Multilayered microcoils are of great importance for the development of advanced electromagnetic microactuators and especially important to develop high-sensitivity microsensors and magnetic field neural stimulators for medical applications. A clean room-free procedure for manufacturing multilayered micrometric coils is presented in this article. The production of miniaturized multilayered coils from tens to hundreds of micrometres long is demonstrated. The microcoils have outer diameters ranging between 150 and 300 μm, arrangements of up to five consecutive layers, and an average fill factor of 85%. This means three times smaller diameters than the smallest diameter ever achieved by winding techniques while keeping a high fill factor and a large number of layers. Such small and highly performant microcoils have never been demonstrated neither by winding processes nor epitaxial growth techniques. These microcoils were tested inside different human body-like environments. Maximum current density versus temperature was measured in air, fat tissue, muscle tissue, and simulated body fluid at 36 °C. A maximum current density of 3600 A/m ² has been measured before coil failure. Experiments demonstrated that current densities of up to 610 A/m ² can safely be supplied to coils without risk of harm to internal tissues. These counterintuitive values are orders of magnitude larger than typical current densities used in macroscale actuators windings.

Overheating of solar cells under normal operational conditions highly reduces their energy harvesting efficiency and produces additional problems related to thermal cycling and performance degradation of the modules. In this paper, a novel cooling system for solar photovoltaics, using the underground as a heat sink, is proposed, theoretically described and experimentally validated. A prototype of the technology (including a single-axis sun tracking mechanism) has been designed, manufactured, and rigorously tested in outdoor conditions during summer 2021 in Spain, under different environmental conditions. The excess heat is removed from the backside of the solar module by a close-loop and single-phase cooling system and then dissipated in the underground, which is at a constant temperature of about 16 °C at relatively low depths at the location where tests were performed. A single U-shaped copper tube, 18 mm in diameter, immersed in a 15.5-m-deep borehole naturally filled with water, is used as an underground heat exchanger. As a consequence of the reduction of the cooled module temperature, its net power generation is significantly increased. A promising improvement of the net power generation of the cooled solar module up to 12.4% has been measured for a coolant flowrate of 1.84 l/min per square meter of solar module, proving the technical feasibility of the approach. In addition, a dependency of the power gain with the pump efficiency, the global radiation, and ambient temperature has been observed.

In this paper, we present a novel method for indirect characterization of eddy currents damping and loss coefficients, as well as the equivalent electrical conductivity of metal foams. The proposed method is based in the measurement of the braking torque when the metal foams are exposed to an alternating magnetic field generated by a set of rotating permanent magnets. Measurements are carried out in a low-frequency range (< 50 Hz) and for high amplitude magnetic fields (up to 0.4 T), both typical values observed in electromechanical devices. This method was used for accurate characterization of a set of open-cell aluminum foams with different compositions and porosities. Experimental results, in good agreement with the theoretical models, confirm the viscous damping behavior of aluminum foams in the tested frequency range. The quadratic dependency of the damping coefficient on the magnetic flux density is also confirmed in the measurement range.

MEMS and micromotors may benefit from the increasing complexity of rotors by integrating a larger number of magnetic dipoles. In this article, a new microassembly and bonding process to integrate multiple Sm₂Co₁₇ micromagnets in a ferromagnetic core is presented. We experimentally demonstrate the feasibility of a multipolar micrometric magnetic rotor with 11 magnetic dipoles made of N35 Sm₂Co₁₇ micromagnets (length below 250 μm and thickness of 65 μm), integrated on a ferromagnetic core. We explain the micromanufacturing methods and the multistep microassembly process. The core is manufactured on ferromagnetic alloy Fe₄₉Co₄₉V₂ and has an external diameter of 800 μm and a thickness of 200 μm. Magnetic and geometric measurements show good geometric fitting and planarity. The manufactured microrotor also shows good agreement among the magnetic measurements and the magnetic simulations which means that there is no magnetic degradation of the permanent magnet during the manufacturing and assembly process. This technique enables new design possibilities to significantly increase the performance of micromotors or MEMS.