Development of High Frequency Linear Arrays using Interdigital Bonded Composites

This paper describes the development of an interdigital bonded (IB) 1-3 composite for use in a 30 MHz 256-element geometrically focused ultrasonic array. The composite was manufactured using two IB operations in the elevation direction and one IB operation as well as one additional dicing step in the azimuth direction. The resultant composite elements had 14 mu m x 19 mu m wide posts separated by 8 mu m wide kerfs. The diced inter-element kerfs were 14 mu m. The finished array had a 50 mu m (1 lambda A) azimuth pitch and 2 mm elevation aperture focused to 8 mm. The measured pulse-echo center frequency was 30 MHz and -6dB bandwidth was 55%. The maximum combined electrical and mechanical crosstalk was less than -27 dB over the range of 10-50 MHz. The measured transmit -3dB directivity was 36 degrees. The measured insertion loss was 29 dB after compensating for attenuation and diffraction.