Sensitivity magnetic field sensors

Sensitive parameters are necessary to compare several high resolution magnetic field sensors. Such parameters can be found with methods of signal theory for LTI-systems. The following chapter explains characteristic functions and operations of the signal analysis for linear local invariant systems and their use in non-destructive testing. 

A number of sensitive magnetic field detection devices have been developed as biosensors giant magnetoresistive (GMR) sensors [4], piezoresistive cantilevers [5], inductive sensors [6], superconducting quantum interference devices (SQUIDs) [7, 8], anisotropic magnetoresistive (AMR) rings [9], and miniature Hall crosses [10]. 

In this case, we can conclude that the small sensor is lightly tilted with an angle of 0,25 degrees. We have concluded, during experimentations, that the measurement of the magnetic field is very sensitive to the angle of inclinaison of the sensor. In this way, we validate the computation of the incident field E (r). We can also expect some difficulties for the validation of the forward problem by experimental data. 

Devices called sensors, which are sensitive to physical influences other than electricity and light, like pressure, temperature, chemical concentrations, or magnetic fields, can convert non-electric signals into electrical ones (see, e.g., the review of Janata [108] for chemical sensors). 

An original technique was developed by Konishi et al. (1969) and extended later on by Narita et al. (1980). This method is known as the small-angle magnetisation rotation (SAMR) method a static bias field H and a tensile stress (o) are applied in the direction of the film a small-amplitude ac driven field H = W max sin(wf) is applied perpendicular to H. It is this ac magnetic field that induces a magnetisation rotation, which can be detected as an induced voltage in a sensor coil wound around the film axis. This response is measured as a function of the applied stress, i.e. of the strain-induced anisotropy. An experimental SAMR set-up is illustrated in fig. 5. The sensitivity of this method was 2 x 10-7 (Narita et al. 1980) and even much higher, namely 10-9 (Hernando et al. 1983). 

Special attention is paid to transport properties (resistance and Hall effect) because they are very sensitive to external parameters being the base for working mechanisms in many types of sensors and devices. The magnetic field and temperature dependences of resistance and Hall effect are considered in the framework of the percolation theory. Various types of magnetoresistances such as giant and anisotropic ones as well as their mechanisms are under discussion. 

Materials with very narrow ESR lines (AHpp < 20 mG) can be used as small-volume and low-power magnetic sensors of great sensitivity. Such devices would have applications as submarine mine detectors, local terrestrial magnetic field detectors [65,66], and for the identification of objects with an added suitable paramagnetic substance [67]. 

Clearly, we need a multiple-sensor system that can simultaneously measure the magnetic field at various positions over the scalp—say, one hundred positions—so that measurements could be completed in a matter of minutes. This would enable us to see patterns of activity as they shift from one area of brain to the next. The problem, though, is that we have to keep the sensors, the detector coils, very cold in liquid helium. You also need a good Dewar, and the present ones are rigid structures. It doesn t take you long to realize, when you study human heads, that they come in different sizes and shapes—round ones, flat ones, heads with corners and edges. To maximize sensitivity, you have to get those coils closer to the head, and we don t have that flexibility with current designs. If we had a room-temperature superconductor, we could do that very easily, because they d all be on tracks that could slide in nicely and you could fit them to a child. 

In the field of sensors, ion-binding block copolymers, which allow the formation of functionalized vesicles, could be of special interest. Vesicles sensitive to magnetic field were obtained from aqueous dispersion of hydrophobic iron oxide nanoparticles and block copolymers of PGA and PBD [272], Sachsenhofer and coworkers reported on the embedding of hydrophobic gold nanoparticles into PEO-PBD polymersomes [273]. Recently, polymer vesicles containing Ru(bpy )32+ units in the wall with a high potential for application in catalysis were introduced [274],... 

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