Sensor device and method for monitoring low-frequency vibration of ancient building structure

Abstract

The invention discloses a sensor device for monitoring low-frequency vibration of an ancient building structure. The sensor device comprises an external excitation receiver and a base, the external excitation receiver and the base are both hollow regular polyhedrons; the external excitation receiver is an anti-magnet, and the outer surface of each side of the external excitation receiver is coated with a layer of electret film; the base is a permanent magnet, and the outer surface of each side of the base is coated with a conductive layer; the external excitation receiver is suspended in the center of the interior of the base under the anti-magnetic effect of the external excitation receiver and the magnetic field effect of the base so as to form an anti-magnetic suspension system; the oppositely disposed electret film and conductive layer are connected by a monitoring circuit to form a capacitor-like structure. The invention further provides a method for monitoring the low-frequency vibration of the historic building structure. According to the invention, effective capture of low-frequency vibration is realized by adopting an anti-magnetic suspension technology, the structure is simple, the cost is low, the energy consumption is low, and non-intrusive deployment and lossless installation can be realized.

Description

Technical Field

[0001] The present invention relates to the technical field of building structure health monitoring. Specifically, it relates to a sensor device and method for low-frequency vibration monitoring of ancient building structures, and is particularly suitable for non-invasive real-time monitoring of low-frequency vibration signals caused by wind loads, seismic activities, and environmental excitations in historical buildings such as wooden structures and masonry structures. Background Art

[0002] As the core carrier of cultural heritage, the structural stability of ancient buildings is vulnerable to the influence of long-term environmental loads and sudden external forces. Research shows that low-frequency vibration (0.1 - 10 Hz) is the main inducement for progressive damages such as loosening of mortise and tenon joints and cracking of walls in ancient buildings. However, existing vibration monitoring technologies have deficiencies in aspects such as sensitivity in the low-frequency band, deployment methods, and environmental adaptability. Specifically, they are manifested as insufficient low-frequency monitoring performance, deployment methods that damage the building body, environmental adaptability, and energy consumption problems: (1) Insufficient low-frequency monitoring performance: The effective frequency response ranges of traditional piezoelectric accelerometers and capacitive sensors mostly concentrate in the high-frequency band (>10 Hz), and there are problems such as low signal-to-noise ratio and serious baseline drift in low-frequency vibration detection. Although some fiber Bragg grating sensors can cover the low-frequency band, their signal demodulation systems are complex and costly, making it difficult to meet the large-scale layout requirements of ancient building groups.

[0003] (2) Deployment methods that damage the building body: The protection of ancient buildings requires that the installation process of monitoring equipment strictly follows the principle of "minimum intervention". In existing technologies, sensors often need to be fixed to load-bearing components such as beams and columns by drilling, gluing, or welding, which not only damages the original structure of the building but also has the risk of vibration transmission distortion due to changes in contact surface stiffness. Although there is non-contact laser vibration measurement technology, it has strict requirements for the cleanliness of the measurement path and cannot work stably on complex geometric surfaces, so its practicability is limited.

[0004] (3) Environmental adaptability and energy consumption problems: Ancient buildings are mostly distributed in remote areas, and the monitoring system needs to have the ability of long-term maintenance-free operation. Existing wireless vibration sensors often rely on high sampling rate modes to operate, resulting in insufficient battery life; while the scheme of using energy harvesting technology to supplement power supply has extremely low energy conversion efficiency (<5%) in low-frequency vibration scenarios.

[0005] Although there have been studies attempting to improve the low-frequency performance of sensors by optimizing MEMS processes, or using flexible substrates to reduce installation impacts, the coordinated optimization of high-sensitivity low-frequency detection, non-invasive deployment, and low-power operation has not been achieved yet. Summary of the Invention

[0006] The object of the present invention is to address the deficiencies of the prior art, and thus provide a sensor device and method for low-frequency vibration monitoring of ancient building structures. The present invention uses anti-magnetic levitation technology to effectively capture vibrations at low frequencies, has the ability to monitor low-frequency vibrations with high precision, high sensitivity, and high signal-to-noise ratio, has a simple structure, low cost, and low energy consumption, and can achieve non-invasive deployment and non-destructive installation.

