Patent Application
20100259752
Not applicable.
The subject technology relates generally to sensors, and more specifically to sensors with fiber Bragg gratings and carbon nanotubes.
A fiber Bragg grating (“FBG”) is a type of distributed Bragg reflector constructed in a short segment of an optical fiber.
The present disclosure describes improved FBG sensors that incorporate carbon nanotubes.
In one aspect of the present disclosure, a sensor is provided. The sensor comprises an optical fiber having a radial direction and an axial direction, the optical fiber configured to transmit light along the axial direction and comprising a fiber Bragg grating (FBG) section. The sensor can further comprise a plurality of carbon nanotubes (CNTs) surrounding at least a portion of the FBG section, the CNTs, when exposed to an external measurand, are configured to cause a change in a spectral response of the FBG section.
In one aspect of the present disclosure, a method of sensing an external measurand is provided. The method can comprise providing a sensor comprising an optical fiber, the optical fiber having at least one fiber Bragg grating (FBG) section and a plurality of carbon nanotubes (CNTs) surrounding at least a portion of the FBG section. The method can further comprise providing light to the optical fiber while the CNTs are exposed to one or more measurands. The method can further comprise determining a change in a spectrum of one of a transmitted portion and a reflected portion of the light. The method can further comprise identifying a measurand that has caused the change.
In one aspect of the present disclosure, a method of sensing an external measurand is provided. The method can comprise providing a sensor comprising an optical fiber, the optical fiber having a fiber Bragg grating (FBG) section and a plurality of carbon nanotubes (CNTs) surrounding at least a portion of the at least FBG. The method can further comprise providing light into the sensor while the CNTs are exposed to one or more measurands, the light having a wavelength bandwidth narrower than a range of wavelengths of interest. The method can further comprise sweeping the wavelength bandwidth of the light until a portion of the light is detected at a particular wavelength bandwidth. The method can further comprise determining a change in a spectrum of the detected portion. The method can further comprise identifying a measurand that has caused the change.
The accompanying drawings, which are included to provide further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention.
In the following detailed description, numerous specific details are set forth to provide a full understanding of the disclosed and claimed embodiments. It will be apparent, however, to one ordinarily skilled in the art that the embodiments may be practiced without some of these specific details. In other instances, well-known structures and techniques have not been shown in detail to avoid unnecessarily obscuring the disclosure. The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any embodiment or design described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments or designs.
It is to be understood that the disclosure teaches just one example of the illustrative embodiment and that many variations of the invention can easily be devised by those skilled in the art after reading this disclosure and that the scope of the present invention is to be determined by the claims of the application.
A spectral response of an FBG as determined from features (e.g., a Bragg wavelength and/or intensity) of a transmitted or reflected portion of the input light provided to (e.g., coupled into) the optical fiber can be changed by strain applied to the FBG section. In addition to being sensitive to strain, the spectral response is sensitive to temperature.
This means that fiber Bragg gratings can be used as sensing elements in optical fiber sensors. The sensitivity of the Bragg wavelength to an applied strain (S) and a change in temperature (ΔT) is approximately given by:
where CS is the coefficient of strain, and CT is the coefficient of temperature.
Therefore, FBGs can be used as sensing elements in optical fiber sensors for monitoring and detecting certain measurands (e.g., particles, chemicals, and energy). In a FBG sensor, a change in (e.g., presence/absence of) the measurand causes a shift in the Bragg wavelength and/or a change in an intensity of the detected light portion (transmitted or reflected). FBGs can thus be used as direct sensing elements for strain and temperature.
The FBG sensor can also be used as transduction elements, converting the output of another sensor, which generates a strain or temperature change from the measurand. For example, FBG gas sensors use an absorbent coating, which in the presence of a gas expands generating a strain, which is measurable by the grating. Technically, the absorbent material is the sensing element, converting the amount of gas to a strain. The FBG then transduces the strain to a change in the Bragg wavelength.
FBGs can find uses in instrumentation applications such as downhole sensors in oil and gas wells for measurement of the effects of external pressure, temperature, seismic vibrations and inline flow measurement. As such they offer a significant advantage over traditional electronic gauges used for these applications in that they are less sensitive to vibration or heat and consequently are far more reliable.
