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A dual-band metasurface (MS) with a wide reception angle operating at Wi-Fi bands (2.4 GHz and 5.4 GHz) is presented for electromagnetic (EM) energy harvesting applications. The MS unit cell comprises a subwavelength circular split ring resonator printed on the low-loss substrate. An air layer is sandwiched between two low-loss substrates to enhance the harvesting efficiency at operating frequencies. One of the main advantages of the proposed MS is that it uses only one harvesting port (via) to channel the captured power to the optimized load (50 Ω), which simplifies the design of a combined power network. According to the results of full-wave EM simulations, the proposed MS has a near-unity efficiency of 97% and 94% at 2.4 GHz and 5.4 GHz, respectively, for capturing the power of incident EM waves with normal incidence. Furthermore, the proposed MS harvester achieves good performance at up to 60° oblique incidence. To validate simulations, the MS harvester with 5 × 5-unit cells is fabricated and tested, and its EM properties are measured, showing good agreement with the simulation results. Because of its high efficiency, the proposed MS harvester is suitable for use in various microwave applications, such as energy harvesting and wireless power transfer.

Energy harvesting (EH) or scavenging is recognized as harvesting energy from ambient energy sources in the surrounding environment. This paper reports a literature review on radio frequency (RF) EH using different metasurface/metamaterial structures based on split-ring resonators (SRRs), electric inductive-capacitive (ELC) resonators, square-patch unit cells, square-ring unit cells, etc. The essential parameters in rectifying antenna (rectenna) design are included, such as receiving antenna efficiency, conversion efficiency, dimensions, supporting substrate properties, frequency band, and overall performance, etc. It is noted that rectenna design using conventional antennas such as microstrip antennas, monopole antennas, slot antennas, dielectric resonator antennas, etc. suffers from low power conversion efficiency with larger size. To overcome the above-mentioned constraints and enhance the conversion efficiency with smaller size, metasurface/metamaterial structures are used as EH collectors. An introduction to EH is discussed, followed by an overview of energy sources in the ambient environment. Several hypothetical and experimental studies on metasurface-based EH systems are summarized. Published version

Metasurface (MS) absorbers with polarization-insensitivity and wide-angle reception features have attracted much attention due to their unique absorption property. A polarization-insensitive broadband MS absorber structure, having wide-angle reception based on square split-ring resonators (SSRRs) and loaded with lumped resistors, is proposed in this paper. The proposed MS unit cell consists of a fixed-thickness FR4 dielectric substrate and a variable air-thickness substrate. The simulation results show that the proposed MS absorber is stable across a wide angular range for both normal and oblique incidences. Furthermore, the simulated results show that some parameters, such as unit-cell geometry and lumped resistors, can be varied to improve the performance of the MS absorber. The experimental results indicate that the proposed MS absorber can be achieved an absorption higher than 90% across the frequency range from 1.89 GHz to 6.85 GHz with a relative bandwidth of 113%, which is in agreement with simulation results. Thus, the proposed MS absorber can be more suitable in RF energy harvesting or wireless power transfer applications.

A broadband electromagnetic metasurface (MS) absorber with a wide-angle coverage is designed and discussed for energy harvesting applications. The proposed MS absorber consists of two split-ring resonators (SRR) forming an X-shaped in the middle and layout is designed on FR4 dielectric substrate. An air gap layer is separated between the dielectric substrate and a ground plane. At normal incidence, the proposed MS structure achieves a higher absorption ratio (>90%) with a 10-dB impedance bandwidth of more than 4 GHz (2.14 GHz-6.4 GHz). For oblique incidence, greater than 85% absorptivity is observed from $0^{\circ}, to 30^{\circ}$ across the frequencies range from 2.14 GHz to 6.4 GHz. Two higher absorption peaks of more than 80% at 2.4 GHz and from 5 GHz to 6.5 GHz for TEM polarization are achieved respectively at 45° and 60°. Furthermore, the absorption mechanism is numerically demonstrated in detail.

A microwave metasurface (MS) absorber for ISM band applications is proposed and studied. The proposed MS structure consists of two metallic layers separated by two dielectric FR4 materials with a thickness of 1.6 mm. An air gap with a thickness of 10 mm placed between the dielectric layers. The proposed MS absorber exhibits near-unity absorption and wider absorption bandwidth at an operating frequency of 2.4 GHz under normal incidence. For oblique incidence, it shows wider absorption bandwidth and an absorption value of more than 93% for different incident angles for TEM-mode and more than 93% at for TE mode. Moreover, a numerical analysis presented to explain the physical interpretation of the absorption mechanism in detail.

A wide-angle and polarization-insensitive metasurface instead of traditional antenna is built as the primary ambient energy harvester. Proposed metasurface harvester can receive electromagnetic (EM) energy from wide angles and received rectified power can be combined by DC combining for EM harvesting system. The reflection coefficient, power distribution, EM harvesting efficiency, and absorption efficiency on the normal and oblique incidences are studied and presented. For a single unit cell with periodic boundary condition, simulation results exhibit that the absorption and harvesting efficiencies are more than 98 and 96%, respectively, under normal incidence at an operating frequency of 2.4 GHz. The results also show that on the oblique incidence of 0°, the maximum absorption efficiency is more than 98% and it can achieve more than 80% reception efficiency at the incidence angle of ±60°.

Electromagnetic Compatibility (EMC) engineers should self-check the antenna’s condition and parameters, including Antenna Factor (AF) and Gain, continuously, by calibrating the antenna. Therefore, several analyses have been done to compare between SAM and SSM in EMC testing lab. Based on the analysis, the antenna to be used inside a 3 m semi-anechoic chamber need to be positioned 1.5 m above the ground plane to avoid the reflection. The Antenna Factor (AF) results show a good agreement with manufacturer data. SAM is recommended as a calibration method in the semi-anechoic chamber because the percentage error is 5% which is lower compared with SSM (18%). This is due to the site imperfection in the EMC lab. The uncertainty for the EMC lab is up to ±4 dB, compared to the calibration test site where allowed uncertainty is ±1 dB. Therefore, an absorber needs to be placed between two antennas. In addition, the phase center of the reference antenna needs to take into consideration for highly accurate AF.