A technique for forming a semiconductor structure in a semiconductor wafer includes the steps of forming an epitaxial layer on a least a portion of a semiconductor substrate of a first conductivity type and forming at least one trench in an upper surface of the semiconductor wafer and partially into the epitaxial layer. The soft magnetic layer suppresses magnetic interaction between a respective one of the magnetic recording domains and neighboring ones of the magnetic recording domains. Furthermore, as the cheap natural fiber is used as a reinforcer, the production cost can be reduced. A cable used for the circumferential surface cable system is lower in stiffness and smaller in ratio of the tension variation to the length variation than that used for the internal surface cable system. The signal generator is a passive impedance network.