Phase Change Material Vanadium Dioxide Research Articles

Tunable and strong circular dichroism metamaterial absorber based on gold-VO2 hybrid structure

The existing terahertz chiral absorber faces a series of issues, including low efficiency, un-tunable absorption, and complex structure. We present a chiral metamaterial absorber integrated with gold and phase-change material vanadium dioxide (VO2) to address the issues above. Our designed metamaterial absorber’s maximum circular dichroism (CD) value, as an ideal chirality-selective meta-absorber, reaches 0.95 when VO2 behaves as a metallic state. However, when VO2 is in the insulator state, the CD value is merely 0.003. Notably, the intrinsic mechanisms of the CD effect are revealed by analyzing the difference in electromagnetic response under left-handed circularly polarized (LCP) and right-handed circularly polarized (RCP) illumination. The designed chiral metamaterial absorber supports the free switching of the CD signal between ‘on’ and ‘off’ states by continuously adjusting the conductivity of VO2 with a CD value ranging from 0 to 0.95. Moreover, the absorption performance of chiral metamaterials is affected by geometric parameters and the angle of incidence. To evaluate the capability of chiral structure in biosensing, three typical avian influenza viruses are sensed by detecting changes in their resonant frequencies and CD values. Finally, the presented chiral-selective absorber with phase-change materials has an important reference value in the terahertz range for constructing chiral light detectors, chiral thermal switching, biosensors, and tunable chiral photonics.

Terahertz-absorbing,dual-polarization converting supersurface structures based on the phase-change material VO2

Dynamically tunable multifunctional hypersurface structures have attracted the interest of researchers due to their good control of electromagnetic waves. Based on this, we have designed a dynamically tunable multifunctional hypersurface structure using the phase change material vanadium dioxide. By changing the state of vanadium dioxide, three functions of efficient broadband wave absorption, linear polarization conversion (LPC) and linear circular polarization conversion (LCPC) can be achieved. At room temperature, the hypersurface is used as a polarization converter to achieve broadband linear polarization conversion in the 0.903 THz range and line-circular polarization conversion with a total bandwidth of 0.608 THz in the 0.522 THz, 0.964 THz and 1.448 THz bands. When the temperature is raised to 68 °C, the hypersurface structure can be used as a broadband absorber, absorbing more than 90% of the incident wave in a wide frequency range of 1.348 THz and showing a large tolerance to variations in the angle of incidence and polarization. The electromagnetic field distribution is used to illustrate the absorption mechanism, and Stokes analysis is introduced to evaluate the polarization transition state. The designed structure can realize three electromagnetic modulation functions by changing the excitation conditions and can cover a wide range of frequency bands. Finally, we used coding to simulate the effect of loss on the wave absorption results in real applications and verified the stability of the structure. Our design provides new ideas for the development of terahertz communication and multifunctional integrated devices.

Bessel beams generation with biphase transition of vanadium dioxide metasurface

Bessel beams are highly attractive due to their non-diffraction properties, parallel processing capabilities, and large capacity. However, conventional methods for generating Bessel beams, such as using spatial light modulators, axicons, and diffraction optical elements, face limitations in terms of system complexity, bulkiness, low uniformity, and limited numerical aperture (NA). In this work, we exploited the phase change material vanadium dioxide (VO2) to generate both transmitted and reflected Bessel beams. Moreover, the self-healing property of Bessel beams was verified. Our results reveal that VO2 in the insulating state achieves a transmittance of 85% in the transmitting mode, while VO2 in the metallic state exhibits a reflection efficiency of 77% in the reflecting mode. This performance indicates the potential applications in efficient switchable metasurfaces.

Switchable Terahertz Metasurfaces for Spin-Selective Absorption and Anomalous Reflection Based on Vanadium Dioxide.

Conventional chiral metasurfaces are constrained by predetermined functionalities and have limited versatility. To address these constraints, we propose a novel chirality-switchable terahertz (THz) metasurface with integrated heating control circuits tailored for spin-selective anomalous reflection, leveraging the phase-change material vanadium dioxide (VO2). The reversible and abrupt insulator-to-metal phase transition feature of VO2 is exploited to facilitate a chiral meta-atom with spin-selectivity capabilities. By employing the Pancharatnam-Berry phase principle, complete 2π reflection phase coverage is achieved by adjusting the orientation of the chiral structure. At the resonant frequency of 0.137 THz, the designed metasurface achieves selective absorption of a circularly polarized wave corresponding to the state of the VO2 patches. Concurrently, it reflects the circularly polarized wave of the opposite chirality anomalously at an angle of 28.4° while maintaining its handedness. This chirality-switchable THz metasurface exhibits promising potential across various applications, including wireless communication data capacity enlargement, polarization modulation, and chirality detection.

