Patent Application
20120325001
The present disclosure is generally related to optical sensors.
In many systems multiple parameters may be sensed in order to monitor operating conditions, such as operating temperatures, pressures, fluid levels, and so forth. Installing sensors and associated wiring may add considerable weight and expense to a system. When multiple sensors are used in a particular area, multiple wires may be used to connect the sensors to a control system that gathers information from the sensors. Installing the multiple sensors may require routing many wires through structures which can be a costly and time consuming process. For example, aircraft fuel tank sensing systems may include multiple sensors inside a fuel tank. Each sensor may be connected to a control system via a wire. Further, each sensor may be associated with a tank penetration to route wires from the sensor to the control system. Since the control system may be distant from the fuel tank, each wire may also be routed through other aircraft structures, such as bulkheads. Providing penetrations for the wiring (in the fuel tank and in the other aircraft structures) as well as routing the wiring can be challenging both during aircraft design and in manufacturing and maintenance of the aircraft. Additionally, the wiring and sensors themselves may add considerable cost and weight to the aircraft.
Optical sensors may have certain advantages over electrical sensors. For example, optical sensors are generally not sensitive to electromagnetic interference. Also, optical sensors may be relatively small as compared to certain legacy sensors. Particular optical sensor assemblies and optical sensor systems disclosed herein may be relatively inexpensive and may provide highly accurate sensing. For example, an optical sensor system may use encapsulated multimode fiber arrays with fiber tip sensors to measure temperature, pressure, or other parameters simultaneously. Such a system may be simple in configuration, flexible, highly tolerant to light source fluctuations, and inexpensive. Additionally, the system can achieve high accuracy while operating in an adverse environment. For example, disclosed optical sensors may be used in aircraft engines and fuel tanks where conditions such as heat and safety concerns may lead to difficulties in applying electrical sensing systems. Additionally, the optical sensors may be considerably smaller than electrical sensors and may use less power. Further, since the optical sensors are not sensitive to electromagnetic interference, no metallic shielding is required and considerable cost and weight savings may be achieved.
In a particular embodiment, an optical sensor assembly includes a substrate, a first photonic crystal sensor coupled to the substrate, and a second photonic crystal sensor coupled to the substrate. The first photonic crystal sensor is configured to reflect a first portion of incident light corresponding to a first reflection spectrum. A first wavelength range of the first reflection spectrum changes in response to changes in a first sensed parameter. The second photonic crystal sensor is configured to reflect a second portion of the incident light corresponding to a second reflection spectrum. A second wavelength range of the second reflection spectrum changes in response to changes in a second sensed parameter. The first reflection spectrum and the second reflection spectrum may be different.
In a particular embodiment, an optical sensor system includes an optical fiber and an optical sensor assembly coupled to a tip of the optical fiber. The optical sensor assembly includes a first photonic crystal sensor configured to exhibit a first reflection spectrum that changes responsive to a first sensed parameter and a second photonic crystal sensor configured to exhibit a second reflection spectrum that changes responsive to a second sensed parameter. The first reflection spectrum and the second reflection spectrum may be different.
In a particular embodiment, a method includes applying light to a first end of an optical fiber. Light reflected by at least one of a first photonic crystal sensor coupled to a second end of the optical fiber and a second photonic crystal sensor coupled to the second end of the optical fiber is detected. The first photonic crystal sensor exhibits a first reflection spectrum that changes responsive a first sensed parameter and the second photonic crystal sensor exhibits a second reflection spectrum that changes responsive a second sensed parameter. The method also includes determining a parameter value of at least one of the first sensed parameter and the second sensed parameter based on the detected light.
The features, functions, and advantages that have been described can be achieved independently in various embodiments or may be combined in yet other embodiments, further details of which are disclosed with reference to the following description and drawings.
Certain sensing systems utilize multiple, independently-targeted, electrical or electromagnetic sensor packages. For example, separate sensors may be used for sensing pressure, temperature, acceleration, and so forth. In certain applications, such as aircraft fuel tanks, using separate sensors for each sensed parameter can cause significant complications. For example, each sensor may be coupled by a wire to a control system and may communicate information about a sensed parameter to the control system using electrical signals. Routing the wiring from each sensor to the control system may require structural penetrations and tank penetrations which can be a considerable design challenge. For example, each structural penetration and tank penetration may introduce safety considerations to be addressed. Further, each structural penetration and tank penetration has an associated installation time and cost. In newer aircraft that utilize carbon fiber skins and structures, shielding that was associated with metal skins and structures is no longer available. Thus, additional compilations and costs may arise due to designing and installing shielding and isolation systems to provide shielding for wiring and sensors.
