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UBC Theses and Dissertations

The theory of fluxgate sensor systems Gao, Zu-Cheng


In recent years, the fluxgate sensor system has become increasingly important for the measurement of magnetic fields. It has become the instrument of choice for some aeronomy research programs, for ocean bottom deployment and for vessel detection by seafloor sensors. It has considerable potential for airborne magnetometry and gradient measurements. This renewed interest arises because the capabilities of the instrument are now known to be much superior to those achieved by earlier designs, and because there is a continued need for sensors with a vector capability. Added practical advantages accrue because it is a rugged instrument, economical to manufacture and has low power requirements. The advances in technology have not been accompanied by corresponding advances in the theoretical understanding of the fluxgate. Prior to publications from the University of British Columbia, most representations were cumbersome, incomplete and sometimes incorrect. The approach presented for the first time in this thesis introduces a gating function which straightforwardly represents the fluxgate mechanism separately from the complications of hysteresis and demagnetization. The characteristics of the gating function are easily measurable and can be regarded as the performance indices of the sensor. The approach also presents a general state equation which is valid not only for single sensors, but also for symmetric multiple sensors (e.g. gradiometers). Then the complete solution set (the monodromy, the general solution and periodic solution) is solved for the state equation. Based on the theories of Floquet-Lyapunov and of Hsu, the instability criterion and the method of calculation are investigated. The generalized instability map, illustrated in a parameter plane, is useful for the design of stable fluxgate sensor systems. The instability has been also checked in the phase space. The sensitivity map presented through this approach can be used to calculate the real signal for a fluxgate sensor with any value of parameters. Moreover, this approach not only formulates an integrated fluxgate theory, but also provides a guide to the selection of operating parameters and components for a practical design.

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