Hawkes J J, Barrow D, Coakley W T
School of Pure and Applied Biology, University of Wales Cardiff, UK.
Ultrasonics. 1998 Aug;36(9):925-31. doi: 10.1016/s0041-624x(98)00019-5.
Ultrasonic standing wave chambers with acoustic pathlengths of 1.1 and 0.62 mm have been constructed. The chambers were driven at frequencies over the range 0.66-12.2 MHz. The behaviour of 2 microns diameter latex microparticles and 5 microns diameter yeast in the chambers has been elucidated. One (flow) chamber had a downstream laminar flow expansion section to facilitate observation of concentrated particle bands formed in the ultrasonic field. A second (microscopy) chamber allowed direct observation of band formation in the field and their characterisation by confocal scanning laser microscopy. Clear band formation occurs when the chamber pathlength is a multiple of half wavelengths at the driving frequency, so that the chamber rather than the transducer resonance has the most influence on band formation in this system. Band formation occurred in half-wavelength steps from a position one quarter of a wavelength off the transducer to a band at a similar distance from the reflector. Ordered band formation was preserved by the laminar flow in the expansion chamber, although bands that formed very close to the wall were dissipated downstream. The microscopy chamber provided evidence of significant lateral particle concentration within bands in the pressure nodal planes. The approaches described will be applicable to the manipulation of smaller particles in narrower chambers at higher ultrasonic frequencies.
已构建出声程长度分别为1.1毫米和0.62毫米的超声驻波腔。这些腔在0.66 - 12.2兆赫的频率范围内驱动。已阐明了直径为2微米的乳胶微粒和直径为5微米的酵母在腔中的行为。一个（流动）腔有一个下游层流扩展段，以便于观察在超声场中形成的浓缩颗粒带。第二个（显微镜）腔允许直接观察场中带的形成，并通过共聚焦扫描激光显微镜对其进行表征。当腔的声程长度是驱动频率下半个波长的倍数时，会出现清晰的带形成，因此在该系统中，对带形成影响最大的是腔而不是换能器共振。带形成以半个波长的步长从距换能器四分之一波长的位置到距反射器类似距离处的带。扩展腔中的层流保持了有序的带形成，尽管非常靠近壁形成的带在下游消散。显微镜腔提供了压力节点平面中带内显著横向颗粒浓缩的证据。所描述的方法将适用于在更高超声频率下对更窄腔中更小颗粒的操控。
