A test apparatus and method for magnetic shielding characterization of nickel alloys with fiber optic sensor

Abstract

The present invention relates to a test apparatus and method for shielding characterization of nickel alloys with magnetic shielding properties, which enables magnetic field permeability efficiency characterization to be performed without damaging the material using an interferometric system of fiber optic sensors under high magnetic field.

Description

[0001] A test apparatus and method for magnetic shielding characterization of nickel alloys with fiber optic sensor

[0002] TECHNICAL FIELD

[0003] The present invention relates to a test apparatus and method for shielding characterization of nickel alloys with magnetic shielding properties, which enables magnetic field permeability efficiency characterization to be performed without damaging the material using an interferometric system of fiber optic sensors under high magnetic field.

[0004] STATE OF THE ART

[0005] Since the 1980s, fiber optic gyroscopes have been widely used as inertial sensors in military and commercial navigation applications for high-precision angular velocity measurement. Fiber optic gyroscopes are based on the principle of phase shift in the interference pattern of light beams propagating in opposite directions in the fiber medium. The magnitude of this phase shift varies in proportion to the magnitude of the angular velocity under the Sagnac Effect. In fiber optic gyroscopes, the magnetic field applied from outside affects the polarization of the light propagating in the fiber. This effect creates bias error in the gyroscope outputs. The effect of this bias error, which cannot be calibrated, on the gyroscope is reduced by the magnetic shielding method.

[0006] In mu-metal materials, the p value gives information about the magnetization of a material. Mu-metals belong to the soft ferromagnetic material group. In current technology, there are a number of measurement methods to measure the magnetic permeability value of materials. However, in the current technique, irreversible damage occurs to the material in order to find the p value.

[0007] The propagation of electromagnetic waves through fiber coils exhibits an inherent sensitivity to DC magnetic fields, highlighting the fundamental interaction between the optical medium and external magnetic influences [1]. The sensitivity to external DC magnetic fields is a result of the Faraday effect, which is primarily governed by first-order magneto-optic interactions. Under constant magnetic fields such as strong magnets as well as the Earth's magnetic field at ~0.5 Gauss levels, fiber optic gyroscope sensors are expected to have a magnetic field sensitivity of approximately <0.1 degrees / Hour / Gauss for tactical grade and <0.01 degrees / Hour / Gauss for navigation grade. For this purpose, the materials with high magnetic permeability are employed in gyroscope designs to reduce magnetic flux density. Fiber optic gyroscope coils are encapsulated in high magnetic permeability materials to reduce the magnetic flux density on the winding, serving as magnetic shielding for the winding.

[0008] Magnetic shielding efficiency (SE) is a parameter used to determine shielding performance. Bo, seen in Equation 1 below, is the intensity of the magnetic field when there is no magnetic shield; Bi is the intensity of the magnetic field when there is a magnetic shield at the same point [2], Magnetic shield efficiency also varies with the physical properties of the shield material. For example, if the shield material is to be chosen as a cylindrical structure, the inner and outer radii of the cylinder have an effect on the magnetic shield efficiency [2],

[0009] In the state of the art, measuring devices such as PPMS (Physical Property Measurement System) [3], SQUID (Superconducting Quantum Interference Device Magnetometer) [4] are used to understand the magnetic efficiency of a material. In order to measure magnetic efficiency in these devices, quantities such as magnetization (M), magnetic permeability (p=B / H)) and magnetic susceptibility (X=M / H) are calculated. As a result of these calculations, M-H and B-H curves are analyzed using a small amount of either powder or bulk sample. Alloys with high nickel content, such as Mu-metals, cause magnetic field curves to flow over them due to their high magnetic permeability. When the applied magnetic field is removed, these materials return to their initial states. For this reason, Mu-metal alloys are shaped and used in shielding applications under high magnetic field effects. In alloys with low magnetic permeability, the p (mu) value can be considered constant. This value is directly proportional to B and H values. In materials intended to be used in magnetic shielding applications, the magnetic flux value should be as high as 1 as possible. However, magnetic permeability measurements can generally be made by damaging the material or by taking a section from the part.