[0007] To achieve the above object, the technical solution adopted by the present invention is: A sensor device for low-frequency vibration monitoring of ancient building structures, comprising an external excitation receiver and a base; both the external excitation receiver and the base are hollow regular polyhedrons, the external excitation receiver and the base have the same shape, and the size of the external excitation receiver is smaller than that of the base; the external excitation receiver is an anti-magnet, and a layer of electret film is coated on each outer surface of the external excitation receiver; the base is a permanent magnet, and a layer of conductive layer is wrapped on each outer surface of the base; the external excitation receiver is suspended at the central position inside the base under its own anti-magnetic effect and the magnetic field of the base to form an anti-magnetic levitation system; the relatively arranged electret film and the conductive layer are connected through a monitoring circuit to form a structure similar to a capacitor.

[0008] Based on the above, the external excitation receiver includes a first housing made of an insulating material, the first housing is a hollow regular polyhedron, and a first assembly hole is provided on each side surface of the first housing to form a hollow structure. An anti-magnetic block is press-fitted in each of the first assembly holes. The anti-magnetic block includes an anti-magnetic matrix layer, and a layer of the electret film is coated on the outer surface of the anti-magnetic matrix layer.

[0009] Based on the above, the material of the anti-magnetic matrix layer is highly oriented pyrolytic graphite.

[0010] Based on the above, the base includes a second housing made of an insulating material, the second housing is a hollow regular polyhedron, and a second assembly hole is provided on each side surface of the second housing to form a hollow structure. A permanent magnet block is press-fitted in each of the second assembly holes. The permanent magnet block includes a strong permanent magnet layer, and a layer of the conductive layer is wrapped on the outer surface of the strong permanent magnet layer.

[0011] Based on the above, the material of the strong permanent magnet layer is neodymium iron boron.

[0012] Based on the above, the material of the conductive layer is a metal conductive material.

[0013] A method for low-frequency vibration monitoring of ancient building structures, using the sensor device for low-frequency vibration monitoring of ancient building structures as described above for monitoring, specifically including the following steps: (1) Fix the sensor device on the main body of the ancient building structure by using magnetic attraction or flexible straps and combining with lightweight packaging technology; (2) When the sensor device is subjected to external low-frequency vibration during operation, the external excitation receiver will respond to the external low-frequency vibration and generate vibration, which will drive the synchronous vibration of each electret film. The capacitance between the relatively arranged electret film and the conductive layer will change, generating electrical signals related to the external low-frequency vibration in each monitoring circuit; (3) By coupling and analyzing each electrical signal, data information related to the external low-frequency vibration can be accurately obtained, realizing effective monitoring of the external low-frequency vibration.

[0014] The present invention has prominent substantial features and remarkable progress compared with the prior art. Specifically, compared with the prior art, the present invention has the following technical advantages: (1) High-precision monitoring ability and high sensitivity to low-frequency vibration: The present invention designs the sensor device as a diamagnetic levitation system by using the diamagnetic levitation principle. The diamagnetic levitation system has the characteristics of no friction and no damping, so that the sensor device has extremely high sensitivity in low-frequency vibration monitoring and can stably detect ultra-low frequency vibration signals of 0.1 - 10 Hz, accurately capturing early hidden dangers such as loosening of tenon-mortise joints and foundation settlement of ancient buildings.

[0015] (2) High signal-to-noise ratio: The present invention converts weak low-frequency vibration signals into stronger electrical signals through the interaction between the electret film and the conductive layer, greatly improving the signal-to-noise ratio; compared with traditional piezoelectric sensors, the sensor device can provide clearer and more reliable vibration signals at low frequencies, reducing the complexity and cost of subsequent signal processing.