In one aspect, an FBG is a small length of single mode fiber that has been specially treated and “etched” in a very specific manner using a high power laser. Depending on how the FBG has been processed and installed, it can be a pass or reject filter, for instance, it can be set to only pass one frequency of light or reject one frequency while passing all others.
In certain embodiments, the fiber core 210 includes a glass fiber material. In other embodiments, the optical fiber 220 includes a polymer (e.g., plastic) fiber material. Each of the first and second FBG sections 212A, 212B can be constructed by “inscribing” or “writing” systematic (periodic or aperiodic) variation of refractive index to the fiber core 210 using an intense ultraviolet (UV) radiation source such as a UV laser. Processes used to inscribe such systematic variation in the fiber core include interference, masking, and point-by-point processes. The choice of a particular process employed depends on the type of grating to be manufactured. In some embodiments, the FBG section is constructed in germanium-doped silica fiber. The germanium-doped fiber is photosensitive, and the refractive index of the core changes with exposure to UV light, the amount of the change being a function of the intensity and duration of the exposure.
In an FBG section, a particular construction (e.g., a spacing or spacings between regions of high and low refractive indices) determines a spectral response (e.g., a Bragg wavelength) of the FBG section. A spectral response may comprise a general shape (e.g., height, width) of the spectrum of an output light 202 and/or one or more “rejects” 230A, 230B at one or more Bragg wavelengths in the spectrum. A “reject” 230A may be a notch (having a certain magnitude) in the spectrum of an output light.
In certain embodiments, the first and second FBG sections 212A, 212B are of the same construction and hence have the same spectral response. In other embodiments, the first and second FBG sections 212A, 212B are of different constructions and hence have different spectral responses (e.g., different response bands and/or Bragg wavelengths). One skilled in the art will recognize that additional FBG sections can be included that have the same or different spectral responses as FBG sections 212A and 212B. Thus, there can be, for example, three, four, five, six, up to 100's of FBG sections. CNTs (e.g., 220A, 220B) can be grown on different types of optical fiber by a multitude of different processes. One exemplary process for growing CNTs on a glass fiber core is described below with respect to
In certain embodiments, the CNTs 220A, 220B comprise a plurality of carbon nanotubes each of which is grown in a radial direction of the fiber core 110 such that an axis of each nanotube thus grown is substantially along the radial direction. The height of such a nanotube can range, for example, from 3 to 150 μm.
A set of CNTs can surround or cover all or portions of the corresponding FBG section. For instance, the CNTs 220A may surround or cover all or portions of the FBG section 212A, and/or the CNTs 220B may surround or cover all or only portions of the FBG section 212B. In one example, the CNTs 220A cover the entire outer surface of the FBG section 212A in both length (e.g., axial) and circumferential (e.g., around the fiber core) directions. In another example, the CNTs 220A cover only a certain portion of the FBG section 212A along the length direction while covering the entire outer surface of the FBG section 212A along the circumferential direction within the covered length portion. In yet another example, the CNTs 220A cover only a portion of the FBG section 212A along the circumferential direction. The portion partially covered along the circumferential direction can extend the entire length of the FBG section 212A or only a portion thereof (e.g., a middle portion of the FBG section 212A). Similar coverage possibilities exist for the CNTs 220B with respect to the FBG section 212B.
In certain embodiments, the CNTs 220A, 220B are grown to possess certain characteristics for efficiently absorbing a measurand 204 of interest, such as certain particles, chemicals, or radiated energy. Radiated energy can include sonar energy and electromagnetic energy impinging on the CNTs.
For absorbing particles, for example, the CNTs 220A, 220B can be grown to possess single-wall CNTs and multi-wall CNTs with functionalization utilizing groups such as carboxylic, amine, nitrates, and hydroxyl groups, which typically contain electron mobility. Particle absorption can cause changes in absorption or reflection of the entire electromagnetic spectrum. For absorbing chemicals, for example, the CNTs 220A, 220B can be grown to possess a particular functionality with the highest available affinity for a particular chemical. Chemical absorption can cause changes in absorption or reflection of the entire electromagnetic spectrum. The CNTs can expand, contract and oscillate in different modes upon absorbing chemicals, radiations, or energy and hence affecting the reflection characteristics of the FBGs.
