Effect of matching layer on acoustic lens on suppressing Lamb wave formation

Therapeutic variable focal length ultrasound transducer (VFLT) for HIFU using linear array and cylindrical lens with low-loss matching layer in front for suppressing Lamb wave has been developed. The cylindrical lens with a thickness of approximately half a wavelength, directly attached to PZT transducer on the other side, has an acoustic matching layer. Numerical simulation of wave propagation was performed using a finite element method. Prototype VFLT with and without the layer were then fabricated and tested. The comparison of the results clearly showed the effect of the layer to suppress Lamb wave formation in the lens. Canine prostate was transrectally treated and successfully coagulated with the transducer with a Lamb wave suppressing matching layer (LWSL) on the lens.