[0016] (3) Simple structure and low cost: The sensor device uses common highly oriented pyrolytic graphite and neodymium iron boron magnets to construct the core diamagnetic levitation structure, without the need for complex and expensive multi-component integration.

[0017] (4) The sensor device is designed based on the diamagnetic levitation principle, without external power supply, low energy consumption, with long-term maintenance-free ability and strong environmental adaptability.

[0018] (5) Non-invasive deployment and non-destructive installation: The sensor device uses a magnetic attraction or flexible strap fixing method without glue and drilling, combined with lightweight packaging technology, without damaging the main body structure of the ancient building, meeting the "minimum intervention" principle of cultural heritage protection. Description of the Drawings

[0019] Figure 1 is an exploded view of the structure of the sensor device for low-frequency vibration monitoring of ancient building structures of the present invention.

[0020] Figure 2It is a schematic structural diagram of the external excitation receiver of the present invention.

[0021] Figure 3 It is a schematic diagram of the external excitation receiver of the present invention suspended at the center inside the base.

[0022] Figure 4 It is a schematic structural diagram of the permanent magnet block of the present invention.

[0023] Figure 5 It is Figure 4 The partial enlarged view at position A in

[0024] Figure 6 It is a schematic structural diagram of the diamagnetic block of the present invention.

[0025] Figure 7 It is Figure 6 The partial enlarged view at position B in

[0026] In the figure: 1. External excitation receiver; 2. Base; 3. Electret film; 4. First housing; 5. Diamagnetic block; 6. Conductive layer; 7. Second housing; 8. Permanent magnet block; 9. Diamagnetic matrix layer; 10. Strong permanent magnet layer. Specific embodiments

[0027] Next, through specific embodiments, the technical solutions of the present invention will be further described in detail.

[0028] As Figures 1-7 shown, a sensor device for monitoring low-frequency vibrations of ancient building structures includes an external excitation receiver 1 and a base 2; both the external excitation receiver 1 and the base 2 are hollow regular tetrahedrons, the external excitation receiver 1 and the base 2 have the same shape, and the size of the external excitation receiver 1 is smaller than that of the base 2.

[0029] Among them, the external excitation receiver 1 is a diamagnetic body, and each outer surface of the external excitation receiver 1 is coated with a layer of electret film 3. Specifically: the external excitation receiver 1 includes a first housing 4 made of an insulating material, the first housing 4 is a hollow regular tetrahedron, and each side surface of the first housing 4 is provided with a first assembly hole to form a hollow structure. A diamagnetic block 5 is press-fitted in each of the first assembly holes. The diamagnetic block 5 includes a diamagnetic matrix layer 9, the material of the diamagnetic matrix layer 9 is highly oriented pyrolytic graphite, and the outer surface of the diamagnetic matrix layer 9 is coated with a layer of the electret film 3.

[0030] The base 2 is a permanent magnet, and each outer surface of the base 2 is wrapped with a layer of conductive layer 6. Specifically: the base 2 includes a second housing 7 made of insulating material. The second housing 7 is a hollow regular tetrahedron, and each side surface of the second housing 7 is provided with a second assembly hole to form a hollow structure. A permanent magnet block 8 is press-fitted in each of the second assembly holes. The permanent magnet block 8 includes a high-strength permanent magnet layer 10. The material of the high-strength permanent magnet layer 10 is neodymium iron boron. The outer surface of the high-strength permanent magnet layer 10 is wrapped with a layer of the conductive layer 6. The material of the conductive layer 6 is a metal conductive material, preferably copper.

[0031] The external excitation receiver 1 is suspended at the central position inside the base 2 under its own diamagnetic effect and the magnetic field of the base 2 to form a diamagnetic suspension system; the relatively arranged electret film 3 and the conductive layer 6 are connected through a monitoring circuit to form a structure similar to a capacitor.

[0032] Diamagnetic suspension is a suspension phenomenon achieved by the special property of the diamagnetism of the highly oriented pyrolytic graphite material used in the external excitation receiver 1 in a magnetic field.

