Abstract: A robust, compact spectrometer apparatus for determining respective concentrations or partial pressures of multiple gases in a gas sample with single as well as multiple and even overlapping, absorption or emission spectra that span a wide spectral range.

Abstract: A remote sensing device for determining at least one characteristic of a vehicle emission plume includes a radiation source, a detector, and a plurality of filters. Either the filters or the detector are movable relative to the other such that different filters, each of which is capable of filtering out radiation except radiation of a predetermined wavelength band, can be used to filter the radiation directed to the detector. Also disclosed is a method for remotely determining at least one characteristic of a vehicle emission plume using a single detector and a plurality of filters wherein either the detector or the filters are positionable relative to one another.

Abstract: A vehicular forward-vision display system includes a night-vision camera for scanning a nighttime image ahead of a vehicle and a head-up display for displaying the scanned nighttime image as a virtual image on a front windshield. Luminance of the displayed image is decreased with decreasing vehicle speed. The luminance of the nighttime image is thereby decreased under a low speed where vision aid is not so necessary. This decreasing of the luminance results in giving a driver relief from the bother of being caught by the scanned image displayed on the front windshield.

Abstract: Optical sensors, more particularly infrared sensors, use an array of MEM micromirrors to chop a light beam impinging on an array of sensors of an imaging device to minimize the influence of thermal noise. The array of micromirrors preferably switches the beam impinging on the array of sensors between an image to be analyzed and an image of a reference black body at a clearly defined temperature. These sensors are not cooled and require no cryogenic devices.

Abstract: A calibration method for radiometric imaging systems that relies on an absolute measurement of scene radiance (thereby requiring a baseline measurement of zero radiance), and a shutter assembly for taking the baseline measurement of zero radiance which is operable under cryogenic temperatures as low as 80.5K (?192.65° C.) in vacuums measuring <10?6 torr (mm Hg). The shutter assembly generally includes an actuator and a shutter mechanism. The actuator is preferably a miniature solenoid assembly capable of operation in extreme environments (e.g. vacuums of <10?6 torr, temperatures below 90K). The shutter mechanism preferably includes a single shutter blade and is also capable of operation when subjected to extreme environments. The method of using the shutter assembly provides a zero radiance reference measurement for an infrared imaging system, thereby providing a basis upon which absolute scene radiance may be determined.

Abstract: A continuously variable diaphragm or swappable fixed aperture for use in thermal infrared cameras, which aperture or diaphragm can be cooled to cryogenic temperatures. The invention contemplates mounting aperture control means, if necessary, in a vacuum or extending the control mechanism through a vacuum in a thermally isolated manner to avoid radiation load on the photocell. The inventive method implements such a diaphragm and control system. The invention makes possible the object of using a single thermal infrared camera under a wide variety of target-scene radiation conditions that may be rapidly changing, with interchangeable or zoom camera lenses requiring matching or different size cold stops, and under other such dynamic situations.

Abstract: A waveguide having a periodic structure and the excitation of exciton polariton as one form of interactions between radiation fields and matter systems are applied to light switching to provide an optical switch that is excellent in light intensity extinction ratio and operable at a speed in the terahertz order. The optical switch includes a polariton and photon interacting region (5) made of a grating (3) formed on a top face of a transparent substrate (2) and a semiconductor layer (4) with which the grating (3) is covered. The polariton and photon interacting region (5) is irradiated from a free space with a controllable light (7) having a preestablished wavelength and also from a free space with a control light (6) having a preselected wavelength to control the transmissivity of the controllable light (7) through the polariton and photon interacting region (5).

