Abstract:
A plurality of voids are introduced into a polymeric material. One or more stress sensitive components in abutment with a portion of the polymeric material are buffered from one or more stresses through employment of the portion of the polymeric material that comprises one or more voids of the plurality of voids. A movement of the portion of the polymeric material is accommodated through compression of one or more of the one or more voids.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
         [0001]    This application contains subject matter which is related to the subject matter of the following application, which is assigned to the same assignee as this application. The below-listed application is hereby incorporated herein by reference in its entirety:  
           [0002]    “POLYMERIC MATERIAL WITH VOIDS THAT COMPRESS TO ALLOW THE POLYMERIC MATERIAL TO ABSORB APPLIED FORCE AND DECREASE REACTION FORCE TO ONE OR MORE SENSOR FIBERS,” by Carlson, et al., co-filed herewith.  
         TECHNICAL FIELD  
         [0003]    The invention relates generally to stress sensitive components and more particularly to buffering stress sensitive components.  
         BACKGROUND  
         [0004]    Polymeric materials in one example are used for buffering sensor fibers. For example, the polymeric material coats the sensor fiber for protection of the sensor fiber. In one example, the polymeric material comprises a potting compound and the sensor fiber comprises an optical fiber. The potting compound comprises a buffer layer for the optical fiber. The optical fiber is wound about a spool in a winding pattern to form a fiber optic coil. A fiber optic gyroscope in one example employs the fiber optic coil to sense a rate of rotation. The fiber optic coil comprises a plurality of windings along the length of the spool and one or more layers of windings. As the optical fiber is wound about the spool, the potting material is applied to the outer surface of the optical fiber. For example, a syringe and brush applicator coats the fiber optic coil with the potting material. The potting material promotes precision in the winding pattern of the fiber optic coil.  
           [0005]    The potting compound in one example fills a space between each of the windings and the layers of windings. For example, the potting compound acts a buffer layer between each of the windings and the layers of windings. Upon expansion of the fiber optic coil, the fiber optic coil applies a force on the potting compound. The potting compound has a high bulk modulus. Thus, in response to the applied force the potting compound applies a reaction force on the fiber optic coil. The reaction force applies a pressure, stress, and/or strain on the fiber optic coil. As one shortcoming, the applied pressure, stress, and/or strain on the fiber optic coil may promote a decrease in performance of the fiber optic coil. For example, the rotation measurement of the fiber optic coil for the fiber optic gyroscope may experience a greater bias error due to the applied pressure, stress, and/or strain.  
           [0006]    Thus, a need exists for a polymeric material that absorbs a larger portion of an applied force from a sensor fiber. A further need exists for a polymeric material that promotes a decrease in reaction pressure, stress, and/or strain applied to a sensor fiber.  
         SUMMARY  
         [0007]    The invention in one embodiment encompasses a method. A plurality of voids are introduced into a polymeric material. One or more stress sensitive components in abutment with a portion of the polymeric material are buffered from one or more stresses through employment of the portion of the polymeric material that comprises one or more voids of the plurality of voids. A movement of the portion of the polymeric material is accommodated through compression of one or more of the one or more voids.  
           [0008]    The invention in another embodiment encompasses a method. A plurality of voids are introduced into a potting compound. A fiber optic sensing coil of a fiber optic gyroscope is encapsulated with a portion of the potting compound that comprises one or more voids of the plurality of voids. A decrease in a bias error of the fiber optic sensing coil is promoted though accommodation of an expansion of the fiber optic sensing coil by a compression of one or more of the one or more voids.  
           [0009]    The invention in yet another embodiment encompasses a method. A plurality of voids are introduced into a polymeric material. One or more stress sensitive components are coated with a portion of the polymeric material that comprises one or more of the plurality of voids. An expansion of the one or more stress sensitive components is accommodated through compression of one or more of the one or more voids. 
       
    
    
     DESCRIPTION OF THE DRAWINGS  
       [0010]    Features of exemplary implementations of the invention will become apparent from the description, the claims, and the accompanying drawings in which:  
         [0011]    [0011]FIG. 1 is a sectional representation of one exemplary implementation of an apparatus that comprises one or more spools and one or more sensor fiber coils.  
         [0012]    [0012]FIG. 2 is a sectional representation of the sensor fiber coil directed along line  2 - 2  of FIG. 1. 
