Instrumentation & Measurement Magazine 24-3 - 56

the diseases of the plants are measured through RGB camera sensors. This indicates RFID sensors need to be combined
with some other important sensors to obtain all plant growth
parameters. Additional information, such as plant disease,
weeds, and pest information, should also be included to make
the system more reliable and robust.

Harvest Quality Monitoring
Harvest quality and safety is a great concern for sellers and
consumers. The freshness of the handpicked fruits/vegetables
needs to be carefully monitored as they have short shelf lives.
Studies showed that the freshness of the fruits/vegetables is
highly dependent upon the relative humidity, environment
temperature, and specific gas concentration. Recently, RFID
tags are being explored to monitor the freshness of vegetables. The tags are fabricated with different types of sensors to
measure different parameters. RFID sensors are now used
to measure the temperature and relative humidity of packaged vegetables. The tags use the add-on microchip and are
developed to operate on HF (13.56 MHz) frequency range.
The proposed RFID sensors could measure the transpiration
process and the water loss process for the vegetables via the
temperature and relative humidity sensors, respectively, to

Fig. 6. A typical example of vegetable quality monitoring with RFID sensors.

detect the texture and quality of the products [87]. Fig. 6 presents a typical example of vegetable monitoring operation with
RFID sensors.
Additionally, a semi-passive, ultra-low power (8.9 mW)
RFID add-on microchip sensor was developed to determine
the freshness of the vegetables. The sensor integrates the
temperature, relative humidity, gas concentration, and light
intensity sensors to comprehend the freshness and logistics
of the fruit (apples) [88]. To obtain the expiration date of the
vine-ripened tomatoes and monitor the food inventory, an
RFID sensor was integrated with a temperature sensor and
integrated with a shelf life monitoring model. Furthermore,
metrics such as outdating cost, penalty cost, and hazard cost
were also defined to analyze the sensitiveness of the models. The results from the developed sensor and model showed
promising performance to comprehend the freshness of vegetables [88].
Freshness of green leafy vegetables are also measured
through their greenness. To measure the greenness of the
leafy vegetables, accumulated ammonia gas needs to be measured. Ammonia gas is toxic to the leafy vegetables, and the
accumulation occurs during the post-harvesting period. The
accumulated ammonia gas can ruin the greenness of the leafy
vegetable and can deteriorate the freshness of the products.
One such study was [89]. The experimental results and analysis depicted that early detection of ammonia gas formation
from the leafy vegetables can define the expiration date and
help to maintain the food quality.
Grains like wheat, rice, peanuts, mustard, and lentils
tend to absorb moisture under normal atmospheric temperature when they are stored in the warehouse or in storage
inventories of farms. The accumulation of moisture content causes a fungus called Aflatoxin, which can deteriorate
the quality of the food grains and also alters the weight and
texture of the grains, affecting the economic value for the
farmers, sellers, and consumers [90]. Thus, it is paramount
to monitor the moisture content of the food grains. Recently,
Sharma et al. [90] developed a low-cost RFID sensor integrated with a chemical sensor (CuMOF sensor) which can
track the gunny bags and can monitor the moisture content
of the grains. A grain monitoring system is also developed

Table 8 - Example of applications of RFID sensors to the harvest quality monitoring
Parameters

Measurement
range

Sensitivity

Quality monitoring [87]

-40-105 °C,
30%-100% RH

2.29%
(temperature),
1.5% (humidity)

Add-on RFID
sensors

13.56 MHz

0.3 cm

50-200 °C

Add-on RFID
sensors

13.56 MHz

Moisture [91]

7%-40% RH

Chipless RFID
sensor

915 MHz

CO2 gas [93]

0%-100%

Add-on RFID
sensors

860 MHz-960 MHz

Temperature of
vegetables [88]

Sensor type

IEEE Instrumentation & Measurement Magazine

Operating
frequency

Detection
distance

May 2021

Instrumentation & Measurement Magazine 24-3

Table of Contents for the Digital Edition of Instrumentation & Measurement Magazine 24-3