Structural color tunable intelligent mid-infrared thermal control emitter

This work proposes a colored intelligent thermal control emitter characterized by adjustable structural color development with a reflection spectrum in the visible light range and intelligent thermal control with temperature switching in the mid infrared wavelength band. In the beginning, we investigate an intelligent thermal control emitter based on a multilayer membrane formed by the phase change material vanadium dioxide, metal material Ag, and dielectric materials Ge and ZnS. By incorporating the thermochromic material vanadium dioxide, the structure exhibits a high emissivity of εH = 0.85 in the range of 3–13 μm wavelength when in the high temperature metallic state, enabling efficient heat radiation. In the low temperature dielectric state, the structure only has a low emission capacity of εL = 0.07, reducing energy loss. Our results demonstrate that the structure achieves excellent emission regulation ability (Δε = 0.78) through the thermal radiation modulation from high to low temperature, maintaining effective thermal control. Furthermore, the thermal control emitter exhibits selective emission of peak wavelength due to destructive interference and shows a certain independence on polarization and incidence angle. Additionally, the integration of structural color adjustment capability enhances the visual aesthetics of the human experience. The proposed colored intelligent thermal control structure has significant potential for development in aesthetic items such as colored architecture and energy-efficient materials.

Study of the photothermal response of a multilayer structure doped with VO2@Au nanoshells

In this paper, we demonstrate a theoretical study of a multiphysics problem to solve for the photothermal response of a one-dimensional multilayer structure containing a layer doped with VO2@Au nanoshells. The VO2@Au nanoshell consists of a gold (Au) shell and a core of the phase change material vanadium dioxide (VO2) where the VO2 core transitions from a semiconductor state to a conductor state at the critical temperature of 68 °C. This behaviour results in thermal induced optical tunability through this reversible phase change of the VO2, due to the temperature dependent optical and thermal properties. The presence of the VO2 core, functioning as an ultra-fast and reversible optical phase-change material, leads to the emergence of photothermal induced bistability. The layer doped with the VO2@Au nanoshell is approximated as an effective medium using the Maxwell-Garnett Theory to enable an analytical solution. In this study, the optical response of the multilayer structure is obtained using the Transfer Matrix Method, while the thermal response for both stationary and transient states is solved using the Green’s Function Method and Kirchhoff’s Transformation. These equations are interconnected through the heat source term in the heat diffusion equations, representing the local heat generation induced by the continuous-wave laser applied to the structure. Our findings indicate that at the wavelengths of 658 nm and 747 nm, there are two distinct photothermal responses arising from the phase change of the VO2 core. At these wavelengths, the absorption of light increases and decreases, respectively, because of the VO2 phase change. This analytical method not only offers a thorough exploration of the fundamentals of induced photothermal responses in multilayer structures but also holds considerable potential for various applications, including solar cells, photothermal therapy, and nanothermal sensors.

Tunable terahertz perfect absorber using vanadium dioxide-based metamaterial for sensing applications

We present a design of terahertz (THz) perfect absorber (TPA) based on thermotropic phase change material vanadium dioxide (VO2). The TPA device is composed of a metal-insulator-metal (MIM) structure, and the top metal layer is tailored to form an inner VO2-based disk structure and an outer Au-based connected-ring structure. The electromagnetic responses of TPA device with different geometric parameters operated in the THz band are investigated, and the perfect absorption is achieved at 2.51 THz. Furthermore, by increasing the temperature applied on VO2 from 313 K to 363 K with an interval of 10 K, the disk structure changes from an insulating phase to a metallic phase. There is an extra resonance mode arises, which induces the resonance of TPA device can be switched from single to dual. Additionally, being exposed to an ambient environment with different refraction indices, the TPA device shows a high-efficient sensing capability with a sensitivity of up to 398 GHz per refractive index unit (RIU). These results indicate that the proposed design opens an avenue for tunable absorbers, actively controllable switches, THz logic devices, and high-efficiency sensors.

