Method for improving directivity of ultrasonic longitudinal wave signal propagation, pre-tightening force sensor and method for determining diameter of electrode layer

Abstract

The invention belongs to the technical field of film sensors, and particularly relates to a method for improving the directivity of ultrasonic longitudinal wave signal propagation, a pre-tightening force sensor and a method for determining the diameter of an electrode layer, and the method for improving the directivity of ultrasonic longitudinal wave signal propagation is applied to the pre-tightening force sensor. The pretightening force sensor comprises a bolt and a film sensor, the bolt comprises a head and a screw with threads, the film sensor comprises piezoelectric layers and electrode layers, and the piezoelectric layers and the electrode layers grow on the top end face of the head in situ layer by layer from inside to outside. And the ultrasonic longitudinal wave signal propagation directivity is improved by enabling the diameter of the ultrasonic longitudinal wave to be matched with the nominal diameter of the bolt. According to the invention, the influence of the size difference between the bolt head and the screw of the pre-tightening force sensor and the diameter of the electrode layer on the pre-tightening force detection precision can be solved, and the accurate measurement of the pre-tightening force is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of thin film sensors, and in particular relates to a method for improving the directivity of ultrasonic longitudinal wave signal propagation, a preload force sensor, and a method for determining the diameter of an electrode layer. Background Art

[0002] The safety of structural connections in extreme environments such as aerospace, oil exploration, and nuclear power is a key factor in the reliable operation of important equipment and facilities, and is also a pain point and difficulty in the industry. Pre-tightening force testing of bolts in important parts can ensure the reliable operation of the structure and reduce the occurrence of engineering accidents.

[0003] At present, the commonly used bolt preload monitoring methods mainly include torque method, sensor implantation method, ultrasonic method, etc., but there are problems such as large errors and damage to the bolt's own stress. The measurement of bolt preload based on the acoustic elastic method has the advantages of real-time, fast and accurate measurement. By recording the propagation time of the ultrasonic longitudinal wave signal in the bolt and calibrating the preload, the real-time preload of the bolt can be measured. Compared with the ceramic patch method, the method of growing the sensor in situ on the bolt end face not only avoids the high failure rate and signal attenuation caused by the coupling layer between the piezoelectric ceramic and the bolt end face, but also has higher detection accuracy.

[0004] Due to the size difference between the bolt head (dispersing the tightening force) and the screw (bearing the load), the ultrasonic echo signal will be reflected and refracted, resulting in signal attenuation and interference, affecting the propagation of the ultrasonic longitudinal wave signal. In addition, the size of the sensor electrode layer directly affects the beam width of the signal. Therefore, how to optimize the electrode layer size of the preload sensor can achieve accurate measurement of the preload force.

[0005] In view of this, the present invention is proposed. Summary of the invention

[0006] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a method for improving the directionality of ultrasonic longitudinal wave signal propagation, a preload sensor and a method for determining the electrode layer diameter. The diameter of the electrode layer of the preload sensor at the top of the bolt head is optimized to solve the size difference between the bolt head and the screw of the preload sensor and the influence of the electrode layer size on the bolt preload detection accuracy.

[0007] In order to solve the above technical problems, the first aspect of the present invention proposes a method for improving the directivity of ultrasonic longitudinal wave signal propagation, which is applied to a preload sensor. The preload sensor includes a bolt and a thin film sensor. The bolt includes a head and a screw with threads. The thin film sensor includes a piezoelectric layer and an electrode layer. The piezoelectric layer and the electrode layer are in-situ grown layer by layer from the inside to the outside on the top surface of the head. The method includes:

[0008] The directivity of ultrasonic longitudinal wave signal propagation is improved by optimizing the diameter of the electrode layer on the top end surface of the head and making it match the nominal diameter of the bolt.

[0009] Based on the method of the first aspect of the present invention, further optionally, the electrode layer includes an inner electrode and an outer electrode, and optimizing the diameter of the electrode layer on the top surface of the head is to optimize the diameter of the inner electrode on the top surface of the head.

[0010] On the basis of the method of the first aspect of the present invention, further optionally, the method comprises:

[0011] The diameter of the inner electrode at the top end surface of the head is designed to be smaller than or equal to the nominal diameter of the bolt and larger than or equal to a minimum threshold.