[0010] In the current literature, regarding magnetic permeability measurements, E. de Toldi's study titled "Understanding and Control of the Magnetic Sensitivity of a Fiber- Optic Gyroscope" presents an analysis. In this work, magnetic permeability efficiency experiments were conducted using a 250 - meter, 4 - layer fiber optic winding and its twisted counterpart. The results of these experiments were compared with theoretical models, and the impact of the fiber's twist angles within the fiber optic winding layers on magnetic permeability was calculated. In the study, magnetic fields were generated along three axes using magnetic coils. The fiber optic coil is rotated and placed between these coils. The magnetic permeability of the magnetic shield placed on the fiber optic coil was measured under a certain magnetic field. In this study, the use of fiber optic coils as magnetic field sensors without rotation is excluded from discussion. Furthermore, the method appears to have limited adaptability to fiber optic gyroscopes with varying sensitivities.

[0011] In the study titled 'Design of high shielding effectiveness magnetic shield for fiber optic gyroscope' published by X. Li, the most widely used technique to prevent fiber optic gyroscopes from being affected by environmental factors, the use of magnetic shield on the coil and the method of minimizing the errors of gyroscopes under magnetic field are explained with FEM solutions. In this study, it is mentioned that the effects of the magnetic shielding material are directly related to the magnetic permeability, thickness and structure of the shielding material. Furthermore, rather than the performance measurements of magnetic shields, the magnetic permeability of magnetic shields and their effects on the gyroscope are discussed through only axial tests. FEM simulations on magnetization effects and the reasons for using the FEM method in this application are explained. In line with the simulation solutions, a magnetic shield design suitable for the dimensions of the gyroscope was proposed and improvements in the gyroscope performance were tested under a certain magnetic field. The test method in this study involves measuring the magnetic shield efficiency in the axial (Z direction) and radial (X and Y direction) axes by placing only a magnetic field measuring sensor. However, it is mentioned here that the measurements of the design-optimized magnetic shields are conducted only using a magnetic sensor, and that a fiber optic gyroscope with navigation-grade sensitivity is not used as a comparison of the measurements. Characterization of materials; material thickness, magnetic permeability, structure, changes in alloy content, defects arising from the production method of the material, etc. cannot be easily distinguished.

[0012] As a result of a research conducted in the state of the art, the application numbered CN106032992A has been found. In said application, the measurement method and device of the magnetic field of the fiber optic gyroscope are mentioned. In this measurement method, measurement is carried out by taking the magnetic field values on the gyroscope in the X axis, Y axis and Z axis. A measuring device that will measure shielding depending on temperature under a certain magnetic field has been studied. For this purpose, magnetic field measurements were made on a magnetic shielded fiber optic gyroscope under temperature control. In the study, the temperature was controlled from -40cC to +70'C. Mag netic permeability measurements were taken with the gyroscope output in this temperature range, with and without a magnetic field. In this case, the gyroscope was exposed to a magnetic field between 0 and 10 Gauss. It is known that the magnetic permeability of Mumetal materials changes slightly with temperature. Likewise, it is known that not only magnetic field errors but also scale factor errors are obtained in gyroscopes under changing temperatures. However, the use of a magnetic shield without temperaturedependent magnetization change is not mentioned here.

[0013] As a result, improvements are being made in systems and methods for magnetic shielding characterization of nickel alloys with fiber optic sensors, so new structures are needed that will eliminate the disadvantages mentioned above and bring solutions to existing systems.

[0014] OBJECT OF THE INVENTION

[0015] The present invention relates to a test apparatus and method for magnetic shielding characterization of nickel alloys with a fiber optic sensor, which meets the above- mentioned requirements, eliminates all disadvantages and brings additional advantages.

[0016] The focus of the present invention is to provide a test apparatus and method for shielding characterization of nickel alloys with magnetic shielding properties, which enables magnetic field permeability efficiency characterization to be performed without damaging the material using an interferometric system of fiber optic sensors under high magnetic field.

[0017] The main object of the present invention is to use a fiber optic gyroscope as a magnetic field sensor and to enable the magnetic flux efficiency to be seen proportionally without damaging the mu-metal material.

[0018] Another object of the present invention is to calculate the magnetic permeability efficiency of mu-metal materials by using a 0.01 h r high precision (navigation grade) fiber optic gyroscope sensor with 1 kilometer PM (polarization conservation) optical fiber coil by controlled experiment method.

[0019] An additional object of the present invention is to enable faster characterization of each magnetic material by using a fiber optic gyroscope with higher sensitivity.

[0020] A subsequent object of the present invention is to provide a more reliable and durable test environment by using commercially available coils.

[0021] The structural and characteristic features of the present invention will be understood clearly by the following drawings and the detailed description made with reference to these drawings. Therefore, the evaluation shall be made by taking these figures and the detailed description into consideration.

