Tristan J. Lawry

A high-performance ultrasonic system for the simultaneous transmission of data and power through solid metal barriers

This paper presents a system capable of simultaneous high-power and high-data-rate transmission through solid metal barriers using ultrasound. By coaxially aligning a pair of piezoelectric transducers on opposite sides of a metal wall and acoustically coupling them to the barrier, an acoustic-electric transmission channel is formed which prevents the need for physical penetration. Independent data and power channels are utilized, but they are only separated by 25.4 mm to reduce the systems form factor. Commercial off-the-shelf components and evaluation boards are used to create realtime prototype hardware and the full system is capable of transmitting data at 17.37 Mbps and delivering 50 W of power through a 63.5-mm thick steel wall. A synchronous multi-carrier communication scheme (OFDM) is used to achieve a very high spectral efficiency and to ensure that there is only minor interference between the power and data channels. Also presented is a discussion of potential enhancements that could be made to greatly improve the power and data-rate capabilities of the system. This system could have a tremendous impact on improving safety and preserving structural integrity in many military applications (submarines, surface ships, unmanned undersea vehicles, armored vehicles, planes, etc.) as well as in a wide range of commercial, industrial, and nuclear systems.

Penetration-free system for transmission of data and power through solid metal barriers

This paper presents a novel system capable of simultaneous high-power and high data-rate transmission through solid metal barriers using ultrasound. By co-axially aligning a pair of piezoelectric transducers on opposite sides of a metal wall and acoustically coupling them to the barrier, an acoustic-electric transmission channel is formed which prevents the need for physical penetrations. Independent data and power channels are utilized, but they are only separated by 25.4 mm (1 in) to reduce the systems form factor. Commercial off-the-shelf components and evaluation boards are used to create real-time prototype hardware and the full system is capable of transmitting data at 12.4 Mbps and delivering 50 W of power through a 63.5 mm (2.5 in) thick steel wall. A synchronous multi-carrier communication scheme (OFDM) is used to achieve a very high spectral efficiency and to ensure that there is only minor interference between the power and data channels. Also presented is a discussion of many potential enhancements that could be made to greatly improve the power and data-rate capabilities of the system. This system could have a tremendous impact on improving safety and preserving structural integrity in many military applications (submarines, surface ships, UUVs, armored vehicles, planes, etc.) as well as in a wide range of commercial, industrial, and nuclear systems.

Electrical optimization of power delivery through thick steel barriers using piezoelectric transducers

In many commercial, industrial, and military applications, supplying power to electronics through a thick metallic barrier without compromising its structural integrity would provide tremendous advantages over many existing barrier-penetrating techniques. The Faraday shielding presented by thick metallic barriers prevents the use of electromagnetic power-transmission techniques. This work describes the electrical optimization of continuouswave power delivery through thick steel barriers using ultrasound. Ultrasonic channels are formed by attaching pairs of coaxially-aligned piezoelectric transducers to opposite sides of thick steel blocks. The thickness of the steel considered is on the order of, or greater than, one quarter wavelength of the acoustic power signal inside of steel, requiring the use of wave propagation theory to properly analyze the system. A characterization and optimization methodology is presented which measures the linear two-port electrical scattering parameters of the transducersteel- transducer channel. Using these measurements, the simultaneous conjugate impedance-matching conditions at both transducers are calculated, and electrical matching-networks are designed to optimize the power transfer from a 50Ω power amplifier on one side of the steel block to a 50Ω load on the opposite side. In addition, the impacts of, and interactions between, transducer and steel geometries are discussed, and some general guidelines for selecting their relationships are presented. Measurements of optimized systems using transducers designed to resonate at 1 MHz with diameters from 12.7 mm to 66.7 mm, and steel block thicknesses from 9.5 mm to 63.5 mm, reveal power transfer efficiencies as high as 55%, and linear delivery of 81 watts through an optimized channel.