Optical technologies and optical sensors may be used to avoid some of these concerns with electrical sensor systems. For example, an optical photonic crystal sensor device may be significantly smaller and lighter than a corresponding electrical sensor. Additionally, electromagnetic interference is not a concern for optical technologies; thus, shielding and isolation concerns may be significantly reduced. Further, embodiments disclosed herein enable sensing from multiple optical sensors via a single optical fiber which reduces a number of structural penetrations and tank penetrations to install multiple sensor systems into a particular area. Using a single optical fiber rather than multiple optical fibers or multiple electrical connections may significantly reduce installation and repair costs as well as weight of a sensor system. Accordingly, cost, reliability, installation time, and other factors may be improved by using optical sensor systems, especially optical sensor systems that include multiple photonic crystal sensors attached to a single optical fiber.
In addition, photonic crystals may be substantially chemically and electrically inert and durable. Thus, photonic crystal sensors may be able to operate reliably in harsh environments, such as high temperature environments, chemically aggressive environments, and high shock or acceleration or vibration environments. For example, glass optical fibers and sensing nodes of the photonic crystals may operate in extreme temperatures upwards of 900 degrees Celsius. In less extreme environments, lower cost polymer materials may be used for the optical fibers which may reduce costs and be lighter weight.
An optical photonic crystal sensor includes a material that is structured to respond to changes in its environment in a manner that modifies a refractive index of the material. This change in the refractive index may result in frequency shifts in the reflection spectrum of the optical photonic crystal sensor. Thus, the reflection spectrum of the optical photonic crystal sensor may be responsive to a parameter sensed within the environment. For example, depending on the configuration of the optical photonic crystal sensor, the refractive index of the optical photonic crystal sensor may shift in response to temperature changes, pressure changes, vibration, acceleration, magnetic forces, etc. Accordingly, by supplying light to an optical photonic crystal sensor and detecting a reflection spectrum from the optical photonic crystal sensor an indication of values of one or more sensed parameters in the environment of the optical photonic crystal sensor may be determined.
The first photonic crystal sensor 106 may be configured to reflect a first portion of incident light that corresponds to a first reflection spectrum of the first photonic crystal sensor 106. A wavelength range of the first reflection spectrum may change in response to changes in a first sensed parameter. For example, the first photonic crystal sensor 106 may have a first structure that is formed of two or more materials, such as a first material that has a first refractive index and a second material that has a second refractive index. In response to changes in the position or orientation of the two or more materials (e.g., due to pressure, temperature, acceleration, vibration, magnetic forces or other physical influences or forces), the refractive index (and the reflection spectrum) of the first photonic crystal sensor 106 may change. To illustrate, the first structure of the first photonic crystal sensor 106 may include holes or other “defects” (i.e., irregularities) within the first material that are filled with the second material. For example, the first material may be a solid, glass or crystalline material and the second material may be a gas, a liquid or another solid (e.g., air, an ambient gas or another material). Since the two or more materials have different refractive indices, changes in the structure of the first material may cause changes in the relative refractive index of the two materials, resulting in an overall shift in the first reflection spectrum of the first photonic crystal sensor 106.
Similarly, the second photonic crystal sensor 107 may have a second structure that is formed of two or more materials. The two or more materials used for the second photonic crystal sensor 107 may be the same materials as used for the first photonic crystal sensor 106, or the second photonic crystal sensor 107 may include one or more materials that are different from materials of the first photonic crystal sensor 106. The second photonic crystal sensor 107 may be configured to reflect a second portion of incident light that corresponds to a second reflection spectrum. A wavelength range of the second reflection spectrum may change in response to a second sensed parameter (e.g., pressure, temperature, acceleration, vibration, magnetic force, etc.). In a particular embodiment, the first reflection spectrum of the first photonic crystal sensor 106 may be different than the second reflection spectrum of the second photonic crystal sensor 107. That is, the first photonic crystal sensor 106 and the second photonic crystal sensor 107 may reflect different wavelengths of light. The first sensed parameter and the second sensed parameter may be the same parameter or may be different parameters.
