Design of a 50-MHz annular array using fine-grain lead titanate

A 50 MHz annular array with six equal-area elements was designed. A novel fine-grain, 1-2 micron particle size, lead titanate was used as the piezoelectric material. The full set of electromechanical properties was calculated using resonance techniques. The low permittivity ((epsilon) s33/(epsilon) 0 equals 180) of the lead titanate allowed a larger overall diameter when matching to 50 ohm electronics, which kept the aspect ratio (width/height) of all the elements above 3. Laser micromachining was used to fully separate the array elements, and a double matching layer scheme was used to acoustically match the device. The array was modeled using both one-dimensional (KLM) and finite element modeling (PZFlex), and good agreement between the two was obtained. Using a broadband excitation, a center frequency of 49 MHz was obtained on the echo reflected from a flat reflector, with an inerstion loss of 20 dB and a bandwidth of 50%. Maximum calculated cross-talk values were below -30 dB between elements.