Abstract: A light sampling system for sampling scattered light from mirrors in an optical switch. The system includes four basic components: an imaging lens, a multi-channel liquid crystal light valve (LCLV), a collecting lens, and a light sensor. Light scattered by each mirror, is collected by the imaging lens, which re-images the light onto the LCLV. The LCLV is divided into multiple regions, one for each mirror to be monitored. Each region can independently be made opaque (“closed”) or transparent (“open”) to light reaching it. Light passing through all open regions of the LCLV is collected by the collecting lens, which focuses the light onto the light sensor. The light sensor registers a response to light passing through the LCLV. Each region of the LCLV can be programmed to be open or closed for any length of time, in any combination or sequence with any other region or regions, depending upon how the user wishes to monitor the scattered light.

Abstract: A robust, compact spectrometer apparatus for determining respective concentrations or partial pressures of multiple gases in a gas sample with single as well as multiple and even overlapping, absorption or emission spectra that span a wide spectral range.

Abstract: Optical sensors, more particularly infrared sensors, use an array of MEM micromirrors to chop a light beam impinging on an array of sensors of an imaging device to minimize the influence of thermal noise. The array of micromirrors preferably switches the beam impinging on the array of sensors between an image to be analyzed and an image of a reference black body at a clearly defined temperature. These sensors are not cooled and require no cryogenic devices.

Abstract: This invention is a micromachined sensor pixel structure that can be fabricated either as a discrete sensor or in array form with application to thermal sensing of radiation receive from various wavelength emitters. The transmissivity of a thermally-isolated microplatform is a sensitive function of temperature. This transmissivity is modulated by incident radiation from sources including infrared sources. The transmissivity of a micromachined structure is interrogated by means of an optical carrier. Readout is obtained by means of conventional silicon optical sensors or imagers. A multiplicity of micromachined pixels can be tailored for specific wavelengths permitting the array to operate as a multispectral imager with windows ranging from ultraviolet to millimeter wavelengths.

Abstract: The invention relates to a method and an apparatus for measuring a coating from paper or board. The measurement is carried out by one detector at different times or by two detectors simultaneously. IR radiation directed at the coating and radiation emerging from the coating are chopped synchronously in blocks. A wavelength band sensitive and insensitive to the absorption are bandpass filtered and measured in both the MIR and NIR region. The absorption strength is measured in a digital signal processing block by comparing the radiation sensitive to absorption to the radiation insensitive to absorption, and the amount of each coating component is determined in the digital signal processing block on the basis of the absorption strength.

Abstract: An IR camera comprises an IR Focal Plane Array having a number of detector elements as sensor devices, an optical system focusing an object onto the Focal Plane Array, and a signal processing system connected to the Focal Plane Array. The camera also has a modular structure comprising a camera housing provided with the Focal Plane Array and the signal processing system, an absorbent/emitting shielding device connected to the camera housing, and an optical focusing system removably mounted to the shielding device.

Abstract: The present invention provides for an improved electromagnetic radiation detector having a micromachined electrostatic chopper/shutter device. The MEMS flexible film chopper/shutter device provides reliability, efficiency, noise reduction and temperature fluctuation compensation capabilities to the associated electromagnetic radiation detector. An electromagnetic radiation detector having an electrostatic chopper/shutter device includes a detector material element and flexible film actuator overlying the detector material layer and moveable relative thereto. The flexible film actuator will typically include an electrode element and a biasing element such that the actuator remains in a fully curled, open state absent electrostatic voltage and moves to a fully uncurled, closed state upon the application of electrostatic voltage. Arrays that incorporate a plurality of electromagnetic radiation detectors and/or electrostatic shuttering devices are additionally provided for.

Abstract: In an infrared imaging device, shutting means 40 is configured so that it can be opened/closed and so as to shut off an infrared radiation coming into an optical system 20 when it is closed. During an imaging operation, the shutting means 40 is opened, and the optical system 20 causes an infrared radiation from an object 70 to form an image on an infrared detector 10. The infrared detector 10 outputs a signal according to the amount of infrared light received by each pixel. Correction means 30 corrects sensitivity variations among pixels, the influence of the infrared radiation from the optical system 20, etc. During a calibration operation, the shutting means 40 is closed, and the correction means 30 determines a correction coefficient for correcting fluctuations in the amount of infrared radiation from the optical system 20 by using the output of the infrared detector 10 imaging the shutting means 40.

