A Spherically-Shaped PZT Thin Film Ultrasonic Transducer with an Acoustic Impedance Gradient Matching Layer Based on a Micromachined Periodically Structured Flexible Substrate

Abstract

This paper presents the microfabrication of an acoustic impedance gradient matching layer on a spherically-shaped piezoelectric ultrasonic transducer. The acoustic matching layer can be designed to achieve higher acoustic energy transmission and operating bandwidth. Also included in this paper are a theoretical analysis of the device design and a micromachining technique to produce the novel transducer. Based on a design of a lead titanium zirconium (PZT) micropillar array, the constructed gradient acoustic matching layer has much better acoustic transmission efficiency within a 20–50 MHz operation range compared to a matching layer with a conventional quarter-wavelength thickness Parylene deposition. To construct the transducer, periodic microcavities are built on a flexible copper sheet, and then the sheet forms a designed curvature with a ball shaping. After PZT slurry deposition, the constructed PZT micropillar array is released onto a curved thin PZT layer. Following Parylene conformal coating on the processed PZT micropillars, the PZT micropillars and the surrounding Parylene comprise a matching layer with gradient acoustic impedance. By using the proposed technique, the fabricated transducer achieves a center frequency of 26 MHz and a −6 dB bandwidth of approximately 65%.

Piezoelectric Micromachined Ultrasonic Transducers with a Cost-Effective Bottom-Up Fabrication Scheme for Millimeter-Scale Range Finding

“…Currently, ultrasound instruments operate at frequencies ranging from tens of kilohertz to thousands of megahertz. They have become effective and important tools in many applications, such as medical imaging, therapeutic ultrasound, non-destructive evaluation, underwater sonar, particle and cell manipulation, and ultrasonic actuation [1,2,3,4]. In addition, an ultrasonic rangefinder has been broadly harnessed for the gesture interface of handheld gadgets, vehicle-driving systems to avoid collision, and robots for detecting obstacles during operations [5,6,7,8,9].…”

Enhancement of Ultrasonic Transducer Bandwidth by Acoustic Impedance Gradient Matching Layer

“…The acoustic impedance gradient material has been proved to exhibit the characteristics of high-frequency conduction, and the quasi-continuous acoustic impedance change can be realized in the range of material by selecting the type of filler and adjusting the filling proportion [ 26 , 27 ]. Therefore, using an artificial acoustic impedance gradient composite is a promising way to solve the above problem [ 27 , 28 ]. In recent years, many researchers have tried to apply impedance gradient composites to ultrasonic transducers with traditional piezoelectric ceramics.…”

“…In recent years, many researchers have tried to apply impedance gradient composites to ultrasonic transducers with traditional piezoelectric ceramics. In 2013, Feng and Liu created a new type of micro piezoelectric ultrasonic transducer, and a gradient matching layer was fabricated by using poly (p-xylene), which improved the transmission rate of acoustic energy and the bandwidth of the transducer [ 27 ]. In 2016, Lu prepared a new anisotropic conical ultrasonic matching layer material by etching the stripped silica fiber bundle in a hydrofluoric acid solution.…”

The influence of impedance mismatch of the medium with gradient change of impedance on acoustic characteristics

“…Li suggested a genetic algorithm approach to optimizing the effective material parameters of an acoustic metamaterial to minimize acoustic impedance mismatch [5]. Feng presented the micro fabrication of an acoustic impedance gradient matching layer on a spherically-shaped piezoelectric ultrasonic transducer [6]. Kimura proposed a wideband polymer ultrasonic transducer having acoustic impedance matching layers [7].…”