WO2007044103A2 - Systeme multiplexe de capteurs a fibre optique - Google Patents

Systeme multiplexe de capteurs a fibre optique Download PDF

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Publication number
WO2007044103A2
WO2007044103A2 PCT/US2006/027648 US2006027648W WO2007044103A2 WO 2007044103 A2 WO2007044103 A2 WO 2007044103A2 US 2006027648 W US2006027648 W US 2006027648W WO 2007044103 A2 WO2007044103 A2 WO 2007044103A2
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WIPO (PCT)
Prior art keywords
fiber
light
sensor
sensors
optical
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PCT/US2006/027648
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English (en)
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WO2007044103A3 (fr
Inventor
Nicholas Lagakos
Joseph A. Bucaro
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The Government Of The United States Of America, As Represented By The Secretary Of The Navy
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Priority claimed from US11/250,709 external-priority patent/US7379630B2/en
Priority claimed from US11/250,708 external-priority patent/US7460740B2/en
Application filed by The Government Of The United States Of America, As Represented By The Secretary Of The Navy filed Critical The Government Of The United States Of America, As Represented By The Secretary Of The Navy
Publication of WO2007044103A2 publication Critical patent/WO2007044103A2/fr
Publication of WO2007044103A3 publication Critical patent/WO2007044103A3/fr

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Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/04—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings formed by bundles of fibres
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
    • G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
    • G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
    • G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
    • G01D5/353—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre
    • G01D5/35383—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using multiple sensor devices using multiplexing techniques
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01H—MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
    • G01H9/00—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means
    • G01H9/004—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means using fibre optic sensors
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
    • G01K11/00—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00
    • G01K11/32—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in transmittance, scattering or luminescence in optical fibres
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
    • G02B6/2804—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
    • G02B6/2804—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers
    • G02B6/2808—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers using a mixing element which evenly distributes an input signal over a number of outputs

Definitions

  • Active sound control systems often require, in addition to actuator and electronic control components, specialized sensor devices.
  • the requirements associated with such sensors to a large part are determined by the particular active control approach employed, as well as the kind of performance expected of the sound controlling system.
  • One type of sensor is the microphone, which measures sound or the existence of atmospheric pressure waves in a particular area of interest.
  • the fiber bundle is disposed within the cartridge housing such that the first end of the transmitting fiber and the first end of each receiving fiber is adjacent to the protected side of the flexible membrane with free space between the first fiber end and the protected side of the flexible membrane.
  • a light sensing means is coupled to second end of said receiving fibers wherein light launched into the transmitting fiber propagates emerges at the polished end, propagates a very short distance in air, and is reflected by the flexible membrane into the receiving fibers, propagates therethrough, and is detected by light sensing means.
  • pressure waves Upon a change in the atmospheric pressure, pressure waves cause the flexible membrane to distort causing a change in the amount of light reflected by the protected side of the flexible membrane.
  • the intensity of the light coupled into the sensing fibers is modulated in relation to the intensity of pressure wave.
  • Figure 1 shows an example embodiment of a fiber optic pressure sensor.
  • Figure 2 shows an example embodiment of a fiber optic pressure sensor used as a microphone.
  • Figure 3 illustrates the dc displacement sensitivity of a one-fiber probe pressure sensor versus the probe end to mirror distance.
  • Figure 4 illustrates the ac displacement sensitivity of a one- fiber probe pressure sensor versus the probe end to mirror distance.
  • Figure 7 illustrates the acoustic sensitivity of a seven fiber probe pressure sensor in the frequency range 10 - 1000 Hz.
  • Figure 8 illustrates the performance characteristics of an exemplary seven fiber microphone/pressure sensor.
  • Figure 9 illustrates a seven fiber static pressure sensor in accordance with an embodiment of the invention in operation.
  • Figure 10 illustrates the results of measuring static pressure using the fiber optic pressure sensor illustrated in Figure 1 or 2.
  • FIG 11 illustrates a sensor system in accordance with an embodiment of the invention.
  • Figure 14A-14B illustrate connectors suitable for use in a sensor system according to an embodiment of the invention.
  • Figure 1 shows an example embodiment of a fiber optic pressure sensor.