Abstract: An apparatus for simulating a blackbody utilizes several plates to absorb and reflect electromagnetic radiation. Electromagnetic radiation entering the apparatus from a certain view is reflected from one plate to another, until the direction of travel of the electromagnetic radiation is reversed. Each time the electromagnetic radiation is reflected, the majority of the electromagnetic radiation is absorbed resulting in a negligible amount of incoming electromagnetic radiation escaping the apparatus.

Abstract: A self-calibrating nulling radiometer for non-contact temperature measurement of an object, such as a body of water, employs a black body source as a temperature reference, an optomechanical mechanism, e.g., a chopper, to switch back and forth between measuring the temperature of the black body source and that of a test source, and an infrared detection technique. The radiometer functions by measuring radiance of both the test and the reference black body sources; adjusting the temperature of the reference black body so that its radiance is equivalent to the test source; and, measuring the temperature of the reference black body at this point using a precision contact-type temperature sensor, to determine the radiative temperature of the test source.

Abstract: The present invention provides for an improved electromagnetic radiation detector having a micromachined electrostatic chopping device. The MEMS flexible film chopping device provides reliability, efficiency, noise reduction and temperature fluctuation compensation capabilities to the associated electromagnetic radiation detector. An electromagnetic radiation detector having an electrostatic chopper device comprises a detector material element, first and second electrodes in electrical contact with the detector material element and electrically isolated from one another. Additionally, the chopper device will incorporate a flexible film actuator overlying the detector material layer and moveable relative thereto. The flexible film actuator will typically include an electrode element and a biasing element such that the actuator remains in a fully curled, open state absent electrostatic voltage and moves to a fully uncurled, closed state upon the application of electrostatic voltage.

Abstract: A background rejection circuit uses the harmonic content of an angularly narrow target to produce a signal. The signal is used to modulate an externally derived audio signal to produce a target indication signal free of background noise.

Abstract: A liquid crystal infrared light chopper includes a polarizer that receives and polarizes incoming infrared light, a layer of ferroelectric liquid crystal material switchable between at least two states, a pair of IR transparent, conductive substrates positioned on either side of the liquid crystal layer and an analyzer that blocks IR light of one polarization state and passes IR light of an opposite polarization state. The liquid crystal layer acts on polarized IR light by changing its polarization if the liquid crystal is in a first state and by not changing its polarization if the liquid crystal is in a second state. Voltages applied to the conductive substrates drive the liquid crystal layer to one of the two states. The analyzer blocks IR light when the liquid crystal layer is in one of the states and passes IR light when the liquid crystal layer is in the second state.

Abstract: A light sampling system for sampling scattered light from mirrors in an optical switch. The system includes four basic components: an imaging lens, a multi-channel liquid crystal light valve (LCLV), a collecting lens, and a light sensor. Light scattered by each mirror, is collected by the imaging lens, which re-images the light onto the LCLV. The LCLV is divided into multiple regions, one for each mirror to be monitored. Each region can independently be made opaque (“closed”) or transparent (“open”) to light reaching it. Light passing through all open regions of the LCLV is collected by the collecting lens, which focuses the light onto the light sensor. The light sensor registers a response to light passing through the LCLV. Each region of the LCLV can be programmed to be open or closed for any length of time, in any combination or sequence with any other region or regions, depending upon how the user wishes to monitor the scattered light.

Abstract: An IR camera comprises an IR Focal Plane Array having a number of detector elements as sensor devices, an optical system focusing an object onto the Focal Plane Array, and a signal processing system connected to the Focal Plane Array. The camera also has a modular structure comprising a camera housing provided with the Focal Plane Array and the signal processing system, an absorbent/emitting shielding device connected to the camera housing, and an optical focusing system removably mounted to the shielding device.

