Development of Conductor-Backed Coplanar Waveguide (CBCWG) Moisture Sensors
Conductor-backed coplanar waveguide (CBCWG)l moisture sensor has been developed for a quick and accurate determination of moisture content in fresh mesocarp of the oil palm ftuits and cocoa beans. The sensor consists of three parts i.e, the coupling system representing the 1ranSition between coa...
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| Main Author: | |
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| Format: | Thesis |
| Language: | English English |
| Published: |
1997
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| Online Access: | http://psasir.upm.edu.my/id/eprint/8633/1/FSAS_1997_18_A.pdf http://psasir.upm.edu.my/id/eprint/8633/ |
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| Summary: | Conductor-backed coplanar waveguide (CBCWG)l moisture sensor has been
developed for a quick and accurate determination of moisture content in fresh
mesocarp of the oil palm ftuits and cocoa beans. The sensor consists of three parts i.e,
the coupling system representing the 1ranSition between coaxia11ine to the CBCWG,
the 2-layer structure of the CBCWG and sensing area. Previous wade done shows a
close relationship between the oil content and moisture content in the oil palm
mesocarp during fruit development The quality of cocoa beaus were also affected by
the moisture content in the beans. Thus, by measuring the moisture content in the oil
pahn mesocarp and cocoa beans, the quality of the oil palm fruit and the cocoa beans
can be obtained indirectly.
A functional relationship has been developed between scattering parameter 821
of the sensor and moisture content of the sample. The reflection and transmission
phenomena in the sensor structure can be represented by a signal flow graph and can
be simplified by using Mason's non-touching loop roles. The calculation of S21 is based
on the quasi-transverse electtomagnetic mode approxima1ion. Based on the theoretical
analysis, computer programmes written in FORTRAN programming language were
developed to do the calculations of the attenuation. A total of four different sensors
were developed in order to find out the effect of different gap between the conducting
S1rip and upper ground plane and protective layers on the attenuation values.
It is found that the big gap sensor gives a better sensitivity as compared to the
small gap sensor. This effect is probably due to the field density in the big gap sensor is
much higher than the small gap sensor. The sensitivity of the sensor is also drastically
affected by the thickness of the protective layer. This is due to the decreasing of the
interaction between the field and the sample as the thickness of the protective layer
increases. A comparison between the theoretical and experimental results for the oil
palm mesocatp was done. A close agreement has been found. The difference in value
ranges from only 1-4dB.
The fine relationship between the attenuation and moisture content for this kind
of sensor gives the possibility for the development of a compact and portable
microwave instrument for assessing the quality of cocoa and oil palm fruits that are sent
to the factory. |
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