Using sound waves to create a smart T-shirt

Imagine wearing a T-shirt that measures your breathing or gloves that translate your hand movements into commands for your computer. Researchers at ETH Zurich, led by Daniel Ahmed, Professor of Acoustic Robotics for Life Sciences and Healthcare, have laid the foundations for just such smart textiles. Unlike many previous developments in this area, which usually use electronics, the ETH researchers rely on acoustic waves passed through glass fibres. This makes the measurements more precise and the textiles lighter, more breathable and easier to wash. ¡°They are also inexpensive because we use readily available materials, and the power consumption is very low,¡± says Ahmed.

Acoustic sensors embedded in fabric

The researchers call their development SonoTextiles. They have transformed normal fabrics into smart sensors that react to touch, pressure and movement. ¡°While research has already been conducted into smart textiles based on acoustics, we are the first to explore the use of glass fibre in combination with signals that use different frequencies,¡± explains Yingqiang Wang, the first author of the study that has been published in the journal external page Nature Electronics.

The researchers have woven glass fibres into the fabric at regular intervals. At one end of each glass fibre is a small transmitter that emits sound waves. The other end of each of the glass fibres is connected to a receiver that measures whether the waves have changed.

Each transmitter works at a different frequency. This means it requires little computing power to determine which fibre the sound waves have changed on. Previous smart textiles often struggled with data overload and signal processing issues, since each sensor location had to be evaluated individually. ¡°In the future, the data could be sent directly to a computer or smartphone in real time,¡± says Ahmed.

When a glass fibre moves, the length of the acoustic waves passing through it changes, as they lose energy. In the case of a T-shirt, this can be caused by body movement or even breathing. ¡°We used frequencies in the ultrasonic range, around 100 kilohertz ¨C well beyond the range of human hearing, which is between 20 hertz and 20 kilohertz,¡± Wang emphasises.

Highly versatile

The researchers have shown that their concept works in the lab. In the future, SonoTextiles could be used in a variety of ways: as a shirt or T-shirt, they could monitor the breathing of asthma patients and trigger an alarm in an emergency.

In sports training and performance monitoring, athletes could receive real-time analysis of their movements, to optimise their performance and prevent injuries. The textiles also have potential for sign language: gloves with this technology could simultaneously translate hand movements into text or speech. They could also be used in virtual or augmented reality environments.

¡°SonoTextiles could even measure a person¡¯s posture and improve their quality of life as an assistive technology,¡± adds Chaochao Sun, who shares first authorship of the study. People who want to improve their posture could receive targeted feedback to correct poor posture. The textiles could also indicate when a wheelchair user needs to change position to prevent pressure ulcers.

Although the everyday usability of SonoTextiles is potentially very high, Ahmed adds that there is still room for improvement in terms of practical application. Glass microfibres worked well as sound conductors in the lab, but they could potentially break in everyday use. ¡°The beauty is that we can easily replace the glass fibres with metal. Sound also propagates effectively through metal,¡± explains Ahmed, adding ¡°We would like to expand our research in this direction and also into other applications.¡± The researchers now want to make the system more robust and examine how the electronics can be better integrated into the textiles.