[0012] On the basis of the method of the first aspect of the present invention, further optionally, different nominal diameter ranges of the bolts correspond to different electrode layer diameters, and a nominal diameter range with a larger nominal diameter corresponds to a larger electrode layer diameter.

[0013] The second aspect of the present invention provides a preload force sensor, which adopts the method of the first aspect of the present invention to improve the directivity of ultrasonic longitudinal wave signal propagation;

[0014] The preload force sensor includes a bolt and a thin film sensor, the bolt includes a head and a screw with a thread, the thin film sensor includes a piezoelectric layer and an electrode layer, the piezoelectric layer and the electrode layer are in-situ grown layer by layer from the inside to the outside on the top surface of the head, the electrode layer includes an inner electrode and an outer electrode, and the diameter of the inner electrode on the top surface of the head is designed to be less than or equal to the nominal diameter of the bolt and greater than or equal to a minimum threshold.

[0015] Based on the method of the second aspect of the present invention, further optionally, the electrode layer includes an inner electrode, and the diameter of the electrode layer at the top end surface of the head is the diameter of the inner electrode;

[0016] Among them: the inner electrode diameter corresponding to the preload force sensor with a nominal bolt diameter of 4mm to 20mm is 2mm to 4mm.

[0017] On the basis of the method of the second aspect of the present invention, further optionally, the inner electrode diameter corresponding to the preload force sensor with a nominal bolt diameter of 8 mm is 4 mm.

[0018] The third aspect of the present invention provides a method for determining the diameter of an electrode layer of a preload sensor, the method being used to determine the diameter of the electrode layer of the preload sensor provided in the second aspect of the present invention on the top end surface of the head, the method comprising:

[0019] Select multiple bolts with different nominal diameters;

[0020] Generating piezoelectric layers and electrode layers respectively on the end faces of the heads of the plurality of bolts from the inside to the outside to form a plurality of preload sensors, wherein the electrode layers of the plurality of preload sensors have different diameters;

[0021] Under the state of applying the excitation voltage, the ultrasonic echo signal strengths of the plurality of preload force sensors are determined, and the electrode layer diameter corresponding to the preload force sensor with the largest ultrasonic echo signal strength is the required electrode layer diameter.

[0022] On the basis of the method of the third aspect of the present invention, further optionally, the ultrasonic echo signal strengths of the plurality of preload force sensors are determined in the following manner:

[0023] Setting a fixed constraint on the lower surface of the head;

[0024] Performing time domain calculation after applying an excitation voltage signal to the electrode layer;

[0025] The excitation voltage satisfies:

[0026] Where: F(t) is the excitation voltage, f is the signal frequency, t is the signal propagation time, T is the signal period, and T=1 / f.

[0027] Based on the method of the third aspect of the present invention, further optionally, the bolt includes a screw rod, and the screw rods of the multiple bolts have the same length.

[0028] After adopting the above technical solution, the present invention has the following beneficial effects compared with the prior art:

[0029] The present application optimizes the diameter of the electrode layer of the preload sensor at the top of the bolt head, and the electrode layer diameter is adapted to the nominal diameter of the bolt, thereby reducing the attenuation and interference of the ultrasonic echo signal caused by reflection, refraction and other phenomena caused by the size difference between the bolt head and the screw, and reducing the influence of the electrode layer diameter on the signal beam width, thereby improving the directionality of ultrasonic longitudinal wave signal propagation. The ultrasonic echo signal intensity of the preload sensor when the excitation voltage is applied can reach the maximum intensity, thereby realizing accurate measurement of the bolt preload.

[0030] The specific implementation modes of the present invention are further described in detail below in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The accompanying drawings are part of the present invention and are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention, but do not constitute an improper limitation of the present invention. Obviously, the drawings described below are only some embodiments. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. In the accompanying drawings:

[0032] Figure 1 This is a comparison chart of the primary echo signals of the M8 preload force sensor with different inner electrode diameters.

[0033] Figure 2 This is a comparison chart of the center frequencies of the M8 preload force sensor with different inner electrode diameters.

