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773 views
05:04 Sep-18-2000

Gharieb Adly Ali

Other, Ultrasonic Researcher
National Institute for Standards,
Egypt,
Joined Oct 1999
1
Elect.Impedance of PZT Pickup


Dear colleagues

For economical purpose I had construct a simple PZT pickup
From PZT -4 Material of Fundamental frequency 2MHZ
When I measured the Electrical Impedance of Pickup against frequency
(Over frequency range 10 KHz to 4 MHZ )
I was found three Peaks
1- first at 250 kHz
2- second at 850 kHz
3- third at 3300 kHz
I Haven't explanation for this result, may be any colleague
has an explanation
Thank you very much



 
05:44 Sep-18-2000

Jim Barshinger

Engineering
General Electric Global Research Center,
USA,
Joined Aug 2000
8
Re: Elect.Impedance of PZT Pickup :
: Dear colleagues

: For economical purpose I had construct a simple PZT pickup
: From PZT -4 Material of Fundamental frequency 2MHZ
: When I measured the Electrical Impedance of Pickup against frequency
: (Over frequency range 10 KHz to 4 MHZ )
: I was found three Peaks
: 1- first at 250 kHz
: 2- second at 850 kHz
: 3- third at 3300 kHz
: I Haven't explanation for this result, may be any colleague
: has an explanation
: Thank you very much

The first and second peaks are most likely lateral resonances in the material. If you only have one lateral dimension, for instance a circular or square ceramic, I would guess that the 250 kHz peak is the fundamental lateral resonance and the 850 kHz peak is the third harmonic of the lateral resonance. The 3300 kHz peak should be your fundamental thickness mode resonance. I'm guessing that you are measuring the parallel resonance which will be a point of maximum real impedance. The series resonance should occur slightly lower in frequency and is a point of minimum real impedance. This should occur at 2 MHz (if you have ground your ceramic to the correct thickness). The center frequency that the device will run at depends on whether your recieving electronics matches better with the series or parallel resonance.

Good luck,
Jim





 


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