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Electromagnetic Testing

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By making careful measurements it is possible to map the strength and<br />

distribution of the driver coil's flux density as it travels down the tube wall. A<br />

graph can be generated, such as Figure 8.4, using experimental data that<br />

shows there are three distinct areas of interest. In an attempt to define the<br />

variations in the alternating current energy distributions that are present in the<br />

tube wall the following terminology has been developed:<br />

• Near Field (direct coupled) Zone - (0-1.5 tube diameters from the driver<br />

coil)<br />

• Transition Zone - (1.5-2 tube diameters from the driver coil)<br />

• Remote Field Zone - (2-3 tube diameters from the driver coil)<br />

Charlie Chong/ Fion Zhang

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