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Author: search.filters.author.Chongcheawchamnan, Mitchai

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    Leaf Sensor for Stomata Transpiration Monitoring Using Temperature and Humidity
    (2018-07-02)
    Pipitsunthonsan, Pronthep
    ;
    Sopharat, Jessada
    ;
    Sirisuk, Phaophak
    ;
    Chongcheawchamnan, Mitchai
    This paper presents a leaf sensor which was designed for stomatal transpiration detection. The sensor consists of a thermocouple, a humidity sensor and a programmed microcontroller. The thermocouple measures temperature difference between the leaf and its surrounding atmosphere while relative humidity of the atmosphere was recorded. The sensor design was verified with the standard tool and the image of stomata captured with a high-gain camera lens. From the experimental results, data collected from the developed sensor indicates the stomatal status. This proves the potentiality of the proposed sensor for stomatal transpiration detection.
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    Single-frequency-based dry rubber content determination technique for in-field measurement application
    (2012-08-27)
    Julrat, Sakol
    ;
    Chongcheawchamnan, Mitchai
    ;
    Khaorapapong, Thanate
    ;
    Patarapiboolchai, Orasa
    ;
    Kririksh, Monai
    In this paper, it is shown that extensive characterization and modeling of dielectric permittivity of rubber latex enables dry rubber content (DRC) to be accurately determined using a measurement at a single microwave frequency. The model is demonstrated in a low-cost sensing system based on a six-port reflectometer that is suitable for application in the field. To develop an accurate model, a wide range of samples (with the DRC in the range 28%-61%) is first measured using the Agilent Technologies 85070E dielectric probe system for a range of frequencies and at temperatures from 15°C to 39°C This data is then used to determine the parameters of a dielectric mixture model, which is based on the assumption that rubber latex is a diphase liquid consisting of the water and solid rubber. To take the effect of temperature and signal frequency on the molecular polarization behavior into account, the dielectric permittivity of the water is described using a Debye-type relaxation spectral function; and the frequency-dependant polarization parameter of neighboring inclusions is applied to the dielectric mixture model. After determining all the model parameters, it is then shown that the measurement of the sample's temperature and dielectric permittivity at a single frequency is sufficient to determine the DRC with a high degree of accuracy. Compared with the measurements made with the standard oven-drying method, using a single 2.5 GHz measurement the technique exhibits 0.36% DRC of mean absolute error with 0.28% DRC standard deviation, over the temperature range 15°C-39°C Finally, the technique is implemented with a six-port reflectometer. The measurement system employing the model is applied and tested with several fresh rubber latex samples. A wide range of measured results confirm the validity of the technique. © 2012 IEEE.
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    Transmission line model for an edge-coupled patch antenna
    (2008-01-01)
    Saksiri, Wiset
    ;
    Chongcheawchamnan, Mitchai
    ;
    Krairiksh, Monai
    In this paper, a simple transmission line model for an edge-coupled patch antenna is presented. The coupled section is modeled with a lump network which represents the mutual admittance between patches and from patch to ground. Theoretical analysis of two edge-coupled patch antenna models are compared by simulation and experiment in antennas designed to operate at the 2 GHz band. The proposed model predicts the return loss of the antenna accurately.
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    Design 2.4/5.8 GHz microstrip-to-coplanar strip transition
    (2007-12-01)
    Meelarpkit, Kumron
    ;
    Phongcharoenpanich, Chuwong
    ;
    Krairiksh, Monai
    ;
    Chongcheawchamnan, Mitchai
    A 2.4/5.8 GHz microstrip (MS)-to-coplanar stripline (CFS) transition (industrial-scientific-medical bands) is presented in this paper. The transition can operate at two bands simultaneously with a stepped impedance transformer and stepped impedance open stub. The circuit is proven with a design on RF060 substrate. Simulated and experimental results of the transitions connected in back-to-back style are in good agreement. The back-to-back transition exhibits return and insertion losses, which are better than 15 dB and 3 dB, respectively.
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    Tri-band Wilkinson power divider using a three-section transmission-line transformer
    (2006-08-01)
    Chongcheawchamnan, Mitchai
    ;
    Patisang, Sumongkol
    ;
    Krairiksh, Monai
    ;
    Robertson, Ian D.
    The analysis and design of a triple-band equal-split Wilkinson power divider are described. The circuit proposed is well matched and isolated at three arbitrary frequencies. The design procedure for the three-section transmission-line transformer based equal-split Wilkinson power divider derived from the ideal transmission-line model is provided. Simulated and experimental results in microstrip technology are presented to verify the idea and the derived equations. © 2006 IEEE.