With the growth in adoption of wearable electronic devices and large, distributed networks of sensors, nontraditional sources of power are sorely needed. Keeping batteries charged may be little more than an inconvenience in consumer electronics, but it quickly becomes an impossible task when dealing with networks of sensors positioned in remote regions of the world. Furthermore, using batteries presents a number of other challenges due to their limited lifespans and the environmental concerns related to their disposal.
Device developers are increasingly turning to energy harvesting techniques to deal with these problems, utilizing sources like solar and wind to keep things running. However, present technologies for converting these sources of energy into electricity are not yet efficient enough. For many applications, we simply cannot generate enough electricity to support them via renewable sources — at least not with reasonably sized and priced energy harvesting units.
Engineers at the University of Surrey in the United Kingdom are looking at another renewable source of energy that may overcome these issues. Their work involves the use of Triboelectric Nanogenerators (TENGs), which are particularly promising due to their lightweight nature, cost-effectiveness, and ability to efficiently harvest energy from daily activities like walking and running. They focused on a specific type of TENG, known as the Free-Standing Mode TENG (FTENG), which is well-suited for scavenging mechanical energy from arbitrary moving objects.
The researchers introduced an innovative design called the Interdigitated Array of Electrodes-based FTENG (IDA-FTENG), which enhances energy harvesting efficiency by increasing the density of electrode pairs within the device. This design allows for a greater interaction volume within the TENG structure, leading to a significant amplification of the surface charge density and, consequently, the output performance.
Furthermore, they systematically explored the impact of various structural parameters — such as electrode width, gap between electrodes, and the number of electrode pairs — on the electrical output of the IDA-FTENG. By optimizing these parameters, the researchers developed a highly efficient IDA-FTENG device with an electrode density that is two orders of magnitude higher than that of traditional TENGs.
Components of the security system (📷: M. Hussain et al.)
It was demonstrated that in addition to serving as an energy harvester, the IDA-FTENG device can also be utilized as a self-powered sensor. The team built a security monitoring system in which the device is used to monitor the status of a hidden lock on an office drawer. The system consists of three copper IDA electrodes mounted on the desk’s sidewall and a slider with polytetrafluoroethylene stripes attached to the drawer. As the drawer opens or closes, the slider moves over the electrodes, generating electrical pulses that are sent to a microcontroller via a rectifier. The microcontroller detects the drawer’s position based on the pulse sequence and can identify whether the drawer is locked or open. If the drawer is opened without authorization, the system triggers a remote buzzer alarm using Bluetooth devices.
While this IDA-FTENG device may not be suitable for all applications, it offers a lot of promise where any type of motion is consistently present. As a result of the team’s efforts, this energy can be efficiently converted to electricity to power all sorts of devices where other renewable sources of energy are insufficient or unavailable.
