LAUSR

Vibration is a common mechanical phenomenon in our daily life; for example, it is present in engines, aircrafts, bridges, buildings, etc. The omnipresent vibration can also serve as a source of energy to power self-powered systems, such as micro-electromechanical systems, remote environmental sensors, homeland security, and even portable/wearable personal electronics.[1] Triboelectric nanogenerators (TENGs), are able to generate electrical output based on contact triboelectrification and electrostatic induction in response to an external mechanical stimuli.[2] Its fundamental physics and output characteristics can be attributed to Maxwell’s displacement current.[3] Additionally, it is a cost-effective, simple, and robust technique for energy harvesting,[1,4–18] and can alternatively serve as an active mechanical motion sensor using its own electrical output without a secondary power source.[19–27] Spring-assisted TENGs are superior for vibration energy harvesting and impact detection at a weak ambient vibration than those without a spring.[5,28–30] For example, Jiang et al.[30] designed a form of spring-assisted TENG for harvesting water wave energy, in which two Cu-PTFE-covered acrylic blocks connected by a spring were placed between two Cu electrodes anchored on two internal walls of a box-like device. Springs store mechanical kinetic energy and potential energy during mechanical triggering for use in subsequent cycles of electricity conversion, transforming low frequency motion into high frequency oscillation, and improving energy harvesting efficiency. The accumulated charge of the spring-assisted TENG increased by 113.0%, and the efficiency improved by 150.3%. Following a similar line, Wu et al.[29] found that integrating a mechanical spring-based amplifier with the ability to amplify both the vibration frequency and amplitude with a TENG improved its low-frequency performance by up to ten times by using the stored potential energy by the spring. Also, Hu et al.[28] installed a contact-separation mode TENG on the front of a suspended 3D helical structure, and used it to harvest wave energy and serve as an active sensor. However, since these aforementioned TENGs were based on hard material (acrylic) attached to Vibration is a common mechanical phenomenon and possesses mechanical energy in ambient environment, which can serve as a sustainable source of power for equipment and devices if it can be effectively collected. In the present work, a novel soft and robust triboelectric nanogenerator (TENG) made of a silicone rubber-spring helical structure with nanocomposite-based elastomeric electrodes is proposed. Such a spring based TENG (S-TENG) structure operates in the contact-separation mode upon vibrating and can effectively convert mechanical energy from ambient excitation into electrical energy. The two fundamental vibration modes resulting from the vertical and horizontal excitation are analyzed theoretically, numerically, and experimentally. Under the resonant states of the S-TENG, its peak power density is found to be 240 and 45 mW m−2 with an external load of 10 MΩ and an acceleration amplitude of 23 m s−2. Additionally, the dependence of the S-TENG’s output signal on the ambient excitation can be used as a prime self-powered active vibration sensor that can be applied to monitor the acceleration and frequency of the ambient excitation. Therefore, the newly designed S-TENG has a great potential in harvesting arbitrary directional vibration energy and serving as a self-powered vibration sensor.