Patent Translate Powered by EPO and Google Notice This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate, complete, reliable or fit for specific purposes. Critical decisions, such as commercially relevant or financial decisions, should not be based on machine-translation output. DESCRIPTION JPS5698622 Ming, letter 10: Title of invention Optical fiber acoustic pressure sensor- 8. Detailed Description of the Invention i State of the State of the State--Mu-Replacement-Study 4 Schools--Ichi Yu-Yu "→ -1 1 The present invention relates to a device which greatly increases the acoustic sensitivity per unit length of the optical fiber acoustic sensor Describe. Several types of optical fiber acoustic sensors are described in the following document, using pressure induced changes in the optical phase of the coherent light transmitted through the optical fiber There is. An example of such a reference is as follows, as is U.S. Pat. Jay A. PCaro et al. 1 Fiber optic acoustic sensor-Applied optics 1.6.1761. (1977) Identical 1 optical fiber to underwater 'turtle story' Journal of a Stake Society America (J, Acoust, Soc, Am,), 62, A5, 1802-4 +, Nov, 1977 'same as above Measurement of the sensitivity of optical fibers for optical fiber applied optics 1.8, 988 (1979) The acoustic sensitivity of such a device is proportional to the optical phase change Δφ per unit pressure change ΔP of the unit fiber length Lfi. . For naked light 7 Ibar EndPage: 1 This amount is given by Here, light propagation constant in β-fibers E = Young elastic modulus of fiber material μ = Poisson's ratio of fiber material n = refractive index of fiber material pn + pu = coefficient of relationship between strain of fiber material and light For most of glass If the values of E and μ + pn + pu are greatly changed over a certain range, it does not occur. The measured value of Δφ / Δp is about 2.6 × 101. It is / λrad / Pa. In this type of optical fiber, it is shown that it can be used for acoustic detection such as underwater phone application as underwater acoustic application. However, the sensitivity is practically limited. In the above-cited eighth article by Pukao et al., When the protective plastic envelope remains on the fiber, its coupling coefficient is one digit thicker than the uncoated fiber. This document brings to mind the following: The plastic jacket is higher than the fiber (... Because it has Poisson's ratio and 05-05-2019 1 compressibility, it extends more than a bare glass fiber and results in tensioning the glass fiber and thereby increased responsiveness. In the present invention, an improved fiber optic acoustic sensor is described in which the coil of the optical fiber is embedded in a mass of material having a lower modulus than the material of the fiber. This structure is very sensitive to the acoustic (i.e. pressure) of such a fiber optic ring sensor. The basic principle of this improved structure is as follows. The harder material, in this case the fiber, carries a large part of the Ls force being applied by pressure. And it is stressed much higher than bare fibers that are actually under the same pressure. This ↓ 15, force increase causes higher strain to increase once more than that of bare fibers and more than that of fibers coated easily with-. The sensitivity of the fiber optic acoustic sensor described herein is due to the pressure induced optical phase shift through the fiber. This phase shift has two main causes. Partly pressure induced changes in fiber length and changes in refractive index within the fiber. The change in length is explained by a simple elastic theory. The change in refractive index is explained by the effect of the distortion-light relationship. And in isotropic materials such as glass-even depending on both the axial and transverse strain components of the fiber. In a cocoon fiber exposed to hydrostatic pressure, stress and cocoon are equal in all directions. The effect on the dephasing of the change in length and the change in refractive index is opposite in sign and equal in magnitude (the net effect is smaller than any of the above two terms since it was found to be equal) . If buried in a mass of material with lower modulus of elasticity than the fiber coil 応 力, the stress and strain in the fiber will vary significantly. The radial stress is somewhat higher than that of the bare fiber, but not larger than that of the axial one. The most important thing is that the axial stress can be greatly increased in the buried fiber. This means that in any composite structure the force element (fiber) bears more force relative to the total load, and, and then, the entire axial cart will layer pressure. This is because the cross-sectional area of the fiber is multiplied. Therefore, much of the pressure applied to the axial force direction of the buried fiber structure is transmitted from the mass of material in front of the fiber. So the axial ratio, changes in force and length are much thicker than bare fibers. This increased axial stress in the buried fiber and the corresponding increase in length change obviously increase the pressure induced optical phase shift and the sound pressure sensitivity. However, there is a second aspect of the sensitivity EndPage: 2 increase in the noon buried fiber. Since the lateral strain in the buried fiber does not increase significantly, the dephasing