     
    
     DETAILED DESCRIPTION  
       [0013]    Turning to FIG. 1, an apparatus  100  in one example comprises a plurality of components such as hardware components. A number of such components can be combined or divided in one example of the apparatus  100 . The apparatus  100  in one example comprises any (e.g., horizontal, oblique, or vertical) orientation, with the description and figures herein illustrating one exemplary orientation of the apparatus  100 , for explanatory purposes.  
         [0014]    The apparatus  100  in one example comprises one or more spools  102  and one or more sensor fiber coils  104 . For example, the apparatus  100  comprises a sensing component of a fiber optic gyroscope. The fiber optic gyroscope in one example comprises a light source, a beam splitter, the sensor fiber coil  104 , and processing electronics. Light from the light source is split by the beam splitter into two counter-propagating waves traveling through the sensor fiber coil  104 . The processing electronics measure a phase relationship between the two counter-propagating beams of light that emerge from opposite ends of the sensor fiber coil  104 . The difference between the phase shifts experienced by the two beams is proportional to the rate of rotation of the fiber optic gyroscope, due to the Sagnac effect, as will be understood by those skilled in the art.  
         [0015]    The spool  102  provides a support structure for the sensor fiber coil  104 . The spool  102  comprises a hub  106  and a flange  108 . The hub  106  in one example comprises a solid or hollow cylindrical member. The flange  108  comprises a rim at an end of the hub  106 . The diameter of the flange  108  is larger than the diameter of the hub  106 . The hub  106  and the flange  108  in one example comprise a rigid material such as steel. In a further example, the hub  106  and the flange  108  comprise a unitary construction and/or integral formation.  
         [0016]    In one example, the hub  106  and the flange  108  directly support the sensor fiber coil  104 . In another example, buffer layers  110  and  112  support the sensor fiber coil  104 . The buffer layer  110  is located on the hub  106  and the buffer layer  112  is located on the flange  108 . For example, the buffer layer  110  is located between the hub  106  and the sensor fiber coil  104  and the buffer layer  112  is located between the flange  108  and the sensor fiber coil  104 . The buffer layers  110  and  112  comprise compressible and/or resilient layers. For example, the buffer layers  110  and  112  comprise a polymeric material, such as a potting compound. The buffer layer  110  in one example comprises a coating on the hub  106 . The buffer layer  112  in one example comprises a coating on the flange  108 . The buffer layers  110  and  112  serve to promote a decrease in strain and strain gradients in the sensor fiber coil  104 .  
         [0017]    The buffer layers  110  and  112  in one example are applied to the spool  102  before the sensor fiber coil  104  is wound about the hub  106 . For example, the buffer layers  110  and  112  are applied to the spool  102  in a liquid or paste form. Next, the buffer layers  110  and  112  are preserved and/or finished. For example, the buffer layers  110  and  112  are cured. In another example, the buffer layers  110  and  112  are pre-formed and then applied to the spool  102 .  
         [0018]    Turning to FIGS. 1 and 2, the sensor fiber coil  104  in one example comprises one or more sensor fibers  202  and a polymeric material  204 . For example, the one or more sensor fibers  202  comprise one or more stress sensitive components and the polymeric material  204  buffers the stress sensitive components from one or more stresses. The sensor fiber  202  in one example comprises an optical path or waveguide for propagation of light. The sensor fiber  202  comprises a relatively high thermal expansion coefficient. During thermal increases, the sensor fiber  202  expands. During thermal decreases, the sensor fiber  202  contracts. The expansions and/or contractions exert circumferential strain on a glass core of the sensor fiber  202 .  
         [0019]    The sensor fiber  202  is wound about the hub  106 , for example, in one or more layers. Each layer in one example is located at a respective approximate distance outward from the hub  106 . For example, a first layer is wound directly on the hub  106 . In another example, the first layer is wound onto the buffer layer  110  atop the hub  106 . Subsequent layers are wound about the first layer. The sensor fiber coil  104  in one example comprises a quadrapole-winding pattern. In another example, the sensor fiber coil  104  comprises a dipole-winding pattern, as will be understood by those skilled in the art.  
         [0020]    The polymeric material  204  in one example comprises a carbon filled silicon material or a silver filled silicon material. For example, the polymeric material  204  comprises a potting compound. The polymeric material  204  serves to bond together turns of the sensor fiber coil  104 . As the sensor fiber  202  is wound about the spool  102 , the polymeric material  204  is applied to the outer surface of the sensor fiber  202 . For example, a syringe and brush applicator coats the sensor fiber  202  with the polymeric material  204 . The polymeric material  204  serves to hold the sensor fiber coil  104  as a wound unit about the spool  102 . For example, the polymeric material  204  is located between adjacent portions of the sensor fiber  202 .  
