Researchers at ETH Zurich developed smart textiles that rely on acoustic waves passed through glass fibers. This makes the measurements more precise and the textiles lighter, more breathable, and easier to wash. The researchers have woven glass fibers into the fabric at regular intervals. At one end of each glass fiber is a small transmitter that emits sound waves. The other end of each of the glass fibers 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 fiber 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. When a glass fiber 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.
More information:
https://www.futurity.org/smart-fabric-sound-glass-fibers-3282452