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Special high-frequency microphone systems were developed, and ultrasonic noise associated with various manufacturing operations was measured in the frequency range 0–1 MHz in order to evaluate typical noise environments for ultrasonically controlled robots. Industrial operations studied include impact, bending, grinding and drilling, laser etching, and high-velocity fluid or air sprays. The first three operations provide little ultrasonic energy above 100 kHz. For these processes, ultrasonic sensors operating above 100 kHz should have an advantage since signal and noise will both fall off with increasing frequency. Ultrasonic emission from laser etching was found to be quite broadband, making such processes less suitable for ultrasonic control. High-velocity fluid or air sprays are most prevalent sources of ultrasonic noise. The noise from these sources rolls off slowly with frequency, and no frequency bands without noise exist for ultrasonic sensing below several hundred kHz. For applications requiring ultrasonic sensing, aerodynamic noise should be reduced.
Bass et al. (Thu,) studied this question.