  • Figure 1 shows a fiber optic pressure sensor featuring a cartridge housing 150 having an end that is exposed to the atmosphere, a thin flexible membrane 140 covering the exposed end of the cartridge housing 150 such that the flexible membrane has an exposed side and a protected side.
  • a fiber bundle 130 is disposed within the cartridge housing, featuring a transmitting fiber 110 having a first and second ends. The first end has a polished finish and the second end is coupled to a light source (not shown).
  • the fiber bundle 130 also features a multitude of receiving fibers 120 disposed around the transmitting fiber 110 with each receiving fiber 120 having first and second ends where the first ends are also polished.
  • the fiber bundle 130 is disposed within the cartridge housing 150 such that the first end of the transmitting fiber 110 and the first end of each receiving fiber 120 is adjacent to the protected side of the flexible membrane 140 with free space between the first fiber end and the protected side of the flexible membrane.
  • a light sensing means (not shown) is coupled to second end of said receiving fibers wherein light launched into the transmitting fiber 110 propagates through the transmitting fiber, emerges at the polished end, propagates a very short distance in air, and is reflected by the flexible membrane 140 into the receiving fibers 120, propagates through the receiving fibers, and is detected by light sensing means (not shown).
  • pressure waves Upon a change in the atmospheric pressure, pressure waves cause the flexible membrane 140 to distort causing a change in the amount of light reflected by the protected side of the flexible membrane into the receiving fibers 120.
  • the intensity of the light coupled into the receiving fibers 120 modulates in relation to the intensity of pressure wave causing the flexible membrane 140 to distort.
  • These pressure waves can be the result of a change in the environment such as a sound, if the sensor is configure to operate as a microphone.
  • Other modes for the pressure sensor are also possible such as an altimeter mode that senses a change in atmospheric pressure, motion sensor or etc.
  • Other sensor modes based on an event that results in a pressure wave are also possible.
  • the type of fiber employed in the example embodiment shown in Figure 1 is generally a multimode fiber having a core that is preferably made of glass.
  • the cladding may be plastic or some other material.
  • fibers with a high numerical aperture are used. Generally fibers with a numerical aperture of > 0.2 are employed. A high numerical aperture provides for greater efficiency in the coupling and transmission of light. Fibers featuring high numerical apertures are not required, however. When employed in systems that have a great distance between the source and membrane a fiber having a high numerical aperture is not critical.
  • multimode fibers with a combination of a thick core and thin clad fiber are preferred.
  • Light incident on clad is lost, thus the core needs to be as close in proximity to the outer perimeter of the clad is possible to ensure efficient light coupling in the core.
  • light coupling within the fiber is maximized with a thick core thin clad structure. This however, does not limit the use of fibers in this device to multimode fibers with thick core thin cladding structures. Varying degrees of effectiveness and light coupling are possible with other fiber configurations.
  • the fiber optic pressure sensor's cartridge housing is constructed of a rigid and lightweight material.
  • a rigid structure provides the sensor with a robust design.
  • Another advantage to the rigid structure is that the sensor is very resistant to vibration, G forces and other structural forces with could impact sensor performance.
  • the cartridge housing features means to adjust the distance between the polished end of the transmitting fiber and the flexible membrane.
  • the system employs a screw type configuration, with a locking nut and an adhesive material applied to the nut to maintain a consistent distance.
  • This configuration also provides the user the ability to adjust the distance from the fiber bundle to the flexible membrane by very small increments, and to lock or otherwise maintain a consistent distance in a dynamic environment. While other attachment and adjustment methods may be applied to the sensor as an adjustment means, to extract optimum performance from the sensor the mechanism must be resistant to vibration and temperature variations. If the distance from the fiber bundle to the membrane is not maintained precisely, the accuracy and sensitivity of the sensor package will suffer.
  • the cartridge housing features means to adjust the tension of the flexible membrane drawn across the exposed end of the cartridge housing. This maybe accomplished via a screw type adjustment or some other means of adjustment.
  • the flexible membrane also features a coating on the protected side to enhance its light reflecting properties, hi a preferred embodiment the flexible membrane is constructed of mylar and features at least one surface coated with thin aluminum film.
  • the aluminum film increases the light reflecting properties of the flexible membrane, however other coatings may be applied to increase the membrane's sensitivity, or toughness.
