Physics Department, Gustavus Adolphus College, 800 College Avenue, Saint Peter, Minnesota 56082, USA.
J Acoust Soc Am. 2011 Oct;130(4):1838-43. doi: 10.1121/1.3628336.
The ultrasound radiation force has been used for noncontact excitation of devices ranging from microcantilevers to acoustic guitars. For ultrasound radiation force excitation, one challenge is formation of standing waves between the ultrasound transducer and the device under test. Standing waves result in constructive/destructive interference causing significant variations in the intensity of the ultrasound field. The standing-wave induced intensity variations in the radiation force can result from minor changes in the transducer position, carrier frequency, or changes in the speed of sound due to changes in ambient temperature. The current study demonstrates that by randomly varying the ultrasound carrier frequency in packets, it is possible to eliminate the negative consequences resulting from the formation of standing waves. A converging ultrasound transducer with a central frequency of 550 kHz was focused onto a brass cantilever. The 267 Hz resonance was excited with the ultrasound radiation force with a carrier frequency that randomly varied between 525 kHz to 575 kHz in packets of 10 cycles. Because each packet had a different carrier frequency, the amplitude of standing wave artifacts was reduced by a factor of 20 compared to a constant frequency excitation of 550 kHz.
超声辐射力已被用于激励各种设备，从微悬臂梁到吉他。对于超声辐射力激励，一个挑战是在超声换能器和待测试设备之间形成驻波。驻波会导致建设性/破坏性干扰，从而导致超声场强度发生显著变化。辐射力中的驻波引起的强度变化可能源于换能器位置、载波频率的微小变化，或者由于环境温度变化导致声速的变化。本研究表明，通过在数据包中随机改变超声载波频率，可以消除形成驻波所带来的负面影响。一个中心频率为 550 kHz 的汇聚超声换能器被聚焦到一个黄铜悬臂梁上。267 Hz 的共振通过超声辐射力以 525 kHz 至 575 kHz 的载波频率激发，每个数据包包含 10 个周期。由于每个数据包的载波频率都不同，与 550 kHz 的固定频率激励相比，驻波伪影的幅度降低了 20 倍。