         [0021]    The polymeric material  204  comprises a solid material  206  and a plurality of voids  208 . The voids  208  fill a controlled volume percentage of the polymeric material  204 . The voids  208  in one example fill up to twenty-five percent of the total volume of the polymeric material  204 . In a further example, the voids  208  fill ten percent of the total volume of the polymeric material  204 . An introduction of the voids  208  into the polymeric material  204  reduces the density of the polymeric material  204 . The introduction of the voids  208  into the polymeric material  204  also promotes a decrease in a bulk modulus of the polymeric material  204 . In a further example, the introduction of the voids  208  into the polymeric material  204  promotes the decrease in the bulk modulus without substantially altering a Young&#39;s modulus of the polymeric material  204 . The bulk modulus (“B”) of the polymeric material  204  is defined by the following exemplary equation:  
           B=V ( dP/dV )  
         [0022]    Where “V” represents the volume of the polymeric material  204 .  
         [0023]    Where “P” represents the external pressure.  
         [0024]    The ratio of bulk modulus (“B”) to Young&#39;s modulus (“E”) of the polymeric material  204  is defined by the following exemplary equation:  
           B/E= 1/[3(1−2ρ)] 
         [0025]    Where “ρ” represents the Poisson&#39;s ratio.  
         [0026]    In one example, the polymeric material  204  with the voids  208  has a lower Poisson&#39;s ratio than the solid material  206  without voids. Since the voids  208  do not substantially alter the Young&#39;s modulus of the solid material  206 , then it follows that a decrease in the Poisson&#39;s ratio results in a decrease in the bulk modulus of the polymeric material  204 . Thus, in one example a decrease in the Poisson&#39;s ratio from 0.499 to 0.490 results in a decrease in the ratio of bulk modulus to Young&#39;s modulus by a factor of ten.  
         [0027]    The bulk modulus of a solid polymer in one example is substantially greater than the bulk modulus of a gas. For example, the bulk modulus of the solid polymer may be ten thousand times greater than the bulk modulus of the gas. Also, thermal pressure coefficients of the solid polymer in one example are substantially greater than the thermal pressure coefficients of the gas. For example, the thermal pressure coefficients of the solid polymer may be three thousand times greater than the thermal pressure coefficients of the gas. Thus, a controlled amount of the voids  208  in the polymeric material  204  decreases the bulk modulus and thermal pressure coefficient of the polymeric material  204 .  
         [0028]    The voids  208  in one example comprise a structure that preserves a space in the solid material  206 . In one example, the voids  208  comprise hollow elastomeric bubbles, for example, hollow elastomeric microspheres. The hollow elastomeric microspheres in one example comprise one or more of microballons and microfibers. For example, the microballons result in microbubbles in the solid material  206  and the microfibers result in microchannels in the solid material  206 . The hollow elastomeric microspheres comprise thin walls that encapsulate a gas to allow for easy compression. For example, the walls of the hollow elastomeric microspheres are strong enough to avoid breakage under pressure, but thin enough to easily compress. Once cured in the solid material  206 , the hollow elastomeric microspheres comprise substantially similar compressibility characteristics as gas bubbles.  
         [0029]    The voids  208  in one example are added to a resin of the solid material  206  in a substantially uniform distribution. For example, the hollow elastomeric microspheres are stirred into the resin of the solid material  206 . A coupling agent in one example is used to increase an adhesion between the hollow elastomeric microspheres and the solid material  206 . The coupling agent in one example comprises organofunctional reactive silane. The coupling agent also promotes a decrease in a rate of settling of the hollow elastomeric microspheres in the solid material  206 . For example, the coupling agent maintains the substantially uniform distribution of the hollow elastomeric microspheres in the solid material  206 . The solid material  206  and the voids  208  are cured to maintain the substantially uniform distribution of the voids  208  within the solid material  206 .  
         [0030]    In one example, the voids  208  comprise one or more gas (e.g., air) bubbles in the solid material  206 . For example, polymeric material  204  comprises an elastomeric foam. The polymeric material  204  is sprayed through an aerator component to introduce the voids  208  into the solid material  206 . The aerator component comprises an aerosol sprayer or an airbrush. The aerator component introduces the gas bubbles into the solid material  206 . The aerator component in one example applies the polymeric material  204  to one or more stress sensitive components to buffer the stress sensitive components from one or more stresses.  