The optical fiber 110 may be coupled to an interrogator system 120. The interrogator system 120 may include one or more light sources 122 and one or more detectors 124. The one or more light sources 122 may provide incident light 112 that may be applied to the first photonic crystal sensor 106 and to the second photonic crystal sensor 107 via the optical fiber 110. In a particular embodiment, the incident light 112 may be applied to the first and second photonic crystal sensors 106-107 substantially simultaneously. For example, the one or more light sources 122 may simultaneously emit light in a wavelength corresponding to the first reflection spectrum of the first photonic crystal sensor 106 and light in a wavelength corresponding to the second reflection spectrum of the second photonic crystal sensor 107. For example, the one or more light sources 122 may include a broad spectrum light source. In another example, the one or more light sources 122 may include two or more separated relatively narrow spectrum light sources, such as laser light sources. The one or more light sources 122, the interrogator system 120, the optical fiber 110, or the substrate 102 may include a filter (not shown) that filters out portions of the spectrum of the incident light 112 that are not used or are not needed by the photonic crystal sensors 106, 107.
The first photonic crystal sensor 106 may reflect first reflected light 114 responsive to the first sensed parameters. Since the reflection spectrum of the first photonic crystal sensor 106 changes in response to the first sensed parameter, the first reflected light 114 may have a wavelength that is indicative of a value of the first sensed parameter. The second photonic crystal sensor 107 may reflect second reflected light 115. The second reflected light 115 may have a second wavelength that is indicative of a value of the second sensed parameter.
The one or more detectors 124 may detect the first reflected light 114 and the second reflected light 115. The one or more detectors 124 may be coupled to one or more processors 126. The one or more processors 126 may receive information indicative of the wavelength of the first reflected light 114, the second reflected light 115, or both, from the one or more detectors 124. In response to the information provided by the detectors 124, the processor 126 may determine a parameter value of at least one of the first sensed parameter and the second sensed parameter.
In a particular embodiment, the sensed parameters may include temperature, pressure, acceleration, vibration, magnetic force, one or more other parameters, or a combination thereof. Although two photonic crystal sensors 106, 107 are shown in
In a particular embodiment, the first reflection spectrum of the first photonic crystal sensor 106 may change in response to the first sensed parameter and in response to the second sensed parameter. For example, when the first photonic crystal sensor 106 is a pressure sensor. The reflection spectrum of the pressure sensor may change as a result of changes in physical dimensions of the structure of the first photonic crystal sensor 106 caused by changes in pressure. The second photonic crystal sensor 107 may be a temperature sensor. The reflection spectrum of the temperature sensor may change as a result of changes in physical dimensions of the structure of the second photonic crystal sensor 107 caused by changes in temperature. In this example, a change in temperature of the first photonic crystal sensor 106 may also change the physical dimensions of the structure of the first photonic crystal sensor 106. This can introduce some error in the pressure sensed by the first photonic crystal sensor 106. In this embodiment, the processor 126 may have access to calibration relationships that may be used by the processor 126 to determine a value of the first sensed parameter based on the first reflected light 114 from the first photonic crystal sensor 106, the second reflected light 115 from the second photonic crystal sensor 107, and the calibration relationship that relates changes in the first reflection spectrum to changes in the first sensed parameter and changes in the second sensed parameter. For example, by comparing information about changes in the first reflection spectrum and changes in the second reflection spectrum, the processor 126 may remove a contribution of the temperature change from a determined pressure value.
In a particular embodiment, at least a portion of the optical sensor system 100 may be disposed within a fuel tank of an aircraft. In this embodiment, light reflected by the first photonic crystal sensor 106 and the second photonic crystal sensor 107 may be used to provide information that is indicative of quantity of fuel present in the fuel tank. For example, by sensing pressure of fuel over the sensor, an estimate of the quantity of fuel may be determined (e.g., based on the density of the fuel or based on a calibration relationship, such as a look-up table). A more accurate estimate may be determined by taking multiple pressure readings (potentially at different locations within the fuel tank), by sensing temperature of the fuel as well as pressure to more accurately estimate density of the fuel, or both. Thus, the optical sensor system 100 may be used to avoid some of the concerns related to use of electrical sensor systems in a fuel tank. For example, the optical sensor system 100 may be significantly smaller and lighter than a corresponding electrical sensor system. Since a single optical fiber (e.g., the optical fiber 110) can be used to connect multiple photonic crystal sensors (e.g., the first photonic crystal sensor 106 and the second photonic crystal sensor 107) to the interrogator system 120, a number of structural penetrations and tank penetrations that may be used to install optical sensor system 100 may be reduced. Additionally, using the single optical fiber 110 may reduce installation and repair costs as well as weight of the optical sensor system 100 relative to an electrical sensor system. Thus, cost, reliability, installation time, and other factors may be improved by using the optical sensor system 100. The optical sensor system 100 may also be substantially immune from electromagnetic interference. Additionally, the optical sensor system 100 may operate reliably in harsh environments, such as high temperature environments, chemically aggressive environments, and high shock or acceleration or vibration environments.