After absorbing particles, chemicals, or energy, certain characteristics (e.g., strain or temperature) of the CNTs undergo a change. For example, when the CNTs absorb chemicals such as acetone, alcohols, hazardous gases, chemicals or biological warfare agent, the CNTs can experience a change in refractive index and/or strain. The changes in the CNTs, in turn, cause a change in the spectral response of the FBG section underlying the CNTs. As another example, when the CNTs absorb a form of radiated energy (e.g., RF or sonar wave), the absorbed energy causes a rise in temperature of the CNTs and of the underlying FBG section. The rise in temperate, in turn, causes a shift in the Bragg wavelength of the FBG section.
In one experimental embodiment, an input light from a 1510 nm laser source was provided to the fiber core. The input light was passed through the CNT-bearing sensor. The light interacts with the CNT-infused FBG, and the output light is received by the photo detector. The transmitted light was observed at 1516 nm or a 6 nm shift from the original wavelength. The FBG with CNTs was then subjected to acetone vapors. The transmitted light wavelength shifted by 3 nm and was observed at 1513 nm. As the acetone evaporated in a few seconds, the transmitted light wavelength returned to its original observed value of 1516 nm.
In operation, input light 201 from a light source (e.g., a laser, not shown), is provided to the fiber core 210. In the illustrated embodiment, the input light 201 is a broadband light having a spectrum or wavelength bandwidth encompassing a full range of wavelengths of interest. In alternative embodiments, however, the input light 201 is a relatively narrowband light having a spectrum or wavelength bandwidth narrower than a full range of wavelengths of interest. In those alternative embodiments, the spectrum or wavelength bandwidth of the input light 201 can be swept across the full range of wavelengths of interest as will be described in detail below with respect to
Returning to
To infuse carbon nanotubes into a glass fiber material, the carbon nanotubes are synthesized directly on the glass fiber material. In the illustrative embodiment, this is accomplished by first disposing nanotube-forming catalyst on the glass fiber, as per operation 402.
Preceding catalyst deposition, the glass fiber material can be optionally treated with plasma to prepare the surface to accept the catalyst. For example, a plasma treated glass fiber material can provide a roughened glass fiber surface in which the CNT-forming catalyst can be deposited. In some embodiments, plasma can be also used to “clean” the fiber surface. The plasma process for “roughing” the surface of the glass fiber materials thus facilitates catalyst deposition. The roughness is typically on the scale of nanometers. In the plasma treatment process craters or depressions are formed that are nanometers deep and nanometers in diameter. Such surface modification can be achieved using a plasma of any one or more of a variety of different gases, including, without limitation, argon, helium, oxygen, ammonia, nitrogen and hydrogen.
As described further below and in conjunction with
With reference to the illustrative embodiment of
In operation 406, CVD-promoted nanotube growth on the catalyst-laden glass fiber material is then performed. The CVD process can be promoted by, for example, a carbon-containing feedstock gas such as acetylene, ethylene, and/or ethanol. The CNT synthesis processes generally use an inert gas (e.g., nitrogen, argon, helium) as a primary carrier gas. The carbon feedstock is provided in a range from greater than 0% to about 15% of the total mixture. A substantially inert environment for CVD growth is prepared by removal of moisture and oxygen from the growth chamber.
In the CNT synthesis process, CNTs grow at the sites of a CNT-forming transition metal nanoparticle catalyst. The presence of the strong plasma-creating electric field can be optionally employed to affect nanotube growth. That is, the growth tends to follow the direction of the electric field. By properly adjusting the geometry of the plasma spray and electric field, vertically-aligned CNTs (i.e., perpendicular to the glass fiber material) can be synthesized. Under certain conditions, even in the absence of a plasma, closely-spaced nanotubes will maintain a vertical growth direction resulting in a dense array of CNTs resembling a carpet or forest.
