An experimental study on coded excitation in CMUT arrays to utilize Simultaneous Transmission Multiple-zone Focusing method with frequency divided sub-band chirps

The frequency bandwidth of CMUTs (capacitive micromachined ultrasonic transducers) is known as relatively broader than that of other ultrasonic transducers. To utilize the wide bandwidth characteristic of the CMUT arrays, in this paper, we report on coded excitation techniques in the CMUT array. Through simulations, STMF (Simultaneous Transmit Multiple-zone Focusing) based ultrasound imaging techniques using orthogonally frequency-divided chirp signals are investigated. In the simulations, the frequency divided sub-band chirps that have orthogonal property are designed within the frequency bandwidth of the CMUT arrays, and simultaneously fired on multiple ranges, in which each signal is focused at a different range, in one transmission event. This paper also presents ultrasound images through a modulation and demodulation process of orthogonal sub-band coded signals. Experiments on the chirp-coded excitation in CMUT arrays are reported in this paper as a feasibility study of the FDMA (frequency division multiple access) like STMF method. In the experiment, mixed two orthogonal chirp signals are simultaneously fired with the CMUT arrays and the received signals are successfully separated into two compressed signals.