Abstract: The present invention provides for an improved electromagnetic radiation detector having a micromachined electrostatic chopping device. The MEMS flexible film chopping device provides reliability, efficiency, noise reduction and temperature fluctuation compensation capabilities to the associated electromagnetic radiation detector. An electromagnetic radiation detector having an electrostatic chopper device comprises a detector material element, first and second electrodes in electrical contact with the detector material element and electrically isolated from one another. Additionally, the chopper device will incorporate a flexible film actuator overlying the detector material layer and moveable relative thereto. The flexible film actuator will typically include an electrode element and a biasing element such that the actuator remains in a fully curled, open state absent electrostatic voltage and moves to a fully uncurled, closed state upon the application of electrostatic voltage.

Abstract: A system for sensitively discriminating against background radiation which tends to swamp and prevent detection of radiation from a source of interest such as IR (Infra-Red) light radiation as may be found on “low observable” aircraft collision avoidance lighting, utilizes the modulation of such radiation as a mechanism for tracking the radiation and discriminating against the background radiation, for example, from other light energy sources.

Abstract: A thermal imaging system comprising a camera (11), a control device (12) which is operable to control movement of the camera (11) and operation of the camera shutter and a computer (13) which includes thermal image processing software which allows manipulation or display of thermal images collected by the camera (11). The camera (11) is operated by use of the control device (12) to expose a thermal image over a selected time interval in order that a thermal image over a particular selected temperature range. The camera shutter is operated at a selected frequency and exposure time of the image is varied to acquire thermal images over different selected temperature ranges. However, preferably every said image, is taken at the same time exposure, which allows display of a continuous real time display of thermal characteristics of the object over this selected temperature range. Thermal information over the other temperature range can also be displayed or used as desired.

Abstract: A device for controlling equipment includes a light projector adapted to project light onto a head of a living body, a light collecting device for collecting the light having passed through the head from the light projector, a light measuring device for measuring an intensity of the light collected by the light collecting device, a memory device for storing a previous history of changes of the intensity of the light measured by the light measuring device, a signal judging circuit for judging if both the intensity of the light measured by the light measuring device and the previous history of changes of the intensity of the light satisfy a predetermined condition, a display device for displaying the intensity of the light measured by the light measuring device and a result obtained by the signal judging circuit, and a control signal generating circuit for generating a control signal to be supplied to an external equipment if the predetermined condition is satisfied.

Abstract: The present invention relates to an apparatus configured for identification of a material and method of identifying a material. One embodiment of the present invention provides an apparatus configured for identification of a material including a first region configured to receive a first sample and output a first spectrum responsive to exposure of the first sample to radiation; a signal generator configured to provide a reference signal having a reference frequency and a modulation signal having a modulation frequency; a modulator configured to selectively modulate the first spectrum using the modulation signal according to the reference frequency; a second region configured to receive a second sample and output a second spectrum responsive to exposure of the second sample to the first spectrum; and a detector configured to detect the second spectrum.

Abstract: Photo acoustic infrared (IR) detector including a chamber for receiving a gas or gas mixture, a window for allowing pulsed or modulated IR radiation into the chamber, and a pressure sensor adapted to measure pressure changes in the chamber as a consequence of absorbed IR radiation. A generally plate-shaped main part has a recess or bore for substantially forming the chamber whereby the window closes the chamber at one side of the main part and whereby the pressure sensor is of the miniature type and is located at the opposite side of the main part in relation to said one side so that the pressure sensor communicates with and closes the chamber at the opposite side, except for a venting channel for the chamber. A cap is provided at said opposite side of the main part so that it encloses the pressure sensor and forms a gas space communicating with the chamber through the venting channel and being substantially larger than the gas volume in the chamber.

