Abstract: An apparatus for measuring deformation of a body includes a transmitting optical fiber for connection to a light source and having a light exit face for radiating light, and at least first and second receiving optical fibers which have their light entrance faces adjacent to each other and which can each be connected to a respective input of an evaluation unit. The optical fibers are so arranged that upon deformation of the body there is a change in the difference between the amounts of light impinging on the light entrance faces of the receiving optical fibers.

Abstract: A fiber optic sensor for measuring strain on and within structures. The sensor includes an optical fiber, two reflective markers, and two thin layers of carrier material. The optical fiber is looped multiple times within the two thin layers of the carrier material. The optical signal circulates multiple times through the sensing region, as it is travels through the multiple loops of optical fiber within the carrier layers. The fiber optic sensor can be embedded within a structure, as that structure is being fabricated, or it can be attached onto a preexisting structure. An optical signal generated from a source such as a laser is input into one end of the optical fiber. The signal is reflected at reflective markers at predetermined positions in the optical fiber. The time delay of the signals received back is then analyzed to calculate the strain in the structure.

Abstract: A sensor and method are disclosed for determining if a region, defined by two end points, in a structure has exceeded a predetermined amount of strain. The sensor has an optical waveguide which has two ends for receiving and emitting light and which is fixable at two locations thereon to respective ones of the end points to define a sensing region therebetween. The sensing region has a first portion with a first length and a first cross-sectional area, and a second portion with a second length and a second cross-sectional area which is smaller than the first cross-sectional area. The lengths and cross-sectional areas are sized so that the optical waveguide has a strain failure point equal to the predetermined amount of strain. The lengths and cross-sectional areas are approximately sized according to the formula R=.alpha.+1/ (.alpha./.beta.

Abstract: A method and apparatus for non-destructive testing of the load bearing characteristics of a structure are disclosed. An interferometer is supported by a beam which is supported away from the surface of the structure to be tested. The interferometer is used to measure a quantity which varies with the distance between the interferometer and a reflecting means supported on the location to be tested. The reflecting means is supported in such a manner as to move responsively with deformations to the said location, and is typically attached to a probe which is urged against the said location. Preferably a force is applied or varied near the location to be tested and comparisons are made over time or as the said force varies. Such a system does not damage the structure, and does not require complicated equipment or processing.

Abstract: A fully distributed optical fiber strain sensor that makes use of the nonlinear Kerr effect and the photoelastic effect. The sensor includes a polarization maintaining optical fiber having a core region and a cladding region where the fiber is embedded within or adhered to a structural element that is to be monitored for strain. Counterpropagating optical pulses interact within the fiber such that the change in refractive index caused by the Kerr effect causes a portion of the pulse intensities to be emitted from the fiber. A strain on the fiber will cause the index of refraction of the core region to change such that a different pulse intensity is emitted from the core region. This change in the loss of pulse intensity can be used to determine the amount of strain on the structure at the interaction region. By taking a strain measurement along two polarization directions and at two different wavelengths, the direction of the strain can also be determined.

Abstract: The invention concerns a method of manufacturing a measuring device of the Fabry-P erot resonator type. The invention likewise concerns a measuring device manufactured by means of the method. The measuring device is particularly intended for measurement of the pressures inside engine cylinders and comprises a cavity and a first part and a second part, said two parts sandwiching the cavity between them. At least the first part, which consists of silicon, supports a spacer layer of silicon dioxide formed through thermal oxidation. The spacer layer which is partially removed through etching, is joined to the second part using the technique known as direct bonding (SDB).

Abstract: A strain indicator of the type wherein a change in length of the strain indicator gives a visual indication of the change in length. The strain indicator has an elongate strip supported at either end such that the curvature of the strip changes with changes in strain. An optical indicator such as a reflector is mounted on the strip so that the change in curvature can be measured.

Abstract: A metallized glass fiber optic is braze-bonded or solder-bonded to a metal shim to form a sensor unit that may be spot welded to a structure for monitoring structural strain. Preferably shim thermal characteristics are selected to match those of the structure being monitored, and a cover plate protects the fiber after attachment to the shim. Alternatively, a non-metallized optical fiber is attached to the metal shim using a special ceramic adhesive coat whose metal constituents thermally match the thermal expansion co-efficient of the shim. After adhesive curing, a protective cover plate is attached. An embodiment for use with an extrinsic Fabry-Perot type sensor provides a metal plate with a fiber-sized groove that guides the target and the transmit/receive fiber optic elements together to form an air gap. Another embodiment metallizes the fiber optic elements with a mask ring having a depressed region into which a cover plate is attached.

