Driving mutually coupled coils using an array of class-E amplifiers

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 lengthy transmission cabling, increasing the MRI hardware cost. An array of on-coil class-E amplifiers is pro-posed for the transmit system to mitigate these problems. Class-E amplifiers are switching type amplifiers capable of achieving 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 ampli-fiers’ operation. Using the state-space model, phase delays are adjusted between gate signals of the amplifiers to obtain 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 behav-ior 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.