Elastic cantilever beam, optical fiber acceleration sensing device and system

Abstract

The application discloses an elastic cantilever beam, an optical fiber acceleration sensing device and system, and belongs to the technical field of optical fiber sensing. The elastic cantilever beam comprises a U-shaped beam body structure, the diameters of beam arms of the beam body structure gradually increase along the direction of an opening end of the beam body structure; a hollow part is arranged between the beam arms, the width of the hollow part gradually increases along the direction of the opening end of the beam body, and a plurality of beam body structures are arranged in parallel and connected through connecting parts to form a multi-period folding structure. The elastic cantilever beam provided by the application is used for acceleration signal sensing through a design of a width-gradually-changing multi-period folding cantilever beam. Under the same size, the deformation amount of the cantilever beam structure can be significantly increased compared with a conventional elastic cantilever beam when force is borne, so that the acceleration signal detection sensitivity of the sensing structure can be improved, and high-sensitivity and low-noise-level acceleration signal detection can be realized.

Description

Technical Field

[0001] This invention belongs to the field of fiber optic sensing technology, and more specifically, relates to an elastic cantilever beam, a fiber optic acceleration sensing device and system. Background Technology

[0002] Among common physical quantities, acceleration is one that contains a wealth of information. For example, abnormal low-frequency vibration signals often precede natural disasters such as earthquakes or tsunamis. Detecting these special acceleration signals using accelerometers can significantly reduce casualties and economic losses. Simultaneously, the resonant frequencies of structures often change significantly after damage occurs. Knowing these changes through accelerometers allows for structural lifespan estimation and health monitoring. Furthermore, accelerometers have important and widespread applications in inertial navigation, pipeline inspection, and oil and gas field exploration.

[0003] Research on electrical accelerometers predates that on fiber optic accelerometers, and electrical accelerometers boast higher technological maturity and wider practical applications. However, electrical accelerometers suffer from inherent limitations. Key electrical components are susceptible to electromagnetic interference from the environment and are highly sensitive to parameters such as temperature and pressure, making them unsuitable for operation in harsh environments. In contrast, fiber optic accelerometers primarily utilize passive materials, significantly reducing the impact of electromagnetic interference. Furthermore, optical fibers offer advantages such as small size, ease of networking, corrosion resistance, and tolerance to harsh temperatures. Therefore, research on fiber optic accelerometers is of significant value.

[0004] Currently, fiber optic accelerometer sensor structures include direct-connected mass block, elastic cylindrical mass block, protrusion-film, and cantilever beam mass block types. Among these, the cantilever beam mass block structure offers high design flexibility and significant room for improvement in structural details, enabling more precise small-size designs, higher signal detection sensitivity, and lower noise levels. However, many cantilever beam mass block structures are relatively fragile due to their small size and thinness, resulting in limited maximum detectable acceleration and restricted sensor dynamic range. Furthermore, preventing fiber breakage during operation in harsh environments is crucial for ensuring long-term stable application of fiber optic accelerometers. Summary of the Invention

[0005] In view of the above-mentioned defects or improvement needs of the existing technology, the present invention provides an elastic cantilever beam, an optical fiber accelerometer and system, thereby solving the technical problems of single-piece cantilever beam mass block type optical fiber accelerometer, such as difficulty in achieving triaxial high-sensitivity signal detection, low signal-to-noise ratio, high crosstalk, and difficulty in miniaturization design.

[0006] To achieve the above objectives, according to one aspect of the present invention, an elastic cantilever beam is provided, comprising a U-shaped beam structure, wherein the diameter of the beam arm of the beam structure gradually increases along the direction of the open end of the beam structure;

[0007] A hollow section is provided between the beam arms, and the width of the hollow section gradually increases along the direction of the opening end of the beam body;

[0008] The beam structure has outwardly extending connecting parts at both ends of the beam arm.

[0009] Preferably, multiple beam structures are arranged in parallel and connected by the connecting part to form a multi-period folding structure.

