Fabrication of one-dimensional linear diagnostic and therapeutic high intensity focused ultrasound (HIFU) phased-arrays using lateral-mode coupling method

Diagnostic and high intensity focused ultrasound (HIFU) phased-arrays provide many advantages over single element transducers, including dynamic focal beam steering capability. These arrays should be fabricated with element-to element pitch smaller than half the wavelength at the resonance frequency to avoid unwanted secondary foci due to grating lobes and side lobes. However, smaller pitch increases the electrical impedance of the array as the resonance frequency increases. The most common way to compensate the impedance increase is to employ electrical matching circuits between an array and RF driving system. However, it is not ideal if the number of array elements increases due to high fabrication cost and effort. In this paper we introduced the lateral mode coupling method to reduce electrical impedance in the fabrication of phased array. Using the lateral mode coupling method, we fabricated and tested one dimensional, linear diagnostic (750 kHz) and HIFU (1.4 MHz) phased-arrays. The averaged electrical impedances of each channel were measured to be 62.3 ± 5.2 Ω for the diagnostic array and 104.5 ± 8.9 Ω at zero phase for the HIFU array, respectively. The averaged maximum surface acoustic intensity of the HIFU array elements was 34 W/cm² prior to failure.