Designing touch-sensitive skins to mimic various functions and properties of natural epidermal tissue is an essential but open challenge. Over the past decades, a number of artificial skins have been developed based on various materials and mechanisms. However, these sensing architectures can be susceptible to external interference and have the potential to suffer from undesirable sensing performance in unstructured and dynamic environments when integrated with robotic systems.

Now, engineers at the SJTU and CMU have designed an iontronic pressure sensor that harnesses ultracapacitive mechanism to achieve enhanced pressure sensing functionality with high bandwidth and sensitivity. Conventional parallel-plate capacitive pressure sensors typically exhibit low signal baseline and thus induce low signal-noise ratio (SNR). To elevate the capacitance baseline, the iontronic capacitor substitutes the intermediate dielectric layer with an ionically conductive hydrogel. This structure generates the electric double layer (EDL) capacitance. There are numerous microscale capacitors with nanometer distance at the interfaces. Thus, the iontronic sensor exhibits ultrahigh capacitance (generally on the orders of nF~μF). When the pressure is applied, the contact area between the layers significantly increases. More microscale capacitors are generated at the interfaces, inducing a large increase of the capacitance.

The ultracapacitive iontronic pressure sensor exhibits desirable sensing properties, including a high sensitivity about up to 44 times higher than the conventional parallel-plate capacitive counterparts, a broad pressure detection range of over four orders of magnitudes from 35 Pa to 330 kPa, fast response time of ~18 ms, high resolution about 0.91% over 113 kPa and good repeatability.

The iontronic pressure sensor can be applied as a wearable electronic skin for healthcare monitoring. Akin to natural skins, the electronic skin can distinguish different pressure regimes and respond to instantaneous pressure stimuli. The single-point pressure sensors can be expanded to a multiplex sensing array with the simultaneous detection capability as a multipoint touch panel.

The touch skin can be integrated within a soft bionic hand and provide sensory information in response to external pressure. It also possesses dynamic response capability required to control the movement of an industrial robot in real time. Moreover, a human-in-the-loop robotic system is demonstrated through a transradial amputee using the neuroprosthetic hand with tactile sensing. The robotic skin can provide an amputee with real-time sensory feedback, which facilitates dexterous manipulation and secure interaction.

“We design and fabricate the touch skin through facile manufacturing methods,” say Guoying Gu, professor of mechanical engineering at SJTU. “This scalable touch skin can provide tactile sensing for soft machines, physiological signal monitoring, industrial robots, and amputee prostheses.”

Gu and his colleagues have published their work in Advanced Materials. Co-authors include SJTU Professor Xiangyang Zhu and PhD student Zequn Shen, along with Carmel Majidi at Carnegie Mellon University in USA. Shen is the first author of this paper.

This work was supported by the National Natural Science Foundation of China, the Science and Technology Commission of Shanghai and Shanghai Jiao Tong University Scientific and Technological Innovation Funds.

Link to the paper: https://doi.org/10.1002/adma.202102069

Source: Institute of Robotics