A highly sensitive immersion-type detection device and method for detecting ultrasonic signals in liquids

Abstract

This invention discloses a highly sensitive detection device and method for immersion-type ultrasonic signal detection in liquids. The invention provides a circular diaphragm with concentric corrugations and a center-thinned structure, and uses this diaphragm as a reflective surface of an optical interference cavity to construct a highly sensitive detection device for immersion-type ultrasonic signal detection in liquids. The diaphragm, used to sense ultrasonic signals, has identical concentric corrugations and a center-thinned structure on both sides, enabling the diaphragm to achieve higher mechanical sensitivity without significantly reducing its natural frequency. The concentric corrugations effectively release initial residual stress introduced during processing and packaging, reducing surface warping and baseline drift. Simultaneously, a replaceable acoustic membrane is constructed in front of the diaphragm, achieving high sound transmission and anti-contamination under long-term immersion in liquid conditions. This detection device can be directly placed in the liquid for detection, improving the sensitivity of ultrasonic signal detection while maintaining a wide frequency range, preventing contamination of the detection element, and ensuring the long-term stability of the detection device.

Description

Technical Field

[0001] This invention belongs to the field of ultrasonic detection, specifically relating to a highly sensitive detection device and method for immersion-type detection of ultrasonic signals in liquids. Background Technology

[0002] Acoustic testing, as a non-contact, long-range, and broadband non-destructive measurement method, has been widely applied in various fields such as condition monitoring and early fault identification. Among these applications, ultrasonic testing in liquid media is also extensive, including online condition monitoring of oil-immersed transformers and bushings, leak assessment of pipelines and storage tanks, pulsation monitoring of hydraulic and lubrication systems, and microfluidics and biomedical imaging. However, rapidly acquiring reliable ultrasonic signals in liquids still faces some challenges. For example, the liquid environment introduces greater noise, and prolonged immersion in liquid can contaminate the detection end. These issues limit the sensitivity and stability of ultrasonic testing in liquids.

[0003] Currently, ultrasonic monitoring in liquids primarily employs electrical detectors. Due to the influence of the liquid environment, these devices often can only be installed on the equipment casing for indirect monitoring. The ultrasonic signal must pass through the liquid, supporting structures, and outer walls before being picked up; signal attenuation and multiple reflections can mask weak ultrasonic waves, leading to insensitive detection and an increased risk of false negatives and missed detections. Furthermore, electrical detectors are bulky and have limited placement options, making them difficult to place close to the detection area, which is unsuitable for monitoring small liquid devices. In contrast, optical fibers offer advantages such as resistance to electromagnetic interference, small size, and the ability to be distributed, making them suitable for ultrasonic monitoring in extreme environments such as high pressure, confined spaces, or high temperatures. However, existing fiber optic ultrasonic solutions still face two key problems: first, insufficient detection sensitivity, failing to simultaneously maintain the required detection frequency bandwidth; and second, the probe tip is constantly exposed to the liquid, making it susceptible to contamination by impurities, leading to sensitivity fluctuations and baseline drift.

[0004] For example, patent application CN119509673A discloses a diaphragm-type EFPI fiber optic acoustic wave sensor with a sensitivity-enhancing structure. This sensor consists of a fiber optic unit, a threaded sleeve, and a sensitivity-enhancing shell connected in sequence. However, because its sensing diaphragm is a circular planar structure, the diaphragm gradually releases internal stress during the detection process, causing the detection result to deviate and resulting in unstable results after multiple measurements. Furthermore, when the detection environment is in an environment with a pressure difference from air, such as underwater or in oil, the diaphragm itself will produce a slight initial deformation, resulting in a narrower detection range and a complex demodulation process. In addition, its sensitivity-enhancing structure is relatively large compared to the sensor structure, making it unsuitable for precise or confined environments.

[0005] Patent application CN112014328A discloses a fiber optic microcavity sensor and its fabrication and signal detection method. This fiber optic microcavity not only enhances the anti-interference capability against factors such as liquid environment temperature and flow rate, but also allows for flexible control of the gas-liquid interface curvature and microcavity length, adjusting the sensor's pressure sensitivity characteristics and improving its performance and applicability. It can meet the needs of different applications for pressure, sound wave, ultrasonic wave, and dissolved gas detection. However, since it is a microcavity generated on the surface of an optical fiber with gas inside, it is impossible to ensure that parameters such as the diameter and curvature of the cavity are the same during fabrication, leading to inconsistencies in the detection device and affecting measurement results. Furthermore, its diaphragm is in direct contact with the external environment, making it susceptible to interference and contamination, especially in complex liquid environments. The diaphragm is easily damaged, affecting sensing results. Additionally, since the detection device is placed directly in a liquid environment, the pressure difference between the inside and outside will generate initial stress in the detection device, causing initial deformation of the gas membrane, which will affect the results during the detection process and reduce detection sensitivity.