Composite phase modulated beam steering controllable reflective metasurface

Terahertz metasurface functional devices as an effective method to control terahertz waves have attracted extensive attention from researchers. In order to enhance the functionality and flexibility of the metasurface and adapt to diverse application scenarios and demands, a beam-steering controllable reflective metasurface is designed by combining the Pancharatnam-Berry phase principle and the phase change material vanadium dioxide in this work. The metasurface unit consists of five layers, they being the top layer that is a metal patterned layer, the third layer that is made of vanadium dioxide and located between the dielectric layers with different thickness, the dielectric layer that is made of polytetrafluoroethylene (PTFE), and the bottom layer that serves as a metal reflective layer. The metasurface units are rotated based on the Pancharatnam-Berry phase principle to obtain four metasurface units with fixed phase differences in between, after which the metasurface units are arranged in two dimensions based on the generalized Snell reflection law to obtain the desired phase-gradient deflected reflection beam. The insulating state-metallic state transition of the vanadium dioxide layer on the metasurface can change the phase gradient of the preset metasurface, thereby realizing the on/off function of deflection. The simulation results show that when the vanadium dioxide is in the insulating state, the phase gradient of the designed metasurface appears, and the metasurface can deflect the vertically incident circularly polarized wave with specific angle anomalies in a operating band of 1.1–2.0 THz; when the vanadium dioxide is in the metallic state, for the same operating band of the same metasurface, the phase gradient of the metasurface disappears, and the metasurface mirror reflects the vertically incident circularly polarized waves, thereby realizing the function switching. This design provides new possibilities for modulating the terahertz reflected beam, which will have potential applications in terahertz wireless communication and radar systems.

Photonic thermal switch via metamaterials made of vanadium dioxide-coated nanoparticles.

In this work, a photonic thermal switch is proposed based on the phase-change material vanadium dioxide (VO2) within the framework of near-field radiative heat transfer (NFRHT). The switch consists of two metamaterials filled with core-shell nanoparticles, with the shell made of VO2. Compared to traditional VO2 slabs, the proposed switch exhibits a more than two times increase in the switching ratio, reaching as high as 90.29% with a 100 nm vacuum gap. The improved switching effect is attributed to the capability of the VO2 shell to couple with the core, greatly enhancing heat transfer with the insulating VO2, while blocking the motivation of the core in the metallic state of VO2. The proposed switch opens pathways for active control of NFRHT and holds practical significance for developing thermal photon-based logic circuits.

Multifunctional metamaterial for realizing absorption and polarization conversion on the basis of vanadium dioxide

In this paper, the phase change material vanadium dioxide (VO2) is introduced to propose a tunable multifunctional metamaterial device, which treats the phase change property of VO2 to realize the switching of absorption, linear to linear (LTL) polarization conversion, and linear to circular (LTC) polarization conversion functions. When VO2 is in metal state, the structure can be applied as an absorber to achieve the wide-band and narrow-band absorption. In the broad frequency area of 2.007–2.803 THz, the absorption is above 90%. And the narrow-band absorption near the center frequency 1.0126 THz reaches 95.04%. When VO2 is in the insulator state, the studied device can be treated as a polarization conversion device to achieve LTL and LTC polarization conversion. In the low frequency range, the device achieves LTL with polarization conversion efficiency (PCR) above 90% when the frequency is between 0.439 and 0.907 THz. In the high frequency range, the structure can be treated as the LTC polarization converter to achieve right-hand circular polarization, left-hand circular polarization (LHCP), and LHCP in the ranges of 2.317–2.329 THz, 2.356–2.531 THz and 2.582–2.633 THz, respectively. In addition, the ellipticity is above 0.9. Finally, the effects of geometric parameters, angle of incidence and polarization angle on the absorption and PCR are also discussed. The proposed structure has great potential for advanced technologies such as imaging, sensing, communication, and stealth.

