**6. Conclusion**

120 Magnetic Sensors – Principles and Applications

Another application of these sensors is in non-distructive testing for a variety of evaluations including medical implants and aircraft structures, the detection of cracks and corrosion in metals. Archeology is another field requiring systems including magnetic field sensors to resolve non-invasively details, the wide range of artifacts (1-1000 nT magnetic induction range ) and cultural objects. This field requires also new means of mapping prehistoric and historic sites in three dimensions rather than traditional two-

High sensitivity and high resolution magnetic sensors are needed in systems for medical diagnostics. Microfluxgate sensors based on MEMS technology can be employed to build cheap and portable systems for locating metallic foreign objects in the human body

Ripka, (2004) showed that fluxgate sensors can be used for mapping the distribution of ferromagnetic particles in the lungs after they are magnetized by strong DC field. Medical applications requiring precise miniaturized magnetic sensors include tracking devices and systems for monitoring magnetic markers such as magnetic "biscuits" and microbeads. Magnetic biscuits can be used for functional tests of digestive tract, while microbeads are used as markers in biotechnology. New types of fluxgate microsensors are being developed for these applications (Vopalensky et al., 2003). Also Hall magnetic sensors have been employed to visualize a magnetically market diagnostic capsule in real time inside human body (Mahfuzul-Aziz, 2008). Tracking devices using fluxgate sensors can be used for monitoring the 3-D position and also orientation of a small permanent magnet which can be attached to body or medical instrument (such as catheter). Another configuration is being used for tracking the motion of the body at further distances: signals from sensors attached

Typically Hall magnetic devices, due to their low sensitivity are employed for position sensing, current sensing, speed detection, electronic compasses. (Lenz & Edelstein, 2006). Silicon-based Hall sensors are widely employed, due to the suitability of integration with electronics (Popovic, 1997). However, higher sensitivity sensors can be obtained with III-V technology, allowing for applications such as biomolecular function detection (Manandhar et al., 2009). Also recently, the Scanning Hall probe microscopy (SHPM) has been developed based on III-V Hall sensors, allowing for quantitative mapping of nanoscale

Others nowadays applications such as geomagnetic measurements, environmental disturbance measurements as well as navigation systems demand for Hall miniaturized devices capable of measuring the vector magnetic field. Beside the cumbersome solution of mounting three Hall sensors with their sensitive axis orthogonal to each other, integrated three axis devices have been developed by employing silicon technology and the so called vertical Hall effect (Schott & Popovic, 1999). However these are often characterized by either different sensitivity for each component of the magnetic field (Schott et al., 2000), or by a cross-sensitivity among the direction-components (Popovic, 1999). Furthermore, offset compensation of vertical Hall element is more difficult than in the case of lateral (planar) Hall elements. In this context new materials and device configurations could open the way to realize reliable vector magnetic field sensors to be

superconducting and ferromagnetic materials (Bending et al., 2009).

dimensional methods.

to the body are collected and processed.

applied in different fields.

(Jing et al. 2009).

In this paper the authors described current research status in magnetic field sensors focusing on devices fabricated by exploiting MEMS technologies. The paper presents advances in some classes of devices such as resonant sensors, fluxgate sensors and Hall sensors that take advantages from these technologies. The authors focused on the description of such microsensors including operation principle, example of realized devices, highlighting the involved fabrication technologies. Possible applications of this new class of compact devices has also been reported.