  • the fiber optic pressure sensor fiber bundle features a single multimode transmitting fiber and a multitude of receiving fibers all encased in a protective tubing.
  • the protective tubing is a stainless steel tubing, yet other type of tubing may be used to encase the fiber bundle.
  • tubing if any, that is used to encase the fiber bundle is not limiting to this invention.
  • the light sensing means is at least one silicon PIN diode.
  • LEDs represent a very efficient way to launch light into the fiber. LED are generally low cost and feature low noise operation in a fiber system. LEDs are also tend to be very stable over extended periods of time. Laser diodes are also applicable, although they increase the expense and complexity of the system. Current laser diodes, also tend to introduce additional noise to the sensor package.
  • One suitable LED for use as a light source is an Optek OPF370A LED emitting light at 850 ran.
  • the fiber optic pressure sensor features a cartridge housing having an end that is exposed to the atmosphere, a thin flexible membrane covering the exposed end of the cartridge housing such that the flexible membrane has an exposed side and a protected side.
  • a fiber bundle is disposed within the cartridge housing, featuring a transmitting fiber having a first and second ends.
  • the first end has a polished finish and the second end is coupled to a light source.
  • the fiber bundle also features a receiving fiber disposed adjacent to the transmitting fiber.
  • the receiving fiber has a first and second end where the first end is also polished.
  • the fiber bundle is disposed within the cartridge housing such that the first end of the transmitting fiber and the first end of the receiving fiber is adjacent to the protected side of the flexible membrane with free space between the first fiber end and the protected side of the flexible membrane.
  • a light sensing means is coupled to second end of the receiving fiber wherein light launched into the transmitting fiber propagates emerges at the polished end, propagates a very short distance in air, and is reflected by the flexible membrane into the receiving fiber, propagates through the receiving fiber, and is detected by light sensing means.
  • FIG. 2 show an exemplar of a pressure sensor having the structure as described above, employed as a microphone.
  • the device uses an LED emitting at 850 nm as the light source 280 with a silicon PIN diode as the light sensing means 290.
  • the fiber bundle 230 disposed within the cartridge housing comprises six multimode receiving fibers 220 surrounding a single multimode transmitting fiber 210.
  • the cartridge housing 150 is formed with screw type adjustments for fiber to membrane distance 153 and for membrane tension 152, and a clamping ring 154 also for setting and maintaining the membrane tension.
  • the fiber bundle 230 is housed within a plastic cartridge made from Noryl.
  • the weight of the sensor is 1.3 grams.
  • the first end has a highly polished finish and the second end of the transmitting fiber is coupled to the light source.
  • the second ends of the receiving fibers are coupled to the light sensing means while the first ends also feature a highly polished finished.
  • the optical fiber features a 200 ⁇ m glass core, and 230 ⁇ m plastic clad, a 500 ⁇ m Tefzel plastic coating, and a numerical aperture of approximately 0.37. The plastic coating is removed.
  • a suitable stripper for removing the plastic coating has an approximately 305 ⁇ m blade hole.
  • the seven fiber bundle is inserted into a stainless steel tube with 1.270 mm outer diameter and 838 ⁇ m inner diameter, so the fiber bundle is contained within the tube, forming a probe.
  • Epoxy is applied to the seven fibers so the fibers form a symmetric bundle close to the tubing end with the transmitting fiber at the center and cured. After curing, the fiber bundle can be cut close to the tubing end and the probe end can be polished.
  • the probe which includes the bundle and the protecting stainless steel tube, is housed within the plastic cartridge housing.
  • the fiber bundle 230 is disposed within the cartridge housing 150 such that the first end of the transmitting fiber and the first end of each receiving fiber is adjacent to the protected side of the flexible membrane 240 with free space between the first fiber end and the protected side of the flexible membrane.
  • the flexible membrane 240 is a 1.27 X 10-3 cm mylar (polyester) layer, having one surface that is coated with a thin aluminum film. The tension on the mylar membrane is adjusted to achieve the desired acoustic bandwidth. The membrane probe separation is also adjusted to achieve the desired bandwidth sensitivity. A somewhat broad dynamic sensitivity maximum was found for a probe - membrane separation between 180 and 250 ⁇ m.
  • pressure waves cause the flexible membrane to distort causing a change in the amount of light reflected by the protected side of the flexible membrane into the receiving fibers.
