Intensity type optical fiber vector hydrophone

Abstract

The invention discloses an intensity type optical fiber vector hydrophone, which belongs to the technical field of vector hydrophones and comprises a shell and an oscillator. The shell is of a hollow rigid structure, fluid can pass through the shell, the hollow part is in the shape of symmetrically-distributed circular truncated cones, and the upper bottom surfaces of the two circular truncated cones are communicated to form a channel; the upper side and the lower side of the channel are communicated with symmetrically-distributed bypass branch pipes, the vibrator is cylindrical, is suspended in the center of the shell, is located in the circular truncated cone channel or in the circular truncated cone channel and the bypass branch pipes, and is connected with the shell through an optical fiber patch cord, and the bypass branch pipes reserve a space for installation of the vibrator under the condition that the amplification performance of the shell is not affected; the vibrator is a strength type optical fiber accelerometer and has the advantages of small size, simple structure, convenience in manufacturing and low cost; the vector hydrophone adopts a mass point vibration velocity amplification structure to improve sensitivity, and the whole structure is compact and can be fixedly installed.

Description

Technical Field

[0001] The invention belongs to the technical field of vector hydrophones, and in particular relates to an intensity-type optical fiber vector hydrophone. Background Art

[0002] Vector hydrophones can extract vector information of the sound field in water. Compared with traditional pressure hydrophones that extract scalar information of the sound field, they are more competitive. The inertial elements for extracting vector information in vector hydrophones can be displacement type, velocity type, and acceleration type, corresponding to the extraction of vibration displacement, vibration velocity and vibration acceleration information of water particles respectively. Currently, vector hydrophones mostly adopt acceleration type, that is, accelerometers are used to extract vibration acceleration information of water particles; usually inertial sensors themselves have directionality, which makes a single vector hydrophone also have directionality, while traditional pressure hydrophones need to form an array and undergo beamforming to have directionality, which makes vector hydrophones more advantageous in applications. The research on vector hydrophones has always attracted the attention of scholars from various countries.

[0003] Fiber optic sensing technology has been around since the 1970s and remains popular in engineering applications today due to its excellent resistance to electromagnetic interference. Fiber optic accelerometers often employ an interferometric structure, where an optical fiber is wrapped around a flexible cylinder or disk. The inertial mass acts on the cylinder or disk. Deformation of the flexible element causes the fiber to stretch or compress, leading to a phase shift. For example, the fiber optic accelerometers described in the references "Common-mode noise self-suppressed 3-component fiberoptic accelerometer based on low-reflectivity Bragg gratings" and "Three-component homovibrational vector hydrophone based on fiber Bragg grating F-P interferometry" use a flexible cylinder as the sensitive element, and a flexible disk as the sensitive element. These accelerometers are difficult to fabricate. Due to the limitations of the flexible element, the vector hydrophone, when adjusted to neutral buoyancy, is typically bulky. Furthermore, the demodulation system is complex and costly.

[0004] Vector hydrophones use inertial sensors as sensitive elements to extract vector information from the underwater sound field. Due to their operating principle, coherent vector hydrophones require a flexible suspension to keep them suspended in the water. This can be very inconvenient for operators during practical application and transportation. Improper suspension can seriously affect the proper functioning of the vector hydrophone. Furthermore, cable movement along with the hydrophone can negatively impact its performance. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention provides an intensity-type optical fiber vector hydrophone, which has a particle velocity amplification function and can be fixedly installed.

[0006] The technical solutions of the present invention are as follows:

[0007] An intensity-type fiber optic vector hydrophone comprises a housing and an oscillator. The housing is a hollow, rigid structure through which fluid can pass. The hollow portion is symmetrically distributed in the shape of a truncated cone, with the upper bottom surfaces of the two cones connected to form a channel. The upper and lower sides of the channel are connected by symmetrically distributed side branch pipes. The oscillator is suspended at the center of the housing, located within the truncated cone channel or within the truncated cone channel and the side branch pipe, and is connected to the housing via an optical fiber jumper.

[0008] The length of the vibrator in the side branch pipe is less than or equal to 1 / 3 of the total length of the vibrator.

[0009] The shell has a particle vibration velocity amplification function, which can improve the sensitivity of the vector hydrophone, and the side branch pipe in the middle part of the shell does not affect the amplification of the particle vibration velocity.

[0010] The side branch pipe structure is cylindrical.

[0011] The optical fiber jumper includes an optical fiber jumper I and an optical fiber jumper II. Part of the optical fiber jumper I and part of the optical fiber jumper II are placed in a side branch tube. The optical fiber jumper I is rigidly connected to the shell and the top of the vibrator, and the optical fiber jumper II is rigidly connected to the shell and the bottom of the vibrator, and the vibrator is suspended in the center of the shell.

