Licheng Deng

Harvesting energy from human walking offers a promising alternative to batteries for powering wearable devices. However, existing energy harvesters suffer from limited power output. So, a novel non-resonant energy harvester was proposed in this paper. The core mechanism of the harvester integrates three components: a helical twin-rod twist rod, a face gear with dumbbell-shaped holes, and a rotor featuring bevel teeth on its upper surface. This core mechanism can efficiently harvest low-frequency reciprocating motion and convert it into unidirectional rotational motion, thereby enabling highly efficient acquisition of low-frequency energy. It offers advantages such as high energy harvesting efficiency and a simple structure. Then an electromagnetic generator converts this rotational energy into electricity. A prototype of the proposed harvester was developed and tested on a vertical reciprocating motion platform. Experiments investigated the influence of parameters including human input energy and mechanical harvesting structure on output performance of the harvester. Application testing demonstrated that manual pressing at 1 Hz successfully illuminated 120 LEDs. When integrated into a shoe heel and tested with a 60 kg person stepping in place at 2 steps per second, the harvester achieved an RMS output voltage of 18.5 V, an output power of 263.27 mW, and a power density of 4.21 mW/cm³. Overall, this research presents a new approach for designing high-efficiency energy harvesters for human walking applications.

To address the narrow bandwidth and low power density of conventional piezoelectric energy harvesters, a novel semicircular arc piezoelectric energy harvesting system with dual folded beams (SAPEH-DFB) is designed in this work. Distinct from traditional linear structures, the unique semicircular geometry integrated with folded beams enables effective multi-directional energy harvesting and significantly broadens the operating bandwidth through multi-mode coupling. Furthermore, a modified self-powered parallel synchronized switch interface (SP-PSSHI) is introduced. By integrating the rectifier bridge structure into the switching circuit, this design improves circuit integration and maximizes energy extraction. This circuit is specifically optimized to mitigate the energy cancellation caused by phase differences among the multiple beams. Experimental results demonstrate that the optimal configuration (PEH B) achieves a broad bandwidth of 58 Hz. It delivers a maximum output power of 5.79 mW with a normalized power density (NPD) of 164.8 μW·g⁻²·mm⁻³, maintaining high performance across multiple vibration modes. In addition, the proposed interface circuit further enhances the output power by up to approximately 15.8% compared to standard circuits, enabling effective power supply in the wearable devices and microsensors.

To realize high power density, low-frequency, multi-directional energy harvesting and efficient energy storage management, a piezoelectric energy harvesting system comprising a centrally symmetric spiral-nested piezoelectric energy harvester (CSS-PEH) and an energy management circuit is proposed in this work. The harvester features a doubly clamped outer beam and a nested dual-spiral inner beam, while the management circuit integrates an SP-PSSHI rectification circuit, BQ25570 IC, and supercapacitor. A three-degree-of-freedom (3-DOF) lumped parameter model and an electromechanical coupling model are established to analyze frequency response and output characteristics. Measured results show that the CSS-PHE has resonant frequencies at 12.8 Hz and 17.2 Hz, with corresponding open-circuit voltages of 73.5 V and 38.7 V. Meanwhile, the SP-PSSHI rectified series circuit achieved maximum output powers of 6.23 mW with the normalized power density (NPD) of 32.4 μW∙g^-2∙mm^-3; the SP-PSSHI rectified parallel circuit delivered maximum output power of 3.21 mW with the NPD of 21.6 μW∙g^-2∙mm^-3. The energy management circuit enables supercapacitor charging up to 4.05 V while maintaining stable 3.3V DC output. Furthermore, the CSS-PEH demonstrates multi-directional energy harvesting capability. Therefore, this piezoelectric energy harvesting system provides stable power supply solutions for many fields, such as intelligent transportation energy harvesting, wireless sensor networks, and so on.

Low frequency vibration is ubiquitous in our daily life and production, such as vehicle vibration.In order to effectively harvest low frequency vibration energy with vibration energy harvester (VEH) , a new method to reduce the resonant frequency of a VEH was proposed. The reduction of resonant frequency of the VEH is achieved through the arc folding beams structure and the negative stiffness magnetic spring. Furthemore, the arc folding beam structure and negative stiffness magnetic spring also result in a more uniform stress distribution of the folding beam and a greater ability to withstand excitation acceleration, which results in high reliability of the VEH. Then the VEH was fabricated and tested. The experimental results indicate that introducing a negative stiffness magnetic spring can effectively reduce the resonant frequency of the VEH and increase the power output of the vibration energy harvester. After introducing a negative stiffness magnetic spring, the resonance frequency of the VEH decreased from 37.6 Hz to 28.8 Hz, a decrease of 30.6%, and the power output of the VEH increased from 5.45 mW to 7.98 mW, an increase of 46.4%. Finally, a detailed analysis of the experimental results was performed in theory using the finite element method. Theoretical analysis and experimental results are basically consistent.

In this work, the frequency doubling effect of thermoacoustic speakers is studied, and a method is analyzed to suppress the frequency doubling effect. Three cases were analyzed by superimposing the DC bias on the AC excitation: (1) DC is less than AC; (2) DC is equal to AC; (3) DC is greater than AC. We found that the frequency doubling effect can be well suppressed by superimposing a larger DC excitation on the AC excitation. The laser scribing technology was used to prepare graphene film in only one step, and the screen printing technology was used to prepare conductive electrodes. The microphone and B&K system was used to record the sound pressure level and study the suppression of frequency doubling effect. Finally, the sound pressure levels with the three different kinds of excitations were measured. The measured results show that they have a good agreement with the theoretical results. The suppression effect will be better when DC amplitude is greater than AC amplitude. Therefore, this work has certain reference significance for the further study and application of thermoacoustic speakers.

An enhanced quarter-spherical acoustic energy harvester (AEH) with dual Helmholtz resonators was designed in this work. Compared with the previous research, this AEH can harvest multi-directional acoustic energy, has a widened resonance frequency band, and has an improved energy conversion efficiency. When the length of resonator’s neck is changed, the acoustic resonant frequency of the two resonators is different. The theoretical models of output voltage and output power were studied, and the relationship of output performance with frequency was obtained. The results showed that this AEH can operate efficiently in a frequency band of about 470 Hz. Its output voltage was found to be about 28 mV, and its output power was found to be about 0.05 μW. The power density of this AEH was found to be about 12.7 µW/cm². Therefore, this AEH could be widely used in implantable medical devices such as implantable cardiac pacemakers, cochlear implants, and retinal prosthesis.