Flexible electronic skin for tactile sensing

Skin is the largest organ of the human body, and it is a multi-functional sensor with high sensitivity to human perception of the external environment, which is of great significance to human survival and development. Electronic skin is a device that simulates natural skin functions and mechanical properties. Flexible tactile sensing electronic skin sensors have tactile sensing functions and flexible properties that mimic human skin, and can be attached to surfaces such as human skin or robots to perceive various stimuli, such as pressure and temperature. The fields of intelligent control system and intelligent robotics have shown huge application prospects. The electronic skin is generally composed of electrodes, dielectric materials, active functional layers, and flexible substrates. When certain external conditions stimulate the electronic skin, the active functional layer converts signals such as strain and temperature into electrical signals that can be detected. Then, the electrode layer accepts and transmits these electrical signals to the data processing module and the display terminal. In practical applications, pressure sensing plays an important role because it can detect a variety of physical movements such as gentle touch, wrist pulse, heart rate and breathing rate. In the past decade, a large number of flexible pressure tactile sensing electronic skins have been developed, most of which are based on piezoresistive, capacitive, piezoelectric, and triboelectric sensing principles. In addition to the flexible tactile electronic skin for pressure sensing, the flexible tactile electronic skin for temperature sensing is also crucial. This is because it can measure the temperature information of the contact object or monitor the temperature change of the surrounding environment, etc. Its principle can be roughly divided into thermoresistive, capacitive and thermoelectric. Electronic skin has gradually realized characteristics such as multifunctional sensing, and its sensitivity and accuracy are constantly improved. With the continuous development of flexible tactile-sensing electronic skin, it is playing an increasingly important role in fields such as intelligent medical treatment, intelligent control system, virtual reality and augmented reality. The research focus of the flexible tactile-sensing electronic skin generally includes the following aspects. First, by improving the sensitivity and other performance of the flexible tactile-sensing electronic skin, it can more accurately detect the pressure, temperature, shape and other information of external objects. Second, by increasing the flexibility of the flexible tactile-sensing electronic skin, it can adapt to various complex surface shapes and movements. Third, by the integration of flexible tactile-sensing electronic skin with other electronic components, it can realize the connection and interaction with other intelligent systems while maintaining the tactile sensing function, and further expand its application field. Fourth, the flexible tactile-sensing electronic skin can not only sense basic physical parameters such as pressure and temperature, but also simulate the multi-mode tactile perception ability of human skin, such as texture, vibration, etc., to form multi-mode perception, which broadens the application scenario of the flexible tactile-sensing electronic skin. This paper mainly reviews the research progress of flexible tactile-sensing electronic skin in recent years, focuses on the sensing mechanisms and working characteristics of different kinds of flexible tactile-sensing electronic skin, and outlines the methods to improve the performance of flexible tactile-sensing electronic skin. In addition, this paper also describes the current challenges and future development prospects of flexible tactile-sensing electronic skin.