Fabrication and performance of a 64 × 5 element 1.5D active matrix array transducer for medical imaging

Compared to 1D phased array probes with a fixed focus in elevation, multi-row arrays can significantly improved the slice thickness throughout image by expanding aperture and dynamic focusing in elevation. This paper describes the design and measurement of a 64 × 5 element 1.5D ultrasonic transducer that enables dynamic focusing and apodization in the elevation direction. We manufactured a transducer with an aperture size of 24 mm × 16 mm using a widely used piezoelectric ceramic (PZT-5H) as the piezoelectric vibrator. The measured center frequency and −6 dB fractional bandwidth of the 1.5D transducer were 3 MHz and 79%, respectively. A two-way insertion loss of −58 dB was obtained at the average center frequency. We carried out a sound field simulation and measured the actual transmitting (one-way) sound field data by using a hydrophone. In this way the sound beam profile in elevation direction was obtained, showing the −6 dB slice thickness measured was about 2 mm throughout the whole range of interest (from near to far field). This provided a much greater focal depth and much better imaging resolution in the elevation direction than can be achieved by using 1D probe.