         [0031]    An air-entrainer in one example introduces and stabilizes the voids  208  into the solid material  206 . The air-entrainer mixes a plurality of gas bubbles into the solid material  206 . The air-entrainer is selected from a plurality of air-entrainers based on a chemical formula of the polymeric material  204 . In one example, the air-entrainer comprises a surfactant with a hydrophobic end and a hydrophilic end. The hydrophilic end is attracted to a base material and the hydrophobic end acts to isolate and stabilize the air bubbles caused by mixing. In another example, the air-entrainer comprises a first end that is attracted to the polymeric material  204  and a second end that is repulsed by the polymeric material  204 . Where the polymeric material  204  comprises a silicone, the air-entrainer in one example comprises a self-assembling monolayer material. The self-assembling monolayer material in one example comprises octadecyltrichlorosilane. Octadecyltrichlorosilane comprises one end that is attracted to silicon and one end that is repulsed by silicon. Thus, octadecyltrichlorosilane promotes a stabilization of the gas bubbles in the solid material  206 .  
         [0032]    A blowing agent in one example introduces the voids  208  into the solid material  206 . For example, the blowing agent comprises a chemical blowing agent. The chemical blowing agent is heated to an elevated temperature for decomposition. Upon decomposition, the chemical blowing agent releases gas bubbles that are trapped within the solid material  206  to form the voids  208 . The blowing agent in one example comprises azodicarbonamide or p-toluene tulfonyl hydrazide. The blowing agent is selected based on a preferred decomposition temperature. For example, azodicarbonamide decomposes around two hundred and ten degrees Celsius and p-toluene tulfonyl hydrazide decomposes around one hundred and twenty degrees Celsius.  
         [0033]    A diffuser in one example introduces the voids  208  into the solid material  206 . The diffuser comprises a diffuser disc with small holes capable of releasing gas bubbles. Before the polymeric material  204  is cured, the diffuser disc is placed at a bottom of a container that holds the solid material  206 . The diffuser disc is activated and begins to release the gas bubbles into the solid material  206  near the bottom of the container. The diffuser disc is raised through the solid material  206  at a steady rate to release the gas bubbles into the solid material  206  in an even distribution up to the top of the container. Then, the diffuser disc is removed from the container and the polymeric material  204  is cured to preserve the gas bubbles.  
         [0034]    A plurality of dissolvable structures in one example introduce the voids  208  into the solid material  206 . For example, the dissolvable structures comprise dissolvable microstructures. The dissolvable microstructures are mixed into the solid material  206 . The dissolvable microstructures are heated to an activation temperature which dissolves the dissolvable microstructures. Once the dissolvable microstructures dissipate, the voids  208  remain in the solid material  206 .  
         [0035]    An applicator brush that comprises a plurality of hollow bristles in one example introduces the voids  208  into the solid material  206 . The applicator brush is connected to a gas supply. During application of the polymeric material  204  to the stress sensitive components, the applicator brush outputs gas through the hollow bristles into the solid material  206 . For example, the hollow bristles create gas bubbles in the solid material  206 .  
         [0036]    A pressure-sensitive foam tape in one example introduces the voids  208  into a potting compound that encapsulates the stress sensitive components. For example, the pressure-sensitive foam tape is formed from the polymeric material  204  with the voids  208 . The pressure-sensitive foam tape is applied to the stress sensitive components. The pressure-sensitive foam tape and the stress sensitive components are then encapsulated with the potting compound. The pressure-sensitive foam tape promotes a reduction in a bulk modulus of the potting compound.  
         [0037]    The voids  208  comprise a diameter that is smaller than a distance of separation between adjacent portions  210  and  212  of the sensor fiber  202 . For example, one or more of the voids  208  fit between the adjacent portions  210  and  212  of the sensor fiber  202 . The voids  208  in one example comprise the hollow elastomeric microspheres with a diameter that is small enough to fit between the adjacent portions  210  and  212  of the sensor fiber  202 . For example, in one implementation the diameter of the voids  208  of the sensor fiber coil  104  for the fiber optic gyroscope is less than fifty micrometers. In a further example, the diameter of the hollow elastomeric microspheres is twelve micrometers.  
