How To Make A Smart Tag Label For Food Preservation

Transcription

1 SMART RFID-LABEL FOR MONITORING THE PRESERVATION CONDITIONS OF FOOD D. CARTASEGNA, A. CITO, F. CONSO, A. DONIDA, M. GRASSI, L. MALVASI, G. RESCIO AND P. MALCOVATI Department of Electrical Engineering, University of Pavia, Via Ferrata 1, Pavia, Italy Abstract. This paper presents an integrated smart label for tracing food information and monitoring its preservation conditions. The system includes humidity, temperature, and light intensity sensors with the respective interface circuits, an A/D converter, and a MHz RFID transponder for transmitting and receiving data, as well as for gathering from an external reader the energy for recharging the on-board microbattery and powering the transmitter. 1. Introduction In the context of attention for food safety, the implementation of microelectronic systems for tracing food products through low-cost miniaturized devices is quite important. These devices shall be able to identify the product, track its path along the complete food distribution chain, and monitor the environmental conditions to which the product is subject over time, in order to verify that the preservation prescriptions are respected [1]. The first step toward the implementation of such tracing systems is the development of a smart RFID label, capable of storing the data concerning the product, monitoring the environmental conditions, and transmit the collected information upon request. A block diagram of the proposed smart RFID label is shown in Fig. 1. The integrated microsystem includes sensors (temperature, humidity, and light intensity) and very low-power circuits (sensor interface circuits, energy management, and conversion circuit, A/D converter, and wireless transceiver). The most important specifications of the proposed smart label are summarized in Table Sensors and interface circuits Each of the three considered sensors is connected to its specific interface circuit, which delivers a voltage output suitable for A/D conversion. One single A/D converter is used for all the sensors, which are therefore read-out sequentially, through a multiplexer. When are not used, both the sensors and the A/D converter are switched-off in order to reduce the power consumption. The temperature P. Malcovati et al. (eds.), Sensors and Microsystems: AISEM 2009 Proceedings, 381 Lecture Notes in Electrical Engineering 54, DOI / _77, Springer Science+Business Media B.V. 2010

2 382 D. Cartasegna et al. sensor (Fig. 2a) exploits the difference between the base-emitter voltages of two bipolar transistors with different emitter areas, to produce a voltage proportional to the absolute temperature T. The bandgap reference used (Fig. 2b), is based on the same basic principle of the temperature sensor, with the addition of two resistors. Table 1. Specification of the proposed RFID smart label. Humidity sensor Range, resolution 10% 90% RH, 1% RH Temperature sensor Range, resolution 40 C 80 C, 0.2 C Light intensity sensor Range, resolution 1,000 W/m 2, 2 W/m Maximum current consumption 30 μa A/D converter Input range peak-peak 1 V differential Resolution 10 bits RFID transceiver Operating frequency MHz Standard ISO Maximum current consumption 150 μa Rectifying antenna Output current, 3.3 V, 100 μa recharging Output current, 1.8 V, 150 μa transmission Power management Regulated output voltage 1.8 V Output current 200 μa

3 Smart Rfid-Label for Monitoring The Preservation Conditions of Food 383 Figure 1. Block diagram of the proposed smart RFID label. The humidity sensor is realized using an interdigitated capacitor coated with polyimide, whose dielectric permittivity changes with the relative humidity (RH). The capacitance variation is read-out using the switched-capacitor (SC) circuit (Fig. 3). The light intensity sensor consists of an integrated reverse-biased photodiode, which delivers a current proportional to the incident light intensity. Figure 2. Temperature sensor and band-gap reference. The developed A/D converter is based on the incremental architecture, implemented with the SC technique. Figure 3. Schematic of the humidity sensor interface circuit.

4 384 D. Cartasegna et al. 3. Power management According to the ISO standard, in order to extract energy for recharging the battery and transmitting the data from the signal emitted by the reader, a RFto-DC magnetic-coupled converter is required. The coupling element is a simple coil with the size of a credit-card and the induced voltage has to be rectified and adapted for powering the subsequent circuits. The full-wave rectifier used, is based on a CMOS structure with crosscoupled gates. This circuit operates as a conventional diode bridge, but achieves a higher efficiency and a lower threshold voltage. The rectified waveform obtained at the output of the circuit is filtered with an external capacitor and then is filtered by an external capacitor and delivered to the two charge pumps, which, using the same structure (Fig. 4), realize both the increasing and regulating functions to the rectified voltage. In order to supply the different circuits we introduced a Low-Drop-Out Voltage Regulator that maintains the required output voltage at the value of 1.8 V, independently of the battery voltage. Figure 4. Schematic of the charge pump. 4. Wireless transceiver The reader and the tag are never transmitting data concurrently, since they are using the same carrier, also used to transfer energy from the reader to the tag. The transmission of data from the tag to the reader is performed by ohmic load Figure 5. Simulation of the voltage at the tag antenna during data transmission (load modulation) with the minimum magnetic field.

5 Smart Rfid-Label for Monitoring The Preservation Conditions of Food 385 modulation of the tag antenna (Fig. 5). The transmission from the reader to the tag is performed by ASK. The receiver in the tag consists of an envelop detector, followed by a comparator and a finite-state machine. 5. Simulation results and conclusions The proposed smart RFID label has been designed using a 0.18-µm CMOS technology. The different blocks, as well as their interactions, have been simulated at transistor-level. All of the blocks achieve the required specifications, both in terms of performance and power consumption, thus demonstrating the feasibility of a smart RFID label for monitoring the preservation conditions of food. References 1. T. Kelepouris, K. Pramatari, and G. Doukidis, RFID-enabled traceability in the food supply chain, Industrial Management and Data Systems, vol. 107, pp , Feb