Jonathan D. Ashdown

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.

An Ultrasonic Through-Wall Communication (UTWC) System Model

Ultrasonic waves at 1 MHz are used to send information across solid walls without the needs for through wall penetrations. A communication channel is established by attaching a set of three ultrasonic transducers to the wall. The first transducer transmits a continuous ultrasonic wave into the wall. The second transducer is mounted on the opposite side of the wall (inside) and operates as a receiver and signal modulator. The third transducer, the outside receiving transducer, is installed on the same side as the first transducer where it is exposed to the signal reflected from the blended interface of the inside wall and inside transducer. Inside sensor data is digitized and the bit state is used to vary in time the electrical load connected to the inside transducer, changing its acoustic impedance in accordance with each data bit. These impedance changes modulate the amplitude of the reflected ultrasonic signal. The modulated signal is detected at the outside receiving transducer, where it is then demodulated to recover the data. Additionally, some of the ultrasonic power received at the inside transducer is harvested to provide energy for the communication and sensor system on the inside. The entire system (ultrasonic, solid wall, and electronic) is modeled in the electrical domain by means of electro-mechanical analogies. This approach enables the concurrent simulation of the ultrasonic and electronic components. A model of the communication system is implemented in an electronic circuit simulation package, which assisted in the analysis and optimization of the communication channel. Good agreement was found between the modeled and experimental results.

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

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

Interference Alignment for Downlink Multi-Cell LTE-Advanced Systems With Limited Feedback

To suppress the co-channel interference in a multi-cell multi-user multiple-input-multiple-output downlink cellular network, a novel interference alignment transceiver beam-forming design along with a low complexity iterative coordinated beam-forming scheme is introduced. While the latter combats the intra-cell interference, the former is utilized to mitigate the inter-cell interference. The proposed schemes consider the codebook-based feedback, which is adopted in the LTE/LTE-advanced systems. Optimal downlink user-specific and cell-specific beam-forming matrices are characterized to maximize the lower bound of expected signal-to-leakage-plus-noise ratio and to minimize the residual inter-cell interference, respectively. Moreover, closed-form expressions for these beam-forming matrices under limited channel state information feedback and in the presence of the quantization error are identified. Simulations are conducted to investigate the performance of the proposed strategy. The results indicate that our scheme can significantly improve the average spectral-efficiency of the underlying network when compared with existing ones where the quantization error is neglected. Furthermore, for a fixed payload size of the codebook, unlike zero-forcing beam-forming in which the sum throughput is bounded as the signal-to-noise ratio (SNR) increases, in our scheme, the performance gap between rank 2 feedback and perfect feedback remains approximately constant as SNR increases.

Fundamentals of Spatial RF Energy Harvesting for D2D Cellular Networks

Energy efficiency is one of the major challenges of 5G networks. As data rates are expected to increase by 1000x from 4G to 5G, energy efficiency will need to improve by about the same amount. Recently, energy harvesting techniques have attracted lots of attention from the scientific community, due to their ability to increase network lifetime. More specific, energy harvesting from ambient radio frequency (RF) signals is of special importance, especially with the recent RF circuit advancements. In this paper, we consider a device-to-device (D2D) communication in underlay cellular networks, where D2D users reuse the spectrum occupied by cellular users. We introduce the concept of spatial RF energy harvesting, where D2D users harvest RF power from uplink cellular transmissions, if it exceeds a predesigned threshold, in a spatial region. Using tools from stochastic geometry, we obtain a closed form expression for the probability of activating RF power conversion circuit by making full use of spatial locations of ambient RF signals. Subsequently, we study the impact of RF energy harvesting region radius to harvest sufficient power on the signal-to-interference (SIR) ratio of D2D network. Simulation results provide insights for the required advancements to design highly efficient RF harvesting circuits.