Dear All,
I have SAW device(Al electrode on LinNbO3) and it was measured by impedance analyzer, Stripwidth= 50 um, resonance frequency = 20.02 MHz. After that I bond PDMS(channel width 100um) on top with plasma and flow the 5-7 um particle. But when I use it, the particle is actually lineup at 19.28 MHz.
Now, I bond with another piece of PDMS, (channel width is still 100 um). Unfortunately, the particle is not lineup at 19.28 MHz anymore.
I know that the resonance frequency may shift by various factors, but how I can I find or predict the exact frequency of particle lineup ?
And What are those factors to make the frequency shift ?
Best Regards,
Yannapol S.
hi,
Based on the parameters and the info that you provided, any oscillating object will change its resonant frequency upon changes in its dimension or increased/decreased in mass of its own or the some external addition of mass. In your case, the SAW is working precisely at 20.02 MHz. The moment you put the PDMS chip on to it, its frequency shifts, a trivial observation. Now to eliminate the discrepancy of variation in the shift of the frequency, make sure you fabricate the PDMS chips with precise dimensions at all cost. The change in the pdms curing agent, temperature, timing and elastomer mass are all deeply influencing factors in this case. Not only these, but the suspension fluid concentration, its flow rate in the channel, relative viscosity if the fluid after addition of the particles and alignment of the channel over the SAW device's active elements are the remaining parameters which will be the deciding factors for controlling your frequency shifts.
Regards
If I was you, I'd make the device and then sweep the frequency range from around 15MHz until you find the signal. As has been pointed out above, the frequency will shift the moment you put something on the surface of the IDT, and the only way I found to find the new frequency is to sweep the range using your frequency generator and watch for activity.
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