| 摘要 |
<p>An interrogator in the form of a Tunnel Reader Programmer or TRP (20) includes field control means in the form of a lining (25, 26) of high permeability magnetic material for providing a low reluctance path for the interrogating field at the periphery of the cavity. Linings (25, 26) are, in this embodiment, produced from ferrite and disposed adjacent to respective walls (6, 8). In this configuration the vast majority of the interrogation field is diverted from the surface of walls (6, 8) and instead flows through the high permeability material parallel to those surfaces. With the reduction in the interrogation field at the surface of the walls (6, 8) due to linings (25, 26) the eddy currents in those walls are greatly reduced. However, the metallic walls continue to provide their screening properties.</p> |