Research on the OAM and reduction of RCS of a dynamically tunable terahertz reconfigurable metasurface

A dynamically tunable reconfigurable metasurface in the terahertz (THz) band combined with the phase-change material vanadium dioxide (VO2) is proposed. Through theoretical and simulation study, the dynamic tunable reconfigurable metasurface designed in this paper works in the wide band of 1.09–2.13 THz frequency, and the polarization conversion ratio of the metasurface can reach more than 95%. Further, the relative bandwidth can reach more than 74%, and it still has good performance after the phase transformation of VO2. A metasurface coded with 3 bits and a special phase arrangement can control the electromagnetic wavefront, generate orbital angular momentum, focus vortices, reflect anomalously, and achieve radar cross section reduction. Therefore, the proposed metasurface has potential applications in secure communication, near-field imaging, wireless transmission, etc.

Tunable smart mid infrared thermal control emitter based on phase change material VO2 thin film

Thermal radiation is one of the three ways of heat transfer, among which the mid-infrared thermal radiation has attracted much attention. At present, static control of thermal emissivity has been unable to meet the practical application, the device of dynamic control of thermal radiation is expected. In this paper, we study an intelligent thermal controlled radiation emitter based on a layered structure formed by phase change material Vanadium Dioxide. The transition denaturation of Vanadium Dioxide can realize the switching process from heat dissipation at high temperature to heat preservation at low temperature. In the mid-infrared wavelength range of 5–13 μm, significant differences in emission characteristics are observed due to variations in the imaginary part of the dielectric constant of Vanadium Dioxide. When it is in the high temperature metallic state, the optimal structural parameters, from top to bottom, are 10 nm, 350 nm, 320 nm, and 200 nm. With these parameters, the structure exhibits an emissivity of 0.78 and a full width at half maximum of 8.03 μm. This configuration achieves effective thermal radiation dissipation, as governed by the Stefan-Boltzmann’s law. On the other hand, when the structure is in the low temperature dielectric state, it exhibits a low absorption effect with an emissivity of 0.10, thus avoiding excessive heat loss. The radiative modulation capability and thermal stability were achieved through the use of thermochromic material Vanadium Dioxide which exhibits temperature switchable behavior. Additionally, the thermal control emitter, utilizing its resonant cavity, enables tunability of peak wavelength and demonstrates a certain degree of independence with respect to polarization and incident angle. The designed emitter structure is simple and easy to fabricate, holding significant prospects for applications in engineering insulation materials, infrared camouflage, and thermal management.

Flexible Terahertz Metamaterials Absorber based on VO2

Terahertz (THz) metamaterials have attracted great attention due to their widely application potential in smart THz devices; however, most of them are fabricated on rigid substrate and thus limit the exploration of flexible THz electronics. In this paper, a flexible THz metamaterial absorber (MMA) incorporated with phase change material vanadium dioxide (VO2) is proposed. The simulation results indicate that two absorption peaks at around 0.24 THz (marked as A) and 0.46 THz (marked as B) can be observed by designing a I-shaped metamaterial combined with split ring structure. The strong absorption over 92% at 0.24 THz is bending-insensitive, but the absorption at 0.46 THz is bending-sensitive, across the bending angle in the range of 0–50 degrees. Moreover, dynamic modulation of the absorption can be achieved across the insulator-metal phase transition of VO2. Particularly, the absorption of the A-peak can be tuned from 99.4% to 46.9%, while the absorption of the B-peak can be tuned from 39.6% to 99.3%. This work would provide significance for the design of flexible THz smart devices.

Interconversion between dual-peak electromagnetically induced transparency and dual-peak electromagnetically induced absorption utilizing metasurface

Utilizing metasurface (MS), the transition between dual-peak electromagnetically induced transparency (EIT) and dual-peak electromagnetically induced absorption (EIA) in four states has been proposed in the terahertz (THz) band with the incidence of a circularly polarized (CP) wave. Additionally, the phase-change material vanadium dioxide (VO2) and photosensitive material silicon (Si) have been adopted. The four state transitions can be achieved by adjusting the pump light and the temperature which is not affected by incident CP waves. With the incidence of the pump light, Si can transform from the insulating state to the metallic state. Similarly, when the temperature exceeds 68 °C, VO2 enters the metallic state. Two different dual-peak EIT (State 1 and State 2) accompanied by slow light effect can be observed by modulating the state of VO2 without the action of Si. However, once Si is in metallic state, two different states of dual-peak EIA (State 3 and State 4) are achieved by changing the state of VO2. Notably, the MS has the property of polarization insensitivity. The theoretical oscillator model and equivalent RLC-circuit model verify the feasibility of dual-peak EIT and EIA.

