平行3線電極を用いた低周波帯での土壌の誘電率測定

カテゴリ：研究会(論文単位)

論文No：IM25010

グループ名：【A】基礎・材料・共通部門 計測研究会

発行日：2025/6/17

タイトル(英語)：Measurement for Soil Dielectric Constant at Low Frequencies Using Three Parallel Wire Electrodes

著者名：柴田 幸司(八戸工業大学),小林 正樹(八戸工業大学),高崎 和之(東京都立産業技術高等専門学校),平栗 健史(日本工業大学)

著者名(英語)： Kouji Shibata(Hachinohe Institute of Technology),Masaki Kobayashi(Hachinohe Institute of Technology),Kazuyuki Takahashi(Tokyo Metropolitan College of Industrial Technology),Takefumi Hiraguri(Nippon Institute of Technology)

キーワード：誘電率測定,平行３線,インピーダンス測定,Dielectric measurement,Parallel three lines,Impedance measurement

要約(日本語)：同軸構造を有する高周波ｺﾈｸﾀの先端に2本のグランド線を配置する電容量型センサーを提案した. 低周波帯での土壌の誘電率の精密測定は, このセンサーにshort, openおよび基準物質（SOM）と比較する公式を適用した. ﾒﾀﾉｰﾙやｴﾀﾉｰﾙの誘電率は, このセンサーや入力ｲﾝﾋﾟｰﾀﾞﾝｽの校正・測定手順を用い, 基準物質を純水として10 - 200MHzの周波数帯域で推定した. 更に, 推定値は遮断円筒導波管反射法による推定値やデバイ分散式の理論値と比較した. 電極を乾いた土壌および複数種類の水分を含む土壌に差し込んだ場合の誘電率も10 – 200MHzで測定して提案手法の有効性を検証した. その結果まず, Nｺﾈｸﾀの平行3線電極を有する静電容量センサーによる10 - 100MHzの周波数での高精度な計測を, ﾒﾀﾉｰﾙやｴﾀﾉｰﾙ等の誘電率の虚部（導電率）が低い試料に対して確認した. 特に, 遮断円筒導波管反射法では不可能な低い周波数（10MHz）でも, 本研究で提案するNｺﾈｸﾀの平行3線の構造を有する電極にて高精度な誘電率推定を確認した. 次に, 上記電極を用い計測したDry soil（乾いた土壌）の誘電率が, 10 - 200MHzにて空気の誘電率に近い値となることも確認した. 更に, 本手法による水分を含む土壌の誘電率の実部は, 先ず10MHzにて水分が多いと水に近い値まで増加した. また, 周波数が増加時も同様な傾向となった. 一方, 最も水分が多い土壌では, 高い周波数で比誘電率は低くなった. そして, 10から200MHzへの変化で比誘電率は減少した. 次に, 本手法によるWet soil（水分を含む土壌）の誘電率の虚部は, 10MHzでは水分が大きくなると虚部の値も増加した. 一方, 水分量が異なる全ての土壌の誘電率の虚部は高い周波数で直線的に減少した. 従い, 本研究で提案されたセンサーによる10 - 100MHzでの水分の違いによる土壌の複素誘電率（導電率）の周波数特性を確認した

要約(英語)：A capacitive sensor with two ground wires placed at the tip of a high-frequency connector with a coaxial structure was proposed. A precise measurement of the soil dielectric constant in the low frequency band was made by applying to this sensor a formula involving comparison with SOM (short, open and reference materials ). The dielectric constants of methanol and ethanol were estimated in the frequency band of 10 - 200 MHz using this sensor and input impedance calibration and measurement procedure, with pure water as the reference material. Moreover, the estimated values were compared with those obtained by the cut-off circular waveguide reflection method and with the theoretical values of the Debye dispersion equation. The validity of the proposed method was also verified by measuring the soil dielectric constant at 10 - 200 MHz when the above electrodes are inserted into dry soil and soil containing several types of moisture. As a result, highly accurate measurement at frequencies from 10 to 100 MHz by the capacitance sensor with parallel 3-wire electrodes and the N connector was first confirmed for samples with low imaginary part of permittivity (conductivity), such as methanol and ethanol. In particular, the electrode with the structure of three parallel wires of the N connector proposed in this study was found to provide highly accurate estimation of dielectric permittivity, even at a frequency (10 MHz), which is impossible with the cut-off circular waveguide reflection method. It was also confirmed that the dielectric constants of dry soil measured with the above electrodes are close to that of air at 10 - 200MHz. Moreover, it was confirmed that the real part of the dielectric permittivity of the soil containing water by the present method increases to a value close to that of water at 10 MHz as the water content increases. A similar phenomenon was also observed when the frequency increased. Meanwhile, for the soil with the highest moisture content, the dielectric constant was lower at higher frequencies. And the relative permittivity decreased with the change from 10 to 200MHz. Next, as for the imaginary part of the dielectric permittivity of wet-soil, it was confirmed that the value of the imaginary part increases with the moisture content at 10MHz. Meanwhile, the imaginary part of the dielectric constants for all soils with different water contents decreased linearly at higher frequencies. Accordingly, the frequency characteristics of the complex permittivity (conductivity) of soil at different moisture contents at 10 - 100 MHz using the sensor proposed in this study are confirmed.

本誌：2025年6月20日計測研究会

本誌掲載ページ：1-6p

原稿種別：日本語

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