Type Of Magnetic Field Sensor Research Articles

Noise and stability of magnetic sensors

High-TC SQUID sensors having 0.4 pT/√Hz at 1 Hz noise at liquid nitrogen temperature are already superior to fluxgate sensors (2.5 pT/√Hz at 1 Hz, 50 pT p-p). Ac-flipped permalloy magnetoresistors have offset of 10 NT and 15 nT p-p noise. The noise properties of semiconductor, induction and other types of magnetic field sensors are discussed.

New optical magnetic field sensor with optional white light source (abstract)

A new type of magnetic field sensor which measures ac electric current utilizing Faraday rotation is proposed. On a Faraday element a stabilized dc bias magnetic field Hb is applied. Output signal is given by the ratio R = I2ω/Iω, where Iω and I2ω are fundamental and second harmonic signals generated by the field Hx which the ac current induces. Since R is calculated as R = Hx/4Hb, we can measure Hx independent not only of light intensity but also of the Verdet constant (and therefore its temperature dependence) of the Faraday element. This was supported by experiments performed at 20–100 °C for HeNe laser (λ=0.633 and 1.15 μm) light on Faraday elements of FR-5 paramagnetic glass and Bi-substituted YIG crystal. The bias field Hb was generated by a stabilized dc current in a coil and using a SmGdCo plastic magnet with very weak temperature dependence of remanent magnetization (<1% at T=20–120 °C). According to theory the equation holds even when broad spectrum polychromatic light is used. This was confirmed by experiments performed with a halogen-lamp white light transmitted through an optical fiber. Calculated signal-to-noise ratio of the sensor with a polychromatic light agreed with experiments.

Differentially DC biased type magnetic field sensor of high sensitivity

The detection principle of a novel magnetic field sensor called the differentially-DC-biased magnetic field sensor which uses a magnetic core is described. The detectable lower limit is extended up to the order of 10/sup -13// square root Hz by virtue of the detection principle used, which is analogous to the equilibrium condition of ordinary bridge circuits. By using two cores, a kind of bridge circuit is constituted. The field to be detected breaks the equilibrium condition, which leads to the variation of incremental permeability. The means adapted to detect the variation with high sensitivity are described.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Distinctive features of magnetic field controlled type magnetic field sensor

A magnetically controlled magnetic field sensor detects an unknown field by realizing a zero magnetic field state in the core. When the core is magnetized by the field to be detected, a magnetizing field which is exactly equal to the unknown field is impressed on the core in the opposite direction, and this opposing field is detected as the output signal. Test results for Co-rich Metglas alloy and Fe/sub 50/Ni/sub 50/ Permalloy cores are presented. The detection characteristics, linearity, dynamic range, and response of this sensor are shown to be practically independent of the external shape of the core and the magnetic property of the core material as long as it has saturation characteristics, and to be independent of the temperature of the core. >