Optical hydrophone structure based on fresnel zone plate sensitization

Abstract

This invention discloses an optical hydrophone structure based on Fresnel zone plate sensitization, belonging to the field of underwater acoustic signal detection technology. It includes a single-mode optical fiber, an elastic cylinder, a Fresnel zone plate, and a metal cavity. The single-mode optical fiber is uniformly and tightly wound around the elastic cylinder, which is located inside the metal cavity. One end of the metal cavity has an acoustic wave incident aperture. The Fresnel zone plate is fixed at the acoustic wave incident aperture of the metal cavity and has several concentric acoustic transmission rings and blocking rings. This invention employs the above-mentioned optical hydrophone structure based on Fresnel zone plate sensitization, which is simple in structure, has few components, and low cost. It possesses good water pressure resistance and electromagnetic interference resistance, making it suitable for complex underwater environments such as marine acoustic exploration and underwater weak target monitoring.

Description

Technical Field

[0001] This invention relates to the field of underwater acoustic signal detection technology, and in particular to an optical hydrophone structure based on Fresnel zone plate sensitization. Background Technology

[0002] Fiber optic hydrophones, due to their significant advantages such as resistance to electromagnetic interference, high bandwidth, easy arraying, and corrosion resistance, have been widely used in various fields including marine acoustic exploration, underwater communication, ship monitoring, and marine environmental monitoring. Currently, most mainstream fiber optic hydrophones are based on fiber optic interferometry or Fabry-Perot (FP) cavity principles. Their core principle is to drive the sensitive element to produce mechanical deformation through sound pressure, which in turn causes changes in the optical properties of the light transmitted in the fiber, such as phase and intensity. Finally, the acoustic signal information is obtained through demodulation.

[0003] However, existing technologies face inherent bottlenecks that are difficult to overcome: First, there is a contradiction between sensitivity and pressure resistance. To improve sensitivity, the mechanical stiffness of the sensitive element needs to be reduced, but reduced stiffness can cause the hydrophone to undergo plastic deformation or even damage in the high-pressure environment of the deep sea. Second, the response to weak low-frequency sound signals is poor. Traditional structures are limited by the mechanical stiffness and recovery speed of the sensitive element, resulting in poor response flatness in the low-frequency range below 1kHz and susceptibility to environmental noise interference, making it difficult to effectively detect weak low-frequency targets in the deep sea. In addition, existing sensitivity enhancement schemes are mostly achieved by optimizing the structure of the sensitive element itself, but the enhancement range is limited and cannot fundamentally solve the problem of low sound energy utilization.

[0004] Fresnel zone plates, as a classic wavefront modulation element, have been widely used in optics, ultrasound, and medical fields. They can modulate the phase of incident waves, causing constructive interference between waves from different paths in a specific region, thus achieving efficient convergence of wave energy and converting minute physical quantities into significant signal changes. However, current applications of Fresnel zone plates are mainly concentrated in land-based sensing and non-underwater acoustic scenarios, and they have not yet been effectively adapted to the acoustic-sensitive structures of hydrophones. Related solutions cannot meet the practical requirements of dynamic underwater acoustic signal detection, high-pressure resistance, and corrosion resistance, making it difficult to apply their wavefront modulation and sensitization advantages in the underwater acoustic field.

[0005] Therefore, there is an urgent need to develop a new type of optical hydrophone that can organically combine Fresnel wavefront modulation technology with fiber optic hydrophone structure in order to break through the sensitivity and low-frequency response bottlenecks of existing technologies and meet the acoustic detection needs in complex underwater environments. Summary of the Invention

[0006] The purpose of this invention is to provide an optical hydrophone structure based on Fresnel zone plate sensitization to overcome the shortcomings of existing fiber optic hydrophones, such as low sensitivity and poor low-frequency weak sound response.

[0007] To achieve the above objectives, the present invention provides an optical hydrophone structure based on Fresnel zone plate sensitization, comprising a single-mode optical fiber, an elastic cylinder, a Fresnel zone plate, and a metal cavity; The single-mode optical fiber is uniformly and tightly wound on the elastic column, which is located inside the metal cavity. One end of the metal cavity has an acoustic wave incident hole. The Fresnel zone plate is fixed at the acoustic wave incident hole of the metal cavity. The Fresnel zone plate has several concentric acoustic transmission rings and blocking rings.

[0008] Preferably, the axial distance between the Fresnel zone plate and the near end face of the elastic cylinder is 5-8 mm.

[0009] Preferably, the length of the elastic column covers the acoustic depth of focus range of the Fresnel zone plate at the design frequency.

