Vibrotactile pulses (e.g. the buzzing of a cell phone or game controller) can provide users with real-time feedback in a computer interface, but it’s not the only way to transmit information through the sense of touch. Modulating the temperature of the surface of a device can also provide additional information to users.
When a current flows through a junction between two different conductors, heat can be generated or removed from the junction. This phenomenon is called the Peltier effect, named after physicist Jean Charles Athanase Peltier. Different conductive materials that exhibit a Peltier effect will generate or remove different amounts of heat proportional to the amount of current running through the junction – the Peltier coefficient measures how much heat is carried for every unit of charge flowing through the device.
A haptic interface can vary the temperature that a user feels by implementing a thermoelectric cooler in its enclosure. Typically, a thermoelectric cooler moves heat from one side of the device to the other side, causing one side of the material to become hot while the other side cools. Such a cooler can act in concert with a heatsink or fan to increase the rate at which heat is transferred, but it can also be used to provide heat to another part of a user’s skin.
When implementing a thermoelectric cooler (Peltier diode) in a haptic interface, there are several performance characteristics to note: operating voltage, current draw, rate of heating/cooling, and typical temperature range. If the current supplied to the Peltier-type cooler is not properly modulated, the temperature can become uncomfortably cold or scaldingly hot.
Peltier diodes do not commonly appear in consumer electronic devices, but several prototype devices and patents incorporate the thermoelectric cooling effect to provide haptic feedback. Students at Cornell University created a haptic glove capable of simulating the temperatures of virtual surfaces using Peltier diodes. Immersion Corporation patented the use of an array of Peltier diodes to provide thermal haptic effects to a user. Qualcomm patented the use of Peltier diodes to convey changes in emotion by warming and cooling the user’s skin. As the number of potential use cases for thermoelectric cooling increases, we may begin to see more computers, game controllers, and consumer devices that change in temperature during use.