M.S. Thesis Defenses by Ziba Arghiani & Abdullah Erkam Arslan

Presentations will take place one after the other.

 

Advisor: Prof. Ergin Atalar

The seminar will be on Wednesday, September 14, 2022 at 2pm

 

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https://zoom.us/j/2510067074?pwd=cE5iaHI3VzFZMGI4WFoyTTBJdzd4Zz09

Meeting ID: 251 006 7074

Passcode: 782764

 

DRIVING MUTUALLY COUPLED COILS USING AN ARRAY OF CLASS-E AMPLIFIERS 

by Ziba Arghiani, M.S. in Electrical and Electronics Engineering

 

Abstract:

Linear radiofrequency (RF) power amplifiers are commonly used in magnetic resonance imaging (MRI) to generate radiofrequency field (B1).

These low-efficiency amplifiers require cooling systems and long transmission cables, increasing the MRI hardware cost. An array of on-coil class-E amplifiers is proposed for the transmit system to mitigate these problems. A class-E amplifier is a switching type amplifier that can achieve 100% power efficiency theoretically. In this dissertation, a state-space model is proposed to simplify interpreting and analysis, and provide insight into the system of on-coil class-E amplifiers. This model can also be employed to find high power and efficiency modes of amplifiers’ operation. Using the state-space model, phase delays are adjusted between gate signals of the amplifiers to achieve high power and efficiency even in the presence of highly coupled coils. In addition, a sampled-data system generated from the state-space model is proposed to analyze the system’s transient behavior by investigating the time constant of the system. To validate the state-space model, a single class-E amplifier and two class-E amplifiers with coupled coils are simulated in LTSPICE. Moreover, novel hardware is designed for the class-E amplifier resulting in a cost-efficient design.

Simulation and experimental results are provided to demonstrate the effectiveness of the proposed model.

 

 

A600W ON-COIL CLASS-E RF POWER AMPLIFIER ARRAY WITH DYNAMIC PHASE CONTROL FOR 3T MRI

by Abdullah Erkam ArslanM.S. in Electrical and Electronics Engineering

 

Abstract:

Due to their size and cooling constraints, conventional Magnetic Resonance Imaging (MRI) places radio frequency (RF) amplifiers away from the scanner. These RF amplifiers are linear and have relatively low efficiency due to the match- ing of 50Ω output impedance for means of transmission with cables. Switching Class-E amplifiers on the other hand by default need a bare RLC network as their load and thus can be directly integrated with the bare unmatched coils and reduce the cost and power losses significantly. This thesis aims to build up on
the previous theses’ line of work including [1, 2, 3, 4, 5]. Instead of mitigating the symptoms, chronic problems of artifacts have been fixed by focusing on their root causes in the FPGA side of the updated design. Driver has been updated, timing problems have been resolved. FPGA design is also extended to support multi-channel phase control.

A dual channel imaging configuration of on-coil Class-E amplifiers with on- the-fly digital fine phase control is presented for 3T MRI. The system can control the phase with less than 2◦ granularity (this setting can be fine tuned down to 0.15◦). Without any mechanical intervention with the coil setup, using merely phase control, illuminated slice depth is modulated to three times its base-size during scantime. B1 field maps are also extracted for another setup.

Periodically linear switching (PLS) circuit model of the Class-E amplifier are derived and computed yielding a simulator with fast and customizable optimization capability. The PLS model is also verified SPICE and theoretical analysis.