A single-element transducer with nonuniform thickness for high-frequency broadband applications

Abstract

The design, fabrication, and evaluation of a high-frequency single-element transducer are described. The transducer has an annular geometry, with the thickness of the piezoelectric material increasing from the center to the outside. This single-element annular transducer (SEAT) can provide a broader frequency range than a conventional single-element transducer with a uniform thickness (single-element uniform transducer, or SEUT). We compared the characteristics of a SEAT and a SEUT. Both transducers used 36 degrees-rotated, Y-cut lithium niobate (LiNbO(3)) material. The SEAT had a diameter of 6 mm and comprised 6 subelements of equal area (electrically connected by a single electrode on each side) whose thickness ranged from 60 microm (center) to 110 microm (outside), which resulted in the center frequency of the subelements varying from 59.8 MHz to 25 MHz. The overall center frequency was 42.4 MHz. The annular pattern was constructed using an ultrasonic sculpturing machine that reduced the root-mean-square value of the surface roughness to 454.47 nm. The bandwidth of the SEAT was 19% larger than that of the SEUT. However, compared with the SEUT, the 2-way insertion loss of the SEAT was increased by 3.1 dB. The acoustic beam pattern of the SEAT was also evaluated numerically by finite-element simulations and experimentally by an ultrasound beam analyzer. At the focus (10.5 mm from the transducer surface), the -6 dB beam width was 108 microm. There was reasonable agreement between the data from simulations and experiments. The SEAT can be used for imaging applications that require a wider transducer bandwidth, such as harmonic imaging, and can be manufactured using the same techniques used to produce transducers with multiple frequency bands.

Design and micromanufacturing technologies of focused piezoelectric ultrasound transducers for biomedical applications

“…To address limitations of the ball pressing method, the mechanical grinding technique was developed, utilizing a high-strength object to gradually wearing down the piezoelectric material until the desired curved shape is achieved. That is, a highstrength object is used to grind the surface of the piezoelectric material until a curved shape is formed [86,87]. For piezoelectric ceramics and piezoelectric single crystals of tens of micrometers, this method has absolute advantages, but for ultra-thin piezoelectric ceramics with thickness less than 10 micrometers, this method will not be applicable.…”