[0012] The optical fiber jumper I and the optical fiber jumper II are naturally extended without applying prestress, thereby reducing the impact on vector information extraction.

[0013] The shell is an epoxy resin shell.

[0014] The oscillator comprises an intensity-type optical fiber accelerometer and a rigid sealing layer, and the average density thereof is the same as that of water.

[0015] The optical fiber jumper I is rigidly connected to the rigid sealing layer at the top of the vibrator, and the optical fiber jumper II is rigidly connected to the rigid sealing layer at the bottom of the vibrator.

[0016] The intensity-type fiber optic accelerometer includes a transmitting fiber and a receiving fiber. The transmitting fiber and the fiber jumper I share a fiber, and the receiving fiber and the fiber jumper II share a fiber.

[0017] The intensity-type fiber optic accelerometer further includes a ceramic ferrule I, a ceramic ferrule II, a tail handle I, and a tail handle II. The transmitting optical fiber passes through the tail handle I and the ceramic ferrule I to form a cantilever beam structure. The receiving optical fiber passes through the tail handle II to the bottom of the ceramic ferrule II, parallel to the transmitting optical fiber. The ceramic ferrule I and the ceramic ferrule II are connected via a ceramic sleeve.

[0018] A gasket I is provided between the ceramic ferrule I and the ceramic sleeve, and a gasket II is provided between the ceramic ferrule II and the ceramic sleeve. The gasket I and the gasket II are distributed up and down, so that the transmitting optical fiber and the receiving optical fiber have an interaxial misalignment, providing an initial pre-bias for the transmitting optical fiber and the receiving optical fiber, making the sensor sensitive to acceleration and having directionality.

[0019] The rigid sealing layer is made of epoxy resin, and the overall density is adjusted by adding additives to achieve neutral buoyancy in water.

[0020] The optical fiber jumper I is rigidly connected to the tail handle I, the optical fiber jumper II is rigidly connected to the tail handle II, the tail handle I is rigidly connected to the ceramic ferrule I, the tail handle II is rigidly connected to the ceramic ferrule II, and the ceramic ferrule I, the ceramic ferrule II and the ceramic sleeve are rigidly connected.

[0021] The beneficial effects of the present invention are:

[0022] 1. The present invention develops a compact, highly sensitive, intensity-type fiber-optic vector hydrophone. The housing design with a side branch provides installation space for the oscillator without affecting the housing's amplification of the particle vibration velocity, thereby reducing the volume of the vector hydrophone.

[0023] 2. The sensitive element of the present invention is a fiber optic accelerometer. The accelerometer of the invention is composed of a transmitting optical fiber and a receiving optical fiber to form an acceleration sensitive structure, and adopts a ceramic ferrule and a ceramic sleeve for structural connection, which increases the alignment accuracy and reduces the manufacturing difficulty.

[0024] 3. Compared with the traditional optical fiber vector hydrophone, the present invention has simple demodulation and low cost, can be rigidly fixed on a carrier, and has high practical value. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a schematic diagram of the structure of an intensity-type fiber-optic vector hydrophone;

[0026] Figure 2 This is a side view of an intensity-type fiber-optic vector hydrophone;

[0027] Figure 3 This is a schematic diagram of the shell structure without a bypass pipe;

[0028] Figure 4 It is the coordinate diagram of impedance transfer coefficient;

[0029] Figure 5 is the relationship diagram between the particle vibration velocity amplification factor and the shell parameters without bypass pipes;

[0030] Figure 6 This is the relationship between the particle velocity amplification factor and the sound wave frequency of the shell without a bypass pipe;

[0031] Figure 7 is the relationship between the shell mass velocity amplification factor and frequency;

[0032] Figure 8 is a schematic diagram of the oscillator structure;

[0033] Among them, 1 is the shell, 2 is the optical fiber jumper I, 3 is the optical fiber jumper II, 4 is the vibrator, 5 is the transmitting optical fiber, 6 is the receiving optical fiber, 7 is the rigid sealing layer, 8 is the ceramic sleeve, 9 is the gasket I, 10 is the gasket II, 11 is the ceramic ferrule I, 12 is the ceramic ferrule II, 13 is the tail handle I, 14 is the tail handle II, and 15 is the side branch tube. DETAILED DESCRIPTION

[0034] In order to make the above-mentioned objects, features and advantages of the present invention more clearly understood, the present invention is further described below with reference to the accompanying drawings:

