Use the ForceSticker

As we wade deeper into the era of intelligent machines, we will need to not only improve the algorithms that power their decision making processes, but also supply them with more accurate and complete information about their surroundings. The success of artificial intelligence systems, whether they are autonomous vehicles, medical diagnostic tools, or virtual personal assistants, relies heavily on their ability to perceive and understand the world around them. The data and information they rely on are the lifeblood of their intelligence, and without the right inputs, their outputs will remain suboptimal.

Much effort has gone into perfecting sensors that can capture crucial visual and auditory data, but there is another major aspect of the world of sensory inputs that lags far behind — force sensing. Any two objects that are in contact exert a force on one another. So to truly understand one’s surroundings, and how to interact with them, knowledge of those forces is necessary. You might even say that these forces surround us and penetrate us, and bind the galaxy together.

Traditionally, force measurements are made with load cells. While load cells get the job done, they are on the bulky side, and tend to be expensive. Moreover, they require a constant source of energy for operation. When you add it all up, that makes load cells a poor choice for portable applications, or applications where a large number of points need to be monitored for applied forces.

A group of engineers at the University of California San Diego was eager to learn the ways of the forces that surround us, so they developed what they call the ForceSticker. Unlike load cells, the ForceSticker is thin, lightweight, and inexpensive. These tiny stickers can also operate without batteries. They instead draw power wirelessly from radio waves — something like a mystical energy field that surrounds all things, you might say.

The ForceSticker devices have a very simple design consisting of only two components, a capacitor and a radio frequency identification (RFID) sticker. The capacitor is made up of a pair of copper strips with a thin sheet of polymer in between. As force is applied to the sensor, the polymer compresses, which brings the conductive copper strips closer together. That in turn increases the electric charge in the capacitor.

The level of electric charge changes the data sent by the RFID sticker, which can be interpreted as a precise measurement of force. This measurement is read by a remote RFID reader that provides the energy needed for the sticker to transmit its data. By modulating RFID signals in this way, the required components are a thousand times smaller than previous technologies.

This is not a one-size-fits-all device, however. The polymer sheet must be adjusted for each use case. Thinner sheets allow ForceSticker to measure smaller forces, whereas thicker sheets can be leveraged to measure larger forces.

A series of experiments conducted by the researchers showed how the sensor might be used in practice. In one demonstration, an artificial knee joint was instrumented with a ForceSticker, showing how knee-impact forces could potentially be measured in vivo. It was also demonstrated how a ForceSticker could be created that can measure the large forces associated with a heavy box sitting on top of it. Such a device could have useful applications in warehouse settings.

Testing showed the sensors to be highly durable, and they can be produced for under two dollars. This combination could eventually lead to a future where sensors based on this technology are placed on all manner of items to collect data. But before that happens, the team will need to work out how the ForceSticker can be mass produced. Moreover, they will need to make it easier to read the data from the device — they are presently working to make that possible using only a smartphone.