Smart finger ring with integrated RFID chip
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Smart finger ring will take the place of keys, money and much more

House keys, wallets or health insurance cards will be “packed” onto your finger in the future. A new 3D printing process can integrate the electronics for the sensitive information into a piece of jewelry.

Smart rings may emerge as a new wearable format that could cut seriously into the popularity of armbands. About a year ago, Oura—the smart ring that can spot COVID-19—was the talk of the town. It was soon followed by devices that track people’s sleep or fitness, serve as a means of payment or could displace smartphones with the help of bone conduction technology.

A ring recently developed by the Fraunhofer Institute for Machine Tools and Forming Technology that includes an integrated RFID tag is designed to hold an individual’s keys, wallet, health insurance card and everything else that is based on sensitive information. What a relief this would be. People would no longer have to frantically search their pockets, jackets or pants if they happened to be locked out of their homes, are unable to find their wallets at the checkout counter or have to locate their vaccination card. Any person who has stored information about his or her blood group or drug intolerances in a ring could gain precious life-saving time following an accident.

Automated electronic integration

But there is something more at play here than the ring itself. The key to the entire idea is the process that is used to integrate electronics into presumably inaccessible places on a component during the production process. In broadest terms, we are talking about a 3D printing process that goes by the name of “powder-bed-based additive manufacturing.” The principle: A laser beam passes over a fine metallic powder. Each area hit by the 80-micrometer beam melts and fuses to create a composite material. A ring containing a cavity for the electronics is created layer by layer. During the process, robots insert an RFID component before the “printing” job continues. The manufacturing process creates completely customized ring designs that are sealed to make devices tamper-proof.

But the RFID chips must be arranged in such a way that the electromagnetic signals can pass through the metal covering them. This form of penetration can best be achieved at frequencies of about 125 kilohertz. This type of arrangement also enables the tag and transmitter to be separated by just one millimeter of metal. The design of the cavity and the placement of the electronics within it play a major role in signal dispersion. If all of this were not enough, the sensitive electronics in the RFID tags must be shielded from temperatures of 1000 degree Celsius produced in the manufacturing process.

One size fits all

Naturally, the technology is not limited to jewelry-like objects. It can actually be used in any place where the conventional electronics-integration process reaches its limits. In one example of such approaches, engineers at the Fraunhofer Institute for Machine Tools and Forming Technology are working on a production-technology application. They are implementing sensors in gear wheels. Once positioned, the sensors wirelessly and continuously transmit the load condition, temperature and other important parameters. Initial signs of damage can be uncovered by analyzing the vibrations on a gear tooth. The sensors draw their power from printed RFID antennas placed on the outside. In the future, this will facilitate a form of monitoring that would be hardly possible before due to the rapid rotation of the gear wheels.

Knowledge base

Fraunhofer Institute for Machine Tools and Forming Technology: KINEMATAM—Implementing a handling system at an additive manufacturing facility

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