Tatsuo Sawada

Ultrasonic propagation velocity in magnetic and magnetorheological fluids due to an external magnetic field

Ultrasonic propagation velocity in a magnetic fluid (MF) and magnetorheological fluid (MRF) changes with the application of an external magnetic field. The formation of clustering structures inside the MF and MRF clearly has an influence on the ultrasonic propagation velocity. Therefore, we propose a qualitative analysis of these structures by measuring properties of ultrasonic propagation. Since MF and MRF are opaque, non-contact inspection using the ultrasonic technique can be very useful for analyzing the inner structures of MF and MRF. In this study, we measured ultrasonic propagation velocity in a hydrocarbon-based MF and MRF precisely. Based on these results, the clustering structures of these fluids are analyzed experimentally in terms of elapsed time dependence and the effect of external magnetic field strength. The results reveal hysteresis and anisotropy in the ultrasonic propagation velocity. We also discuss differences of ultrasonic propagation velocity between MF and MRF.

Experimental analysis of clustering structures in magnetic and MR fluids using ultrasound

The formation of clustering structures in magnetic and MR fluids has an influence on ultrasonic propagation. We propose a qualitative analysis of these structures by measuring properties of ultrasonic propagation. Since magnetic and MR fluids are opaque, the non-contact inspection using this ultrasonic technique can be very useful for analyzing the inner structures of magnetic and MR fluids. We measured ultrasonic propagation velocity in a hydrocarbon-based magnetic fluid and MR fluid precisely. Based on these results, the clustering structures of these fluids were analyzed experimentally in terms of elapsed time dependence, effect of external magnetic field strength and angle, and hysteresis phenomena. A comparison of ultrasonic velocity propagation between magnetic and MR fluid was discussed.

Damping characteristics of a magnetic fluid tuned liquid column damper under static magnetic fields

Magnetic fluid tuned liquid column damper (MF-TLCD) is a new semiactive damper. This device can exhibit high damping effect by tuning its natural frequency to the excitation frequency. In this study, the vibration characteristics of a magnetic fluid under a static magnetic field were investigated by linear analysis and experiment with single-degree-of-freedom oscillation. Moreover, MF-TLCDwas installed within a structure and oscillated in double-degrees-of-freedom. It was confirmed that MF-TLCD could achieve high performance compared with the conventional TLCD by controlling the magnetic field.

Cluster formation in two-dimensional channel flow of a magnetic fluid under uniform magnetic field

The two-dimensional channel flow of a magnetic fluid was experimentally investigated. When a magnetic field is applied to a magnetic fluid, ferromagnetic particles aggregate along the direction of the magnetic field and form clusters. The pressure drop of the magnetic fluid flow changes according to cluster formations. The effect of the applied magnetic field on the pressure drop was determined. The ultrasonic propagation velocity was also measured to clarify the effect of cluster formations.

Hysteresis phenomena of ultrasonic velocity change in magnetorheological fluids

The magnetorheological response of magnetorheological flu ids (MRF) results from the polarization induced in the suspended particles by application of an external magnetic field. We proposed a qualitative analysis of these effect s by measuring properties of ultrasonic propagation. Hysteresis was appeared when magnetic field increased to and decrease d from the certain value, 290 mT in our experiment. The change rate of the ultrasonic wave propagation velocity increased during the increasing process of the external magnetic field. However, it was kept almost the same value during the decreasing process. Smart materials have some properties which can be altered or tuned using an external field. Examples include materials that exhibit ferroelectricity, pyroele ctricity, piezoelectricity, a shape memory effect, electrostriction, magnerostriction, electrochromism, p hotomagnetism and photochromism. Most of these materials tend to be used in their solid state, i.e. in a polyc rystalline or a single crystal form as bulk materials or thin films deposited on appropriate substrates . There is also a class of smart materials known as field responsive fluids. These include magnetorheol ogical fluids (MRF), magnetic fluids, electrorheological (ER) fluids and certain types of polymer ic gels. These materials are different from the conventional smart materials, in that they are soft materia ls (typically dispersions or gels) rather than solids (1). MRFs are formed by magnetizable micron-size particles suspended in a nonmagnetic fluid. The physical bases of the remarkable characteristics of these fl uids are somewhat simple. In the absence of an external magnetic field, these suspensions behave as no n-Newtonian fluids. When an external magnetic field is applied, a magnetic dipole moment is induce d in the magnetic particles. The magnetic interaction between the resulting induced dipoles causes particles to aggregate forming a clusters aligned in the magnetic field direction (2). These cluster structure s restrict the motion of the fluid, thus increasing the viscosity of the MRF. MRFs usually show yield stress strongly depending on the amplitude of the external magnetic field. The key to the numerous technology applications of MRF lies in their reversible rheological transition which is closed to the rapid change in the inner microstructures (3). Therefore a detailed understanding of the inner structures and dynamics due to the application of an external magnetic field is needed in order