[0022] BRIEF DESCRIPTION OF FIGURES

[0023] In order to understand the advantages of the present invention with its structure and additional elements, it shall be evaluated with the following defined figures. Figure 1 is a representative view of a test apparatus for the magnetic shielding characterization of nickel alloys with the fiber optic sensor of the invention.

[0024] Figure 2 is a test apparatus for the magnetic shielding characterization of nickel alloys with the fiber optic sensor of the invention and the graphical view of the magnetic shield performance test results in the method.

[0025] REFERENCE NUMBERS

[0026] 1. Magnetic shielding elements

[0027] 2. Fiber coil

[0028] 3. Magnetic field coils

[0029] 4. Optical table

[0030] 5. Photodiode (PD)

[0031] 6. Transimpedance amplifier (TIA)

[0032] 7. Controller

[0033] 8. Analog to Digital Converter (ADC)

[0034] 9. Computer

[0035] 10. Power supply

[0036] 11. Controller unit

[0037] DETAILED DESCRIPTION OF THE INVENTION

[0038] In this detailed description, a test apparatus for magnetic shielding characterization of nickel alloys with the inventive fiber optic sensor and preferred embodiments of the method are described for the purpose of a better understanding of the subject matter only and in a non-limiting manner.

[0039] The invention, whose test apparatus is given in Figure 1 , is a test apparatus and method for shielding characterization of nickel alloys with magnetic shielding properties. This enables magnetic field permeability efficiency characterization to be performed without damaging the material using an interferometric system consisting of fiber optic sensors under high magnetic field. The test apparatus seen in Figure 1 comprises the following:

[0040] • Magnetic field coils (3) placed to create a magnetic field, • A power source (10) that provides power to the magnetic field coils (3),

[0041] • A controller unit (11) that controls the changing potential difference in order to create a constant magnetic field in the magnetic field coils (3),

[0042] • A fiber optic coil (2) placed on the Z axis,

[0043] • Magnetic shield elements (1) covering the fiber coil (2) to prevent shifts that may occur under the magnetic field formed in the magnetic field coils (3),

[0044] • An optical tray (4) that holds the optical elements together

[0045] • A current-conducting photodiode (5),

[0046] • A transimpedance amplifier (6), which converts the current transmitted from the photodiode (4) into voltage,

[0047] • A controller (7) that controls the amount of current passing through the mechanism,

[0048] • An ADC (8) that converts the analogue voltage signal coming through the transimpedance amplifier (6) into a digital signal,

[0049] • A gyroscope sensor that receives rotation information,

[0050] • A computer (9) that controls the magnetic coils and the outgoing / incoming signal from the fiber optic gyroscope.

[0051] In a preferred embodiment of the present invention, 1100 metres of fiber winding (2) wound with a 16 - layer winding method is used. Thus, by using a fiber optic coil with higher sensitivity, the characterization of each magnetic material can be done more quickly. In addition, a more reliable and durable test apparatus can be established by using commercially available coils. In this way, this proposed test apparatus and method is a preferable method as it is both easier and adaptable to fiber optic gyroscopes with different sensitivities. Here, magnetic field coils (3) are placed in the test apparatus to apply a ±6.5 Gauss magnetic field in the X-Y and Z axes. The power to the magnetic field coils (3) is provided by the power supply (10). The controller unit (11 ) is the circuit element in which the changing potential difference is controlled in order to create a constant magnetic field due to a constant current in the magnetic field coils (3). When current is applied to the magnetic field coils (3) in the experimental setup, shifts occur in the interference pattern of the fiber coil (2) due to the Sagnac Effect, resulting the angular velocity in degrees per hour. Meaning, shifts in this interference pattern cause location information to change. Magnetic shield elements (1) are placed on the fiber coil (2) in order to prevent these shifts in the Sagnac interference pattern under the magnetic field. The control of the magnetic coils and the outgoing / incoming signal from the fiber optic sensor are controlled and processed by a computer (9).

