脈衝式超音波聲鉗時序理論模型

控制小粒子在科學界上是屬於重要的討論的議題。雷射光鉗提供了很好的捕捉方法來控制小粒子的運動，在許多領域上都運用了雷射光鉗來完成重要的研究。但由於雷射光的物理限制，減少了能夠被應用在深層物質的可能性。聲鉗是被聲波所驅動，所以在非真空介質下，聲波會比電磁有更好的傳遞效率。在之前的聲鉗研究中，均是使用連續的駐波架構來捕捉小粒子，但由於架構上的特性，導致應用上也受到了限制。於是本研究希望提出使用單一探頭並使用脈衝波的模式來捕捉小粒子的方法，並經由理論和模擬來驗證可行性。在本研究中，先對於粒子在脈衝聲場中受力情況做分析討論，藉由受力的狀態來決定粒子的運動情形。分析運動模式可以瞭解小粒子是否被超聲波聲場所捕捉。一開始的模擬條件是設定粒子位於超音波聲場中心軸上，只單獨討論粒子在中心軸的受力情況。對於不同的參數進行分析和模擬，可發現到使用f-number越小的探頭、聲阻抗和水越接近及半徑越大的粒子，對於被捕捉的可能性就會越好。除此之外，也探討了粒子中心偏軸的受力情況，發現離軸時，會受到拉力而把粒子拉回中心軸。同樣重複一維的模擬參數，會發現在一維較佳的狀態下，二維也同樣會有較大的捕捉區域。最後，將透過分析及討論來驗證模擬演算法的合理性，在符合物理意義下，將會證明脈衝聲鉗的可能性。也希望在未來可應運該技術來進行生物體內粒子的控制。

關鍵字

光鉗；脈衝聲鉗

並列摘要

Manipulating small particles is an important issue in the scientific area. The optical tweezers provide a good tool for capturing the small particles. Many studies were accomplished by the optical tweezers. Due to the physical limitations of the laser, the application of the optical tweezers in the deeper material is impossible. Acoustic tweezers are motivated by the sound wave. Sound wave can propagate in the non-vacuum medium with higher efficiency than the electromagnetic wave does. Previous studies of acoustic tweezers were based on the structure of using dual-transducer mode with standing wave to capture small particles. However, such experimental structure limited the applications. In this thesis, we are going to propose a new method with a single-element transducer to capture the small particles by a pulsed-mode sound wave. In this study, the force analysis exerted on the small particles in the pulse-mode and time-course acoustics fields would be discussed first. Based on the force distribution results obtained from the acoustic field, the motion of the particle can be calculated by the iteration method. The tract of the small particle can be an index to be determined the particle was trapped by the acoustic field or not. The first condition was set that the particle was located at the central z-axis. The results were only considered the force for the central z-axis. The simulation parameters were including transducer f-number, particles acoustic impedance and their radius. From the results, the small f-number transducer, particles with water-like acoustic impedance and larger sizes would be the best conditions for the trapping of acoustic tweezers. In addition, the cases of the particles no longer located at the central z-axis were also considered. The results demonstrate very similar conclusions of those in one-dimension cases. Finally, the feasibility of pulse-mode acoustic tweezers was discussed. Potential application of the technique is to control the small particles such as drugs in the human or animals’ studies.

並列關鍵字

optical tweezers ； pulse-mode acoustic tweezers

參考文獻

[1] D. G. Grier, “A revolution in optical manipulation,” Nature, vol. 424, pp. 810-816, 2003.

[2] A. Ashkin, “Acceleration and trapping of particles by radiation pressure,’’ Physical Review Letter, vol. 24, pp. 156–159, 1970.

[3] A. Ashkin, J. M. Dziedzic, J. E. Bjorkholm, and S. Chu, “Observation of a single-beam gradient force optical trap for dielectric particles,” Optics Letters, vol. 11, pp. 288-290, 1986.

[4] A. Ashkin, “Forces of a single-beam gradient laser trap on a dielectric sphere in the ray optics regime,” Biophysical Journal, vol. 61, pp. 569-582, 1992.

[5] J. Hu and A. K. Santoso, “A π-shaped ultrasonic tweezers concept for manipulation of small particles,” IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, vol. 51, pp. 1499-1507, 2004.

國際替代計量

脈衝式超音波聲鉗時序理論模型

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