# Freshness Monitoring of Packaged Vegetables
## 4 Intelligent Packaging (IP)
### Data Carriers
#### 4.3.1 Rfid
However, more research and development are needed in terms of finding less bulky inexpensive circuits to ensure the practicality of such techniques in monitoring freshness without much affecting the final product cost or even the packaging and processing cost [147]. Other smart sensors with RFID tags for vegetable ripening evaluation were demonstrated [190; 191]. Another smart RFID label, introduced in [128], used several sensors' temperature, humidity, and ammonia. This system can be used in logistic chains monitoring. The storage area or the display units can have these labels installed to monitor real-time temperature variations. These smart tags can be attached to each bagged or packaged vegetables. Thus, more information can be extracted about the freshness of vegetables or even about the growth rate of pathogens. The multisensory platform that was made of printed electronics is then integrated with a screen-printed HF RFID antenna label, from where the data can be read through an RFID reader. In general, during the measurement mode, the data from sensors are measured one by one, then are written in memory until it is read by an external reader. The presence of a resistance temperature detector (RTD) on the RFID label is not only to provide temperature reading, but also to act as temperature compensator for the other two sensors (humidity and ammonia) because of the strong dependence of ambient absolute humidity and the sensitivity of their sensing layers to temperature. The RTD values were in the range of 500-550 \(\Omega\) with a measuring range of -10 \({}^{\circ}\)C to 80 \({}^{\circ}\)C. In addition, the resolution of this sensor was 1 \({}^{\circ}\)C [128]. The humidity sensor uses the variation of dielectric constant with water vapor. This constant is much higher than the one in interdigitated electrode's (IDE). Therefore, absorption of moisture will be reflected as an increase in the capacitance, and hence humidity can be measured. This sensor gives relative humidity, after compensating for temperature. The advantage in this RFID label is that the usual drawback of cross-sensitivity between temperature and humidity, which was noticed in earlier studies in printed RTD and humidity sensors [167], is absent. The reason for that is the DP protection layer on top of the RTD, which has a low water vapor permeability, preventing a direct contact between water vapor and the RTD [128]. The source of power in this system is a battery with a capacity of 150 mAh. It can last up to 57 days knowing that the periodicity of the measurement is every 60 min for a duration of 30 s. This lifetime is enough for monitoring storage and display temperature and humidity variations and can provide a real time update [128]. TempTRIP(r) RFID temperature tags are a commercial example of this technology used to monitor and record the temperature and time throughout the supply chain, and data can be collected later through readers [192]. It has an operating range of \(-\)30 \({}^{\circ}\)C \(\pm\) 50 \({}^{\circ}\)C and temperature accuracy of \(\pm\)0.2 \({}^{\circ}\)C [193]. Another example is Easy2 log(r) which is a semi-passive RFID tag that is also used to monitor temperature with an operating range of \(-\)20 \({}^{\circ}\)C \(\pm\) 70 \({}^{\circ}\)C and temperature accuracy of \(\pm\)0.5 \({}^{\circ}\)C [194].