Fabrication of high frequency ultrasonic needle transducers for pulsed wave Doppler

High frequency ultrasonic needle transducers were fabricated using a 25 μm poly(vinylidene fluoride-tetrafluoroethylene) film as the active piezoelectric material. The active element was bonded to a conductive silver epoxy backing material using an unloaded epoxy. The active element was housed within a polyimide tube and needle housing. The measured center frequency and bandwidth of the device was 45 MHz and 49% respectively. The electrical impedance magnitude and phase were 459 Ω and -86° respectively. In order to improve device sensitivity a series inductor was used to tune the transducer. Tuning the transducer reduced the bandwidth by 50%. The intended use of this device is for in-vivo high frequency pulsed wave Doppler detection of retinal blood flow in the microcirculation.