         [0038]    In one example, the voids  208  reserve space in the solid material  206  to increase a compressibility of the polymeric material  204 . For example, the voids  208  promote an increase in an amount of an applied force the polymeric material  204  can absorb. Upon an introduction of the applied force to a portion of the polymeric material  204 , one or more of the voids  208  compress to allow the portion of the polymeric material  204  to absorb a portion of the applied force. For example, the applied force pushes a portion of the solid material  206  into the space previously reserved by the voids  208 . The voids  208  also promote a decrease of a reaction force generated by the portion of the polymeric material  204  in response to the applied force. Since the voids  208  allow the polymeric material  204  to absorb a larger portion of the applied force, the magnitude of the reaction force from the polymeric material  204  is decreased.  
         [0039]    In one example, as the temperature of the sensor fiber coil  104  increases, one or more of the sensor fiber  202  and the polymeric material  204  expand. Due to the expansion, the sensor fiber  202  exerts a thermal pressure on the polymeric material  204  and the polymeric material  204  exerts a thermal pressure on the sensor fiber  202 . The voids  208  compress to promote a decrease in the thermal pressure that the polymeric material  204  exerts on the sensor fiber  202 . For example, when the polymeric material  204  expands, the solid material  206  expands into the space previously reserved by the voids  208  rather than adding to the thermal pressure that the polymeric material  204  exerts on the sensor fiber  202 .  
         [0040]    Contact between the sensor fiber  202  and the polymeric material  204  in one example introduces a stress, strain, stress gradient, and/or strain gradient in the sensor fiber  202 . The stress and/or strain may degrade the performance of the sensor fiber  202 . For example, the stress and/or strain may reduce the polarization maintaining properties of the sensor fiber  202 . The voids  208  compress to promote a decrease in the magnitude of any stress, strain, stress gradient, and/or strain gradient applied by the polymeric material  204  to the sensor fiber  202 .  
         [0041]    In one example, the polymeric material  204  encapsulates the sensor fiber  202  for the fiber optic gyroscope. The compression of the voids  208  promotes a decrease in measurement bias errors of the fiber optic gyroscope. For example, the decrease in the magnitude of the stress, strain, stress gradient, and/or strain gradient applied by the polymeric material  204  to the sensor fiber  202  promotes an increase in accuracy and a decrease in the rotation sensing bias error of the fiber optic gyroscope. The compression of the voids  208  promotes a decrease in a Shupe coefficient of the fiber optic gyroscope.  
         [0042]    In another example, the polymeric material  204  encapsulates one or more electrical components, for example, electronic and optical sensor equipment. A power supply in one example employs the polymeric material  204  as a potting compound for the electrical components. The voids  208  of the polymeric material  204  in one example compress under pressure to avoid structural failure to one of the electrical components such as a glass-bodied diode. The reduced bulk modulus and increased compressibility of the polymeric material  204  due to the voids  208  are advantages for electrical component encapsulation. For example, the reduced bulk modulus and increased compressibility of the polymeric material  204  promotes a decrease in likelihood that contact with the polymeric material  204  will damage the electrical components. In one example, the polymeric material  204  encapsulates an optical coupler. The reduced bulk modulus of the polymeric material  204  allows for complete coverage of the optical coupler with the polymeric material  204 . An acoustic sensor in one example employs the polymeric material  204  to buffer an optical fiber from a sensing component. For example, the reduced bulk modulus of the polymeric material  204  promotes a decrease in an amount of acoustic noise that reaches the optical fiber.  
         [0043]    In yet another example, the polymeric material  204  with the plurality of voids  208  is used to create the buffer layers  110  and  112 . For example, the buffer layers  110  and  112  comprise the plurality of voids  208 . As a further example, the polymeric material  204  of the sensor fiber coil  104  and the buffer layers  110  and  112  are made from substantially the same material. Thus, the reduced bulk modulus and increased compressibility characteristics of the polymeric material  204 , described herein, are substantially similar to the bulk modulus and compressibility characteristics of the buffer layers  110  and  112  that comprise the plurality of voids  208 . The plurality of voids  208  in the buffer layers  110  and  112  promote a decrease in contact forces between the spool  102  and the sensor fiber coil  104 .  
         [0044]    The steps or operations described herein are just exemplary. There may be many variations to these steps or operations without departing from the spirit of the invention. For instance, the steps may be performed in a differing order, or steps may be added, deleted, or modified.  
         [0045]    Although exemplary implementations of the invention have been depicted and described in detail herein, it will be apparent to those skilled in the relevant art that various modifications, additions, substitutions, and the like can be made without departing from the spirit of the invention and these are therefore considered to be within the scope of the invention as defined in the following claims.