Matched all-pass filtering of the received echoes for range improvement in medical ultrasound imaging

The purpose of this work was to investigate a possibility of using chirp waveforms in very high frequency ultrasound medical imaging to increase range resolution and concurrently maximize penetration depth. It is shown that the improvement in range resolution can be achieved by using appropriately designed all pass matched filter at the receiver input. The paper describes in depth theoretical optimization process and computer simulation of the matched 96-th order all pass filter for chirp waveforms of 1 μs duration in the frequency range 30 MHz-50 MHz. A prototype of 24-th order filter was constructed to verify the results of analytical and numerical methods. Excellent agreement was observed between the theoretical predictions and experimental data. Continuation of this work will include design and optimization of superwide bandwidth transducers.