to be wheeled around" class="blkBorder img-share" height="574" id="i-6e15eca8ffd3be6b" src="http://i.dailymail.co.uk/i/pix/2015/11/26/20/2ED1676900000578-0-image-m-9_1448570031596.jpg" width="634" /><br />
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The five-foot 
six-inch android is capable of eye movements, response to eye-to-eye 
contact and can recognise body language. She is designed act like a 
human with rubber 'skin' and a woman's face - but it is unable to walk 
and has to be wheeled around</div>
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<img alt="Robot engineer Hiroshi Ishiguro (left), US actress Bryerly Long (2nd right) and Japanese actor Nijiro Murakami (right) help android actress Geminoid F wave to the audience before the premiere of new movie 'Sayonara'" class="blkBorder img-share" height="424" id="i-99d540d5199dc3c3" src="http://i.dailymail.co.uk/i/pix/2015/11/26/20/2ED67A8B00000578-0-image-a-18_1448570309578.jpg" width="634" /><br />
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<div class="imageCaption">
Robot engineer Hiroshi Ishiguro 
(left), US actress Bryerly Long (2nd right) and Japanese actor Nijiro 
Murakami (right) help android actress Geminoid F wave to the audience 
before the premiere of new movie 'Sayonara'</div>
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<div class="mol-para-with-font">
<span style="font-size: 1.2em;">The
 current version of Geminoid F cost $108,600 (£72,000), which Ishiguro 
hopes may take the technology closer to the mainstream.</span></div>
<div class="mol-para-with-font">
<span style="font-size: 1.2em;">She
 can smile, furrow her brows and move her mouth. It can also talk and 
sing - playing recordings, or 'mouthing' other people's voices.</span></div>
<div class="mol-para-with-font">
<span style="font-size: 1.2em;">The robot is equipped with motorised actuators, powered by air pressure, which allow her to 'copy' human facial expressions.</span></div>
<div class="mol-para-with-font">
<span style="font-size: 1.2em;">Geminoid F has already taken the film industry by storm, becoming the first android to star in a film.</span></div>
<div class="mol-para-with-font">
<span style="font-size: 1.2em;">Earlier
 this year, she co-starred in a Japanese movie named 'Sayonara', about 
the after-effects of a nuclear power plant meltdown.</span></div>
<div class="mol-para-with-font">
<span style="font-size: 1.2em;">Geminoid
 F - or Leona in the film - is referred to by director Koji Fukada as an
 'actress,' and the android is even listed as a member of the cast in 
the end credits.</span></div>
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<i><span style="font-weight: bold;">COULD HUMANS SOMEDAY FALL IN LOVE WITH ROBOTS? </span></i>
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<img alt="The film 'Ex Machina', in which a computer programmer falls in love with a droid, may not be as far-fetched as you think" class="blkBorder img-share" height="281" id="i-2c8aea0354469b5c" src="http://i.dailymail.co.uk/i/pix/2015/11/26/20/2ED74E8500000578-3335552-The_film_Ex_Machina_in_which_a_computer_programmer_falls_in_love-a-23_1448571435596.jpg" width="400" /></div>
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<i>The film 'Ex Machina', in which a computer programmer falls </i></div>
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<i>in love with a droid, may not be as far-fetched as you think</i></div>
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<div class="mol-para-with-font">
<i><span style="font-size: 1.2em;">The film 'Ex Machina', in which a computer programmer falls in love with a droid, may not be as far-fetched as you think.</span></i></div>
<div class="mol-para-with-font">
<i><span style="font-size: 1.2em;">A new study has found that humans have the potential to emphasise with robots, even while knowing they don't have feelings.</span></i></div>
<div class="mol-para-with-font">
<i><span style="font-size: 1.2em;">It
 follows previous warnings from experts that humans could develop 
unhealthy relationships with robots, and even fall in love with them.</span></i></div>
<div class="mol-para-with-font">
<i><span style="font-size: 1.2em;">The
 discovery was made after researchers asked people to view images of 
human and humanoid robotic hands in painful situations, such as being 
cut by a knife.</span></i></div>
<div class="mol-para-with-font">
<i><span style="font-size: 1.2em;">After
