Phase-canceled backing structure for lightweight ultrasonic transducer

The overall weight of a medical ultrasonic transducer mainly depends on the weight of the backing layer. Therefore, a reduction of the thickness and the weight of the backing layer can be very useful for various types of array transducers whereby the user suffers from the inconvenience of the heavy weight. However, the backing layer with reduced thickness can cause distortions of the transmitted and received signals due to severe ripples reflected from the back-wall of the backing layer. In this study, a novel backing structure is proposed to solve this problem. The suggested backing layer is composed of multiple backing materials with different acoustic impedances to cancel the phases of the reflected signals. The rearmost material can dissipate the residual energy through the absorption effect. To verify these effects, a finite-element-method (FEM) simulation was conducted, and 4.5 MHz single-element transducers were fabricated. Although the thickness of the suggested backing layer was reduced by 1/5 compared with the conventional thick bulk-type backing layer, the ripples caused from the backing layer were successfully minimized. Therefore, the proposed backing structure can be a potential way to reduce the thickness of the backing layer resulting in a lightweight ultrasonic transducer.