Xiao Zhang’s research while affiliated with Shenzhen University and other places

Multichannel neural monitoring systems are crucial in the accurate diagnosis and treatment of epilepsy by continuously recording neural activity, allowing precise identification of epileptic zones. These systems demand an ultrawide-band (UWB) antenna with wireless power reception capability to facilitate high-data-rate communication and battery-free operation for the development of compact and long-lasting neural devices. This paper introduces a compact (9 × 11 × 0.25 mm 3) battery-free implantable UWB system with an integrated rectifier for multichannel epilepsy monitoring, wirelessly powered by a novel 2.4 GHz smart cap-based transmitter (Tx) antenna. Extensive simulations and measurements are conducted to analyze the system's performance. The implantable system exhibits a measured ultrawide bandwidth of 6.8 GHz (1.2-8 GHz) with peak gain values of-16.5,-23, and-24.1 dBi at 2.4, 4.8, and 5.8 GHz, respectively. The proposed wearable smart cap-based Tx antenna efficiently transfers power to the UWB implant system in various scenarios, including lateral and rotational misalignments, achieving a measured transmission coefficient (|S21|) of-20.06 dB at a 15 mm distance while ensuring user comfort and mobility. Moreover, the compact rectifying circuit achieves a maximum conversion efficiency of 78.4% at a low input power of 6 dBm across a 2 kΩ load. In addition, the safety of the system was validated using a realistic human head model to ensure compliance with the IEEE specific absorption rate limits. The features and performance metrics demonstrate that the proposed UWB implant system, powered by a wearable smart cap, offers a promising solution for safe, continuous, and battery-free multichannel epilepsy monitoring applications. Index Terms-Epilepsy monitoring, internet of medical things, neural activity tracking, smart cap, ultra-wideband (UWB), wireless power transfer (WPT).

This letter proposes a novel filtering antenna with an alternated form of radiative and non‐radiative resonators. The coupling effects between radiative and non‐radiative resonators are thoroughly analyzed with proposed equivalent circuit models. Within its passband, the continuous phase changes between two radiators are discussed in detail. To obtain an in‐phase superposition between two radiators at central frequency, the original half‐wavelength non‐radiative resonator is prolonged to one wavelength. Meanwhile, the phase shifting between two radiators yields a continuous beam steering performance in the passband. With the help of the proposed circuit model, the conditions for obtaining the maximum radiation gain, the key factors affecting the antenna bandwidth, and the prediction of the scanning range are discussed. The proposed method can indeed benefit the entire design procedure quantitatively rather than qualitatively. Finally, a prototype is demonstrated and fabricated. The results show that a third‐order filtering antenna is successfully designed with a relatively high gain of 9.84 dBi and a wide frequency scanning range of −29° to 21°. The proposed antenna enjoys a rather simple structure without extra feeding networks.

Multichannel neural monitoring systems are crucial in the accurate diagnosis and treatment of epilepsy by continuously recording neural activity, allowing precise identification of epileptic zones. These systems demand an ultrawide-band (UWB) antenna with wireless power reception capability to facilitate high-data-rate communication and battery-free operation for the development of compact and long-lasting neural devices. This paper introduces a compact (9 × 11 × 0.25 mm3) battery-free implantable UWB system with an integrated rectifier for multichannel epilepsy monitoring, wirelessly powered by a novel 2.4 GHz smart cap based transmitter (Tx) antenna. Extensive simulations and measurements are conducted to analyze the system’s performance. The implantable system exhibits a measured ultrawide bandwidth of 6.8 GHz (1.2–8 GHz) with peak gain values of -16.5, -23, and -24.1 dBi at 2.4, 4.8, and 5.8 GHz, respectively. The proposed wearable smart cap-based Tx antenna efficiently transfers power to the UWB implant system in various scenarios, including lateral and rotational misalignments, achieving a measured transmission coefficient (|S21|) of -20.06 dB at a 15 mm distance while ensuring user comfort and mobility. Moreover, the compact rectifying circuit achieves a maximum conversion efficiency of 78.4% at a low input power of 6 dBm across a 2 kΩ load. In addition, the safety of the system was validated using a realistic human head model to ensure compliance with the IEEE specific absorption rate limits. The features and performance metrics demonstrate that the proposed UWB implant system, powered by a wearable smart cap, offers a promising solution for safe, continuous, and battery-free multichannel epilepsy monitoring applications.