Abstract: Methods and apparatus for generating uniform reference sources for use in calibrating multiple-detector imaging devices. In exemplary embodiments, a plano-plano reference lens is inserted at a non-focusing position in the optics path of a multiple-detector imaging device. The reference lens includes a highly polished side coated with a semi-reflective film and a rough polished side coated with an anti-reflective coating. The smooth polished side causes the detector array to see a reflected image of itself and a portion of the incoming scene energy simultaneously. The energy emitted by the detector array thus mixes with the scene energy to create a detected photon flux level which is dependent upon, but deviates in a controlled manner from, that of the scene energy alone. At the same time, the rough polished side and the thickness of the reference lens blur the detected image to eliminate scene structure and to provide a uniform photon flux level at each detector in the array.

Abstract: A non-mechanical modulating device for use in infrared detection. The device is of particular use in the 8-14 &mgr;m range and has application in thermal imaging cameras and gas sensing systems. The modulator comprises a germanium element and a means of varying the carrier concentration. In particular, the variation of the hole concentration gives rise to the absorption of infrared radiation due to interband transitions between the light and heavy hole bands in the split valence band in germanium. The variation in hole concentration may be initiated in any convenient way, for example, by the irradiation of the germanium with visible or near infrared light, by the electrical injection of free carriers across a germanium diode structure or by electron impact on the germanium surface following acceleration under vacuum. In the case where the variation in carrier concentration is initiated by optical means, the surface of the germanium is treated so as to produce a low surface recombination velocity.

Abstract: An imaging system having an imaging sensor providing sensor signals in response to incident light and control signals, control circuitry configured to generate control signals for controlling said imaging sensor, signal processing circuitry for generating image data in response to said sensor signals, and a light selective element for selecting the incident light encountered by said imaging sensor, the light selective element comprising an ionically-colored glass having a surface that is treated with a chemical stabilizer.

Abstract: An infrared gas analyzer is formed of a source of infrared rays for emitting infrared flux; an infrared flux interrupting device for chopping the emitted infrared flux from the source of the infrared rays; a condensing optical system for obtaining a predetermined solid angle in the emitted infrared flux to thereby form a condensed flux; and a multi-reflection cell disposed at an outlet of the condensing optical system, to which the condensed flux is supplied and a gas to be measured is fed. The multi-reflection cell has a multi-reflection optical system formed of a plurality of concave mirrors. The analyzer also includes an infrared level detector for detecting an amount of infrared rays with a wavelength band absorbed by a component gas to be analyzed and contained in the infrared rays emitted by the multi-reflection cell.

Abstract: A pyroelectric IR sensor equipped with a chopper for opening and closing a shielding plate so that infrared rays emitted from an object are allowed to be incident onto a pyroelectric sensor unit and intercepted therefrom, and having a structure capable of providing a large shielding width for the shielding plate without enlarging the chopper. Piezoelectric members are formed on a thin elastic sheet composed of a planar sheet having a tip to which a shielding plate is attached, except for a partial region which functions to magnify oscillations for enlarging displacement of the shielding plate.

Abstract: Thermal imaging chopper (22) having a frame (42) with an open window (47) and a covered window (48). The covered window (48) is preferably covered with a material that partially blocks a selected amount of thermal radiation from a scene and randomly scatters the remaining thermal radiation from the scene that is transmitted through the covered window. The open window (47) allows unrestricted transmission of thermal radiation from the scene.

Abstract: A sensor with radiation detectors with two or more photoconductor elements and bias polarity switching of one element to emulate mechanical chopping of input radiation. This electronic chopping permits higher chopping frequencies than mechanical chopping for bolometers because the scene settling time does not limit electronic chopping. The detectors may be within a single vacuum integrated circuit package with separate narrow passband filters for chemical spectral analysis.

Abstract: A shutter 3 which can be momentarily held open and immediately closed, is disposed adjacent to an aperture stop 4 in an optical system, and a temperature sensor 5 is provided for measuring the temperature of the shutter 3. The blades of the shutter 3 can be utilized as a reference heat source. With the shutter 3 disposed adjacent to the aperture stop 4, the optical equivalence in the case when a reference heat source is inserted and in the other case, is not spoiled. A shutter 202 which can be readily momentarily held open and immediately closed under control of a shutter controller 203, is disposed at the optical pupil position of a combination lens 201. When the shutter 202 is closed, thermal image data is stored in a shading memory 208.