  • the intensity of the light coupled into the receiving fibers modulates in relation to the intensity of pressure wave causing the flexible membrane to distort.
  • a single fiber may be used as the transmitting and receiving fiber.
  • the light source and the means for sensing the received light are both coupled to the fiber end.
  • the light is launched from the fiber into the flexible membrane and is reflected back into the same fiber.
  • it is suitable to use a multimode optical fiber with a 200 ⁇ m glass core, and 230 ⁇ m plastic clad, a 500 ⁇ m Tefzel plastic coating, and a numerical aperture of approximately 0.37.
  • the probe housing is a stainless steel tube of 902 ⁇ m outer diameter and 584 ⁇ m inner diameter. To form the probe, the fiber is inserted in the tubing with its coating and epoxy is applied on the fiber.
  • FIG. 3 illustrates the displacement sensitivity of the one-fiber probe.
  • the displacement sensitivity of the one fiber probe can be studied by mounting it on a micrometer translator which can be displaced manually against a mirror mounted on a piezoelectric transducer (PZT4 cylinder of 2 inch outer diameter and 3 inch length) which can be vibrated electrically. The probe is displaced manually against the mirror in steps of 25.4 ⁇ m using a micrometer translator. Results are shown in Fig. 3 where the power of the reflected light coupled into the same fiber is plotted vs. the probe - mirror distance. As can be seen from this figure, maximum displacement sensitivity is achieved in the 0 - 150 ⁇ m probe - mirror distance.
  • the one fiber probe can also be dynamically displaced against the mirror by vibrating the PZT transducer electrically.
  • the displacement amplitude of the vibrating mirror can be obtained from the output of a small reference accelerometer (for example, the Endevco 2250A) mounted close to the mirror.
  • Results are shown in Figure 4, which shows the ac displacement sensitivity as a function of the probe - mirror distance.
  • the sensitivity is maximum and approximately constant in the 0 - 150 ⁇ m region, in agreement with the dc displacement results of Figure 3.
  • Figure 5 illustrates the dc displacement sensitivity of the 7 fiber probe, which was studied in a similar way to that of the one - fiber probe, hi Figure 5, the reflected light power coupled into the 6 receiving fibers is plotted vs. the probe - mirror distance.
  • the maximum displacement sensitivity is achieved for a probe - mirror distance of about 180 250 ⁇ m and is about 9.38 x 10-11 W/A, where A is equal to 10 -8 cm.
  • the maximum sensitivity region for the one fiber probe is found at close to zero probe-mirror distance, while the maximum sensitivity region for the seven fiber probe, the maximum sensitivity is achieved at a greater distance.
  • Another difference is that with the seven fiber probe, significantly higher light power is detected. This is believed to be due primarily to the coupler used in the one fiber probe which reduces the power by at least about 50%.
  • Figure 6 illustrates the displacement sensitivity plotted as a function of the probe mirror distance for the seven-fiber probe. These results were obtained in a similar way as the Figure 4 results for the one-fiber probe. As can be seen from this figure, maximum displacement sensitivity is achieved in the probe - mirror distance range of 180 - 250 ⁇ m, in agreement with the dc displacement results of Figure 5.
  • This maximum displacement sensitivity range indicates that an optimum probe - reflecting surface distance can be about 220 ⁇ m. From Figures 6 and 4, it is apparent that the maximum ac displacement sensitivity of the seven fiber probe is about 13 dB higher than that of the one fiber probe.
  • the increased sensitivity difference and the high cost of the multimode coupler used in the one fiber probe make a seven-fiber probe sensor better for some applications than a one fiber probe sensor, even though the one fiber probe sensor uses only one fiber instead of seven. In other applications, for example, in remote sensing applications in which longer fiber lengths are needed, a one-fiber probe sensor can be a better choice.
  • the displacement sensitivity of the 7 fiber probe was calculated from the signals of the probe and the reference accelerometer and was found to be equal to 6.35 x 10 -11 W/A. This result is slightly less than the 9.35 x 10 -11 W/A sensitivity calculated from the dc displacement procedure, the results of which are shown in Figure 5.
  • a good PIN detector can detect a fraction of a picowatt ac signal, the minimum detectable displacement limited by the detector noise is: minimum detectable displacement > 0.01 A.
