ABSTRACT
Spiral inductors are required to realise high inductance in radio frequency (RF) circuits. Although their fabrication by using micro-electrical-mechanical systems, thin films, actuators, etc., has received considerable research attention, current approaches are both complex and expensive. In this study, we designed and fabricated a thermal spiral inductor by using a three-dimensional (3D) printed shape-memory polymer (SMP). The proposed inductor was inspired by kirigami geometry whereby a two-dimensional (2D) planar geometric shape could be transformed into a 3D spiral one to change the inductance by heating and manually transform. Mechanical and electromagnetic analyses of the spiral inductor design was conducted. Hence, in contrast with the current processes used to manufacture spiral inductors, ours can be realised via a single facile fabrication step.
ABSTRACT
In this paper, a MEMS (Micro Electro Mechanical Systems)-based frequency-tunable metamaterial absorber for millimeter-wave application was demonstrated. To achieve the resonant-frequency tunability of the absorber, the unit cell of the proposed metamaterial was designed to be a symmetric split-ring resonator with a stress-induced MEMS cantilever array having initial out-of-plane deflections, and the cantilevers were electrostatically actuated to generate a capacitance change. The dimensional parameters of the absorber were determined via impedance matching using a full electromagnetic simulation. The designed absorber was fabricated on a glass wafer with surface micromachining processes using a photoresist sacrificial layer and the oxygen-plasma-ashing process to release the cantilevers. The performance of the fabricated absorber was experimentally validated using a waveguide measurement setup. The absorption frequency shifted down according to the applied DC (direct current) bias voltage from 28 GHz in the initial off state to 25.5 GHz in the pull-down state with the applied voltage of 15 V. The measured reflection coefficients at those frequencies were -5.68 dB and -33.60 dB, corresponding to the peak absorptivity rates of 72.9 and 99.9%, respectively.
ABSTRACT
Functional metasurfaces help wireless communication to reach beyond current electromagnetic control device limitations. However, current reconfigurable functional metasurfaces require separate systems for function control. In particular, it is difficult to realize millimeter-wavelength regimes due to the increasing number of active elements with the reduction in unit cell size. This paper proposes a four-dimensional printed memory metasurface to memorize absorption and reflection function in millimeter-wavelength regimes. Thus, metasurfaces with electromagnetic absorption and reflection functions can be realized through mechanical shape memory by memorizing electromagnetic properties using four-dimensional printed structures. The desired electromagnetic performance was experimentally demonstrated and deformation time to memorize the initial structure was measured. The results confirmed that the proposed four-dimensional printed metasurface has potential for considerable contribution to multifunctional wireless devices such as smart electromagnetic wave control systems in reconfigurable intelligent surface, stealth, and wireless sensing systems.
ABSTRACT
Liquid materials' characterization using commercial probes and radio frequency techniques is expensive and complex. This study proposes a compact and cost-effective radio frequency sensor system to measure the dielectric constant using a three-material calibration. The simplified approach measures reflection coefficient magnitudes for all four materials rather than the complex values in conventional permittivity detection systems. We employ a sensor module based on a circular substrate-integrated waveguide with measured unloaded quality factor = 910 to ensure measurement reliability. Miniaturized quarter-mode substrate-integrated waveguide resonators are integrated with four microfluidic channels containing three known materials and one unknown analyte. Step-wise measurement and linearity ensures maximum 4% error for the dielectric constant compared with results obtained using a high-performance commercial product.
ABSTRACT
This paper proposes a gain-enhanced metamaterial (MM) absorber-loaded monopole antenna that reduces both radar cross-section and back radiation. To demonstrate the proposed idea, we designed a wire monopole antenna and an MM absorber. The MM absorber comprised lumped elements of subwavelength unit cells and achieved 90% absorbance bandwidth from 2.42-2.65 GHz. For low-profile configurations, the MM absorber was loaded parallel to and 10 mm from the monopole antenna, corresponding to 0.09 λ0 at 2.7 GHz. The monopole antenna resonated at 2.7 GHz with a 3.71 dBi peak gain and 2.65 GHz and 6.46 dBi peak gain, before and after loading the MM absorber, respectively. Therefore, including the MM absorber increased peak gain by 2.7 dB and reduced back radiation by 15 dB. The proposed antenna radar cross-section was reduced by 2 dB compared with a monopole antenna with an artificial magnetic conductor.