[0010] According to another aspect of the present invention, an optical fiber acceleration sensing device is provided, including the above-mentioned elastic cantilever beam, and further including a sensor outer frame and a first sensing component, a second sensing component and a third sensing component disposed within the sensor outer frame.

[0011] The first sensing component, the second sensing component, and the third sensing component are each provided with a central mass block and multiple elastic cantilever beams. The elastic cantilever beams are disposed between the central mass block and the sensor outer frame, and the connecting part is used to connect the central mass block and the sensor outer frame.

[0012] The first sensing component is used to detect acceleration signals parallel to the plane of the sensing device;

[0013] The second sensing component is used to detect acceleration signals parallel to the plane of the sensing device;

[0014] The third sensing component is used to detect acceleration signals perpendicular to the plane of the sensing device.

[0015] Preferably, the first sensing component has two sets of elastic cantilever beams symmetrically arranged on both sides of the central mass block. The elastic cantilever beams are two parallel beam structures connected by a connecting part to form a folded structure.

[0016] Preferably, the second sensing component has two sets of elastic cantilever beams symmetrically arranged on both sides of the central mass block. The elastic cantilever beams are two parallel beam structures connected by a connecting part to form a folded structure.

[0017] Preferably, the third sensing component has four sets of elastic cantilever beams symmetrically arranged around the central mass block, wherein each set includes two elastic cantilever beams with their open ends facing each other.

[0018] Preferably, the outer frame of the sensor is provided with an optical fiber slot for placing an optical fiber; the optical fiber slots are respectively arranged along the direction of movement of the central mass block perpendicular to the first sensing component and the second sensing component.

[0019] According to another aspect of the present invention, an optical fiber acceleration sensing system is provided, including the above-described optical fiber acceleration sensing device, and further including: a laser, an optical fiber circulator, and an optical demodulation device.

[0020] The laser is connected to the first interface of the fiber optic circulator, and the laser generated by the laser is emitted through the second interface of the fiber optic circulator.

[0021] The sensing device is connected to the second interface of the fiber optic circulator via an optical fiber to receive the outgoing light from the second interface. After the outgoing light is output through the end face of the optical fiber, it is reflected back into the optical fiber by the side of the central mass block and interferes. The interference light signal is emitted through the third port of the fiber optic circulator.

[0022] The optical demodulation device is connected to the third interface of the fiber optic circulator to receive the interference light signal and extract the signal changes of the sensing device, thereby reconstructing the acceleration signal to be measured.

[0023] In summary, compared with the prior art, the above-described technical solutions conceived by this invention can achieve the following beneficial effects:

[0024] 1. The elastic cantilever beam proposed in this invention uses a multi-period folded cantilever beam with gradually varying width for acceleration signal sensing. Under the same size, this cantilever beam structure can significantly increase the deformation under stress compared to a conventional elastic cantilever beam. Therefore, it can improve the acceleration signal detection sensitivity of the sensing structure and is conducive to achieving high-sensitivity and low-noise acceleration signal detection.

[0025] 2. The fiber optic accelerometer proposed in this invention can realize monolithically integrated triaxial acceleration signal detection. The detection of acceleration signals in three orthogonal directions is accomplished by three sensing structures. The monolithic sensing structure is formed in one piece through silicon micromachining, without the need for subsequent assembly. This avoids the errors and orthogonal crosstalk caused by the assembly and preparation of traditional triaxial accelerometers, and makes it easier to achieve triaxial acceleration signal detection with low orthogonal crosstalk.

[0026] 3. The fiber optic acceleration sensing system proposed in this invention is based on the principle of optical interference. The light signal is reflected from the side of the central mass block. After passing through the fiber optic circulator, the two reflected beams interfere with each other. The acceleration signal is generated by the optical interference microcavity. The method is simple and easy to implement, and the structure is stable. It can achieve high-precision acceleration signal detection at a lower cost. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the structure of the elastic cantilever beam proposed in this invention;

[0028] Figure 2This is a schematic diagram of the fiber optic acceleration sensing device proposed in this invention.

[0029] Figure 3 This is a schematic diagram of the fiber optic acceleration sensing system proposed in this invention.