The operation of disposing a catalyst on the glass fiber material can be accomplished by spraying or dip coating a solution or by gas phase deposition via, for example, a plasma process. Thus, in some embodiments, after forming a solution of a catalyst in a solvent, catalyst can be applied by spraying or dip coating the glass fiber material with the solution, or combinations of spraying and dip coating. Either technique, used alone or in combination, can be employed once, twice, thrice, four times, up to any number of times to provide a glass fiber material that is sufficiently uniformly coated with CNT-forming catalyst. When dip coating is employed, for example, a glass fiber material can be placed in a first dip bath for a first residence time in the first dip bath. When employing a second dip bath, the glass fiber material can be placed in the second dip bath for a second residence time. For example, glass fiber materials can be subjected to a solution of CNT-forming catalyst for about 4 seconds to about 90 seconds depending on the dip configuration and linespeed. Employing spraying or dip coating processes, a glass fiber material with a surface density of catalyst of less than about 5% surface coverage to as high as about 80% coverage, in which the CNT-forming catalyst nanoparticles are nearly monolayer. In some embodiments, the process of coating the CNT-forming catalyst on the glass fiber material produces no more than a monolayer. For example, CNT growth on a stack of CNT-forming catalyst can erode the degree of infusion of the CNT to the glass fiber material. In other embodiments, the transition metal catalyst can be deposited on the glass fiber material using evaporation techniques, electrolytic deposition techniques, and other processes known to those skilled in the art, such as addition of the transition metal catalyst to a plasma feedstock gas as a metal organic, metal salt or other composition promoting gas phase transport.
The catalyst solution employed can be a transition metal nanoparticle which can be any d-block transition metal. In addition, the nanoparticles can include alloys and non-alloy mixtures of d-block metals in elemental form or in salt form, and mixtures thereof. Such salt forms include, without limitation, oxides, carbides, and nitrides. Non-limiting exemplary d-block transition metal NPs include Ni, Fe, Co, Mo, Cu, Pt, Au, and Ag and salts thereof and mixtures thereof. In some embodiments, such CNT-forming catalysts are disposed on the glass fiber by applying or infusing a CNT-forming catalyst directly to the glass fiber material. Many of these transition metal catalysts are readily commercially available from a variety of suppliers, including, for example, Ferrotec Corporation (Bedford, N.H.).
Catalyst solutions used for applying the CNT-forming catalyst to the glass fiber material can be in any common solvent that allows the CNT-forming catalyst to be uniformly dispersed throughout. Such solvents can include, without limitation, water, acetone, hexane, isopropyl alcohol, toluene, ethanol, methanol, tetrahydrofuran (THF), cyclohexane or any other solvent with controlled polarity to create an appropriate dispersion of the CNT-forming catalyst nanoparticles. Concentrations of CNT-forming catalyst can be in a range from about 1:1 to 1:10000 catalyst to solvent.
In some embodiments, after applying the CNT-forming catalyst to the glass fiber material, the glass fiber material can be heated to a softening temperature. This can aid embedding the CNT-forming catalyst into the surface of the glass fiber material and can encourage seeded growth without catalyst “floating.” In some embodiments heating of the glass fiber material after disposing the catalyst on the glass fiber material can be at a temperature that is between about 500° C. and 1000° C.
The step of synthesizing carbon nanotubes can include numerous techniques for forming carbon nanotubes, including those disclosed in co-pending U.S. Patent Application Publication No. US 2004/0245088 which is incorporated herein by reference. The CNTs grown on fibers of the subject technology can be accomplished by techniques known in the art including, without limitation, micro-cavity, thermal or plasma-enhanced CVD techniques, laser ablation, arc discharge, and high pressure carbon monoxide (HiPCO). In some embodiments, acetylene gas is ionized to create a jet of cold carbon plasma for CNT synthesis. The plasma is directed toward the catalyst-bearing glass fiber material. Thus, in some embodiments, synthesizing CNTs on a glass fiber material includes (a) forming a carbon plasma; and (b) directing the carbon plasma onto the catalyst disposed on the glass fiber material. The diameters of the CNTs that are grown are dictated by the size of the CNT-forming catalyst as described above. In some embodiments, the sized fiber substrate is heated to between about 550° C. and about 800° C. to facilitate CNT synthesis. To initiate the growth of CNTs, two gases are bled into the reactor: a process gas such as argon, helium, or nitrogen, and a carbon-containing gas, such as acetylene, ethylene, ethanol or methane. CNTs grow at the sites of the CNT-forming catalyst.
