Ultrasonic thickness testing with Arduino

Projects General Guidance
1

I am totally new to Arduino and I'd like some thoughts and advice on a project I'm considering.

I have seen numerous projects for building an ultrasonic range finder where the Arduino is used to time the delay between an initial ultrasonic pulse and the sound being reflected from the object. In the case of ultrasonic thickness gauges, an ultrasonic pulse is sent through a transducer held in direct contact with the object being measured and the time it takes for the sound to be reflected back to the transducer is converted to distance. It seems to me that the only real difference between an ultrasonic range finder and a thickness gauge is the type of transducer used.

Thickness gauge transducers are relatively cheap compared to the price of the instrument itself (which can run into the thousands of dollars for a decent unit) and I am wondering if this is the type of thing that can be done with the relatively inexpensive Arduino. The thickness gauge transducers operate on a frequency of either 5 MHz or 7 MHz with 5 MHz being the most popular. I would be using this to measure the thickness of steel plate and need a resolution of 0.001". The speed of sound in carbon steel is 0.23 Inch/µSecond and to be able to successfully measure that I would need to be able to time the pulses between pulses with a precision of 0.002 µSecond. The measurements are typically taken about 20 times per second.

Is this something that is even within the capabilities of the Arduino? What model would you suggest, and can anyone provide any feedback on the feasibility of this? I appreciate the help!

2

I would need to be able to time the pulses between pulses with a precision of 0.002 µSecond.

Directly resolving 2 nanoseconds on a device with a cycle time of 62.5 nanoseconds is a tough call.
An Arduino might be able to control external hardware to do the measurement, and provide a means of displaying the result, but not make the measurement itself.

3

I haven't used an Arduino (yet!) but you do not need to drive an ultrasonic transducer at it's nominal frequency (say 5-10MHz). Once excited by the input pulse the piezoelectric crystal will oscillate at a frequency determined by it's physical dimensions, hence why each probe has it's own stipulated frequency. So good news - you only need to excite the probe at about 500Hz. You do need a very short pulse width though - around half the stipulated probe wavelength. That's driving the probe, you would still need to digitise the returned signal - probably at around 10 times the probe frequency to reproduce the waveform reasonably well. good luck, I wouldn't mind trying this myself!