Design and Micro-Fabrication of Focused High-Frequency Needle Transducers for Medical Imaging

Abstract

In this study, we report an advanced fabrication technique to develop a miniature focused needle transducer. Two different types of high-frequency (100 MHz) transducers were fabricated using the lead magnesium niobate-lead titanate (PMN-0.3PT) and lithium niobate (LiNbO3) single crystals. In order to enhance the transducer’s performance, a unique mass–spring matching layer technique was adopted, in which gold and parylene play the roles of the mass layer and spring layer, respectively. The PMN-0.3PT transducer had a 103 MHz center frequency with a −6 dB bandwidth of 52%, and a signal-to-noise ratio (SNR) of 42 dB. The center frequency, −6 dB bandwidth, and SNR of the LiNbO3 transducer were 105 MHz, 66%, and 44 dB, respectively. In order to compare and evaluate the transducers’ performances, an ultrasonic biomicroscopy (UBM) imaging on the fish eye was performed. The results showed that the LiNbO3 transducer had a better contrast resolution compared to the PMN-0.3PT transducer. The fabricated transducer showed an excellent performance with high-resolution corneal epithelium imaging of the experimental fish eye. These interesting findings are useful for the future biomedical implementation of the fabricated transducers in the field of high-resolution ultrasound imaging and diagnosis purpose.

High Acoustic Impedance and Attenuation Backing for High-Frequency Focused P(VDF-TrFE)-Based Transducers

“…This decrease in the center frequency stems from the fact that the P(VDF-TrFE) films operate gradually in the λ/2 towards the λ/4 mode. According to the value of the thickness coupling factor of the P(VDF-TrFE) (in our case 27%), which is lower than that of conventional PZT ceramics (typically 57% [ 21 ]), sensitivity must be favored and in this case backing with a high acoustic impedance must be retained while maintaining a sufficiently high bandwidth for imaging applications. For example, for Z b = 40 MRayl, the relative sensitivity is −2.3 dB, with a relative bandwidth of 70%, which are sufficient values for our imaging application.…”