Each of the photonic crystal sensors 206-209 may be associated with a different reflection spectrum. The reflection spectrum of each of the photonic crystal sensors 206-209 may change responsive to one or more sensed parameters. For example, the reflection spectra of the first photonic crystal sensor 206 and the second photonic crystal sensor 207 may each change responsive to the same sensed parameter, such as temperature. In another example, the reflection spectra of the third photonic crystal sensor 208 and the fourth photonic crystal sensor 209 may each change responsive to a second sensed parameter, such as pressure. Information descriptive of changes in the sensed parameters may be transmitted via the optical fiber 210 by way of the reflection spectra of the photonic crystal sensors 206-209. Information from the one of the photonic crystal sensors 206-209 may be differentiated from information from another of the photonic crystal sensors 206-209 based on the different wavelengths of the reflection spectra from the photonic crystal sensors 206-209. Thus, the optical sensor assembly 200 may include two or more photonic crystal sensors that together provide an indication one or more sensed parameters.
The reference photonic crystal sensor 405 may act as a reference relative to one or more of the other photonic crystal sensors 406-409. The covering layer 404 may at least partially shield the reference photonic crystal sensor 405 from the ambient environment to enable differentiation of various sensed parameters. For example, the reference photonic crystal sensor 405 may be subject to temperature in the ambient environment but may be at least partially shielded from pressure changes in the ambient environment. Thus, information from the reference photonic crystal sensor 405 may be used to isolate temperature and pressure affects sensed by one or more of the other photonic crystal sensors 406-409. For example, the second photonic crystal sensor 406 may have a reflection spectrum that changes responsive to a first sensed parameter and is responsive to a second sensed parameter. The third photonic crystal sensor 407 may likewise have a reflection spectrum that changes responsive to the first sensed parameter and is responsive to the second sensed parameter. The referenced photonic crystal sensor 405 may have a reflection spectrum that changes responsive only to the second sensed parameter. Thus, the reference photonic crystal sensor 405 may be used to determine a parameter value of the first sensed parameter independently of the second sensed parameter, to determine a parameter value of the second sensed parameter independently of the first sensed parameter, or both, by isolating affects of one sensed parameter from affects from the other sensed parameter.
The optical sensor assembly 508 may include a first photonic crystal sensor 510 and a second photonic crystal sensor 511. The first photonic crystal sensor 510 may be configured to exhibit a first reflection spectrum that changes responsive to a first sensed parameter. The second photonic crystal sensor 511 may be configured to exhibit a second reflection spectrum that changes responsive to a second sensed parameter. The first sensed parameter and the second sensed parameter may be the same or may be different. For example, the first photonic crystal sensor 510 and the second photonic crystal sensor 511 may sense pressure within the aircraft fuel tank 512. In another example, the first photonic crystal sensor 510 may sense pressure and the second photonic crystal sensor 511 may sense temperature within the aircraft fuel tank 512.
The reflection spectra of the first photonic crystal sensor 510 and the second photonic crystal sensor 511 may be different. Thus, the interrogator system 504 may identify and differentiate information from the photonic crystal sensors 510, 511 based on a wavelength of reflected light from the optical sensor assembly 508. The optical sensor system 500 may enable estimation of the quantity of fuel present in the fuel tank 512 based on light reflected to a light detector of the interrogator system 504. Thus, light associated with multiple sensors within the fuel tank 512 may be reduced as well as a number of penetrations required to enable sensors to provide sensing information to onboard systems may be reduced since multiple sensors may provide information via a single optical fiber 506. The optical sensor system 500 may be used to avoid some of the concerns with electrical sensor systems. For example, the optical sensor system 500 may be significantly smaller and lighter than a corresponding electrical sensor system. Since a single optical fiber (e.g., the optical fiber 506) can be used to connect multiple photonic crystal sensors (e.g., the first photonic crystal sensor 510 and the second photonic crystal sensor 511) to the interrogator system 504, a number of structural penetrations and tank penetrations to install optical sensor system 500 may be reduced. Additionally, using the single optical fiber 506 may reduce installation and repair costs as well as weight of the optical sensor system 500 relative to an electrical sensor system. Thus, cost, reliability, installation time, and other factors may be improved by using the optical sensor system 500. The optical sensor system 500 may also be substantially immune from electromagnetic interference. Additionally, the optical sensor system 500 may operate reliably in harsh environments, such as high temperature environments, chemically aggressive environments, and high shock or acceleration or vibration environments.
