SPARTACUS: Self Powered Augmented RFID Tag for Autonomous Computing and Ubiquitous Sensing

SPARTACUS is a fully passive RFID device conceived to enable new classes of applications which cannot be managed neither with standard RFID tags nor with the augmented ones presented so far in the literature since SPARTACUS ensure self-powering, self-computation, self-reasoning, RFID Gen2 compliance, sensing, alerting, and long working ranges at the same time.

In Fig. 1, the architecture of  SPARTACUS is illustrated.

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Figure 1. SPARTACUS Architecture

SPARTACUS is thought to provide a fully bidirectional and proactive communication with any Gen2 RFID reader, is provided with 16 Kbit of public and 16 Kbit of private FRAM, can manage both on-board (light and temperature in the presented version) and external sensors, can perform autonomous computing and, eventually, can drive actuators and alarms. In this way, very challenging applications can be afforded with RFID-based solutions, as envisioned in the last section of the paper.

First of all SPARTACUS mounts a Gen2 compliant UHF RFID chip guaranteeing a writing sensitivity as good as the reading one. Moreover, it is provided with a dedicated input allowing the wired access to 16Kbits of FRAM. This means that a) if at a certain distance the device can be read, then at the same distance a command, an instruction or whatever datum can also be definitely written wirelessly in its memory. b) Such a memory can also be read and written also in wired way. c) This can be done as many times as needed as FRAM instead of EEPROM is used.

Secondly, SPARTACUS is provided with an ultra low power microcontroller (MCU) and with a second 16 Kbit bank of FRAM, which is a private memory accessible only through the MCU itself. The MCU has a double task. On the one hand it can sample possible on-board or external sensors and after a potential processing can write sensed data into the RFID memory to make them available at the wireless Gen2 frontend. On the other hand, the MCU can perform computation on the basis of both local data, such as sensed values and contents of private memory, and context data, which could for instance be sent by an RFID reader and collected in the wirelessly accessible memory. In such a way SPARTACUS can also ask for extra info, take autonomous decisions and, on such a base, pilot actuators and generate alert signals.

Thirdly, SPARTACUS being a fully passive device, it is provided with a RF harvesting block which, exploiting the electromagnetic energy emitted by the RFID reader, powers MCU, memory banks, sensors, actuators and alert devices.

Finally, SPARTACUS is equipped with two specifically designed antennas with orthogonal polarization feeding RF energy harvester and RFID chip respectively.

In order to preserve the energy efficiency, the designs of the antennas and of each RF section have been carefully performed, taking into account mutual coupling between the two RF frontends, accurately measuring the input impedance at both frontends, and minimizing the electromagnetic coupling between the two antennas. In addition, proper solutions have been implemented to separate DC and RF signals.

In Fig. 2-a the layout of SPARTACUS core, designed through EAGLE CAD Software, is shown. The device is compact with a size of only 2.1 x 1.2 cm2.

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a)

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Figure 2. SPARTACUS: (a) Core circuitry, (b) Final version.

Once designed SPARTACUS has been preliminarly tested by reproducing a real application scenario highlighting the SPARTACUS capability of sensing environmental events, reasoning, and undertaking actions. The test has been performed in a standard office room, by moving SPARTACUS  under the reader coverage area, and by artificially changing both the environmental light and temperature according to the timelines reported in Fig. 3-a and Fig. 3-b for a total test time of 300 s. On the one hand, the reader has been equipped with an external temperature sensor and set to periodically communicate sensed data to SPARTACUS. On the other hand, SPARTACUS has been programmed to sense the light level, and turn on a LED when and only when both light and temperature exceed certain thresholds. As shown in Fig. 3-c, the LED is correctly activated by SPARTACUS in correspondence of the thresholds since the green spike represent an alarm event.

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Figure 3. SPARTACUS Test result: (a) reader temperature; (b) SPARTACUS light level, (c) LED trigger

Bibliography 

[1]   L. Catarinucci, R. Colella, D. De Donno, L. Tarricone, “Fully-Passive Devices for RFID Smart Sensing,” IEEE International Symposium on Antennas and Propagation (AP-S), Lake Buena Vista, Florida, USA, July 7-13, 2013.

[2]   L. Catarinucci, R. Colella, D. De Donno, and L. Tarricone, “RFID augmented devices for autonomous sensing and computation,” Proceedings of the 2013 IEEE European Microwave Conference (EuMC), pp. 999-1002, Nuremberg, Germany.

[3]   R. Colella, D. De Donno, L. Tarricone, and L. Catarinucci, “Advances in the Design of Smart, Multi-Function, RFID-Enabled Devices,” IEEE International Symposium on Antennas and Propagation (AP-S), Memphis, Tennessee, USA, July 6-12, 2014.

[4]   D. De Donno, R. Colella, L. Tarricone, and L. Catarinucci, “Novel Fully-Passive Multifunction  RFID-Enabled Devices,” IEEE European Microwave Conference (EuMC), Rome, Italy, October 5-10, 2014.