High-Performance Thermo-Magnetic Micro-Harvester – HiPerTherMag

The goal of this project is to demonstrate thermo-magnetic power generation (TMG) using giant magneto-caloric materials (MCM) as working substance to convert low grade waste heat into electricity. We shall show that MCM based TMG can become a leading technology for a new generation of efficient high power density micro-generators oriented towards applications in smart-buildings, data-centers, MEMS and IoT related autonomous systems. This will be achieved through the design and assembly of an efficient high power density TMG device. Our previous studies show that an active and thermodynamically optimized control of the cyclic transformations is the key to improve system performances. Therefore nowadays the real key towards a breakthrough advance beyond the state of the art, in the field, is to achieve an optimal and fully controlled thermodynamic cycle. This poses the problem to properly integrate the active material with the field source (i.e. the micro-magnet array) and to achieve a full thermal and mechanical control of the device.The originality of our approach relies on the fact that we shall address the power/efficiency trade-off from a fundamental thermodynamic standpoint, using it as an input to design the active material, the device, and their thermal and dynamic coupling. The finite time thermodynamics approach, taking into account entropy production along non-quasistatic transformations, will guide the tasks devoted to the design of a beyond state-of-the-art TMG device, to the optimization of physical properties of the active materials, and to the proper integration of the working substance in the system. We shall proceed by:
(a) thermodynamic modeling of a TMG using caloric material as a working substance, here we shall focus on the interplay between the active substance equation of state, the thermal exchanges in finite time (non quasi-static exchanges), and the achievable efficiency at maximum power;
(b) production and characterization of MCM films with optimized properties, the main goal here is to maximize the adiabatic temperature change and to minimize all the irreversible processes taking place at the phase change (i.e. hysteresis and transition kinetics);
(c) design and realization of a thermal switch to take full control of heat exchanges all along the thermodynamic TMG cycle, the key goals here are a high ratio between high (on) and low (off) thermal conductance states, a thermal conductance of the on state as high as possible, and a short switching time;
(d) design and integration of an optimized micro-magnet array, the goal here is twofold, on the one hand we need an appropriate maximum field to fully achieve the phase transition, on the other we must wisely control the spatial shape of the field to properly tune its intensity all along the thermodynamic cycle using small displacements of the caloric film;
(e) design and realization of the Mechanical-to-Electrical energy conversion transducer, integrated into the thermal switch: the objective is, according to the transduction mechanism considered (piezoelectric, magnetic or capacitive), to design the structure exhibiting the highest conversion efficiency while respecting the constraints imposed by the mechanical and thermal behavior of the MCM film.
(f) finally we shall compare power density and efficiency of our fully assembled device to existing thermal micro-generators. In this way, connecting advanced material characterization and optimization, with innovative system design, and thermodynamic simulation of key technological properties of the device, we shall show that the use of giant magnetocaloric materials into TMG micro-devices can push the current TMG’s technology readiness level (TRL) from 3 to 4.