Determining Resonance Frequency
When exposed to an AC electric field, a piezoelectric ceramic
element changes dimensions cyclically, at the cycling frequency
of the field.
As the frequency of cycling is increased from zero, the
ceramic element's oscillations approach a frequency at which
impedance is minimum. At this minimum impedance frequency
(fm) or resonance frequency (fr.)
the ceramic element will vibrate most readily, and will most
efficiently convert the electrical energy input into mechanical
energy.
As the cycling frequency is further increased, impedance
increases to a maximum -- the maximum impedance frequency
(fn) or antiresonance frequency (fa).
For some applications (ultrasonic motors, other high power
applications) it can be advantageous to operate a piezoelectric
ceramic element at its antiresonance frequency, rather than at
its resonance frequency.
The composition of the ceramic material and the shape and
volume of the element determine the resonance frequency.
Generally, a thicker element has a lower resonance frequency
than a thinner element of the same composition and shape. Values
for minimum impedance / resonance frequency and maximum
impedance / antiresonance frequency can be determined by using
the system illustrated here. The procedure follows:
- Set the switch to A.
- Place the ceramic element into position.
- Adjust the frequency generator to give a
maximum voltage
value on the voltmeter. This value is the resonance
frequency.
- Set the switch to B.
- Adjust R4 to give a voltage value on the voltmeter equal
to the value in step 3. This value is the impedance
resonance (Zr).
- Set the switch to A.
- Adjust the frequency generator to give a
minimum voltage
value on the voltmeter. This value is the antiresonance
frequency.
System for Determining Resonance Frequency and Antiresonance
Frequency of a Piezoelectric Ceramic Element
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