Abstract: A cladded birefringent pressure sensor for use in a pressure-sensing system. The sensor is a single composite plate consisting of two plates each with different indices of refraction. One surface of the sensor is exposed to the environmental pressure under measurement. A collimated broad band light source is transmitted via a fiber optic cable, a polarizer and a birefringent bias element which transmits a wavelength/polarization component of light through the sensor. An external force applied to the sensor adds a stress-induced component to the polarized lightwave. The lightwave exits the sensor and is captured by a second polarizer producing a modulated light spectrum. A focusing element collects the light and transmits it down another fiber optic cable. The cable transmits the light to an opto-electronic interface where the fringe pattern is extracted and a computer compatible signal is generated for a CPU.

Abstract: A system and method for absolute, high resolution and accurate strain measurement includes a low-coherence light source (12) transmitting light through a strain sensor (18) and into an interferometer (26). The interferometer (26) has a high-coherence light source (48) that parallels the light from the low-coherence light source (12). The output of the interferometer is detected by a photodetector (46). The photodetector (46) is connected to a phase measuring circuit (30), that is in communication with a controller (28). The controller (28) is also connected to a motor (44) that adjusts the optical path lengths in the interferometer (38). The phase change in the high-coherence source from the fringe pattern (68) of the strain sensor (18) before and after a strain is applied to the device under test is used to determine the strain.

Abstract: Apparatus for the remote measurement of physical parameters comprising sensing means (1) for sensing at least one physical parameter, instrumentation means (2) for interrogating the sensing means (1) and making a measurement, cable means (3) for communicating between the sensing means (1) and the instrumentation means (2), container means (4) for containing the sensing means (1) and the cable means (3) prior to installation of the sensing means (1), container holder means (5) for providing a support for the container means (4) at a convenient location, channel means (6) for providing a channel between the container means (4) and a measurement location where the channel is suitable for accepting the cable means (3) and the sensing means (1), and cable installation means (9) for installing the sensing means (1) and cable means (3) from inside the container means (4) into the channel means (6) and placing the sensing means (1) at the measurement location.

Abstract: The present invention is arranged such that: laser light is irradiated onto the surface of a specimen over a predetermined length thereof in the direction of elongation to be measured; that scattering light of the laser light reflected from the specimen surface is photoelectrically converted to obtain speckle pattern data; out of the speckle pattern data thus obtained, the data from two zones on the specimen which are separated from each other by a predetermined distance in the elongation direction, are initially set as observation point data; with the use of the observation point data, the amounts of movement of the speckle patterns from the two zones on the specimen are calculated; the zones serving as observation point data sources are shifted in the speckle pattern movement direction each time the calculation results of the speckle pattern movement amounts reach a predetermined amount; and the elongation of the specimen between the initially set two zones is calculated based on (i) the shift amounts of th

Abstract: A birefringent active fiber laser sensor includes one or more fiber lasers 12, 14, 16, each having a pair of Bragg gratings 18, 20, embedded in a fiber 10 and excited by a common pump light 30. At least one of the lasers 12, 14, 16 has a laser cavity wit a predetermined birefrigence and a lasing light at a first lasing frequency along a first polarization axis, and at a second fusing frequency along a second polarization axis. A difference frequency between the first and the second lasing frequencies is related to the magnitude of the birefringence, and the birefringence varies in response to a perturbation. Output light 104 from each of the lasers 12,14,16 is fed to a defraction grating 106 which splits the beam 104 into different wavelength groups, each group having the two lasing frequencies and polarizations of a given laser.

Abstract: In a stress measuring, system sensor driving power and a signal sensed by a sensor are transmitted and received in the form of a light pulse signal to thereby improve a noise resistant property as well as a measuring accuracy and reliability. The stress measuring system includes a sensor head disposed at a sensing location and a measuring device disposed at a location remote from the sensing location. The sensor head includes a sensor having a sensing section for sensing a change in stress as a change in the natural frequency of an oscillation string, an output section for outputting a light pulse sensing signal corresponding to the natural frequency sensed by the sensing section and a driving section for causing oscillation at the natural frequency of the oscillation system of the sensing section in response to a driving light pulse signal.