[0052] In an example application of the invention, the experiment performed with the test apparatus set up in Figure 1 is explained below: Here, first the magnetic shield elements (1) are placed on the fiber coil (2). In the magnetic field coils (3), a magnetic field of 6.5 Gauss magnitude is created by passing a current of 6500 mA under a voltage of approximately 37.8 V through the power supply (10). The magnetic field formed in the magnetic field coils (3) is kept constant during the entire experiment. Magnetic field coils (3) comprise two serially connected magnetic rings and the resistance occurring during the experiment is around 5.8 Q. By passing current through the magnetic field coils (3), a magnetic field is created in the (-X), (+X), (-Y), (+Y), (-Z), (+Z) axes, respectively. During the formation of a homogeneous magnetic field by passing current through the magnetic field coils (3), overheating of the magnetic field coils (3) was tried to be controlled not by the intensity of the current but by its duration. When the experiment starts, after 5 minutes of static measurement (no magnetic field), a magnetic field is created by passing current through the -X axis for 5 minutes and rotation information is obtained by the fiber optical gyroscope simultaneously. In order to prevent heating in the magnetic field coils (3), the stationary test is continued for 5 minutes, then the current direction is reversed and spent 5 minutes in the +X direction and a magnetic field is created again, and rotation information is obtained with the gyroscope sensor. After the magnetic field in the -X and +X directions is applied and finished, the stationary test is taken again for 5 minutes to prevent heating. (5 minutes static test -> 5 minutes rotation on (-) axis -> 5 minutes static test -> 5 minutes rotation on (+) axis -> 5 minutes static test). The magnetic performance measurement for the X axis is carried out in the same order for the other axes. When applying magnetic fields to both the stationary test and the (-X), (+X), (-Y), (+Y), (+Y), (-Z), (+Z) axes, it was not a problem if the duration of the experiment was 5 minutes or longer, but when moving from one axis to the other axis (when there was no static test between the two axes), a magnetic field of the desired magnitude could not be generated. In addition, there is fluctuation in the magnitude of the magnetic field. For this reason, various durations were tried, and it was decided that the optimum duration was 5 minutes to prevent heating in the coils and to create a homogeneous constant magnetic field.

[0053] In basic terms, the permeability of a magnetic material can be calculated by using the Hall effect sensor and the permeability efficiency of the material based on the size of the magnetic field. In this study, the rotation information on the fiber optic gyroscope is recorded under an external magnetic field and the shift in rotation over time is observed. This amount of shift is considered as the magnetic shielding efficiency of the magnetic material. For this reason, in the experiment, magnetic shielding efficiency was analysed by comparing the rotation information against time when there was a magnetic shield and when there was no magnetic shield. While the application of a magnetic field affects the fiber optic gyroscope in the most general sense from both radial axes (X, Y) and axial axis (Z), this effect was observed mostly in the Z axis in the experimental apparatus. Figure 2 shows the graph of magnetic shield performance test results. Without magnetic shielding, the fiber optic gyroscope is clearly exposed to the magnetic field in both the radial axis and the axial axis. Since the light traveling through the fiber is directly exposed to the magnetic field, its polarization changes and deviates from its current position. When there is a magnetic shield, due to the magnetic properties of the shield material, it reduces this external effect by flowing the externally applied magnetic field. Thus, it gives values close to the real rotation information. In this experiment described specifically for the invention, this value was observed to be approximately 9 degrees / hour. Magnetic shield sensitivity is directly proportional to the amount of shift in the fiber optic gyroscope per total magnetic field applied. This information is obtained from the graph in Figure 2. Looking at the -Z and +Z regions in the absence of a magnetic shield, when a magnetic field is applied from outside, the rotation is around 8.3 degrees / hour for the -Z region, while for the +Z region this value is around 9.8 degrees / hour. The average for these two regions is calculated and divided by the total magnetic field. A similar process is calculated for the case of a magnetic shield. The ratio between these two calculations provides a comparable magnetic permeability measurement. radial -or axia sensitivity) Magnetic sensitivity = —;- : — — [degr ee / hour / Gauss]

[0054] Total magnetic fie id Based on the effect of the magnetic field on the Z axis, the magnetic sensitivity was calculated as 0.11 degrees / hour / Gauss without magnetic shielding material, while the rotation was calculated as 0.0059 degrees / hour / Gauss with a reduction of 18 times in the presence of a magnetic shield. In case of a magnetic shield, an approximately 18 times improvement in magnetic permeability efficiency is observed. This characterized magnetic shield has a magnetic field sensitivity of <0.01 degrees / Hour / Gauss at the navigation grade. With the method presented in this study, magnetic permeability can be measured directly, and whether different mu-metal materials provide tactical or navigation grade sensitivity can be characterized quickly and without harm to the material.

