High-frequency ultrasound transducer by using inversion layer technique for intravascular ultrasound imaging

Inversion layer technique can increase the centre frequency (f(0)) and the -6 dB bandwidth of the ultrasound transducer without reducing thickness of active material. However, it suffers from the reduced -6 dB bandwidth when the centre frequency is increased more than 1.5f(0). A modified inversion technique is proposed and applied it to high-frequency intravascular ultrasound (IVUS) transducer. The performance was computationally verified by using finite element method (FEM) simulation. The proposed IVUS transducer consists of two sub-elements with each aperture size of 0.6 x 0.6 mm, and each sub-element has different types of inversion layer using PMN-PT and PZT-5H. The initial thickness of overall active material was designed for 40 MHz centre frequency and the FEM simulation showed that the centre frequency was increased by about 1.8f(0) maintaining the -6 dB fractional bandwidth compared with the conventional transducer.