Abstract: A chopper is provided of solid state construction. Two layers are provided adjacent one another with the area between the layers defining one or more diffusion zones. One or more voltage potentials may be applied across the second layer to correspond to the diffusion zones. At an initial state the voltage potentials are either zero or some predetermined value which causes the index of refraction of the two layers to be substantially the same. At a second state the voltage potential equals some predetermined value to cause the index of refraction of the second layer to be different from that of the first layer. The difference in index of refraction between the layers creates a diffraction grating in the respective diffusion zone to diffuse that portion of an incident signal passing through the diffusion zone.

Abstract: Thermal imaging chopper (20) may comprise a disk (40) formed of a thermally transmitting material. The disk (40) may include a structure (44) operable to randomly scatter thermal radiation of the scene (14).

Abstract: An infrared imaging microscope uses spatial encoding to divide an sample being examined into a plurality of pixel regions. The spatial encoding is provided by a digitally controlled mask, which is preferably a multiple mirror array, and which masks the imaging radiation directed from a radiation source to the sample. The signal reflected or transmitted from the sample is detected using a single-element detector. As the mask pattern provided by the mask changes, the output signal of the detector is monitored, and the spectroscopic composition of each of the pixel regions is resolved using a spatial decoding method, such as a Hadamard transform. The digital control of the mask allows fast, easily-implemented changes to the masking pattern, and provides a low processing load relative to imaging devices that use multiple-element detectors.

Abstract: A system and method are set forth for photoacoustical analysis of isotope and other compounds having telltale absorption wavelengths between 1700-2500 nm. The system and method includes a Co:Mg F.sub.2, optical parametric oscillator (OPO) or diode laser tunable between 1700-2500 nm which is directed into a sample at energies sufficient to generate detectable acoustical emissions. A microphone detects the emissions for processing and analysis. The system and method is adapted to detect stable isotope compounds such as .sup.13 CO.sub.2 as well as other chemical compounds. For non-gaseous compounds, a CO.sub.2 or diode laser is used to photoablate the gaseous sample contacting the suspected compound.

Abstract: A blur film is made of a polymeric film material transmissive to infrared energy of a selected waveband, which is affixed to a surface of a substrate transmissive to energy of the same selected infrared waveband. The blur film has a texture or a plurality of lenslets thereon, where the surface of each lenslet is a surface of revolution. In a spatial-filter wheel application, the blur film and substrate are affixed to a support, which in turn is rotatably mounted on a drive. The support is structured such that a portion of its circumference is covered by the blur film and a portion of its circumference is not covered by the blur film. The spatial-filter wheel is rotated in front of a detector to produce alternating blurred and direct images on the detector.

Abstract: A respiratory gas monitor for measuring the concentration of certain gases in a respiratory gas stream has a compact and unitary lid assembly having an integral low-profile motor and a cylindrical infrared light beam chopper. The lid assembly also contains a motor position sensor and flex circuit for passing electrical signals through epoxy sealed orifices in the lid to a processing and control unit in the monitor. The flexible circuit uses releasable connectors to facilitate removal of the monitor from an external controller and the removal of the lid assembly from the bottom portion of the monitor.

Abstract: A disc having a plurality of slits radially each of which have approximately the same width as a diameter of a photoreceptor of the sensor, and a rotary chopper, are arranged to coaxially rotate. When one of the slits faces a sensor, the disc and the chopper are rotated at a rotational speed so that the incident infrared radiation into the sensor is chopped 2-16 times by the chopper. At least two sets of sensors, each set of which comprises a plurality of sensors for sensing infrared radiation of different wavelength bands to one another, the sensors being arranged behind the chopper and the disc along a radial direction centered at the rotational axis of the chopper, are provided.