Abstract: A method for determining the residual stress in an unsupported region of a thin film. The method includes the steps of (a) optically exciting the film with a spatially and temporally varying optical excitation field to launch counter-propagating acoustic modes along at least one wavevector; (b) diffracting a portion of an optical probe field off the excited acoustic modes to generate a time-dependent signal field at the excitation wavevector; (c) detecting the signal field to generate a time-dependent, light-induced signal; (d) analyzing the light-induced signal to determine the frequencies of the acoustic modes; (e) partially determining the dispersion of at least one mode; and, (f) comparing the measured dispersion to that calculated using a mathematical model to allow the residual stress properties of the unsupported region of the film to be determined.

Abstract: An apparatus for monitoring the growth of surface cracks in materials includes a means for applying a load to a specimen to simulate actual use of the specimen, means for illuminating the specimen, means for capturing images of the specimen, and means for processing the images to monitor crack growth in the specimen. Optionally, the means for processing can be used to control the other means.

Abstract: A fracture detecting apparatus for identifying fractures in a metallic workpiece includes a fiber optic element securely affixed to the workpiece with a metallic material, such as a metallic solder. Accordingly, a fracture in the portion of the metallic workpiece to which the fiber optic element is attached will damage the fiber optic element. A light source and a detector are connected to the fiber optic element for transmitting light therethrough and receiving the transmitted light, respectively. The detector determines, based upon the reflection or attenuation of the transmitted light, if the fiber optic element has been damaged. Accordingly, a damaged fiber optic element as well as the fracture in the underlying metallic workpiece which caused the damage to the fiber optic element may be detected and repaired prior to causing additional damage to the metallic workpiece.

Abstract: An apparatus for monitoring the growth of surface cracks in materials includes a servo-hydraulic test machine which applies a load to a specimen according to a predetermined loading regime designed to induce crack growth in the specimen, a UV laser for illuminating the specimen with a light having a frequency greater than the frequency of incandescent light, a UV video camera and a two dimensional imaging computer. Optionally, the two dimensional imaging computer can be used to control the servo-hydraulic test machine.

Abstract: A remote active multipoint fiber laser sensor includes a plurality of fiber lasers 12,14,16, each having a pair of Bragg gratings 18,20, embedded in a fiber 10 and excited by a common pump light 30. The lasers 12,14,16 lase at different longitudinal modes (lasing wavelengths) and emit light 32,34,36, at their respective wavelengths .lambda.1,.lambda.2,.lambda.n. The lasing wavelength of each laser shifts due to perturbations, such as strain or temperature, applied thereto. The output light 32,34,36 is fed to a spectrum analyzer 50 where the wavelength shift is analyzed. A signal processor 54 reads the wavelength shift and provides a signal on lines 56 indicative of the perturbation at each of the lasers/sensors 12-16. Alternatively, a single laser may be used as a single sensor. Alternatively, birefringent fiber may be used as the fiber cavities 21 and the two polarizations are beat together to form a lower difference or "beat" frequency, thereby allowing lower frequency detection devices to be used.

Abstract: A system based on integrated optical technologies for the measurement and diagnostics of physical parameters on whatever structure, by the use of optical sensors, made by the fiber embedded Bragg grating method and by the use of a planar integrated optics device for the analysis of the optical signal. The sensors may be embedded or bonded to the structure, allowing the measurement of parameters like strain and temperature, in either a static or dynamic regime. The system pertains to the technical field of the diagnostics and measurements of mechanical or thermal parameters and to the application field of ground, water and aerospace transportation and also to the application field of construction.

Abstract: Torque on a rotating or stationary shaft is measured by an apparatus that includes a light source for emitting light along a light path; a reflection grating fixed to the shaft along the light path reflecting and diffracting the light; and a light detector having a plurality of light detecting elements for receiving the reflected and diffracted light. Torque on the shaft produces a change in the grating spacing of the grating, which in turn produces a change of diffraction angle of the reflected light, thereby causing a different element of the light detector to receive the light.

