An electromagnetic Helmholtz resonator comprised of a capacitor with an aperture is investigated theoretically and experimentally. It is proposed that this resonance may be described using effective impedances describing the capacitor and aperture, similar to lumped element descriptions of the acoustic Helmholtz resonator. The dipole impedance of an electromagnetic aperture is derived and verified using the finite element method. Incorporating standard network relations, the aperture impedance can be used to calculate radiated power. Measurements of a capacitor demonstrates that the transmitted voltage through the capacitor is modified by induced charges. An induced voltage is introduced, and predictions agree with observations. Measurements of a capacitor with an aperture in the grounded plate indicate that induced currents cancel the imaginary impedance of the aperture, and double the real impedance. The observed impedance is close to predictions using the derived aperture impedance, confirming the utility of the aperture impedance in describing the system. The numerically obtained aperture electromagnetic fields are similar to the Birkeland current distribution and the cross polar cap potential in the Earth's polar ionosphere, motivating a model where the polar ionosphere is treated as an effective aperture. It is proposed that this effective aperture interacts with the capacitor formed between the Earth and ionosphere, creating an electromagnetic Helmholtz resonator. Predictions made with this model agree with measurements of transmitted power and phase velocity by FAST during a geomagnetic substorm, measurements of the Ionospheric Alfvén Resonator, and oscillations recorded by ground based magnetometers. The same effective aperture behavior is expected in sunspots and polar coronal holes. A peak is predicted in Alfvén wave power across the transition region for waves with a 5 min. period that delivers an average power over 100 W/m2 to the corona, sufficient to heat the quiet corona and launch the solar wind. Applied to sunspots, a minimum umbral temperature of 3750 K is predicted with a peak in transmitted power at 3 min., consistent with observations. A prototype electromagnetic guitar and associated methods to obtain music are also presented. These instruments replace the acoustic systems normally employed for musical instruments with electromagnetic equivalents and music samples are presented.
*U.S. PATENTS PENDING 20070017344, 20070017345, 20070214940
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|Advisor:||Heelis, Roderick A., Earle, Gregory D.|
|School:||The University of Texas at Dallas|
|School Location:||United States -- Texas|
|Source:||DAI-B 70/09, Dissertation Abstracts International|
|Keywords:||Dipole impedance, Electromagnetic Helmholtz resonators, Helmholtz resonators, Sunspots|
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