[0035] Example 1

[0036] like Figure 1-2 As shown, an intensity-type fiber-optic vector hydrophone includes an epoxy resin cylindrical structure shell 1 and an oscillator 4; the shell 1 is a hollow structure that allows fluid to pass through, and the hollow part is symmetrically distributed in the shape of a truncated cone. The upper and lower surfaces of the two truncated cones are connected to form a truncated cone channel; the upper and lower sides of the truncated cone channel are connected to symmetrically distributed side branch pipes 15. The oscillator 4 is suspended at the center of the shell 1 by an optical fiber jumper using a two-point suspension method, located in the truncated cone channel or in the truncated cone channel and the side branch pipe 15, and is connected to the shell 1 through the optical fiber jumper.

[0037] The length of the vibrator 4 placed in the side branch pipe 15 does not exceed 1 / 3 of the total length.

[0038] The branch pipe 15 is cylindrical in structure.

[0039] The oscillator is composed of an intensity-type fiber optic accelerometer and a rigid sealing layer 7 arranged outside the intensity-type fiber optic accelerometer.

[0040] The optical fiber jumper includes optical fiber jumper I 2 and optical fiber jumper II 3. Part of optical fiber jumper I 2 and part of optical fiber jumper II 3 are placed in the side branch tube 15. The optical fiber jumper I 2 is rigidly connected to the rigid sealing layer 7 at the top of the shell 1 and the vibrator 4. The optical fiber jumper II 3 is rigidly connected to the rigid sealing layer 7 at the bottom of the shell 1 and the vibrator 4. The optical fiber jumper I 2 and optical fiber jumper II 3 are naturally stretched without applying prestress, thereby reducing the impact on vector information extraction.

[0041] The housing 1 is an epoxy resin housing.

[0042] The housing 1 amplifies the particle velocity, with the best amplification occurring at the center. However, the center's limited space makes it difficult to install the sensor. Increasing the center's radius also compromises the housing's amplification. Therefore, the present invention proposes a centrally located bypass tube 15, which reserves space for the vibrator 4 and significantly reduces the hydrophone's size.

[0043] The branch pipe 15 in the middle of the shell does not affect the amplification of the particle vibration velocity, as shown below:

[0044] In the present invention, the outer shell has the function of amplifying the particle vibration velocity. When the shell does not include the branch pipe 15 structure,

[0045] like Figure 3 As shown in the figure, under the action of the plane wave acoustic field, the vibration velocity amplification factor at the center of the shell can be expressed as:

[0046]

[0047] In formula (1), ρ0 is the density of water, c0 is the speed of sound in water, k is the wave number of the sound wave, L is the length of the shell, S1 is the cross-sectional area of ​​the hollow part in the middle of the shell, b and d are the impedance transfer coefficients, j is the imaginary unit, Z0 is the radiation impedance of a circular piston with infinitesimal thickness and zero mass under an infinite baffle, and the radius of the piston is the shell radius r2. Z0 can be expressed as:

[0048]

[0049] The expressions for b and d are

[0050]

[0051] kε in formula (3) i =tan -1 (kx i ), i = 1, 2, x1 and x2 are the position coordinates of r1 and r2, and the origin of the coordinate system is the cone angle of the cone (x = 0), such as Figure 4As shown, S2 is the cross-sectional area of ​​the outer contour of the shell. Substitute (2) and (3) into (1), select parameters f = 1Hz, r2 = mr1, L = 2nr1 to perform numerical calculation on (1), and the calculation results are as follows: Figure 5 As shown in the figure, it can be seen that as the length of the shell increases, the amplification factor gradually increases. Finally, as L continues to increase, the amplification factor gradually approaches the ratio m of r2 and r1. In actual design, according to Figure 5 Select appropriate structural parameters to obtain ideal amplification gain.

[0052] The influence of different frequencies on the velocity amplification coefficient of the shell mass is analyzed. Select parameters r1 = 0.5 cm, r2 = 5 cm, L = 20 cm (m = 10, n / m = 2), and the frequency range is 1 Hz-10 kHz. The calculation results of formula (1) are as follows: Figure 6 As shown in the figure, it is shown that the shell structure has a significant amplification effect on the particle vibration velocity. At low frequencies, the amplification effect does not change with frequency, which meets the requirements of sensing and is the working frequency band of the intensity-type fiber optic vector hydrophone. The selected parameter m = 10, Figure 6 It can be seen that the amplification effect basically reaches the limit value m.

[0053] The above analysis shows that the amplification effect depends on the ratio of r2 to r1. While maintaining this ratio constant, the larger r1, the larger r2. r2 is the shell radius. An excessively large r2 results in an overly large overall structure for the vector hydrophone, limiting its application scenarios. Therefore, the bypass tube 15 is introduced.

