Self-powered triboelectric wearable biosensor using Scotch tape†

A novel self-powered wearable triboelectric biosensor concept is proposed in this paper, which consists of Scotch tape and a metalized polyester sheet (Al/PET). The Scotch tape is the sensing element by exploring the interaction between the tape polypropylene backing material and the acrylic adhesive layer when pressing and releasing. The polypropylene surface only has partial positive charges because of a nonpolar surface, while the acrylic adhesive has a polar surface with positively and negatively charged and neutral regions. Atomic size gaps are formed because of the attractive and repulsive areas at the interface due to van der Waals forces. These density depleted regions act as ‘geometric’ gaps to produce triboelectric charges via contact and separation on a microscopic scale. This leads to our wearable biosensor design for measuring human body motion. Associated skin contraction and relaxation during body motion will activate the contact and separation between the polypropylene and acrylic adhesive layer when the sensor assembly is adhered to the skin. Various demonstrations were conducted to detect different body motions, including elbow flexion at a low angle, forearm protonation, forearm supination, knee flexion/extension, proximal interphalangeal flexion/extension, temple motion due to eye blinking, and temporomandibular opening. Unique features can be identified which are associated with different body motions. Moreover, the measurements from our triboelectric sensor correlate well with the results from a commercial electromyography (EMG) sensor in an isokinetic leg extension test, which leads to a new method of measuring human muscle activation.