自動平衡ブリッジと終端開放同軸線路によるMHz帯での液体の複素誘電率測定

カテゴリ: 研究会(論文単位)

論文No: IM22019

グループ名: 【A】基礎・材料・共通部門 計測研究会

発行日: 2022/11/22

タイトル(英語): Complex Permittivity Measurement of Liquids at MHz Band Using the Automatic Balance Bridge and an Open-Ended Coaxial Line

著者名: 柴田 幸司(八戸工業大学)

著者名(英語): Shibata Kouji(Hachinohe Institute of Technology)

キーワード: 誘電率測定|液体|同軸線路|校正|Ｓ１１|インピーダンス測定|Dielectric measurement|Liquids|Coaxial line|Calibration|S11|Impedance measurement

要約(日本語): 本研究では, 低周波帯での液体の誘電率測定時の精度の向上を目的として, Nｺﾈｸﾀにて給電する終端開放同軸線路の治具とSOMと比較する公式を組み合わせた液体の誘電率測定に必要となる各終端条件でのｲﾝﾋﾟｰﾀﾞﾝｽ測定に, 自動平衡ブリッジ回路に基づくｲﾝﾋﾟｰﾀﾞﾝｽｱﾅﾗｲｻﾞを用いた. そして先ず, 市販の校正キットにて1 - 101MHzの周波数帯域で測定器のSOL校正を行い, その後に治具を取り付けて先端がshort, open及び基準・未知物質の液体を挿入時の入力ｲﾝﾋﾟｰﾀﾞﾝｽを測定した. 更に, この測定値をSOMと比較する公式に代入して未知物質の複素誘電率を推定した. その際, 各液体の誘電率は集中定数法（容量法）に基づく手法でも推定値して先の結果と比較した. 更に, これらの結果は治具の構造, 事前のSOL校正の手順（校正面での同軸ｺﾈｸﾀの種類）, 誘電率の推定手法およびｲﾝﾋﾟｰﾀﾞﾝｽの測定器の組み合わせの違いによる入力ｲﾝﾋﾟｰﾀﾞﾝｽの測定値や複素誘電率の推定値と過去の結果も含めて比較および評価した. その結果, 特に50MHz以下の低周波帯では, Nｺﾈｸﾀにて給電する終端開放同軸線路とSOMと比較する公式を組み合わせた場合に入力ｲﾝﾋﾟｰﾀﾞﾝｽの実部が最も低くなった. そして, この現象に伴う複素誘電率の虚部の低下も確認した. 最後に, 各条件の組み合わせによる液体の誘電率の推定値の差異を5 - 101MHzの周波数特性としても比較して考察した. その結果, 本稿で提案した液体の誘電率測定法により下限周波数が拡張できる可能性が確認できた.

要約(英語): In this study, a method for calibrating and measuring impedance combined with a jig for an open-ended coaxial line with an N-connector and a formula involving comparison with SOM (short, open and material) was discussed for the purpose of improving the accuracy when measuring the dielectric constant of liquids in the low frequency band. For this purpose, an impedance analyzer based on an auto-balancing bridge circuit was used to measure the impedance at each termination condition of the jig. The instrument was first SOL (short open and load) calibrated in the frequency band from 1 to 101MHz with a commercially available calibration kit at the tip of the coaxial cable attached to the instrument. Next, the input impedance was measured when the tip was short, open, and a reference or unknown liquid was inserted after a jig was attached to the tip of the coaxial cable. The complex permittivity of the unknown material was then estimated by substituting the above measured values into the formula involving comparison with the SOM termination. At that time, the complex permittivity of each liquid was also estimated by a method based on the lumped constant method (capacitance method) and compared with the previous results. Moreover, measurements were made by changing the structure of the jig, the procedure for pre-calibration of SOL (the kind of connectors on the calibration plane), the estimation method of the permittivity, and the kind of impedance measuring instruments. The measured values of the input impedance and the estimated values of the complex permittivity associated with the above combinations were also compared and evaluated. The results show that the real part of the input impedance is low when the open-ended coaxial line fed by the N connector and the formula involving comparison with SOM termination are combined, especially in the low frequency band below 50MHz. Moreover, a decrease in the imaginary part of the complex permittivity was also confirmed with the above phenomenon. Finally, the difference in the estimated value of the dielectric constant of the liquid due to each combination of conditions was compared and discussed as the frequency characteristics from 5 to 101MHz. The results indicated the possibility that the lower frequency limit could be extended by the liquid permittivity measurement method proposed in this paper.

本誌: 2022年11月25日計測研究会

本誌掲載ページ: 7-12 p

原稿種別: 日本語

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