Sensor-Tag based on the ID-modulation technique

Integration between passive RFID tags and sensors has been one of the first research topics at the RFID Division of EML2. The idea consists of giving the tag extra sensing capabilities so that, when interrogated, besides the ID code, also one or more physiological parameters could be sent towards a standard Gen2-compliant RFID reader.

In particular,  from 2005 to 2007, one of the first examples in literature of fully-passive devices enabling RFID-sensing has been realized (and patented). It is called Sensor-Tag. The Sensor-Tag, differently from canonical commercial RFID tags, can be connected to any generic sensor provided with a digital output and can transmit the measured value.  All of this while preserving the advantages of RFID technology in terms of both ease of use and cost-effectiveness.

In order to design the Sensor-Tag, the architecture of a standard Tag has been radically modified. In particular, a digital input for the interconnection with a sensor has been introduced. Moreover, a logic unit has been  designed for codifying the information coming from the sensor in a format compatible with the RFID standard.

Although the design project is rather complex and involves competences on microwave circuits, antenna design, and digital electronics, the working principle is vice versa simple and effective, as illustrated in Fig. 1. In particular, on the left there is an example of canonical RFID tag, on the right the basic idea behind the Sensor-Tag is  sketched. An antenna, a digital/RF hybrid unit, a certain number of RFID chips and a digital input are represented.

SensorTag1
Fig. 1 – A commercial passive UHF RFID tag (left) and Sensor-Tag scheme (right).

In particular, the digital control on the one hand selects a specific subset of RFID chips, and consequently a specific subset of ID codes, on the basis of the measured sensor value, on the other hand controls a network of RF switches.

In Fig. 2, a photo of one of the prototyped Sensor-Tag is shown.  It is composed of four antenna specifically designed, four RFID chips, a control unit, four RF switches, and a digital input.

SensorTag2
Fig. 2 – One of the realized Sensor-Tags.

In Fig. 3 the result of a test aimed at verifying the ability of the Sensor-Tag of performing RFID-sensing is reported. In particular, in blue, the temperature measured through a wired temperature sensor is reported. In red, the temperature measured by the Sensor-Tag, quantized, transmitted towards an RFID reader and reconstructed is sketched. Apart from the quantization effects, the graphs are in optimal agreement, thus demonstrating the appropriateness of the proposed approach.

SensorTag3
Fig. 3 – Temperature measurements through the Sensor-Tag.

Bibliography

Catarinucci, L., Colella, R., Tarricone, L.,
“A Cost-Effective UHF RFID Tag for Transmission of Generic Sensor Data in Wireless Sensor Networks”,
IEEE Transaction on Microwave Theory and Techniques (MTT) – Special Issue on RFID Technology, 2009. ISSN: 0018-9480.