Abstract: The design of transducers utilizing finite length sensor paths is discussed. Within the framework of linear elastostatics of an isotropic homogeneous material the normal, transverse, and shear components of strain along a path can be integrated over a finite length to separate and yield external loading components. These displacement measurements over a long distance accommodate the use of fiber optic displacement sensors. The use of optical interferometric sensors in contrast with electrical strain gauges, has the potential to allow the precision and range of the component measurement to scale with the geometry of the device rather than the maximum strain in the instrument. It becomes possible by virtue of these scaling properties to construct a better transducer. The design of transducers that measure all six resultant-load components using both electrical strain gauges and fiber-optic interferometric sensors are described. An advanced torsion sensor and a linear acceleration transducer are also discussed.

Abstract: Disclosed is a structure at least partially comprising a composite material, the material being made by means of sheets of fibers embedded in a matrix, the different sheets forming plies of the material, the material comprising intrinsic means for the detection and localization of a mechanical irregularity, these means comprising at least one polarization-maintaining birefrigent optical fiber having a so-called slow axis and a so-called fast axis, embedded in the matrix and describing a known path inside the material, wherein the optical fiber is included inside a casing with an internal diameter that is greater than the external diameter of the fiber.

Abstract: An optical fiber strain sensor is provided which remembers the maximum stn a structure has experienced in a given timeframe. A pair of multi-mode optical fibers with flat ends meet end-to-end within a microbore capillary tube with which the fibers have frictional contact. The fibers are fastened to the structure at two points a known distance apart on either side of the capillary tube. Increasing strain in the structure pulls the fiber ends apart in proportion to the amount of strain; however, when strain is decreasing, the fibers buckle rather than move closer together. Therefore, the maximum strain is reflected as a maximum distance between the fiber ends. When the maximum strain experienced is to be measured, the free end of one fiber is connected to a light source and the free end of the other fiber is connected to a detector.

Abstract: An optical fiber strain sensor is provided which remembers the maximum stn a structure has experienced in a given timeframe. A reflective surface is fixed at one location on the structure, and a multi-mode optical fiber with a flat end is fixed at another location on the structure and is positioned so that its flat end is in contact with the reflective surface. A microbore capillary tube attached to the reflective surface encloses the fiber at its flat end and frictionally retains it in contact with the reflective surface. Increasing strain in the structure pulls the fiber end away from the reflective surface in proportion to the amount of strain; however, when strain is decreasing, the fiber buckles rather than moving closer to the reflective surface. Therefore, the maximum strain is reflected as a maximum distance between the fiber end and the reflective surface.

Abstract: A system for detecting one or more vehicles, such as a train, on a rail track, includes at least one optical conductor extending near and parallel to the rail track with a light source and light detector coupled thereto. One or more sensors are coupled to the rail track and include the light conductor, which sensors affect the light attenuation in the light conductor locally upon the presence of the vehicle. The sensor includes a free elongated element, which is connected to the mass of the sensor housing via an elastic hinge connection. One end of the element lies against the light conductor running through the sensor housing, which one end subjects the conductor to a microbending in dependence on displacement of the rail.

Abstract: A method is provided for determining surface shear magnitude and direction at every point on a surface. The surface is covered with a shear stress-sensitive liquid crystal coating and illuminated by white light from a normal direction. A video camera is positioned at an oblique angle above the surface to observe the color of the liquid crystal at that angle. The shear magnitude and direction are derived from the color information. A method of calibrating the device is also provided.

Abstract: A method for measuring residual stress in a material comprising the steps of establishing a speckle pattern on the surface with a first laser then heating a portion of that pattern with an infrared laser until the surface plastically deforms. Comparing the speckle patterns before and after deformation by subtracting one pattern from the other will produce a fringe pattern that serves as a visual and quantitative indication of the degree to which the plasticized surface responded to the stress dung heating and enables calculation of the stress.

Abstract: An optical fiber water sensor includes a mandrel having a convex or concave shape adjacent to an optical fiber which is adjacent to a water swellable material held in a reservoir. Upon coming in contact with water, the material swells and deforms a section of the optical fiber about a contour defined by the mandrel thus attenuating a signal propagating through the fiber which is detected by an optical detector to indicate the presence of water.