In some embodiments, the CVD growth is plasma-enhanced. A plasma can be generated by providing an electric field during the growth process. CNTs grown under these conditions can follow the direction of the electric field. Thus, by adjusting the geometry of the reactor vertically aligned carbon nanotubes can be grown radially about a cylindrical fiber. In some embodiments, a plasma is not required for radial growth about the fiber. For glass fiber materials that have distinct sides such as tapes, mats, fabrics, plies, and the like, catalyst can be disposed on one or both sides and correspondingly, CNTs can be grown on one or both sides as well.
As described above, CNT-synthesis is performed at a rate sufficient to provide a continuous process for functionalizing spoolable glass fiber materials. Numerous apparatus configurations facilitate such continuous synthesis as exemplified below.
In some embodiments, CNT-infused glass fiber materials can be constructed in an “all plasma” process. In such embodiments, glass fiber materials pass through numerous plasma-mediated steps to form the final CNT-infused product. The first of the plasma processes, can include a step of fiber surface modification. This is a plasma process for “roughing” the surface of the glass fiber material to facilitate catalyst deposition, as described above. As described above, surface modification can be achieved using a plasma of any one or more of a variety of different gases, including, without limitation, argon, helium, oxygen, ammonia, hydrogen, and nitrogen.
After surface modification, the glass fiber material proceeds to catalyst application. This is a plasma process for depositing the CNT-forming catalyst on the fibers. The CNT-forming catalyst is typically a transition metal as described above. The transition metal catalyst can be added to a plasma feedstock gas as a precursor in the form of a ferrofluid, a metal organic, metal salt or other composition for promoting gas phase transport. The catalyst can be applied at room temperature in the ambient environment with neither vacuum nor an inert atmosphere being required. In some embodiments, the glass fiber material is cooled prior to catalyst application.
Continuing the all-plasma process, carbon nanotube synthesis occurs in a CNT-growth reactor. This can be achieved through the use of plasma-enhanced chemical vapor deposition, wherein carbon plasma is sprayed onto the catalyst-laden fibers. Since carbon nanotube growth occurs at elevated temperatures (typically in a range of about 500 to 1000° C. depending on the catalyst), the catalyst-laden fibers can be heated prior to exposing to the carbon plasma. For the infusion process, the glass fiber material can be optionally heated until it softens. After heating, the glass fiber material is ready to receive the carbon plasma. The carbon plasma is generated, for example, by passing a carbon containing gas such as acetylene, ethylene, ethanol, and the like, through an electric field that is capable of ionizing the gas. This cold carbon plasma is directed, via spray nozzles, to the glass fiber material. The glass fiber material can be in close proximity to the spray nozzles, such as within about 1 centimeter of the spray nozzles, to receive the plasma. In some embodiments, heaters are disposed above the glass fiber material at the plasma sprayers to maintain the elevated temperature of the glass fiber material.
Another configuration for continuous carbon nanotube synthesis involves a special rectangular reactor for the synthesis and growth of carbon nanotubes directly on glass fiber materials. The reactor can be designed for use in a continuous in-line process for producing carbon-nanotube bearing fibers. In some embodiments, CNTs are grown via a chemical vapor deposition (CVD) process at atmospheric pressure and at elevated temperature in the range of about 550° C. to about 800° C. in a multi-zone reactor. The fact that the synthesis occurs at atmospheric pressure is one factor that facilitates the incorporation of the reactor into a continuous processing line for CNT-on-fiber synthesis. Another advantage consistent with in-line continuous processing using such a zone reactor is that CNT growth occurs in seconds, as opposed to minutes (or longer) as in other procedures and apparatus configurations typical in the art.
The processor 502 may include a general-purpose processor or a specific-purpose processor for executing instructions and may further include an internal memory 519, such as a volatile or non-volatile memory, for storing data and/or instructions for software programs. The instructions, which may be stored in a memory 510 and/or 519, may be executed by the processor 502 to control and manage access to the various networks, as well as provide other communication and processing functions. The instructions may also include instructions executed by the processor 502 for various user interface devices, such as a display 512 and a keyboard or keypad (not shown).
The processor 502 may be implemented using software, hardware, or a combination of both. By way of example, the processor 502 may be implemented with one or more processors. A processor may be a general-purpose microprocessor, a microcontroller, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA), a Programmable Logic Device (PLD), a controller, a state machine, gated logic, discrete hardware components, or any other suitable device that can perform calculations or other manipulations of information.
