Conductive thread — embroidery thread that can carry an electrical current — often is combined with other types of electronics to create fabric that lights up or communicates. This thread also has magnetic properties that can be manipulated to store either digital data, or visual information like letters or numbers. This data can be read by a magnetometer, an inexpensive instrument that measures the direction and strength of magnetic fields, and is embedded in most smartphones.
Smart fabric has been created that can store data — from security codes to identification tags — without needing any onboard electronics or sensors. Since it is electronics-free, the fabric can be ironed or put into a washer and dryer. To demonstrate the technology, pass-codes to an electronic door lock were stored on a patch of conductive fabric sewn to a shirt cuff (see figure). The door was unlocked by waving the cuff in front of an array of magnetometers.
Conventional sewing machines were used to embroider fabric with off-the-shelf conductive thread whose magnetic poles start out in a random order. By rubbing a magnet against the fabric, the researchers were able to physically align the poles in either a positive or negative direction that can correspond to the 1s and 0s in digital data.
Like hotel card keys, the strength of the magnetic signal weakens by about 30 percent over the course of a week, though the fabric can be re-magnetized and re-programmed multiple times. In other stress tests, the fabric patch retained its data even after machine washing, drying, and ironing at temperatures of up to 320 °F. This is in contrast to many smart garments that still require onboard electronics or sensors.
The researchers also demonstrated that the magnetized fabric could be used to interact with a smartphone while it is in one's pocket. They developed a glove with conductive fabric sewn into its fingertips that was used to gesture at the smartphone. Each gesture yields a different magnetic signal that can invoke specific actions. In tests, the phone was able to recognize six gestures — left flick, right flick, upward swipe, downward swipe, click, and back click — with 90 percent accuracy.
Future work will focus on developing custom textiles that generate stronger magnetic fields and are capable of storing a higher density of data.