Intelligent and passive RFID tag for Identification and Sensing

Transcription

1 Zürich University Of Applied Sciences Institute of Embedded Systems InES Intelligent and passive RFID tag for Identification and Sensing (Presented at Embedded World, Nürnberg, 3 rd March 2009) Dipl. Ing. FH. Sven Keller Prof. Dr. Marcel Meli Contact: Marcel.Meli@zhaw.ch 1 1

2 Outline Who we are Introduction The case for intelligent and passive RFID Tags Challenges Our solution (work in progress) Tests and results Conclusions, future work 2 2

3 Who we are: InES, design examples Activities of the Wireless Systems Group Microcontrollers (Atmel, CoolRisc, Microchip, Propeller, PSoC/PRoC, Freescale,XMOS...) Wireless PAN systems (BT,ULPBT, , ZigBee/6LoWPAN) WirelessUSB, ANTS, Nanotron,... RFID (125 KHz MHz, UHF), RFID radar, pairing Activities in Low Power, use of Energy Harvesting, positioning 32x16 mm, 32-bit micro+radio / ZigBee compatible Portable RFID reader with Wireless PAN link Single chip (PRoC) 3 3

4 Who we are: InES/Wireless, design examples No Batteries Wireless Battery-less switch Very Low Power microcontroller + Radio, Use of EH module Compatible with / ZigBee Easy and intuitive pairing (Touch and Pair, Point and Pair) Ethernet to Gateway, with PoE (Jennic, Arm Cortex, ) Install And Forget Multichannel sniffer to monitor based protocols All channels can be monitored (1 microsecond accuracy) 4 4

5 Introduction What are RFID tags Circuits that will wirelessly communicate their identity by using the RF field of a reader Identity or another information is sent to the reader when required Passive tags They draw their energy from the reader Active tags Get their energy from another source (batteries) Frequency of operation LF: 125KHz -140 KHz (proximity, magnetic coupling) HF: MHz (proximity, magnetic coupling) UHD: 868 MHz, 900 MHz (long distance, electromagnetic) 5 5

6 Introduction Diagrams taken from datasheet of EM4102 (125KHz tag), EM Marin 6 6

7 Introduction What are RFID sensors? Sensors values are sent in place of identity, or mixed with identity Communicate their measurements to RFID reader. Several readers can be linked together (RSN RFID Sensor Networks) Temperature/humidity sensor Sensor in the body Active (external power source) Sometimes the sensor needs a lot of energy Passive Get their energy from the reader (magnetic/electromagnetic) Need no extra supply Can be used in environment where change of battery is difficult or impossible 7 7

8 Case for RFID sensors Current RFID tags/sensors: Mostly state machines with a sensor Dedicated devices (built for a particular application) Little flexibility in the type of sensor Little flexibility in adapting to other protocols There are also some intelligent tags, but most use external power sources Use of FPGA/CPLDs,ARM based micros,... The WISP is a passive sensor based on the MSP430 Works down to 1.8 volt 8 8

9 Case for intelligent and passive RFID sensors Introduces flexibility Different types of sensors can be connected without using dedicated chips Use of the microcontroller to enhance sensing (e.g. Averaging, filtering) Adaptation to different RFID protocols (load new programs) Allows emulation Emulation of RFID protocols (check robustness, speed,anticollision schemes,...) Passive emulation (nearer to real product), smaller size, cheaper Enhances security Use of processor power to implement better security (compared to state machines) 9 9

10 Challenges to overcome in order to realise intelligent and passive RFID sensors Low power consumption is critical Harvest and store energy Adding a programmable controller for intelligence (but which micro?) Controller should be fast enough to implement needed schemes Energy requirements at start up should be low Enough energy should be stored up to run sensor and protocols Precision in timing should be good enough for reliable communications Enough memory to allow implementation of protocols 10 10

11 Our solution (HW). The microcontroller - Works from 0.9V 3.3V (allows gains in distance) - Programmable DC/DC converter (for parts that need higher voltage) - Uses internal multiplier to run between 0.9v and 2v - CoolRISC CPU, 7.5 Mips at 15 MHz (more processing power if needed) - Specs typ 1 Mips (3V) better than most micros - Timers (can be used for modulation, timing) - Wake up counter (can be used for energy accumulation) - ADC (for Analog sensors that can live with 10 bits) - Comparator /voltage monitoring features (useful for energy accumulation) - 16K Flash (emulation of identity, protocols,...) - EEPROM Emulation, SPI - Easy to use serial programming and debugging interface 11 11

12 Our solution (HW). The micro 12 12

13 Our solution (HW). The micro Micro has already been used in low power applications such as battery-less switches - for ZigBee (2.4 GHz) (with Atmel Radio) - with BT low energy compatible radio (EM Marin EM9201) - for 868MHz (with Semtech SX1211) 13 13

14 Our solution (HW). The system Antenna Rectifier (Multiplier) storage Single or Dual limit low power comparator Power Switch Modulator (chosen according to frequency) Clock extraction Data extraction Sensor Micro 14 14

