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.