[0055] In our invention, temperature-related scale factor errors are eliminated by controlled calibrations. Rotation errors under the magnetic field are reduced by magnetic shielding. In the invention, characterization measurements of magnetic shields are made under controlled room temperature. For this reason, our measurements are unaffected by the temperature effects and temperature-related magnetization changes, unlike the mentioned studies.

[0056] In our invention, since the measurements of magnetic shields are made not with a magnetic sensor but with a fiber optic gyroscope with navigation grade sensitivity, the characterization of materials rather than the design of magnetic shields; material thickness, magnetic permeability, structure, changes in alloy content, defects arising from the production method of the material, etc. can be easily distinguished. In this way, the most sensitive magnetic shield that can be used in navigation grade fiber optic gyroscope applications can be selected.

[0057] References

[0058] [1] Chalkov V.V., Shevchenko A.N. Studying the atomic gyroscope magnetic shield residual magnetization by comparing parametric resonance signals. J. Phys. Conf. Ser. 2020; 1536:012013. Doi: 10.1088 / 1742-6596 / 1536 / 1 / 012013.

[0059] [2] Design of high shielding effectiveness magnetic shield for fiber optic gyroscope, Optic, Volume 198, December 2019, 163160. [3] Study on the Effect of Temperature on Magnetization of Permanent Magnet,

[0060] Zhang Tu, Yiliang Lv, Liang Li, 2021 IEEE 2nd China International Youth Conference on Electrical Engineering.

[0061] [4] K., Gramm, L. Lundgren and 0. Beckman (Institute of Technology, University of Uppsala, Box 534, S-751 21 Uppsala, Sweden), SQUID magnetometer for magnetization measurements, Physical Scripta (Sweden) 13, 93-95, 1916.

Claims

CLAIMS1. A test apparatus for shielding characterization of nickel alloys with magnetic shielding properties, which enables magnetic field permeability efficiency characterization without damaging the material, characterized by comprising:• Magnetic field coils (3) placed to create a magnetic field,• A power supply (10) that provides power to the magnetic field coils (3),• A controller unit (11) that controls the changing potential difference in order to create a constant magnetic field in the magnetic field coils (3),• A fiber coil (2) placed on the Z axis,• Magnetic shield elements (1) covering the fiber coil (2) to prevent shifts that may occur under the magnetic field formed in the magnetic field coils (3),• A current-conducting photodiode (5),• A transimpedance amplifier (6), which converts the current transmitted from the photodiode (4) into voltage,• A controller (7) that controls the amount of current passing through the mechanism,• An ADC (8) that converts the analogue voltage signal coming through the transimpedance amplifier (6) into a digital signal,• A gyroscope sensor that measures rotation information,• A computer (9) that controls the magnetic coils and the outgoing / incoming signal from the fiber optic gyroscope.

2. The test apparatus according to claim 1 , characterized by comprising an optical table (4) holding the optical elements together.

3. The test apparatus according to claim 1 , characterized by comprising 1100 meters of fiber coil (2) wound by 16 - layer winding method.

4. A method for shielding characterization of nickel alloys with magnetic shielding properties, which enables magnetic field permeability efficiencycharacterization without damaging the material, characterized by comprising following process steps:• Generation of a constant magnetic field in the magnetic field coils (3) in the (-X), (+X), (-Y), (+Y), (+Y), (-Z), (+Z) axes respectively by supplying current through a power supply (10),• Covering the fiber coil (2) placed on the Z axis with magnetic shielding elements (1) to prevent shifts that may occur under the magnetic field,• In order to prevent overheating in the magnetic field coils (3), controlling not by the intensity of the current supplied, but by the duration of the current supplied, and the rotation information is obtained with the gyroscope sensor when there is a magnetic field for a certain period of time and when there is no magnetic field for a certain period of time,• Recording the rotation information on the fiber optic gyroscope sensor and observing how much shift there is in rotation against time,• As a result of the observation, to calculate the magnetic efficiency, the permeability efficiency of the material is calculated depending on whether the magnetic shield elements (1) are on the fiber optic gyroscope sensor or not.

5. The method according to claim 4, characterized in that; in order to prevent heating in the magnetic field coils (3), the permeability efficiency of the material is calculated according to whether the magnetic shield elements (1) are on the fiber optic gyroscope sensor or not by taking the rotation information with the gyroscope sensor for 5 minutes without magnetic field and 5 minutes under magnetic field in all axes respectively.

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