Serial and Parallel Active Decoupling Characterization Using RF MEMS Switches for Receiver Endoluminal Coils at 1.5 T

Abstract

MEMS (Micro Electro Mechanical System) switches were assessed and compared to PIN diode in fulfilling the task of active decoupling of Receiver Endoluminal Coils (RECs). Three prototype RECs with the PIN diode in parallel (pPIN), MEMS in parallel (pMEMS) and MEMS in series (sMEMS) with the REC loop were built. Quality factors (Q-values), decoupling efficiency and switching delays were characterized on bench and Signal-to-Noise Ratios (SNRs) established on images at 1.5 T. Q-values were equal to 62.5, 41.2 and 65.1 for pPIN, sMEMS and pMEMS, respectively. In the decoupled state, reflection coefficients S11 and S21 at resonance frequency both indicated proper decoupling. Switching delays were less than 0.7 µs and 10 µs for pPIN and MEMS RECs, respectively. Decoupling/coupling delays of MEMS remained compatible with most Magnetic Resonance (MR) clinical applications. For all prototypes, MR images displayed no signal saturation and similar elliptical image sensitivity patterns. No artifacts due to active decoupling failure were observed. Mean SNR values obtained with pMEMS REC were higher than those obtained with sMEMS REC but lower than with pPIN REC because of the use of additional instrumentation to render the scanner compatible with the MEMS utilization. MEMS in parallel are an interesting alternative to PIN diode for decoupling and could lead to better SNR with a compatible MR system (dedicated control signal). The MEMS in series can be used for both decoupling and reconfiguration of the REC loop geometry for colon wall examination.

Electromagnetic Simulation of Signal Distribution of Various RF Endoluminal Loop Geometries with Coil Orientation: Towards a Reconfigurable Design

“…Moreover, to place the MEMS in series with the loop coil adds an additional resistance. As shown in a previous work [29] comparing coil prototypes with a reference coil using a PIN diode in parallel with MEMS placed in series, the quality factor was reduced from 62 to 41. It is, however, not possible to strictly and even theoretically consider similar comparisons because MEMS allow for the use of a common conductor, which cannot be done when using, for instance, two independent coils.…”

“…MEMS switches were successfully used (i) to open or close portions of metallic conductors and thus to reconfigure loop coil geometry [23], (ii) to shift the resonance frequency in the case of dual-tuned RF coils [24,25], (iii) to get high RF shimming performances (high localized B 0 homogeneity) [26], (iv) to control and automatize a wireless power transfer system [27], and finally (v) to control multiple receiver coil arrays with reduced power consumption and cabling system improving the SNR [28]. A recent work [29] demonstrated the feasibility and the impact of using MEMS switches on endoluminal coils for fulfilling the task of serial and parallel active decoupling and studied their impact on the image quality.…”

Two-section branch-line hybrid couplers based broadband transmit/receive switch

“…The enhanced mode eGaN FETs in [16] showed an advantage over PIN diodes in B0 and B1 homogeneity and the amount of biased power to work, but it revealed less image SNR. Micro electromechanical system (MEMS) based switches [21], [22] were designed and compared to topologies based on PIN diodes and they showed higher isolation, and lower DC switching voltage. These switches have not been broadly used in MRI applications.…”

Manufacturing and Testing of Radio Frequency MEMS Switches Using the Complementary Metal Oxide Semiconductor Process

“…Radio frequency microelectromechanical system switches (MSSs) are higher performances in high frequency than solid-state switches [ 1 ]. The MSSs switches have been applied in reconfigurable antenna [ 1 ], microelectromechanical system (MEMS) satellites [ 2 ], wireless sensors [ 3 ], switchable bandpass filters [ 4 ], power amplifier [ 5 ], and receiver endoluminal coils [ 6 ]. Several radio frequency microelectromechanical system switches were developed utilizing silicon micromachining technology.…”