A plasma device serves as an antenna, single or stacked plasma frequency selective surfaces, single or stacked plasma antenna arrays, plasma lamps, plasma limiters, plasma switch, plasma windows or plasma phase shifters. An electromagnetic wave signal is controlled to have a plasma frequency matched as nearly as possible to the frequency of incident electromagnetic signals for maximizing the antenna aperture and efficiency. Matching the frequencies permits the plasma device to have a physical size and shape substantially independent of the conventional optimal size and shape for a given transceived signal frequency. The plasma device plasma frequency is adjustable for tuning to different incident signal frequencies, thereby providing flexibility not available from conventional metal antennas.

 
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> Methods and apparatus for analyzing ultrasound images

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