Waveguides for acoustic power and communication channels

Abstract

Channels that extend axially along a length of pipe were simulated extensively using frequency-domain finite element analysis. Channels using a wedge shaped intermediary between the transducers and the pipe wall were the focus as prior research indicated that wedges improve channel efficiency. Numerous conclusions were drawn including that maximum channel efficiency increases as the intermediary wedges get shallower (incident angle increases towards 90 degrees) and excitation frequency increases.

Finally, the problem of delamination of transducers from their steel substrates due to unequal thermal expansion was examined. Multiple epoxy adhesives were tested including one that maintained integrity at temperatures up to 150 degrees Celsius. Use of transition plates between the transducers and the steel substrates with intermediate coefficients of thermal expansion was also considered. Nickel-iron alloys kovar and invar proved to be effective at reducing the interfacial stresses that cause delamination while only slightly reducing acoustic performance.

A second research aim was probing the feasibility and behavior of “acoustic fiber”, the acoustic analogue to optical fiber. Again, frequency-domain FEA was employed. Heuristics governing the relationships between efficiency, physical dimensions, and frequency were produced.

A system for remote sensing of sealed or inaccessible environments has been developed which relies on acoustic waves for power transfer and communication. Acoustic waves are sent into a physical structure from the accessible side and harvested on the inaccessible side. The energy harvested is used to power a sensor and communications circuitry which sends the sensor reading back to the accessible side encoded in acoustic waves.