Biological systems provide an ideal template for state-of-the-art biomimetic electronics, typified by humanoid robots, artificial receptors, actuators, and prosthetics. Similar to skin's mechanoreceptors, tactile sensors that are highly responsive to mechanical stimuli in the surrounding environment have been deployed in various applications in autonomous devices, human-machine interfaces (HMIs), and virtual/augmented reality. However, tactile sensors only work when physically touched or intruded, but do not respond to pre-contact stimuli. Therefore, it is crucial to develop advanced sensors capable of detecting proximal pre-contact events, which requires the development of reliable sensing systems that go beyond the contact mode paradigm. However, pre-contact detection remains challenging because it involves weak signals that need to be accurately detected at practical distances. Previous work has demonstrated pre-contact or non-contact detection based on photosensitive elements, electromagnetic techniques, or ultrasonic sensors. These strategies typically rely on sensing infrared radiation or the visible spectrum, which are heavily influenced by environmental parameters such as ambient light, weather changes, and temperature. Furthermore, with the development of soft robotics and stretchable electronics (28), future contactless sensors or interfaces will also need to be sufficiently flexible or stretchable.

Research results

Artificial tactile sensors form the basis of touch-based human-machine interface applications. However, they are unable to respond to remote events until physical contact. Some fish, such as sharks, use electro-receptive somatosensory systems for long-range environmental perception. Inspired by this ability, the team of Academician Wang Zhonglin and Researcher Pu Xiong of the Beijing Institute of Nano-Energy and Systems of the Chinese Academy of Sciences designed a soft artificial electroreceptor for sensing approaching targets. This electroreceptor is facilitated by an elastic electret capable of encoding environmental pre-contact information into a series of voltage pulses, acting as a unique pre-contact human interface. Applications of electroreceptors are demonstrated in an early warning system, robotic control, game manipulation, and 3D object recognition. These abilities to sense proximal pre-contact events can enrich the functions and applications of HMI electronics. The related research was published in the journal Science Advances under the title of "Bioinspired soft electroreceptors for artificial precontact somatosensation".

Research Highlights

1. Inspired by the shark inductive system, a flexible transparent artificial electroreceptor was designed using durable and biocompatible components. The susceptor adopts a single-electrode configuration, and its structure includes a layer of thermoelectric elastic electret, a layer of conductive organic hydrogel as an ion electrode, and a layer of encapsulated silica-based PDMS. 2. On this basis, a multifunctional contactless human-machine interface is designed to determine the orientation of the target, manipulate the robot arm, and successfully play computer games. Aided by machine learning algorithms, it also demonstrates the feasibility of an artificial electroreceptor matrix in discriminating the surface profile of a target. 3. This work provides insights into the perception of complex and multi-dimensional environments using soft devices, which may find broad applications in wearable devices, soft robotics, smart prosthetics, augmented reality, and more.

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Fig. 1. Bioinspired soft electroreceptor.

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Fig. 2. The characteristics of the electroreceptor for precontact sensing.

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Fig. 3. Noncontact HMIs based on the electroreceptor.

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Fig. 4. Bioinspired electroreceptor matrix for artificial proximal somatosensory system.

Summary and Outlook

The demand for more functional human-machine interaction requires induction systems that go beyond traditional direct-contact modes. Taking initial inspiration from the shark's electricity-receiving strategy, the authors fabricated a stretchable, transparent artificial electroreceptor that senses approaching targets by detecting the electric charge they naturally carry. Artificial electroreceptors are able to encode environmental pre-contact information into voltage pulses, and various types of targets, including metals, glass, plastics, polymers, and natural materials, can be successfully sensed. Human-machine interfaces without physical contact were then developed to demonstrate a variety of applications, including sensing approaching objects, manipulating robotic arms, and playing computer games. Combined with machine learning algorithms, the feasibility of building an artificial proximal somatosensory system for 3D object recognition using the electroreceptor matrix is ​​also demonstrated.

Compared with state-of-the-art non-contact sensors such as laser, radio frequency, and ultrasonic sensors, the electroreceptor may have shortcomings in distance sensing accuracy; while the electroreceptor is more responsive when the distance is shortened, which may be advantageous, Because short-range accuracy can be a limitation of laser or ultrasonic sensors. Furthermore, these unique advantages will make our electroreceptor more competitive in certain applications, including (i) its inherent softness, stretchability, transparency, and Biocompatibility; (ii) the sensor has negligible power consumption as it itself generates a voltage signal from motion; and (iii) works with a wide variety of materials, whether transparent, conductive, magnetic or not . Therefore, the proposed strategy to realize electrical perception with soft devices is considered to enrich the dimension of perception, and it is envisaged that electronic devices for human-computer interaction beyond the contact mode paradigm will become the mainstream means of interaction, especially in this COVID-19 pandemic.

Literature link

Bioinspired soft electroreceptors for artificial precontact somatosensation, Sci. Adv. 8, eabo5201 (2022), https://www.science.org/doi/full/10.1126/sciadv.abo5201

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