Abstract: A displacement measuring method and device is disclosed in which speckle amplitude interferometry within a single speckle feature or a small number of features of a speckle pattern is used to achieve sub-fringe accuracy with a single detector and to measure displacement of the object under investigation with sub-wavelength accuracy at measurement speeds consistent with real-time control of manufacturing processes. The same technique applied to multiple spots on a sample with optical means for causing interference between different combinations of scattered fields, including fields from different illuminated spots, permits measurements of the total sample motion.

Abstract: The present invention is a method and an apparatus for the precise quantitative measurement of the magnitude of force exerted at the points of contact on a high density electrical interconnect that quantitatively determines the magnitude of the force. The invention includes the steps of establishing a pressing relationship between a photoelastic material and the high density interconnect, coupling plane-polarized light into the photoelastic material stressed as a result of the pressing relationship with the high density interconnect, coupling of the polarized light being at 45 degrees with the direction of pressing, capturing an image of the fringe pattern of the plane polarized light exiting the stressed photoelastic material, the fringe pattern comprising of fringes wherein the number of fringes varies with the magnitude of the pressing force, and counting the number of fringes produced to determine the magnitude of force exerted on the photoelastic member.

Abstract: Methods and apparatus for automatically analyzing anti-nodal patterns formed in the outer skin of a semi-monocoque structure when it is excited to vibrate at a resonant frequency at which out-of-plane displacement is optimized. The described principles of analysis may be utilized to analyze a recorded image of the anti-nodal patterns obtained by holographic interferometry, or to directly examine the anti-nodal pattern by scanning a test area of the surface with a beam of coherent radiation, e.g., a laser beam, and utilizing the Doppler effect, measuring, recording and displaying a contour map showing out-of-plane displacement of the surface for analysis. In the holographic record case, comparison of the fringe density of the anti-nodes against the density of any fringes which may occur along normally fringe-free lines of underlying structure reveals the type and location of any structural faults.

Abstract: A fiber optic probe for detecting scattered light, with transmitting and receiving fibers having slanted ends and bundled together to form a bevel within the tip of the probe. The probe comprises a housing with a transparent window across its tip for protecting the transmitting and receiving fibers held therein. The endfaces of the fibers are slanted, by cutting, polishing and the like, so that they lie in a plane that is not perpendicular to the longitudinal axis of the respective fiber. The fibers are held in the tip of the probe using an epoxy and oriented so that lines normal to the slanted endfaces are divergent with respect to one another. The epoxy, which is positioned substantially between the transmitting and receiving fibers, is tapered so that the transmitting fiber, the epoxy and the receiving fiber form a bevel of not more than 20 degrees. The angled fiber endfaces cause directing of the light cones toward each other, resulting in improved light coupling efficiency.

Abstract: An embedded optical sensor has a plurality of layers 10-20 and an optical fiber 21 with a fiber grating 28, disposed between the layers 14,16. The layers 10-20 comprise filaments 22 and resin 24 which have different thermal expansion coefficients and the filaments 22 are oriented so as to create unequal transverse residual stresses that act through the geometry of a resin-rich region that surrounds on the grating 28 in the fiber 21. The unequal transverse residual stresses cause birefringence in the grating 28, thereby causing the grating 28 to reflect light 32 having two wavelengths with a predetermined separation, each along a different polarization axis. The wavelength separation and average wavelength between such separation have different sensitivities to temperature and strain, thereby allowing independent temperature and strain measurements using only a single grating.

Abstract: A force sensor and a force sensing method use crystal rods as both force responsive elements and light transmission media in combination with light input circuitry and processing circuitry to sense an applied force, such as oil or gas well pressure or fluid flow friction.

Abstract: A method is provided for determining shear direction wherein a beam of white light is directed onto the surface of a liquid crystal coating to cause the white light to be dispersed (reflected) from the surface in a spectrum having bands of different colors in a fixed spatial (angular) sequence. The system is calibrated by locating a observer, e.g., a video and movie camera, such that a particular color band (preferably at or near the center of the reflected spectrum) is observed to thereby provide a reference color band. Because the application of shear causes either clockwise or counterclockwise rotation of the reflected spectrum dependent on the direction of the shear, a determination is then made of the reflected color band observed by the observer when the surface of the liquid crystal is subjected to shear to thereby determine the direction of the shear based on the directional (rotation) relation of the observed color band with respect to the reference color band in the spatial sequence of color bands.

