Bayram Baris, Kupnik Mario, Yaralioglu Goksen G, Oralkan Omer, Ergun Arif Sanli, Lin Der-Song, Wong Serena H, Khuri-Yakub Butrus T
Edward L. Ginzton Laboratory, Stanford University, CA 94305, USA.
IEEE Trans Ultrason Ferroelectr Freq Control. 2007 Feb;54(2):418-30. doi: 10.1109/tuffc.2007.256.
Crosstalk is the coupling of energy between the elements of an ultrasonic transducer array. This coupling degrades the performance of transducers in applications such as medical imaging and therapeutics. In this paper, we present an experimental demonstration of guided interface waves in capacitive micromachined ultrasonic transducers (CMUTs). We compare the experimental results to finite element calculations using a commercial package (LS-DYNA) for a 1-D CMUT array operating in the conventional and collapsed modes. An element in the middle of the array was excited with a unipolar voltage pulse, and the displacements were measured using a laser interferometer along the center line of the array elements immersed in soybean oil. We repeated the measurements for an identical CMUT array covered with a 4.5-microm polydimethylsiloxane (PDMS) layer. The main crosstalk mechanism is the dispersive guided modes propagating in the fluid-solid interface. Although the transmitter element had a center frequency of 5.8 MHz with a 130% fractional bandwidth in the conventional operation, the dispersive guided mode was observed with the maximum amplitude at a frequency of 2.1 MHz, and had a cut-off frequency of 4 MHz. In the collapsed operation, the dispersive guided mode was observed with the maximum amplitude at a frequency of 4.0 MHz, and had a cut-off frequency of 10 MHz. Crosstalk level was lower in the collapsed operation (-39 dB) than in the conventional operation (-24.4 dB). The coverage of the PDMS did not significantly affect the crosstalk level, but reduced the phase velocity for both operation modes. Lamb wave modes, A0 and S0, were also observed with crosstalk levels of -40 dB and -65 dB, respectively. We observed excellent agreement between the finite element and the experimental results.
串扰是超声换能器阵列各元件之间的能量耦合。这种耦合会降低换能器在医学成像和治疗等应用中的性能。在本文中，我们展示了电容式微机械超声换能器（CMUT）中导波界面波的实验演示。我们将实验结果与使用商业软件包（LS-DYNA）对一维CMUT阵列在常规模式和塌陷模式下运行的有限元计算结果进行了比较。用单极电压脉冲激励阵列中间的一个元件，并使用激光干涉仪沿着浸没在大豆油中的阵列元件中心线测量位移。我们对覆盖有4.5微米聚二甲基硅氧烷（PDMS）层的相同CMUT阵列重复了测量。主要的串扰机制是在流固界面传播的色散导模。尽管发射元件在常规操作中的中心频率为5.8 MHz，分数带宽为130%，但观察到色散导模在2.1 MHz频率处具有最大幅度，截止频率为4 MHz。在塌陷操作中，观察到色散导模在4.0 MHz频率处具有最大幅度，截止频率为10 MHz。塌陷操作中的串扰水平（-39 dB）低于常规操作中的串扰水平（-24.4 dB）。PDMS的覆盖对串扰水平没有显著影响，但降低了两种操作模式下的相速度。还分别观察到兰姆波模式A0和S0，其串扰水平分别为-40 dB和-65 dB。我们观察到有限元结果与实验结果非常吻合。
