DEVELOPMENT OF THE LASER ULTRASONIC MICROMANIPULATOR

非接触和非破坏性的操纵技术，如液体中微米级颗粒的输送、捕获和分离，目前在生物技术和微机械加工领域引起了极大的兴趣。光学镊子是一个已知的非接触式操纵小颗粒的例子。使用来自激光光束的辐射压力。然而，对于折射率较小或金属的粒子来说，捕获是困难的。此外，光学势垒的窄宽度也是连续操纵小粒子的一个显著限制。以前，我们已经提出了基于甚高频(VHF)超声辐射力的微米级液体颗粒的超声微操纵(UMM)技术。利用视觉反馈技术，我们演示了沿圆形和字符图案对聚苯乙烯球体的二维操纵。在本研究中，我们开发了一种新型的激光超声微操作器(Lumm)，其中声辐射力和光辐射力都作为互补的非接触力。所有实验流明由中心频率为49 MHz的声泄漏波换能器、最大功率为5 mW、波长为675 nm的基波二极管和生物显微镜组成。利用流明模型，我们成功地从大量直径为12μm的聚苯乙烯小球中去除了不需要的颗粒，从而实现了对液体中特定颗粒的快速选择，并利用流明模型根据斯托克斯定律估算了超声辐射力的水平分量和测量到的颗粒机械运动释放捕获的临界速度。这些结果的一部分已在IEEE 2000超声波研讨会上发表。未发表的结果将在不久的将来公布。

Noncontact and nondestructive techniques for manipulation, such as transportation, trapping, and separation of micron-sized particles in liquid, are currently of considerable interest in areas of biotechology and micromachining. Optical tweezers are a known example of noncontact manipulation of small particles. Radiation pressure from laser beams is used. However, trapping is difficult for particles that have a small refractive index or are metallic. Also, the narrow width of optical potential wells is a significant limitation for the continuous manipulation of the small particles. Previously we have proposed ultrasonic micromanipulation (UMM) techniques for micron-sized particles in liquid based on the radiation forces of very-high-frequency (VHF) ultrasound. Using the visual feedback technique we demonstrated two-dimensional manipulation of a polystyrene sphere along a circle and character patterns.In this study, we have developed a new laser ultrasonic micromanipulator (LUMM) in which the acoustic radiation force and optical radiation force are both used as complementary noncontact forces. All experimental LUMM consists of an acoustic leaky wave transducer of center frequency 49 MHz, a Baser diode with a maximum power 5 mW at 675 nm and a biological microscope. Using the LUMM, we have carried out successfully the rapid selection of a specific particle in liquid by the removal of unwanted particles from large number of 12-μm-diameter polystyrene spheres.The LUMM was also used to estimate the horizontal component of the ultrasonic radiation force by using Stokes law and the measured critical velocity at which the trapping is released by mechanically moving particles. Parts of these results are presented in IEEE 2000 Ultrasonics Symposium. The unpublished results will be presented in near future.