Abstract: A robot link deflection gauge providing precise measurement of the deformation of a robot link due to load and acceleration forces. The robot link deflection gauge of the present invention includes at least one light source, a plurality of lenses and corresponding position sensitive detectors positioned at the ends of the robot arm link to accurately measure the relative position and orientation of a first (or destination) end relative to a second (or source) end of each robot arm link. Each lens has an optical axis which is positioned to receive light from the light source and focus the light into a light spot on the surface of the corresponding position detector. As the robot link is deformed so that the destination end is displaced and rotated relative to the source end, the light is transmitted away from the optical axis of each lens causing the light spot to be displaced along the surface of the respective position sensitive detector.

Abstract: An optical fiber stress detector in which the light beam transmitted in the optical fiber which has to detect stresses is modulated in amplitude by a microwave alternating signal. The signal coming from the fiber is demodulated and then transmitted to a detector which measures the phase-shift existing between the demodulated signal and a signal derived from the modulation alternating signal. Application to the detection of stresses in any composite structures such as public constructive works, aircraft wings etc.

Abstract: A fiber optic vibration sensor utilizes two single mode optical fibers supported by a housing with one optical fiber fixedly secured to the housing and providing a reference signal and the other optical fiber having a free span length subject to vibrational displacement thereof with respect to the housing and the first optical fiber for providing a signal indicative of a measurement of any perturbation of the sensor. Damping or tailoring of the sensor to be responsive to selected levels of perturbation is provided by altering the diameter of optical fibers or by immersing at least a portion of the free span length of the vibration sensing optical fiber into a liquid of a selected viscosity.

Abstract: Fiber optic sensing means for the detection and measurement of events such as dynamic loadings imposed upon elastic materials including cementitious materials, elastomers, and animal body components and/or the attrition of such elastic materials are provided. One or more optical fibers each having a deformable core and cladding formed of an elastomeric material such as silicone rubber are embedded in the elastic material. Changes in light transmission through any of the optical fibers due the deformation of the optical fiber by the application of dynamic loads such as compression, tension, or bending loadings imposed on the elastic material or by the attrition of the elastic material such as by cracking, deterioration, aggregate break-up, and muscle, tendon, or organ atrophy provide a measurement of the dynamic loadings and attrition.

Abstract: The optical sensor includes a support (2), an optical fiber (15) and two elements (9, 10) mounted on the support (2) in such a manner as to move as a function of the variations of a quantity to be measured, such as pressure. The attenuation of an optical radiation in the optical fiber (15) deformed by reverse bending is measured. The support (2) is constructed in the form of a bending beam including two end parts (2b, 2c) bearing on two fixed abutments and a central part (2a) connected to a metal membrane (16) actuated as a function of the variations of the quantity to be measured. The optical fiber (15) is disposed between the two movable elements (9, 10) in the form of a comb, each fixed on an end part (2b, 2c) of the support. The elements (9, 10) include active surfaces coming into contact with the fiber (15) to produce a variable reverse bending of the fiber (15) in the course of their relative movement.

Abstract: Presented is a strain measurement transducer incorporating a load-beam subject to deflection when a load is applied, and a non-load-bearing beam mounted on the load beam in a manner to preclude displacement of the non-load-bearing beam when the load beam is displaced. A source of light is mounted on the non-load-bearing beam, cooperating with an optical mask, to project a beam of light energy which impinges onto a set of multiple photodiodes in proportion to the degree of displacement of the photodiodes with the load-bearing beam in relation to the stationary source of the light energy. The photodiodes transmit electrical signals proportional to the degree of illumination to an electronic circuit that processes the signals and indicates the magnitude of the load imposed on the load beam, or indicates its deflection in a selected unit of measurement.

Abstract: An arrangement for measuring mechanical properties of foil material (10), preferably paper. The arrangement includes a material excitation unit (12) and a material sensing detection unit (14). The two units are connected electrically to a common arithmetical unit (18). This unit is intended to register and convert electrical signals deriving from the two first mentioned units (12, 14) in a manner to produce final signals which represent the material properties to be measured. The excitation unit (12) includes a laser which, through electromagnetic radiation, is intended to generate in the gaseous atmosphere surrounding the material local transient gas-pressure pulses within variable surface zones which are well-defined geometrically, without the excitation unit coming into contact with the material. These gas pressure pulses cause the material (10) to stretch locally in the boundary regions of the zones, such stretching of the material being necessary to the measuring process.

