Magnetic Sensors Based on Amorphous Ferromagnetic Materials: A Review <s> Applications <s> Presents a review of fluxgate magnetometry based on a survey of the literature and on the work of the author and colleagues. The theory is outlined and an evaluation of the merit of the different types of sensors is made based on the sensor geometry. The design of a second-harmonic feedback magnetometer is discussed with respect to sensor configuration, frequency response, noise, offset, temperature dependence and long-term stability. Examples of the parameters are compiled from the literature and some new results on the long-term stability are presented. <s> BIB001 </s> Magnetic Sensors Based on Amorphous Ferromagnetic Materials: A Review <s> Applications <s> The change in length of ferromagnetic amorphous ribbons produced by current annealing has been studied. From these results an estimation of the volume change produced by these treatments has been performed and the results (a decrease of 3.37% in volume), related with the anisotropy and magnetization changes observed in previous works. <s> BIB002 </s> Magnetic Sensors Based on Amorphous Ferromagnetic Materials: A Review <s> Applications <s> 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. <s> BIB003 </s> Magnetic Sensors Based on Amorphous Ferromagnetic Materials: A Review <s> Applications <s> A new sensor for magnetic field detection and mechanical displacement is presented. The active element is a CoFeSiB magnetic amorphous wire having 125 μm in diameter. Using different wire lengths can modify both the magnetic field and the displacement range. Moreover, this sensor could be successfully used for the detection and measurement of 3D magnetic fields. <s> BIB004 </s> Magnetic Sensors Based on Amorphous Ferromagnetic Materials: A Review <s> Applications <s> Abstract A novel linear actuator with inherent sensing capabilities is developed from a linear variable differential transformer (LVDT). By superposition of dc currents upon high-frequency excitation signals, the coils of the LVDT are capable of exerting a push/pull force on the armature while retaining the original displacement-sensing function. LC resonant circuits and active bandpass filters are designed to effectively isolate the sensing signals from the dc energizing sources. Linearity and sensitivity of the device are largely preserved compared to the original LVDT. For actuation, it is found that the magnetic force on the armature can be maximized by energizing a specific combination of the three coils according to armature positions. A simple control algorithm is developed for closed-loop control. It is implemented with an 8-bit microcomputer. Real-time testing shows that rest-to-rest control can be achieved with positioning errors of 0.02–0.04 mm and settling time below 0.2 s. <s> BIB005 </s> Magnetic Sensors Based on Amorphous Ferromagnetic Materials: A Review <s> Applications <s> Abstract This article established a useful method of solving the state equation of fluxgate sensor in which only basic detection circuit parameters were used. The solution of the equation was given, and the stability of the solution as well as critical resistance was discussed carefully. We also introduced stability condition of fluxgate by an inequality, the physical meaning of this inequality was discussed by simplifying it with maximum energy transfer condition. Experiments on different fluxgate sensors were performed, and the results show good agreements with calculation results. <s> BIB006 </s> Magnetic Sensors Based on Amorphous Ferromagnetic Materials: A Review <s> Applications <s> Abstract Vector fluxgate sensors have to operate at high temperatures for various applications. In drilling processes with greater drilling depths fluxgate sensors and corresponding electronic circuits are required to operate in a high temperature environment of up to 250 °C for a prolonged period of time. We present an accordant three-axis vector fluxgate system consisting of three single Vacquier-type fluxgate sensors and the signal processing electronics. The high temperature stability is achieved by selecting appropriate materials, mainly for the fluxgate core. The electronic circuits are built using commercially available silicon-on-insulator processed active and appropriate passive devices. The sensor system was characterized in a high temperature environment (up to 250 °C) by evaluating sensitivity, noise, crosstalk, excitation current amplitude and bandwidth. We found a system sensitivity of 28 kV/T (at room temperature) with an acceptably low temperature coefficient of 6.8 × 10 −4 °C −1 and a room temperature flux density noise of 43 pT/(Hz) 1/2 at 1 kHz. At 250 °C the noise values decrease by approximately 50%. <s> BIB007
This kind of sensor is already known for 60 years BIB001 . The first magnetometers were developed during the thirties to be used in magnetic studies of the atmosphere or during the Second World War to detect submarines. Afterwards they have been used to find minerals or for magnetic measurements in the outer space. They have also been adapted for detection and surveillance devices and for the non-destructive characterization of minerals. Unlike magnetometers used for detection or geometrical earth measurements, space magnetometers must not be change detectors but absolute measurement instruments with a wide dynamic range of operation. They show important restrictions due to their weight and consumption and must guarantee a correct operation even under big temperature fluctuations. The need for absolute measures of the planetary fields requires a high zero level stability (which implies minimum drifts), low noise level within the measuring instrument and a good thermal stability BIB006 BIB003 BIB007 . Other types of magnetometers are used for surveillance (weapon detectors) and process control (motor speed, passage detection etc.). For these applications, compact, cheap and low consumption devices are required, even if their sensitivity and stability is worse, because they can be frequently adjusted without great efforts. LVDT are mainly used as position sensors and, when modifying their reels and core shape, as angle sensors. LVDTs with E shape  are used as remote position sensors, able to operate even with a wall in between the reel system and the magnetic core. Indirectly they are used as deformation sensors, as for example on beams deformation measures or in some deformation tension measuring devices BIB002 . The same way, they are used to measure deformations on pressure sensors diagrams or, coupled to a resort, like strength sensors. As an example of the versatility of this kind of sensor, Figure 16 shows a density sensor that uses a LVDT and a small magnetic actuator  . The LVDT acts as a zero device that feeds back to the magnetic actuator so that the small hollow sphere can maintain a static levitation in the fluid. Another LVDT version consists of a ferromagnetic core, linked with the movable part that moves around a solenoid, changing its self-induction coefficient with respect to the core position. Its value must by read by means of alternating current bridges or in a differential way BIB005 BIB004 . 