[0030] In all the accompanying drawings, the same reference numerals are used to denote the same elements or structures, wherein: 1-first sensing component; 2-second sensing component; 3-third sensing component; 4-central mass block; 5-elastic cantilever beam; 6-sensor outer frame; 7-fiber optic slot. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0032] like Figure 1 As shown, the present invention proposes an elastic cantilever beam, including a U-shaped beam structure, wherein the diameter of the beam arm of the beam structure gradually increases along the direction of the open end of the beam structure; a hollow portion is provided between the beam arms, and the width of the hollow portion gradually increases along the direction of the open end of the beam; and outwardly extending connecting portions are provided at both ends of the beam arm of the beam structure.

[0033] To further explain, multiple beam structures are arranged in parallel and connected by the connecting parts to form a multi-period folding structure.

[0034] Specifically, the elastic cantilever beam structure features a hollow center and gradually decreasing spacing between the inner and outer rings at both ends. This gradually changing width design significantly improves the deformation of the elastic cantilever beam under stress. The multi-cycle folding of the elastic cantilever beam further enhances its sensitivity. Compared to a conventional S-shaped cantilever beam, under designed dimensional conditions, finite element simulation results show that when the acceleration signal direction is parallel to the beam plane and perpendicular to the beam side, the deformation at the stressed end of this cantilever beam is approximately five times that of the S-shaped cantilever beam; when the acceleration signal direction is perpendicular to the beam plane and perpendicular to the beam side, the deformation at the stressed end is approximately twice that of the S-shaped cantilever beam. This cantilever beam structure significantly improves the acceleration signal detection sensitivity of the sensing structure within the same size, which is beneficial for reducing the minimum detectable acceleration of the sensor and for miniaturizing the sensor size.

[0035] like Figure 2As shown, this invention proposes an optical fiber accelerometer, comprising a sensor outer frame 6 and a first sensing component 1, a second sensing component 2, and a third sensing component 3 disposed within the sensor outer frame 6. Each of the first sensing component 1, the second sensing component 2, and the third sensing component 3 is provided with a central mass block 4 and multiple elastic cantilever beams 5. The elastic cantilever beams 5 are disposed between the central mass block 4 and the sensor outer frame 6, and a connecting portion is used to connect the central mass block 4 and the sensor outer frame 6. The first sensing component 1 is used to detect acceleration signals parallel to the plane of the sensing device; the second sensing component 2 is used to detect acceleration signals parallel to the plane of the sensing device; and the third sensing component 3 is used to detect acceleration signals perpendicular to the plane of the sensing device.

[0036] Specifically, the sensing device comprises three parts, each used for triaxial acceleration signal sensing. Each part has multiple elastic cantilever beams distributed around the central mass block 4. The central mass block 4 is connected to the sensor outer frame 6 through the elastic cantilever beam structure.

[0037] Furthermore, the elastic cantilever beam structure adopts the width-gradient cantilever beam described above, which can obtain a high-sensitivity acceleration sensing structure; grooves are engraved on the outer frame of the sensor to form fiber optic slots 7 for placing optical fibers. The optical fibers are fixed in the fiber optic slots 7 and the end face of the optical fibers is cut flat. Thus, the end face of the optical fibers and the side of the central mass block can form an optical interference microcavity for acceleration signal sensing.

[0038] Furthermore, in the fiber optic accelerometer, when a certain part of the sensing component is subjected to an acceleration signal in its sensitive direction, the outer frame 6 of the sensor vibrates, and the central mass block 4 will move relative to the outer frame 6 due to inertia. The change in the distance between the central mass block 4 and the outer frame 6 causes the elastic cantilever beam 5 to be stretched and compressed. At the same time, the distance between the optical fiber and the outer frame 6 of the sensor will also change, thereby realizing optical signal modulation and acquiring the acceleration signal.

[0039] Furthermore, for the two sensing structures of the fiber optic accelerometer for detecting acceleration signals within the plane of the structure, an optical fiber is placed perpendicular to the side of the central mass block in the fiber optic trench. For the sensing structure for detecting acceleration signals perpendicular to the plane of the structure, an optical fiber is placed perpendicular to the plane of the sensing structure and fixed by an external encapsulation structure. One end of the optical fiber forms a microcavity with the side of the central mass block, and the other end is connected to an optical fiber circulator for transmitting interference light signals to reconstruct the acceleration signal to be detected.

