Abstract: In one embodiment, a return flux linear alternator employs a magnet assembly that includes a pair of permanent ring magnets with opposing polarity and a pair of air gaps. The additional permanent ring and air gap complete a magnetic flux loop of the alternator rather than the magnet pole, as in traditional designs. An alternator coil assembly includes a pair of oppositely wound coil sections that each linearly move through a respective one of the pair of air gaps. In addition, the return flux linear alternator may employ a variety of structures to increase mechanical strength, including a reinforcement fabric, and a variety of structures to increase electrical efficiency, including a thermally conductive but electrically nonconductive spacer between the coil sections and multiple pairs of electrical leads.

Abstract: In one embodiment, a photoacoustic effect measurement instrument for measuring a species (e.g., a species of PM) in a gas employs a pair of differential acoustic cells including a sample cell that receives sample gas including the species, and a reference cell that receives a filtered version of the sample gas from which the species has been substantially removed. An excitation light source provides an amplitude modulated beam to each of the acoustic cells. An array of multiple microphones is mounted to each of the differential acoustic cells, and measures an acoustic wave generated in the respective acoustic cell by absorption of light by sample gas therein to produce a respective signal. The microphones are isolated from sample gas internal to the acoustic cell by a film. A preamplifier determines a differential signal and a controller calculates concentration of the species based on the differential signal.

Abstract: This invention provides a coil and magnet assembly that is operatively interconnected with an oscillating free piston that moves along an axis. A coil mounting disk is operatively connected to a coil assembly. A magnet assembly is mounted on a magnet base. The magnet assembly is coaxial with respect to the coil assembly. The coil assembly and the magnet assembly are in oscillating motion with respect to each other in conjunction with oscillating motion of the free piston. A spring assembly comprising a plurality springs, symmetrically positioned about the axis, extend between the magnet base and the coil mounting disk, so as to move in conjunction with the oscillating motion along the axis. At least some of the springs are conductive and electrically connect the mounting disk to the magnet base. The piston can reside in a casing that is part of either a two-stroke engine or a fluid pump.

Abstract: In one embodiment, a frequency generator produces an excitation signal, a local oscillator signal, and a reference signal at a difference frequency of the excitation signal and local oscillator signal. The excitation signal is applied to a physical system to produce a response signal, which is mixed with the local oscillator signal. A filter selects a difference frequency component. The frequencies of the excitation signal and/or local oscillator signal are varied, such that the magnitude of the difference frequency is constant, but a sign of the difference frequency changes from positive to negative. The phase shift of the difference frequency component, with respect to the reference signal, at each of the two signs of the difference frequency, is measured. The measured phase shift at the negative sign is subtracted from the measured phase shift at the positive sign, and the difference is divided in half, to produce a result.

Abstract: In one embodiment, a frequency generator produces an excitation signal, a local oscillator signal, and a reference signal at a difference frequency of the excitation signal and local oscillator signal. The excitation signal is applied to a physical system to produce a response signal, which is mixed with the local oscillator signal. A filter selects a difference frequency component. The frequencies of the excitation signal and/or local oscillator signal are varied, such that the magnitude of the difference frequency is constant, but a sign of the difference frequency changes from positive to negative. The phase shift of the difference frequency component, with respect to the reference signal, at each of the two signs of the difference frequency, is measured. The measured phase shift at the negative sign is subtracted from the measured phase shift at the positive sign, and the difference is divided in half, to produce a result.

Abstract: This invention provides a system and method that enables the use of incoherent light sources, such as light emitting diodes, to provide for the detection of gaseous species which exhibit broadband absorption features (e.g., nitrogen dioxide and the halogen gases). The light emitting diode (LED) is an ideal light source for such an arrangement in that it can be modulated at high frequencies (allowing for omission of external modulation equipment) and provides sufficient illumination within a reasonably narrow wavelength band as compared to, for instance, an incandescent light source. A further advantage of a LED as a light source compared to alternatives such as a gas discharge or arc lamp is that the light output of the LED is highly stable, limited by the stability of the current source used to drive it. Use of a confocal or near-confocal resonant optical cavity maximizes coupling of the light source to the cavity.

Abstract: A miniature, two cycle engine with a linear electrical generator is presented. The piston attaches to the spring and a moving coil is also attached to the spring and/or rod assembly distal from the cylinder head. The spring is formed with an integral end fitting from one piece of preferably titanium stock. A permanent magnet is arranged where the coil moves within the magnet air gap to produce electrical power. The system operates at the resonant frequency of the spring and active mass. A glow plug provides the ignition source and hydrocarbon fuel is used. The package is about an inch wide and about 2-3 inches long, and it weighs about 30 grams.

Abstract: A method and apparatus for detecting fluorescence from sunlit plants is based on spectral line discrimination using the A-band and B-band absorption of atmospheric oxygen. Light from a plant including scattered sunlight and the fluorescence from chlorophyll is passed through a chopper into a cell containing low-pressure, high-purity oxygen. A-band or B-band wavelengths present in the light are absorbed by the oxygen in the cell. When the chopper is closed, the absorbed light is remitted as fluorescence into a detector. The intensity of the fluorescence from the oxygen is proportional to the intensity of fluorescence from the plant.

