Determining sensor bandwidth

I'm currently working on a project making use of ultrasonic proximity sensors. Unfortunately it seems as though well-documented ones are very few and far between (when compared to PIC or MOSFET datasheets).

As such I'm struggling to determine the bandwidth of these sensors. My understanding of bandwidth is that it is the frequency corresponding to the -3db attentuation point of a signal. How does this relate to a sensor?

(On a side note, can anyone explain the lack of quality in these datasheets? Am I looking in the wrong place? Vishay and Texas Instruments are really comprehensive, and then these datasheets barely have more than the sensor dimensions.)

• Datasheets for semiconductor devices are the best out there. Electromechanical devices like sensors are generally much less well specified, with a lot more information that you're just expected to know (or, these days, that the manufacturer doesn't really understand themselves). – TimWescott May 8 at 22:51

Imagine a plate moving back and forth sinusoidally in front of your sensor. If the bandwidth of the sensor is much greater than the frequency of the motion, then the output of your sensor will track the motion very well.

For example if the output sensitivity is 1 V per meter, and your plate is moving +/- one meter, your sensor will put out a +/- 1 V sinusoidal signal.

Now, if the plate is moving back and forth at the bandwidth of the sensor, even though the plate is still moving +/- 1 meter, the output of your sensor will put out 3 dB less, or +/- 0.707 V.

If the plate is moving much faster than the bandwidth of the sensor you would see only a very small signal on the output.

So the sensor bandwidth is a measure of the ability of the sensor to follow changes in the sensed quantity.

As to the lack of data in datasheets the only advice is caveat emptor. If your design depends on anything that's not specified, (and not just as a typical spec) you are rolling the dice.

• if you spend only 10 cents for a sensor, don't expect consistency and predictability and reliability; friend of mine tinkers with piezos, and the output voltage easily varies 5:1 across production runs. – analogsystemsrf May 8 at 22:55