[0006] Patent CN112345894B discloses an FP sensor for ultrasonic detection of partial discharge in liquid environments. The designed detection device is a common circular structure, which has low detection sensitivity, cannot release initial stress, and is prone to baseline drift. In addition, the detection device is only sealed with glue, which is easily damaged by the glue when placed in liquid. At the same time, the increase of glue will put a load on the detection diaphragm itself, weakening the mechanical sensitivity of the detection.

[0007] Therefore, issues such as how to improve the detection sensitivity and stability of existing detection devices for ultrasonic signals in liquids need to be addressed. Summary of the Invention

[0008] Most existing ultrasonic detection devices in liquids are electrical, which cannot penetrate the liquid to detect near the source, potentially failing to capture minute signals. Furthermore, existing fiber optic FP interferometer reflective films are often uniformly thick circular films or single-sided thin films, which suffer from limited sensitivity and poor long-term stability. To address these engineering challenges, the primary objective of this invention is to provide a liquid ultrasonic detection method based on a fiber optic FP interferometer cavity. This method utilizes a highly sensitive, immersion-type ultrasonic signal detection device, enabling high-sensitivity and stable ultrasonic signal detection in liquids.

[0009] Another object of the present invention is to provide a circular diaphragm with concentric corrugations and a thinner center, used in the aforementioned highly sensitive immersion-type detection device for detecting ultrasonic signals in liquids. This circular diaphragm is used to sense ultrasonic signals. Both sides of the diaphragm have the same concentric corrugated and thinned-center structure, enabling the diaphragm to achieve higher mechanical sensitivity without significantly reducing its natural frequency. Simultaneously, the concentric corrugations effectively release the initial residual stress introduced during processing and packaging, reducing surface warping and baseline drift.

[0010] Another objective of this invention is to provide the aforementioned highly sensitive immersion-type detection device for detecting ultrasonic signals within liquids. This device uses a circular diaphragm with concentric corrugations and a thinning center as a reflective surface of the optical interference cavity, i.e., the detection diaphragm. Simultaneously, a replaceable acoustically transparent diaphragm and an outer encapsulation are constructed in front of the detection diaphragm. Specifically, an ultra-thin acoustically transparent diaphragm that allows only sound waves to pass through is sandwiched at the front end of the outer encapsulation, maintaining a non-contact distance from the circular diaphragm with concentric corrugations and a thinning center, thus achieving high sound transmission and anti-contamination under long-term immersion in liquid conditions. This detection device can be directly placed in liquids for detection, improving the sensitivity of ultrasonic signal detection while maintaining a wide frequency range, preventing contamination of the detection element, and ensuring the long-term stability of the detection device. In other words, this detection device simultaneously balances sensitivity, bandwidth, and stability, making it suitable for ultrasonic detection in various liquid applications.

[0011] To achieve this objective, the present invention adopts the following technical solution:

[0012] In a first aspect, the present invention provides a method for intra-liquid ultrasonic detection based on a fiber optic FP interferometer cavity, comprising the following steps:

[0013] (1) Connect the fiber core of the detection device to one output end of the circulator via an optical fiber, and connect the other output end of the circulator to the photodetector in the demodulation system; connect the input end of the circulator to the narrow bandwidth tunable laser.

[0014] (2) The detection device is placed in the liquid to be tested to perform ultrasonic detection to obtain ultrasonic signals, and then the time domain and frequency domain signals of the measured ultrasonic signals are obtained by converting ultrasonic signals into optical interference signals into electrical signals.

[0015] The detection device described in step (1) is a highly sensitive immersion detection device for detecting ultrasonic signals in liquids, consisting of fiber optic components and an external encapsulation sleeve.

[0016] The optical fiber element includes a circular diaphragm with concentric corrugations and a thinning center, an optical fiber core, a ceramic ferrule, and an optical interference cavity;

[0017] The circular diaphragm with concentric corrugations and a thinner center serves as a reflecting surface of the optical interference cavity, is in perpendicular contact with the optical interference cavity, and is located at the right end of the optical interference cavity.

