Fabrication of a PMN-PT single crystal-based transcranial Doppler transducer and the power regulation of its detection system.

Qingwen Yue,Haosu Luo,Xi'An Wang,Di Lin,Dongxu Liu,Wei Wang,Wenning Di

doi:10.3390/s141224462

Abstract

Doppler sonographic measurement of flow velocity in the basal cerebral arteries through the intact skull was developed using a pulsed Doppler technique and 2 MHz emitting frequency. Relaxor-based ferroelectric single crystals Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) were chosen to be the piezoelectric transducer material due to their ultrahigh piezoelectric coefficients, high electromechanical coupling coefficients and low dielectric loss. The pulse-echo response of the transducer was measured using the conventional pulse-echo method in a water bath at room temperature. The −6 dB bandwidth of the transducer is 68.4% and the sensitivity is −17.4 dB. In order to get a good match between transducer and detection system, different transmission powers have been regulated by changing the impedance of the transmitting electric circuit. In the middle cerebral artery (MCA) measurement photograph results, as the transmission power is increasing, the detection results become clearer and clearer. A comparison at the same transmission power for different transducers shows that the detection photograph obtained by the crystal transducer was clearer than that obtained with a commercial transducer, which should make it easier for doctors to find the cerebral arteries.

Highlights

Ultrasonic transducers are widely used in medical detection, nondestructive evaluation, underwater sonar and so on [1,2,3]
Because the material properties such as dielectric constant and mechanical quality factor are very different between single crystals and PZT ceramics, when the fabricated transducer is analyzed as an equivalent circuit, the value of the electric impedance in a single crystal-based transducer is bigger than that in a PZT ceramics-based transducer which leads to an impedance mismatch when the single crystal-based transducer works with the current detection systems
By using the detection system, the Doppler sonographic measurement of middle cerebral artery (MCA) was done under different transmission powers

Summary

Introduction

Ultrasonic transducers are widely used in medical detection, nondestructive evaluation, underwater sonar and so on [1,2,3]. [9,10], lead zirconate titanate (PZT) ceramics are the most popular piezoelectric materials used in the fabrication of ultrasonic transducers because of their high performance and ease of manufacturing [11,12,13,14]. Because the material properties such as dielectric constant and mechanical quality factor are very different between single crystals and PZT ceramics, when the fabricated transducer is analyzed as an equivalent circuit, the value of the electric impedance in a single crystal-based transducer is bigger than that in a PZT ceramics-based transducer which leads to an impedance mismatch when the single crystal-based transducer works with the current detection systems. Concerning the difference in acoustic impedance between PZT ceramics and PMN-PT single crystals, the acoustic impedance of the matching layer should be carefully concerned when designing the transducer. A PMN-PT single crystal-based 2 MHz TCD transducer has been fabricated.

Preparation of PMN-PT Single Crystals

Fabrication of the PMN-PT-Based TCD Transducer

Acoustic Characterization of the TCD Transducer

The Detecting System

Power Regulation and the Doppler Sonographic Measurement of MCA

Conclusions