Yong-Xin Guo’s research while affiliated with City University of Hong Kong and other places

Uncertainty quantification (UQ) of high-speed circuits by Monte Carlo (MC) simulations is highly time-consuming, whereas surrogate-model-based UQ is much more efficient. In this article, a surrogate modeling framework based on proper orthogonal decomposition (POD), polynomial chaos expansion (PCE), and deep neural network (DNN) is proposed for the UQ of high-speed circuits, which is called POD-enhanced multi-PCE DNN (POD-MPCE-DNN). In the POD-MPCE-DNN model, the DNN block extracts low-dimensional features from high-dimensional uncertain parameters. These low-dimensional features are then fed into the multi-PCE (MPCE) blocks to predict the POD coefficients. The predicted POD coefficients are used to calculate circuit responses by the inverse POD (IPOD) block. The whole framework well addresses the challenges of high-dimensional inputs and outputs in surrogate-based UQ for high-speed circuits. Furthermore, analytical formulas for calculating the mean and variance of circuit responses are derived from the POD-MPCE-DNN model. Numerical examples of the UQ for radio frequency (RF) low-noise amplifier (LNA) circuits and high-speed links are provided to validate the POD-MPCE-DNN model. Compared with conventional surrogate models, the POD-MPCE-DNN model achieves the highest accuracy. Moreover, it realizes much higher efficiency than circuit MC simulations in the UQ of high-speed circuits.

Programmable metasurfaces (PMSs) exhibit great potentials in target detection techniques, because they can take actions to change channel propagation characteristics which introduces further degrees of freedom for system optimizations. However, responses of most traditional PMSs are sensitive to incident angles of impinging electromagnetic waves, resulting in a failure of angular estimation to dynamic targets coming from different directions. Herein, by proposing a fully resonant structure and introducing a mode-alignment technology, we report an isotropic angle-insensitive PMS whose phase response is stable with respect to different incident angles in both elevation- and azimuth-planes. A radar scheme that uses such a PMS as a periscope is also demonstrated, to detect drones in a non-line-of-sight (N-LOS) scenario which usually happens in an urban environment. Our proposed scheme enables those targets even falling in shadow areas caused by high buildings to be successfully detected and tracked, which shows promising potentials in N-LOS target detections.

Radiofrequency harvesting using ambient wireless energy could be used to reduce the carbon footprint of electronic devices. However, ambient radiofrequency energy is weak (less than -20 dBm), and thermodynamic limits and high-frequency parasitic impedance restrict the performance of state-of-the-art radiofrequency rectifiers. Nanoscale spin rectifiers based on magnetic tunnel junctions have recently demonstrated high sensitivity, but suffer from a low a.c.-to-d.c. conversion efficiency (less than 1%). Here, we report a sensitive spin rectifier rectenna that can harvest ambient radiofrequency signals between -62 and -20 dBm. We also develop an on-chip co-planar waveguide-based spin rectifier array with a large zero-bias sensitivity (around 34,500 mV/mW) and high efficiency (7.81%). Self-parametric excitation driven by voltage-controlled magnetic anisotropy is a key mechanism that contributes to the performance of the spin-rectifier array. We show that these spin rectifiers can wirelessly power a sensor at a radiofrequency power of -27 dBm.

Radiofrequency harvesting using ambient wireless energy could be used to reduce the carbon footprint of electronic devices. However, ambient radiofrequency energy is weak (less than −20 dBm), and the performance of state-of-the-art radiofrequency rectifiers is restricted by thermodynamic limits and high-frequency parasitic impedance. Nanoscale spin rectifiers based on magnetic tunnel junctions have recently demonstrated high sensitivity, but suffer from a low a.c.-to-d.c. conversion efficiency (less than 1%). Here we report a sensitive spin rectifier rectenna that can harvest ambient radiofrequency signals between −62 and −20 dBm. We also develop an on-chip co-planar-waveguide-based spin rectifier array with a large zero-bias sensitivity (around 34,500 mV mW⁻¹) and high efficiency (7.81%). The performance of our spin rectifier array relies on self-parametric excitation, driven by voltage-controlled magnetic anisotropy. We show that these spin rectifiers can be used to wirelessly power a sensor at a radiofrequency power of −27 dBm.

In this paper, two new methods are proposed for miniaturizing planar ultra-wideband horizontally-polarized omnidirectional Vivaldi antenna arrays. In the first method, the order of a power divider is decreased by means of feeding two neighboring Vivaldi antenna elements in series as a sub-array, or termed as a double-Vivaldi antenna element and thus the layout area required for a feeding network is reduced. Therefore, the layout problem of a conventional circular Vivaldi antenna array with a confined size is solved. Meanwhile, non-uniform elements with different taper rates are used to solve the in-band peak gain variation that is caused by a disc monopole mode. In this way, a non-uniform series-fed double-Vivaldi antenna array is presented. In the second method, a folded loop structure is introduced for an electrical size reduction of the aforementioned array. As a result, a lower resonant frequency is obtained. Measured results show that the final design has advantages of a large operating bandwidth, a small footprint of π × (0.284λ _max ) ² and a high gain. Besides, a clear design flowchart is given.

In this letter, a modified compact ultra-wideband directional bow-tie antenna is designed and used for underwater ground-penetrating radar (GPR) measurement. The antenna features a compact size of 89 × 89 × 50 mm³, achieved through the use of a crescent-shaped, double-layer patch structure and a cylindrical reflective cavity with grooves. In addition, a novel electromagnetic wave-absorbed medium is presented and filled within the reflective cavity, improving the time-domain performance of the antenna. The assembled antenna was measured in an artificial lake. The measurement results show that the proposed antenna has a wide operating band of 157–600 MHz, and a gain of 2.76–7.77 dBi in the main-lobe direction. Furthermore, a field radar experiment is also conducted in the lake. The radar image shows a clear target response, indicating that the antenna can be used well for underwater detection.

In this paper, a novel compact dual-polarized wearable antenna is proposed for into-body bio-telemetric applications. Dual polarization is realized by utilizing a meandered rectangular loop and an open-ended slot, which are both designed on a flexible printed circuit board (FPCB). The inner patch with an open-ended slot not only serves as a capacitive loading for the adjacent loop, but also generates a new orthogonal radiation by properly adjusting the structure of the modified T-shaped open slot. The simulated wearable antenna maintains wide -10 dB impedance bandwidths of 2.26-2.78 GHz (21.22%) for the rectangular loop element and 2.20-2.71 GHz (20.82%) for the open-ended slot element, with in-band port isolation of more than 25 dB. Moreover, for evaluating the into-body communication link with both polarization and spatial diversities, a proof-of-concept design of the linearly polarized in-body antenna is also reported with varied positions and orientations inside the homogeneous phantom. And a comprehensive link measurement is conducted by adopting multiple proposed wearable antennas which tightly attach to the phantom surface with specific separation distances. The measured results indicate a peak transmission performance of 38.9 dB with a 60 mm implant depth. And the dual-polarized and spatial configurations of the wearable antennas also enable the synthesis of the into-body communication link to mitigate the uncertain positions and rotations of the in-body antenna in practical scenarios.