Highly sensitive and selective flexible anisotropic strain sensor based on liquid metal/conductive ink for wearable applications

Abstract

Although many high-performance wearable strain sensors have been developed, they are limited to uniaxial strain monitoring, which makes it challenging to meet the monitoring needs of complex multidimensional motion in practical applications. This study effectively constructed an anisotropic strain sensor by combining two materials that exhibit different responses to external stimuli (strain): liquid metal and conductive ink. In particular, the maximum gauge factors of this anisotropic strain sensor in conductive ink direction and liquid metal direction are 158.9 and 1.9, respectively. Both directions display outstanding dynamic stability, frequency independence, and durability over 3000 cycles. Furthermore, the integrated sensor formed by the orthogonal stack of two anisotropic strain sensors can distinguish the strain magnitude and direction (an outstanding selectivity of 3.7). The mechanism of the sensor's selective sensing ability is analyzed, and the broad application of the sensor in complex motion monitoring, human-computer interaction, and multi-component control is demonstrated. This research discovery provides new ideas and methods for constructing anisotropic wearable strain sensors. It creates conditions for the development and practical application of multifunctional wearable devices.