House key, wallet, health insurance card, hotel key card – a smart finger ring being developed by Germany’s Fraunhofer Institute for Casting, Composite & Processing Technology could replace all these.

Produced by a 3D printing process, the ring has an integrated RFID chip, tamper-proof, sealed and invisible. The technology of integrating electronics during 3D printing can of course be used for other applications too.

Now, where’s my house key — could I have left it in the office? And when we want to pull out our wallet at the supermarket checkout, we often find that it’s somehow made way to the bottom of the shopping bag in all the hustle and bustle. A smart ring could soon put an end to such frantic searches.

Concealed inside the ring is an RFID tag that is able to pay at the checkout, open the smart front door, act as a health insurance card when attending a medical appointment or replace the key card in a hotel. It might also be possible to save medical data such as blood group or drug intolerances on the chip. This means in an accident, the emergency physician would have all the necessary information to hand.

Researchers at Fraunhofer IGCV developed the intelligent ring at the Multimaterial Center Augsburg. The large-scale project, sponsored by the Bavarian Ministry of Economic Affairs, Regional Development & Energy, is divided into ten individual projects, including the Kinematam project, which came up with the idea and the demonstrator model of the smart ring.

More important than the ring itself, however, are the manufacturing process and the ability to integrate electronics while a component is being produced, even at places within the component that would otherwise be inaccessible; inside a ring, for example. In the broadest sense, 3D printing is a production process that uses powder bed-based additive manufacturing.

A laser beam is guided over a bed of fine metal powder. At the point where the 80µm laser spot hits the powder, the powder melts and then solidifies to form a composite material; the rest of the metal, which is not exposed, retains its powder form. The ring is built up layer by layer, with a cavity left for the electronics.

Midstream, the process is halted. A robot automatically picks up an RFID component from a magazine and places it in the recess before the printing process continues. This precisely controllable production technology is opening the door to a host of possibilities for realising completely individualised ring designs. And the chip is sealed by the ring, making it tamper-proof.

Even though 3D printing itself has been around for a long time, the main focal point of the development was the expansion of the laser beam melting unit by the internally developed automated process that places the electronics.

“Converting the hardware technology to allow electronic components to be integrated during the manufacturing process is unique,” said Maximilian Binder, senior researcher at Fraunhofer IGCV.

The second focus of the development was to answer this question: How can the electromagnetic signals from the RFID chip be sent through metal? Metal is normally an effective shield against signals. The research team carried out numerous simulations and experiments, and found a suitable answer.

“We use a frequency of 125kHz,” said Binder. “This has a shorter range – which is exactly what we want here – and is less effectively shielded by the metal.”

Plus, the tag is affixed in such a way that its signals have to penetrate just one millimetre of metal. The design of the cavity and the way the electronics are embedded into it are also instrumental in propagating the signal since the walls can reflect or absorb the signals.

Another challenge was to protect the sensitive electronics of the RFID tags from the high temperatures, reaching over 1000˚C, involved in the manufacturing process.

The technology can be used wherever the conventional method of integrating the electronics proves difficult. The researchers are working, for example, on an application in the production technology sector. They are implementing sensors in gear wheels, the aim being for them to send, live during operation, information about the load state, temperatures at various positions, and other important parameters to an evaluation unit wirelessly. Is initial damage already occurring on a tooth? The measured vibrations should show that.

The integrated sensors receive the energy they need via a printed RFID antenna on the outside. The sensors then work passively, meaning without a battery or other separate power supply. Consequently, the integrated sensors will, in the future, be able to realise a monitoring potential that would otherwise not have been possible due to the fast rotational speed of the gear wheels.