電気端子からみたSパラメータの周波数特性を用いた液体の音速測定 Velocity Measurement in Liquid Using Frequency Characteristics of S parameter at the Electrical Port of Transducer

連続波を用いて液体の音速測定を行うために,圧電振動子・バッキング・試料・反射体を分布定数線路モデルで表し,音速測定系をその縦続接続したものと考えて,圧電振動子の電気端子におけるSパラメータを計算した。この結果から電気端子からみたSパラメータが周波数に対して周期的に変化し,その周期Δfと試料長Lから液体中の音速が測定できることを述べている。周波数-Sパラメータ特性から振動子の共振持性を取り除いてΔfを求める方法,およびLを高精度で測定する方法を示した。試料に20℃の水を用いて実験を行い,文献値と0.1%以内で一致する値が得られた。

The measurement system for sound velocity in liquid using continuous wave signal is modeled by the cascade connection of transmission lines which correspond to sample, ultrasonic transducer with backing and reflector. From the calculated results of S-parameter at the electrical port of the transducer, sound velocity v can be obtained both from the frequency periods Δf of frequency-S parameter characteristics and the sample length L. Transducer's resonance effect is subtracted from f-S parameter characteristics to extract the accurate information of velocity. For the precise measurement, an improved method for obtaining L are described. The experiment with water at 20℃ and frequency of 5 MHz is carried out to evaluate our method and system. Experimental result shows agreement between our method and literature within 0.1% has been established.