A full-duplex ultrasonic through-wall communication and power delivery system

This paper presents a method for two-way ultrasonic communication and power delivery through thick metallic enclosures without physical penetration. Acousticelectric channels are implemented using a pair of coaxially aligned piezoelectric transducers having 25.4 mm diameters and 1 MHz nominal resonant frequencies, mounted on steel walls having lengths in the range of 57.15 to 304.8 mm. A protocol is described which uses ultrasonic waves to achieve simultaneous bidirectional communication through the metallic enclosures. It is shown that such channels are very frequency selective, and a carrier frequency selection and tracking algorithm is presented to choose a frequency of operation at which both adequate power delivery and reliable full-duplex communication are achieved. Using this algorithm, sufficient power is harvested to allow for the continuous operation of internal electronics which require an aggregate of less than 100 mW. Reliable communication of sensor data is achieved at rates in excess of 30 kbps.

A high-temperature acoustic-electric system for power delivery and data communication through thick metallic barriers

In many sensing applications that monitor extreme environmental conditions within sealed metallic vessels, penetrating vessel walls in order to feed through power and data cables is impractical, as this may compromise a vessels structural integrity and its environmental isolation. Frequent servicing of sensing equipment within these environments is costly, so the use of batteries is strongly undesired and power harvesting techniques are preferred. Traditional electromagnetic power delivery and communication techniques, however, are highly ineffective in these applications, due to Faraday shielding effects from the metallic vessel walls. A viable, non-destructive alternative is to use piezoelectric materials to transmit power through thick metallic barriers acoustically. We present critical elements of a high-temperature battery-less sensor system prototype, including power harvesting, voltage regulation, and data communication circuitry able to operate up to 260°C. Power transmission is achieved by coaxially aligning a pair of high-temperature piezoelectric transducers on opposite sides of a thick steel barrier. Continuous-wave excitation of the outside transducer creates an acoustic beam that is captured by the opposite transducer, forming an acoustic-electric link for power harvesting circuitry. Simultaneously, sensor data can be transmitted out of the high-temperature environment by switching the electrical impedance placed across the leads of the inside transducer, creating a reflection-based amplitude modulated signal on the outside transducer. Transducer housing, loading, and alternatives for acoustic couplants are discussed. Measurement results are presented, and it was found that the system can harvest up to 1 watt of power and communicate sensor data up to 50 kbps, while operating at 260°C.

Mechanical Design Implications on Power Transfer Through Thick Metallic Barriers Using Piezoelectric Transducers

Traditionally, power transfer through thick metallic barriers has required physical penetrations and wire feed-throughs, which reduces structural integrity and limits the environmental isolation provided by the barrier. The Faraday shielding presented by these barriers, however, prevents efficient transfer of electromagnetic power, limiting many RF coupling techniques. More recently, the use of ultrasound has been shown as an effective non-destructive technique for transmitting large amounts of power (100s of watts) through solid metallic mediums. By using two coaxially aligned piezoelectric transducers loaded onto opposite sides of the barrier through an acoustic couplant, an ultrasonic channel is formed through which efficient power delivery is possible. This work presents finite element modeling and simulations that help characterize the impacts of many mechanical design factors on the power transfer efficiency of these ultrasonic channels, including: transducer-wall coupling effects, transducer and wall resonance modes, transducer dimensions, and barrier composition and dimensions. Physical channel measurements are also presented to show the strong correlation between the finite element simulations and the systems modeled.Copyright

Analytical modeling of a sandwiched plate piezoelectric transformer-based acoustic-electric transmission channel

The linear propagation of electromagnetic and dilatational waves through a sandwiched plate piezoelectric transformer (SPPT)-based acoustic-electric transmission channel is modeled using the transfer matrix method with mixed domain two-port ABCD parameters. This SPPT structure is of great interest because it has been explored in recent years as a mechanism for wireless transmission of electrical signals through solid metallic barriers using ultrasound. The model we present is developed to allow for accurate channel performance prediction while greatly reducing the computational complexity associated with 2- and 3-dimensional finite element analysis. As a result, the model primarily considers 1-dimensional wave propagation; however, approximate solutions for higher-dimensional phenomena (e.g., diffraction in the SPPTs metallic core layer) are also incorporated. The model is then assessed by comparing it to the measured wideband frequency response of a physical SPPT-based channel from our previous work. Very strong agreement between the modeled and measured data is observed, confirming the accuracy and utility of the presented model.

