Active time-reversal based phased array ultrasound system for accurate focusing through biological tissue layers

Ultrasonic phased array technology enables flexible and controllable beamforming through precise phase delay control of individual array elements in the transducer, facilitating dynamic focusing, beam steering, and beamforming. This study presents a 64-channel system achieving 1 ns delay resolution using FPGA-based phase-locked loops. Through systematic testing and calibration of the delay error in the phased array transmission driving system, the actual delay error was successfully controlled within 1 ns. Furthermore, to address the focal shift issue in multi-layer soft tissues, this research implemented active time reversal and phase compensation methods for focal shift correction. Experimental results demonstrate that the proposed system not only exhibits excellent driving and phase modulation capabilities but also effectively reduces tissue-induced focal shift.