Waterproof human-machine interface generates power

Wearable human-machine interface devices (HMIs) can be used to control machines, computers, music players and other systems. A challenge for conventional HMIs is the presence of sweat on human skin.

In Applied Physics Reviews, scientists at UCLA described how they developed a waterproof HMI that is stretchable and inexpensive. The device is based on a soft magnetoelastic sensor array that converts mechanical pressure from the press of a finger into an electrical signal.

The device involves two main components. The first is a layer that translates mechanical movement to a magnetic response. It consists of a set of micromagnets in a porous silicone matrix that can convert gentle fingertip pressure into a magnetic field variation.

The second component is a magnetic induction layer consisting of patterned liquid metal coils. These coils respond to the magnetic field changes and generate electricity through the phenomenon of electromagnetic induction.

“Owing to the material's flexibility and durability, the magnetoelastic sensor array can generate stable power under deformations, such as rolling, folding, and stretching,” said author Jun Chen, from UCLA. “Due to these compelling features, the device can be adopted for human-body powered HMI by transforming human biomechanical activities into electrical signals.”

The power required to run the HMI comes from the wearer's movements. This means no batteries or external power components are required, rendering the HMI more environmentally friendly and sustainable.

According to the team, it was tested in real-world situations, including in the presence of a water spray, such as might exist in the shower, a rainstorm, or during vigorous athletic activity. The device worked well when wet, since the magnetic field was not greatly affected by the presence of water.

The investigators studied fabrication and assembly techniques to optimise the device’s biomechanical-to-electrical energy conversion. They found they could achieve a balance between performance and flexibility by controlling the flexible film’s thickness and the magnetic particles’ concentration.

To test the system, they carried out a series of experiments in which a subject applied finger taps to turn a lamp off and on and control a music player. Researchers believe the tests promise new applications for versatile, water-resistant HMIs.