[0010] Preferably, the metal cavity, Fresnel zone plate, and external connection are sealed with epoxy resin sealant to achieve a watertight seal.

[0011] Preferably, both ends of the single-mode optical fiber pass through the metal cavity and are fused with optical fiber patch cords.

[0012] Preferably, the elastic column is made of polyurethane or silicone rubber material, with a diameter of 10-15 mm and a length of 20-30 mm.

[0013] Preferably, the Fresnel zone plate is made of stainless steel or titanium alloy, and its designed operating frequency is 100Hz-1kHz with 8-16 rings.

[0014] The preferred manufacturing method is as follows: S1. First, wrap the single-mode optical fiber evenly and tightly around the elastic cylinder, leaving some fiber at both ends. S2. Then, the elastic cylinder, metal cavity, and Fresnel zone plate wrapped with optical fiber are assembled with sealant to form the basic structure of the optical hydrophone. S3. The stripped and cut single-mode optical fiber is fused with the patch cord to connect to the demodulation system for enhancing the sensitivity of the sound field.

[0015] Therefore, the beneficial effects of the optical hydrophone structure based on Fresnel zone plate sensitization described above in this invention are as follows: (1) The present invention has fewer components, reducing costs and failure risks, and facilitating production deployment; (2) The present invention can specifically enhance sound waves of a particular frequency, filter out interference, and improve the detection accuracy of target sound waves; (3) The Fresnel zone plate of the present invention can enhance sound waves, amplify changes in optical fiber signals, and improve the detection capability of weak sound waves; (4) The present invention uses light as a signal carrier and can still work stably in complex electromagnetic environments.

[0016] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the overall structure of an embodiment of the optical hydrophone structure based on Fresnel zone plate sensitization of the present invention; Figure 2 This is a schematic diagram of the Fresnel zone plate in this embodiment; Figure 3 This is a schematic diagram of the elastic column in this embodiment.

[0018] Figure Labels 1. Single-mode fiber; 2. Elastic cylinder; 3. Fresnel zone plate; 4. Metal cavity. Detailed Implementation

[0019] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0020] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0021] Example 1: like Figure 1-3 As shown, the present invention provides an optical hydrophone structure based on Fresnel zone plate sensitization, which mainly consists of a single-mode optical fiber 1, an elastic column 2, a Fresnel zone plate 3, and a metal cavity 4.

[0022] The metal cavity 4 is made of 316L stainless steel and is a cylindrical structure with one open end. It has an inner diameter of 18mm, a length of 40mm, and a wall thickness of 2mm. The open end of the metal cavity 4 serves as the acoustic wave entrance aperture, and its diameter matches the outer diameter of the Fresnel zone plate 3, being 16mm. Two 1mm diameter lead holes are formed on the side wall of the metal cavity 4 for leading out the single-mode optical fiber 1.

[0023] The Fresnel zone plate 3 is made of a 0.5mm thick titanium alloy sheet, designed to operate at a frequency of 500Hz, and has 12 rings, consisting of 12 concentrically alternating acoustic transmission and blocking rings. The Fresnel zone plate 3 is fixed to the acoustic wave entrance of the metal cavity 4 with epoxy resin sealant, and its central axis coincides with the central axis of the metal cavity 4.

[0024] The elastic cylinder 2 is made of polyurethane material, with a diameter of 12mm and a length of 25mm, and is coaxially mounted inside the metal cavity 4. The axial distance between the Fresnel zone plate 3 and the near-end face of the elastic cylinder 2 is set to 6mm. This distance corresponds to the focal length of the Fresnel zone plate 3 at a frequency of 500Hz, ensuring that the focal point of the sound waves converges in the central region of the elastic cylinder 2. The 25mm length of the elastic cylinder 2 covers the acoustic depth of field (approximately 20mm) of the Fresnel zone plate at 500Hz, ensuring a stable sensitization effect within the operating frequency band.

[0025] Single-mode fiber 1, made of G.652D type, is uniformly and tightly wound around the outer surface of elastic cylinder 2, with no gaps between adjacent fiber turns. After winding, both ends of single-mode fiber 1 are led out through two lead holes on the side wall of metal cavity 4, and the lead holes are sealed with epoxy resin sealant. The fiber leads are fused to a standard FC / PC type fiber optic patch cord, and the fusion joint is protected by a heat-shrinkable protective tube. The other end of the fiber optic patch cord is connected to an external phase demodulation system.

