Logistics information monitoring by means of rfid sensor tag

Logistics Information Monitoring By Means of RFID Sensor Tag
Lih Guong Jang
Information & Communication Technology Department
ITRI
Hsinchu, Taiwan
LihGuong@itri.org.tw
Sung-Fei Yang
ITRI
Hsinchu, Taiwan
doz@itri.org.tw
Tai-Shen Ho
ITRI
Hsinchu, Taiwan
hots@itri.org.tw
Li-Yen Lai
ITRI
Hsinchu, Taiwan
Brucelai@itri.org.tw
Chin-Chung Nien
ITRI
Hsinchu, Taiwan
CCN@itri.org.tw
Abstract—Evolution of RFID Tag is advanced from ID-functioned
application phase into the sensor-integrated stage, leading to a
more diversified application era. Semi-Passive RFID Temperature
Sensing Tag applied in logistics field features tracking and real-
time functions. The price-performance ratio, especially for the type
of “time-temperature” Semi-Passive RFID Sensing Tag, is even
more outstanding.
This paper reveals that temporal domain temperature
monitoring can be achieved by a Semi-Passive “time-temperature”
sensing tag when it is applied to logistics field. Vendors can apply
it either in off-line temperature data recording or online real-time
wireless transmission.
Keywords- Reader; sensor tag; RFID; semi-passive
I. INTRODUCTION
During the delivery of the products, lacking of real-time
sensing and alerting functions as well as the emergency
handling mechanism leads to the occurrence of merchandise
heat exposure and re-freezing and it degrades the quality of
the products seriously. Those reasons are influential for
customers while making purchase decisions. By Semi-
Passive RFID Temperature Sensing Tag, remote real-time
monitoring and precise controlling mechanism can be
achieved during the delivery, benefiting to the improvement
of cold-chain fresh-maintained tracking technology, together
with the advantages of cost reduction and quality sustain.
Semi-Passive RFID Temperature Sensing Tag introduced
in this paper features sensitive temperature sensing function
and history data recording mechanism. To extend the battery
life, intelligent switch is incorporated to appropriately switch
off the circuit with high power consumption. In the
meantime, low power circuit design with deep-sleep
firmware programming is also incorporated. In order to
improve the data transmission and reading in distance,
antenna is designed by both couple and loop approaches,
which increase the impedance and inductive magnetic flux
density, reaching to antenna size down and antenna gain
effects.
II. SENSOR TAG ARCHITECTURE
As for hardware design [1] for Semi-Passive RFID
Temperature Sensing Tag, the following points regarding
application environment should be taken into account:
(1) Inside the airtight steel cargo container, boxes densely
stacked cause the shielding of radio waves, interference
and transmission loss; and
(2) To effectively keep temperature for the light-weighted
boxes, the size of the Temperature Sensing module is
restricted. Other impacts on temperature sustain include
the physical factor of cargos.
Therefore, high power is required to overcome the
restrictions in communication.
RF interface used for Semi-Passive RFID Temperature
Sensing Tag is EM4325 RFID chip, compliance with EPC
Class3 Gen-2 and ISO / IEC 18000-6:2010 Type C and Type
D compatible [2][3], is supplied from EM Microelectronic.
This is the chip with serial peripheral interface and is capable
of connecting with external temperature detection circuit.
Temperature detection circuit consists of a sensing controller
(Ti MSP 430), EEPROM (capable of temperature data
storage), power-saving and long life rating circuit design and

