Triboelectric-Electromagnetic Hybrid Energy Harvester for Functional Light-Emitting Diodes Inserted Portable Devices

Light-emitting diode (LED) is currently being used in various fields thanks to its unique advantages, such as long lifespan and cost-effectiveness, in comparison to conventional incandescent light bulbs that use relatively high electrical energy. Functional LEDs can emit visible, infrared (IR), and ultraviolet (UV) light, depending on the length of the wavelength range from 275 to 850 nm. Visible LEDs are essential for electronic device displays and lighting. IR LEDs, which emit longer wavelength light, are used in infrared communication, sensing, and medical health care. UV LEDs, which emit ultraviolet rays with a shorter wavelength than visible light, are used in material processing, security, and sterilization. Functional LEDs with various wavelengths have great potential when used in portable electronic devices due to diverse and versatile functionality, in addition to the advantages of energy efficiency. Here, the consideration of a suitable power supply method is essential, as functional LED inserted portable electronic devices need to operate multiple LEDs simultaneously or fully depending on demand without an external power supply. In this regard, research on self-powered portable energy harvesters that are grid independent is highlighted to maximize the advantages of portable electronic devices with functional LEDs. This can increase the possibility that portable electronic devices with functional LEDs can be used in a variety of fields from daily life, security, and healthcare to industry. In this study, we propose a portable triboelectric-electromagnetic hybrid energy harvester (P-THE) for the operation of functional LEDs that emit light with various wavelengths, including IR, visible, and UV. P-TEH can drive functional LEDs using biomechanical energy to serve a portable and extensive purpose. To enhance electrical output, a planetary gear train is introduced to convert low-frequency biomechanical energy from human motion into high-frequency rotational movement, which is a major factor for electrical power output. Triboelectric nanogenerator (TENG) based on the coupling of triboelectrification and electrical charge induction have the advantages of diverse material selection and a simple operating mechanism. One of the notable advantages of TENG is that it can generate high electromotive force. Electromagnetic generator (EMG), which has successfully utilized with its long history, can produce high current output. Considering the characteristics of TENG and EMG, we experimentally demonstrated successful hybridization of TENG and EMG, showing that it is possible to provide both high electromotive force and high current for functional LED operation on demand. P-TEH can operate 250 visible light LEDs, 50 IR LEDs, and multiple UV LEDs using biomechanical energy. Furthermore, demonstrations of various applications, such as healthcare prototype devices with IR LEDs, identification of counterfeit documents, and material processing with UV LEDs, are presented. Consequently, P-THE is expected to extend the range of applications of future portable electronic devices in various fields without an external power source.