Amplitude Sweep Test

The strain amplitude sweep test examines effect of shear strain on the dynamic moduli of the MRE sample [120]. This test allows to define a linear viscoelastic (LVE) region of the MRE. Figure 7a shows the G' of the MRE sample as a function of strain amplitude [121]. The strain range is measured from 0.01% to 1% and is measured at 3 different magnetic field intensities. As shown in the figure, the low strain region has a plateau region where the G', called LVE regime, remains constant. As the strain increases, the G' tends to decrease gradually, and as the strength of the magnetic field increases, the G' rises.

**Figure 7.** (**a**) Storage Modulus versus strain amplitude sweep and (**b**) storage modulus versus angular frequency sweep (Closed symbol:CI/γ-Fe2O3 based MRE, open symbol: Pure CI based MRE) [121].

Frequency Sweep Test

Figure 7b is a frequency sweep test graph [121] of both G' and G" displayed according to frequency. The constant strain was determined as 0.02% in the LVE region of the strain amplitude sweep test. The measured data range is 1~100 rad/s. As the magnetic field strength increases, the dynamic modulus of the sample increases. At the same magnetic field strength, the G' of CI/γ-Fe2O3 based MRE is higher than that of pure CI based MRE as in the amplitude sweep test.
