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A rubber “skin” developed at the University of Houston allows a robotic hand to sense the difference between hot and cold temperatures. The semiconductor material supports new applications in stretchable electronics, including medical implants, health monitors, and human-machine interfaces.

Cunjiang Yu, Assistant Professor of mechanical engineering and lead author of a paper published in the journal Science Advances, said the rubber-composite technology offers a valuable and flexible alternative to time-honored, rigid semiconductors.

Research led by Cunjiang Yu, Bill D. Cook Assistant Professor of mechanical engineering, has created an artificial skin that allows a robotic hand to sense hot and cold. (Credit: University of Houston)

“Traditional semiconductor materials are all brittle. In other words, if you stretch them, they rupture,” Dr. Yu told Tech Briefs. “By putting rubber into a semiconductor, we are actually adding a mechanical stretchability into this brittle material.”

Under the Skin

The basis of the stretchable composite semiconductor is a hardened, silicon-based polymer known as polydimethylsiloxane, or PDMS. The skin features tiny nanowires to transport electric current.

The rubber semiconductor is sensitive to the temperature. A temperature increase induces a higher carrier density, and thus makes the material more conductive.

Yu and the team – Hae-Jin Kim, Kyosung Sim, and Anish Thukral from the UH Cullen College of Engineering – placed the electronic skin on a robotic hand to sense the temperature of hot and iced water in a cup.

The sensor system also detected different levels of the strain signals on the robotic hand, sent by the Houston engineers, and reproduced the data as American Sign Language.

“The robotic skin can translate the gesture to readable letters that a person like me can understand and read,” Yu said in an earlier press release.

Grasping the Future

Along with smart robotic surfaces, Yu believes the technology can be used in wearable technologies like human-machine interfaces and health monitoring systems.

One analyst sees similar advanced applications for the rubber semiconductor technologies, specifically in the fields of military and biomedical engineering.

Artificial skin would not only enhance a system’s appearance, but also significantly improve a robot’s sensing capabilities and interactions with the environment and users, said Dr. Shahin Nazarian, Senior Research Scientist in Electrical and Computer Engineering at the Los Angeles, CA-based consulting firm Quandary Peak.

“It is also a positive step towards flexible integrated circuits in the form of rubber, plastic, and paper,” said Nazarian. “Furthermore, it will help with the resilience of ICs and systems.”

The University of Houston semiconductor is designed to allow the electronic components to retain functionality even after the material is stretched by 50 percent.

According to Yu, the team is now developing multi-functionalities for the technology, increasing the sensory skin sensitivities, and building rubbery integrated circuits, logic gates, and sensor systems.

A major advantage of the robotic skin, said Yu, is that the technology can be easily taken to market.

“For the first time, everything can be made with commercially available material, and can be securely manufactured in large scale,” said the professor.

What do you think? How could flexible integrated circuits be used? Share your comments below.

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