Smart finger ring features an integrated RFID chip

Researchers at the Fraunhofer Institute for Casting, Composite and Processing Technology IGCV have produced a multifunctional ring with an integrated RFID chip, which could be used for paying for goods at the checkout, unlocking doors, acting as a health insurance card and more. It might even be possible to save medical data such as our blood group or drug intolerances on the chip, so that in an accident, the emergency physician would have all the necessary information to hand.

The ring is produced via 3D printing, though in technical jargon the process would better be described as ‘powder bed-based additive manufacturing’ in which a laser beam is guided over a bed of fine metal powder. At the point where the 80 µm 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 system 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. The chip is sealed by the ring, making it tamperproof.

While 3D printing 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. As noted by Maximilian Binder, Senior Researcher and Group Manager in the Additive Manufacturing unit at Fraunhofer IGCV, “Converting the hardware technology to allow electronic components to be integrated during the manufacturing process is unique.”

Thanks to the integrated RFID tag, the ring produced by the 3D printing process can act as a door opener. Image ©Fraunhofer IGCV.

The second focus of the development was to figure out how the electromagnetic signals from the RFID chip can be sent through metal, which is normally an effective shield against signals. The research team carried out numerous simulations and experiments — and found a suitable solution.

“We use a frequency of 125 kHz,” Binder said. “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 1 mm. 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.

The technology can be used wherever the conventional method of integrating the electronics proves difficult. For example, the researchers are currently implementing sensors in gear wheels in the production technology sector — 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 in a wireless fashion. 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 be able to realise monitoring that would otherwise not have been possible due to the fast rotational speed of the gear wheels.

Top image caption: The smart ring with integrated electronics is only slightly bigger than a normal finger ring. Image ©Fraunhofer IGCV.

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