Re: Pulser de-polarization

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Re: Pulser de-polarization
Posted by: Gerhard Splitt , E-mail: sp@kk-a-col.mhs.compuserve.com, on September 08, 1996 at 13:22:50:
In Reply to: Re: Pulser de-polarization posted by : Bill Grandia on September 07, 1996 at 22:24:24:
: : Lately PC style Pulser-receivers have provided a
: : selection of pulse shaping features such as positive,
: : negative or bipolar (as well as energy level, duration,
: : etc). Traditionaly a negative spike or squarewave
: : pulse has been used on transducers. Is it possible
: : to deteriorate polarization of poled piezoceramics
: : using positive squarewave pulsing?
: It is known that a piezo-electric element always ages with time, especially in the first few weeks after manufacturing, even without operating the element.
: When operating the element with a driver voltage opposed to the polarization direction, the deterioration speed in enhanced. For this reason, it is expected that the positive portion of the bipolar square wave driver acts destructively. From experience, driving a PZT5A element with a toneburst (400 kHz, 16 cycles at 500 Hz PRF) over a period of several years, no noticeable deterioration has been noticed.
The depolarization with a "wrong" pulser polarization only occurs at high values of the electric field strength which then will act as a depolarization field
This is true only for high frequncy piezoceramic (above 10 MHz) and for high pulser voltages (over 500 Volts).
Therefore it is clear that at 400 kHz with a tonburst pulser no deterioration effect was observed.
Of course, at elevated temperatures the depolarization will occur at lower critical values.
Gerhard Splitt

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: : : Lately PC style Pulser-receivers have provided a : : : selection of pulse shaping features such as positive, : : : negative or bipolar (as well as energy level, duration, : : : etc). Traditionaly a negative spike or squarewave : : : pulse has been used on transducers. Is it possible : : : to deteriorate polarization of poled piezoceramics : : : using positive squarewave pulsing? : : It is known that a piezo-electric element always ages with time, especially in the first few weeks after manufacturing, even without operating the element. : : When operating the element with a driver voltage opposed to the polarization direction, the deterioration speed in enhanced. For this reason, it is expected that the positive portion of the bipolar square wave driver acts destructively. From experience, driving a PZT5A element with a toneburst (400 kHz, 16 cycles at 500 Hz PRF) over a period of several years, no noticeable deterioration has been noticed. : The depolarization with a "wrong" pulser polarization only occurs at high values of the electric field strength which then will act as a depolarization field : This is true only for high frequncy piezoceramic (above 10 MHz) and for high pulser voltages (over 500 Volts). : Therefore it is clear that at 400 kHz with a tonburst pulser no deterioration effect was observed. : Of course, at elevated temperatures the depolarization will occur at lower critical values. : Gerhard Splitt

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