Beamforming Microwave-Induced Thermoacoustic Imaging for Screening Applications

This paper presents a beamforming microwaveinduced thermoacoustic (TA) imaging system for screening applications. Near-field/quasi-near-field beamforming with multiple applicators focuses the radio-frequency (RF) energy to the target location in depth and enhances the TA signal generation, thereby lowering the peak-power requirements of the solid-state RF power amplifier (PA). More importantly, the proposed beamforming method reduces surface heating at the skin interface by distributing the excitation power over multiple sites and, hence, reducing the per-element peak at a similar acoustic signal-tonoise ratio (SNR). A 3-D printed setup in a conformal configuration is designed and used to demonstrate signal enhancement with RF focusing. By tuning the phase of each channel, the system can focus RF energy to specific locations and steer the focal point location across the region of interest. With a four-element array, measurements confirm a 15.8-dB acoustic intensity SNR improvement compared with a single power-limited excitation and 3.8-dB improvement compared to a PA with the same total peak power (i.e., 4× Pout). The results herein suggest the potential benefits of the proposed beamforming system and imply further enhancements once scaled to a larger array.