# How to figure out the current drawn by a 40kHz ultrasonic transducer?

I have some 40kHz ultrasonic transducers (the same type as which you find in the common Arduino ultrasonic distance sensors.) All information comparable to a datasheet I got was: I don't get how to read it or how to calculate the current drawn, which I need to know when making or buying a amplifier. It does show the capacitance at 1kHz. I guess they use that as a worst case scenario or such, however they don't show graphs showing how it behaves at different frequency ranges, at different voltage ranges, and above all it doesn't seem to show units.

Since it is a very commonly used ultrasonic transducer perhaps someone knows how to calculate the maximum current draw at a specific frequency and voltage, and/or a better datasheet or information or a close enough estimation of what current it will draw or what unit the value is in.

• Use the capacitance to calculate the impedance at the frequency you're driving it at. Of course, the capacitance they give you is only at 1kHz so it will be different at other frequencies but at least you can ballpark it. You can't do much more without curves. You can also measure it with an LCR meter if it is in front of you. May 14 at 17:28
• @DKNguyen Hi, I found this site: allaboutcircuits.com/tools/capacitor-impedance-calculator based on what you said, so I can just use that formula on that page? XC=1/2πfrequencyCapacitance. May 14 at 19:21
• Yes, that is the equation. Note that it is actually an imaginary number. It's not a real impedance like Ohms for resistance. There is normally a j or i in there. But for the purposes you mentioned so far it doesn't yet matter. Also note that it is for a single frequency component (a sine-wave). So if you put a square wave through it, it will be a sum of the currents for all the sine waves that are required to produce the square wave. May 14 at 19:22
• Oh I guess the unit is not listed. How sloppy. That should be pF. It's definitely not nF, let alone uF or F. May 14 at 19:45
• You just do the same thing with 1st, 3rd, 5th, 7th, 9th, harmonics and add up the currents. Square waves are odd sinusoidal harmonics infinite. Look up a square wave. I would stop at 5th. May 14 at 20:05