Department of Micro- and Nanotechnology, Technical University of Denmark, DTU Nanotech Building 345 East, DK-2800, Kongens Lyngby, Denmark.
Lab Chip. 2010 Mar 7;10(5):563-70. doi: 10.1039/b920376a. Epub 2010 Jan 27.
A new method is reported on how to measure the local pressure amplitude and the Q factor of ultrasound resonances in microfluidic chips designed for acoustophoresis of particle suspensions. The method relies on tracking individual polystyrene tracer microbeads in straight water-filled silicon/glass microchannels. The system is actuated by a PZT piezo transducer attached beneath the chip and driven by an applied ac voltage near its eigenfrequency of 2 MHz. For a given frequency a number of particle tracks are recorded by a CCD camera and fitted to a theoretical expression for the acoustophoretic motion of the microbeads. From the curve fits we obtain the acoustic energy density, and hence the pressure amplitude as well as the acoustophoretic force. By plotting the obtained energy densities as a function of applied frequency, we obtain Lorentzian line shapes, from which the resonance frequency and the Q factor for each resonance peak are derived. Typical measurements yield acoustic energy densities of the order of 10 J/m(3), pressure amplitudes of 0.2 MPa, and Q factors around 500. The observed half wavelength of the transverse acoustic pressure wave is equal within 2% to the measured width w = 377 microm of the channel.
一种新方法用于测量为粒子悬浮声泳设计的微流控芯片中超声共振的局部压力幅度和 Q 因子。该方法依赖于在充满水的直硅/玻璃微通道中跟踪单个聚苯乙烯示踪微球。该系统由附在芯片下方的 PZT 压电换能器驱动，并通过施加在其 2 MHz 本征频率附近的交流电压驱动。对于给定的频率，通过 CCD 相机记录多个粒子轨迹，并拟合到微球声泳运动的理论表达式。从曲线拟合中，我们获得声能量密度，从而获得压力幅度以及声泳力。通过将获得的能量密度作为施加频率的函数绘制，我们得到了洛伦兹线形状，从中可以得出每个共振峰的共振频率和 Q 因子。典型的测量结果产生的声能密度约为 10 J/m(3)，压力幅度为 0.2 MPa，Q 因子约为 500。观察到的横向声压波的半波长与测量的通道宽度 w = 377 µm 相差在 2%以内。
