Flexible waterproof sensors can control smart devices, such as lamps, music players

Handheld 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 Used Physics Assessments, by AIP Publishing, scientists from the UCLA describe their development of a scalable, inexpensive, and waterproof type of HMI. The device is based on an array of soft magnetoelastic sensors that converts mechanical pressure from finger pressure into an electrical signal.

The device consists of two main components. The first component is a layer that translates mechanical motion into a magnetic response. It consists of a set of micro-magnets in a porous silicone matrix that can convert light fingertip pressure into a magnetic field variation.

The second component is a magnetic induction layer composed of coils of patterned liquid metal. These coils react to variations in the magnetic field and generate electricity through the phenomenon of electromagnetic induction.

“Due to the flexibility and durability of the material, the network of magnetoelastic sensors can generate stable power under deformations, such as rolling, bending and stretching,” said author Jun Chen, from UCLA. “With these compelling features, the device can be adopted for HMI powered by the human body by transforming human biomechanical activities into electrical signals.”

The power needed to make operate the HMI comes from the movements of the wearer. This means that no batteries or other external power components are needed, making the HMI more environmentally friendly and strong.

The device has been tested in a variety of real-world cases, including the presence of a stream of water, such as might exist in the shower, a rainstorm, or during vigorous athletic activity. The device worked well when wet, as the magnetic field was not greatly affected by the presence of water.

Researchers studied a range of manufacturing and assembly techniques to optimize the device’s conversion of biomechanical energy into electrical energy. They discovered that they could achieve a balance between effectiveness and flexibility by controlling the thickness of the versatile film and the concentration of the magnetic particles.

To test their system, the investigators conducted a series of experiments in which a subject applied finger taps to turn a lamp on and off and control a music player.

“Our magnetoelastic sensor network works not only wirelessly like the on/off buttons of a lamp, but also controls the control functions of a music player, representing play, pause, next and previous actions,” Chen said.

These tests promise new applications for versatile, water-resistant HMIs that can be used to control many kinds of smart devices.

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