Development of different frequency up-conversion components in vibration energy harvesters

Miscellaneous vibration energy harvesters have significant potential for converting ambient vibration energy into electrical power, enabling the self-powering of wireless sensors and implantable or wearable electronic devices. However, the frequencies of many environmental vibrations, such as walking, waves, and bridge vibrations, are typically very low (<10 Hz). Consequently, energy conversion efficiency is compromised due to the theory that the output power is proportional to the cube of the working frequency. To address this issue, vibration energy harvesters utilizing frequency up-conversion techniques have gained considerable attention. This review aims to provide a comprehensive analysis of frequency up-conversion techniques for vibration energy harvesting over decades and to uniquely classify them into various categories based on their structural characteristics, including springs, elastic beams, cantilever beams, and combined structures. Each structural type possesses its advantages and limitations. A thorough understanding of the different structural forms of vibration energy harvesters will aid in proposing and developing new types with superior performance, consequently support net zero.