due to refractive index change does not increase as quickly as due to the change in length. The net optical phase shift is the difference between both the change in length and the change in refractive index. [In buried fibers this difference may even increase more quickly than by changes in length alone. The improvement in sensitivity over uncoated fibers depends on the ratio of the modulus of elasticity of the fiber to the modulus of the embedded material and the ratio of the thickness to the radius of the fiber. Once the ratio of the 24th eye is high enough, it is almost 05-05-2019 2 impossible to obtain the lessons of the sensitivity, but if these ratios are large, the improvement of the acoustic sensitivity is as thick as the dog temperature. The sensitivity improvement also depends on the value of the Poisson's ratio of the fiber and the buried material. Referring now to FIG. 2, at 10, it is buried in a solid mass 12 made of a material having a lower modulus of elasticity than the fiber material, eg light such as molten hydrofluoric acid '7 Ivar) The coil 11 of the r-j bar is shown. The low modulus material may be, for example, a thermoset or heat fusible material such as bite rubber. Plans have been made that the greatest increase in acoustic sensitivity is obtained by the use of a buried material with low modulus and low Poisson's ratio. This material should also be able to be molded around the fiber. Materials with low modulus also tend to have high Poisson's ratio values, but many types of soft plastic can increase (or increase) the sensitivity. Several boron rubber formulations and one polyurethane formulation are used to achieve a 100-fold or greater sensitivity increase over bare fiber optics. The following is a trace of some of the ingredients used. General Elect 1 Luk company Ha rubber) LTV 615) LTV 602, Ferris di-through 1 mold compound (Fenis 5ee-ThruMo1dCompound) manufactured by JE Erler エ イ ト Eight, and polyurethane PFL-1574 manufactured by Product Research & Chemical Co. In some applications, fiber optic acoustic sensors must work under high static pressure. Under these conditions, it may not be desirable to select the two softest investment materials for the greatest increase in acoustic sensitivity. Soft materials with low modulus will experience large static strain due to high static pressure. Thus, the fibers embedded in this material will also be very distorted. Fiber breakage can be experienced under such conditions. Moreover, the elastic properties of the investment material alter the function of the static pressure, such as reducing the acoustic sensitivity of the sensor, making the response non-proportional, and under large strains. In the case of such high static pressure, a compromise can be made to choose a material waiting for a higher modulus as the implantation material, 1 and its properties are not so affected by static pressure. The acoustic sensitivity will be less if softer investment material is supported, but the fiber will be less likely to break and the response of the acoustic sensor will depend on static pressure (01 In the case of, etc., many more tl II like eg epoxy, polystyrene, polytetrafluoroethylene! A heat-resistant material 41 or a heat-resistant% 41 is suitable. Referring now to FIG. 3, at 20 a cylinder 22 with a fiber optic coil 21 and a hollow core 28 is shown which has also been filled in a cylinder made of a material having a lower modulus than the fiber material at 20. It is done. That is, the fiber can be buried in the lower modulus hollow structure. And the shape of the structure is designed to increase the stress D in some direction of the structure when exposed to isotropic pressure. For example, when applied to an external pressure Pb'-thin-walled hollow sphere, the tangential stress of the spherical shell is somewhat thicker than P. Similarly, when the pressure P is applied to the outside of a thin-walled hollow cylinder closed at both ends by an end plate, the axial stress of the wall can be greater than P. (10) EndPage: axial stress and optical phase induced by pressure in 3 fibers in a structure where the fibers are embedded so that they run predominantly in the direction of maximum stress The slippage can be increased somewhat more than if the 05-05-2019 3 fibers are embedded in a uniform mass of the same elastic material. In hollow structures made of such lower modulus materials, one example is a relatively thin-walled hollow sphere of lower modulus material in which the fiber is embedded in the material It can mean circumferentially wound ones. The second example is a relatively thin-walled hollow cylinder made of an elastic material closed at both ends by end plates, which are predominantly vertically wound, embedded in the fiber or the material. It can. And the eighth example is a similar cylinder, but it could mean that the fibers are wound circumferentially (r). . 4. Brief Description of the Drawings FIG. 1 is a view showing an embodiment of a conventional optical fiber acoustic pressure sensor. FIG. 2 and FIG. 8 are views of one non-inventive embodiment. 0υ1.0.20 ····························································································· Block material Patent applicants Honeywell Inc. Attorney's attorney Eiji Matsushita 02) EndPage: 4 05-05-2019 4
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