Abstract: The invention provides an IR modulator for synchronized interruption of an IR beam path in a thermal imaging device. A layer made of thermorefractive material is arranged in the beam path, and means are provided for changing the temperature of the thermorefractive layer.

Abstract: A pyroelectric IR sensor equipped with a chopper for opening and closing a shielding plate so that infrared rays emitted from an object are allowed to be incident onto a pyroelectric sensor unit and intercepted therefrom, and having a structure capable of providing a large shielding width for the shielding plate without enlarging the chopper. Piezoelectric members are formed on a thin elastic sheet composed of a planar sheet having a tip to which a shielding plate is attached, except for a partial region which functions to magnify oscillations for enlarging displacement of the shielding plate.

Abstract: An optical gas analyzer for measuring the percentage of components in a gas phase by IR absorption, containing a power source, a measuring path containing the gas sample, a photoelectric receiver with an evaluation circuit arranged downstream of it, which receiver detects the IR radiation from the measuring path, and a plurality of filters, which can be introduced one after another into the beam path at a predetermined filter change frequency f, wherein measured signals belonging to the filters are sent by the receiver due to the radiation extinction in the measuring path, is to be improved such that different components in the gas sample can be detected in a simple manner and at good selectivity.

Abstract: The disclosed gas analyzer (10) provides two separate folded optical paths (16 and 18) from a single source (12) to a single detector array (14) via a polychromatic filter (26). One optical path (16) passes through a sample gas chamber (24) containing a gas to be analyzed and the other path (18) passes through a reference chamber (30) containing a reference gas. On each optical path (16 or 18), radiation from the source (12) is collected by upstream optics (22 or 28) to form a converging beam (16b, c or 18b, c), thereby reducing or eliminating the need for collection optics at the detector array (14).

Abstract: An aircraft has an exhaust flame or plume which can be modulated to communicate. A sound emitter is mounted to the aircraft for emitting acoustic waves into the exhaust plume. An encoder will control the emitter at selected digital sequence to provide a digital message. The flame or plume will radiate at a frequency range of interest depending on the type of aircraft. The sound waves cause the frequencies to change from a continuous spectrum to a spectrum which has a much lower amplitude. A detector remotely located from the aircraft will detect radiation. It filters frequencies outside of the frequency range of interest. It will discriminate between the modulated pattern and the continuous pattern. This output provides the digital code that was encoded by the encoder. A decoder will decode the message for the recipient.

Abstract: An instrument is provided for measuring the temperature of an object from infrared radiation emitted by the object. The instrument includes a radiation detector, a temperature indicating device connected to the detector, and a modulator disposed in a path of a radiation beam from the object for converting the beam into a series of pulses when the modulator is vibrated in and out of the path. The modulator includes a primary piezoelectric element adapted to vibrate when subjected to driving signals at a frequency related to the resonant frequency of the modulator, and a secondary piezoelectric element connected with and driven by the primary piezoelectric element. The secondary piezoelectric element is electrically insulated from the primary piezoelectric element. The modulator also includes a blocking element connected with the secondary piezoelectric element and disposed to move in and out of the path of the beam.

Abstract: A pyrometer for measuring the electromagnetic radiation emitted by an object comprises a first detector to which the radiation is delivered through an optical system as well as a second detector to which the radiation emanating from a reference element is delivered through the same optical system. The temperature of the reference element is monitored and a rotary optical modulator periodically enables and disables the delivery of radiation to the detectors. The output signals from the two detectors are processed to determine the difference therebetween. The sensed temperature of the reference element is taken into account as a part of determining the difference between the two detector output signals. In this way it is possible for the characteristic radiation of the optical system largely to be suppressed. The optical modulator comprises a semi-circular disk having a polyethylene terephthalate substrate coated on each side with metal. The disk is rotated through 180.degree.