T type thermocouple temperature sensing and conversion
devices, which is shown as follows:
Figure 1. Sensor-Tag hardware architecture diagram
Software is complied with the low-power hardware
circuit design requirement, including active devices with
deep-sleep functions (MCU, power detection IC, EEPROM),
together with electronic switch and firmware to implement
deep-sleep functions, at the same time, to achieve peripheral
power-saving control.
Whether sensor tag receives an external command or
records temperature with automatic timing is proceeded by
main procedure process mixing with external interrupt
mechanism to wake up low power deep-sleep mode to
achieve the optimum battery life. Figure 2 shows the sensor-
Tag firmware architecture.
Figure 2. Sensor-Tag firmware architecture diagram
Command from RFID reader is transmitted by RFID
transceiver to main procedure process. To implement the
process, main procedure process follows the corresponding
command function and pre-set parameter values based on
command / response unit. If it is set as time relevant
command, then timer process is activated. If it is set as
inventory command, then temperature data analysis process
is activated.
Besides, when automatic timing interrupts in the timer
process, sensor tag move to implement temperature data
analysis and storage process.
A. Antenna Design
Since the antenna is operated in the cargo container, a
harsh environment and compact form factor design is
required, the antenna mentioned in this paper is designed
based on 925 MHz, 1/4 spectrum, with both couple and loop
approaches, which increase the impedance and inductive
magnetic flux density to facilitate the conjugate match,
reaching to antenna size down and antenna gain effects,
which enables effective reading distance to 4.5m in the cargo
container.
Figure 3. Antenna far field radiation pattern simulation diagram
The size for antenna is 52×15mm2
, and tag antenna is
integrated with temperature sensor circuit. FR4 glass fiber
substrate is used withεr = 4.3 for dielectric constant and
loss tangentδ = 0.02 for dissipation factor. The input
impedance for EM4325 Tag IC is ZA=7.9-j158Ω, the far
field radiation pattern is simulated by HFSS and the results
shown as Figure 3.
B. Sensor Tag Hardware Prototype
During the delivery of the products, power consumed by
Semi-Passive RFID Temperature Sensing Tag is mainly
from the temperature logger and reader response. Therefore,
select energy saving components and power supply turn-off
circuit design, adopt exchange power saving mechanism of
optimum temporal domain – power control algorithm for
power management, and replace power-consumed standby
mode to interrupt operation mode for MCU accompanying
with deep-sleep mode to achieve efficient power control.
As shown in Figure 4, Semi-Passive RFID Temperature
Sensing Tag module is developed by using FR4 glass fiber
substrate and the size is 6.8 x 6.2 cm. Min components for
sensor tag include:
The sensor control, in which a 16-bit RISC CPU is
adopted from TI MSP430, is with 1.8V to 3.6V low supply
voltage and 0.1uA to 300uA current. The TI CPU Serial
communication interface functions as asynchronous UART
or synchronous SPI interface. In this development we apply
SPI as a main data Bus design features.
The storage function of temperature logger design
includes the SPI Bus serial EEPROM memory with 2.5V to
5.5V and 5mA operation power supply, providing from
Micro Chip 25LC1024.
The temperature sensing design includes the T type
compensated thermocouple wire (constantan and copper
junction) and the temperature conversion ADC IC: MAXIM
MAX31855TASA+T IC (hot-junction compensation and
digitizes the signal from a T type thermocouple). The

converter resolves temperatures to 0.25℃, allows readings as
high as +400℃ and as low as -250℃. This ADC IC has SPI
interface and require 3V to 3.6V and 1.5mA operation power
supply.
Figure 4. Sensor-Tag prototype
C. Sensor Tag Software Design
According to the study from Hoffman [4], about 30% of
temperature-sensitive products suffers from value loss during
transportation, indicating that during the refrigerated
transportation, if the storage temperature increases
(decreases) 10℃, the biochemical reaction (plant respiration)
of fresh fruits and vegetables will increase 2 to 3 times
(reduced to 1/2 to 1/3), in other words, the storage life of
fresh fruits and vegetables reduces 2 to 3 times. In fact,
different types of fresh fruits and vegetables have different
storage temperature configuration, if lower than the optimum
temperature storage in some fresh fruits or vegetables, the
hypothermia disability is easy to happen, and therefore the
accuracy of temperature monitoring becomes very important
Temperature fluctuation detecting and recording for
insulated box can be reviewed and regarded as reference
before next shipment for fruits and vegetables is arranged, in
order to reduce the losses caused during long-journey
transportation. The Semi-Passive RFID Temperature Sensing
Tag developed in this study can receive information writing
from RFID Reader, or track the real-time temperature back
to backend control center from RFID reader.
The two main function of the microcontroller
programming for the management of data access and
external communications, in which data access can be
implemented via two approaches: (1) Users can set up sensor
tags to proceed automatic timer recording and the length of
time can be determined by users. (2) Users can remote
control at the back-end control center.
The core state machine diagram of Sensor tag is shown
as Figure 5 and the main functions are illustrated as follows:
(1) In the Waiting Power state, sensor tag continues waiting
for power supply. It enters into the Tag initial state when
power supply is completed. (2) In the Sensor Tag Initial state,
the MCU procedure process initializes the peripheral I/O port
interface, loads parameters from flash memory and performs
self-test procedures. When the self-test is completed, it enters
into the Protocol initial state. (3) In the Protocol initial state,
the MCU procedure process initializes the ISO/IEC 18000-
6C protocol modules. When it is complete, the process
thread enters into the Waiting command state. (4) In the
Waiting command state, the MCU procedure process
continues waiting for a command. After a command is
received, the process thread enters into the Executing
command state. (5) In the Executing command state, the
MCU procedure process will check the CRC format. If the
CRC fails, it will react with an error code return. In the
contrast, if the CRC check is successful, the command will
start execution. The main process return the execution results
after the command is executed, and return to the Waiting
command state. (6) When the sensor tag battery is less than
1/2 power supply, the main process will immediate access to
the Low Power state. (7) When the main process enters into
Fail state, it means self-test fails. It is necessary to check the
sensor component if there are connection error or incorrect
firmware parameters setting.
Figure 5. Sensor-Tag core state machine diagram
III. SYSTEM INTEGRATION
The backend control center application provides user
interface along with an entry point for user operation. Users
remote control RFID Reader’s access to sensor tag data
through RF signal (transmit energy to tag and read
information back from it by detecting the backscatter
modulation). Within the effective distance, the sensor tag
will receive the transponder signals from interrogator, and
then based on the communication protocol setup and internal
logic operation results; the sensor tag will backscatter the RF
carrier from interrogator backscatter modulation, and act as a
carrier for return data from the sensor tag.
We apply the Chunghwa Telecom 3G/GPRS
telecommunications services and ITRI corporate internet for
the prototype system integration testing. The Vehicle
simulation device has COM port to TCP function for the
UHF RFID Reader connection, and can transmit the sensor
tag data to the backend (Control center simulation). Figure 6
shows the application architecture and prototype
specification are listed as follows:
• 1 insulated box （rate of heat loss (U-value）<0.424
W/m2K，±2℃，60L，weight<5.5kg）

• 2〜3 eutectic plates (2.6kg weight each, thermal
storage capacity 100〜120KCal）
• 1 RFID Semi-Passive RFID Temperature Sensing
Tag
• 1 telematic module (GSM/GPRS)
• 1 RFID Reader （EPC C1G2 certified）
• 2 RFID antennas
• Working Frequency ： UHF
• Communication Protocol ： ISO18000-6C （ EPC
C1G2）
• Reading Range：4.5m
• Power Supply：12VDC
Figure 6. Sensor-Tag application architecture diagram
A. Power Consumption Test Result
The component quantity for the schematic design is
optimized, including the MCU, Memory, Real Time Clock,
Temperature Conversion IC, Temperature Sensor and RFID
Tag IC, among which the MCU is configured into working
mode and deep sleep mode. When the MCU, memory and
peripherals operate temperature recording for <2 seconds as
shown in Figure 7, a 1400mAh battery operated in the
1.8mA power consumption latest up to six months or
more.
Figure 7. Sensor-Tag current test recoding diagram
B. Temperature Accuracy Test Result
The temperature sensing component used in the
Sensor tag is T-type thermocouple sensors, featuring the
rapid response. The temperature measurement range is
designed from -30℃ to 60℃. Measurement is implemented
by using an insulated box with two eutectic plates inside.
The test results are shown in Figure 8. Upon the comparison
among the Sensor Tag introduced in this paper, commercial
industrial thermometer and standard thermometer, the error
is within 0.2~0.6℃.
Figure 8. Sensor-Tag temperature test recoding diagram: (a)effect by
power ON/Off, (b) 0.2~0.6℃ difference, (c) 0.5~1.1℃ difference
IV. CONCLUSION
The semi-passive RFID temperature sensing tag
introduced in this paper uses thermocouple wire, which is
closely related to the compensation coefficient, the
temperature-sensing thermocouple wire length and material
type.
T-type thermocouple wire (constantan and copper
junction) transmits signal to the circuit through the
MAX31855 T+ and T- terminal blocks connection. The IC
modulation circuit converts the thermocouple’s signal into a
voltage compatible with the input channels of the ADC.
Before converting the thermocouple voltage into
equivalent temperature value, it requires compensation for
thermocouple “cold” junction (MAX31855 T+ and T-)
and the difference of the actual reference value of 0℃.
Through the cold junction compensation, MAX31855
proceeds detection, correction and calculation the
thermocouple temperature for the reference junction
temperature fluctuation.
Typically, temperature sensor and logger devices require
a specific machine to read out temperature data. However,
RFID Reader can obtain information in real-time to the users
from our developed semi-passive RFID temperature sensing
tag. Besides, precise controlling mechanism can be achieved
during the delivery, benefiting to the improvement of cold-
chain fresh-maintained tracking technology, together with
the advantages of cost reduction and quality sustain.
REFERENCES
[1] Sensor-enabled RFID tag handbook. BRIDGE - Building Radio
frequency IDentification solutions for the Global Environment,
January 2008
[2] Specification for RFID Air Interface. EPC Radio-Frequency Identity
Protocols Class-1 Generation-2 UHF RFID. Protocol for
Communication at 860 MHz-960 MHz. Version 1.1.0.。
[3] Specification for RFID Air Interface. EPC Radio-Frequency Identity
Protocols Class-1 Generation-2 UHF RFID. Conformance
Requirements. Version 1.0.4.。
[4] Hoffman, W. (2006). “Hot Market, Cool Freight. Journal of
Commerce,” 2006,1, 1.

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