Ultrasonic propagation characteristics of a magnetic fluid under AC magnetic fields

An experimental study in ultrasonic propagation characteristics of a magnetic fluid under AC magnetic fields was conducted. Sound velocities in a magnetic fluid increased with elapsed time of the AC magnetic fields. Moreover, rapid decreases in sound velocities in a magnetic fluid were observed when the AC magnetic fields were stopped. These results were similar to those for DC magnetic fields. Dependence of frequencies and magnitudes of AC magnetic fields on sound velocities in a magnetic fluid was observed. Moreover, anisotropy was found in each frequency of the AC magnetic fields.

Frequency Analysis of Semi-Active Tuned Magnetic Fluid Column Damper with Two Electromagnets

A new semi-active tuned liquid column damper (TLCD) that uses magnetic fluid as its working fluid (MF-TLCD) is presented. An MF-TLCD alters the natural frequency of the magnetic fluid column that forms the resident liquid inside the MF-TLCD by applying a magnetic field. We investigated the damping characteristics of an MF-TLCD equipped with two electromagnets, and also the transition of the natural frequency, which is strongly related to the damping performance. The coupled structure-MF-TLCD system was investigated both experimentally and by numerical analysis. The momentum equation of an MF-TLCD and its numerical solution are presented. The numerical results are validated by comparison with experimental results.

Two-layer sloshing of magnetic fluid and silicone oil under horizontal magnetic field

This study investigates the behavior of two-layer sloshing using a magnetic fluid and silicone oil. To obtain basic relations, a linear theory is employed. After obtaining those relations, theoretical values of free-surface displacement, resonant frequency, and resonant pressure amplitude are compared with experimental results. Experimental data are obtained using a laser sensor and four pressure transducers. Free-surface displacement is measured by the laser sensor. Resonant frequency is measured by both the laser sensor and pressure transducers. Resonant pressure amplitude is recorded by the pressure trans- ducers. The results demonstrate that the theory employed in this study is effective as a first estimation of two-layer sloshing. However, to describe the behavior of a two-layer magnetic fluid sloshing more precisely, a nonlinear analysis that considers magnetic force is necessary.

Experimental Investigation into the Effect of a Magnetic Field on Magnetorheological Fluids under an Impact Load

The apparent viscosity of magnetorheological (MR) fluids changes in the presence of a magnetic field. The stronger the magnetic field applied, the more the apparent viscosity increases. An increase in the apparent viscosity increases the restriction on the flow of MR fluids. In this study, we perform a qualitative analysis to investigate the effect of a magnetic field on MR fluids under an impact load. An experimental apparatus that consists of a drop-test tower was developed to simulate the impact load, and an MR fluid in a U-pipe was subjected to the impact load via a piston rod. In the experiment, we measured the displacement and velocity of the piston rod. On the basis of the results, the influence of a given magnetic field on the behavior of MR fluids under an impact load is discussed.

Ultrasonic Investigation of the Effect of Volume Fraction on the Clustering Structures of Magneto-Rheological Fluids

The rheological response of magnetorheological fluid (MRF) results from the polarization induced in the suspended particles by application of an external magnetic field. Characteristics of an MRF depend on the volume faction, that is the percentage of magnetic particles in the carrier liquid. We propose a qualitative investigation of these volume fraction effects by measuring properties of ultrasonic wave propagation velocity in MRFs having various volume fractions. The ultrasonic wave propagation velocity changes under the effect of an external magnetic field as a result of arrangement of clusters along the direction of the field in the MRF.