Reflectionless bandpass filters (BPF) have been realized in the waveguide and planar circuits; however, the literature does not report reflectionless air‐filled coaxial BPF. In this article, an X‐band input‐reflectionless air‐filled coaxial BPF is presented. The proposed filter has two transmission zeros (TZs) at the lower and upper stopband, respectively, to improve the selectivity. An equivalent circuit of this filter is provided to explain its reflectionless filtering response, which contains a BPF section and a bandstop filter (BSF) section. For verification, a reflectionless BPF centered at 10.2 GHz with an in‐band fractional bandwidth (FBW) of 6.39% has been designed and fabricated. The frequency range of measured 10‐dB return loss is from 4.75 to 13.00 GHz (10‐dB‐absorption FBW of 80.9%), showing a very attractive wideband reflectionless filtering behavior.

A quad-mode unified design approach for dual-band and tri-band dual-sense circularly polarized (CP) antennas is proposed. The four boresight radiating modes are obtained by loading an open-ended stub and a series resonator on the patch. The characteristic mode analysis (CMA) is employed to reveal the operational principles of the patch. The implementation of dual-band and tri-band dual-sense CP radiation is achieved using the same four modes. The unified antenna structure, which allows switching between dual-band and tri-band dual-sense CP radiation states within the same configuration, is realized by manipulating the modes. This is accomplished by simply adjusting the position of the shorting pin. The measurement results have confirmed the effectiveness of this method, with the multiband dual-sense CP antennas achieving a 3 dB axial ratio (AR) bandwidth of 1.14%-2.31%.

In this letter, we propose an extremely high-scanning-rate slot array antenna utilizing uniplanar-coupled waveguide cavities, allowing for easy fabrication and a low-profile planar implementation. In contrast to the current technique employing an alternating electric and magnetic coupling topology, the proposed new architecture relies on a combination of pure-magnetic coupling topology and phase reversal radiators, which allows high-scanning-rate beam scanning around the broadside. We design and fabricate both metallic waveguide and substrate integrated waveguide implementations to showcase the effectiveness of the proposed technique. Experimental results demonstrate that the two uniplanar-coupled waveguide antennas can scan angle ranges of 65 $^{\circ }$ and 70 $^{\circ }$ , respectively, within a 40 MHz frequency band centered at 4 GHz (equivalent to a 1% bandwidth). Compared to state-of-the-art methods, these proposed frequency-scanning antennas exhibit exceptionally high scanning rates, ease of fabrication, and a low-profile implementation.

In this letter, a novel pin-loaded self-decoupling method is proposed based on the fringing-field reshaping of the TM ₁₁ -mode circular patch antenna. At first, the primary cause of coupling is demonstrated to be attributed to the fringing field of the radiating patch, and the conventional antenna pair under the E -plane array arrangement always suffers from strong electric coupling, leading to poor isolation. Then, a shorting pin is strategically loaded to the coupling edge of each patch, by which the initial strong electric field density is strategically redistributed to be a local minimum, contributing to the significant isolation improvement. Furthermore, a prototype of the highly-isolated antenna pair is manufactured and measured. The results illustrate the achievement of high isolation over 20 dB and remained symmetric broadside radiation pattern. Finally, the proposed method is respectively demonstrated on the multiple-input--multiple-output (MIMO) arrays with more radiators and asymmetrical configuration, showcasing its efficacy for versatile decoupling.