Design and characterization of an inverse layer dual frequency ultrasound transducer

Contrast enhanced ultrasound imaging, such as harmonic imaging, or sub-harmonic imaging, is known for the ability to offer enhanced resolution and contrast-to-tissue ratio. However, the finite bandwidth of the conventional ultrasound transducer restricts its development. The recently proposed dual frequency ultrasound transducers which are designed for harmonic imaging use only one active layer in the receiving mode, such that they are not capable of sufficiently detecting the harmonic components without microbubble contrast agents. In this paper, an inverse layer dual frequency ultrasound transducer which aims to improve the harmonic response during contrast ultrasound imaging has been studied to solve this problem. A prototype transducer composed of two anti-poled piezoelectric ceramics with the thickness of 190 μm and 110 μm respectively was designed, fabricated and characterized. The KLM equivalent circuit of this inverse layer dual frequency transducer was deduced to optimize the design parameters and to predict the device performance. The pulse-echo experiment was conducted to characterize the acoustic response. The fundamental frequencies of the fabricated transducer were measured to be 14.4 MHz and 24.0 MHz, respectively. Third harmonics were shown on the sepctrum of the pulse signal, approving of successfully detecting non-linear signals using the prototype transducer.