Acoustic Tweezers: A further study 丁孝鈞

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1 Acoustic Tweezers: A further study 丁孝鈞

2 Outline Introduction about acoustic tweezers Method of acoustic tweezers Mechanism of acoustic tweezers

3 Introduction to acoustic tweezers Acoustic tweezers: Using acoustical method to trap small particles. Method: With an single transducer to generate pulse wave to capture particles. transducer Small particle Sound wave

4 Introduction to acoustic tweezers Transducer input wave: continuous wall or surrounding black: transmit red: reflect standing wave standing wave is easily affected by surrounding

5 Method of acoustic tweezers First radiation force: F =< V P> For constant particle volume: p F = =< V P>= V < P> t Fg = V < P> Rsin 2θ i T 2 [sin(2θ i 2 θr) + Rsin(2 θi) 2 1+ R + 2Rcos2θ r Fs = V < P> 1+ Rcos2θ i T 2 [cos(2θ i 2 θr) + Rcos(2 θi) 2 1+ R + 2Rcos2θ r

6 Method of acoustic tweezers Flow chat Simulate the time course of acoustic field :P Calculate the gradient of the average P : <P> Calculate the force F Use the iteration method to find the track of the particle

7 Method of acoustic tweezers -30 ns to foci 0 ns to foci Gradient plot 30 ns to foci

8 Method of acoustic tweezers The net force of a particle The force-axis diagram at given time T

9 Method of acoustic tweezers Iteration method

10 Method of acoustic tweezers Track of particle Converge S.H.M. being captured

11 Method of acoustic tweezers Track converge Unbound track

12 Trapping model 1. Contact 2. Shake the particle wave particle particle

13 Trapping model 3. Wave leaves the particle, and acoustic field exerts no force on particle during PRI. particle wave Position A Position B

14 Trapping model 4. Viscosity will decrease the speed of particle particle v The force comes from viscosity

15 Initial condition ex: position density volume Mechanism of acoustic tweezers ex: wave form viscosity prf pressure..etc. Particle track

16 Pulse-Trapping system Particle contacts with wave first part Particle moves within PRI second part work time second part (order): 10 4 first part (order): 1

17 First part When particle contacts with the sound wave 1 2 vt () t+ at () t xt ( + t) xt ( ) 2 vt ( + t) = vt ( ) + at ( ) t at ( + t) at () Axt ( ( + t), t+ t) Axt ( (),) t A(x,t):=the acceleration at given time t and given position x

18 First part acceleration caused by viscosity acceleration caused by acoustic field When wave contacts with particle, viscosity can be ignored.

19 Second part :During PRI dv m = kv dt dv k = dt v m exp( k v = v ) 0 t m dx k v = = v0 exp( t ) dt m m k x( t ) = v0 exp( k m k = 6πµ r μ : viscosity r : particle radius m : particle mass This imply: When PRI becomes longer, no significant change occurs. t ) 1 + x 0

20 A tool which may be able to help study the system Phase plot

21 Phase plot When wave contacts with particle Particle moves Within PRI. PRI:0.001 s

22 Converge to the same point

23 Black: without viscosity Blue: with viscosity

24 Viscosity increase the chance of convergence The velocity of the particle: -1*10-4 >2*10-5

25 with viscosity all tracks converge to -25μm

26 Without viscosity Only three tracks converge viscosity increases the converge range

27 Conclusion From the discussion above, viscosity plays an import role in the pulse trapping model. Although viscosity takes part of the trapping model, the sound wave still dominate the whole system. To obtain a better system stability, the waveform should be smooth.

28 Future work To design a better waveform which may increase the stability Study all factors such as density, particle size and pressure etc. Study the stream flow which caused by acoustic pressure.

29 Thanks for your attention

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