Development of a Dual Frequency Microwave Moisture Sensor System Based Circular Microstrip Antenna
A dual frequency microwave moisture sensor based on far field reflection technique using two circular microstrip antenna pairs was developed and used to measure moisture content of various lossy liquid solutions. The sensor used two dielectric resonator oscillators as microwave sources in the X-b...
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| Main Author: | |
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| Format: | Thesis |
| Language: | English English |
| Published: |
2005
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| Subjects: | |
| Online Access: | http://psasir.upm.edu.my/id/eprint/6219/1/FS_2005_17.pdf http://psasir.upm.edu.my/id/eprint/6219/ |
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| Summary: | A dual frequency microwave moisture sensor based on far field reflection technique
using two circular microstrip antenna pairs was developed and used to measure
moisture content of various lossy liquid solutions. The sensor used two dielectric
resonator oscillators as microwave sources in the X-band with oscillating
frequencies of 8.48 and 10.69 GHz. Two wideband coaxial detectors were used to
measure the amplitude of the reflected signals.
Theoretical calculation based on quasi-static cavity model with infinite ground plane
approximation for circular microstrip antenna was carried out to evaluate design
parameters such as antenna radius at resonance, efficiency, gain, bandwidth, feed
point location ... etc. To this end a Visual Basic program was written and
documented to evaluate all the design parameters needed Antennas edge separation distances and E-plane configurations were considered
carefully to reduce mutual coupling between elements. The final layout was printed
on a single dielectric substrate. Radiation characteristics of the antennas, Sparameters
and input impedances at resonance were measured using vector network
analyzer and they compared satisfactory to theoretical simulations.
The optimum thickness of the sample holder and the air gap between the antennas
and the sample holder were evaluated experimentally to ensure maximum signals at
the detectors. Good agreements to theoretical expected values were found. The
analysis of the complex electromagnetic waves in this reflected-type system is
presented using signal flow graphs and solved by Mason's non-touching loops rules.
The whole sensor system was interfaced to a personal computer through data
acquisition card. This automated the calibration procedures and facilitated the
switching time between the sources. Graphical user interface panel was written in
LabView language to guide the user through calibration measurements and.
As an application example, the whole system was tested using diluted rubber latex
with moisture content ranging from 39.8 to 95.2% wet basis. The sensor has
predicted moisture contents with standard error of performance of *O.49% moisture
content using weighted average calibration method. Moisture contents of latex
samples in temperature range of 25 to 63°C were measured successfully with an
accuracy off 1.3% MC wet basis compared to standard oven drying method |
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