Steven W. Wright

Design and Fabrication of Heat Storage Thermoelectric Harvesting Devices

Thermoelectric energy harvesting requires a substantial temperature difference ΔT to be available within the device structure. This has restricted its use to particular applications such as heat engine structural monitoring, where a hot metal surface is available. An alternative approach is possible in cases where ambient temperature undergoes regular variation. This involves using a heat storage unit, which is filled with a phase-change material (PCM), to create an internal spatial temperature difference from temperature variation in time. In this paper, key design parameters and a characterization methodology for such devices are defined. The maximum electrical energy density expected for a given temperature range is calculated. The fabrication, characterization, and analysis of a heat storage harvesting prototype device are presented for temperature variations of a few tens of degrees around 0 °C, corresponding to aircraft flight conditions. Output energy of 105 J into a 10- Ω matched resistive load, from a temperature sweep from +20 °C to -21 °C, then to +25 °C is demonstrated, using 23 g of water as the PCM. The proposed device offers a unique powering solution for wireless sensor applications involving locations with temperature variation, such as structural monitoring in aircraft, industrial, and vehicle facilities.

Performance of phase change materials for heat storage thermoelectric harvesting

Heat storage energy harvesting devices have promise as independent power sources for wireless aircraft sensors. These generate energy from the temperature variation in time during flight. Previously reported devices use the phase change of water for heat storage, hence restricting applicability to instances with ground temperature above 0 °C. Here, we examine the use of alternative phase change materials (PCMs). A recently introduced numerical model is extended to include phase change inhomogeneity, and a PCM characterization method is proposed. A prototype device is presented, and two cases with phase changes at approximately −9.5 °C and +9.5 °C are studied.

Aircraft Strain WSN Powered by Heat Storage Harvesting

The combination of ultra-low-power wireless communications and energy harvesting enables the realization of autonomous wireless sensor networks. Such networks can be usefully applied in commercial aircraft where wireless sensing solutions contribute to weight reduction and increased ease of installation and maintenance. This paper presents, for the first time, a complete energy-autonomous wireless strain monitoring system for aircraft. The system is based on a multimode wireless time-division multiple access (TDMA) medium access control (MAC) protocol that supports automatic configuration and a time-stamping accuracy better than 1 ms. The energy supply depends solely on an innovative thermoelectric energy harvester, which takes advantage of the changes in environmental temperature during takeoff and landing. The system was successfully integrated and passed the functional and flight-clearance tests that qualify it for use in a flight-test installation.

Thermoelectric generator design in dynamic thermoelectric energy harvesting

This paper reports an analysis of thermoelectric generator design for dynamic thermoelectric harvesting. In such devices, the available energy for a given temperature cycle is finite and determined by the heat storage unit capacity. It is shown by simulation and experimentally that specific thermoelectric generator designs can increase the energy output, by optimizing the balance between heat leakage and dynamic response delay. A 3D printed, doublewall heat storage unit is developed for the experiments. Output energy of 30 J from 7.5 gr of phase change material, from a temperature cycle between ± 22 °C is demonstrated, enough to supply typical duty-cycled wireless sensor platforms. These results may serve as guidelines for the design and fabrication of dynamic thermoelectric harvesters for applications involving environments with moderate temperature fluctuations.

Acoustic energy transmission in cast iron pipelines

In this paper we propose acoustic power transfer as a method for the remote powering of pipeline sensor nodes. A theoretical framework of acoustic power propagation in the ceramic transducers and the metal structures is drawn, based on the Mason equivalent circuit. The effect of mounting on the electrical response of piezoelectric transducers is studied experimentally. Using two identical transducer structures, power transmission of 0.33 mW through a 1 m long, 118 mm diameter cast iron pipe, with 8 mm wall thickness is demonstrated, at 1 V received voltage amplitude. A nearlinear relationship between input and output voltage is observed. These results show that it is possible to deliver significant power to sensor nodes through acoustic waves in solid structures. The proposed method may enable the implementation of acousticpowered wireless sensor nodes for structural and operation monitoring of pipeline infrastructure.

