Magnetic flux

When a magnetic field is present in a vacuum, there is a scalar physical quantity called the magnetic flux, denoted O, expressed in weber (Wb), and defined by the following equation  

When a magnetic flux passes through N coils of a solenoid, it induces inside the electrical circuit an electromotive force, emfor U, expressed in volts. This phenomenon is called electromagnetic induction, and according to the Faraday s law, the electromotive force induced inside the electrical circuit is proportional to the rate of change of the magnetic flux  

In addition, Lem s law indicates that the induced voltage exhibits an opposed direction to the flux change producing it 

Replacing the magnetic flux by the product of the magnetic induction by the coil surface area we obtain  

This relation is important because it indicates that an electric current can be generated inside a solenoid by varying a magnetic field strength inside it. Applying this simple principle it is then possible to measure the magnetic field and magnetization of materials. 

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To increase the magnetic flux (very weak reluctance). 

Eddy currents and the magnetic flux that is associated to them are proportional to the radial distance of the coil center. The magnetic flux is proportional to the probe induction and consequently to the passing current. The theoretic calculation of this induction is given by the following equation ... 

While the conventional Eddy current read out uses induced voltage and voltage amplification, the SQUID read out operates the probe as a magnetic flux transformer. This demands to minimize the resistivity of the pick up loop. 

The variation of the Z of the solenoid mark a transfer of energy at distance between the solenoid and the conducting piece. The variation of the impedance is due to the modification of the magnetic flux d) crossing the solenoid. In fact, the flux differs in amplitude and in phase when the conducting piece is near the solenoid. Similarly, the flux will be influenced by the presence of defect. 

For presentation in this paper a Hall probe of a Gaussmeter (Bell, Series 9900) is used to test the function of the sensor combination. It determined the magnetic flux B . 

Johnston D Aboveground storage tank floor inspection using magnetic flux leakage Material Perform t.31 no 10 1990 p.36-39. 

Principle of Magnetic Flux Leakage for detection of wall loss... 

The equation describes the manner in which the nuclear magnetization, M, at position r and time t processes about the magnetic flux density, B, in which it is found. The constant y is the magnetogyric ratio of the nuclides under study. The precessional frequency, co, is given by the Lannor equation. 

Magnetic fluids Magnetic flux leakagf Magnetic inductions Magnetic level indicator Magnetic materials... 

H, for which J = 0, is the intrinsic coercivity whereas the usual coercivity, for which S = 0, is denoted by H or H. For permanent magnets, the value (BH), the maximum energy product, is an important measure of quaHty. The value (BH), iadicated ia the secoad quadrant of Figure 1, represents the poiat of maximum efficieacy where a givea amouat of magnetic flux is produced by the smallest amouat of material. 

Fig. 1. Schematic of magnetic flux leakage tests where H,B represents an external appHed magnetic field. See text, (a) Saturated material having no crack,...

High temperature is an important requirement for the attainment of fusion reactions in a plasma. The conditions necessary for extracting as much energy from the plasma as went into it is the Lawson criterion, which states that the product of the ion density and the confinement or reaction time must exceed 10 s/cm in the most favorable cases (173). If the coUisions are sufficiently violent, the Lawson criterion specifies how many of them must occur to break even. Conventional magnetic confinement involves fields of as much as 10 T (10 G) with large (1 m ) plasmas of low densities (<10 particles/cm ) and volumes and reaction times of about 1 s. If the magnetic flux can be compressed to values above 100 T (10 G), then a few cm ... 

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