Acoustic time reversal focusing in water using FPGA based platform

Abstract

This paper discusses the focusing behavior by means of acoustic time reversal in water. A self-developed FPGA-based platform (on a ZynqMP Ultrascale+) serves as a basis for generating a high-resolution local and temporal focusing. This platform allows synchronous excitation of up to 32 transducers at a sampling rate of 4.8 MSa/s and 8 bit amplitude resolution. Furthermore, the chosen filter and amplifier technology is presented and the FPGA platform is compared to a commercial analog system. The measurement of the sound pressure field within the liquid is performed by a needle hydrophone coupled to a 3D sound field scanner system. The analog time-reversed impulse responses generated in the calibration step of the methodology are converted via a frequency and resolution dependent pulse width modulation (PWM) for the subsequent synchronous FPGA control. The focus point is evaluated with respect to its amplitude, spatial deflection and the contrast ratio of the focus point to its acoustically unaddressed environment. The focus quality is examined with respect to a different number of transducers and at different target positions.