Acoustic power delivery to pipeline monitoring wireless sensors

&NA; The use of energy harvesting for powering wireless sensors is made more challenging in most applications by the requirement for customization to each specific application environment because of specificities of the available energy form, such as precise location, direction and motion frequency, as well as the temporal variation and unpredictability of the energy source. Wireless power transfer from dedicated sources can overcome these difficulties, and in this work, the use of targeted ultrasonic power transfer as a possible method for remote powering of sensor nodes is investigated. A powering system for pipeline monitoring sensors is described and studied experimentally, with a pair of identical, non‐inertial piezoelectric transducers used at the transmitter and receiver. Power transmission of 18 mW (Root‐Mean‐Square) through 1 m of a 118 mm diameter cast iron pipe, with 8 mm wall thickness is demonstrated. By analysis of the delay between transmission and reception, including reflections from the pipeline edges, a transmission speed of 1000 m/s is observed, corresponding to the phase velocity of the L(0,1) axial and F(1,1) radial modes of the pipe structure. A reduction of power delivery with water‐filling is observed, yet over 4 mW of delivered power through a fully‐filled pipe is demonstrated. The transmitted power and voltage levels exceed the requirements for efficient power management, including rectification at cold‐starting conditions, and for the operation of low‐power sensor nodes. The proposed powering technique may allow the implementation of energy autonomous wireless sensor systems for monitoring industrial and network pipeline infrastructure. HighlightsAcoustic power transfer of 18 mW at a distance of 1 m through pipes is demonstrated.The method relies on impedance matching and transmitter/receiver resonance.Acoustic powering of pipeline sensors is adequate through empty and full pipes.The voltage at the receiver is large enough for cold‐starting power management.

Scaling of dynamic thermoelectric harvesting devices in the 1-100 cm3 range

Aircraft sensors are typically cable powered, imposing a significant weight overhead. The exploitation of temperature variations during flight by a phase change material (PCM) based heat storage thermoelectric energy harvester, as an alternative power source in aeronautical applications, has recently been flight tested. In this work, a scaled-down and a scaled-up prototype are presented. Output energy of 4.1 J per gram of PCM from a typical flight cycle is demonstrated for the scaled-down device, and 3.2 J per gram of PCM for the scaled-up device. The observed performance improvement with scaling down is attributed to the reduction in temperature inhomogeneity inside the PCM. As an application demonstrator for dynamic thermoelectric harvesting devices, the output of a thermoelectric module is used to directly power a microcontroller for the generation of a pulse width modulation signal.

Three-Dimensional Printed Insulation For Dynamic Thermoelectric Harvesters With Encapsulated Phase Change Materials

Energy harvesting devices have demonstrated their ability to provide power autonomy to wireless sensor networks. However, the adoption of such powering solutions by the industry is challenging due to their reliance on very specific environmental conditions such as vibration at a specific frequency, direct sunlight, or a local temperature difference. Dynamic thermoelectric harvesting has been shown to expand the applicability of thermoelectric generators by creating a local spatial temperature gradient from a temporal temperature fluctuation. Here, a simple method for prototyping or short-run production of such devices is introduced. It is based on the design and 3-D printing of an insulating container, insertion of a phase change material in encapsulated form, and use of commercial thermoelectric generators. The simplicity of this dry assembly method is demonstrated. Two prototype devices with double-wall insulation structures are fabricated, using a stainless-steel and a plastic phase change material encapsulation and a commercial TEG. Performance tests under a temperature cycle between 25C show energy output of 43.6 and 32.1J from total device masses of 69 and 50g, respectively. Tests under multiple temperature cycles demonstrate the reliability and performance repeatability of such devices. The proposed method addresses the complication of requiring a wet stage during the final assembly of dynamic thermoelectric harvesters. It allows design and customization to particular size, energy, and insulation geometry requirements. This is important because it makes dynamic harvesting prototyping widely available and easy to reproduce, test, and integrate into systems with various energy requirements and size restrictions.

Inductive energy harvesting from variable frequency and amplitude aircraft power lines

This paper presents a non-contact method of harvesting energy from an aircraft power line that has an AC current of variable amplitude and a frequency range of 360-800 Hz. The current and frequency characteristics of the aircraft power line are dependent on the rotation speed of the electrical generators and will therefore change during a flight. The harvester consists of an inductive coil with a ferrite core, which is interfaced to a rectifier, step-down regulator and supercapacitor. A prototype system was constructed to demonstrate reliable output voltage regulation across a supercapacitor that will supply a peak power of 100 mW under duty cycled load conditions. The system could fully charge a 40 mF supercapacitor to 3.3 V in 78 s from a power line current of 1.5 Arms at 650 Hz.

Harvesting energy from aircraft power lines

There are two simple methods of supplying power to a wireless, low-power sensor in an aircraft: a battery, or direct access to the aircraft power line. In the former, the battery will eventually need to be replaced whilst the latter option, which is highly intrusive and difficult to retrofit into existing aircraft, increases the weight and presents installation issues when large numbers of sensors are deployed. This paper presents initial experimental results of a non-intrusive method of harvesting energy by induction from aircraft power lines, in order to supply power to an aircraft wireless sensing application. The harvester comprises an inductive coil wound around a magnetic core, with the complete setup clamped around a single-phase AC power line.