ABSTRACT
An optically transparent metamaterial absorber that can be obtained using inkjet printing technology is proposed. In order to make the metamaterial absorber optically transparent, an inkjet printer was used to fabricate a thin conductive loop pattern. The loop pattern had a width of 0.2 mm and was located on the top surface of the metamaterial absorber, and polyethylene terephthalate films were used for fabricating the substrate. An optically transparent conductive indium tin oxide film was introduced in the bottom ground plane. Therefore, the proposed metamaterial absorber was optically transparent. The metamaterial absorber was demonstrated by performing a full-wave electromagnetic simulation and measured in free space. In the simulation, the 90% absorption bandwidth ranged from 26.6 to 28.8 GHz, while the measured 90% absorption bandwidth was 26.8-28.2 GHz. Therefore, it is successfully demonstrated by electromagnetic simulation and measurement results.
ABSTRACT
This study focused on the radome and proposed an absorber with a meta-dome structure for ultra-wideband radar absorption using an FR-4 dielectric material on the metasurface absorber for protection. In addition to protecting the absorber, the metasurface absorber exhibited ultra-wideband frequency absorptivity from radar signals, with an absorptivity band from 4.6-12 GHz, including the C and X frequency bands of radar signals. A wide incidence angle should also be considered in addition to the absorption frequency band. Experimental results were obtained for all polarization angles at normal incidence for 5-14 GHz. Sensitivity to incident angle from 0° to 40° in the transverse electric mode and 0° to 60° in the transverse magnetic mode were observed. The proposed concept was demonstrated using full-wave simulation and experimental measurements.
ABSTRACT
In this paper, we propose a subwavelength metamaterial unit cell for low-frequency electromagnetic absorber applications. To realize a periodic array for a metamaterial absorber, the footprint size and thickness of a unit cell must be miniaturized to a subwavelength. We achieved the electrical size of the unit cell as 0.027λ × 0.027λ × 0.043λ at 2.4 GHz by introducing the inductive lump elements to a symmetric square-loop resonator. The performance of the proposed absorber was demonstrated by full-wave simulations and measurements. An inductance tolerance of 2% yielded errors of 1.2% and 1.25% in the absorptivity and absorption frequency, respectively. A prototype with 13 × 27 unit cells was fabricated and its absorptivity was measured to be 99.6% at 2.4 GHz.
ABSTRACT
In this study, we propose a thermal frequency reconfigurable electromagnetic absorber using germanium telluride (GeTe) phase change material. Thermally-induced phase transition of GeTe from an amorphous high-resistive state to a crystalline low-resistive state by heating is used to change the resonant frequency of the absorber. For full-wave simulation, the electromagnetic properties of GeTe at 25 °C and 250 °C are characterized at 10 GHz under normal incidence for electromagnetic waves. The proposed absorber is designed based on the characterized electromagnetic parameters of GeTe. A circular unit cell is designed and GeTe is placed at a gap in the circle to maximize the switching range. The performance of the proposed electromagnetic absorber is numerically and experimentally demonstrated. Measurement results indicate that the absorption frequency changes from 10.23 GHz to 9.6 GHz when the GeTe film is altered from an amorphous state at room temperature to a crystalline state by heating the sample to 250 °C. The absorptivity in these states is determined to be 91% and 92%, respectively.
