Fang Haoyu, Qiu Zhen, Mulholland Anthony J, O'Leary Richard L, Gachagan Anthony
IEEE Trans Ultrason Ferroelectr Freq Control. 2018 Dec;65(12):2429-2439. doi: 10.1109/TUFFC.2018.2874384. Epub 2018 Oct 8.
Wider operational bandwidth is an important requirement of an ultrasound transducer across many applications. In nature, it can be observed that several hearing organs possess a broad operating bandwidth by having a varying length scales structure. Moreover, conventional 1-3 piezoelectric composite transducers have been widely recognized for their wider bandwidth over their piezoelectric ceramic counterparts. In this paper, a novel 1-3 piezoelectric composite design using a fractal geometry, known as the Sierpinski Gasket (SG), is proposed in order to explore the potential of further extending the operational bandwidth and sensitivity of the transducer. Two equivalent 1-3 piezocomposite designs are compared to this end, one with a conventional periodic parallelepiped-shaped pillar structure and one with the SG fractal geometry, both theoretically, using a finite-element analysis package, and experimentally. The transmit voltage response and open-circuit voltage response are used to illustrate bandwidth improvement from the fractal composite design. Following the simulation results, a 580-kHz single-element transducer, utilizing the proposed SG fractal microstructure, is fabricated using a pillar placement methodology. The performance of the prototyped device is characterized and compared with a conventional 1-3 composite design, as well as with a commercial ultrasound transducer. In the one-way transmission mode, a bandwidth improvement of 27.2% and sensitivity enhancement of 3.8 dB can be found with the SG fractal design compared to an equivalent conventional composite design and up 105.1% bandwidth improvement when compared to the commercial transducer. In the one-way reception mode, the bandwidth improvement for the SG fractal design is 2.5% and 32.9% when compared to the conventional and commercial transducers, respectively.
更宽的工作带宽是超声换能器在许多应用中的一项重要要求。在自然界中，可以观察到一些听觉器官通过具有不同长度尺度的结构而拥有较宽的工作带宽。此外，传统的1-3型压电复合材料换能器因其比压电陶瓷换能器具有更宽的带宽而得到广泛认可。本文提出了一种采用分形几何结构（即谢尔宾斯基垫片（SG））的新型1-3型压电复合材料设计，以探索进一步扩展换能器工作带宽和灵敏度的潜力。为此，比较了两种等效的1-3型压电复合材料设计，一种具有传统的周期性平行六面体柱状结构，另一种具有SG分形几何结构，分别从理论上、使用有限元分析软件包以及通过实验进行比较。发射电压响应和开路电压响应被用于说明分形复合材料设计带来的带宽改善。根据模拟结果，采用柱状放置方法制造了一个利用所提出的SG分形微结构的580 kHz单元素换能器。对该原型设备的性能进行了表征，并与传统的1-3型复合材料设计以及商用超声换能器进行了比较。在单向传输模式下，与等效的传统复合材料设计相比，SG分形设计的带宽提高了27.2%，灵敏度提高了3.8 dB，与商用换能器相比带宽提高了105.1%。在单向接收模式下，与传统换能器和商用换能器相比，SG分形设计的带宽分别提高了2.5%和32.9%。