 studying their electrical brain signals, they found humans responded 
with similar immediate levels of empathy to both humans and robots.</span></i></div>
<div class="mol-para-with-font">
<i><span style="font-size: 1.2em;">But the beginning phase of the so-called 'top-down' process of empathy was weaker toward robots.</span></i></div>
<div class="mol-para-with-font">
<i><span style="font-size: 1.2em;">The
 study was carried out by researchers at Toyohashi University of 
Technology and Kyoto University in Japan, and provides the first 
neurophysiological evidence of humans' ability to empathise with robots.</span></i></div>
<div class="mol-para-with-font">
<i><span style="font-size: 1.2em;">These results suggest that we empathise with humanoid robots in a similar way to how we empathise with other humans.</span></i></div>
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<img alt="The robot was created by Hiroshi Ishiguro Laboratory at Osaka University who plan on creating a better model in the future. 'Our final goal is creating some artificial intelligence by using this robot,' Kohei Ogawa, assistant professor said" class="blkBorder img-share" height="423" id="i-d39985e153afe5d" src="http://i.dailymail.co.uk/i/pix/2015/11/26/20/2EB8B47500000578-0-image-a-19_1448570878328.jpg" width="634" /><br />
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The robot was created by Hiroshi 
Ishiguro Laboratory at Osaka University who plan on creating a better 
model in the future. 'Our final goal is creating some artificial 
intelligence by using this robot,' Kohei Ogawa, assistant professor said</div>
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<img alt="The robot is equipped with motorised actuators, powered by air pressure, which allow her to 'copy' human facial expressions " class="blkBorder img-share" height="423" id="i-a70d327652dc723d" src="http://i.dailymail.co.uk/i/pix/2015/11/26/20/2ED67A9700000578-0-image-a-14_1448570090464.jpg" width="634" /><br />
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The robot is equipped with motorised actuators, powered by air pressure, which allow her to 'copy' human facial expressions </div>
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<br /></div>
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<div class="mol-para-with-font">
<span style="font-size: 1.2em;">While robots have featured prominently in many films, most are played by real actors or created using visual effects. </span></div>
<div class="mol-para-with-font">
<span style="font-size: 1.2em;">Prof Ishiguro has designed several robots made to look like humans in the past - even building one in his own image.</span></div>
<div class="mol-para-with-font">
<span style="font-size: 1.2em;">The professor has said that one day robots could fool us into believing they are human. </span></div>
<div class="mol-para-with-font">
<span style="font-size: 1.2em;">In
 the film, shown in the competition section of the Tokyo International 
Film Festival, the robot stays loyal to its owner - played by Bryerly 
Long - as the nation evacuates following a nuclear disaster.</span></div>
<div class="mol-para-with-font">
<span style="font-size: 1.2em;">Fukada
 said working with the android was easier than directing people, 
although he said had to watch not to break the robot as its repairs 
would come with a 10 million yen ($83,000 or £55,000) bill.</span></div>
<div class="mol-para-with-font">
<span style="font-size: 1.2em;">'The android doesn't complain, never gets hungry and doesn't need to sleep at all,' he said at the film festival office.</span></div>
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<img alt="The robot co-stars alongside a human in the film 'Sayonara' set in the aftermath of a deadly nuclear power plant meltdown in Japan" class="blkBorder img-share" height="423" id="i-3022c711b79befb7" src="http://i.dailymail.co.uk/i/pix/2015/11/01/21/2E056D6C00000578-0-image-a-45_1446414846260.jpg" width="634" /><br />
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The robot co-stars alongside a human 
in the film 'Sayonara' set in the aftermath of a deadly nuclear power 
plant meltdown in Japan</div>
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Fukada said working 
with the android was easier than directing people, although he said had 
to watch not to break the robot as its repairs would come with a 10 
million yen ($83,000 or £55,000) bill </div>
</div>
<i>By

