Fen Xia

Inductive link intended to deliver energy to implantable devices is recently becoming a popular method. To improve link efficiency, the compensated capacitors are adopted to resonate at the same frequency with the power transfer frequency on both sides. However, there is limited research on link efficiency and output power concerning quality factors, the selection between serial–parallel (SP) and serial–serial (SS) topologies, as well as coil design. This study delves into the efficiency of SP and SS topologies using rigorous mathematical derivations with reflected impedance models in terms of quality factors. It introduces a selection factor to help choose topology based on link efficiency. Results show that SS is better when the load quality factor ( $Q_{L}$ ) is lower than the selection factor, and vice versa. The study also examines the performance limits of both topologies concerning frequency, inductance, and load impedance. It proposes a specific $Q_{L}$ for maximum efficiency and a coil design procedure considering specific absorption rate limitations. By leveraging simulations and the design procedure, the study manufactures a pair of flexible coils for biomedical use. The designed link achieves a 62.99% efficiency under a 500 $\Omega$ load, with an overall efficiency of 46.96% including a passive rectifier.

The recent COVID-19 pandemic has caused tremendous damage to the social economy and people’s health. Some major issues fighting COVID-19 include early and accurate diagnosis and the shortage of ventilator machines for critical patients. In this manuscript, we describe a novel solution to deal with COVID-19: portable biosensing and wearable photoacoustic imaging for early and accurate diagnosis of infection and magnetic neuromodulation or minimally invasive electrical stimulation to replace traditional ventilation. The solution is a closed-loop system in that the three modules are integrated together and form a loop to cover all-phase strategies for fighting COVID-19. The proposed technique can guarantee ubiquitous and onsite detection, and an electrical hypoglossal stimulator can be more effective in helping severe patients and reducing complications caused by ventilators.

The recent COVID-19 pandemic has caused tremendous damage to social economy and people’s health. Some major issues fighting COVID-19 include early and accurate diagnosis and the shortage of ventilator machines for critical patients. In this work, we propose a closed-loop solution to deal with COVID-19: portable biosensing and wearable photoacoustic imaging for early and accurate diagnosis of infection and magnetically neuromodulation or minimally invasive electrical stimulation to replace the traditional ventilation. Proposed technique can guarantee ubiquitous and onsite detection, and electrical hypoglossal stimulator can be more effective in helping severe patients as well as reducing complications caused by ventilators.

Obstructive sleep apnea (OSA), a common sleep disorder disease, affects millions of people. Without appropriate treatment, this disease can provoke several health-related risks including stroke and sudden death. A variety of treatments have been introduced to relieve OSA. The main present clinical treatments and undertaken research activities to improve the success rate of OSA were covered in this paper. Additionally, guidelines on choosing a suitable treatment based on scientific evidence and objective comparison were provided. This review paper specifically elaborated the clinically offered managements as well as the research activities to better treat OSA. We analyzed the methodology of each diagnostic and treatment method, the success rate, and the economic burden on the world. This review paper provided an evidence-based comparison of each treatment to guide patients and physicians, but there are some limitations that would affect the comparison result. Future research should consider the consistent follow-up period and a sufficient number of samples. With the development of implantable medical devices, hypoglossal nerve stimulation systems will be designed to be smart and miniature and one of the potential upcoming research topics. The transcutaneous electrical stimulation as a non-invasive potential treatment would be further investigated in a clinical setting. Meanwhile, no treatment can cure OSA due to the complicated etiology. To maximize the treatment success of OSA, a multidisciplinary and integrated management would be considered in the future.

A dispersive delay structure, or phaser, is an integral part of analogue signal processor. A phaser is a circuit, whose group delay can be engineered to obtain the desired response as a function of frequency. Traditionally, phasers have been implemented in circuits or waveguide structures, but they can never deal with electromagnetic waves in free space due to limitation of natural materials. To resolve this drawback, a novel metasurface‐based structure, spatial phaser, for analogue signal processing in the spatial domain is proposed. A general design theory is put forward to realize the spatial phaser for manipulating the dispersive delay of electromagnetic waves. To demonstrate this method, three spatial phasers with different group‐delay responses are elaborately devised and a prototype that exhibits a positive‐triangular group delay from 8 to 10 GHz is fabricated. The experimental and simulation results show good agreement. This work will facilitate the development of real‐time analogue signal processing in spatial domain for applications in radars, electronic countermeasures, and other related areas.

A novel designed, compact uniplanar Vivaldi antenna for microwave imaging is proposed in this paper. With its broad bandwidth and end-fire radiation performance, it is especially suitable for microwave imaging systems. In the proposed antenna, a novel feed structure is proposed. A CPW feed is embedded into the Vivaldi patches, which ensures the whole structure to be compact and simple. The Vivaldi patches leads to wide bandwidth, high gain and very good front to back ratio compared to conventional antennas. The bandwidth is about 14.9 GHz (1.2 - 16.1 GHz) in terms of the 10dB return loss. Gain of the antenna is 7.0 dBi, and the front-to-back ratio is 16 dB.

In this letter, we propose a wideband patch antenna for the head imaging systems. It is composed of a patch and the ground, and both structure are largely token off in comparison with normal patch antenna. By analyzing the structure of this antenna, we could obtain the band is mainly controlled by three parameters. Extensive simulations demonstrate that patch antenna provides wideband operation with -10 dB bandwidths of 71.1% at the frequency of 1.23 - 2.63 GHz. Moreover, the radiation patterns are almost the bi-directional and the gains are all above 3 dBi at entire operation frequencies.

In this letter, we propose a dual-band filter using open stub-loaded resonators. The dual-band filter is analysed by transmission line theory and the physical dimensions of the structure can be easily deduced for 5G application. Thus, based on full-wave simulation, the proposed design is verified.