Adjustable strong circular dichroism based on a tricircular arc metasurface.

Circular dichroism has promising applications in biology, molecular chemistry, and other fields. The key to obtaining strong circular dichroism is to introduce symmetry breaking into the structure, which leads to a great difference in the response to different circularly polarized waves. Here, we propose a metasurface structure based on three circular arcs, which produces strong circular dichroism. The metasurface structure combines the split ring with the three circular arcs and increases the structural asymmetry by changing the relative torsional angle. The causes of the strong circular dichroism are analyzed in this paper, and the influence of metasurface parameters on it is discussed. According to the simulation data, the response of the proposed metasurface to different circularly polarized waves varies greatly, with absorption of up to 0.99 at 5.095THz for a left-handed circularly polarized wave and a maximum circular dichroism of over 0.93. In addition, the incorporation of the phase change material vanadium dioxide on the structure allows flexible modulation of circular dichroism and modulation depths of up to 98.6%. The change of angle within a certain range has little effect on the structural performance. We believe that this flexible and angle robust chiral metasurface structure is suitable for complex reality, and large modulation depth is more practical.

Switchable Wideband Terahertz Absorber Based on Refractory and Vanadium Dioxide Metamaterials

Achieving actively tunable metamaterial absorption is a significant development direction. Phase-transition materials have attracted growing interest for the use in nanophotonics owing to their flexibility. In this work, we firstly demonstrate a wideband terahertz refractory absorber that achieves more than 90% absorptance in the range of 1.71--3.31 THz. The metal composing the structure is refractory metal, which could function in high-temperature conditions and complex electromagnetic environment. Then, we incorporate phase-change material vanadium dioxide (VO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) film to this refractory absorber, realizing high reflection of more than 93% in the metallic state, while the wideband perfect absorption peak over 98% is obtained in the insulating state. Calculated results show that metamaterial absorber obtains switchable functions. Furthermore, the tunable absorber has polarization-insensitive behavior. So, our designed absorber with dynamic tunable characteristics provides flexibility to adjust the absorption performance and has significant value in application. The proposed architecture offers a novel method for creating dynamic and multi-functional photonic devices in phase-change materials.

Active tuning hBN phonon polaritons and spontaneous emission rates based on VO&lt;sub&gt;2&lt;/sub&gt; and graphene

&lt;sec&gt;Active tunability of phonon dispersion and spontaneous emission (SE) are still open problems due to their exciting potential applications. In view of the fact that polaritons are very sensitive to the dielectric environment, in this study, with the help of the differences in optical property between the phase change material vanadium dioxide (VO&lt;sub&gt;2&lt;/sub&gt;) during the phase transition from the insulating state to metallic state and the tunable surface plasmon polaritons (SPPs) in graphene, a heterostructure composed of hyperbolic material hexagonal boron nitride (hBN) and graphene and VO&lt;sub&gt;2&lt;/sub&gt; is proposed to investigate the active tunability of hBN phonon polaritons (PhPs). In order to illustrate the underlying physical mechanism of the above heterostructures, the dispersion distributions of the above heterostructures are calculated and represented by the imaginary part of the p-polarized Fresnel reflection coefficient of the heterostructure, meanwhile the dispersion relation of the hBN/VO&lt;sub&gt;2&lt;/sub&gt; heterostructure in hyperbolic region is verified by the quasi-static approximation method.&lt;/sec&gt;&lt;sec&gt;Results indicate that the active tunability of hBN PhPs inside type-I and type-II hyperbolic bands can be achieved by controlling VO&lt;sub&gt;2&lt;/sub&gt; phase transition in hBN/VO&lt;sub&gt;2&lt;/sub&gt; heterostructure. The PhP dispersion change of the hBN/VO&lt;sub&gt;2&lt;/sub&gt; heterostructure is mainly caused by the change of the VO&lt;sub&gt;2&lt;/sub&gt; dielectric function when VO&lt;sub&gt;2&lt;/sub&gt; substrate changes from the insulating state into metallic state, which affects the total Fresnel reflection coefficient of the heterostructure, finally resulting in the PhP dispersion change of hBN/VO&lt;sub&gt;2&lt;/sub&gt; heterostructure. When graphene is introduced into the hBN/VO&lt;sub&gt;2&lt;/sub&gt; heterostructure, coupled hyperbolic plasmon-phonon polaritons (HPPPs) are obtained within type-I and type-II hyperbolic band of hBN, while the surface plasmon-phonon polaritons (SPPPs) are generated outside its hyperbolic bands. Moreover, comparative analysis of SE rates is presented for a quantum emitter positioned with the hBN/VO&lt;sub&gt;2&lt;/sub&gt; and graphene/hBN/VO&lt;sub&gt;2&lt;/sub&gt; heterostructure, revealing that the SE rates of these heterostructures can be modulated by the passive means including changing the hBN thickness and distance between the dipole emitter and the proposed heterostructure, and also by the active means including tuning VO&lt;sub&gt;2&lt;/sub&gt; phase states and graphene chemical potential without changing structural configurations. This study provides a theoretical guidance in realizing active tunability of both phonon dispersion and SE rate of the natural or artificial anisotropic optical materials by using functional materials including phase change materials and graphene.&lt;/sec&gt;