[0034] Figure 3 This is a comparison chart of ultrasonic echo signals of M4~M20 preload force sensors with different inner electrode diameters.

[0035] Figure 4 The present invention is a flow chart for determining the electrode layer diameter of a preload sensor according to an embodiment of the present invention.

[0036] Figure 5 The present invention is a two-dimensional axisymmetric model for determining the diameter of the electrode layer of the preload sensor.

[0037] Among them: 1. bolt; 11. head; 12. screw; 2. thin film sensor; 21. piezoelectric layer; 22. electrode layer.

[0038] It should be noted that these drawings and textual descriptions are not intended to limit the conceptual scope of the present invention in any way, but are intended to illustrate the concept of the present invention for those skilled in the art by referring to specific embodiments. DETAILED DESCRIPTION

[0039] In the description of the present invention, it should be noted that the terms "inside", "outside", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0040] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "contacted", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0041] Embodiment 1

[0042] This embodiment proposes a method for improving the directivity of ultrasonic longitudinal wave signal propagation, which is applied to a preload sensor. The preload sensor includes a bolt and a thin film sensor. The bolt includes a head and a screw with a thread. The thin film sensor includes a piezoelectric layer and an electrode layer. The piezoelectric layer and the electrode layer are grown in situ on the top surface of the head layer by layer from the inside to the outside. The method includes: improving the directivity of ultrasonic longitudinal wave signal propagation by optimizing the diameter of the electrode layer on the top surface of the head and adapting it to the nominal diameter of the bolt.

[0043] This embodiment optimizes the electrode layer diameter and adapts the electrode layer diameter to the nominal diameter of the bolt, thereby reducing the attenuation and interference of the ultrasonic echo signal caused by reflection, refraction and other phenomena caused by the size difference between the bolt head and the screw, and reducing the influence of the electrode layer diameter on the signal beam width, thereby improving the directionality of ultrasonic longitudinal wave signal propagation. The ultrasonic echo signal intensity of the preload sensor when the excitation voltage is applied can reach the maximum intensity, thereby realizing accurate measurement of the bolt preload.

[0044] Further optionally, the electrode layer includes an inner electrode and an outer electrode, and optimizing the diameter of the electrode layer at the top end surface of the head is optimizing the diameter of the inner electrode at the top end surface of the head. Since the effective area of ​​the electrode layer that really works is the inner electrode, the diameter of the inner electrode of the electrode layer can be directly optimized. In other achievable methods, the diameter of the entire electrode layer composed of the inner electrode and the outer electrode of the electrode layer can also be optimized.

[0045] Further optionally, the method includes: designing the diameter of the inner electrode at the top end of the head to be less than or equal to the nominal diameter of the bolt and greater than or equal to a minimum threshold. The minimum threshold is the minimum diameter of the inner electrode that can be grown in situ at the top end of the bolt head. The ultrasonic echo signal intensity of the inner electrode within this range is large, and the directionality of ultrasonic longitudinal wave signal propagation is good.

[0046] Further optionally, different nominal diameter ranges of the bolt correspond to different inner electrode diameters, and the larger the nominal diameter range, the larger the inner electrode diameter corresponding to the nominal diameter range. In practical applications, a mapping table of nominal diameter range and inner electrode diameter can be prepared, and the inner electrode diameter suitable for the bolt of the required specification can be determined by referring to the mapping table according to the bolt specification to be used. By simply generating an electrode layer on the top surface of the required bolt head according to the determined inner electrode diameter, a preload sensor that can improve the directionality of ultrasonic longitudinal wave signal propagation and accurately measure the bolt preload can be obtained.

[0047] Among them, according to the mapping table of nominal diameter range and inner electrode diameter, different preload sensors with bolt nominal diameters within the same nominal diameter range can use the same inner electrode diameter, and the inner electrode diameter does not change with the change of the bolt nominal diameter, which can effectively avoid the change of the inner electrode size affecting the signal beam width and achieve accurate measurement of the bolt preload. Preload sensors with bolt nominal diameters within different nominal diameter ranges use different inner electrode diameters, and the larger the nominal diameter, the larger the inner electrode diameter corresponding to the nominal diameter range, so as to adapt to the change in size between the bolt head and the screw, and reduce the size difference between the bolt head and the screw and the influence of the inner electrode diameter on the transmission of ultrasonic longitudinal wave signals.

