Meiling Li

Compact, multi-functional receiving coils are essential for implantable medical devices (IMDs). In this paper, we propose an integrated toroidal rectifier that consolidates coupling, rectification, and filtering functions into a single power pick-up coil. This design employs only a minimal component set: two thin-film circuits, two compensation capacitors, two rectifier diodes, and one filter capacitor. In contrast to the traditional strategies that employ three independent modules on the receiver side—a power pick-up coil, a rectifier, and a filter—the proposed multi-functional toroidal rectifier can directly output DC power, making it highly suitable for implantation in the human body. Its operating principle is briefly illustrated in this study. Experimental results demonstrate that an AC-DC power transfer efficiency of 49.98% is achieved at an operating frequency of 40.68 MHz. Moreover, with a 1 W system power input, the specific absorption rates are 4.84 W/kg for a 1-g tissue mass and 2.25 W/kg for a 10-g tissue mass, both well within the regulatory safety limit. This highly integrated architecture resolves the trade-off between receiver-side compactness and functional completeness in IMDs, laying a technical foundation for next-generation implantable systems.

Self-resonant (SR) coils employ distributed compensation components in place of lumped components, enabling efficient power transfer and high integration. However, existing SR coils are restricted to four low-order compensation networks: SS, SP, PS, and PP. The higher-order double-sided LCC compensation topology has proven superior. Unfortunately, no pair of SR coils that can implement the double-sided LCC compensation topology has been available. This paper proposes an IPT system with double-sided self-resonant LCC coils, which integrates the necessary compensation components with the main coil in a distributed manner on a single substrate, eliminating the need for lumped elements. Formulas for resonant frequency, power transfer efficiency (PTE), output current, and power are provided. Advantageously, the proposed IPT system offers four benefits: constant current output independent of AC load, high PTE, independence of resonant frequency from coupling coefficients, and no damage to the front-end power supply during no-load operation. These advantages are experimentally demonstrated, achieving a PTE of 91% between coils at a 35 mm gap.

This letter presents a compact, broadband, global navigation satellite system (GNSS) antenna with wide axial ratio (AR) beamwidth. The proposed antenna consists of multiple coplanar metal patches, square dielectric substrate and compact transformed metallic cavity. Owing to the coupling feeding between those coplanar metal patches, the proposed antenna can realize a relatively broad bandwidth in the operating frequency band. Meanwhile, by utilization of single-layer coplanar coupling technology, the present antenna is only 0.30λ0×0.30λ0×0.07λ0. In order to increase half-power beamwidth and AR beamwidth, claw patches and a compact transformed metallic cavity are introduced. Simulation and measurement results show that the proposed antenna possesses a broadband frequency range from 1.05 GHz to 1.73 GHz that meets the operating frequency of all satellite navigation systems, and the maximum AR beamwidth range is achieved from -104° to 98° (1.575 GHz) by using the diffraction effect of the electromagnetic wave in the transformed metallic cavity.

Self-resonant (SR) coils replace lumped with distributed compensation components, enabling efficient power transfer and high integration. However, current SR coils function merely as series (S) or parallel (P) resonant tanks, thereby supporting merely four low-order compensation networks: SS, SP, PS, and PP. High-order compensation networks have demonstrated superiority over low-order counterparts, providing enhanced safety, stability, and design flexibility. Unfortunately, no SR coil currently with high-order compensation network characteristics. This article proposes a novel SR coil with LCC compensation characteristics that integrates the required compensation components in the form of distributed structures with the main coil on a single substrate, eliminating lumped components. To verify feasibility, a pair of SR coils, incorporating a normal SR coil, are fabricated, which constitute a SR coil inductive power transfer (IPT) system with LCC-S compensation characteristics. Different with traditional LCC-S systems, the compensation inductor in the proposed SR coil participates in power transfer. Therefore, corresponding formulas for the resonant frequency, ac–ac power transfer efficiency (PTE), output voltages and power are provided. Favorably, the proposed IPT system exhibits three advantages: a constant voltage output independent of the ac load, high ac–ac PTE over a wide range of ac load values, independence of resonant frequency from coupling coefficients, and no damage to the front-end power source during no-load operation. Experimental results demonstrate a coil-to-coil PTE of 93.2% and dc–dc efficiency of 80.5% over a 35 mm spacing gap. In addition, a LED monitor is successfully powered, indicating its potential for application in electronic devices, such as mobile phones and laptops.

This paper proposes a compact low-profile 5G Multiple-input multiple-output (MIMO) antenna system. The system comprises four antenna elements: two main antennas, and two diversity antennas. The two main antennas are symmetrical to each other, and both cover the identical frequency bands of 700 - 960 MHz and 1710 - 6000 MHz, while the two diversity antennas are also symmetrical to each other and cover the 1710-6000 MHz band. The proposed main antenna exhibits polarization orientation differences at different frequencies; thus, arranging four antennas enables adjacent antennas to have mutually orthogonal polarizations, thereby achieving low mutual coupling. Moreover, the overall size of the MIMO antenna system is only 74 mm × 74 mm × 11 mm, and the isolation between each antenna exceeds 10 dB. Experimental test results indicate that the MIMO antenna system performs excellently, meeting the requirements for practical engineering applications, and particularly demonstrates significant size advantages in MIMO antenna applications.

