| 摘要 |
Method and apparatus for sensing electric fields with a dipole antenna, wherein the antenna generates an antenna signal representative of electric field potential, includes a signal generator for generating mixing signals having known characteristics, variable capacitors for generating first output signals representative of the antenna signal, wherein the capacitance of the variable capacitors is varied by the mixing signals such that the antenna signal is frequency translated. A signal processor processes the first output signals to generate a second output signal representative of the electric field. In a preferred embodiment of the invention, the mixing signals are a quadrature pair of sine waves. In an especially preferred embodiment, the variable capacitors are each a frame, a speaker mounted to the frame. The speaker cones move in response to a signal applied to each speaker. A first plate is attached to the cone and a second plate is attached to the frame, wherein movement of the cone moves the first plate relative to the second plate. In a still further embodiment, an isolation member is provided to generate a third output signal which is isolated from one half of the dipole, i.e., the floating antenna reference. In such embodiment the antenna effective length variation, due to different measurement devices adding varying conductor lengths to the ground reference, is minimized. It is preferred for the isolation member to be an optical isolator.
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