Finite Element Modeling and Simulation of a Two-Transducer Through-Wall Ultrasonic Communication System

A finite element simulation of a through-wall ultrasonic communication system which permits data to be transferred from the inside of a sealed metal vessel to the outside without the need for physical penetrations is introduced. Two transducers are aligned axially on either side of a thick solid stainless steel wall. The outside transducer is forced with a continuous sinusoidal voltage at the crystal’s nominal 1 MHz longitudinal resonant frequency, launching a wave into the wall. The transmitted beam is partially reflected off of the inside of the wall where the inside transducer is located. The amplitude of the reflected wave is modulated by switching the electrical impedance placed across the leads of the inside transducer. The reflected wave is received at the outside transducer and the continuous wave amplitude is sensed to detect the transmitted data bits. The system is modeled and simulated using a commercial finite element modeling package. A coupled stress-strain and piezoelectric analysis is performed using an axisymmetric geometry. The model represents an existing system from which physical measurements were taken. Excellent correlation between the model and system were observed and the model has been used to further optimize the communication system.Copyright

High-rate ultrasonic communication through metallic barriers using MIMO-OFDM techniques

This paper presents methods to achieve high data transmission rates through metallic barriers using ultrasonic signalling techniques. Due to the frequency selective nature of acoustic-electric channels, orthogonal frequency division multiplexing (OFDM) is employed which achieves high spectral efficiency. Multiple parallel channels are used to further increase data rates. Multiple-input multiple-output (MIMO) techniques are used to reduce crosstalk that would otherwise greatly limit performance and achievable data rates. Several crosstalk mitigation techniques are investigated and their theoretical capacity performances are determined for the general case of A transmitters and A receivers (i.e. A×A MIMO). A physical MIMO acoustic-electric channel array is formed using a 40 mm (1.575 in) thick steel barrier with seven pairs of 4 MHz nominal resonant frequency piezoelectric disk transducers, each with 10 mm (0.394 in) diameter. To investigate the effects of crosstalk, the transducers are closely spaced, and each transmitter-receiver pair is coaxially aligned on opposing sides of the metallic barrier. It is shown that, with the use of crosstalk mitigation techniques, the aggregate multichannel capacity performance scales linearly with the number of channels used and approaches 700 Mbps at high average signal-to-noise ratio (SNR) levels. Finally, the use of bit-loading techniques are explored using several levels of rectangular quadrature amplitude modulation (QAM), and the achievable data rates are compared with each other and to the multichannel theoretical capacity performances.

Multi-channel data communication through thick metallic barriers

This paper explores the use of multiple communication channels to transmit data at high rates, without physical penetrations, through thick metallic barriers using ultrasound. Two parallel acoustic-electric channels are formed in close proximity utilizing two pairs of coaxially aligned piezoelectric transducers mounted on, and acoustically coupled to, opposing sides of a metal wall. Each channel employs orthogonal frequency division multiplexing (OFDM) which can achieve a high spectral efficiency in frequency selective channels. The two-transmitter-two-receiver MIMO configuration is studied and analytical expressions of channel capacity are determined for the raw channels as well as for several co-channel interference cancellation techniques and they are verified using a Monte-Carlo simulation. It is shown that excessive crosstalk between the channels can lead to marginal increases or decreases in capacity over the single channel when no interference suppression is used. Several interference cancellation structures, including zero forcing, eigenmode transmission, and minimum mean-square error (MMSE) are investigated to mitigate this effect. It is shown that their aggregate capacity may approximately double that of either channel used independently. It is also determined that, in a relatively static MIMO acoustic-electric channel, a minimal complexity adaptive approach such as the Least Mean Squares (LMS) algorithm may be used while achieving a similar capacity to more complex structures.