[0018] The fiber core serves as the fiber end face of the optical interference cavity, and is partially embedded in the ceramic ferrule and connected to the left end of the optical interference cavity.

[0019] The external encapsulation sleeve includes an acoustic membrane and an outer encapsulation body. The acoustic membrane is fixed to the right end of the outer encapsulation body. The cavity formed by the two is used to install optical fiber elements. The circular membrane with concentric corrugations and thinning at the center in the optical fiber elements is located on the same side as the acoustic membrane and maintains a non-contact distance.

[0020] The circular diaphragm with concentric corrugations and a thinning center has the following structure:

[0021] The two sides of the circular interference cavity reflective diaphragm have the same structure, and the radius of the diaphragm is R. o The thickness is H; the radius of the central thinning region is R. i The thickness is h; concentric corrugations are set at a radius of R. i ~R m Region; The thickness of the concentric ripples is H, the amplitude height is A, the period length is L, and the number of periods is N;

[0022] Among them, R i <R i +L*N<R m <R o , h < H.

[0023] Preferably, N is a positive integer.

[0024] More preferably, N is a positive integer, and 1≤N≤10.

[0025] Preferably, in the circular diaphragm, except for the concentric corrugated area, the other areas are smooth planes.

[0026] Preferably, the concentric ripples include at least one of equidistant concentric ripples, non-equidistant concentric ripples, equal-height concentric ripples, or gradually varying-height concentric ripples.

[0027] Preferably, the corrugated structure of the concentric corrugations includes at least one of sine, circular arc, trapezoidal and rectangular shapes.

[0028] Preferably, the material of the circular diaphragm with concentric corrugations and a thinning center includes at least one of metal, non-metal, semiconductor, and polymer.

[0029] Preferably, the fabrication process of the circular film with concentric ripples and a thinner center includes at least one of semiconductor processes, two-photon 3D printing methods, and laser etching technology.

[0030] Semiconductor processes can perform precise micro-machining on the surface of films, enabling the fine fabrication of films; two-photon 3D printing methods can print structures on the ends of optical fibers, enabling the miniaturization of devices and their application in signal detection within the human body; laser etching technology can carve microstructures inside optical fibers, achieving precision device fabrication through subtractive processing.

[0031] Preferably, the ceramic ferrule has a fixing element for fixing the optical fiber core into the ceramic ferrule.

[0032] Preferably, the surface of the optical fiber core that is not embedded with a ceramic ferrule is covered with an optical fiber core cladding.

[0033] Preferably, the ceramic ferrule and the optical interference cavity are covered with an optical element package.

[0034] Preferably, the acoustic membrane is fixed to the right end of the outer encapsulation body by at least one of the following methods: snap fastener, pressure ring, and threaded ring.

[0035] Preferably, the outer package has a locking slot for fixing optical components.

[0036] Preferably, the outer encapsulation body has a through hole at its left end for fixing the fiber optic core cladding covering the surface of the fiber optic core in the optical element.

[0037] Preferably, the outer encapsulation body is made of a corrosion-resistant material, including at least one of 316 stainless steel, titanium alloy, polyetheretherketone (PEEK), and polyetherimide (PEI).

[0038] Preferably, the material of the sound-permeable membrane is a corrosion-resistant and sound-permeable material, including at least one of fluorinated ethylene propylene copolymer (FEP), polytetrafluoroethylene (PTFE), polyterephthalate polymer (Parylene-C), and ultrathin polyimide.

[0039] Preferably, the demodulation system in step (1) includes a computer, which is connected to a photodetector in the demodulation system for displaying time-domain waveforms and transformed frequency-domain spectra.

[0040] Preferably, the liquid to be tested in step (2) includes at least one of transformer oil, lubricating oil, water, seawater, solvent, blood, and physiological saline.

[0041] Specifically, the present invention detects ultrasonic signals generated in liquids, such as partial discharge in transformer oil and ultrasonic positioning underwater.

