Publications

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A high bandwidth piezoelectric transducer technology for high data rate communications across metallic barriers is presented and discussed. To properly characterize the channel, a linear time-invariant (LTI) model of the device is obtained using frequency fitting methods on the S-parameter measurements of the communication network. The corresponding impulse response of the channel is derived from the poles and residues used to fit the frequency data. A recursive formulation of the impulse response of complex poles is advanced and analyzed. The channel characteristics were used to estimate the trans-barrier data rate employing orthogonal frequency division multiplex (OFDM) as used in a powerline communication (PLC) standard. An off-the-shelf PLC system is used to communicate through a metallic barrier and data rates exceeding 70 Mbps were achieved as predicted by the model. The methods described here are useful for estimating the physical data rate achievable by trans-barrier communication systems using piezoelectric transducers.

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For systems that require complete metallic enclosures (e.g., containment buildings for nuclear reactors), it is impossible to access interior sensors and equipment using standard electromagnetic techniques. A viable way to communicate and supply power through metallic barriers is the use of elastic waves and ultrasonic transducers, introducing several design challenges that must be addressed. Specifically, the use of multiple communication channels on the same enclosure introduces an additional mechanism for signal crosstalk between channels: guided waves propagating in the barrier between channels. This work numerically and experimentally investigates a machined phononic crystal to block MHz Lamb wave propagation between ultrasonic communication channels, greatly reducing wave propagation and the resulting crosstalk voltage. Blind grooves are machined into one or both sides of a metallic barrier to introduce a periodic unit cell, greatly altering the guided wave dispersion in the barrier. Numerical simulations are used to determine a set of groove geometries for testing, and experiments were performed to characterize the wave-blocking performance of each design. The best-performing design was tested using piezoelectric transducers bonded to the barrier, showing a 14.4 dB reduction in crosstalk voltage. The proposed periodic grooving method is a promising technique for completely isolating ultrasonic power/data transfer systems operating in a narrow frequency range.

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ROL-PEBBL is a C++, MPI-based parallel code for mixed-integer PDE-constrained optimization (MIPDECO). In these problems we wish to optimize (control, design, etc.) physical systems, which must obey the laws of physics, when some of the decision variables must take integer values. ROL-PEBBL combines a code to efficiently search over integer choices (PEBBL = Parallel Enumeration Branch-and-Bound Library) and a code for efficient nonlinear optimization, including PDE-constrained optimization (ROL = Rapid Optimization Library). In this report, we summarize the design of ROL-PEBBL and initial applications/results. For an artificial source-inversion problem, finding sources of pollution on a grid from sparse samples, ROL-PEBBLs solution for the nest grid gave the best optimization guarantee for any general solver that gives both a solution and a quality guarantee.

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Ultrasounds have been investigated for data communication to transmit data across enclosed metallic structures affected by Faraday shielding. A typical channel consists in two piezoelectric transducers bonded across the structure, communicating through elastic mechanical waves. The rate of data communication is proportional to the transmission bandwidth, which can be widened by reducing the thickness of the transducers. However, thin transducers become brittle, difficult to bond and have a high capacitance that would draw a high electric current from function generators. This work focuses on investigating novel transducer shapes that would allow to provide a constant transmission across a large bandwidth while maintaining large-enough thickness to avoid brittleness and electrical impedance constraints. The transducers are shaped according to a staircase thickness distribution, whose geometry has been designed through an analytical model describing its electro-mechanical behavior formulated for this purpose.

For systems that require complete metallic enclosures, it is impossible to power and communicate with interior electronics using conventional electromagnetic techniques. Instead, pairs of ultrasonic transducers can be used to send and receive elastic waves through the enclosure, forming an equivalent electrical transmission line that bypasses the Faraday cage effect. These mechanical communication systems introduce the possibility for electromechanical crosstalk between channels on the same barrier, in which receivers output erroneous electrical signals due to ultrasonic guided waves generated by transmitters in adjacent communication channels. To minimize this crosstalk, this work investigates the use of a phononic crystal/metamaterial machined into the barrier via periodic grooving. Barriers with simultaneous ultrasonic power and data transfer are fabricated and tested to measure the effect of grooving on crosstalk between channels.

Several applications, such as underwater vehicles or waste containers, require the ability to transfer data from transducers enclosed by metallic structures. In these cases, Faraday shielding makes electromagnetic transmission highly inefficient, and suggests the employment of ultrasonic transmission as a promising alternative. While ultrasonic data transmission by piezoelectric transduction provides a practical solution, the amplitude of the transmitted signal strongly depends on acoustic resonances of the transmission line, which limits the bandwidth over which signals are sent and the rate of data transmission. The objective of this work is to investigate piezoelectric acoustic transducer configurations that enable data transmission at a relatively constant amplitude over large frequency bands. This is achieved through structural modifications of the transmission line, which includes layering of the transducers, as well as the introduction of electric circuits connected to both transmitting and receiving transducers. Both strategies lead to strong enhancements in the available bandwidth and show promising directions for the design of effective acoustic transmission across metallic barriers.

Several applications, such as underwater vehicles or waste containers, require the ability to transfer data from transducers enclosed by metallic structures. In these cases, Faraday shielding makes electromagnetic transmission highly inefficient, and suggests the employment of ultrasonic transmission as a promising alternative. While ultrasonic data transmission by piezoelectric transduction provides a practical solution, the amplitude of the transmitted signal strongly depends on acoustic resonances of the transmission line, which limits the bandwidth over which signals are sent and the rate of data transmission. The objective of this work is to investigate piezoelectric acoustic transducer configurations that enable data transmission at a relatively constant amplitude over large frequency bands. This is achieved through structural modifications of the transmission line, which includes layering of the transducers, as well as the introduction of electric circuits connected to both transmitting and receiving transducers. Both strategies lead to strong enhancements in the available bandwidth and show promising directions for the design of effective acoustic transmission across metallic barriers.

For systems that require complete metallic enclosures (e.g., containment buildings for nuclear reactors), it is impossible to access interior sensors and equipment using standard electromagnetic techniques. A viable way to communicate and supply power through metallic barriers is the use of elastic waves and ultrasonic transducers, introducing several design challenges that must be addressed. The objective of this work is to investigate the use of piezoelectric transducers for both sending and receiving power and data through a metallic barrier using elastic waves at ultrasonic frequencies above 1 MHz. High-fidelity numerical and simplified analytical models are developed for ultrasonic transmission and novel strategies are explored to eliminate crosstalk between channels.

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