Liquid-Powered Interface Gives Digital Tech a Real Feel

Techies and desk jockeys that spend an inordinate amount of time in the digital world sometimes find within themselves a longing for something more tangible. The empty experience of clicking on a digital button or tapping on a touchscreen display can get them dreaming of a time when complex machines were a tangle of buttons, switches, and blinking lights. That was something that you could really get your hands on!

But after a moment’s reflection, one will realize that physically getting up and going across the room to find the right switch to kick off the execution of a Python script is not exactly efficient. So maybe we don’t want to actually go back to the user interfaces of yesteryear, but a group led by researchers at the University of Bath has come up with an alternative that could give us something physical to interact with, while keeping the interface compact and efficient. Their system, called HydroHaptics, provides programmable force feedback and shapeshifting to turn physical objects into versatile interfaces.

HydroHaptics is built around a hydrostatic transmission — a sealed hydraulic cell that links two flexible surfaces through a fixed volume of liquid. Because the liquid is incompressible, any motion or pressure applied to one surface instantly transmits to the other. This bi-directional coupling allows the system not only to push back against a user’s touch but also to sense the input at the same time.

Interactions are driven by the system’s haptic engine, which is composed of a brushless DC motor paired with a lead screw to translate rotational motion into linear displacement. When the motor moves, it displaces fluid inside the hydraulic cell, creating pressure changes that can be felt as resistance, clicks, or vibrations on the deformable surface. Conversely, when the user presses or deforms the surface, the pressure feedback allows the motor to respond dynamically, simulating a range of tactile sensations from a soft cushion to a firm button click.

The system also contains a rolling diaphragm through which the haptic engine can act on a cell’s liquid. This silicone membrane flexes smoothly as the liquid moves within the sealed chamber, making room for fluid to flow into. The team experimented with a variety of materials, and found that each choice brings unique interaction qualities, from stretchable and squishy to firm and crisp.

This unique design allows HydroHaptics to outperform existing technologies in terms of speed and fidelity. Pneumatic approaches, which rely on air pressure for operation, often suffer from sluggish response times and imprecise control due to air’s compressibility. Microhydraulic systems, while more precise, are usually confined to small buttons or rigid setups. HydroHaptics sidesteps both limitations, achieving a 10-newton force change in under 100 milliseconds and rendering subtle oscillations up to 10 hertz with precision.

A user study involving 18 participants showed that people could identify different haptic effects, like clicks, vibrations, and resistive forces, with an average accuracy of over 82%. The system could even distinguish user gestures with nearly 90% accuracy, hinting at applications beyond feedback, such as input recognition.

HydroHaptics points to a future where soft, shapeshifting interfaces offer both the expressiveness of touch and the efficiency of digital control. It may not bring back the clunky switches and knobs of old control panels, but it just might make the smooth surfaces of our modern devices feel a little more alive.