Advance combines sensing directly into objects’ materials with applications for assistive tech and intelligent furniture.

Researchers at MIT have created a new way to 3D-print mechanisms that can detect the force being applied to objects. These structures can be quickly prototyped because they are only one piece of material. A designer could use this method to prototype swiftly “interactive input devices,” such as a joystick, switch, or handheld controller.

The researchers used metamaterials to integrate electrodes in structures made of metamaterials. These are materials that have been divided into grids of repeating cells. The researchers also developed editing software to help users create these interactive devices.

“Metamaterials are capable of supporting different mechanical functions. If we make a metamaterial door handle, can we know if the handle is being turned and, if so, how many degrees? Jun Gong, a co-lead author and a former visiting Ph.D. student from MIT, is now a research scientist for Apple.

Gong co-authored the paper with Olivia Seow (a graduate student at MIT Department of Electrical Engineering and Computer Science) and Cedric Honet (a research assistant at MIT Media Lab). Jack Forman, an MIT graduate student, and Stefanie Mueller (senior author) are co-authors. She is an associate professor at EECS and a Computer Science and Artificial Intelligence Laboratory member. Next month, the research will be presented at Association for Computing Machinery Symposium (ACCM) on User Interface Software and Technology.

“What I find most fascinating about this project is its ability to integrate sensing directly in the material structure objects. Mueller says this will allow for new intelligent environments where things can feel every interaction with them. Mueller says that a couch or chair made of our innovative material could sense the user’s body and use this information to either query specific functions (such as turning on the TV) or collect data to help with analysis (such as correcting and detecting body posture).

Embedded electrodes

Metamaterials are composed of a grid of cells. When the user applies force, some flexible interior cells stretch or compress.

Researchers took advantage of this and created “conductive shear cells,” flexible cells with two walls made of conductive filament and one wall made from the nonconductive filament. The conductive walls act as electrodes.

The conductive shear cells expand or contract when a user applies force (moving a joystick handle or pressing buttons on a controller) to the metamaterial mechanism. This causes the distance between the electrodes to change and creates an overlapping area. These changes can be measured using capacitive sensing to calculate the magnitude, direction, rotation, and acceleration.

The researchers made a metamaterial joystick with four conductive shear cells embedded around its base in each direction (left, right, up, left, and right). The distance and area between opposing conductive walls change as the user moves the joystick, allowing them to sense the direction and magnitude of each force applied. These values were used to create inputs for a “PACMAN” game.

Designers can create unique handles for people who have limited grip strength. This is possible by understanding the forces that joystick users apply.

Researchers also designed a music controller that conforms to the user’s hand. The user presses one of the flexible buttons to compress the conductive shear cells and send the input to a digital synthesizer.

This 3D-printed metamaterial mechanism incorporates copper-colored capacitive sensors electrodes that can sense compression. Credit: Courtesy of the researchers

This could allow a designer to quickly design and modify unique input devices for a computer, such as a squeezable volume controller or bent stylus.

Software solution

The 3D editor MetaSense developed by researchers, allows rapid prototyping. You can either manually incorporate sensing into your metamaterial design, or the software will automatically place the conductive cells at optimal locations.

“The tool simulates how an object will deform when applying different forces. Then, it uses this simulation to determine which cells have the most significant distance change. Gong states that the cells that are most likely to change the most are the best candidates for conductive shear cells.

Although MetaSense was designed to be simple, the researchers encountered difficulties printing complex structures.

“In a multilateral 3D Printer, one nozzle is used for nonconductive filament while one is used for conductive filament. It isn’t easy because different materials can have very other properties. Finding the right speed and temperature takes a lot of parameter tuning. He says that 3D printing technology will continue to improve, and users will find it easier in the future.

The researchers hope to improve MetaSense’s algorithms for more complex simulations.

They also plan to develop more conductive shear cell-based mechanisms. Gong suggests that incorporating hundreds of thousands or more conductive shear cells into an effective agent could allow for high-resolution real-time visualizations of the user’s interaction with an object.