Flanched-Cross: An Efficient Cell Geometry for Beam Steering Metasurfaces with Orthogonal Polarisation Handling Capability

Geometry plays an important part in the characteristics of meta-cells used to design beam steering metasurfaces. One of the most desirable aspects of these cells is a large phase shift range that can be achieved with good transmission amplitude. However, the existing and most commonly used geometries for these cells are not able to produce a complete 360° phase range with an acceptable level of transmission amplitude. In this article, we present a new cell geometry, Flanched-Cross, that has superior transmission properties due to its unique shape and parametric variability than the commonly used geometries. The results are verified in simulation and further confirmed through prototyping and measurement. One- and two-dimensional steering are also performed for a dual-polarised base array to confirm the applicability of Flanched-Cross cell for beam steering purposes.

Flanched-Cross: An Efficient Cell Geometry for Beam Steering Metasurfaces with Orthogonal Polarisation Handling Capability

Geometry plays an important part in the characteristics of meta-cells used to design beam steering metasurfaces. One of the most desirable aspects of these cells is a large phase shift range that can be achieved with good transmission amplitude. However, the existing and most commonly used geometries for these cells are not able to produce a complete 360° phase range with an acceptable level of transmission amplitude. In this article, we present a new cell geometry, Flanched-Cross, that has superior transmission properties due to its unique shape and parametric variability than the commonly used geometries. The results are verified in simulation and further confirmed through prototyping and measurement. One- and two-dimensional steering are also performed for a dual-polarised base array to confirm the applicability of Flanched-Cross cell for beam steering purposes.

5G Millimeter-Wave Beamforming System using Substrate Integrated Waveguide

Beamforming is a key element of 5G that uses advanced antenna technologies to focus a wireless signal to a defined direction. Butler Matrix (BM) as a beamforming network is used to control the beam direction by utilizing the amplitude and the output phase. A particular technique for designing BM is through substrate integrated waveguide (SIW), which is used to realize the bilateral edge wall vias where the waveguide mode propagates through to support the current flow and reduce the loss of surface wave. Unlike conventional BM, the proposed design requires only hybrid couplers and phase shifter without any crossover. In this BM structure, the SIW hybrid coupler is designed, with two phase shifters of -90°, and one phase shifter of -180° to control the amplitude and phase shifting. This results in an optimized transmission amplitude and output phase difference. The BM also circumvents any crossover, to provide minimal losses. The hybrid coupler exhibits Sii and Sij characteristics at 28 GHz, with values of -27.35 dB for return loss, -3.9 dB for insertion loss, -3.2 dB for coupling, and -26.54 dB for the isolation. In the BM design, high transmission efficiency is observed where the return loss is less than -10 dB, while minimal transmission amplitudes are obtained within the values of ‒6 ± 3 dB. The three-port BM is designed using SIW with minimal loss and the phase difference at each respective output port of the BM shows values of 0°, -120°, and 120°. The three consecutive beams with the gains of 11.1 dBi for port 1 excitation, 9.06 dBi for port 2 excitation and 10.4 dBi for port 3 excitation is achieved when the antenna array is fed to the BM, and each of the radiated beams has beam angles of 0, -27 and 27 degrees.

Multipole resonance and Vernier effect in compact and flexible plasmonic structures

Spoof surface plasmons in corrugated metal surfaces allow tight field confinement and guiding even at low frequencies and are promising for compact microwave photonic devices. Here, we use metal-ink printing on flexible substrates to construct compact spoof plasmon resonators. We clearly observe multipole resonances in the microwave frequencies and demonstrate that they are still maintained even under significant bending. Moreover, by combining two resonators of slightly different sizes, we demonstrate spectral filtering via the Vernier effect. We selectively address a target higher-order resonance while suppressing the other modes. Finally, we investigate the index-sensing capability of printed plasmonic resonators. In the Vernier structure, we can control the resonance amplitude and frequency by adjusting a resonance overlap between two coupled resonators. The transmission amplitude can be maximized at a target refractive index, and this can provide more functionalities and increased design flexibility. The metal-ink printing of microwave photonic structures can be applied to various flexible devices. Therefore, we expect that the compact, flexible plasmonic structures demonstrated in this study may be useful for highly functional elements that can enable tight field confinement and manipulation.

Early Assessment of Acute Ischemic Stroke in Rabbits Based on Multi-Parameter Near-Field Coupling Sensing

Background: Maintaining normal supply of cerebral blood flow (CBF) and preventing secondary damage caused by acute ischemic stroke (AIS) are essential to the treatment of cerebrovascular diseases. Nevertheless, there hasn’t been fully accepted method targeting continuous assessment of AIS in clinical. Methods: Near-field coupling (NFC) sensing can obtain the electromagnetic properties related to the volume of intracranial components with advantages of noninvasiveness, strong penetrability and real-time monitoring. In this work, we built a multi-parameter monitoring system that is able to measure the phase and amplitude changes in electromagnetic wave reflection and transmission. For investigating its feasibility in AIS detection, sixteen rabbits were chosen to establish AIS models by bilateral common carotid artery ligation and then were enrolled for monitoring experiments.Results: During the six hours after AIS, the reflection amplitude (RA) shows a decline trend with a range of 0.69dB and reflection phase (RP) has an increased variation of 6.48°. Meanwhile, transmission amplitude (TA) and transmission phase (TP) decrease 2.14dB and 24.29° respectively. The statistical analysis illustrates that before ligation, three hours after ligation and six hours after ligation can be effectively distinguished by the four parameters individually. When all those parameters are regarded as recognition features in BP network, the classification accuracy of the three different periods reaches almost 100%.Conclusion: These results prove the feasibility of multi-parameter NFC sensing to assess AIS, which is promised to become an outstanding point-of-care testing method in the future.

Glucose Level Sensing Using Single Asymmetric Split Ring Resonator

In this article, a biosensor composed of a single metamaterial asymmetric resonator is specifically designed for sensing the glucose level of 1 µL of solution. The resonator has two gaps, and one of them ends with a semicircle shape on which the glucose solution is placed. This design helps in confining the drops of glucose solutions in a specific area where the field is maximally confined in order to enhance the electromagnetic wave-matter interaction. Six samples of glucose solutions with concentrations that cover hypoglycemia, normal and hyperglycemia conditions that vary from around 41 to 312 mg/dL were prepared and examined by this biosensor. The resonance frequency redshift was used as a measure of the changes in the glucose level of the solutions. Without glucose solution, an excellent agreement between the measured and simulated transmission amplitude was observed. The increase in glucose concentrations exhibited clear and noticeable redshifts in the resonance frequency. This biosensor revealed a 0.9997 coefficient of determination, which implies an excellent prediction fitting model. More importantly, a sensitivity of 438 kHz/(mg/dL) was observed over the range of concentrations of the aqueous solution.

Polarization Independent Achromatic Meta-Lens Designed for the Terahertz Domain

In recent years, metasurface-based focusing elements have gradually become an indispensable type of terahertz lenses. However, the meta-lens often suffers from chromatic aberration due to the intrinsic dispersion of each element, especially in the broadband application scenarios. In this paper, we design and demonstrate a silicon-based achromatic meta-lens working from 0.6 to 1.0 THz, which is polarization insensitive because of the adopted symmetrical structures. The simulated focal length and the full width at half maximum (FWHM) of the foci at different frequencies prove the achromatic behavior of our meta-lens compared with the chromatic counterpart. We also show that the focus shift incongruence of our design originates from the transmission amplitude distribution of the meta-lens. This article not only provides an achromatic planar lens working at terahertz domain but also reveals the importance of the amplitude distribution in the achromatic metasurface design.