[0026] The assembly process in this embodiment is as follows: ① First, the metal cavity 4, Fresnel zone plate 3, and elastic cylinder 2 are processed and manufactured to ensure that the dimensional accuracy of each component meets the design requirements; ② Wrap the single-mode fiber 1 evenly and tightly around the outer surface of the elastic column 2, leaving sufficient length of single-mode fiber 1 at both ends; ③ Place the elastic cylinder 2 with the optical fiber wound inside the positioning area of ​​the metal cavity 4, and adjust its position so that the axis of the elastic cylinder 2 coincides with the central axis of the metal cavity 4. ④ Place the Fresnel zone plate 3 at the acoustic wave inlet of the metal cavity 4, adjust the axial distance between it and the near end face of the elastic column 2 to 6mm, and then seal and fix the connection between the Fresnel zone plate 3 and the metal cavity 4 with epoxy resin sealant. ⑤ Pass both ends of the single-mode fiber 1 through the lead hole on the side wall of the metal cavity 4, and seal the lead hole with epoxy resin sealant. ⑥ Fusion splice the lead-out end of single-mode fiber 1 to the fiber optic patch cord; ⑦ Connect the fiber optic patch cord to the phase demodulation system, set the operating parameters of the demodulation system, and complete the assembly and debugging of the hydrophone.

[0027] The working process of this embodiment is as follows: When underwater acoustic waves are incident on the Fresnel zone plate 3, the acoustic waves are split into multiple wavelets and undergo constructive interference in the region of the elastic cylinder 2, forming a focal point for the convergence of acoustic energy. The enhanced sound pressure causes significant radial and axial deformation of the elastic cylinder 2, which in turn causes tensile deformation of the single-mode optical fiber 1 wound on it, resulting in a change in the phase of the light transmitted in the single-mode optical fiber 1. The phase-changed optical signal is transmitted to the phase demodulation system via an optical fiber jumper. The demodulation system converts the optical phase change into an electrical signal and performs analysis and processing to finally obtain information such as the intensity and frequency of the incident acoustic wave.

[0028] Therefore, the present invention adopts the above-mentioned optical hydrophone structure based on Fresnel zone plate sensitization. By combining the acoustic wavefront modulation characteristics of the Fresnel zone plate with the optical fiber acoustic sensing structure, the directional focusing and amplification of incident sound energy is achieved, which significantly improves the hydrophone's ability to detect low-frequency and weak sound signals, while taking into account the structure's water pressure resistance, anti-interference and ease of production.

[0029] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A structure of an optical hydrophone based on Fresnel zone plate sensitization, characterized in that: Including single-mode fiber, elastic cylinder, Fresnel zone plate and metal cavity; The single-mode optical fiber is uniformly and tightly wound on the elastic column, which is located inside the metal cavity. One end of the metal cavity has an acoustic wave incident hole. The Fresnel zone plate is fixed at the acoustic wave incident hole of the metal cavity. The Fresnel zone plate has several concentric acoustic transmission rings and blocking rings.

2. The Fresnel zone plate sensitized optical hydrophone structure of claim 1, wherein: The axial distance between the Fresnel zone plate and the near end face of the elastic cylinder is 5-8 mm.

3. The optical hydrophone structure based on Fresnel zone plate sensitization according to claim 1, characterized in that: The length of the elastic column covers the acoustic depth of focus range of the Fresnel zone plate at the design frequency.

4. The optical hydrophone structure based on Fresnel zone plate sensitization according to claim 1, characterized in that: The metal cavity, Fresnel waveplate, and external connection are sealed with epoxy resin sealant to achieve a watertight seal.

5. The optical hydrophone structure based on Fresnel zone plate sensitization according to claim 1, characterized in that: Both ends of the single-mode optical fiber pass through the metal cavity and are fused with optical fiber patch cords.

6. The optical hydrophone structure based on Fresnel zone plate sensitization according to claim 1, characterized in that: The elastic column is made of polyurethane or silicone rubber material, with a diameter of 10-15mm and a length of 20-30mm.

7. The optical hydrophone structure based on Fresnel zone plate sensitization according to claim 1, characterized in that: The Fresnel zone plate is made of stainless steel or titanium alloy and is designed to operate at a frequency of 100Hz-1kHz with 8-16 rings.

8. The optical hydrophone structure based on Fresnel zone plate sensitization according to claim 1, characterized in that, The production method is as follows: S1. First, wrap the single-mode optical fiber evenly and tightly around the elastic cylinder, leaving some fiber at both ends. S2. Then, the elastic cylinder, metal cavity, and Fresnel zone plate wrapped with optical fiber are assembled with sealant to form the basic structure of the optical hydrophone. S3. The stripped and cut single-mode optical fiber is fused with the patch cord to connect to the demodulation system for enhancing the sensitivity of the sound field.

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