[0054] When the branch pipe is introduced, it is equivalent to introducing a new impedance Z in the center of the shell. p ,

[0055]

[0056] In formula (4), S0 is the cross-sectional area of ​​the side branch pipe 15, l is the length of the side branch pipe 15, and the particle velocity amplification factor is corrected to

[0057]

[0058] In formula (5), a and c are impedance transfer coefficients, which can be expressed as

[0059]

[0060] Z can be expressed as

[0061]

[0062] Substituting equations (4), (6), and (7) into equation (5), and numerically calculating equation (4) under the same parameters r1 = 0.5 cm, r2 = 5 cm, and L = 20 cm, we can obtain the relationship between the particle velocity amplification factor and the frequency, as follows: Figure 7 As shown in the figure, it can be found that, under the same parameters, the presence or absence of the side branch pipe 15 has almost no effect on the amplification factor of the shell, and the introduction of the side branch pipe 15 does not reduce the amplification factor. The introduction of the side branch pipe 15 reduces the shell volume while ensuring the amplification structure of the shell, providing installation space for the vibrator.

[0063] In the present invention, the sensitive element of the vibrator 4 is an intensity-type fiber optic accelerometer, such as Figure 8 As shown, the intensity-type fiber optic accelerometer includes a transmitting optical fiber 5 and a receiving optical fiber 6. The transmitting optical fiber 5 is the same optical fiber as the fiber jumper I2, and the receiving optical fiber 6 is the same optical fiber as the fiber jumper II3. The transmitting optical fiber 5 and the receiving optical fiber 6 are obtained by removing the coating and protective layer of the fiber jumper. The transmitting optical fiber 5 passes through the tail handle I13 and the ceramic ferrule I11 to form a cantilever beam structure. The receiving optical fiber 6 passes through the tail handle II14 to the bottom of the ceramic ferrule II12, parallel to the transmitting optical fiber 5. The receiving optical fiber 5 and the transmitting optical fiber 6 are rigidly connected to the ceramic ferrule via the tail handle. The ceramic ferrule I11 and the ceramic ferrule II12 are connected via a ceramic sleeve 8. A gasket I9 is ​​provided between the ceramic ferrule I11 and the ceramic sleeve 8, and a gasket II10 is provided between the ceramic ferrule II12 and the ceramic sleeve 8. The gaskets I9 and II10 are arranged above and below each other. The rigid sealing layer 7 of the oscillator 4 is composed of epoxy resin.

[0064] The optical fiber jumper I2 is rigidly connected to the tail handle I13, the optical fiber jumper II3 is rigidly connected to the tail handle II14, the tail handle I13 is rigidly connected to the ceramic ferrule I11, the tail handle II14 is rigidly connected to the ceramic ferrule II12, and the ceramic ferrule I11 and the ceramic ferrule II12 are rigidly connected to the ceramic sleeve 8.

[0065] When the intensity-type fiber optic accelerometer is operating, light is emitted from the transmitting fiber 5 through the fiber optic patch cord I 2, received by the receiving fiber 6, and then routed through the fiber optic patch cord II 3 to the receiving device. When the intensity-type fiber optic accelerometer 4 is subjected to vibration, the transmitting fiber 5 bends, causing the energy received by the receiving fiber 6 to change, thus enabling acceleration sensing. The intensity-type fiber optic accelerometer is encapsulated in a rigid sealing layer 7 and has an adjustable overall density. It exhibits neutral buoyancy in water and vibrates with particles in the water, demonstrating excellent vector sensing performance.

[0066] The intensity-type fiber optic vector hydrophone can be rigidly fixed to a carrier when in use, without the need for a flexible suspension device. When there is a sound field around the vector hydrophone, the sound wave is amplified by the shell and acts on the vibrator 4. The fiber optic accelerometer inside the vibrator extracts the vibration acceleration information of the vibrator to measure the vibration state of the water particle. The relationship between the vibration velocity of the vibrator 4 and the vibration velocity of the water particle at the geometric center of the vibrator when there is no intensity-type fiber optic vector hydrophone is:

[0067]

[0068] Where v is the vibration velocity of the vibrator 4, v0 is the vibration velocity of the particle in the medium, A is the acoustic field vibration velocity amplification factor of the shell 1, ρ is the average density of the vibrator 4, ρ0 is the density of the water medium, and δ is the exposure ratio, that is, the ratio of the length of the vibrator 4 exposed outside the branch pipe 15 to its total length. Since the vibrator is neutrally buoyant, the average density is the same as the density of the water medium, then formula (6) is simplified to

[0069]

[0070] When the exposure ratio is 1, the vibrator 4 is not immersed in the side branch 15. At this time, the vibration velocity ratio is A, and the housing 1 brings A times the gain to the vector sensor. When the exposure ratio is not 1, the vibrator 4 is partially immersed in the side branch 15. According to formula (7), the gain will be reduced, but it can provide installation space for the vibrator and reduce the overall volume of the vector hydrophone. To ensure an 80% gain effect, the exposure ratio is at least 2 / 3, that is, the length of the vibrator 4 immersed in the side branch 15, and the maximum length is 1 / 3 of the total length.

