HaptiCoil offers a fresh approach to the physical button, using a hydraulically-coupled speaker to deliver haptic feedback and detect touches.
Physical buttons may still be essential in many interfaces, but in an era dominated by touchscreens, they often feel outdated. A team of engineers at the University of Illinois Urbana-Champaign is changing that with HaptiCoil — a groundbreaking system that transforms traditional buttons into dynamic, tactile interfaces.
HaptiCoil is designed for rapid prototyping of soft, compact, and highly customizable haptic buttons. Unlike the basic vibration motors found in smartphones, HaptiCoil can deliver a wide range of sensations across a 1–500 Hz bandwidth, offering a richer, more responsive touch experience.
At the core of HaptiCoil is a mass-produced, waterproof planar micro-speaker. Rather than producing sound, the speaker’s movements are redirected through a unique hydraulic mechanism using regular tap water. This motion pushes against a soft silicone membrane, creating distinct tactile feedback that users can feel. All this is managed by a Teensy 4.0 development board, which controls both the actuation and sensing.
Innovatively, the system detects button presses by measuring changes in the speaker coil’s self-inductance — deformation caused by a press alters the coil’s properties in a way the system can easily track. Even better, HaptiCoil achieves this with just two electrical connections, keeping the hardware design refreshingly simple.
To build a HaptiCoil button, the team 3D-prints a small, clear resin chamber slightly larger than the speaker, bonds the speaker to it, and attaches a flexible silicone membrane. After filling the chamber with tap water and sealing it, the button is ready — compact, durable, waterproof, and easily integrated into various devices.
The engineers envision HaptiCoil as a versatile tool for industries like spatial computing, digital inking, and even remote control design. Thanks to its modular nature, developers can quickly customize button size, shape, and feedback style, encouraging rapid innovation in haptic interaction. With HaptiCoil, the humble button is getting a much-needed upgrade — and the future of tactile interfaces just got a lot more exciting.
