Ramesh K. Pokharel

This article presents a new design for a compact four-resonator wireless power transfer (WPT) system tailored for biomedical implants (BIs). The design features symmetric transmitter (Tx) and receiver (Rx) units, each comprising two resonators and incorporates a stacked metamaterial (MTM) structure with near-zero permeability to enhance magnetic coupling and focus the field toward the RX. This configuration improves power transfer efficiency (PTE), increases transmission distance, and mitigates misalignment effects. This study also investigates the impact of lateral and angular misalignments on the proposed WPT system. An equivalent circuit model is developed to analyze system behavior, and simulations with a human phantom model confirm safe operation via specific absorption rate (SAR) analysis. The system is further integrated with a high-efficiency rectifier and demonstrated in a battery-charging experiment.

Wireless power transfer using beamforming technology has recently gained significant attention for sensor networks and embedded systems. This technology uses array antennas and mid-range RF power (15–20 dBm) rectifiers for efficient power delivery to sensors. Despite its potential, research on mid-range RF power CMOS rectifiers remains limited. Addressing this gap, we propose a high-efficiency pMOS-based rectifier employing a body-biasing technique—a proven method for enhancing device performance—specifically designed for wideband and mid-range RF power RF applications. Conventional rectifiers often depend on precise input impedance matching to achieve high power conversion efficiency (PCE), which restricts bandwidth and limits practicality in dynamic environments. To overcome these challenges, the proposed design integrates a modified matching network, combined with dynamic body-biasing, which lowers the pMOS threshold voltage and minimizes power losses. Simulations reveal a peak PCE of 60.5%, with efficiency exceeding 50% across a broad frequency range up to 2.5 GHz—significantly outperforming traditional designs. Unlike conventional impedance-matching solutions, this rectifier maintains robust performance under input mismatches, making it well-suited for beamforming-based WPT systems. This study highlights the potential of integrating body-biasing with advanced matching networks for efficient wideband rectifiers.

The use of multi-band matching for rectifiers leads to design complexity. Instead, recent advancements suggested self-matched branches combined in parallel to enable multi-band operation. However, this method controls only the imaginary part. In this paper, we propose an efficient dual-band rectifier with compact realization. The rectifier consists of two self-matched parallel branches. Each branch provides comprehensive impedance control over real and imaginary parts in the corresponding band independent of the design frequency. The branch impedance matching is analyzed theoretically, and design equations are presented. To verify the proposed theory, a compact dual-band rectifier was fabricated with a compact area of only 0.42 cm² after excluding the area required for the RF connector. The measured RF-DC power conversion efficiency (PCE) was >50% for input power (P_in) ranging from −5.5 dBm to 11 dBm at 390 MHz with a peak of 69%. Also, the PCE was >50% for P_in ranging from −4 dBm to 12 dBm at 690 MHz with a peak of 68%. The fabricated rectifier operates with a wide load range from 0.5 KΩ to 3 KΩ with PCE > 50% at both bands when P_in = 5 dBm.

This study introduces a comprehensive system for glucose level measurement using a compact two-port rectangular dielectric resonator (RDR) to validate the system’s accuracy against traditional invasive glucometer measurements. The system features a voltage-controlled oscillator (VCO) that generates a 2.47 GHz frequency. A power detector converts the RF signal to DC voltage levels, and a multimeter facilitates the interpretation. The primary sensor component is energized via a rectangular aperture-coupling mechanism in the ground plane. The RDR acts as a sensor because of the varying dielectric permittivity linked to different glucose concentrations, leading to unique resonance frequencies and magnitude shifts. The bare sensor's resonance frequency was designed to be at 3.28 GHz, shifting to 2.47 GHz when loaded with a human finger. The Cole-Cole method modeled the human thumb with the blood layer in simulation. An electrical prototype enhanced detection, providing a 39 E-02 MHz/mg/dL resolution at 2.47 GHz. The RDR sensors' S-parameters highly correlated with laboratory-based testing, achieving 92.68% accuracy. Compared to home-based invasive glucometer measurements, the proposed Continuous Glucose Monitoring (CGM) system with a two-port RDR sensor measures diabetes value changes with 92.08% precision.

The use of multi-band matching for rectifiers leads to design complexity. Instead, recent advancements suggested self-matched branches combined in parallel to enable multiband operation. However, this method controls only the imaginary part. In this letter, we propose an efficient dual-band rectifier with compact realization. The rectifier consists of two self-matched parallel branches. Each branch provides comprehensive impedance control over real and imaginary parts in the corresponding band independent of the design frequency. The branch impedance matching is analyzed theoretically, and design equations are presented. To verify the proposed theory, a compact dual-band rectifier was fabricated with a compact area of only 0.42 cm2 after excluding the area required for the RF connector. The measured RF-DC power conversion efficiency (PCE) was > 50% for input power (Pin) ranging from -5.5 dBm to 11 dBm at 390 MHz with a peak of 69%. Also, the PCE was > 50% for Pin ranging from -4 dBm to 12 dBm at 690 MHz with a peak of 68%. The fabricated rectifier operates with a wide load range from 0.5 KΩ to 3 KΩ with PCE > 50% at both bands when Pin=5 dBm.

This paper presents an efficient wideband data recovery circuit (DRC) for forward data transfer in the over-coupled mode of dynamic SWPDT systems. In the over-coupled mode, where the operating frequency varies, conventional DRCs often become ineffective due to their limited operating frequency range. To address this issue, we propose a wideband DRC using amplitude shift keying (ASK) with on–off keying (OOK) modulation. The proposed circuit also eliminates the need for diodes and averaging circuits, which are typically required in traditional designs. The proposed circuit achieves data recovery by passing the OOK-modulated signal through a proposed Voltage-to-Time Converter (VTC), followed by a comparator and inverter. Implemented in 180 nm CMOS technology, the circuit occupies an area of 2440 μm² and a power consumption of 52.08 μW. The circuit can operate across a wide range of carrier frequencies. It was tested and validated with OOK-modulated signals at 5 MHz, 50 MHz, and 150 MHz, confirming its versatility and robustness. The prototype circuit enables wireless data transmission in critically coupled, weakly coupled, and over-coupled modes of WPT systems, achieving a 2 Mb/s data rate without requiring receiver repositioning.

In this paper, a novel H-slot antenna system is presented for combating termites. Considering the effect of the moisture content in the presence of termites, a non-invasive technique that is based on detecting the moist spots of wood is introduced. The proposed sensing antenna system consists of two identical microstrip-fed H-slot antennas and a reflector at a distance of 1 cm. Based on the transmission coefficient level between the antennas, the moisture within the wood is detected. By utilizing the reflector, the system can achieve multiband operation and enhance the simulated gain to approximately 8.76 dBi, thereby improving its detection capability. The proposed single antenna was built on a commercial low cost FR4 substrate with compact dimensions of 20 mm × 20 mm × 1.6 mm. Through optimization of the stub dimensions, the proposed antenna resonates effectively at 4.2 GHz. Simulation results demonstrate that the system can achieve excellent moisture sensing capabilities not only across the wood surface but also to a depth of 0.95 inch using a perfect electric conductor (PEC) reflector. Regardless of the wood type, the proposed sensor also can identify moisture levels of 30%. The complete sensing system has been manufactured, and simulation results have been validated through measurements, confirming the efficiency of the proposed system as a moisture sensor for wooden structures.