Hall-effect probes

At very high frequencies, the current is measured by assessing one of the effects that it produces. Several techniques are possible, e.g. (1) measuring the temperature rise when the current flows through a known resistance or (2) using a Hall-effect probe to measure the electromagnetic field created by the current. 

Most spectrometers measure the magnetic field by a Hall effect probe consisting of a sensor mounted on one of the pole faces of the magnet. However, such estimates of the value of B inside the cavity are not sufficiently accurate to be used for g-factor determinations. There are two ways around this problem (i) measure the spectrum of a solid free radical such as dip-henylpicrylhydrazyl (DPPH), which has a well-known g-value (2.0028), at least once during acquisition of the desired spectrum or (ii) use of an NMR gaussmeter probe inserted in or near the cavity several times during the collection of the spectrum. 

Hall effect The development of a transverse electric field in a current-carrying conductor placed in a magnetic field. Hall-effect probes are used to measure magnetic field intensities. See also Drift, EXB. 

The sensor of the third method is a Hall-effect device situated in a magnetic field of two differential arranged exiting coils. Fig. 3 shows the construction of the sensor probe. 

Due to the symmetrical construction the resulting magnetic field between the two coils is zero in y-direction, if a conductive structure is symmetrically situated in the area a (see fig. 3) in the near of the probe. A resulting field is detectable by the Hall-effect device, if there are unsym-metrics in the structure in area a. The value of the Hall voltage is proportional to the detected magnetic field. 

Later on. Song et al. [19] performed a four-point resistivity measurement on a large bundle of CNTs of 60 pm diameter and 350 pm distance between the two voltage probes. They interpreted their resistivity, magnetoresistanee and Hall effect results in terms of semimetallie conduction and 2D weak localisation as for the case of disordered turbostratie graphite. 

One form of the gaussmeter that is used commonly in the laboratory consists of a cmient carrying semicon-ducfii element called the Hall probe, which is placed perpendicular to the m nefic field being measured. As a consequence of the so-called Hall effect, a volt e per-... 

Part Two of this volume is entitled Introduction. It too has four chapters. Chapter 5 presents a study of the influence of diverse fields on flames Chapter 6 discusses a classic application of the Peltier effect Chapter 7 is devoted to metal/plasma interaction, and more speciffcally to the Langmuir probe, and finally Chapter 8 discusses space propulsion by the Hall effect. 

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