A frequency-domain technique for noninvasive, ultrasonic fluid detection in submerged sealed canisters

Abstract

There are situations where canisters containing specialized parts and/or materials are submerged underwater for storage or safety purposes. In some cases, leaks in the canisters can be detrimental and must be detected as early as possible. The present research describes an ultrasonic method for determining the presence of fluid in sealed, submerged canisters. In this research, the canisters are metallic and are filled with a random array of loose objects. The technique is based on two phenomena: the radiation damping effect of the internal fluid on the container wall and spectral signatures that result from internal reflections within the canister. The experiment utilizes a pair of piezoelectric transducers with a lateral separation of 27 mm. The transducers are placed at a standoff distance of 5 mm from the container wall and traverse the vertical dimension of the canister on a stepper-slide assembly. The transmitter is swept between 0.8–4.0 MHz and a frequency spectrum is collected. By analyzing the contributions to the spectrum from internal radiation damping and internal reflections separately, it can be determined whether the container wall is fluid or air backed. Current results demonstrate that fluid levels as low as 1 cm can be detected.