Abstract: A propeller according to an embodiment includes a hub and a series of blades extending outward from the hub. Each blade of the series of blades includes a core and a skin covering the core. The core may be formed of a ceramic first material and the skin is formed of a second material different than the ceramic first material. The ceramic first material of the core may be ceramic Si3N4 (silicon nitride), yttria-toughened zirconia ceramic, or alumina-zirconia ceramic, and the second material of the skin may be a polymer. The polymer skin is configured to function as a shock absorber protecting the ceramic core, and the ceramic core is configured to provide rigidity to maintain the shape of the propeller blades under aerodynamic loading, which enables improved aerodynamic efficiency and reduced noise generation.

Abstract: A sine wave oscillating circuit arrangement useful in generating an electromagnetic field, for example, comprises a resonant circuit including an inductor through which the current is tightly controlled and a capacitor connected in parallel, to which dc pulses are applied at a repetition rate equal to the resonant frequency. The current flowing in the inductor is sensed in phase detector and amplitude detectors. The results of these evaluations are applied to cascaded pulse position and pulse width and/or amplitude modulators. A current switching driver circuit driven by pulses from the modulator is connected to the resonant circuits for modifying the dc pulses applied for maintaining the sine wave current in the inductor at the proper amplitude and phase relationship and energy content inversely as the potential across the sampling resistor in the resonant circuit. The energy dissipated in damping the resonant circuit in one cycle of operation is replaced in the next cycle.