[0040] like Figure 2As shown, the first sensing component 1, the second sensing component 2, and the third sensing component 3 represent three sensing structures to detect triaxial acceleration signals. The acceleration signals detected by the first sensing component 1 and the second sensing component 2 are parallel to the plane of the sensing structure and their respective fiber optic slots, while the acceleration signals detected by the third sensing component 3 are perpendicular to the plane of the sensing structure and perpendicular to the central mass block.

[0041] Furthermore, the central mass block in each sensing component is located at the center of the silicon substrate, occupying most of the space of the entire sensing structure. This is beneficial for increasing the mass of the central mass block, thereby improving the energy conversion efficiency of the overall mechanical energy conversion structure.

[0042] Furthermore, the elastic cantilever beams on each side of the central mass block are symmetrical about the center of the sensing structure, and these elastic cantilever beams connect the central mass block and the sensor's outer frame. The elastic cantilever beam structure is designed as a multi-period folding cantilever beam with a gradually changing beam width. This gradually changing width design allows for a smaller stiffness coefficient within a given size, resulting in greater deformation when detecting acceleration signals and improving the sensor's acceleration signal detection sensitivity. Simultaneously, the multi-period folding elastic cantilever beam reduces the gap between the spring beams, increasing the equivalent deformation length of the sensing structure after receiving an acceleration signal. Theoretically, the more periods there are, the smaller the equivalent stiffness coefficient of the entire elastic cantilever beam will be, meaning the sensing structure will have a higher response sensitivity to acceleration signals. Therefore, this elastic cantilever beam structure design facilitates sensor miniaturization while ensuring high-sensitivity acceleration signal detection.

[0043] When the acceleration signal to be measured is applied to the sensing device, the outer frame of the sensor vibrates synchronously with the external vibration signal. Due to inertia, the central mass block will move relative to the outer frame of the sensor. Let its relative displacement be Δz. The mechanical sensitivity of the overall sensing structure can be expressed as follows:

[0044]

[0045] Where Q=Mω0 / C is the mechanical quality factor, ω0=(K / M)1 / 2 is the resonant angular frequency, damping ratio ξ=C / [2(MK)1 / 2], M is the mass of the central mass block, K is the equivalent elastic coefficient of the elastic cantilever beam, and C is the damping. The change in the distance between the central mass block and the outer frame of the sensor will bring about the stretching and compression of the elastic cantilever beam. At this time, the elastic cantilever beam structure with a smaller equivalent elastic coefficient K will not only constrain the displacement of the central mass block, but also bring about a larger relative displacement, thereby improving the mechanical sensitivity of the acceleration sensing device.

[0046] like Figure 3As shown, the present invention proposes an optical fiber accelerometer sensing system, comprising an optical fiber accelerometer sensing device, a laser, an optical fiber circulator, and an optical demodulation device; the laser is connected to a first interface of the optical fiber circulator, and the laser light generated by the laser is emitted through a second interface of the optical fiber circulator; the sensing device is connected to the second interface of the optical fiber circulator via an optical fiber, and is used to receive the emitted light from the second interface; the emitted light is output through the end face of the optical fiber and is reflected back into the optical fiber by the side of the central mass block, where it interferes; the interference light signal is emitted through a third port of the optical fiber circulator; the optical demodulation device is connected to the third interface of the optical fiber circulator, and is used to receive the interference light signal and extract the signal changes of the sensing device, thereby reconstructing the acceleration signal to be measured.