  • Pressure can be detected by replacing the mirror used in the fiber probe with a reflecting surface such as a reflecting membrane.
  • the membrane used in a one or seven fiber pressure sensor such as the one shown in Figures 1 and 2 can be a 12.7 ⁇ m mylar film whose surface is metallized with a thin aluminum coating.
  • the reflecting membrane can be placed at an optimum distance from the probe end for maximum sensitivity and the membrane's tension can be set to an optimum tension for achieving the desired microwave bandwidth.
  • the cartridge provides mechanisms for applying the desired membrane tension and for clamping the probe in place at the optimum membrane-probe end distance.
  • the optimum membrane-probe end distance can be found in practice by adjusting the distance, monitoring the detected light from the receiving fibers, and taking into account the Figure 5 and Figure 6 calibration for the seven fiber probe. Similarly, Figures 3 and 4 can be used to determine the optimum membrane-probe end distance for a one-fiber probe.
  • the pressure response of the seven fiber probe microphone illustrated in Figures 1 and 2 can be found by placing it in a high pressure microphone calibrator, for example, type 4221 Bruen & Kjaer (B&K).
  • a reference microphone for example, a 1/4" pressure field 4938 B&K microphone, with a 2669 B&K preamplifier and a 2690 B&K amplifier can be used.
  • a pulse is applied on the pressure calibrator and the output signals of the fiber and the 4938 microphones are recorded and stored in a Macintosh computer using a ML750/M PowerLab recorder. About 1 mW light power is coupled into the transmitting fiber from the LED which is driven at 100 mA.
  • the detector is a PIN silicon detector, model PDA 55 made by Thorlabs.
  • Results are shown in Figure 7, in which the acoustic sensitivity of the fiber microphone is plotted in the frequency range of 50 - 1000 Hz.
  • the frequency response of the acoustic sensitivity of the fiber optic microphone is frequency independent in this frequency range, with the probe exhibiting about the same sensitivity over a range of 0.2 Hz to 1 IdHz.
  • the frequency response of the fiber optic microphone was studied also at frequencies much higher than 1 kHz and was found to be frequency independent.
  • the noise equivalent power (NEP) of a good detector is approximately 0.17 pW/Hz 1/2 (e.g., the EG&G model HUV-1100 PIN detector with a preamplifier), which corresponds to a minimum detectable pressure of 41 dB re 1 ⁇ Pa/Hz 1/2 .
  • the minimum detectable pressure will be higher than 41 dB it would be higher than 41 dB re 1 ⁇ Pa/Hz 1/2 .
  • the light source is the OPF 370A Optek LED driven by a LD-3620 Lightwave Technology Power supply and the detector is a PDA 55 PhorLabs PIN whose output is stored directly into 3582 A HP spectrum analyzer.
  • the minimum detected pressure for this arrangement was found to be 84 dB re 1 ⁇ Pa/Hz 1/2 .
  • Figure 8 illustrates the main characteristics of the exemplary seven fiber microphone described herein compared to commercially available microphones, the 4938 B&K and the 130A10 Modal Shop.
  • the fiber microphone linearity results are comparable to the 4938 B&K microphone and better than the 130A10 Modal Shop microphone.
  • the acceleration sensitivity of the fiber microphone which was found to be higher than that of the other two microphones, is believed to be due primarily to the lead noise.
  • the diaphragm diameter is less than 1/8 inch in the fiber microphone compared to 1/4 inches in the comparison microphones. An increase of this diameter affects the bandwidth and minimum detectable pressure, as discussed further herein.
  • the size, weight, cost, and electrical requirements of the fiber microphone are lower than that of the comparison microphones.
  • the comparison microphones require a preamplifier to minimize EMI.
  • the dynamic range of the pressure sensor is higher than 60 dB and its linearity is 1%.
  • the acceleration sensitivity which can introduce significant noise in a dynamic environment, was studied by mounting the pressure sensor on a piezoelectric shaker. The sensor was vibrated along the fiber - probe axis and perpendicularly to it. The axial and transverse acceleration sensitivities of the sensor were found to be 3 Pa/g and 1 Pa/g, respectively.
  • the minimum detectable pressure and bandwidth of a microphone with a diaphragm can be determined by the following equations, in which T is the tension, pm is the density, and r is the radius of the diaphragm:
  • x/p r 2 /(4T) , where x is the displacement of the diaphragm generated by an applied pressure p.