15 Energy Voltage Harvested energy (and voltage) decreases with distance To drive the processor and sensor directly, the harvested voltage must be at least be equal to VDDmin of processor/sensor The energy must also be sufficient to power the circuit. Saved energy Accumulate energy (using a capacitor and control circuit) and start the microcontroller/sensor when there is enough energy Minimum voltage must still be reached (unless a booster is used) Start up time of tag/sensor is longer The saved energy must so be used that it is enough for sensor processing and communication (energy efficient instruction set) 15 15

16 Our Solution (HW) 868 MHz dipole antenna Foreseen for data/clock extraction (not yet integrated) Voltage multiplier Energy accumulation EM6819 microcontroller and programming interface 16 16

17 Emulated tag (sending id like an EM1222) Features 64 bit ID number,data rate: Up to 256 kbit/s Frequency : 869 MHz, MHz, 2.45 GHz On-chip oscillator, On-chip rectifier Typical Applications Suited for long range, high-speed item identification Supply chain management, tracking and tracing Access control, asset control Licensing, auto-tolling, animal tagging Sports event timing 17 17

18 Emulated tag (sending id like an EM1222) Emulated features 64 bit ID number,data Id, (64 bits data, 11 bits header and CRC) 64 Kb/s Frequency : 869 MHz On-chip oscillator at 500 KHz Emulated Application Item identification 18 18

19 Our solution (software to emulate the tag) Procedure Run the microprocessor at a speed that will allow modulating at the proper data rate Address and header calculated and stored in microprocessor RAM (C code) Modulation routine written in assembler Start up, initialise sleep timer, go in sleep mode (make up for the energy lost at reset and initialisation) Wake up, send data, go in sleep mode for a given time to allow recharge of tank capacitor We can run the micro at 1Mhz (0.5 Mips) (Average power consumption at 2v is less than 50uA), which is just enough to achieve the modulation at the speed we want. For higher data rate, we can go up with the CPU clock

20 Tests (hardware used) Lab reader with variable output power capable of reading emulated UHF Tags (up to 500mW) EMDB412 with SkyeModule M9 UHF Ecotag reader from Trolley Scan reader (up to 3W). Used only to get more power. Not compatible with emulated tag 20 20

21 Results Tag at 2m from reader (500mW). 147nF buffer capacitor used to clearly show the changes on supply The Micro sends the identity (or id + sensor data) and then goes into sleep mode. Modulating signal from port pin Harvested power. Voltage on micro supply During sleep, the supply rises again 21 21

22 Results Tag at 2m from reader (500mW). 147nF buffer A better view of the modulation sequence The voltage sinks as the tag starts to send its information. The sending last about 1.2 ms. The energy is more that enough to send the data, even while using such a small capacitor as buffer V i = 3v. V i = 2v, C=147nF 22 22

23 Results Distance-Voltage-Measure PrintV1.2, no load, 10 stages, without zenerdiode 5V1 PrintV1.1, no load, 4 stages, without zenerdiode 5V1 PrintV1.2, 10 stages, load programm sleep, with zenerdiode 5V1 PrintV1.2, 10 stages, Rload = 39kOhm, with zenerdiode 5V1 generated voltage U [V] distance [m] The harvester power decreases with distance. The measurement show that up to about 2m, the voltage is still high enough for the emulated tag to send its identity (red curve). 44uF buffer capacitor, RFID reader at 500mW 23 23

24 Results generated voltage U [V] Distance-Voltage-Measure PrintV1.2, no load, 10 stages, R = 1MOhm, Pout=3W PrintV1.2, no load, 10 stages, R = 39kOhm, Pout=3W PrintV1.2, no load, 10 stages, R = 1MOhm, Pout=1W PrintV1.2, 10 stages, Rload = 39kOhm, Pout=1W distance [m] 44uF buffer capacitor, RFID reader at 1W and 3W. 39Kohms will be about the equivalent resistor for the emulated tag (at max current consumption). It can be seen that 6m range is possible using 1W (red curve) 24 24

25 Conclusions We have a platform that can be used as basis for intelligent passive RFID sensors So far, range > 2 meters for UHF (not optimised) The use of low power microcontrollers opens the door to integration of different types of sensors and the implementation of different RFID protocols

26 Future work We are just at the beginning. There is a lot to do. HW Improvement of range by optimising the RF front end Size reduction Consideration of other low power microcontrollers, especially those offering more memory and peripherals (Atmel?...) SW Implementation of different RFID algorithms In UHF (Including parts of Gen2) In the MHz In 125 KHz 26 26

27 Future work and thanks Applications Use of the tag for security tests/applications Use of the tag for early verification of new RFID protocols Thanks to EM Marin for their help 27 27

28 More information? Prof. Dr. Marcel Meli, Head of Wireless Systems Group Zurich University of Applied Sciences (ZHAW) Institute of Embedded Systems (InES) Technikumstr. 9 CH-8401 Winterthur Phone:

29 Questions???? 29 29