A machine-readable medium (e.g., 519, 510) that stores software for control, analysis and other processing functions can be one or more machine-readable media. Software shall be construed broadly to mean instructions, data, or any combination thereof, whether referred to as software, firmware, middleware, microcode, hardware description language, or otherwise. Instructions may include code (e.g., in source code format, binary code format, executable code format, or any other suitable format of code).
Machine-readable media may include storage integrated into a processing system, such as might be the case with an ASIC. Machine-readable media (e.g., 510) may also include storage external to a processing system, such as a Random Access Memory (RAM), a flash memory, a Read Only Memory (ROM), a Programmable Read-Only Memory (PROM), an Erasable PROM (EPROM), registers, a hard disk, a removable disk, a CD-ROM, a DVD, or any other suitable storage device. In addition, machine-readable media may include a transmission line or a carrier wave that encodes a data signal. Those skilled in the art will recognize how best to implement the described functionality for the processing system 502. According to one aspect of the disclosure, a machine-readable medium is a computer-readable medium or computer-readable storage medium encoded or stored with instructions and is a computing element, which defines structural and functional interrelationships between the instructions and the rest of the system, which permit the instructions' functionality to be realized. Instructions can be, for example, a computer program including code.
The light control module 506 may be a hardware module or a software module or a combination of both (e.g., a firmware) and may contain hardware components and/or control programs that are configured to control the light source 550A (e.g., laser), which can be broadband or narrowband. The light control module 506 is configured to send one or more control signals to the light source 550A via an output port 524, thereby causing the light source 702 to provide light (201 of
In the illustrated example of
In the illustrated transmission (reject)-type sensing system 500A, the photodetector 560A (e.g., photodiodes) is disposed at an output side (e.g., end of the optical fiber) of the CNT-bearing FBG sensor 200A. The transmitted light portion is detected by the photodetector 560A, which converts the detected transmitted light portion into an electrical signal. The electrical signal output of the photodetector 560A is received by a signal conditioning/conversion module 514 via an input port 522. The signal conditioning/conversion module 514 conditions (e.g., filters and amplifies) the electrical signal and converts (e.g., digitizes) it into a digital representation. The digital representation is then received and processed (e.g., analyzed) by the processor 702 to determine change(s) in the spectrum of the transmitted light portion and identify one or more measurands that have caused the change(s).
One difference between the transmission-type sensing system 500A of
It shall be appreciated that the illustrated embodiments of
In certain embodiments, a CNT-bearing FBG sensor (e.g., 200A, 200B) is calibrated at least once before the sensor is used for monitoring and detecting anticipated measurands. In some embodiments, the sensor is calibrated periodically. The calibration procedure involves passing light through the sensor without exposing the CNT-infused FBGs (e.g., 205F, 205G, 205H, 205I) to anticipated measurands, and receiving and analyzing one of reflected and transmitted light portions to establish an original finger print, which can include one or more reference Bragg wavelengths and/or a peak or integrated light intensity.
Subsequently, the CNT-infused FBGs (e.g., 205F, 205G, 205H, 205I) are exposed to various anticipated measurands (e.g., particles, chemicals, energy). For example, after an exposure to a particular anticipated measurand, light is again provided to the sensor, and a transmitted/reflected light portion is received by a photodetector (e.g., 560A, 560B). The signal generated by the photodetector reveals a different fingerprint (e.g., a shifted Bragg wavelength and/or a different peak/integrated intensity), due to the different state of the CNTs. The difference between the original fingerprint and the new fingerprint resulting from the absorbed measurand is then quantified.
This process is repeated for a variety of different anticipated measurands (e.g., contaminants, agents, environmental conditions) that the sensor is intended to monitor and detect. In this way, the behavior of the CNT-bearing FBG sensor is characterized for all anticipated measurands. A look-up table of the differences for all monitored conditions can be created and stored in a computer-readable memory (e.g., 519, 510). In some embodiments, in addition to or in lieu of the look-up table of the differences, an entire spectrum of the transmitted and/or reflected light portion is stored in a memory for use during a monitoring and detecting process.
Once calibrated, the CNT-bearing FBG sensor can then be deployed and periodic readings taken by passing a laser light into the sensor and obtaining the updated fingerprint. If a change is observed that matches a previously established change listed in the look-up table, then an alert can be issued. In addition to using a frequency/wavelength based fingerprint, the sensor could be configured to measure attenuation of one or more frequencies or phase shift, using appropriate equipment (e.g., a Mach Zehnder interferometer for determining phase shift).