[0071] In summary, the present invention proposes a novel structure of an intensity-type fiber-optic vector hydrophone; its characteristic is that the proposed vibrator includes an intensity-type fiber-optic accelerometer, which has the advantages of small size, simple structure, easy production and low cost; the particle velocity amplification structure is used as the shell of the vector hydrophone, which can improve the sensitivity, and the side branch pipe 15 in the shell will not affect the amplification effect of the shell on the particle velocity, and the overall structure of the vector hydrophone is compact and can be fixedly installed.

Claims

1. An intensity-type fiber optic vector hydrophone, characterized by: The invention comprises a shell (1) and an oscillator (4); the shell (1) is a hollow rigid structure, the hollow part is in the shape of symmetrically distributed truncated cones, the upper bottom surfaces of the two truncated cones are connected to form a channel; the upper and lower sides of the channel are connected to symmetrically distributed side branch pipes (15); the oscillator (4) is suspended at the center of the shell (1), located in the truncated cone channel or the truncated cone channel and the side branch pipe (15), and is connected to the shell (1) via an optical fiber jumper.

2. The intensity-type fiber optic vector hydrophone according to claim 1, characterized in that: The vibrator (4) comprises an intensity-type optical fiber accelerometer and a rigid sealing layer (7), and its average density is the same as that of water.

3. The intensity-type fiber optic vector hydrophone according to claim 1, wherein: The length of the vibrator (4) in the side branch pipe (15) is less than or equal to 1 / 3 of its total length.

4. The intensity-type fiber optic vector hydrophone according to claim 1, wherein: The side branch pipe (15) is cylindrical in structure.

5. The intensity-type fiber optic vector hydrophone according to claim 1 or 2, characterized in that: The optical fiber jumper comprises an optical fiber jumper I (2) and an optical fiber jumper II (3), part of the optical fiber jumper I (2) and part of the optical fiber jumper II (3) are placed in a side branch tube (15), the optical fiber jumper I (2) is rigidly connected to the housing (1) and the top of the vibrator (4), and the optical fiber jumper II (3) is rigidly connected to the housing (1) and the bottom of the vibrator (4), and the vibrator (4) is suspended at the center of the housing (1).

6. The intensity-type fiber optic vector hydrophone according to claim 4, characterized in that: The optical fiber jumper I (2) and the optical fiber jumper II (3) are naturally extended.

7. The intensity-type fiber optic vector hydrophone according to claim 5, characterized in that: The optical fiber jumper I (2) and the optical fiber jumper II (3) are rigidly connected to the rigid sealing layer (7).

8. The intensity-type fiber optic vector hydrophone according to claim 7, characterized in that: The intensity-type fiber optic accelerometer in the oscillator (4) includes a transmitting fiber (5) and a receiving fiber (6), wherein the transmitting fiber (5) shares a fiber with the fiber jumper I (2), and the receiving fiber (6) shares a fiber with the fiber jumper II (3).

9. The intensity-type fiber optic vector hydrophone according to claim 8, characterized in that: The intensity-type fiber optic accelerometer in the oscillator (4) further comprises a ceramic ferrule I (11), a ceramic ferrule II (12), a tail handle I (13) and a tail handle II (14); the transmitting optical fiber (5) passes through the tail handle I (13) and the ceramic ferrule I (11) to form a cantilever beam structure; the receiving optical fiber (6) passes through the tail handle II (14) to the bottom of the ceramic ferrule II (12) and is parallel to the transmitting optical fiber (5); the ceramic ferrule I (11) and the ceramic ferrule II (12) are connected via a ceramic sleeve (8).

10. The intensity-type fiber optic vector hydrophone according to claim 9, characterized in that: A gasket I (9) is provided between the ceramic ferrule I (11) and the ceramic sleeve (8), and a gasket II (10) is provided between the ceramic ferrule II (12) and the ceramic sleeve (8), and the gasket I (9) and the gasket II (10) are distributed up and down.

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