There are many situations in which it's important to know how much force one object is applying to another item. A small, thin sticker has been designed to measure and relay such data, without requiring wires or batteries.
Known as the ForceSticker, the device is being developed by scientists at the University of California San Diego. Among other things, it could be utilized to monitor the weight of stacked packages in warehouses, ensure that artificial knee joints aren't harming adjacent cartilage, or even provide robots with a sense of touch.
At the heart of the ForceSticker is a capacitor which is about the size of a grain of rice. It consists of a soft polymer sheet sandwiched between two conductive strips of copper. The polymer compresses as external force is applied to the sticker, bringing the two strips closer to one another. As a result, the electrical charge of the capacitor increases.
The other main component of the ForceSticker is an RFID (radio frequency identification) tag, which gets temporarily powered up by a radio signal emitted from a handheld RFID reader. That tag utilizes an integrated antenna to relay a modified version of the signal back to the reader – the signal now contains information on the linked capacitor's present charge level. Custom software then converts that data into a measurement of applied force.
By varying the softness of the polymer used in the capacitor, it's possible to make ForceStickers which are quite sensitive – for measuring small amounts of force – or less sensitive, for measuring larger amounts. In tests conducted so far, a very sensitive sticker was utilized to monitor force in a model knee joint, while a less sensitive one was used to monitor the weight of various large objects placed in a box.
In both cases, the ForceStickers still worked after more than 10,000 force applications. The stickers were also relatively cheap to manufacture, with each one costing about US$2 – that figure ought to drop significantly if production is scaled up. What's more, users should ultimately be able to utilize their smartphone in place of a dedicated RFID reader.
"Humans, by nature, possess an inherent ability to sense force," said the lead scientist, Prof. Dinesh Bharadia. "Providing this force-sensing ability to electronic devices and medical implants could be a game-changer for many industries."
A paper on the research is being presented at the UbiComp 2023 conference in Mexico.
Source: UC San Diego