[0048] Embodiment 2

[0049] This embodiment proposes a preload force sensor, which adopts the method proposed in the first embodiment to improve the directivity of ultrasonic longitudinal wave signal propagation.

[0050] Wherein: the preload force sensor includes a bolt and a thin film sensor, the bolt includes a head and a screw with threads, the thin film sensor includes a piezoelectric layer and an electrode layer, and the piezoelectric layer and the electrode layer are in-situ grown layer by layer from the inside to the outside on the top surface of the head.

[0051] Wherein: the piezoelectric layer and the electrode layer are deposited layer by layer on the end face of the bolt head by physical vapor deposition (PVD), chemical vapor deposition (CVD), sputtering, evaporation or electroplating. The material of the bolt includes at least one of carbon steel, stainless steel, titanium alloy and aluminum alloy, the material of the piezoelectric layer includes at least one of AlN (aluminum nitride), ZnO (zinc oxide) PZT (lead zirconate titanate) and LiNbO3 (lithium niobate), and the material of the electrode layer is at least one of Ag (silver), Mo (molybdenum), Ti (titanium) and Al (aluminum). The thickness of the piezoelectric layer is preferably 0.1μm-30μm, and the thickness of the electrode layer is preferably 0.1μm-50μm.

[0052] In a preferred embodiment, a transition layer is formed between the piezoelectric layer and the end face of the bolt head, and the transition layer has the performance of reducing the contact interface stress between the piezoelectric layer and the bolt. An insulating protective layer is also provided between the piezoelectric layer and the electrode layer, and the insulating protective layer does not undergo structural transformation at the working temperature, which can reduce the influence of the external environment on the piezoelectric layer and play the role of electrical insulation isolation between the piezoelectric layer and the electrode layer.

[0053] Further optionally, the electrode layer includes an outer electrode and an inner electrode, the outer electrode is in a ring shape, the inner electrode is in a circular shape, and the inner electrode is located in the inner ring of the outer electrode. Since the effective area of ​​the electrode layer that really works is the inner electrode, and the diameter of the inner electrode at the top surface of the bolt head corresponds to the nominal diameter of the bolt, and is designed to be less than or equal to the nominal diameter of the bolt and greater than or equal to the minimum threshold, wherein the minimum threshold is the minimum diameter at which the inner electrode can grow in situ at the top of the bolt head. Within this range, the inner electrode can effectively reduce the size difference between the bolt head and the screw, and the inner electrode size has little effect on the intensity of the ultrasonic echo signal. The ultrasonic echo signal has a high intensity, and the ultrasonic longitudinal wave signal has good directionality, which can effectively improve the accuracy of bolt preload detection.

[0054] In one example, the inner electrode diameter of the preload sensor corresponding to the bolt with a nominal diameter of 4 mm to 20 mm is 2 mm to 4 mm, and the ultrasonic echo signal strength of the preload sensor under the state of applying the excitation voltage is at the maximum strength, which can accurately detect the preload force of the bolt. For example, the inner electrode diameter of the preload sensor corresponding to the bolt with a nominal diameter of 8 mm is 4 mm.

[0055] Reference Figure 1 The bolts shown have a nominal diameter of 8 mm, and the inner electrode diameters of the top surface of the bolt head are 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, and 7 mm, respectively. Figure 1 It can be seen that as the inner electrode diameter increases, the ultrasonic echo signal intensity first increases and then decreases. When the inner electrode diameter is 4 mm, the ultrasonic echo signal intensity is the largest.

[0056] Reference Figure 2 The center frequency comparison diagram of multiple preload force sensors is shown in Figure 1. The nominal diameter of the bolt is 8 mm, and the inner electrode diameter of the top surface of the bolt head is 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, and 7 mm respectively. Figure 2 It can be seen that as the diameter of the inner electrode increases, the center frequency gradually decreases. The ultrasonic propagation speed c is related to the medium. From λ=c / f, it can be seen that as the frequency f decreases, the wavelength λ will increase, thereby enhancing the penetration ability of the ultrasonic echo signal. However, when the inner electrode diameter is greater than 4mm, the intensity value of the center frequency decreases. It can be seen that the ultrasonic echo signal intensity is the largest when the inner electrode diameter corresponding to the preload sensor with a nominal bolt diameter of 8mm is 4mm, which can accurately detect the bolt preload.