In certain embodiments, the input light is a broadband light having a spectrum that encompasses a full range of wavelengths of interest. Taking the example of the CNT-bearing FBG sensor 200 of
The process 600 proceeds to operation 620 in which a portion of the light provided into the CNT-bearing FBG sensor is detected. In the sensing system 500A of
The process 600 proceeds to operation 630 in which a change in a spectrum of the detected light portion is determined by a processor (e.g., 502). In certain embodiments, the operation 630 includes obtaining a spectrum of a corresponding one of the transmitted light portion and the reflection light portion. Taking the example of
The process 600 then proceeds to operation 640 in which a measurand (e.g., particles, chemicals, or energy) that has caused the change is identified by the processor. In certain embodiments, the identification operation 640 involves identifying a measurand that is found to cause the determined change during a previous calibration procedure. For example, assume that the change in the spectrum of the detected light portion determined at the operation 630 is a negative 125 nm shift in the second Bragg wavelength 203B (
In certain alternative aspects, instead of utilizing a broadband light discussed above with respect to the process 600, a narrowband light having a relatively narrow wavelength bandwidth or spectrum is utilized, and the spectrum or wavelength bandwidth of the light is scanned or swept across a full response range of interest for monitoring and detecting one or more anticipated measurands in one or more locations.
The process 700 begins at start state 701 and proceeds to operation 710 in which light (e.g., input light 201) from a light source (e.g., laser 550A, 550B) is provided to the CNT-bearing FBG sensor (e.g., 200A, 200B) while the CNTs in the CNT-infused FBGs (e.g., 205F, 205G, 205H, 205I) are exposed to one or more measurands. As discussed above, the light has a spectrum or wavelength bandwidth that is narrower than a full response range of interest. For example, the light can have a 50 nm bandwidth while the full response range of interest is 600 nm (e.g., from 1,200 nm to 1,800 nm). In some embodiments, the light source 550 (
The process 700 proceeds to operation 720 in which a portion (reflected or transmitted) of the input light, if any, is detected by a photodetector (e.g., 560A, 560B), and then to decision state 730 in which it is determined whether a change has been absorbed in a spectrum of the detected light portion. In certain embodiments, the operation 730 involves calculating a shift in a Bragg wavelength from a reference Bragg wavelength. In other embodiments, the determination involves calculating a change (e.g., increase or decrease) in a peak or integrated intensity of the detected light portion. In some embodiments, the operation 730 involves steps of first determining whether any light portion has been detected at all with the input light set at the current wavelength bandwidth and, if there was a detected light portion, then focusing on (e.g., fine sweeping) the current wavelength bandwidth to obtain a spectrum of the detected light portion and determining a change (e.g., a shift in Bragg wavelength) in the spectrum. For example, in some embodiments, the CNT-bearing FBG sensor does not reflect a significant portion of the input light unless the CNTs are exposed to a measurand. In such cases, if the measurand were not present, there would not be any detected light portion. In that case, the decision state 730 determines that there is no change in the spectrum of the detected light portion (No).
If it is determined at the decision state 730 that there is no change in the spectrum of the detected light portion (No), either because there is no change in features (e.g., Bragg wavelength or intensity) of the spectrum of the detected light portion, or because no light portion (e.g., reflected portion) has been detected, the process 700 proceeds to operation 740 where the wavelength of the light is switched (e.g., increased) to a new wavelength bandwidth (e.g., 1,250-1,300 nm). Subsequently, another light measurement is taken with the new wavelength bandwidth at the operation 720, and another determination is made as to whether there is a change in the spectrum of a detected light portion, if any, with the new wavelength bandwidth at the decision state 730.
On the other hand, if it is determined at the decision state 730 that there is a change in the spectrum of the detected light portion in the current wavelength bandwidth (Yes), the process 700 proceeds to operation 750 in which a measurand that caused the change is identified. As discussed above with respect to the process 600 of
The process 700 then proceeds to operation 760 in which it is determined whether a sweep of a full response range of interest (e.g., 1,200-1,800 nm) has been completed. If the answer is No, the process 700 proceeds to the operation 740 where the wavelength of the light is switched to a new wavelength bandwidth, followed by the operation 720 and the decision state 730 as discussed above. On the other hand, if it is determined at the decision state 760 that the sweep has been completed (Yes), the process 700 ends at state 709.
