Ultrasound Imaging in Mid-Air Using Phased Polymer PMUT Array

This paper describes the further development of large area (13x13 mm
²
) polymer PMUT arrays operating at relatively low frequency (233.4 kHz) for mid-air imaging applications. An improved frequency uniformity across more elements enables an output efficiency of 71 %. Transmission beamforming is implemented in one dimension and 3D acoustic field measurements correlate well with simulations. Steering angles are confirmed to be accurate within 1° and peak pressures exceeding 2 Pa/V are achieved with a FWHM beam width around 6 mm. Initial imaging experiments demonstrate the ability to locate a 4-mm target within a 60 mm lateral and 70 mm vertical range.