3. INTRODUCTION
Moisture, commonly quantified by the volumetric water
content (VWC), is an important parameter in agriculture
due to its great influence on plant growth, nutrient
transport, and soil properties.
This work presents a novel use of battery-less
chipless sensor tags by offering a low-cost solution
to the pressing requirement of wide-area
monitoring of soil VWC in agricultural fields.
4. METHODOLOGY
• Working Principle Of Wireless Reader
The interrogator/reader consists of an RF source that sends the
interrogation signal to the ground. The signal impinges on the sensor
and backscatters from its surface.
The backscattered signal containing information of
the surrounding soil VWC is collected by the reader.
The collected data can be sent to the cloud servers and be processed
to extract the soil parameters.
5. METHODOLOGY
The sensor tag consists of
resonators each with a
resonant frequency.
An increase in the soil VWC
will cause a big change in the
effective dielectric constant
surrounding the sensor tag
and will result in a noticeable
change in its resonant
frequency.
6. PRINCIPLE
The chipless sensor tags use a wireless interrogation
approach with linearly polarized backscattered signal.
If the transmitter and receiver are in the same
polarization cluttering occurs and it becomes difficult
for the reader to filter the desired information.
This can be avoided by using a receiver and
transmitter that operate in cross-polarization.
8. Design Of Sensor Tag
Shorted dipole mainly depends on the resonant frequency
band in which the sensor tag needs to operate.
Commercial horn antennas operate above 500 MHz. A band
that is closer to the 915 MHz ISM (Industry, Scientific and
Medical) band is used here.
The lengths of the resonators are chosen to be 9 cm and 10
cm.
9. Fabrication
• i.Laser cutting the acrylic sheet.
• ii.Attaching copper tapes onto
the substrate.
• iii.Laser patterning of copper
tapes
• iv.Encapsulation of PDMS.
• v.Trimming the edges.
10. Experiment
S21(calibrated)(d B) = 10log10|S21(tag) − S21(isolation)|
Above is the equation for getting the calibrated S21
measurement.
Measuring the complex S21 without the sensor tag in front of
the reader gives us the S21(isolation).
Measurement taken with sensor tag in front of reader gives us
S21(tag)
11. Experiment
The measurements of the soil VWC at different
measurement points are conducted with a commercial
sensor also (Decagon 5TE).
VWC = 4.3 × 10−6ε 3 eff− 5.5 × 10−4ε 2 eff+ 2.92 × 10−2εeff
− 5.3 × 10−2
This is Topp equation for converting dielectric constant into
VWC.
12. Result
A DUAL-RESONATOR SENSOR TAG
EXPERIMENT IN AIR
Initially sensor tag is
oriented in such a way that
the resonators are tiled by
45o clockwise in one case
and 45o counterclockwise in
other case.
14. Conclusion
• ● The sensor tag can operate with
more than one resonator on the
substrate without one interfering
with the other.
• ● The sensor tag has a long
detectable range of 2.5 m with a
greater range than many previously
reported chipless wireless
sensors(Table).
• ● The sensor tag is applicable for
VWC change of 4% to 27% which is
normally seen agricultural fields.
15. Reference
• 1.S. Gopalakrishnan, J. Waimin, N. Raghunathan, S. Bagchi, A.
Shakouri and R. Rahimi, "Battery-Less Wireless Chipless Sensor Tag
for Subsoil Moisture Monitoring," in IEEE Sensors Journal, vol. 21, no.
5, pp. 6071-6082, 1 March1, 2021, doi: 10.1109/JSEN.2020.3039363.
• 2.: Liu, L.; Chen, L. Characteristic Analysis of a Chipless RFID Sensor
Based on MultiParameter Sensing and an Intelligent Detection
Method. Sensors 2022, 22, 6027. https://doi.org/10.3390/
s22166027.
• 3.F. Costa, S. Genovesi, and A. Monorchio, “Reading chipless RFID
located on metallic platforms by using cross-polar scattering,” in
Proc. 31st URSI Gen. Assem. Sci. Symp. (URSI GASS), Beijing, China,
Aug. 2014, pp. 1–4. 22 THANK
