A Toe-tally Immersive Haptic Interface

Haptic interfaces have become an important technology in the field of virtual reality (VR) and augmented reality (AR), providing users with a heightened level of immersion and interactivity. These interfaces primarily target the fingers and hands, allowing users to feel and interact with virtual objects and environments in a more tactile and realistic manner. The benefits they offer are numerous, transforming the way we engage with digital content and bridging the gap between the virtual and physical worlds.

One of the most significant advantages of haptic interfaces in VR and AR is the enhancement of sensory feedback. By providing users with tactile sensations such as vibrations, pressure, and texture, haptic interfaces allow them to perceive and interact with virtual objects as if they were real. This not only adds a new dimension of realism but also enhances the overall sense of presence, making users feel more connected to the virtual environment. For example, when a user reaches out to touch a virtual object, they can feel its shape, texture, and even subtle vibrations associated with its behavior, creating a truly immersive experience.

A pair of researchers at The University of Chicago have just unveiled a new technology that provides a haptic interface for an area that does not receive a lot of attention — the feet. This interface, called FeetThrough, not only provides artificial tactile stimulation, but allows real-world stimulation to pass through as well because of its unique design. This feature makes FeetThrough especially well suited for AR applications, or minimal interfaces that are virtually transparent to the user, only supplying subtle tactile cues when needed.

Traditionally, foot-based haptic interfaces rely on vibration motors to provide vibrotactile stimulation. While this technique can provide convincing effects under the right circumstances, it has a number of drawbacks. For example, the vibration motors are bulky and prevent the bottoms of the feet from making contact with the ground, which serves to disconnect the user from their actual surroundings. Moreover, it is challenging to provide fine targeting of one particular region using vibrations, which makes the resolution of the interface quite low.

FeetThrough breaks from this current paradigm and instead leverages electrotactile stimulation. This allows the device to be produced in the form of a very thin sheet that one can feel normal sensations through. The sheet, a flexible PCB, is covered in an array of 60 electrodes that span from the ball of the foot to the heel. The state of each electrode is controlled by a shift register, which is in turn programmed by an ESP32 DevKit-C microcontroller development board.

Whereas the effects of a vibration motor would be felt by surrounding areas of the skin, the stimulation provided by the electrodes is more precise. This gives FeetThrough a higher level of resolution, allowing it to reproduce more accurate physical sensations, and in precise regions of the foot.

These benefits do come with some caveats, however. The electrodes must have a direct attachment to the skin, and the positioning of the grid must be correct. Further, a wearer of the device must undergo a calibration process for proper operation. Vibrotactile methods do not have these requirements, which can be cumbersome for certain use cases.

However, for many applications, the benefits are likely to outweigh these considerations. The team showed how FeetThrough could be used to augment VR experiences, for example. In one demonstration, it was shown that the feet could be used to identify hidden, virtual objects on the ground, while still retaining the ability to interact naturally with the actual ground. In another demonstration, it was shown that the haptic interface could be used to provide navigational cues. A virtual arrow on the ground could show the user which way to go.

At present the researchers are working to make their system ready for everyday use. Towards that end, they hope to build FeetThrough into articles of clothing, like socks, and also automate the calibration process.