Using Piezoelectric Devices To Transmit Power Through Walls
- Friday, 30 May 2008
It would not be necessary to make holes in walls for wires.
A method denoted wireless acoustic- electric feedthrough (WAEF) has been conceived for transmitting power and/or data signals through walls or other solid objects made of a variety of elastic materials that could be electrically conductive or nonconductive. WAEF would make it unnecessary to use wires, optical fibers, tubes, or other discrete wall-penetrating signal-transmitting components, thereby eliminating the potential for structural weakening or leakage at such penetrations. Avoidance of such penetrations could be essential in some applications in which maintenance of pressure, vacuum, or chemical or biological isolation is required.
In a basic WAEF setup (see figure), a transmitting piezoelectric transducer on one side of a wall would be driven at resonance to excite ultrasonic vibrations in the wall. A receiving piezoelectric transducer on the opposite side of the wall would convert the vibrations back to an ultrasonic AC electric signal, which would then be detected and otherwise processed in a manner that would depend on the modulation (if any) applied to the signal and whether the signal was used to transmit power, data, or both.
The basic WAEF concept admits of variations. In one potentially important class of variations, different frequencies (in particular, those of lower- and higher-order resonances) would be used to transmit different signals through a wall in the same direction or in opposite directions. For example, an exterior ultrasonic transducer on a vessel could be excited at the fundamental resonance frequency to transmit power through the wall to an interior ultrasonic transducer to activate instrumentation inside the vessel, while the interior ultrasonic transducer could be excited at the frequency of a higher- order resonance to transmit data signals from the interior instrumentation to an external computer.
An electromechanical-network model has been derived as a computationally efficient means of analyzing and designing a WAEF system. This model is a variant of a prior model, known in the piezoelectric- transducer art as Mason’s equivalent-circuit model, in which the electrical and mechanical dynamics, including electro-mechanical couplings, are expressed as electrical circuit elements that can include inductors, capacitors, and lumped-parameter complex impedances. The real parts of the complex impedances are used to account for dielectric, mechanical, and coupling losses in all components (including all piezoelectric-transducer, wall, and intermediate material layers). In an application to a three-layer piezoelectric structure, this model was shown to yield the same results as do solutions of the wave equations of piezoelectricity and acoustic propagation in their full complexity.