# Freshness Monitoring of Packaged Vegetables
## 4 Intelligent Packaging (IP)
### Data Carriers
#### 4.3.1 Rfid  
RFID tags are devices that use electromagnetic field to monitor various measurements and are capable of communicating the readings through a reader that emits radio frequency waves to capture the data stored on the chip with the use of antenna in the RFID. Figure 16 shows a schematic diagram  
Figure 15: (a) Food FreshTM indicator. (b) Monitor Mark indicator. of components in a RFID system. Since the RFID tags have only antennas, other sensors and indicators are usually added to be used for freshness monitoring. To utilize the functionality of this technology, many sensors and indicators are added to these tags. RFID tags can be classified into three main types [187]:  
1. Passive tags with no batteries on the chip and are powered through the electromagnetic induction produced from placing the reader nearby. This type has a long shelf life, but a relatively short reading distance. 2. Semi passive tags that have a battery to power the chip, but the reader is essential to power broadcasting of the signal. This type is in active most of the time, and it also has a long shelf life. 3. Active tags that have their own battery to power. Table 7 provides a comparison of important features among passive, semi-passive, and active tags [188; 189; 1; 1; 23]. In recent years, there is an increasing trend toward employing these tags as a part of smart packaging systems. RFID tags are more convenient than barcode technology and can store more data while simultaneously providing real-time monitoring for more than one type of information (temperature, humidity, product information). Packaged vegetable monitoring normally uses the high frequency (HF) range. However, there are many factors that need to be considered with the use of this technology in smart packaging, for instance, their cost needs to be low for commercial use. The lifespan of such tags should cover the lifetime of the products monitored through the choice of appropriate battery life span in active tags, for instance. In addition, signal loss due to absorption by water in human bodies or moisture in packages may lead to low-level microwave signals which are maybe difficult to detect [105]. In [147], a vegetable monitoring system using RFID tags was integrated with respiration gas sensors to evaluate the quality of the monitored vegetables. The idea relied on measuring the amount of respiration gases: oxygen and carbon dioxide produced in the package. As shown earlier, the freshness of vegetables and fruits depends on the ratio of these two gases. To quantify the respiration rate, respiration quotient (RQ) defined as the ratio between the volume of CO\({}_{2}\) to O\({}_{2}\) per unit time is used. If \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Feature** & **Active** & **Semi-Passive** & **Passive** \\ \hline \multirow{3}{*}{Power} & \multirow{3}{*}{Battery} & Use battery to power chip, & \\  & & and power from reader to & Power from reader \\ \cline{1-1}  & & send data & \\ \cline{1-1}  & & & \\ \cline{1-1}  & & & \\ \cline{1-1}  & & & \\ \cline{1-1}  & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Comparison of important features among active, semi-passive, and passive tags. Figure 16: Radio frequency identification (RFID) technology. RQ is more than 1, then the freshness of packaged vegetables and fruits are degrading. This experiment was tried on green mume stored in plastic package for several days using different low-density polyethylene (LDPE) packages. It shows that RQ >1 as the quality deteriorates. The oxygen sensor used was a galvanic type, while the carbon dioxide sensor was a thermal conductive type. These sensors were connected to the RFID antenna forming RFID tags and placed inside a leafy greens package to monitor the gas concentration with storage. It shows how the oxygen concentration decreases while the carbon dioxide increases, indicating deterioration of the vegetables monitored. With the LED color changing from blue (fresh) to red (not fresh), indication of the freshness can be achieved.