Design of a high frequency annular array for medical ultrasound

This paper reports the results of an effort of developing a 50 MHz annular array which incorporates a fine grain lead titanate as the piezoelectric material. The array achieves a better sensitivity than a comparable PVDF annular array and demonstrates low lateral coupling for reduced cross-talk. Using resonance techniques, the lead titanate has been fully characterized. The ceramic shows a clamped permittivity (ε₃₃^s/ε₀) equal to 180, a thickness coupling k_t, of 0.49 and a planar coupling, k_p, of 0.08. This material was fabricated into an annular array with an overall diameter of 5 mm and six equal-area elements. Separation of the elements was achieved using laser micromachining. Utilizing the waveforms from one-dimensional modeling, intensity field calculations predicted a maximum -6 dB lateral beamwidth of 160 μm over a six focal-zone region covering a 10 mm depth. Application of a triangular electrical apodization scheme across the elements resulted in a reduction in grating lobe amplitude below -26 dB.