Electronics
in an office or laying in a bed.” Because of this, wearables that use TENGs can also benefit by having a battery system attached, though not all TENG- based wearables require this extra energy storage.
Piezoelectric nanogenerators (PENGs) PENGs are similar to TENGs but they aren’t as well-established. PENGs use the piezoelectric effect to create electricity – which happens when a piezoelectric material is subjected to a mechanical force (such as movement of the wearer). This force causes the ions in the material to rearrange at the atomic level, causing a charge imbalance within the material lattice: with positive charges on one face of the material and negative charges on the other. This charge imbalance creates a current that can be used by the components of the wearable. Like TENGs, PENGs are using nanomaterials (or nanostructured materials) as the active piezoelectric materials due to their small size and efficient electrical properties, with materials such as hexagonal boron nitride (h-BN), TMDCs, doped graphene and group III and IV monochalcogenide materials being the prime choices. However, there are reasons why TENGs are preferred over PENGs, Yao explains. “PENGs can only be deployed on body parts of frequent movement [or] motion, such as the bottom of the feet, and mechanical abrasion of the layers can
affect the lifetime of these products. PENGs cannot also sustain energy when the body is still.” Plus, TENGs currently provide a higher output, primarily because they can work with smaller motions than PENGs can. However, PENGs do still have a high energy conversion, and can harvest energy from a wide range of human motion, which makes them suitable for a lot of different applications. As new small-scale piezoelectric materials get discovered, more efficient PENGs might be developed in the future. However, when it comes to health wearables, both TENGs and PENGs are the two front-running technologies in the nanogenerator space – there are other nanogenerators as well, but they are nowhere near as mature as these two. “It’s not necessarily about a single type of device, but rather the integration of multiple devices to leverage their complementary benefits,” says Yao. “For instance, combining a battery with TENG and solar devices can provide alternating power solutions tailored to different environments, enhancing energy sustainability.” Harvesting energy using multiple technologies is going to be the way forward for developing robust wearable devices that can work in all fitness and medical environments. As different ways of producing energy mature, we will start to see a wider range of sustainable medical devices with advanced wireless capabilities becoming available that can be constantly attached to a user for as long as needed. ●
Audemars is a trusted supplier to world leading medical device manufacturers. We specialize in miniature custom components for active implantable, interventional and wearable medical devices and other critical applications. Our proprietary, low-stress processes for machining permanent magnet materials (NdFeB and SmCo) de- liver maximum magnetic perfor- mance in the smallest dimensions possible. Micro-coil capabilities thin as 10 micron. Contact us for your custom needs.
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