Alexandros Elefsiniotis

Investigation of the Performance of Thermoelectric Energy Harvesters Under Real Flight Conditions

Energy-autonomous wireless sensor nodes (WSNs) in aircraft, acting as health monitoring systems (HMS), have the potential to reduce aircraft maintenance costs. Thermoelectric energy harvesting is a solution for self-powered systems, since it captures enough energy to power up a WSN. The energy harvesting device used in this work consists of a thermoelectric generator (TEG) attached to the inner part of the fuselage and to a thermal storage device, in order to artificially enhance the temperature difference between the bottom and the top surface of the TEG during take-off and landing. In this study, the results of 28 flight tests during a 6-month flight campaign of two identical energy harvesting devices are presented. The results are clustered into two different classes, each having its own characteristics. The two classes comprise typical, similar to standard European short/mid-range flights, as well as atypical flight profiles, where specific flight tests have been performed. In addition, for each class, different parameters such as flight altitudes, flight duration, and temperature profiles are investigated. Moreover, a detailed comparison between a typical and an atypical flight profile is given. In general, for a typical flight profile, the experimental results are in good agreement with simulations predicting the energy output. The average energy output is sufficient to power up a wireless sensor.

Efficient Power Management for Energy-Autonomous Wireless Sensor Nodes for Aeronautical Applications

Efficient power management is a key component for energy-autonomous wireless sensor nodes. Thermoelectric energy harvesting is a possible solution for powering such sensor nodes. In this paper, we present a power management circuit that has significant improvements compared with earlier versions. Advancements were made to the rectifier part and the storage controller. The improved rectification circuit is able to control the p-metal–oxide–semiconductor (p-MOS) transistors with a negative instead of zero voltage at the gate. Furthermore, modifications to enhance the total efficiency of the storage controller are applied. The storage controller is a direct current (DC)–DC converter and is controlled by a pulse frequency modulation signal, provided by a microcontroller. In the modified version, the microcontroller is always in low-power mode, and an external circuit is used to control the storage controller. Changes in the software are applied so that the microcontroller is always set in low-power mode. The runtime with and without a load are compared, and the overall self-discharge time is evaluated.

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.

Design and material aspects for thermoelectric energy harvesting devices in aircrafts

Greener, more power efficient technologies as well as cost reduction are driving forces in energy efficient systems. Energy autonomous wireless health monitoring systems can potentially reduce aircraft maintenance costs by requiring no conventional power supply or supervision and by providing information of the health of an aircraft without human interaction. Thermoelectric energy harvesting seems the best choice for aircraft related applications, since sufficient energy can be generated to power up a wireless sensor node. The general concept is based on an artificially enhanced temperature difference across a thermoelectric generator (TEG), which is created by attaching one side to the fuselage and the other side to a thermal mass, which, in this case, is a phase change material. In detail, two different geometries and three different container materials are evaluated. As input and output parameters, the temperature profiles as well as the voltage of the TEGs are given. The output power and the total energy are determined by connecting a load resistor in parallel. Furthermore, the power to weight ratio for each combination is provided according to theoretical considerations and experimental tests done in a climate chamber mimicking a real flight profile.

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.

Hybrid energy storage system for wireless sensor node powered by aircraft specific thermoelectric energy harvesting

This paper describes an approach for efficiently storing the energy harvested from a thermoelectric module for powering autonomous wireless sensor nodes for aeronautical health monitoring applications. A representative temperature difference was created across a thermo electric generator (TEG) by attaching a thermal mass and a cavity containing a phase change material to one side, and a heat source (to represent the aircraft fuselage) to the other. Batteries and supercapacitors are popular choices of storage device, but neither represents the ideal solution; supercapacitors have a lower energy density than batteries and batteries have lower power density than supercapacitors. When using only a battery for storage, the runtime of a typical sensor node is typically reduced by internal impedance, high resistance and other internal losses. Supercapacitors may overcome some of these problems, but generally do not provide sufficient long-term energy to allow advanced health monitoring applications to operate over extended periods. A hybrid energy storage unit can provide both energy and power density to the wireless sensor node simultaneously. Techniques such as acoustic-ultrasonic, acoustic-emission, strain, crack wire sensor and window wireless shading require storage approaches that can provide immediate energy on demand, usually in short, high intensity bursts, and that can be sustained over long periods of time. This application requirement is considered as a significant constraint when working with battery-only and supercapacitor-only solutions and they should be able to store up-to 40-50J of energy.

Aircraft harness measurement campaign and investigations on introducing one pair Ethernet

In this paper, the results of a measurement campaign on the data harness of an A321 aircraft will be presented. The S-parameters of the cabin harnesses of an existing system are illustrated, and these parameters will be used to model a cabin architecture based on the existing harnesses. This A321 aircraft, where the measurements were performed, is a 20-year-old aircraft; hence possible cable aging will be discussed. The currently used aeronautical-certified cables show a great potential on introducing new technologies to the aircraft cabin, driven from the automotive industry (like 100BASE-T1 or 1000BASE-T1), thus increasing the available bandwidth by a factor of up to 500 times compared with the existing systems, without increasing the most important factor for aircrafts, weight.

Towards a Deterministic Mixed Criticality High Availability Seamless Redundancy (HSR) Ring

There is a growing trend for real-time Ethernet in nearly all industrial branches. While each industry has its own Ethernet-based protocols in networks, the High Availability Seamless Redundancy (HSR) network is currently of interest to the automation industry. A key factor and main benefit of HSR is its built-in fault-tolerance against the failure of a single communication link. However, it lacks mechanisms to guarantee certain bandwidth to applications. In this paper we propose a mechanism to guarantee packet arrival within a certain time while still offering best-effort traffic in order to support for mixed criticality traffic. Furthermore, a mathematical model is developed, that describes the upper latency limit of the proposed mechanism. We compare HSR with and without the proposed extension using an OMNeT++ simulation and show its advantages and weaknesses.

Multi-objective optimization of aircraft networks for weight, performance and survivability

With a current utilization of around 25% of its total weight, optimization of cabling and harness plays an important role in the design of an aircraft. This is a multi-objective optimization problem as the physical properties of the harness (e.g., length and weight) as well as the logical properties of the underlying network (survivability and performance) have to be taken into account. We propose in this paper to investigate this multi-objective optimization problem and provide different algorithms to solve it. We first focus on expressing it as a mixed integer binary linear program. Due to the complexity of solving this class of linear programs, we propose various heuristics for providing a good solution to this problem.