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Resonant frequency of Piezoelectric material

  1. Aug 26, 2016 #1
    So i have a piezoelectric film deposited in the metal substrate and i want to determine the resonant frequency. Basically i can determine the resonant frequency base on the dimensions. But i need to proved it using experimental set-up. So i applied AC Voltage to the material then the material will vibrate and using oscilloscope i can determine the oscillations of the material. from that i can determine the frequency. The problem is, when i'm trying to vary the amplitude voltages the frequency that the oscilloscope detected is in not fixed (ranging from the 1KHz=1MHz). so it tried to vary the frequency of the AC voltage but the detected Amplitude voltage in the oscilloscope is constant as the frequency varies. So how i can determine the resonant frequency by applying different frequency of ac voltage?
     
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  3. Aug 27, 2016 #2

    DrSteve

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    Don't you want to sweep the frequency at constant amplitude and look for resonant enhancement of the piezo material at the resonant frequency?
     
  4. Aug 27, 2016 #3

    tech99

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    I presume that there are two electrodes, so that a voltage can be applied to the material.
    The primary resonance is of the series type, so we expect to see a drop in impedance at fo. So all you need to do really is to measure the magnitude of the impedance across the frequency range. I presume you know that resonance will occur within the frequency range you have mentioned.
    My suggestion is to supply a current to the electrodes from the signal generator via a high value of resistor, maybe 100 k, and connect the CRO across the electrodes so it can measure voltage. Then look for the very sharp dip at resonance. The dip is very sharp, and may be only 100Hz wide at 1 MHz, for instance.
    As a matter of interest you do not even need an X timebase for this measurement. I realise you will use a digital scope, but I do not have experience of them for this type of experiment.
     
  5. Aug 27, 2016 #4
    Yes sir you're right! basically another way is to measure the current across the piezoelectric material as the frequency varies. But i need to plot the voltage vs. frequency. So using oscilloscope i can determine the voltage amplitude due to vibration, But then as i said no change in voltage amplitude as frequency varies.

    As you said i need to set the resistance to 100k ohms? why? the parameters that i used are: Voltage amplitude =10V, Resistance = 50 ohms, Cycle percent = 50%, delay = 0.00ns and frequency = 1-100hz.
     
  6. Aug 27, 2016 #5
    yes sir!
     
  7. Aug 27, 2016 #6

    tech99

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    If you sweep automatically, remember that the bandwidth is so very narrow, maybe 100 Hz, that it has a slow response time and you might miss it. For instance, if you sweep over 1 MHz bandwidth, and the peak is 100 Hz wide, that is 10^4 slots to look for. If each takes 1/100 second, that is 100 seconds minimum for the complete sweep.
    Regarding your circuit. We are looking for a series resonance, which has a low impedance. You are using a "voltmeter" to obtain an indication of current, so you need to place a high resistance in series with the generator so that, by voltage divider action, the low impedance resonance is seen as a dip in voltage. If you rely in the generator resistance, 50 ohms, it will not create a large dip at resonance because the impedance of the resonator might be similar.
    Be careful not to mix up the ground side of the signal generator and the CRO.
     
  8. Aug 27, 2016 #7
    No sir, i vary the frequency manually (from 1-100hz because the simulation results fall at 50hz). I will take note your suggestion but i need to plot voltage vs. frequency.
     
  9. Aug 27, 2016 #8
    Is CRO a special type of oscilloscope?
     
  10. Aug 27, 2016 #9
    So this is the set-up your trying to say? if i set the resonant frequency i will detect higher amplitude voltage?
     

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  11. Aug 27, 2016 #10

    tech99

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    I suggested putting a high value resistor in series with the generator output.
    A CRO is a Cathode Ray Oscilloscope, but don't worry about that.
     
  12. Aug 28, 2016 #11
    This one sir?
     

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