[0047] To further explain, the laser is connected to port 1 of the fiber optic circulator, and the incident light enters the sensing fiber of the sensing device from port 2. The end of the fiber is cut flat, and the optical microcavity formed by the fiber end face and the side of the mass block can be regarded as an optical interference microcavity. Since the reflectivity of the fiber end face is as low as about 4%, the interference can be approximated as two-beam interference. The light intensity of the optical signal obtained by two-beam interference can be expressed as:

[0048]

[0049] Where I1 and I2 represent the light intensities of the two beams reflected from the side of the central mass block, and δ is the phase difference between the two beams, which can be expressed as:

[0050] S = Zn * OPD

[0051] OPD represents the optical path difference between two reflected beams. When the sensing device receives an acceleration signal, the distance between the side of the central mass block and the end of the fiber optic sensing arm changes, resulting in a change in the optical path difference between the two reflected beams. This change in optical path difference leads to a phase change in the interference signal. The phase-modulated optical signal returns to port 2 of the fiber optic circulator through the fiber and then enters port 3. Port 3 of the fiber optic circulator is connected to an optical demodulation device, which receives the interference signal from port 2. The optical demodulation device extracts the phase change of the interference signal and reconstructs the acceleration signal to be measured.

[0052] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A fiber optic accelerometer, characterized in that, It includes an elastic cantilever beam (5), a sensor outer frame (6), and a first sensing component (1), a second sensing component (2), and a third sensing component (3) disposed within the sensor outer frame (6). The elastic cantilever beam (5) includes a U-shaped beam structure, wherein the diameter of the beam arm of the beam structure gradually increases along the direction of the opening end of the beam structure; A hollow section is provided between the beam arms, and the width of the hollow section gradually increases along the direction of the opening end of the beam structure. The beam arm of the beam structure is provided with outwardly extending connecting parts at both ends; Multiple beam structures are arranged in parallel and connected by the connecting part to form a multi-period folding structure; The first sensing component (1), the second sensing component (2) and the third sensing component (3) are each provided with a central mass block (4) and multiple elastic cantilever beams (5). The elastic cantilever beams (5) are disposed between the central mass block (4) and the sensor outer frame (6). The connecting part is used to connect the central mass block (4) and the sensor outer frame (6). The first sensing component (1) is used to detect acceleration signals parallel to the plane of the sensing device; The second sensing component (2) is used to detect acceleration signals parallel to the plane of the sensing device; The third sensing component (3) is used to detect acceleration signals perpendicular to the plane of the sensing device.

2. The fiber optic accelerometer sensor according to claim 1, characterized in that, The first sensing component (1) has two sets of elastic cantilever beams symmetrically arranged on both sides of the central mass block (4). The elastic cantilever beams are two beam structures arranged in parallel and connected by a connecting part to form a folded structure.

3. The fiber optic accelerometer sensor according to claim 2, characterized in that, The second sensing component (2) is provided with two sets of elastic cantilever beams symmetrically arranged on both sides of the central mass block (4). The elastic cantilever beams are two beam structures arranged in parallel and connected by a connecting part to form a folded structure.

4. The fiber optic accelerometer sensor according to claim 3, characterized in that, The third sensing component (3) is provided with four sets of elastic cantilever beams symmetrically arranged around the central mass block (4), each set including two elastic cantilever beams with open ends facing each other.

5. The fiber optic accelerometer sensor according to claim 4, characterized in that, The sensor outer frame (6) is provided with an optical fiber slot (7) for placing optical fibers; the optical fiber slot (7) is respectively arranged along the movement direction of the central mass block perpendicular to the first sensing component (1) and the second sensing component (2).

6. A fiber optic accelerometer sensing system, characterized in that, The fiber optic accelerometer as described in claim 5 further includes: a laser, a fiber optic circulator, and an optical demodulation device; The laser is connected to the first interface of the fiber optic circulator, and the laser generated by the laser is emitted through the second interface of the fiber optic circulator. The sensing device is connected to the second interface of the fiber optic circulator via an optical fiber to receive the outgoing light from the second interface. After the outgoing light is output through the end face of the optical fiber, it is reflected back into the optical fiber by the side of the central mass block and interferes. The interference light signal is emitted through the third port of the fiber optic circulator. The optical demodulation device is connected to the third interface of the fiber optic circulator to receive the interference light signal and extract the signal changes of the sensing device, thereby reconstructing the acceleration signal to be measured.

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