Ellie Zolfagharifard | dailymail.co.uk/</i><br />
<br />
<br /></div>

The 'world's sexiest robot' revealed

The 'world's sexiest robot' revealed. An eerily life-like robot has been turning heads at the World Robot Exhibition in Beijing this week. Named Android Geminoid F, the robot has a legion of fans,…

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Was The Turkey Shoot down Planned?

RuAF strike on Islamic State 'oil storage' near al-Tabaqa …

Low Altitude Guardian II (LAG II), Laser Weapon Stars On TV

</div>
</header>
  <article class="content-basic basic-sidebar">
    <div class="content-main basic-sidebar">
<div class="panel-pane pane-entity-field pane-node-body">
  
                
  
  
    
  <div class="field-body inContentAds-processed">
    <div class="media media-element-container media-default full-width color-processed" data-adafter="false">
<div class="caption-wrapper">
  <div class="field-title">
    Low Altitude Guard II<br />

</div>
<div class="field-body">
    This laser is powerful enough so that when linked to a fire 
control radar, it could potentially also shoot down enemy artillery 
shells, rockets and missiles.<br />

</div>
CNTV </div>
<div class="caption-wrapper">
 </div>
<div class="caption-wrapper">
<b>An extreme solution to paparazzi drones.</b> </div>
</div>
<div data-adafter="false">
Laser weapons are not just the stuff of <em>Star Wars: The Force Awakens</em>,
 but also now a real technology of growing importance to war. On 
November 7, 2015, a  CCTV newscast showed that China is making great 
progress in this new weapons area, showing images of  a laser weapon, 
the Low Altitude Guardian II (LAG II), destroying airborne targets at a 
military test site.</div>
<div class="media media-element-container media-default full-width color-processed" data-adafter="false">
<br />
<img alt="China laser weapon low altitude guard II" class="full-width unveil-processed full-visible" data-lgsrc="http://www.popsci.com/sites/popsci.com/files/styles/large_1x_/public/low_altitude_guard_ii_2.jpg?itok=t1Gg1j2c" data-medsrc="http://www.popsci.com/sites/popsci.com/files/styles/medium_1x_/public/low_altitude_guard_ii_2.jpg?itok=Bg6wfZ5e" data-smsrc="http://www.popsci.com/sites/popsci.com/files/styles/small_1x_/public/low_altitude_guard_ii_2.jpg?itok=3zHnwhoW" data-src="http://www.popsci.com/sites/popsci.com/files/styles/medium_1x_/public/low_altitude_guard_ii_2.jpg?itok=Bg6wfZ5e" height="480" src="http://www.popsci.com/sites/popsci.com/files/styles/medium_1x_/public/low_altitude_guard_ii_2.jpg?itok=Bg6wfZ5e" width="640" /><div class="caption-wrapper">
  <div class="field-title">
    Surprise!<br />

</div>
<div class="field-body">
    The LAG II has a removable dome that protects the laser's 
electro-optical camera and active components when not in combat (also 
good for camouflaging the laser when in transit).<br />
<br />

</div>
</div>
</div>
<div data-adafter="false">
Claimed to be China's most powerful laser weapon
 in the public domain (there are reports of more powerful but classified
 anti-satellite lasers), the LAG II is built by the Chinese Academy of 
Physics Engineering and Jiuyuan High Tech Equipment Corporation. Similar
 in size to the U.S. Marines' Ground-Based Air Defense Directed Energy 
On-The-Move, it is mounted on a wheeled, towed carriage that carries its
 turret, power components, which can be pulled by a light truck. The LAG
 II's turret, when its protective dome retracts, uses its 
electro-optical sensor to acquire and track targets autonomously, before
 destroying it upon command from a human operator. The LAG II could be 
upgraded with datalinks to off vehicle radars, which would allow the 
engagement of higher speed targets like rocket artillery.</div>
<div class="media media-element-container media-default full-width color-processed" data-adafter="false">
<br />
<img alt="China laser weapon low altitude guard II" class="full-width unveil-processed full-visible" data-lgsrc="http://www.popsci.com/sites/popsci.com/files/styles/large_1x_/public/open_sesame.jpg?itok=eSVj6BOK" data-medsrc="http://www.popsci.com/sites/popsci.com/files/styles/medium_1x_/public/open_sesame.jpg?itok=F1GFBjMD" data-smsrc="http://www.popsci.com/sites/popsci.com/files/styles/small_1x_/public/open_sesame.jpg?itok=XV7sIFXq" data-src="http://www.popsci.com/sites/popsci.com/files/styles/medium_1x_/public/open_sesame.jpg?itok=F1GFBjMD" height="480" src="http://www.popsci.com/sites/popsci.com/files/styles/medium_1x_/public/open_sesame.jpg?itok=F1GFBjMD" width="640" /><div class="caption-wrapper">
  <div class="field-title">
    Open Sesame<br />

</div>
<div class="field-body">
    With the push of a button and turn of a dial, a Chinese soldier 
prepares the LAG II for firing by operating its side mounted console to 
un-dome the laser. While the laser autonomously seeks and tracks aerial 
targets, human operators in a separate vehicle give it the orders to 
fire.<br />

</div>
<div class="field-credit">
    CNTV<br />
  <br />

</div>
</div>
</div>
<div data-adafter="true">
The LAG II follows quickly on the heels of the 
Low Altitude Guard I, a stationary laser weapon with a 10 kilowatt beam,
 which was only unveiled in November 2014 for export.  The LAG I's laser
 has a range of two kilometers, but is less powerful due to its intended
 usage as a counter-drone system for law enforcement and 
counterterrorist missions.</div>
<div data-adafter="true">
Along with more powerful but classified 
anti-satellite lasers, China's tactical lasers will bring its 
anti-access/area denial tactics to lightspeed.</div>
</div>
</div>
</div>
</article><span><br /></span></div>
<span class="author"><i><span class="label">By</span>
  
    Jeffrey Lin and P.W. Singer |  Popular Science</i>  
</span><br />
<br />
<br /></div>

Low Altitude Guardian II (LAG II), Laser Weapon Stars On TV

Low Altitude Guard II This laser is powerful enough so that when linked to a fire control rada…

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