In response to the light applied to the first end of an optical fiber, light may be detected, at 604. The detected light may be reflected by a first photonic crystal sensor coupled to a second end of the optical fiber, by a second photonic crystal sensor coupled to the second end of the optical fiber, or by both the first photonic crystal sensor and the second photonic crystal sensor. As previously explained, more than two photonic crystal sensors may be coupled to the second end of the optical fiber, such as the four photonic crystal sensors 206-209 of
Using two photonic crystal sensors as an example, the first photonic crystal sensor may be configured to exhibit a first reflection spectrum that changes responsive to a first sensed parameter. The second photonic crystal sensor may be configured to exhibit a second reflection spectrum that changes responsive to a second sensed parameter. The first sensed parameter and the second sensed parameter may be the same or may be different. A wavelength of the first reflection spectrum and a wavelength of the second reflection spectrum may be different.
The method may also include, at 606, determining a parameter value of at least one of the first sensed parameter and the second sensed parameter based on the detected light. For example, the parameter value may be determined based on light reflected by the first photonic crystal sensor, based on light reflected by the second photonic crystal sensor, or based on both. For example, the first photonic crystal sensor may exhibit a change responsive to the first sensed parameter and in responsive to the second sensed parameter. Light reflected by the second photonic crystal sensor may be used to determine a value of the first sensed parameter by providing information about an affect of the second sensed parameter on the first photonic crystal sensor. In another example, the system may include a third sensor. The third sensor may be another photonic crystal sensor, such as the reference photonic crystal system 405 of
In an illustrative embodiment, a computing device 710 of the computing system 700 may include at least one processor 720. The processor 720 may be configured to execute instructions to implement a method of determining a parameter value using an optical sensor system, such as the method described with reference to
The system memory 730 may include volatile memory devices, such as random access memory (RAM) devices, and nonvolatile memory devices, such as read-only memory (ROM), programmable read-only memory, and flash memory. The system memory 730 may include an operating system 732, which may include a basic input/output system (BIOS) for booting the computing device 710 as well as a full operating system to enable the computing device 710 to interact with users, other programs, and other devices. The system memory 730 may also include one or more application programs 734.
The processor 720 also may communicate with one or more storage devices 740. The storage devices 740 may include nonvolatile storage devices, such as magnetic disks, optical disks, or flash memory devices. In an alternative embodiment, the storage devices 740 may be configured to store the operating system 732, the applications 734, the program data 736, or any combination thereof. The processor 720 may communicate with the one or more communication interfaces 760 to enable the computing device 710 to communicate with other computing systems 780. In a particular embodiment, the storage devices 740 may store information that is used by the processor to determine a parameter value using an optical sensor system. For example, the storage devices 740 may include a calibration relationship that relates changes in one or more reflection spectra to changes in sensed parameters.
The illustrations of the embodiments described herein are intended to provide a general understanding of the structure of the various embodiments. The illustrations are not intended to serve as a complete description of all of the elements and features of apparatus and systems that utilize the structures or methods described herein. Many other embodiments may be apparent to those of skill in the art upon reviewing the disclosure. Other embodiments may be utilized and derived from the disclosure, such that structural and logical substitutions and changes may be made without departing from the scope of the disclosure. For example, method steps may be performed in a different order than is shown in the figures or one or more method steps may be omitted. Accordingly, the disclosure and the figures are to be regarded as illustrative rather than restrictive.
Moreover, although specific embodiments have been illustrated and described herein, it should be appreciated that any subsequent arrangement designed to achieve the same or similar results may be substituted for the specific embodiments shown. This disclosure is intended to cover any and all subsequent adaptations or variations of various embodiments. Combinations of the above embodiments, and other embodiments not specifically described herein, will be apparent to those of skill in the art upon reviewing the description.
The Abstract of the Disclosure is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. In addition, in the foregoing Detailed Description, various features may be grouped together or described in a single embodiment for the purpose of streamlining the disclosure. This disclosure is not to be interpreted as reflecting an intention that the claimed embodiments require more features than are expressly recited in each claim. Rather, as the following claims reflect, the claimed subject matter may be directed to less than all of the features of any of the disclosed embodiments.
