| 摘要 |
<p>The present invention provides a material for the construction of external coverings accessible by humans or animals. The coverings may enclose high voltage, high frequency apparatus, for example in MRI systems (fig. 1), where coils may operate in air or gas at a pressure lower than atmospheric pressure, to reduced acoustic noise. The covering provides for increased breakdown voltage between the high voltage source and the patient, by adaptation of materials and structures. The covering comprises a tray shaped element 32 closed by a porous covering 34, defining an enclosed cavity 38. The cavity may contain foils 39 of an electrically non-conductive material, for acoustic damping. The cavity 38 is at atmospheric pressure due to the pores 36. In use, the covering carries a greater proportion Vs of the RF voltage Vrf (fig.2) across it, thereby reducing the voltage Vg across the gap 22 (which is at low pressure) and reducing likelihood of breakdown.</p> |
