• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.8
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• pp.571-575
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• 2018

The moisture content of a coffee bean affects its permittivity, and changing the moisture content of a coffee bean changes the taste of the coffee. The variation in the moisture content of a coffee bean can be predicted by the change in frequency and reflection coefficient values with respect to the variation in the permittivity of the bean when it is placed on a patch antenna. In this study, a dual-band patch antenna is designed, which has a moisture measurement band of 3.8~4 GHz that can measure the moisture level of a material; the antenna has a Wi-Fi transmit and receive band of 2.45 GHz. Through simulations and measurements, this study proved that the level of return losses changed from 3.6 to 4 GHz when the moisture content of a coffee bean changed from 2 to 15%. The moisture levels of rice and other beans can be measured with the designed antenna, which can be applied to various applications.

• Journal of Biosystems Engineering
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• v.32 no.4
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• pp.237-246
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• 2007

In this study, the microwave free-space transmission technique was used to measure the dielectric property of powdered food at microwave frequencies. The sample holder was designed and fabricated to transmit the microwave signals ranging from 1 to 15GHz. From the microwave propagation theory the equation expressing the dielectric property of powdered food was derived and validated by standard dielectrics. The dielectric property of powdered food such as wheat flour, coffee powder and milk powder was measured and analyzed. In the uniform range of bulk density of material, the real parts of permittivity of the food samples increased with the increase of moisture content, bulk density and temperature of the samples. The propagation properties such as attenuation and phase shift increased linearly as the moisture density of the food samples increased. As a measuring frequency of the moisture content, the X-band was recommended.