  • the radius and tension of the diaphragm can be chosen to satisfy the required minimum detection pressure, bandwidth, and size of the microphone.
  • the pressure sensors described herein and illustrated in Figures 1 and 2 are suitable for sensing dynamic pressure changes and for use as microphones. These pressure sensors are also suitable for static pressure sensing.
  • Figure 9 A illustrates a fiber optic probe 910 having a centrally arranged transmitting fiber 912 surrounded by six receiving fibers 914. Static pressure p is applied to the flexible membrane 916.
  • Figure 9B illustrates a multi-fiber optic pressure sensor 910 in accordance with Figure 1 or 2 operating in a test set up to demonstrate measurement of static pressure p.
  • the fiber optic probe 910 is placed in a closed end of a liquid-filled U-tube manometer 920, with an opposite end 924 of the U-tube manometer open to the atmosphere.
  • An optical source 950 such as a light emitting diode is coupled to a transmitting fiber 960 through connectors 952 and 953. Light generated by the optical source is transmitted through the connectors, through a length of optical fiber, , through another pair of connectors 954 and 955 and into the probe 910, where it travels from the polished end of the transmitting fiber 912 a short distance to the flexible membrane 916 illustrated in Figure 9C. The light is reflected by the membrane 916 toward the receiving fibers 914 that are arranged around the transmitting fiber 912.
  • a portion of the reflected light is received by the one or more receiving fibers 914, and is transmitted through the receiving fibers via connectors 956 and 957, a length of optical fiber 980, through another pair of connectors 958 and 959, and into a power meter 97O.
  • the intensity of the light received by the power meter 970 corresponds to the static pressure p to which the sensor 910 is subjected.
  • Figure 10 is a graph 180 illustrating the results of measuring static pressure in the arrangement of Figure 9 A - 9C. As seen in Figure 10, the detected light power in microwatts is linearly related to the static pressure in centimeters water.
  • the sensitivity of the sensor of Figure 1 as tested in the arrangement of Figure 9A-9C is 10 microwatts divided by 68.4 cm water, or approximately 1.6 x 10 "9 Watts/Pascal.
  • the same sensor is estimated to have a dynamic sensitivity of 1.53 x 10 "9 W/Pa.
  • the dynamic range is found to be at least 4 x 10 .
  • the sensor has a variation of 0.0004 inches of water over a measurement period of about 4 hours.
  • the measurement resolution is at least 0.001 inches of water using the pressure sensor 910 at a light level of 150 ⁇ W , and about 0.0005 inches of water with a lower light level of 50 ⁇ W .
  • the sensor 910 together with a light source and a receiver, can be used to measure static pressure in any desired location and is not limited to the arrangement illustrated in Figure 9B.
  • the pressure sensor can be placed at locations within the human body to measure pressure.
  • FIG 11 illustrates a fiber optic sensor system arranged to measure environmental characteristics at several locations and/or take different kinds of measurements at the same location.
  • Each LED 101 is coupled to a length of large diameter optical fiber 119 through a pair connectors 102, 103.
  • Smaller diameter optical fibers 113, 114, and 115 can be arranged to receive light from the connector pair 104, 105 couples the larger diameter optical fiber 119 to multiple smaller diameter optical fibers.
  • the larger diameter optical fiber is 400 microns in diameter and the three 200 micron core diameter optical fibers 113, 114, and 115 are arranged to receive equal amounts of light from the larger diameter optical fiber 119.
  • the connectors maintain the smaller optical fiber with a large part of its core area abutting the core of the larger diameter fiber. More or fewer than three optical fibers can be used to receive light from the larger diameter optical fiber 119.
  • a large diameter optical fiber 119 with a 400 micron core and a 0.37 numerical aperture can efficiently provide light into three 200 micron core diameter, 0.37 numerical aperture fibers 113, 114, and 115. If the optical fiber 119 has a core diameter of 600 microns and a numerical aperture of 0.37, six of the 200 micron core diameter fibers can be efficiently supplied with light, allowing each LED to supply light to 6 transmitting fibers, and allowing each current source to power 36 sensors at a low cost.
