Characterization of commercial cmut microphone By SLDV (scanning laser doppler vibrometer)
A depackaged commercial MEMS microphone from knowles SPU0414HR5H-SB
This page it to give an overview of the experimental aspect(which is the most interesting part) of the project. I am thankful for the support of my advisor Prof. Neal Hall and the fancy state of the art equippments in the lab.
Next, by electrical excitation, the CMUT is driven and the velocity is measured using the LDV to determine its resonance frequency
This will help us determine the fundamental mode of the deivce
The surface vibration profile established by SLDV(scanning laser doppler vibrometer) as a function of time(sinusoid input)
It can be seen that the diaphragm pulled in at such high voltage, the displacement of the diaphragm reaches 6um!
The diaphragm is driven at 200kHz sine wave(which corresponds to the second harmonic), the point is (the donut shape of the vibration is clearly seen by the scanning LDV!)
I think it is quite an interesting plot, if you were to compare this with the small signal transfer function, you will see the bandwidth is enlarged due to the nonlinear effect associated with pulling in the CMUT diaphragm
A related publication to evaluate the behaviour of a CMUT under pull-in is put here:https://link.springer.com/chapter/10.1007/978-3-031-36999-5_33