On Fri, 9 Feb 2001 18:01:41 -0500, you wrote:

>> Yes, both sine waves.  I intend to filter the driving signal to clean =
up
>the
>> 40KHz signal into a pure sine wave.. The next question is, will an
>ultrasonic
>> transducer respond to 40KHz sine just as well as square wave??
>
>How "well" it responds has to do with the transducer and the desired =
effect.
>A square wave contains much of its power in the fundamental, but also =
has
>significant harmonics, with the first harmonic being at 3 times the
>fundamental.  If the transducer can't "see" 120KHz, then it shouldn't
>matter.  Even if it can respond to 120KHz, it still won't matter if the =
rest
>of the system doesn't care if 120KHz signals are present.
Most piezos are basically capacitors, and driving them is basically
about charging and discharging that capacitance, so harmonic content
is not usually an issue - the capacitance and mechanical inertia takes
care of it (this may be less the case for low-mass ultrasonic units).
Max output usually happens if you charge and discharge the piezo
capacitance as quickly as possible, i.e. with a square wave. The
current waveform will tend to look pretty spiky, as it would driving a
pure capacitance. Square wave drive also means you lose less power in
the driver.=20
=20

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