Optimal Design Of The Ultrasonic Needle And Its Applications Into Micro Manipulation

Acoustic needles have important applications in generation of acoustic force, acoustic streamingand micro-vibration excitation, etc. Acoustic radiation force and acoustic streaming provide thepossibility of acoustically manipulation of small particles. Trapping, agglomeration, and deformation ofsmall particles have been achieved, using a properly controlled sound field.One of design purposes of acoustic needle is to obtain a big vibration velocity at the tip of acousticneedle. Although the design of vibration excitation mechanism and size of acoustic needle is critical inobtaining a big vibration velocity at the tip of acoustic needle, few people have researched theoptimization methods for the vibration excitation mechanism and size. This problem is hindering thefurther application of acoustic needle.To response to the above stated challenges, in the work reported by the thesis, first, the dependenceof vibration displacement at the tip of acoustic needle on vibration excitation methods andconfigurations of acoustic needle are investigated experimentally and theoretically; then, a new methodwhich utilizes the anti-nodes of a stainless needle in flexural vibration to adsorb liquid droplets wasproposed and researched.Author proposed the dependence of vibration displacement at the tip of acoustic needle on thevibration excitation method and acoustic needle configuration. The acoustic needle is excited bysandwich type piezoelectric transducer. The effects of some physical factors on the vibration at the tipof acoustic needle have been investigated and clarified experimentally and theoretically. The physicalfactors include the length, location and orientation of the vibration excitation section of acoustic needleon piezoelectric transducer, the mode pattern of the driving plate of piezoelectric transducer, and lengthportion of the conical section in the whole needle.Author reported a method which utilizes the anti-nodes of a stainless needle in flexural vibration toadsorb liquid droplets. The adsorption capability depends on the needle vibration and liquid propertiessuch as viscosity, specific acoustic impedance, and density, as well as the needle diameter. A physicalmodel based on the hypothesis that ultrasound decreases the intermolecular cohesive force of liquid hasbeen proposed, which can explain the experimental phenomena quite well. The method proposed in thispaper can be used to extract droplets from liquid without using micro channel or tubular structures.This research work has potential applications in many areas, such as the optimization of theacoustic needle, the extraction of droplets from liquid without using micro channel or tubular structures,the control of the shape of droplets, etc.