Ricardo Ehrenpfordt

Packaging of Small-Scale Thermoelectric Generators for Autonomous Sensor Nodes

This paper focuses on packaging of small-scale thermoelectric generators (TEGs) for energy harvesting applications in sensor nodes for industry 4.0 and for the Internet of Things. The TEGs are suitable to enable self-powered sensor systems with unlimited energy lifetime, but they have to withstand high mechanical loads during the assembly and packaging process and further stress due to the mismatch of the coefficient of thermal expansion of the different materials. Devices with different underfills (UFs) and stress decoupling thermal adhesives were evaluated with a shear force test apparatus and a four-line bending test together. In addition to these mechanical tests, the thermal influence of the UF on the system performance was investigated with measurements, finite element method, and computational fluid dynamics simulations. The shear force per area could be enhanced up to the factor of two by using capillary UF. All TEGs with and without UFs passed the reliability investigations without any electrical defects. All TEGs with UF passed the given quality criteria with the four-line bending test. With some of the stress decoupling thermal adhesives, the TEGs could withstand the loads without UF. The simulation model was evaluated with a measurement setup, and the differences between the simulation model and the measurements concerning the temperature difference of the TEGs were in an acceptable range (<21%). Furthermore, the influence of the UF on the temperature difference of the TEGs in the given measurement scenario was smaller than 15%, which makes the application of a UF a realistic approach.

Packaging of thin film thermoelectric generators for autonomous sensor nodes

This paper focuses on packaging of thin film thermoelectric generators (TEG) for energy harvesting applications in sensor nodes for the internet of things (IoT). The TEGs have to be robust against mechanical stress caused by the assembly and packaging process steps and the mismatch of the coefficients of thermal expansion of the used materials. In this work, the mechanical stability of TEGs was evaluated by using a shear force test apparatus and a four line bending test. Furthermore the influence of underfill and stress decoupling thermal adhesives on the mechanical performance was investigated. It could be shown that underfill between the two substrates improves the shear force stability of the investigated thermoelectric generators. During mechanical tests the internal electrical resistance of the modules was monitored. It was observed, that the electrical shutdown coincides with the mechanical shutdown of the generator. By using selected thermal adhesives with and without underfill a sufficient robustness of the thermoelectric generator against typical warpage as known from a standard molded land grid array (LGA) sensor package was achieved.

Application of human motion energy harvesters on industrial linear technology

Energy autonomous sensors for I4.0 applications powered by kinetic energy harvesters (KEHs) are widely discussed – especially in terms of vibration harvesting. Typically, industrial linear stages offer weak vibrations, so other inertia-based harvesting methods are investigated. This study investigates the usability of human motion energy harvesters in industrial linear motion technology for the first time. Two KEHs – harvesting swing or shocks, respectively – are tested while controlling the parameters velocity, acceleration, and jerk-limitation according to the real applications’ parameter ranges. The swing-KEH and the shock-KEH harvested up to 106 and 124 mW, respectively. Furthermore, a parameter study is performed assuming constant driving lengths with optimised stroke rates to obtain a generalised power and energy profile for each harvester. The analytically obtained overall average power is 22 mW for the swing-KEH and 14 mW for the shock-KEH. The analytical investigation revealed that a reciprocal dependency of performance and velocity exists for both KEHs, respectively. Both experimental and analytical parts show that the wireless sensor node for I4.0 on industrial linear stages can be powered by harvesters made for human motions.