Innovation of flexible electronic technology and application prospects of electronic skin of humanoid robots

Compared with traditional bulk devices, flexible electronic technology has brought revolutionary changes. This technology makes electronic devices thin, soft, and even elastic, similar to paper or film. In the application field of flexible electronics, electronic skin is particularly eye-catching.

Design and function of electronic skin

Electronic skin is an electronic device that mimics human skin through flexible electronic technology. It not only needs to have the softness of skin, but more importantly, it needs to have tactile perception. Electronic skin can not only mimic the functions of skin, but also go beyond skin, helping humans to obtain physical and chemical signals from the environment and human body, and improving the ability to interact with the environment or themselves.

Skin and touch perception

As the largest organ in the human body, the skin is the main carrier of touch. We can feel the hardness of an object because the pressure receptors in the skin can distinguish the hardness of an object based on the force of contact. Electronic skin can also sense the hardness of an object through pressure. Piezoresistive is the simplest and most commonly used way to achieve this function. It uses the changes in conductive materials when they are deformed to achieve sensing.

Application of flexible pressure sensors

Flexible pressure sensors can not only sense pressure, but also sense the shape of objects. Researchers at MIT designed a low-cost, retractable tactile glove with 548 piezoresistive pressure sensors distributed on the glove, which can record the pressure values ​​sensed by each sensor in detail. With these data, they trained the robot to identify different objects.

Integration and application of electronic skin

Through flexible electronic technology, combined with flexible stretch sensors, etc., electronic skin with tactile sense can be constructed. The most direct application of electronic skin is. Robots with tactile sense can read pressure signals in the environment more accurately, thereby achieving more precise, diverse and effective actions. For example, current robots have difficulties in grasping and manipulating small, soft objects, and the fine mechanical feedback provided by electronic skin will help solve this problem.

Artificial afferent nerves and conversion of touch sensation

Although the perception of objects can be achieved at the sensor level, it is still a challenge to effectively convert sensor signals into neural electrical signals that the brain can understand. Scientists have invented artificial afferent nerves through bionic technology. This artificial afferent nerve includes a piezoresistive pressure sensor, an organic oscillator, and a synaptic transistor. The pressure sensor obtains pressure information, and the ring converts the pressure signal into a voltage pulse. The synaptic transistor integrates and converts these pulse signals into synapses, and then connects with the efferent nerves in the body to form a complete single synaptic reflex arc.

Experiments on cockroach legs and brain-computer interface technology

Scientists connected artificial afferent nerves to the efferent nerves on the cockroach's legs, applied pressure through pressure sensors, and successfully drove the movement of the cockroach's legs. This experiment demonstrated the potential for the application of artificial nerves in organisms. In addition, through brain-computer interface technology, tactile experience can be achieved by stimulating specific areas and cells of the brain with encoded signals. Although the current understanding of the neural encoding of perception is limited and the development of brain-computer interface technology still needs breakthroughs, this provides possibilities for the conversion of tactile signals in the future.

The mechanism by which cockroach legs are controlled by artificial nerves (Image source: Science)

Other applications of flexible electronics

In addition to establishing a tactile system, flexible electronic technology can also enable various sensors to have the general properties of skin, such as softness, stretchability, and self-healing. These sensors can be covered on the skin or clothes to sense the environment and itself anytime and anywhere. In addition, electronic skin can also sense the intensity of ultraviolet rays in sunlight, humidity, magnetic fields, the approach of objects, etc., or non-invasively monitor physiological indicators such as blood sugar in body fluids, and collect EEG, EMG, and ECG information through other physical and chemical principles. These applications demonstrate the broad prospects of flexible electronic technology in many fields.