A switchable integrated absorber and radiator is proposed in this letter based on a planar ultra-wideband modular antenna (PUMA) structure integrated with PIN diodes. The switchable PUMA can serve as a resistor-free absorber by utilizing the semi-conductive mode of PIN diodes, or a radiator when the diodes are off. Additionally, a simplified-fed method for PUMA array is proposed, achieving excellent radiation performance comparable to a fully-fed array with per-element excitation. A 9 × 9 PUMA array prototype is fabricated and measured. For linear polarization, the measured 10 dB RCSR (radar cross-section reduction) bandwidths are 4–15.6 GHz (normal incidence), 4.3–14.8 GHz (TM 70°), and 5.8–16.6 GHz (TE 30°). For circular polarization, the 10 dB RCSR bandwidth are 4–15.6 GHz (normal incidence) and 5.5-14.9 GHz (CP 45°). Meanwhile, the prototype exhibits a measured -10 dB radiation bandwidth of 9.17-9.9 GHz and a peak gain of 14.9 dBi at 9.5 GHz. This work provides a new approach to designing integrated radiator and absorber structures, with potential applications in satellite or aircraft communications.

The MHz inductive power transfer (IPT) system has broad application prospects due to its high safety, longer transmission distance, and better tolerance for misalignment. However, the increase in frequency will lead to an increased loss of lumped components, such as inductors and capacitors, in peripheral circuits, thereby reducing efficiency. This is currently the bottleneck problem encountered by MHz IPT. To address this key challenge, researchers have tried to remove the lumped components in the peripheral circuit while ensuring the functions of the IPT system. One successful and beneficial attempt is the self-resonant coil, which replaces traditional lumped resonant capacitors with distributed capacitors formed by coil turn-to-turn capacitance, ensuring compensation for leakage inductance and eliminating reactive power. This innovative integration makes efficiency and integration greatly improved. In this article, the novel coil named Recticoil, on which the rectification function is integrated further, is proposed for efficient compact IPT. Recticoil can directly output dc power without additional compensation and rectification circuits. By analyzing a toroidal coil where two separate conductors generate a voltage differential, and incorporating two diodes, resulting in a dc output. Subsequently, the self-resonant coil replaces the toroidal coil to form Recticoil, and the equivalent circuits of Recticoil are given and analyzed. In addition, the analysis and test method of rectification efficiency is given. The experimental results show that the Recticoil achieves a rectification efficiency as high as 97.25% at 6.78 MHz, outperforming both the bridge rectifier and the Class E rectifier. Additionally, the compact construction of Recticoil eliminates the volume of traditional rectifiers. All of these advantages of Recticoil render it a promising candidate for applications in wearables and miniaturized devices.

The Smith chart is a graphical approach for solving impedance matching problems in the microwave circuit design, which provides visualized traces, but it is not applicable to address impedance discontinuities graphically, especially for multiple-impedance transmission lines (TLs) within microwave networks. In this letter, a novel transformation of normalization standard (TNS) method is proposed, which is applied to the Smith chart to solve the aforementioned problem. Then, TNS traces are derived and applied to the classical Smith chart, obtaining an improved Smith chart. In addition, the TNS idea is applied to the microwave circuit design examples. The proposed TNS method provides a convenient visualized way for the design of microwave circuits with multi-impedance TLs.

This study first proposes a planar alternating winding coil (PAWC) integrating a magnetic backplate, adopting a dual-sided alternating winding architecture on dielectric substrates. The proposed PAWC system features three fundamental characteristics: load-independent constant-current output, broad-range high-efficiency power transfer, and inherent no-load protection. During no-load operation, the transmitter exhibits high-impedance characteristics, effectively entering a zero-current shutdown state that completely prevents the overcurrent risks typical of series-series (S-S) compensated systems. When the receiver approaches the charging position, the system autonomously shifts to a zero-reactance operating mode at the same working frequency, achieving efficient power transfer without supplemental compensation networks. This design enables state switching purely through relative coil positioning, eliminating the need for additional sensing or switching components. Experimental validation confirms 92.8% coil-to-coil transfer efficiency at 5 mm separation, with efficiency exceeding 90% across 50−300 Ω load variations. These advancements offer particular value for safety-critical applications, including smart home ecosystems and medical implants, where the system's self-regulating switching capability and robust efficiency significantly enhance operational reliability.

Self-resonant (SR) coils with high quality factor $Q$ play a critical role for wireless energy transmission systems. In this article, a new single-layered spiral SR coil is introduced based on coplanar waveguide, which consists of two gradual-width spiral copper traces. Compared with traditional equal-width coils, the proposed coil increases the conductive area at specific location. This design significantly reduces loss during the current transmission, further improving $Q$ of the coil. The simulation and experimental tests have confirmed that the proposed coil exhibits an outstanding $Q$ of 436 at a resonant frequency of 13.58 MHz, which is the highest $Q$ of the same frequency and size at present, and indicates a good application prospect for future inductive power transfer (IPT) transmission system.