Could We Soon Power Our Electronic Devices with Wearable Energy Harvesters

Making Electronic Devices Flexible

With smartphones, we have become used to carrying electronics with us all the time. This is, however, still done with a bulky block of metal and plastic, which, if anything, is getting bigger and heavier every year.

The next step would be to incorporate electronic devices in our attire more seamlessly. This has already started with wearable electronics like smartwatches and other health-focused wearables.

One step further would be to integrate electronics into our clothing directly. But for that, it would need to be very flexible and lightweight. There has been solid progress made in that direction:

• Bending screens are now routinely integrated into high-end smartphones by Samsung and Huawei.
• Bendable and stretchable batteries made of polymers are being developed.
• Microprocessors can be bent too.

So, if screens, batteries, and even processors are now flexible and bendable, what is still blocking us from having wearables integrated into our clothing? Powering them all is still a serious roadblock.

But this might change, thanks to a discovery by Korean researchers at the Daegu Gyeongbuk Institute of Science and Technology (DGIST), Hannam University, Yonsei University, Korea Advanced Institute of Science and Technology (KAIST), Korea Institute of Industrial Technology (KITECH) and Jeonbuk National University.

They developed a wearable energy harvester that is 280x more efficient than conventional devices, using a new type of piezoelectric energy harvester.

It was published in ACS Nano, under the title “Curvature-Specific Coupling Electrode Design for a Stretchable Three-Dimensional Inorganic Piezoelectric Nanogenerator¹”.

Triboelectric And Piezoelectric Devices

Energy harvesters are systems producing energy from movements. There are mostly two types, based on whether they work on the triboelectric effect or piezoelectric effect.

Triboelectric generators are what is generally called electrostatic, or what happens when two objects touch or slide against each other. This can generate some electricity but is often too weak to power electronics.

Piezoelectric is the effect of generating electricity in response to mechanical stress like bending, squeezing, etc. Until now, most piezoelectric energy harvesters have been made using organic or composite-based piezoelectric materials, which have low energy efficiency.

Pr Jang’s team was using another type of material: lead zirconate titanate (PZT).

Source: DGIST

PZT Piezoelectric Generator

PZT has long been known to have excellent piezoelectric performance, but it is also hard and brittle. Therefore, using it in stretchable devices and counting on movement to generate power was unlikely to create a durable generator for wearables.

So, the researchers looked at how to design a PZT-based 3D structure that would be insensitive to deformation and guarantee stretchability while keeping the piezoelectric capability.

The first step was to create a curved electrode with a convex shape that produces power when stretched.

Source: ACS Nano

They then assemble strings of these electrodes into each other, similar to the mesh of a fabric or a wicker basket.

Source: ACS Nano

Ironing Out Problems

Because the electrodes are interlaced, they could easily cancel each other out. To avoid this, the electrodes were divided into convex and concave regions according to the direction of the induced output voltage.

The current can be created by any motion of the body, as tested by the researchers on the knee, hand, or even fingers.

Source: ACS Nano

This created a very efficient piezoelectric generator, displaying both extreme stretchability and the highest current density for any device of this type.

Source: ACS Nano

“Developing this highly efficient stretchable piezoelectric energy harvester technology is a major achievement of this research. We expect this technology to become useful after commercialization and lead to the practical use of wearable energy harvesters.”

Pr. Kyung-In Jang – DGIST Department of Robotics and Mechatronics Engineering

Applications

Wearables

The most direct application would be to power electronics integrated into clothing when we move, such as while walking.

This could be useful for wearable devices, especially health monitoring devices that could then not be reliant on regular battery charging.

Medical Implants