Abstract: Methods and apparatus for dimming light sources are described herein. In the described examples, a bias circuit selectively biases a switch during a half-cycle of a line current after a delay. In some examples, the delay of the bias circuit is adjustable by a user to adjust the amount of light a light source emits. A charge circuit substantially biases the switch for a period of time in the event the bias circuit experiences an operating condition that may cause the switch to become open during the half-cycle of the line current. As a result of the charge circuit, the light source coupled to the line current does not experience substantial flickering.

Abstract: Methods and apparatus for self-starting dimmable ballast circuits are disclosed. In the described examples, a dimmable ballast circuit includes a rectifier, an energy storage device, a driver circuit, and a resonant circuit that are configured to actuate the light source such as a fluorescent lamp. The power source is coupled to the light source via a single resonant circuit that includes power factor correction therein. Further, the resonant circuit is selectively configured to start the light source without requiring a separate starter circuit. Further, energy storage device is a capacitor that stores high frequency energy and continually recycles energy in the circuit, resulting in a circuit with a large power factor. Because the current flowing in the circuit is substantially sinusoidal, the described examples generally have an ideal power factor.

Abstract: Methods and apparatus for powering dimmable ballast circuits are disclosed. In the described examples, a dimmable ballast circuit includes a rectifier, an energy storage device, a driver circuit, and a resonant circuit that are configured to actuate the light source such as a fluorescent lamp. Specifically, energy storage device is a capacitor that stores a high frequency energy and continually recycles energy in the circuit, resulting in a circuit with a large power factor. Further, because the current flowing into the resonant circuit is substantially sinusoidal, the circuit generally has an ideal crest factor, thereby increasing the lifespan of the light source.

Abstract: A current interruption circuit for interrupting current flow from a source of DC power to a load includes: an electronically controllable primary switch device adapted to be series coupled between the DC power source and the load, the primary switch device having a voltage thereacross which is proportional to a current flowing therethrough when biased in an on state. The circuit also includes a voltage sensing circuit adapted to sense the voltage across the primary switch device and produce a control signal in response thereto; and a gate drive circuit adapted to receive the control signal and bias the primary switch in an off state when the control signal indicates that the voltage across the primary switch has exceeded a predetermined value.

Abstract: Method and apparatus for in vivo or in vitro selective deposition of microwave power patterns in lossy dielectric materials, particularly biological tissue. Configured as a needle-like probe, a miniature coaxial cable (1) having a circumferential gap (12) in the shield (2) is wrapped with an electrically thin dielectric substrate (18). The cable center conductor (6) extends immediately past gap (12) and is shorted to cable shield (2). A thin conductive dipole resonator (21) is positioned on substrate (18) and over gap (12) to achieve inductive coupling between the cable center conductor (6) and the dipole resonator (21) through gap (12). The ends of the dipole resonator (21) are capacitively (22) loaded so as to make the current on resonator (37) more uniform and to greatly reduce and stabilize the resonant frequency to be essentially insensitive to the dielectric properties of the surrounding material.

Abstract: A highly sensitive, direct-contact, in situ sensor for nondestructively measuring or monitoring the complex dielectric and conductive properties of solids, liquids, or gasses at microwave frequencies. A metal microstrip dipole resonator (11) is etched on the surface of a dielectric substrate (12) which is bonded to a copper ground plane (14). The dipole resonator is electromagnetically driven by mutual inductive coupling to a short nonresonant feed slot (13) formed in the ground plane (14). The slot (13) is driven by a coaxial feed line (7) or a microstrip feed line (16) extending from a swept microwave frequency source (2) which excites the incident wave (17). Alternatively, the metal resonator is omitted and the length of the slot (15) is increased so that it becomes the resonator. In use, the sensor is placed in close physical contact with the test material (9) having complex dielectric constant .epsilon.* (=.epsilon.'-j.epsilon.") or conductivity .sigma..