[0033] Specifically, when highly oriented pyrolytic graphite is in a magnetic field environment, according to the principle of electromagnetic induction, highly oriented pyrolytic graphite will generate an induced magnetic field opposite to the direction of this magnetic field, and then exhibit a weak repulsive characteristic to this magnetic field. From a microscopic perspective, this characteristic stems from mechanisms such as the orbital motion of electrons inside the material. When a magnetic field is applied to highly oriented pyrolytic graphite, it will cause a change in the motion state of its internal electrons. According to the microscopic manifestation form of Lenz's law, electrons will generate a reverse magnetic field that resists the change of the magnetic field, so that the overall highly oriented pyrolytic graphite exhibits a diamagnetic effect.

[0034] Neodymium iron boron magnets have the ability to provide a stable and appropriately strong magnetic field environment, while highly oriented pyrolytic graphite has significant diamagnetism. Its relevant parameters such as the diamagnetic coefficient can ensure that a repulsive force sufficient to overcome external forces such as gravity is generated in this specific magnetic field environment. Finally, the external excitation receiver 1 whose main body is made of highly oriented pyrolytic graphite material can achieve a suspended state. Based on this diamagnetic suspension method, the entire diamagnetic suspension system has a series of excellent working characteristics such as frictionless, low damping, and weak stiffness due to the suspension of the object. These characteristics lay a good foundation for the application of the sensor in aspects such as low-frequency signal detection.

[0035] A method for monitoring low-frequency vibration of ancient building structures uses the sensor device for monitoring low-frequency vibration of ancient building structures as described above. Specifically, it includes the following steps: (1) The sensor device is fixed on the main body of the ancient building structure by magnetic attraction or flexible straps in combination with lightweight packaging technology, so that the main body structure of the ancient building does not need to be damaged, which conforms to the "minimum intervention" principle of cultural heritage protection and realizes non-invasive deployment and non-destructive installation. (2) When the sensor device is subjected to external low-frequency vibration during operation, the external excitation receiver 1 will respond to the external low-frequency vibration and generate vibration, which will drive the electret films 3 to vibrate synchronously. The capacitance between the relatively arranged electret films 3 and the conductive layer 6 will change, generating electrical signals related to the external low-frequency vibration in each monitoring circuit. (3) By coupling and analyzing each electrical signal, data information related to the external low-frequency vibration can be accurately obtained, realizing effective monitoring of the external low-frequency vibration.

[0036] Specifically, during the actual operation of the sensor device, when the sensor device is subjected to external excitation (external low-frequency vibration), the external excitation receiver 1 suspended at the center inside the base 2 will vibrate due to the external excitation. Since each outer surface of the external excitation receiver 1 is coated with an electret film 3, the vibration of the external excitation receiver 1 will drive the electret films 3 to vibrate synchronously.

[0037] In this sensor, the electret film 3 on the outer surface of the external excitation receiver 1 and the conductive layer 6 on the outer surface of the base 2 exactly form a structure similar to a capacitor. When the electret film 3 vibrates synchronously with the external excitation receiver 1, the distance between the relatively arranged electret film 3 and the conductive layer 6 will change slightly. According to the capacitance calculation formula: C = εS / d, where C is the capacitance, ε is the dielectric constant, S is the equivalent area of the electrode plate, d is the distance between the electrode plates, and the change of the distance d causes the capacitance C to change.

[0038] According to the capacitance definition formula: C = Q / U, where C is the capacitance, Q is the charge carried by the two electrode plates, and U is the voltage between the two electrode plates.

[0039] Since the electret surface carries fixed charges, which is equivalent to Q remaining unchanged, when the capacitance changes, the voltage U between the two electrode plates will change, and then the voltage change is collected through the monitoring circuit. This voltage change is the electrical signal related to the external low-frequency vibration, and its amplitude, frequency and other characteristics correspond to the amplitude, frequency and other parameters of the external low-frequency vibration.

