1. Proposed Oxygen Concentration Monitoring System of Food Packaging
Monitoring Oxygen Concentration in the Food Package Usingf a Novel RFID Tag with a Self-Powered Colorimetric Oxygen Sensor
Kihwan Eom , Jinsu Han
Department of Electronics and Electrical Engineering, Dongguk University
Introduction
Radiofrequency identification (RFID) technology has replaced existing barcodes to facilitate network and intelligent product management and distribution while ensuring security, safety, and environmental friendliness. In particular, as RFID and sensor technologies have advanced, more and more attention is being paid to smart RFID tags to fuse these two technologies.
Intelligent food packaging can provide consumers with reliable and accurate information on food quality and safety by monitoring the condition of packaged foods or the surrounding environment. It can be achieved by three main technologies: (1) indicators, which aim to provide qualitative information on food quality by means of a color change: (2) sensors, which allow for a rapid and definite quantification of analytics in foods: and (3) data carriers, such as barcodes and RFID tags, which are specifically intended for storage, distribution, and traceability purposes .
Various factors related to the quality and safety of packaged foods (e.g., temperature, oxygen, carbon dioxide, and volatile amines) has been monitored using visual indicators and smart RFID tags .
However, it is necessary to monitor them using smart RFID tags with colorimetric indicators, which not only enable consumers to check food quality and safety with the naked eye, but also transmit the information with additional data such as details of food and manufacturer. Therefore, smart RFID tags integrated with sensor-type indicators is essential for intelligent food packaging .
This paper reports an oxygen concentration monitoring system for intelligent food packaging using a passive RFID tag integrated with a self-powered colorimetric oxygen sensor. Oxygen concentration is one of the most interesting parameters in food packaging because oxygen is involved in the biochemical and microbial spoilage of foods.
The proposed system is composed of UHF band RFID tag, self-powered colorimetric oxygen sensor, interface circuit, reader, and server. This online monitoring system can display the oxygen concentration quantitatively as well as qualitatively, and divided into four grades: very high, high, medium, and low. In order to test the performance of our new system, we have monitored the oxygen concentration in a package of tomatoes online.
Proposed Oxygen Concentration Monitoring System of Food Packaging
Figure 1 shows the block diagram of proposed oxygen concentration monitoring system of food packaging.
Figure 2 illustrates the block diagram of passive type UHF band RFID tag.
The Speedway revolution UHF RFID reader was used for monitoring, and the specifications are shown in Table 1.
A self-powered colorimetric oxygen sensor is self-generation-type Zn-MB cell non-enzymatic sensor, and reduction electrode was performed using a carbon paper (JNT40) and methylene blue hydrate, and oxide electrode was performed using the zinc.
Color changes of Zn-MB cell depending on oxygen concentration at 25℃ are shown in Figure 3 .
< Fig. 1 Block diagram of proposed monitoring system >
< Fig. 2 Block diagram of Passive type UHF band RFID tag >
< Fig. 3 Color changes of Zn-MB cell depending on oxygen concentration >
Table 1. Specifications of the RFID reader
Characteristics
Content
Interface protocol
EPC global UHF Class 1 Gen 2 / ISO C
RF frequency
900MHz ~ 930MHz
RF range
10cm ~ 10m
Transmit power
+10.0 ~ 30.0dBm
Power consumption
24V
Operating temperature
-20°C ~+50°C

2. < Fig. 5 The interface circuit >
The voltages generated at a constant current density were plotted against the oxygen concentration, and As shown in Figure 4, this plot gave a straight line, which was expressed in Equation (1).
The interface circuit of the sensor-type oxygen indicator is shown in Figure 5.
Figure 6 is a photograph of the combined system of the RFID tag and the colorimetric oxygen sensor.
The program of monitoring system based on Microsoft Foundation Classes (MFC), and monitoring system interface consists of 3 level of hierarchy, and is shown in Figure 7.
The grade of oxygen concentration was determined based on the color of sensor-type oxygen indicator, and Table 2 is a description of each grade obtained from the experimental data.
Figure 8 shows the flow chart of the oxygen concentration monitoring system of food packaging.
Figure 9 shows the main interface of the software. In the figure, Box A shows the four grades of the test result, Box B shows the received data from the tag, Box C shows the measured data.