Certain aspects of monitoring/detection processes (e.g., processes 600 and 700) of the present disclosure can be implemented in a processor (e.g., 502 of
In certain aspects of the disclosure, FBGs are employed in optical communications systems such as notch filters, optical multiplexers and demultiplexers with an optical circulator, or Optical Add-Drop Multiplexers (OADMs).
It is understood that the specific order or hierarchy of steps in the processes disclosed is an illustration of exemplary approaches. Based upon design preferences, it is understood that the specific order or hierarchy of steps in the processes may be rearranged. Some of the steps may be performed simultaneously. The accompanying method claims present elements of the various steps in a sample order, and are not meant to be limited to the specific order or hierarchy presented.
In the previous description, numerous specific details are set forth, such as specific materials, structures, processes, etc., in order to provide a better understanding of the present disclosure. However, the present disclosure can be practiced without resorting to the details specifically set forth herein. In other instances, well-known processing techniques and instrumentalities have not been described in order not to unnecessarily obscure the present disclosure.
Examples of embodiments of the present disclosure and a few examples of its versatility are shown and described herein. It is to be understood that the present disclosure is capable of use in various other combinations and environments and is susceptible of changes and/or modifications within the scope of the inventive concept as expressed herein.
The foregoing description is provided to enable any person skilled in the art to practice the various embodiments described herein. While the foregoing embodiments have been particularly described with reference to the various figures and embodiments, it should be understood that these are for illustration purposes only and should not be taken as limiting the scope of the invention.
There may be many other ways to implement the invention. Various functions and elements described herein may be partitioned differently from those shown without departing from the spirit and scope of the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art in view of the present disclosure, and generic principles defined herein may be applied to other embodiments. Thus, many changes and modifications may be made to the invention, by one having ordinary skill in the art in view of the present disclosure, without departing from the spirit and scope of the invention.
A reference to an element in the singular is not intended to mean “one and only one” unless specifically stated, but rather “one or more.” The term “some” refers to one or more. Pronouns in the masculine (e.g., his) include the feminine and neuter gender (e.g., her and its) and vice versa. Headings and subheadings, if any, are used for convenience only and do not limit the invention. Underlined and/or italicized headings and subheadings are used for convenience only, do not limit the invention, and are not referred to in connection with the interpretation of the description of the invention.
Terms such as “top,” “bottom,” “front,” “rear” and the like as used in this disclosure should be understood as referring to an arbitrary frame of reference, rather than to the ordinary gravitational frame of reference. Thus, a top surface, a bottom surface, a front surface, and a rear surface may extend upwardly, downwardly, diagonally, or horizontally in a gravitational frame of reference.
A phrase such as an “aspect” does not imply that such aspect is essential to the subject technology or that such aspect applies to all configurations of the subject technology. A disclosure relating to an aspect may apply to all configurations, or one or more configurations. A phrase such as an aspect may refer to one or more aspects and vice versa. A phrase such as an “embodiment” does not imply that such embodiment is essential to the subject technology or that such embodiment applies to all configurations of the subject technology. A disclosure relating to an embodiment may apply to all embodiments, or one or more embodiments. A phrase such an embodiment may refer to one or more embodiments and vice versa.
All structural and functional equivalents to the elements of the various embodiments of the invention described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and intended to be encompassed by the invention. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the above description. No claim element is to be construed under the provisions of 35 U.S.C. §112, sixth paragraph, unless the element is expressly recited using the phrase “means for” or, in the case of a method claim, the element is recited using the phrase “step for.” Furthermore, to the extent that the term “include,” “have,” or the like is used in the description or the claims, such term is intended to be inclusive in a manner similar to the term “comprise” as “comprise” is interpreted when employed as a transitional word in a claim.
The present application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/169,063, entitled “SENSORS COMPRISING FIBER BRAGG GRATINGS AND CARBON NANOTUBES” filed on Apr. 14, 2009, which is hereby incorporated by reference in its entirety for all purposes.
| Number | Date | Country | |
|---|---|---|---|
| 61169063 | Apr 2009 | US |
