Sensor fields

Magnetic Field Sensors on 3D-Eddy-Current Testing. 

Special probe geometries and combinations of different types of magnetic field sensors make an important contribution to the further improvement of the eddy-current testing method and results in new applications. 

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. 

Comparison of different magnetic field sensor systems... 

The following examples represent the importance of the impulse response for the comparison of different magnetic field sensors. For presentation in this paper only one data curve per method is selected and compared. The determined signals and the path x are related in the same way like in the previous chapter. 

So, a comparison of different types of magnetic field sensors is possible by using the impulse response function. High amplitude and small width of this bell-formed function represent a high local resolution and a high signal-to-noise-characteristic of a sensor system. On the other hand the impulse response can be used for calculation of an unknown output. In a next step it will be shown a solution of an inverse eddy-current testing problem. 

Due to its importance the impulse-pulse response function could be named. .contrast function". A similar function called Green s function is well known from the linear boundary value problems. The signal theory, applied for LLI-systems, gives a strong possibility for the comparison of different magnet field sensor systems and for solutions of inverse 2D- and 3D-eddy-current problems. 

To operate the MPI or LPI equipment at stable and reprodncable inspection conditions modern units are equipped with a monitoring and control system called "Quality Assurance Package" (termed QAP). The QAP System is ba.sed on an industrial PC with a bus system and field sensors. It ensures that process parameters important for the reproducability of the MPI or LPI are controlled an held between defined limits by a central computer system. It can be adapted to any old system, as well as integrated into new systems. 

Provide appropriate preventive maintenance of instruments and field sensors... 

Control and supervision systems should be designed with circuit monitoring and self-diagnostic testing to verify that the field sensors and devices are electrically active and connected. The system should alarm when an electrical fault is detected. 

This chapter provides an overview of the basic principles and designs of such sensors. A chemical sensor to detect trace explosives and a broadband fiber optic electric-field sensor are presented as practical examples. The polymers used for the trace explosive sensor are unpoled and have chromophores randomly orientated in the polymer hosts. The electric field sensor uses a poled polymer with chromophores preferentially aligned through electrical poling, and the microring resonator is directly coupled to the core of optical fiber. 

For an RF electric field sensor, bandwidth (speed) is another important requirement. The speed of a resonator is determined by the cavity ring down time r = QX/c. As in any devices using resonating structures, a trade off between sensitivity (which increases with Q) and speed (which decreases when Q increases) has to be made. At the wavelength of 1.55 pm, Q factors of 104 and 106 translates to a sensor bandwidths of 20 GHz and 200 MHz, respectively. 

All-Dielectric Radio Frequency Electric Field Sensor... 

Fig. 2.16 (a) A schematic drawing of polymer microring resonator couple to a side polished optical fiber, (b) A microscope image of the fabricated EO polymer electric field sensor, (c) SEM image of resonators fabricated on the polished flat of a free standing fiber. The scale bar in the picture represents 100 pm. Reprinted from Ref. 15 with permission. 2008 Institute of Electrical and Electronics Engineers... 

Fig. 2.17 The output of the RF electric field sensor at 550 MHz and 10 dBm RF input. Reprinted from Ref. 15 with permission. 2008 Institute of Electrical and Electronics Engineers...

Zhang, F. Chen, F. Qiu, K., An integrated electro optic E field sensor with segmented electrodes, Microw. Opt. Tech. Lett. 2004, 40, 302 305... 

Densmore, A. Xu, D. X. Waldron, P. Janz, S. Cheben, P. Lapointe, J. Delage, A. Lamontagne, B. Schmid, J. H. Post, E., A silicon on insulator photonic wire based evanes cent field sensor, IEEE Photon. Technol. Lett. 2006, 18, 2520 2522... 

Silicon Photonic Wire Evanescent Field Sensors... 

Different concentrations of BG bacterial spores (103 107 spores per mL) were introduced into the electric field sensor chip-based flow cell and an appropriate... 

The threat described in the first part of this chapter spurred increased investment in research and development technologies to prevent, detect, and respond to terrorist attacks. One specific area of research, sensors, particularly for chemical and biological agents and radioactive materials, in addition to radar and sonar, is the subject of this book. After describing the threat, this chapter goes on to discuss the use of sensors, fielded sensor capabilities, and existing gaps in sensor capabilities. 

Buried-line magnetic field sensors detect changes in a local magnetic field that are caused by the movement of metallic objects within that field. This type of sensor can detect ferric metal objects worn or carried by an intruder entering a protected area on foot as well as vehicles being driven into the protected area. 

Figure 21. Schematic diagram of (a) an evanescent field sensor, and (b) a simple waveguide circuit where the sensor is incorporated into a Mach-Zehnder interferometer.

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