Axial Magneto-Inductive Effect in Soft Magnetic Microfibers, Test Methodology, and Experiments

Soft, amorphous, ferromagnetic microfibers under small axial tension exhibit a weak magneto-induction (MI) effect when an applied axial magnetic field is utilized to excite the fiber. Previous investigators have demonstrated this effect with small coils applied directly to the microfiber. In this report, evidence is presented that the MI effect can be generated remotely by applying a known external magnetic field from a Helmholtz coil. Excitation fields of 26 muT at frequencies ranging from 100 Hz to 1000 Hz generated a nominal 0.2 muT peak impulse response from the pre-tensioned microfiber; the axial MI response was demonstrated to be a function of the induced axial pre-tensioning. Dominant response variables include fiber length, its degree of pre-tensioning (i.e. induced strain) the magnetic field drive frequency, the applied magnetic field, and the uniformity of the applied field in aligning the domain fields within the strand. A number of fiber strand compositions were tested and mounted to dog-bone-type specimens in various ways. The results of these tests are relayed in this report, as well as a summary of results and recommendations for continued research in this area.