  • the LEDs can each provide light to several 200 micron transmitting fibers directly without an intermediate larger diameter fiber 119, this can result in a large variation in light into the fibers.
  • an LED providing light directly to three 200 micron core diameter, 0.37 NA fibers can result in a variation of light intensity of up to 300%.
  • Arranging the larger diameter optical fiber 119 between the LED and the smaller diameter transmitting fibers couples the light more uniformly into the transmitting fibers, and can reduce the variation between light intensities in the transmitting fibers to less than 10%.
  • the larger diameter optical fiber 119 illustrated in FIG. 1 IA-I IE is about six inches in length, and however, can be longer or shorter.
  • Each of the optical fibers 113, 114, and 115 extends to a different sensor 116, 117, and 118 and is connected to the transmitting optical fiber for that sensor.
  • Receiving fibers of the sensors 116, 117, and 118 receive the reflected light, as discussed in previous paragraphs related to Figures 1, 2, and 9A - 9C.
  • the receiving fibers can transmit the light directly to the photodetectors, or can be coupled to lengths of fiber via connector pairs for transmission to the photodetectors.
  • the photodetectors convert the received light from the fiber optic sensors to electrical signals.
  • the sensors 116, 117, and 118 can each be a 7 fiber pressure sensor as shown in
  • the sensors could be a pressure sensors with a different number of fibers, strain sensors, temperature sensors, or other fiber-optic based environmental sensors.
  • the receiving fibers can be abutingly connected to a larger diameter optical fiber, with the larger diameter optical fiber being large enough to receive light from all the six receiving fibers.
  • a 600 micron core diameter fiber 125 can be arranged to couple the light in the six receiving 200 micron core diameter fibers 123 into a PIN detector 126.
  • suitable components are suitable for the sensors and sensor devices, although it will be recognized that many other components may also be used.
  • One suitable current source is manufactured by Wavelength Electronics, model no. LDD200- IM. LEDs can be the OPF370A models at 100 mA supplied by Optek.
  • Suitable 200 micron core diameter fiber is manufactured by OFS, headquartered in Norcross, Georgia, USA, and is identified by model number CFO 1493- 10.
  • Suitable 400 micron core diameter fiber is manufactured by OFS, identified as model number CF01493-12.
  • Suitable 600 micron core diameter fiber is manufactured by OFS, identified as model number CF01493-14.
  • a suitable PIN detector is manufactured by Advanced Photonics, headquartered at Camarillo, California, USA, and identified by model number SD 100-41-21-231.
  • Suitable fiber, PIN, and LED connectors are available from Fiber Instrument Sales (FIS), headquartered in Oriskany, New York, USA, and identified by model numbers #Fl-0061830 and #5014741. Connectors can be modified if necessary to accommodate the larger diameter optical fibers and the multiple smaller diameter fibers to be connected.
  • Figure 12 illustrates a multiplexed sensor system with each current source supplying six LEDs 101, and each LED supplying light to six sensors 141.
  • a larger diameter fiber 142 is arranged to receive light from the LED via a connector pair.
  • a connection is arranged at the end of the larger diameter optical fiber 142 to couple light into six smaller diameter fibers 144.
  • Each smaller diameter fiber 144 transmits the light D to an individual sensor 141, in this example, a fiber optic microphone, hi this example, each LED supplies light to six sensors via the six smaller diameter fibers receiving light from the larger diameter fiber.
  • the sensors 141 can be the seven fiber pressure sensor illustrated in FIG. 1, or any other desired optical fiber based sensor. In this example, six receiving fibers in the sensors 141 transmit light via connectors and a length of larger diameter optical fiber 149 to photodetectors 146.
  • the sensors can also be dynamic pressure sensors, strain, displacement, acceleration, temperature, and bio-chemical sensors.
  • the multiplexed sensor systems of Figures 11 and 12 can also be used for temperature-compensated pressure sensing, or to compensate for other noise sources.
  • two sensors 116 and 117 in Figure 1 IA can be located near each other so they are exposed to approximately the same temperature, with one of them being exposed to a reference pressure, and the other exposed to the pressure to be sensed.
  • the detector results can be compared to eliminate or minimize thermal and/or other noise effects.
  • FIG. 13-14 illustrate fiber optic connection components suitable for use in the sensor systems of FIG. 9, 11 and 12.
