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Aiming at the cracking failure of the modified epoxy resin encapsulated module as a result of interface failure under high low temperature cycles, numerical simulation and experimental studies were carried out. Firstly, the residual stress field in the encapsulated module was reconstructed after measuring the curing residual stresses in epoxy resin using the hole-drilling method. Temperature-dependent material models were developed after testing the mechanical and thermal characteristic parameters of encapsulated module components, such as modified epoxy resin, in high and low temperature conditions. Then, a finite element model of a high-reduction encapsulated module with multiple components, multiple interfaces, and complicated contacts was established considering residual stress and temperature effects. To simulate the failure behaviour of the resin-embedded part interfaces, the cohesive zone model was utilized. Finally, the stress and strain of the encapsulated module under high and low temperature cycles were simulated, and their distribution features and cracking failure mechanism were analyzed. The results indicate that regardless of the heating/cooling process, significant due to a mismatch in thermal expansion coefficients between the resin and the embedded parts. As the temperature approaches the glass transition temperature Tg, the difference grows dramatically. The resulting thermal stress, together with the residual stress, led to the interface failure in encapsulated module. The numerical results were in good agreement with the high and low temperature cycle test results of the encapsulated module, which verified the effectiveness of the analysis method and the established finite element model. The investigation provides an important reference for the high-reliability design of the encapsulation module.

In order to reduce the natural frequency of the piezoelectric vibration energy harvester, improve the output power of the piezoelectric vibration energy harvester, and meet the demand of power supply for the low-power wireless switch in the low-frequency vibration environment, an asymmetric hybrid supported beam piezoelectric vibration energy harvester is proposed. The theoretical model of the hybrid support beam was established. The correlation factors affecting the open-circuit voltage and the total output power of the hybrid braced beam were analyzed. The dimensional parameters of the hybrid supported beam piezoelectric energy harvester were optimized by using the optimization method of orthogonal experiments. Different coincidence degrees experiments were used to further optimize the structural design of the hybrid support beam. The test results show that the maximum output power is 770 μW, when the external excitation frequency is 1.0 g and the external resistance is 50 kΩ. Finally, a wireless switch test system was established, and the piezoelectric vibration energy harvester was experimentally verified to be capable of powering the wireless switch. [ABSTRACT FROM AUTHOR]

In order to reduce the natural frequency of the piezoelectric vibration energy harvester, improve performance of the piezoelectric vibration energy harvester, and meet the requirements of energy acquisition in the low-frequency vibration environment, a variable-section circular piezoelectric vibration energy harvester is presented. The dynamic model and electromechanical coupling model of variable-section circular piezoelectric vibration energy harvester are established. The main factors affecting the output performance of piezoelectric vibration energy harvester are analyzed. The structure parameters of piezoelectric vibration energy harvester are optimized by orthogonal experiment. An experimental platform is built to test output voltage and output power of piezoelectric vibration energy harvester. The experimental results show that when the number of energy harvester is 4 and the external load is 180KΩ, the parallel output power can reach 0.213mW, which can meet the requirements of micro-power device power supply. [ABSTRACT FROM AUTHOR]