Design of standalone wireless impedance matching (SWIM) system for RF coils in MRI

Abstract

The radio frequency (RF) power transfer efficiency of transmit coils and the signal-to-noise ratio (SNR) at the receive signal chain are directly dependent on the impedance matching condition presented by a loaded coil, tuned to the Larmor frequency. Sub-optimal impedance condition of receive coils significantly reduces coil sensitivity and image quality. In this study we propose a Standalone Wireless Impedance Matching (SWIM) system for RF coils to automatically compensate for the impedance mismatch caused by the loading effect at the target frequency. SWIM uses a built-in RF generator to produce a calibration signal, measure reflected power as feedback for loading change, and determine an optimal impedance. The matching network consists of a capacitor array with micro-electromechanical system (MEMS) RF switches to electronically cycle through different input impedance conditions. Along with automatic calibration, SWIM can also perform software detuning of RF receive coils. An Android mobile application was developed for real-time reflected power monitoring and controlling the SWIM system via Bluetooth. The SWIM system can automatically calibrate an RF coil in 3 s and the saline sample SNR was improved by 24% when compared to a loaded coil without retuning. Four different tomatoes were imaged to validate the performance of SWIM.

Discussion and Demonstration of RF-MEMS Attenuators Design Concepts and Modules for Advanced Beamforming in the Beyond-5G and 6G Scenario—Part 1

“…The RF micro electro-mechanical systems (RF-MEMS) are becoming progressively more popular in the development of the devices that are commonly found in modern radio front ends, since their low power consumption, insertion loss, together with their superior isolation and wideband linearity, make them a favorable candidate for microwave and millimeter-wave (mmWave) applications [22]. For this reason, different RF components were developed in the past years, ranging from switching matrixes [23], filters [24], and impedance matching networks [25], to phase shifters [26] and attenuators [27]. As compared to the other kind of devices, the field of RF-MEMS attenuators has been relatively less investigated to date.…”

Effect of Polypyrrole on the Capacitance Enhancement of the Spherical ZnS–ZnO/g-C3N4 Nanocomposite for Supercapacitor Applications

“…The carbon electrodes did not serve the required purpose and did not meet the market requirements due to their rather low energy density, this is considered a major drawback, so we nd that researchers are looking for noncarbon electrode materials such as electrodes with Faraday capacitance. They also expect in the future to produce capacitors with a very large capacity (pseudo capacitors) [7][8][9].…”