  • FIG. 13A shows a ST adaptor 151 modified to receive a LED 101, and a ST connector 152 modified to have a bore sufficient to receive the larger diameter optical fiber core.
  • FIG. 13B shows the connectors 151 and 152 in their connected position. The end of the large diameter fiber in the connector 152 is held in position abutting or slightly separated from the LED surface by a spring-loaded mechanism in the connector/adaptor pair.
  • FIG. 14A and 14B show the ST connector 152 modified to receive a larger diameter optical fiber, a ST adaptor 155, and a ST connector 156 modified to have a bore sufficient to receive the multiple smaller diameter optical fibers.
  • the ends of the small diameter fibers in the connector 156 are held in position abutting or slightly separated from the surface of the larger diameter fiber in the connector 152 by spring-loaded mechanism in the connector/adaptor pairs.
  • the connectors and adaptors can be modified to include any number of optical fibers suitable for use in the systems of FIG. 9, 11, and 12.
  • a fiber 147 can be arranged centrally so it is surrounded by the smaller diameter optical fibers 148.
  • the central fiber 147 When the smaller diameter optical fibers are arranged to receive light from a larger diameter fiber 143 or from a LED, the central fiber 147 will have a light intensity of about three times the light intensity in the surrounding optical fibers, and the surrounding optical fibers will have approximately equal light intensities.
  • the central fiber can be used to provide light to a sensor, for communication or for any other desired purpose.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Measuring Fluid Pressure (AREA)
  • Optical Transform (AREA)
  • Length Measuring Devices By Optical Means (AREA)

Abstract

L'invention concerne un système multiplexé de capteurs à fibre optique comprenant une première fibre optique (119) présentant une première extrémité agencée pour recevoir de la lumière provenant d'une source lumineuse, au moins deux capteurs à fibre optique (116, 117) et des fibres optiques de petits diamètres (113, 114) agencées entre la première fibre optique et l'un des capteurs pour transmettre la lumière de la première fibre optique à ce capteur. Les capteurs peuvent être des capteurs de pression statique ou dynamique, des capteurs de contrainte, des capteurs de température ou d'autres capteurs environnementaux. L'invention concerne un capteur de pression statique à fibre optique présentant un boîtier de cartouche (200) dont une extrémité est exposée à l'atmosphère, une membrane souple mince (240) recouvrant l'extrémité exposée du boîtier de cartouche, et un faisceau de fibres (230) monté à l'intérieur du boîtier de cartouche, présentant une première extrémité polie pour transmettre la lumière à travers la membrane, le boîtier étant agencé pour maintenir la membrane à une certaine distance de la première extrémité de la fibre, dans une direction longeant un axe de fibres, un espace libre étant situé entre la première extrémité de fibres et le côté protégé de la membrane souple.
PCT/US2006/027648 2005-10-07 2006-07-14 Systeme multiplexe de capteurs a fibre optique WO2007044103A2 (fr)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
US11/250,709 2005-10-07
US11/250,709 US7379630B2 (en) 2002-05-28 2005-10-07 Multiplexed fiber optic sensor system
US11/250,708 2005-10-07
US11/250,708 US7460740B2 (en) 2002-05-28 2005-10-07 Intensity modulated fiber optic static pressure sensor system

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2273275A1 (fr) * 2009-07-09 2011-01-12 Lutz Nolte Traitement des déchets
WO2011003963A3 (fr) * 2009-07-09 2011-03-31 Lutz Nolte Détecteur de pression

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5146083A (en) * 1990-09-21 1992-09-08 The United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration High temperature fiber optic microphone having a pressure-sensing reflective membrane under tensile stress
US5279793A (en) * 1992-09-01 1994-01-18 Glass Alexander J Optical osmometer for chemical detection

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5146083A (en) * 1990-09-21 1992-09-08 The United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration High temperature fiber optic microphone having a pressure-sensing reflective membrane under tensile stress
US5279793A (en) * 1992-09-01 1994-01-18 Glass Alexander J Optical osmometer for chemical detection

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2273275A1 (fr) * 2009-07-09 2011-01-12 Lutz Nolte Traitement des déchets
WO2011003963A3 (fr) * 2009-07-09 2011-03-31 Lutz Nolte Détecteur de pression

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