Abstract: An off-axis cavity absorption cell (10) includes astigmatic mirrors (22, 28). The cell design is based on a prototype design that yields a closed beam path having a desired geometry, but the mirrors are fabricated so that the ratios of their radii of curvature are actually larger than those calculated for the prototype. To achieve the desired closed beam path, the mirror spacing is adjusted from that of the prototype design, and the planes of their axes of greatest curvature are oriented out of the alignment that characterizes the prototype design. If the mirrors' manufacturing process yields errors in the curvature-radius ratios within certain prescribed limits, a cell of this design can be adjusted to achieve the closed beam path by simply changing the mirror separation and the "twist angle" between their respective planes of maximum curvature radius.

Abstract: In a laser emitter-receiver system, a tunable diode laser provides a beam of coherent light having a selected frequency. An infrared detector spaced from the source detects the light transmitted along the beam path between the source and the detector and produces a corresponding output in response thereto. A heating laser provides radiation to the diode laser to heat, and thereby to change the frequency of, the latter laser. The radiation from the heating laser is varied periodically to modulate the intensity of the radiation incident on the diode laser thereby to frequency-modulate the diode laser output over a selected tuning range. A controller responsive to the detector output regulates the current to the diode laser to minimize selected frequency components of the modulated light beam from that laser so that the power output of the diode laser varies minimally when that laser is tuned over the selected tuning range.

Abstract: A detector for a gas analyzer includes a thermal detector, an absorptive film on the surface of said thermal detector, and an enclosure containing a reference gas of the gas species of interest such that the thermal detector is in thermal contact with both the absorptive film and the reference gas. During irradiation, the absorptive film absorbs radiation which passes through the reference gas and causes the thermal detector to generate a corresponding output. When the irradiation is terminated, the heat content of the reference gas, which will be dependent upon the amount of the radiation absorbed, will be communicated to the thermal detector to cause the thermal detector to provide a second output representing the amount of radiation absorbed by the reference gas.

Abstract: A method and apparatus for operating a dual-frequency gas laser so as to controllably switch between frequencies makes use of a cavity so tuned that the comb of resonant frequencies is not commensurate with the frequency difference between the laser operating frequencies, and, in a preferred embodiment, with one of the resonant frequencies tuned to coincide with one of the operating frequencies. The cavity length and overall gain at each frequency are so selected that the spacing between resonant frequencies is greater than the breadth above unity gain of the individual peaks of the gain vs. frequency curve. The active material is subjected to a magnetic field which may be varied in a controlled manner. In a preferred embodiment, this field is applied normal to the optical axis of the resonant cavity, and an optical element within the cavity is arranged to act as a plane polarizer with its plane of polarization normal to the magnetic field.

Abstract: A method of making a light equalizer comprises the steps of mixing two different powdered crystalline materials, each of a slightly different index of refraction so as to provide scattering of selected wavelengths of light. The materials are compacted under pressure to form an integral body containing a plurality of light scattering centers. The exterior surfaces of the body are covered with a reflective coating except for two opposite ends through which the selected wavelengths of light can be transmitted so as to provide a substantially uniform distribution of light at its output.

Abstract: A method of making a light equalizer comprises the steps of selecting a powdered crystalline material capable of being compressed to form a body transparent to selective wavelengths of light. The material is compressed to a point short of complete transparency so as to provide a plurality of light scattering centers throughout the bulk of the body. A stack of the bodies are formed in which the bodies are disposed along a common axis. The exterior surfaces of the stack thus formed are covered with an internally reflective coating except for two opposite ends thereof, so that light of selected wavelengths transmitted through the stack will be substantially uniformly distributed at the output of the stack.

Abstract: A methane detector comprising a He-Ne laser in which the plasma tube forms a portion of the resonant cavity and the laser can be stimulated to emit at two different atomic resonances at separate wave numbers .nu..sub.1 and .nu..sub.2, one of which is more strongly absorbed by methane than the other. Means such as a beam splitter disposed in the resonant cavity, are provided for directing two beams outwardly from the cavity to a pair of detectors each provided in the path of a respective beam. The cavity is tuned so that its length L meets the criterion m/2L = .nu..sub.1 -.nu..sub.2, m being a number of half integers. Means are provided for cyclically varying the gain of the laser across one free spectral range through some tuned center value.

Abstract: An optical system is provided to minimize the angle-dependent transmission characteristics of interference filters, the optical system including a light equalizer having an output aperture across which each area element exhibits substantially the same emission intensity regardless of the distribution of light into the input aperture of the equalizer. The output aperture of the equalizer is disposed at the focal surface of collimating optics and the resultant collimated light constitutes the input to the interference filter.The equalizer is embodied in a transmissive element which is divided into pairs of transmissive channels, the number of such pairs increasing with the distance from the input aperture. The interface between the adjacent channels is, at least in part, leaky as by being substantially half transmissive half reflective. The exterior surface of the equalizer is covered with an internally reflective coating except for the input and output apertures.

Abstract: A light equalizer having an output aperture across which each area element exhibits substantially the same emission intensity regardless of the distribution of light into the input aperture of the equalizer. The equalizer is embodied in a stack of a plurality of transmissive elements, a number of which provide a multiplicity of light scattering centers. The exterior surface of the equalizer is covered with an internally reflective coating except for the input and output apertures.