[0042] This detection method acquires and demodulates ultrasonic signals in liquids through a "ultrasonic signal-optical interference signal-electrical signal" link. First, the ultrasonic signal is converted into an optical signal. An optical signal emitted by a narrow-bandwidth tunable laser is transmitted via optical fiber to the optical interference cavity of the detection device. A circular diaphragm at the front of the device senses the ultrasonic waves in the liquid. The micro-pressure generated by the ultrasound causes a slight deformation of the diaphragm, changing the cavity length of the optical interference cavity and modulating the phase of the light within the cavity, generating an optical interference signal. Subsequently, the optical interference signal is converted into an electrical signal by a photodetector. The intensity of the interfered light fluctuates periodically with the cavity length. The photodetector converts this intensity change into a corresponding electrical signal, which is displayed as a time-domain waveform and a transformed frequency-domain spectrum on a computer. By adjusting the optical path structure or employing different optical demodulation strategies, the stability and sensitivity of the detection can be further improved.

[0043] Secondly, the present invention provides a circular diaphragm with concentric corrugations and a thinning center, as described above.

[0044] This invention designs a circular diaphragm with concentric corrugations and a centrally thinned structure as a reflective surface of an optical interference cavity. This diaphragm increases axial displacement without significantly reducing the natural frequency, thereby achieving higher mechanical sensitivity. The concentric corrugated structure also serves to release initial residual stress, preventing baseline drift in the detection device.

[0045] This invention can modify various parameters inside a circular diaphragm with concentric corrugations and a centrally thinned structure, such as R, according to different application scenarios. o -R m The width, number of corrugations, radius of the thinned area, and thickness of the thinned area are all adjusted to achieve tunable membrane performance, making it suitable for a variety of applications.

[0046] Thirdly, the present invention provides the above-mentioned highly sensitive detection device for immersion-type detection of ultrasonic signals in liquids.

[0047] First, this invention employs a circular diaphragm with concentric corrugations on both sides and a thinner center as a reflecting surface of the optical interference cavity. This improves the mechanical sensitivity of the device without significantly reducing its natural frequency, thereby enhancing the linearity and repeatability of signal detection. Second, addressing the need for long-term immersion in liquids, a replaceable outer encapsulation and acoustically transparent membrane isolation protection system is designed. This system allows sound signals to pass through while preventing liquid particles from contaminating the reflecting surface. The outer encapsulation and acoustically transparent membrane are tightly connected, and the membrane maintains a non-contact distance from the circular diaphragm with concentric corrugations and a thinner center, ensuring sufficient space for membrane vibration and achieving high sound transmission and anti-contamination under long-term oil and water immersion conditions. The optical interference cavity consists of an optical fiber end face reflecting surface (optical fiber core) and the aforementioned circular diaphragm reflecting surface with concentric corrugations and a thinner center. The cavity length and reflectivity can be selectively changed according to different transmission requirements. This detection device supports direct probe immersion in liquid, achieving high sensitivity, wide bandwidth, and long-term stable liquid ultrasonic detection. The detection device described herein can increase the sensitivity of ultrasonic monitoring in liquids, and the parameters of the circular diaphragm with concentric corrugations and a thinning center (such as the center thinning radius, thickness, and concentric corrugation parameters) can be adjusted according to different detection needs, achieving tunable performance of the detection probe. Furthermore, the acoustic diaphragm and outer encapsulation can be replaced to adapt to different detection scenarios without disassembling the optical components. Therefore, the detection device of this invention can achieve high sensitivity, wide frequency response, and long-term reliability in liquids, and is suitable for monitoring and analyzing ultrasonic signals in liquid media such as partial discharge and underwater ultrasonic detection, possessing feasibility for engineering and large-scale application.

[0048] The detection device described in this invention can be arrayed or distributed, and can achieve localization and imaging of ultrasound in liquids through the arrangement of multiple probes at multiple angles, thereby achieving functions such as ultra-high sensitivity detection.

[0049] The detection device of the present invention employs multiple demodulation methods for signal detection, including intensity demodulation, phase demodulation, and white light interference.

[0050] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0051] (1) The circular diaphragm structure with concentric corrugations and central thinning proposed in this invention can alleviate the problems of insufficient mechanical sensitivity, long-term drift, and poor engineering usability of detection devices for ultrasonic testing in liquids. Through the central thinning and external concentric corrugations, the sensitivity is improved without significantly sacrificing bandwidth, and the initial stress is released. The circular diaphragm with concentric corrugations and central thinning proposed in this invention is suitable for long-term online monitoring in complex environments such as oil and strong electromagnetic fields. Its geometric parameters can be tuned through parametric design to achieve a balance between requirements, facilitating array manufacturing and multi-faceted applications. In addition, the acoustic membrane and outer encapsulation proposed in this invention can prevent the detection device from being contaminated by impurities in the liquid, extend the service life of the detection device, and allow the outer encapsulation and acoustic membrane to be replaced to adapt to different detection environments.

