−6 dB Focus-steering Region of a Fully-electronically Planar HIFU Phased Array: A Preliminary Experimental Evaluation

Abstract

Through the hydrophone measurement of acoustic fields, this paper experimentally illustrates the spatial distributions of the focusing amplitudes and deviations of a 6144-element fully-electronically focused HIFU phased array with an element spacing of λ/2, and further evaluates its −6 dB focus-steering region. In the measured region of a cylinder 30 mm above the array and with a radius of 90 mm and a height of 170 mm, the ultrasonic spatial focusing is achieved via the acoustic ray theory to compensate each element's initial emitting phase. Experimental results show that the maximal and minimal ones of all maximal peak-to-peak voltages in the measured region are 2.59 V and 0.78 V, respectively. The maximal total, radial and axial focusing deviations are 4.41 mm, 3.71 mm and 3.60 mm, respectively. Besides, considering the maximal peak-to-peak voltages of all focuses decreasing by no more than 6 dB relative to the maximum of 2.59 V, the −6 dB focus-steering region will be at least a cylinder with a radius of 70 mm and a height of 170 mm. In such a region, the minimal one of the maximal peak-to-peak voltages is 1.33 V, while the maximal total, radial and axial focusing deviations are 3.62, 3.06 and 3.60 mm, respectively. Therefore, this 6144-element HIFU phased array shows outstanding ability in fully-electronic ultrasound focusing.