[0040] The sensor device adopts a regular tetrahedron structure. When its four faces face the same external low-frequency vibration, each can output an electrical signal. Subsequently, by coupling and analyzing these four electrical signals, data information related to the external low-frequency vibration can be accurately obtained, realizing effective detection of the external low-frequency vibration and providing accurate data support for various subsequent application scenarios.

[0041] In other embodiments, the external excitation receiver 1 and the base 2 may also be hollow regular hexahedrons, regular octahedrons, etc., and the design principles are the same as those of this embodiment.

[0042] 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 the preferred embodiments, those of ordinary skill in the art should understand that: it is still possible to modify the specific implementation manners of the present invention or perform equivalent replacements for some technical features; without departing from the spirit of the technical solutions of the present invention, they should all be covered by the scope of the technical solutions claimed in the present invention.

Claims

1. A sensor device for low-frequency vibration monitoring of ancient building structures, characterized in that: It comprises an external excitation receiver and a base; the external excitation receiver and the base are both hollow regular polyhedrons, the external excitation receiver and the base have the same shape, and the size of the external excitation receiver is smaller than the base; the external excitation receiver is a diamagnetic body, and each side of the outer surface of the external excitation receiver is coated with an electret film; the base is a permanent magnet, and each side of the outer surface of the base is wrapped with a conductive layer; the external excitation receiver is suspended at the inner center position of the base under the diamagnetic effect of itself and the magnetic field of the base to form a diamagnetic suspension system; The electret film and the conductive layer disposed opposite to each other are connected via a monitoring circuit to form a capacitor-like structure.

2. The sensor device for low-frequency vibration monitoring of ancient building structures according to claim 1 is characterized in that: The external excitation receiver includes a first shell made of insulating material, the first shell is a hollow regular polyhedron, each side of the first shell is provided with a first assembly hole to form a hollow structure, and each first assembly hole is interference fit with an anti-magnetic block, the anti-magnetic block includes an anti-magnetic matrix layer, and the outer surface of the anti-magnetic matrix layer is coated with a layer of the electret film.

3. The sensor device for low-frequency vibration monitoring of ancient building structures according to claim 2 is characterized in that: The material of the antimagnetic matrix layer is highly oriented pyrolytic graphite.

4. The sensor device for low-frequency vibration monitoring of ancient building structures according to claim 1 is characterized in that: The base includes a second shell made of insulating material, the second shell is a hollow regular polyhedron, each side of the second shell is provided with a second assembly hole to form a hollow structure, each of the second assembly holes is interference fit with a permanent magnet block, the permanent magnet block includes a strong permanent magnet layer, and the outer surface of the strong permanent magnet layer is wrapped with a layer of the conductive layer.

5. The sensor device for low-frequency vibration monitoring of ancient building structures according to claim 4 is characterized in that: The material of the strong permanent magnet layer is neodymium iron boron.

6. The sensor device for low-frequency vibration monitoring of ancient building structures according to claim 4 is characterized in that: The conductive layer is made of a metallic conductive material.

7. A method for low-frequency vibration monitoring of ancient building structures, characterized in that: The monitoring is performed using the sensor device for low-frequency vibration monitoring of ancient building structures as described in any one of claims 1 to 6, specifically comprising the following steps: (1) The sensor device is fixed on the ancient building structure by using magnetic attraction or flexible straps combined with lightweight packaging technology; (2) When the sensor device is subjected to external low-frequency vibration during operation, the external excitation receiving body will vibrate in response to the external low-frequency vibration, thereby driving each of the electret films to vibrate synchronously, and the capacitance between the relatively arranged electret films and the conductive layer will change, so that each of the monitoring circuits will generate an electrical signal related to the external low-frequency vibration; (3) By coupling and analyzing each electrical signal, data information related to external low-frequency vibration can be accurately obtained, thereby achieving effective monitoring of external low-frequency vibration.

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