[0052] (2) The circular diaphragm with concentric corrugations and a thinner center designed in this invention does not require a large external sensitizing shell to focus the sound. It can improve mechanical sensitivity by relying only on the thinner center area and the concentric corrugated structure, reducing the mass of the detection device and excessive damping. It can achieve high bandwidth while maintaining miniaturization and has stronger environmental adaptability.

[0053] (3) The present invention adopts a standardized package with a coaxial shell and a fixed cavity length, resulting in higher manufacturing consistency; an acoustically transparent window (sound-transmitting membrane) is set at the front end and sealed, which physically isolates the detection element (optical element) from the liquid, and the pressure difference inside and outside the optical interference cavity remains consistent, making the detection more stable. At the same time, a non-contact micro-gap is maintained between the sound-transmitting membrane and the detection membrane (a circular membrane with concentric corrugations and a thinning center), avoiding contamination and improving the detection sensitivity while maintaining the bandwidth.

[0054] (4) This invention achieves higher mechanical sensitivity by designing a circular diaphragm structure with concentric corrugations and a thinner center, which can release initial residual stress and reduce diaphragm warping and baseline drift. Simultaneously, this invention adds an acoustically transparent membrane to the outside of the detection device, avoiding the risk of corrosion and penetration of adhesive in the liquid and protecting the optical components. The acoustically transparent membrane can be replaced without modifying the optical cavity, maintaining high sensitivity, stability, and maintainability in long-term online underwater applications. Attached Figure Description

[0055] Figure 1 This is a planar schematic diagram of a circular diaphragm with concentric corrugations and a thinning at the center, where (a) is a top view of the circular diaphragm, (b) is a front view of the circular diaphragm, and (c) is a partial cross-sectional view of the concentric corrugations on the left half of the circular diaphragm.

[0056] Figure 2 This is a three-dimensional schematic diagram of a circular diaphragm with concentric corrugations and a thinning at the center. (Left) is the front view, and (Right) is the 45° view.

[0057] Figure 3 Finite element simulation diagram of the first natural frequency and displacement of a circular diaphragm with concentric corrugations and a thinning center;

[0058] Figure 4 This is a cross-sectional view of the detection device;

[0059] Figure 5 A comparison of the first-order natural frequency and sensitivity values ​​of a circular diaphragm with concentric ripples and a thinner center;

[0060] Figure 6 The time-domain and frequency-domain plots of the ultrasonic signal detected in water in Example 3 are shown.

[0061] Figure 7 This is a sensitivity response diagram for ultrasonic detection in water in Example 4;

[0062] Figure 8 This is a time-domain plot of ultrasonic testing performed in water on day 1 of Example 5;

[0063] Figure 9 This is a time-domain plot of ultrasonic testing performed in water on day 16 of Example 5;

[0064] Among them, R o Let R be the radius of the circular diaphragm. m R is the maximum radius of the concentric corrugated region, Ri is the radius of the central thinning region, H is the thickness of the circular diaphragm and the concentric corrugations, h is the thickness of the central thinning region, L is the period length of the concentric corrugations, A is the amplitude height of the concentric corrugations, N is the number of periods of the concentric corrugations, 1-1 is a circular diaphragm with concentric corrugations and central thinning, 1-2 is the fiber core, 1-3 is the ceramic ferrule, 1-4 is the package of the optical element, 1-5 is the cladding of the fiber core, 1-6 is the fixing element, 1-7 is the optical interference cavity, 2-1 is the acoustic membrane, 2-2 is the outer package, 2-3 is the slot, and 2-4 is the through hole. Detailed Implementation

[0065] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the implementation of the present invention is not limited thereto.

[0066] Unless otherwise specified in the embodiments of this invention, the conditions shall be performed according to conventional conditions or conditions recommended by the manufacturer. All raw materials and reagents used, unless otherwise specified, are commercially available conventional products.

[0067] Example 1

[0068] A circular diaphragm with concentric corrugations and a thinning center has the following structure:

[0069] The circular diaphragm has the same structure on both sides, and the radius of the diaphragm is R. o The thickness is H; the radius of the central thinning region is R. i The thickness is h; concentric corrugations are set at a radius of R. i ~R m Region; The thickness of the concentric ripples is H, the amplitude height is A, the period length is L, and the number of periods is N;

[0070] Among them, R i <R i +L*N<R m <R o h < H, N is 2;

[0071] The concentric ripples are equidistant concentric ripples; the ripple structure of the concentric ripples is sinusoidal.

[0072] In the diaphragm, except for the concentric corrugated areas, all other areas are smooth planes.

[0073] like Figure 1 The schematic diagram of the planar structure shown is as follows: (a) is the top view of the circular diaphragm, (b) is the front view of the circular diaphragm, and (c) is a partial cross-sectional view of the concentric corrugations on the left half of the circular diaphragm.

[0074] Figure 2 This is a three-dimensional schematic diagram of a circular membrane with concentric corrugations and a thinning at the center. (Left) is the front view, and (Right) is the 45° view. The corrugated structure and the thinning region at the center can be clearly observed.

[0075] The natural frequency and mechanical sensitivity of the diaphragm were simulated using the finite element method, and the simulation results are shown in the figure below. Figure 3 As shown, the natural frequency is chosen as the first natural frequency of the diaphragm, and the maximum displacement of the center of the diaphragm is the mechanical sensitivity of the diaphragm. The corrugated diaphragm exhibits the standard mode shape with the maximum center displacement after being subjected to uniform surface force, which meets the detection requirements of the fiber optic FP interferometer cavity.

[0076] Example 2

[0077] A highly sensitive immersion-type detection device for detecting ultrasonic signals in liquids, such as Figure 4 As shown, it consists of optical fiber components and an external encapsulation sleeve;

[0078] The optical fiber element includes a circular diaphragm (1-1) with concentric corrugations and a thinner center, an optical fiber core (1-2), a ceramic ferrule (1-3), and an optical interference cavity (1-7) as described in Example 1.

[0079] The circular diaphragm (1-1) with concentric corrugations and thinning at the center serves as a reflecting surface of the optical interference cavity (1-7), is in perpendicular contact with the optical interference cavity (1-7), and is located at the right end of the optical interference cavity (1-7).

[0080] The fiber core (1-2) serves as the fiber end face of the optical interference cavity (1-7), and is partially embedded in the ceramic ferrule (1-3) and connected to the left end of the optical interference cavity (1-7); the fiber core (1-2) not embedded in the ceramic ferrule (1-3) is covered with a fiber core cladding (1-5).

[0081] The ceramic ferrule (1-3) has a fixing element (1-6) for fixing the optical fiber core (1-2) into the ceramic ferrule (1-3);

[0082] The ceramic ferrule (1-3) and the optical interference cavity (1-7) are covered with an optical element package (1-4).

[0083] The external encapsulation sleeve includes an acoustic membrane (2-1) and an outer encapsulation body (2-2). The acoustic membrane (2-1) is fixed to the right end of the outer encapsulation body (2-2) by a snap-fit ​​method. The cavity formed by the two is used to install optical fiber elements. The circular membrane (1-1) with concentric corrugations and thinning at the center in the optical fiber element is located on the same side as the acoustic membrane (2-1) and maintains a non-contact distance.

[0084] The outer packaging (2-2) has a locking slot (2-3) for fixing optical components;

[0085] The outer encapsulation body (2-2) has a through hole (2-4) at its left end for fixing the fiber core cladding (1-5) covering the surface of the fiber core (1-2) in the optical element.

[0086] The material of the outer encapsulation body (2-2) is polyetheretherketone (PEEK);

[0087] The sound-permeable membrane (2-1) is made of polytetrafluoroethylene.

[0088] Comparative Example 1

[0089] An unstructured circular membrane with radius R o The thickness is H, and both sides of the membrane are smooth planes.

[0090] Comparative Example 2

[0091] A circular diaphragm with concentric corrugations has the following structure:

[0092] The circular diaphragm has the same structure on both sides, and the radius of the diaphragm is R. o The thickness is H; concentric corrugations are set at a radius of R.i ~R m Region; The thickness of the concentric ripples is H, the amplitude height is A, the period length is L, and the number of periods is N;

[0093] Among them, R i <R i +L*N<R m <R o h < H, N is 2;

[0094] The concentric ripples are equidistant concentric ripples; the ripple structure of the concentric ripples is sinusoidal.