Abstract: A power amplifier for use in medical and veterinary testing and therapy. A tunable pulse-width-modulated signal generator is connected to a gating element to provide a digital waveform suitable for comprehensive control of the waveform shape and average output power provided by the apparatus. The digital waveform controls a power driver. Through use of a high-Q resonant circuit including a capacitor and a primary winding of a coil assembly, a voltage of about 150-400 volts is increased to about 10 kilovolts at the primary winding. The coil assembly has a secondary:primary turns ratio of 10:1, resulting in a signal of about 100 kilovolts at the output of the secondary winding. This arrangement produces a corona discharge at a discharge pin connected to the secondary winding. A manual tuning embodiment and a self-tuning embodiment are disclosed.

Abstract: The invention is method and apparatus for in situ mechanical adjustment of electromagnetic power coupled through an aperture or slot. In its preferred form this adjustment of coupling is achieved by electrically connecting two thin, curved conductive leaf springs (20) to ground plane (14) at the ends of the coupling aperture or slot (12). The springs (20) are curved so as to bend away from the center of the aperture or slot opening (12). The aperture or slot is usually enclosed by a metal backing cavity (22) to prevent radiation from the rear of the aperture or slot and to provide a method for mechanically adjusting the position of springs (20) over the aperture or slot (12), e.g., by adjustment of screws (24). By advancing or retracting screws (24), leaf springs (20) are caused to progressively cover or uncover aperture or slot (12), thereby adjusting the electric field across the aperture or slot (12) and the coupled electromagnetic power through the aperture or slot (12).

Abstract: Method and apparatus for in vivo or in vitro sensing of complex dielectric properties of lossy dielectric materials, particularly biological tissue. Configured as a needle-like dielectric sensor, a coaxial cable (1) having a circumferential gap (12) in the shield (2) is wrapped with an electrically thin dielectric substrate (18). The cable center conductor (6) extends immediately past gap (12) and is shorted to cable shield (2). A thin conductive dipole resonator (16) is positioned on substrate (18) and over feed gap (12) to achieve inductive coupling between the cable center conductor (6) and the dipole resonator (16) through gap (12). Superstrate (22), which could be a dielectric catheter, covers the entire sensor assembly (10). By measurement of the resonator resonant frequency and the input impedance matching factor at the resonant frequency, the real and imaginary dielectric components (.epsilon.', .epsilon.") of the test material into which the sensor is inserted are determined.

Abstract: A microwave signal is transmitted from a transmitting antenna through a transfer medium to an electrically modulated and mechanically spun microwave scatterer. The scatterer may include an electric field responsive antenna, such as a dipole, for measurement of the electric field, or a magnetic field responsive antenna, such as a loop, for measurement of the magnetic field. An impedance within the scatterer is electrically modulated at an audio frequency, and the scatterer is mechanically spun at an angular frequency substantially below that at which it is electrically modulated. The scatterer thereby re-radiates to a receiving antenna a signal at the microwave source frequency which is modulated at both the frequency of electrical modulation and the mechanical spinning frequency of the scatterer.

Abstract: A microwave signal is transmitted from a transmitting antenna through a transfer medium to an electrically modulated and mechanically spun microwave scatterer. The scatterer may include an electric field responsive antenna, such as a dipole, for measurement of the electric field, or a magnetic field responsive antenna, such as a loop, for measurement of the magnetic field. An impedance within the scatterer is electrically modulated at an audio frequency, and the scatterer is mechanically spun at an angular frequency substantially below that at which it is electrically modulated. The scatterer thereby re-radiates to a receiving antenna a signal at the mocrowave source frequency which is modulated at both the frequency of electrical modulation and the mechanical spinning frequency of the scatterer.

Abstract: The present invention makes it possible to provide a guided wave antenna having a radiation pattern which can be controlled electronically, by control signals derived from a computer or any other suitable source. In this way, the directional characteristics of the antenna can be adjusted and/or scanned rapidly, without any mechanical manipulation of the antenna. In one embodiment, a guided radio wave is launched along an antenna surface having an array of elements which provide variable non-uniform surface impedance adapted to be controlled by electronic signals. For example, each variable impedance element may comprise a wave guide section having one end leading from the antenna surface. Each wave guide section may include a solid-state electronic reflection amplifier having charcteristics which can be varied by supplying control signals to the amplifier, to vary the magnitude and phase angle of the wave reflected from the reflection amplifier.