Abstract-The method is based on two-axis generation of a quasi-static rotating magnetic field and three-axis sensing. Two mutually orthogonal coils fed with phase-quadrature currents comprise the excitation source, which is equal to a mechanically rotating magnetic dipole. The resulting excitation field rotates elliptically at any position in the near-field region. The ac part of the squared field magnitude is a sinusoidal wave at twice the excitation frequency. The following set of parameters uniquely characterize the excitation at the sensor's position: the phase of the squared field waveform, relative to the excitation currents, the minimum field value, the ratio of the field extremes, and the orientation of the excitation field plane. Simple and explicit analytical expressions are given which relate the first three parameters to the azimuth, elevation, and distance from the source to the sensor, respectively. The orientation of the sensor axes, relative to the plane of the excitation, can easily be determined by comparing the phase and amplitude of the measured signals against the phase and amplitude of the excitation field at the sensor's position. Apart from simplicity, the proposed method increases the speed of tracking; a single period of excitation is in principle sufficient to obtain all of the information needed to determine both the sensor's position and orientation. A continuous sinusoidal excitation mode allows an efficient phase-locking and accurate detection of the sensor output. It also improves the electromagnetic compatibility of the method.Index Terms-Elliptically rotating excitation field, magnetic position and orientation tracking, magnetic position measurement, magnetic sensing, magnetic tracking system, rotating magnetic dipole field.

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A new important advantage has been discovered for the fundamental-mode operation of the orthogonal fluxgate employing an amorphous wire. It has been found that a great enough dc bias practically completely suppresses the magnetic noise generated in the fluxgate core by the ac-bias field; the fluxgate resolution becomes limited only by the excess electric noise in the ac-bias current. As a result, the magnetometer resolution increases by a factor of 60 and reaches 10 pT/ √ Hz at frequencies above 2 Hz. The suppression of magnetic noise can be explained by excluding magnetization reversals in the fluxgate core. In the fundamental mode, the fluxgate core is kept saturated continuously due to the unipolar bias, and magnetization varies by coherent rotation. Practically no magnetic noise is generated in this case. In the second-harmonic mode, magnetization is reversed by the bipolar bias. This causes nucleating domains and generating intensive magnetic noise in the fluxgate core.

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Converse magnetoelectric effect in ferromagnetic shape memory alloy/piezoelectric laminate Appl. Phys. Lett. 95, 022501 (2009)