R2 = 0.998
Oxygen Concentration (%) = × Voltage (mV) (1)
< Fig. 4 Dependence of the sensor voltage on oxygen concentration at 25°C >
< Fig. 5 The interface circuit >
< Fig. 7 Three Level of monitoring system >
< Fig. 6 The photograph of the combined system of RFID tag and oxygen sensor >
< Fig. 8 The flow chart of the oxygen concentration monitoring system >
< Table 2. Description of each grade >
Status
O2 Concen.(%)
O2 Sensor out(mV)
Indicator Color
Very High
15<
450<
Blue
High
10~15
300~450
Light Blue
Medium
5~10
150~300
Pale Blue
Low
<5
<150
Colorless
<Fig. 9 Interface of the software >

3. Experiments Conclusions
We put tomatoes in the food package for the oxygen concentration experiment, and Figure 10 is a photograph of experimental device.
Experimental conditions were a temperature of 25°C and a humidity of 30%.
First we conducted experiments for the recognition distance when configured with only the low pass filter circuit to the interface circuit.
Tables 3 shows the maximum recognition distance of vinyl and plastic food packaging were 3 meters and 2 meters, respectively.
The next experiments were for the interface circuit configured as a filter and the storage capacitor, and experimental conditions were the same as above.
Tables 4 shows the maximum recognition distance of vinyl and plastic food packaging were 3.1 meters and 2.07 meters, respectively.
A storage capacitor increased the recognition distance.
We first put tomatoes in a closed plastic package, opened the box after 27 hours, and then closed it again after 3 hours. During this period of 36 hours, the oxygen sensor voltage was online measured every 3 hours.
The environmental conditions were a temperature of 25°C, a humidity of 30%, and a distance was 2 meters.
Figure 11 shows an experimental graph of the oxygen concentration in a package of tomatoes.
As shown in Figure 11, the voltage decreased gradually to 420 mV for 27hours, implying the oxygen concentration in the package declined from 20% to 14%. This is because the tomatoes in the plastic box breathed to consume oxygen.
Figure 12 shows the monitoring screen of the oxygen concentration in the package after 18 hours.
< Table 3. Recognition distance of the monitoring system without storage capacitor >
Vinyl Package
Plastic Package
Distance(m)
Success rate(%)
<3
100
<2
3.5 85
2.5 4 70 3
< Fig. 10 The photograph of experimental device >
< Table 4. Recognition distance of the monitoring system with storage capacitor >
Vinyl Package
Plastic Package
Distance(m)
Success rate(%)
<3.1
100
<2.07
3.58 85
2.55
4.05 70
3.03
< Fig. 11 Oxygen concentration in a package of tomatoes >
< Fig. 12 The monitoring screen >
Conclusions
Recently many consumers are becoming more interested in the quality and safety of food, and demand information about them.
Also the indicator is one of food packaging technology and gives information about the change of colors. Therefore, it is absolutely necessary to have a system in which oxygen concentration can be confirmed at a long distance which is a distribution process, and consumers can check color change at a close distance.
The smart RFID tag integrated with a sensor-type indicator is essential for intelligent food packaging.
In this study, we have monitored the oxygen concentration in the food package using a new system composed of passive UHF band RFID tag, self-powered colorimetric oxygen sensor, interface circuit, reader, and server.
The interface circuit is a passive type, and the storage capacitor of interface circuit can be used as an auxiliary power source for the passive RFID tag.
This monitoring system can show the oxygen concentration with four grades: Very High, High, Medium, and Low. The grade of oxygen concentration was determined based on the color of sensor-type oxygen indicator and the experimental data.
This online monitoring system exhibited changes in the oxygen concentration with time in a package of tomatoes quantitatively.
First we experimented for the recognition distance when configured with only the low pass filter circuit to the interface circuit. The maximum recognition distance of vinyl and plastic food packaging were 3 meters and 2 meters, respectively.
The next experiments were for the interface circuit was configured as a filter and the storage capacitor. The maximum recognition distance of vinyl and plastic food packaging were 3.1 meters and 2.07 meters, respectively. Using a storage capacitor, we increased the recognition distance.
In addition, it displayed the oxygen concentration with color changes and thus enabled consumers to sense the oxygen in a food package even with the naked eye.