[0095] In the diaphragm, except for the concentric corrugated areas, all other areas are smooth planes.

[0096] Comparative Example 3

[0097] A circular membrane with a central thinning has the following structure:

[0098] The circular diaphragm has the same structure on both sides, and the radius of the diaphragm is R. o The thickness is H; the radius of the central thinning region is R. i The thickness is h;

[0099] Among them, R i <R o h < H; both the central thinning region and the non-thinning region are smooth planes.

[0100] Figure 5 The diagram shows a comparison of the first-order natural frequency and sensitivity values ​​of the different circular diaphragms described in Example 1 and Comparative Examples 1-3. In this example, the corrugated diaphragm of the present invention has a very small first-order natural frequency value and a significant improvement in mechanical sensitivity.

[0101] Example 3

[0102] (1) Assemble the optical detection device: Connect the fiber core of the high-sensitivity detection device for immersion detection of ultrasonic signals in liquid obtained in Example 2 to one output end of the circulator through the optical fiber, and connect the other output end of the circulator to the photodetector in the demodulation system; the photodetector is then connected to the computer to read and display the time domain and frequency domain spectra of the measured ultrasonic signal; the input end of the circulator is connected to a narrow-bandwidth tunable laser to incident detection light, and the laser wavelength is locked at the orthogonal operating point of the detection device to obtain the maximum response.

[0103] (2) The high-sensitivity immersion-type ultrasonic signal detector from step (1) is placed in water for ultrasonic detection, while all other optical path devices are placed in the air. The circular diaphragm of the detector detects the ultrasonic signal. The micro-pressure generated by the ultrasound causes a slight deformation of the circular diaphragm, thereby changing the cavity length of the optical interference cavity and modulating the phase of the light inside the cavity, generating an optical interference signal. Subsequently, the optical interference signal is converted into an electrical signal by a photodetector. The intensity of the light after interference fluctuates periodically with the cavity length. The photodetector converts this intensity change into a corresponding electrical signal and sends it to a computer for time-domain recording and spectrum analysis display through the acquisition system.

[0104] The results are as follows Figure 6 As shown: Figure 6 The time-domain waveform of the ultrasonic signal acquired by this detection device and its frequency-domain spectrum obtained after Fast Fourier Transform (FFT) are presented. The time-domain waveform shows that the detection device can capture the original waveform of the ultrasonic pulse completely and continuously, and the waveform is periodically uniform and has a clear envelope. The spectrum obtained after performing FFT on this time-domain signal shows that the dominant frequency of the measured signal is approximately 42 kHz, with a significant dominant frequency component on the spectral line accompanied by several small harmonic components, concentrated energy, and relatively low noise. This spectrum further demonstrates that the detection device of this invention has a good frequency response to ultrasound in liquids.

[0105] Example 4

[0106] Simultaneously, ultrasonic detection was performed on both the electrical detection device (standard hydrophone) and the optical detection device assembled in Example 3. The hydrophone and the detection device from Example 3 were placed in water, with all other conditions identical. Maintaining the same output ultrasonic frequency but varying the sound pressure, frequency signals at different sound pressures were detected, and the time-domain plots on the computer were observed. The peak-to-peak value of each time-domain plot on the computer was taken as the response of the detection device at that sound pressure, and the peak-to-peak values ​​at each sound pressure were connected to obtain a sensitivity response plot. A linear fit was performed on the five points, and the slope of the resulting linear curve corresponded to the sensitivity of the detection device. For example... Figure 7 As shown in the figure, the slope of the optical detection device is greater than that of the electrical detection device. Given that the sensitivity of the standard electrical detection device is 5 mV / Pa, the calculated sensitivity of the optical detection device based on the slope is 69 mV / Pa, which is significantly higher than the sensitivity of the standard electrical detection device.

[0107] Example 5

[0108] The detection device of Example 3 was placed in the same water and ultrasonic tests were performed at 15-day intervals, with the specific operation being the same as in Example 3. Figure 8 and 9The figures show the time-domain plots of two tests conducted 15 days apart. It can be seen that the time-domain plots almost overlap, with only slight deviations in peak-to-peak values, but these deviations are negligible, indicating that the detection device of this application has good stability.

