This paper reviews recent achievements in the technology and design of fluxgate sensors and magnetometers. The major recent trends were decreasing of the sensor size, power consumption and price, and, on the other hand, increasing of the precision in the large range of the measured fields. The potential frequency range was increased up to units of kHz. Present fluxgate sensors have a resolution comparable with high-temperature superconducting quantum interference devices (SQUIDs), while their precision is the best of vectorial field sensors.

Advances in fluxgate sensors

This paper begins with an overview of nanostructured magnetoelastic materials, namely the amorphous ferromagnetic alloys, detailing how the material structure gives rise to unique magnetic and physical properties suitable for sensor applications, such as a high magnetostriction coefficient, high magnetoelastic coupling, as well as low coercive force and anisotropy field. With the correlation between the material structure and the magnetic and physical properties established, we then show how these unique properties are utilized for measuring multiple physical parameters such as stress/strain, liquid density and viscosity, fluid flow velocity, coating elasticity, ambient temperature, and chemical analyte concentrations including glucose, pH, carbon dioxide, and ammonia.

Magnetism-based sensors

A functional study of the TFS-3 type fluxgate sensor with amorphous magnetic material cores is made. The magnetic material used in these sensors is Romanian amorphous material Co68.25Fe4.5Si12.25B15 thin ribbon produced at the Institute of Technical Physics, Iasi and prepared by rapid quenching from the melt on a rotating copper wheel. The sensor's functional parameters and thermostability were measured. The sensor sensitivity is between 4.5 and 5.5 μV nt−1 and for fields greater than 100 nT does not depend on temperature variation in the range +20 to +70°C. Also the temperature variation does not influence the noise of the sensor which does not exceed 600 pTpp. The offset thermostability corresponds to a thermal drift of 1 nT °C−1 over the whole mentioned temperature range. The ability of sensors to measure a.c. magnetic fields by means of the two side bands of the second harmonic was studied using Fourier analysis. The study was done for a.c. field frequencies of up to 15 kHz, at excitation frequencies up to 30 kHz. For an induction field up to 26 μTpp the response is linear, showing the possibility of using the sensor for also measuring low frequency a.c. fields.

Functional study of fluxgate sensors with amorphous magnetic materials cores

A new method suitable for the single core fluxgate magnetometer has been proposed. The method makes use of the coupling property of odd and even harmonics generated by the self-product of the induced voltage during the magnetization of ferromagnetic material by an external field superposed on the AC driving magnetic field. The power difference between the two half-periods of magnetization was expressed by the coupling of odd and even harmonics, which is proportional to the external field under the condition that Hext<<HAC and HAC is constant, where Hext and HAC are the external magnetic field and AC driving field amplitude respectively.

http://iopscience.iop.org/article/10.1088/0957-0233/6/7/007/pdf

Amitava Mitra

Papers

A simple fluxgate magnetometer using amorphous alloys