第 4 章 磁性流体中の超音波伝播特性と内部構造解析 - 伝播速度によるアプローチ 44
4.12 磁場印加方法 (sweep rate) による伝播特性
Sweep rateとは，印加磁場強度の時間変化率であり，これを一定で磁場を掃引することは，一
定の時間に同じ割合で磁場を増加させることを示す。例えば，磁性流体に500mTを印加する場合，
同じ印加磁場強さでも，60分かけて500mTに達するように磁場を掃引するのと，10分で500mT に達するように磁場を掃引するのでは，内部構造変化にも差が生じると考えられる。この解析を 行うため，sweep rateを一定にしたうえで，伝播速度を計測し，内部構造変化を比較した。図3.1 における，⑧直流安定化電源をパソコンによって制御することで一定の割合で磁場を掃引するよ うにした。
磁場掃引方法は，最大磁場の530mTに達するまで100分，50分，25分，12.5分かけて磁場が 増加するようにsweep rateを設定し掃引した。なお，単位時間あたりの磁束密度の増加量dB/dt は，100分で5.30mT/min，50分で10.6mT/min，25分で21.2mT/min，12.5分で42.4mT/min である。この方法で磁場を掃引しながら伝播速度変化を測定している。
測定結果を図4.48～図4.53に示す。図は，それぞれW-40，HC-50，EXP04019の磁性流体に おける結果であり，横軸に時間軸と磁場をとることで2通りの方法で結果を示している。
図4.9: Ultrasonic propagation velocity in W-40 and HC-50
図 4.10: Ultrasonic propagation velocity in HC-50, EXP04019 and EXP01052
図4.11: Elapsed time dependence of ultrasonic propagation velocity in W-40 and HC-50
図 4.12: Elapsed time dependence of ultrasonic propagation velocity in EXP04019 and EXP01052
図4.13: Elapsed time dependence of ultrasonic propagation velocity in EXP04019
図4.14: Elapsed time dependence of ultrasonic propagation velocity in EXP01052
図 4.15: Hysteresis of ultrasonic propagation velocity in HC-50 forφ= 0◦
図4.16: Hysteresis of ultrasonic propagation velocity in HC-50 for φ= 45◦
図4.17: Hysteresis of ultrasonic propagation velocity in HC-50 for φ= 90◦
図4.18: Hysteresis of ultrasonic propagation velocity in EXP04019 forφ= 0◦
図 4.19: Hysteresis of ultrasonic propagation velocity in EXP04019 forφ= 45◦
図 4.20: Hysteresis of ultrasonic propagation velocity in EXP04019 forφ= 90◦
図4.21: Hysteresis of ultrasonic propagation velocity in EXP01052 forφ= 0◦
図 4.22: Hysteresis of ultrasonic propagation velocity in EXP01052 forφ= 45◦
図 4.23: Hysteresis of ultrasonic propagation velocity in EXP01052 forφ= 90◦
図 4.24: Magnetic field dependence of ultrasonic propagation velocity in EXP04019 and EXP01052
図4.25: Anisotropy of ultrasonic propagation velocity in HC-50①
図4.26: Anisotropy of ultrasonic propagation velocity in HC-50②
図4.27: Anisotropy of ultrasonic propagation velocity in HC-50③
図4.28: 3D anisotropy form of ultrasonic propagation velocity in HC-50
図4.29: Detail of anisotropy of ultrasonic propagation velocity in W-40
図4.30: Detail of anisotropy of ultrasonic propagation velocity in HC-50
図4.31: Detail of anisotropy of ultrasonic propagation velocity in EXP04019
図4.32: Detail of anisotropy of ultrasonic propagation velocity in EXP01052
図4.33: Ultrasonic propagation velocity in diluted water-based magnetic fluids
図4.34: Ultrasonic propagation velocity in diluted kerosene-based magnetic fluids
図 4.35: Elapsed time dependence of ultrasonic propagation velocity in diluted water-based magnetic fluids in 500mT andφ= 0◦
図 4.36: Elapsed time dependence of ultrasonic propagation velocity in diluted water-based magnetic fluids in 500mT andφ= 90◦
図 4.37: Elapsed time dependence of ultrasonic propagation velocity in diluted kerosene-based magnetic fluids in 500mT andφ= 0◦
図 4.38: Elapsed time dependence of ultrasonic propagation velocity in diluted kerosene-based magnetic fluids in 500mT andφ= 90◦
図4.39: Anisotropy of ultrasonic propagation velocity in 40wt% water-based magnetic fluid
図4.40: Anisotropy of ultrasonic propagation velocity in 30wt% water-based magnetic fluid
図4.41: Anisotropy of ultrasonic propagation velocity in 20wt% water-based magnetic fluid
図4.42: Anisotropy of ultrasonic propagation velocity in 10wt% water-based magnetic fluid
図 4.43: Anisotropy of ultrasonic propagation velocity in diluted water-based magnetic fluids under 100mT
図 4.44: Anisotropy of ultrasonic propagation velocity in diluted water-based magnetic fluids under 200mT
図 4.45: Anisotropy of ultrasonic propagation velocity in diluted water-based magnetic fluids under 300mT
図 4.46: Anisotropy of ultrasonic propagation velocity in diluted water-based magnetic fluids under 400mT
図 4.47: Anisotropy of ultrasonic propagation velocity in diluted water-based magnetic fluids under 500mT
図 4.48: Elapsed time dependence of ultrasonic propagation velocity in W-40 as a function of sweep rate
図 4.49: Magnetic flux density dependence of ultrasonic propagation velocity in W-40 as a function of sweep rate
図 4.50: Elapsed time dependence of ultrasonic propagation velocity in HC-50 as a function of sweep rate
図 4.51: Magnetic flux density dependence of ultrasonic propagation velocity in HC-50 as a function of sweep rate
図4.52: Elapsed time dependence of ultrasonic propagation velocity in EXP04019 as a function of sweep rate
図4.53: Magnetic flux density dependence of ultrasonic propagation velocity in EXP04019 as a function of sweep rate