Skin‐Adhesive Flexible Force Sensors Based on Piezoelectric Poly(l‐lactic acid) for Human Behavior Recognition

The application of biodegradable films based on the piezoelectric effect of poly‐l‐lactic acid (PLLA) in sensors, transducers, actuators, and so on has gradually become one of the emerging research focuses. In this work, a flexible PLLA sensor with UV‐curable acrylate film packaging is proposed for human behavior recognition. The acrylic films with different proportions have different mechanical and surface properties, showing good flexibility, ductility, and skin adhesion. The morphology and crystal structure of the PLLA films and UV curable substrate obtained under the various postprocessing conditions and different proportions are examined by scanning electron microscopy, X‐ray diffraction, Raman, and ATR‐FTIR spectroscopy. In addition, by comparing six groups of PLLA films with different treatment conditions, the device made on film stretched four times and annealed for 8 h has the best performance. This sensor has good response ability to impact, vibration, and bending strain, and can be applied to human behavior recognition, such as touch, wrist bending, and swallowing. In this work, first time the relationships between the performances of the piezoelectric sensors are combined with flexible skin‐adhesive substrate for human behavior recognition and the physical properties of the poly‐l‐lactic acid (PLLA) films. The intensity of the piezoelectric signal of the sensor based on the PLLA film is influenced by its structural features in the synthesis and postsynthesized processing.