Abstract: A pressure actuated sensor device (20) has an upper plate (21) functionally cooperating with an optical fiber (26) so that when pressure is applied onto the upper plate (21) light transmitted through the optical fiber is attenuated. The optical fiber (26) in the device (20) is sandwiched between one layer (24) made of a flexible material and a second layer (25) of rigid wires.

Abstract: Vibrations within ceramic matrix and metal matrix composite materials are controlled by applying an excitation voltage to an array of piezoelectric actuators mounted to the surface of such materials. The actuators are driven in response to the phase shift of monochromatic light transmitted through a grid of optical fibers embedded within the composite materials. Applications include active vibration suppression, de-icing, and on-line structural integrity monitoring.

Abstract: A railway track circuit system utilizing an optical sensor which emits a vehicle detection light signal when a railway vehicle is present in a track section. A reference light signal is also generated by a light emission source. A detector in optical communication with the optical sensor receives the vehicle detection light signal. Information contained in the vehicle detection light signal is interpreted by a processor to detect the railway vehicle. In presently preferred embodiments, the sensor may comprise an elongated optical fiber conductor extending along the track section or a plurality of cascaded localized sensors. The sensor may generally also be utilized as a communication medium to pass communication data between opposite ends of the track section. Depending on the exigencies of the particular application, the sensor may be located within the track section in a number of ways.

Abstract: A remote seismic sensing system is provided which operates as a bipolarized, differential mode, LDI (laser differential interferometry) system to detect electrical signals produced at a remote location. In preferred embodiments, the system is used in seismic surveying to detect array signals. An amplified array signal (the electrical signal is coupled to an array retroreflector apparatus (target). The array signal is obtained from an array of seismic detectors, e.g., geophones or hydrophones. The amplified array signal increases the velocity of a Doppler shifting optical component on the target. The target converts a defused sensing beam into two polarized return sensing signals, both of the return sensing signals having been Doppler shifted by the target to contain frequency components that represent motions, e.g., ground motions and wind motions, that are common to both signals and to contain a difference signal which represents the array signal.

Abstract: A remote sensing system is provided which operates as a bipolarized, differential mode, LDI (laser differential interferometry) system to detect an electrical signal produced at a remote location. The system is adapted to reduce the effects of turbulence induced frequency fluctuations by using an array retroreflector apparatus which converts a single sensing beam into a single return beam having two, overlapping, transversely polarized sensing signals; thus, turbulence induced noise will be common mode to both return signals and cancel at the receiver.In preferred embodiments, the system is used to remotely detect an amplified array signal from a plurality of seismic detectors (e.g., geophones or hydrophones) connected to form an array at the remote location. The target is coupled to common motions at the selected location and the amplified array signal is coupled to an optical component within the target.

Abstract: A pressure sensor includes a liquid crystal positioned between transparent, electrically conductive films (18 and 20), that are biased by a voltage (V) which induces an electric field (E) that causes the liquid crystal to assume a first state of orientation. Application of pressure (P) to a flexible, transparent film (24) causes the conductive film (20) to move closer to or farther from the conductive film (18), thereby causing a change in the electric field (E'(P)) which causes the liquid crystal to assume a second state of orientation. Polarized light (P.sub.1) is directed into the liquid crystal and transmitted or reflected to an analyzer (A or 30). Changes in the state of orientation of the liquid crystal induced by applied pressure (P) result in a different light intensity being detected at the analyzer (A or 30) as a function of the applied pressure (P).

Abstract: A self-exciting optical strain sensor (20) includes dual parallel bridges (22,24) having parallel facing surfaces (32,34). Light energy (38) entering a Fabry-Perot cavity (36) formed by this surfaces (32,34) induces a periodic buildup and release of energy in the cavity (36) which is directly related to the natural resonant frequency of the bridges (22,24). Analysis of the intensity of light emitted (50) from the cavity (36) determines the bridge natural frequency.