ABSTRACT
In this study, we propose a broadband frequency-reconfigurable metamaterial absorber using a novel switchable ground plane (SGP). A double resistive square-ring resonator is introduced for broadband absorption. The distance between the top resonator pattern and the ground plane determines the resonant frequency; the proposed SGP is thus capable of switching the absorption frequency band. The SGP can be either ground or reactive, by switching the PIN diodes on and off, respectively. The SGP is placed as the middle layer, between the top pattern and the bottom ground plane. In the low frequency band, the SGP becomes reactive and the bottom ground plane works as the ground plane of the absorber. In the high frequency band, the SGP works as the ground plane and the bottom ground plane does not affect the absorber. The proposed idea is demonstrated via full-wave simulations and measurements. The absorption of the fabricated sample with 27 × 27 unit cells is measured under normal incidence. When the PIN diodes of the SGP are turned on, an absorption higher than 90% is achieved between 3.5-11 GHz. When the PIN diodes of the SGP are turned off, an absorption higher than 90% is achieved between 1.7-5.2 GHz.
ABSTRACT
In this study, the novel electronically switchable broadband metamaterial absorber, using a PIN diode, is proposed. The unit cell of the absorber was designed with a Jerusalem-cross resonator and an additive ring structure, based on the FR-4 dielectric substrate. Chip resistors and PIN diodes were used to provide both a broadband characteristic and a switching capability. To satisfy the polarization insensitivity, the unit cell was designed as a symmetrical structure, including the DC bias network, electronic devices, and conductor patterns. The performance of the proposed absorber was verified using full-wave simulation and measurements. When the PIN diode was in the ON state, the proposed absorber had a 90% absorption bandwidth from 8.45-9.3 GHz. Moreover, when the PIN diode was in the OFF state, the 90% absorption bandwidth was 9.2-10.45 GHz. Therefore, the absorption band was successfully switched between the low-frequency band and the high-frequency band as the PIN diode was switched between the ON and OFF states. Furthermore, the unit cell of the proposed absorber was designed as a symmetrical structure, and its performance showed insensitivity with respect to the polarization angle.
ABSTRACT
A stretchable electromagnetic absorber fabricated using screen printing technology is proposed in this paper. We used a polydimethylsiloxane (PDMS) substrate to fabricate the stretchable absorber since PDMS exhibits good dielectric properties, flexibility, and restoring capabilities. DuPont PE872 (DuPont, Wilmington, CT, USA), a stretchable silver conductive ink, was used for the screen printing technique. The reflection coefficient of the absorber was measured using a vector network analyzer and a waveguide. The proposed absorber was designed as a rectangular patch unit cell, wherein the top of the unit cell acted as the patch and the bottom formed the ground. The size of the patch was 8 mm × 7 mm. The prototype of the absorber consisted of two unit cells such that it fits into the WR-90 waveguide (dimensions: 22.86 mm × 10.16 mm) for experimental measurement. Before stretching the absorber, the resonant frequency was 11 GHz. When stretched along the x-direction, the resonant frequency shifted by 0.1 GHz, from 11 to 10.9 GHz, demonstrating 99% absorption. Furthermore, when stretched along the y-direction, the resonant frequency shifted by 0.6 GHz, from 11 to 10.4 GHz, demonstrating 99% absorption.
ABSTRACT
In this paper, we propose a stretchable radio-frequency (RF) strain sensor fabricated with screen printing technology. The RF sensor is designed using a half-wavelength patch that resonates at 3.7 GHz. The resonant frequency is determined by the length of the patch, and it therefore changes when the patch is stretched. Polydimethylsiloxane (PDMS) is used to create the substrate, because of its stretchable and screen-printable surface. In addition, Dupont PE872 (Dupont, NC, American) silver conductive ink is used to create the stretchable conductive patterns. The sensor performance is demonstrated both with full-wave simulations and with measurements carried out on a fabricated sample. When the length of the patch sensor is increased by a 7.8% stretch, the resonant frequency decreases from 3.7 GHz to 3.43 GHz, evidencing a sensitivity of 3.43 × 107 Hz/%. Stretching the patch along its width does not change the resonant frequency.
