Dear All, I am trying to actuate the particle inside the microfluidic channel by SAW but my current function generator can only generate a 20MHz signal.
The diameter of my particle is around 8 micron.
In the first paper, they show the relationship between particle diameter and frequency. http://pubs.acs.org/doi/abs/10.1021/ac402607p
From their formula, 2 micron diameter particle was deflected with 280MHz or upper
But the another example is standing wave,
http://pubs.rsc.org/en/content/articlelanding/2008/lc/b716321e#!divAbstract
They manipulated 1.9 micron diameter particle with 38.2 MHz
I am so confused. Do they define "particle movement or deflection" with a different meaning?
If I need to control particle at the center, which frequency should I use?
Last thing, how can I know the estimated power I should use in particle deflection?
Since my equipment and the size of microchannel etc. are different from the other papers.
Best Regards,
Yannapol S.
Hi,
In most cases particles are not excited at their resonances. A standing wave is established to first trap a particle; in that case you can design a chamber and find the resonance frequency of the chamber. The frequency would depend based on the chamber dimensions. There are numerous way to manipulate or maneuver particles in an acoustic field. One way is to trap a particle at the node of the standing waves and change the frequency to change the spatial nodal position to move the trapped particle. Usually the distance you can move is limited by the resonance frequency of the transducer, which peaks at a certain frequency with narrow bandwidth.
I hope I answer some of the concerns.
regards,
Any acoustic wavelength will result in a net force towards the nodal positions for any particle size in a standing wave (for typical water/polymer particle solutions). There is, however, a minimum particle size that can be trapped for a particular wavelength, below which fluid drag (from acoustic streaming) will dominate particle motion (see http://pubs.rsc.org/en/content/articlepdf/2012/lc/c2lc40612h). For ~10Mhz order SAW, anything larger than a micron in diameter should be fine. The travelling wave force scales with F~f^4, so you won't be able to induce much of this for frequencies less than 20MHz. In terms of what frequency you should use, just use the resonant frequency of your SAW transducer (f = 3960/wavelength for lithium niobate).
You can use two set of IDTs and place your channel in the center of these two IDTs. If your channel is relatively big so that you have at least 1 pressure node in your channel, then you can trap a particle which is bigger than 1 micron as David explained. Once you trap a particle, you can change the phase between two IDTs to change the position of the node which will result in particle translation. You need two function generators for this kind of operation tough. check papers from this group related to SSAW. http://www.esm.psu.edu/~juh17/
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