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This paper proposes a piezoelectric energy harvester that concentrates force on the piezoelectric element by parallel springs. When vibrating, the force exerted by the mass is released at three equal points on the surface of the brass substrate through three parallel springs. This concentrated release of energy through the spring amplification effect facilitates large deformation of the piezoelectric ceramic sheet, resulting in a higher charge output. The results show that under the combined action of a 14 g annular hollow mass and a 0.3 mm wire diameter stainless steel spring, the energy harvester based on the lead zirconate titanate ceramic exhibited an outstanding output power of 1.0–32.1 mW at a low resonance frequency with acceleration amplitudes of 0.5–3 g (1 g = 9.8 m/s2). More importantly, to match the vibration frequency of the actual environment, this paper optimized the structure of the harvester and proposed that the harvester can be designed by selecting the weight of the mass block, the parameters and number of springs, and the shape of the brass substrate. The energy harvester designed in this study is expected to capture energy from low-frequency natural environments and exhibit outstanding output performance, which can provide guidelines for future efforts in this direction. [ABSTRACT FROM AUTHOR]

Single-phase Mn50Ni40In10−xCux (x = 0, 1, 2, 4, 6, 8, and 10) Heusler alloys were synthesized by melt-spinning method. Martensitic transformation is retained within the whole composition range studied. The substitution of Cu for In leads to a drastic increase in the martensitic transformation temperature TM from below room temperature to above 750 K, and enhances the antiferromagnetic character of the martensite. The increase in TM is related to the increasing electron concentration e/a and decreasing cell volume V with Cu doping. The energy difference between martensite and austenite also increases with Cu doping, which tends to elevate the TM. Cu doping can enhance the metallic bonding character in NiMn-based magnetic shape memory alloys (MSMAs) and is a grain refining strategy of their ribbons. The oriented columnar grains in In-rich samples change to fine equiaxial grains in Cu-rich samples. All this has a positive effect on the strength and ductility. The tensile strength of the Mn50Ni40Cu10 ribbon is 3.6 times higher than that of Mn50Ni40In6Cu4. So, Mn–Ni–Cu can be a promising all-d-metal Heusler alloy platform for developing MSMAs with interesting properties. [ABSTRACT FROM AUTHOR]

Magnetic shape memory alloys Mn2NiGa1−xCux (x = 0–0.7) melt-spun ribbons were synthesized, and their crystal structure, martensitic transformation, and magnetic and transport properties were studied. In Mn2NiGa1−xCux, unusual composition dependences of these properties were observed: the lattice parameter increases with Cu-doping, though Cu has a smaller atomic radius compared with Ga. The martensitic transformation temperature decreases with increasing Cu content at first and reaches a minimum at x = 0.3 and then increases rapidly as Cu content increases further. The variation tendency of magnetization is just opposite. When Cu content gets higher, a semiconductor-like to metal-like crossover in electron transport properties is observed. The martensite resistivity also changes from lower than that of austenite to higher than that. First-principles calculations indicate that these unusual properties are related to the competing occupation of Cu between A and D sites. Cu-doping can also enhance the metallic bonding in Mn2NiGa1−xCux, which can reduce the intrinsic brittleness and improve their mechanical properties. All this provides a fresh idea and method for the development of NiMn-based solid-state refrigeration materials. [ABSTRACT FROM AUTHOR]