Transition from electromagnetically induced transparency to Electromagnetically Induced Absorption Utilizing Phase-Change Material Vanadium Dioxide Based on Circularly Polarized Waves

A circular-polarization metastructure (MS) with switchable functions connected to the transition from electromagnetically induced transparency (EIT) to electromagnetically induced absorption (EIA) is theoretically proposed under the action of circularly polarized (CP) waves in the terahertz (THz) band. Additionally, we use the phase-change material vanadium dioxide (VO 2 ) to achieve functional transformation. The MS is mainly composed of two metal bright modes and a VO 2 resonator. When the VO 2 is insulating, the EIT with a high and wide transmission window is realized between 0.460 THz and 0.911 THz due to the coupling between two bright modes. Once VO 2 reaches the metal state, the original high transmission window is transformed into the high absorption window and the phenomena from EIT to EIA (vice versa) are successfully achieved from 0.460 THz to 0.911 THz. The group delays and group index of EIT are 161 ps and 1126, respectively. The simulation results of EIT and EIA are verified by fitting the theoretical two-oscillator model. • The proposed MS provides a new idea to manipulate the transition between EIT and EIA. • Multiple parameters can be adjusted to manipulate the transmission amplitude and frequency. • The presented structure is great transparency or absorption for the EM wave. • The thickness of the proposed MS is subwavelength. • The proposed MS can be applied to antenna fields and wave plates.

Switchable dual-function metasurfaces with electromagnetic induction transparency-like and absorption

Two terahertz switchable metasurfaces with dual-function are proposed in this paper. Both metasurfaces contain a periodically arranged pattern layer made of silver, which is mounted on the stacking layer of polyimide and phase change material vanadium dioxide (VO2). The simulation results show that the designed metasurfaces can be converted from multi-band absorbers to electromagnetically induced transparency-like (EIT-like) analogs. When VO2 is in conductive state, the above metasurfaces work as dual-band absorber and tri-band absorber respectively, with absorptivities over 90 %; while VO2 is in insulating state, both structures are EIT-like. The physical mechanism of absorption and EIT-like effect is explained by the surface current distribution. In addition, by adjusting the structural parameters, the peak frequency of the absorbers and the window bandwidth of the EIT-like changes. Meanwhile, the dual-function of the metasurfaces can be maintained within a certain range of incidence and polarization angles. These results show that the switchable metasurfaces can achieve potential applications of modulators, optical buffers, and sensors at terahertz frequencies in the infrared light range.

Design of Thermal-Switchable Absorbing Metasurface Based on Vanadium Dioxide

This letter presents a thermal-switchable absorbing metasurface (TSAM) based on the phase-change material vanadium dioxide (VO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ). A thin film of VO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> was deposited on a sapphire substrate by a magnetron sputtering and then sliced into tiny chips, which can be regarded as thermal-switchable resistors. The surface structure of the TSAM element is realized by loading four VO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> chips into a square metallic loop. Polytetrafluoroethylene is used as the substrate due to its high thermal conductivity compared with foam. The TSAM is on the “absorbing” mode when it is heated underneath and is switched into the “reflecting” mode at room temperature. The absorbing mode is characterized by a wideband absorption (8–22 GHz). A TSAM prototype was fabricated and measured to verify this design.