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.
Proc. SPIE. 8763, Smart Sensors, Actuators, and MEMS VI
KEYWORDS: Sensors, Resistance, Transmission electron microscopy, Sensor networks, Energy harvesting, Structural health monitoring, Thermoelectric materials, Chemical elements, Neodymium, Temperature metrology
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.
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.