[0109] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for intra-liquid ultrasonic detection based on a fiber optic FP interferometer cavity, characterized in that, Includes the following steps: (1) Connect the fiber core of the detection device to one output end of the circulator via an optical fiber, and connect the other output end of the circulator to the photodetector in the demodulation system; connect the input end of the circulator to the narrow bandwidth tunable laser. (2) The detection device is placed in the liquid to be tested to perform ultrasonic detection to obtain ultrasonic signals, and then the time domain and frequency domain signals of the measured ultrasonic signals are obtained by converting ultrasonic signals into optical interference signals into electrical signals. The detection device described in step (1) is a highly sensitive immersion detection device for detecting ultrasonic signals in liquids, consisting of fiber optic components and an external encapsulation sleeve. The optical fiber element includes a circular diaphragm with concentric corrugations and a thinning center, an optical fiber core, a ceramic ferrule, and an optical interference cavity; The circular diaphragm with concentric corrugations and a thinner center serves as a reflecting surface of the optical interference cavity, is in perpendicular contact with the optical interference cavity, and is located at the right end of the optical interference cavity. The fiber core serves as the fiber end face of the optical interference cavity, and is partially embedded in the ceramic ferrule and connected to the left end of the optical interference cavity. The external encapsulation sleeve includes an acoustic membrane and an outer encapsulation body. The acoustic membrane is fixed to the right end of the outer encapsulation body. The cavity formed by the two is used to install optical fiber elements. The circular membrane with concentric corrugations and thinning at the center in the optical fiber elements is located on the same side as the acoustic membrane and maintains a non-contact distance. The circular diaphragm with concentric corrugations and a thinning center has the following structure: Both sides have the same structure and a radius of R. o The thickness is H; the radius of the central thinning region is R. i The thickness is h; concentric corrugations are set at a radius of R. i ~R m Region; The thickness of the concentric ripples is H, the amplitude height is A, the period length is L, and the number of periods is N; Among them, R i <R i +L*N<R m <R o h < H, N is a positive integer.

2. The method for intra-liquid ultrasonic detection based on fiber optic FP interferometer cavity according to claim 1, characterized in that, N is a positive integer, and 1 ≤ N ≤ 10.

3. The method for intra-liquid ultrasonic detection based on a fiber optic FP interferometer cavity according to claim 1 or 2, characterized in that, In the circular diaphragm with concentric corrugations and a thinning center, the areas other than the concentric corrugated structure are smooth planes.

4. The method for intra-liquid ultrasonic detection based on a fiber optic FP interferometer cavity according to claim 1 or 2, characterized in that, The concentric ripples include at least one of equidistant concentric ripples, non-equidistant concentric ripples, equal-height concentric ripples, and gradually varying-height concentric ripples. And / or, the corrugation structure of the concentric corrugations includes at least one of sine, circular arc, trapezoidal and rectangular.

5. The method for intra-liquid ultrasonic detection based on fiber optic FP interferometer cavity according to claim 1, characterized in that, The ceramic ferrule has a fixing element for fixing and embedding the optical fiber core into the ceramic ferrule; And / or, the surface of the optical fiber core that is not embedded with a ceramic ferrule is covered with an optical fiber core cladding; And / or, the ceramic ferrule and the optical interference cavity are covered with an optical element package.

6. The method for intra-liquid ultrasonic detection based on a fiber optic FP interferometer cavity according to claim 1 or 5, characterized in that, The acoustic membrane is fixed to the right end of the outer encapsulation body by at least one of the following methods: snap fasteners, pressure rings, and threaded rings; And / or, the outer package has locking slots for securing optical components; And / or, the left end of the outer encapsulation body is provided with a through hole for fixing the fiber core cladding covering the surface of the fiber core in the optical element.

7. The method for intra-liquid ultrasonic detection based on a fiber optic FP interferometer cavity according to claim 1 or 5, characterized in that, The material of the outer encapsulation includes at least one of 316 stainless steel, titanium alloy, polyetheretherketone, and polyetherimide; And / or, the material of the acoustic membrane includes at least one of fluorinated ethylene propylene copolymer, polytetrafluoroethylene, polyterephthalate polymers and ultrathin polyimide.

8. The method for intra-liquid ultrasonic detection based on fiber optic FP interferometer cavity according to claim 1, characterized in that, The demodulation system in step (1) includes a computer, which is connected to a photodetector in the demodulation system for displaying time-domain waveforms and transformed frequency-domain spectra; And / or, the test liquid in step (2) includes at least one of transformer oil, lubricating oil, water, seawater, solvent and physiological saline.

Images