Can this ultrasonic emitter be DC driven?

Question

The datasheet of this ultrasonic specifies that the maximum driving voltage is 10 Vrms, which suggests that it should be driven by an AC.

Is my assumption correct? Can the emitter be DC driven?

score 2 · Accepted Answer · edited Apr 13 '17 at 12:32

2

Yes, it needs to be AC driven at it's nominal frequency (40kHz)

You can just apply a square wave of this frequency to the base/gate of a transistor with emitter/source to ground and put the transducer from collector/drain to +V. You can also use an inductor in parallel with the capacitance of the transducer to form a tank for increased amplitude (see this previous question)

You can use the PWM module for this to spare more time for your main loop, or a timer with interrupt, or if you are not using a microcontroller use a 555, or anything else capable of generating your square wave (or sine wave)

edited Apr 13 '17 at 12:32

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1

answered Feb 03 '13 at 00:03

Oli Glaser

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Thanks. Could you please clarify what you mean by "just PWM it with transistor"? – Randomblue Feb 08 '13 at 20:41
Sorry, yes - I just meant apply a square wave of that frequency using e.g. a PWM peripheral. I edited to clarify, you can drive it with a sine wave at that frequency also if you wish. – Oli Glaser Feb 08 '13 at 20:52
I been able to get a square wave using an ARM STM32. The wave is 40kHz, varying between 0V and 3.3V. How will I achieve the negative voltages? – Randomblue Feb 09 '13 at 10:24
@Randomblue - You don't need negative voltages relative to your circuit ground, just the 0 - +3.3V (with current limiting resistor) will do to drive the transistor base. – Oli Glaser Feb 09 '13 at 20:58

score 1 · Answer 2 · answered Feb 03 '13 at 00:03

Right on the first page of the datasheet is this chart:

Clearly these things want about 40 kHz. Even just 35 kHz is about 20 dB down in output. DC (0 Hz) won't do anything useful.

This should also be clear just from the function of the device itself. It is some kind of ultrasonic transducer. I didn't look at the datasheet enough to see if it is piezo or magnetic, but most of these things are piezo. In any case, DC isn't ultrasound. You wouldn't be using these devices in the first place if you weren't trying to emit 40 kHz ultrasound.

Can this ultrasonic emitter be DC driven?

2 Answers2