[0057] Reference Figure 3 The comparison chart of ultrasonic echo signals of preload force sensors with different inner electrode diameters for bolts with nominal diameters of 4 mm to 20 mm is shown in the figure. Figure 3It can be seen that when the inner electrode diameter is 2mm~4mm, the intensity of the ultrasonic echo signal is the highest, and the bolt size has little effect on the intensity of the ultrasonic signal. Generally speaking, when the inner electrode diameter of the preload sensor is larger, the directivity of the ultrasonic echo signal is better, so the reflection of the bolt head will be reduced. However, under the premise that the voltage received by the inner electrode remains unchanged, as the inner electrode diameter increases, the voltage acting on the piezoelectric layer per unit area decreases, thereby reducing the conversion of electrical energy / mechanical energy. The inner electrode diameter corresponding to the preload sensor with the largest ultrasonic echo intensity does not change significantly with the bolt size. Therefore, when the inner electrode diameter corresponding to the preload sensor with a nominal bolt diameter of 4mm~20mm is 2mm~4mm, the ultrasonic echo intensity is the largest, and the bolt preload can be accurately detected.

[0058] The following are specific examples of the inner electrode diameters of several preload force sensors corresponding to the nominal diameters:

[0059] Example 1: The inner electrode diameter of the preload force sensor with a bolt nominal diameter of 4 mm is 2 mm-3 mm, and the optimal value is 2 mm;

[0060] Example 2: The inner electrode diameter of the preload sensor with a bolt nominal diameter of 6 mm is 2 mm-3 mm, and the optimal value is 2 mm;

[0061] Example 3: The inner electrode diameter of the preload force sensor with a bolt nominal diameter of 8 mm is 2 mm-4 mm, and the optimal diameter is 4 mm;

[0062] Example 4: The inner electrode diameter of the preload force sensor with a bolt nominal diameter of 12 mm is 2 mm-3 mm, and the optimal value is 2 mm;

[0063] Example 5: The inner electrode diameter of the preload force sensor with a bolt nominal diameter of 14 mm is 2 mm-3 mm, and the optimal diameter is 3 mm;

[0064] Example 6: The inner electrode diameter of the preload force sensor with a bolt nominal diameter of 16 mm is 2 mm-3 mm, and the optimal value is 2 mm;

[0065] Example 7: The inner electrode diameter of the preload force sensor with a bolt nominal diameter of 18 mm is 2 mm-3 mm, and the optimal diameter is 3 mm;

[0066] Example 8: The inner electrode diameter of the preload force sensor with a bolt nominal diameter of 20 mm is 2 mm;

[0067] Embodiment 3

[0068] Combination Figure 4 The flowchart shown and Figure 5The two-dimensional axisymmetric model for determining the diameter of the electrode layer of the preload sensor is shown. This embodiment proposes a method for determining the diameter of the electrode layer of the preload sensor. The method of this embodiment is used to determine the diameter of the electrode layer of the preload sensor proposed in Example 2 on the top surface of the bolt head. The method includes the following steps:

[0069] Step 1: Select multiple bolts with different nominal diameters;

[0070] Step 2: generating piezoelectric layers 21 and electrode layers 22 respectively on the end faces of the heads of the plurality of bolts from the inside to the outside, so as to form a plurality of preload force sensors, wherein the diameters of the electrode layers 22 of the plurality of preload force sensors are different;

[0071] Step three: Under the state of applying the excitation voltage, determine the ultrasonic echo signal strengths of the plurality of preload sensors, and the diameter of the electrode layer 22 corresponding to the preload sensor with the largest ultrasonic echo signal strength is the required diameter of the electrode layer 22 .

[0072] Specifically, the screw rods of the selected multiple bolts are the same length to ignore the attenuation of the ultrasonic signal intensity over distance. Exemplarily, the screw rods of the selected multiple bolts are all 35 mm. