## 4 Electric and Dynamic Characteristics  
Changes in electrical resistivity to the pressing transverse force measured by NFE are shown in Figure 9. The figure also presents a comparison of three cases: magnetic field only (mag. ); electric field only (i.e., the use of electrolytic polymerization without the magnetic field; elec. ); and both electrolytic polymerization and magnetic field (mag. + elec.). The first is the case of MCF rubber by the previous method of making MCF rubber by just drying under a magnetic field application. The third is the case of MCF rubber made by the present new method. The figure also presents the results for PSER made of NR-latex (PSECR), and MCF rubber made of silicon oil rubber, consisting of 3 g Ni (No. 123), 3 g Cu powder with twig-shaped particles on the order of \(\mu\)m (MF-D2 by Yamaishi Co. Ltd., Noda, Japan), 4 g kerosene-based MF with 50 wt.% Fe\({}_{3}\)O\({}_{4}\) (HC-50, Taiho Industry Co. Ltd., Takatsuki, Japan), and 10 g silicon oil rubber (SH9550, Shin-Etsu Chemical Co., Ltd, Tokyo, Japan) which is the case of MCF rubber by the previous method vulcanized under a constant temperature and application of a magnetic field (silicon oil rubber, mag.). Electrical resistivity in the rubbers made of NR-latex was smaller than in those made of PSER and silicon oil MCF rubber. In particular, the sensitivity of NR-latex MCF rubber was larger than that of silicon oil MCF rubber, in accord with previous research. The electrical resistivity of elec. and mag. were the largest. As the C=C bonds are polarized, and their electrolytically polarized direction lined up with the direction of the magnetic cluster, more electric current flowed. The rapid decrease in electric resistance in the mag. + elec. was particularly large compared to the other cases. This indicates a larger switching effect, which means that the F\({}_{\text{s}}\) can be as small as possible. F\({}_{\text{s}}\) of MCF rubber (NR-latex, mag. + elec.) is 0.1 mN. This is far above the value that is required in a haptic sensor as described in the previous Introduction section. As previously mentioned, this is important in order to reflect the sensitivity of human skin. As a result, the new method of making MCF rubber with both electrolytic polymerization and a magnetic field is effective for producing a haptic sensor utilizing  
Figure 9: Electric characteristics of MCF rubber made by the new method in the case of NFE, compared among three electric and magnetic field conditions, and among NR-latex, silicon oil, and PSERR rubber. normal force. Incidentally, other results of the electrical resistivity of PSECR are shown in Figure 10(a) in the Appendix A. The PSECR is less sensitive than MCF rubber made by the new method. Therefore, the MCF rubber made by the new method can be utilized in the various haptic sensing fields as described in the previous Introduction section. The change in electric current flowing inner the rubber to shear force measured by SFE is shown in Figure 10. The normal force changed under shearing motion according to the elasticity of the MCF rubber; the initial normal force before moving is indicated as \"Initial normal force\". The figure also presents a comparison of the five cases shown in Figure 9. The more the electric current is, the more sensitive the rubber in the case of utilizing as a sensor with shearing motion. The electric current in rubbers made of NR-latex was larger than that in PSECR and silicon oil MCF rubber. The electric current in electrolytic polymerization without the magnetic field was smaller than that of mag. and mag. +- -  
The relation between strain and stress is shown in Figure 11. In general, in the case of filled rubber, the stress-strain responses have a well-known hysteresis curve and stress softening (Mullins effect) [28; 29]. According to the effect, the stress-strain curve at the first time is different from that after the first, and the stress-strain curves after the first are almost the same as far as the maximum tensile force is the same.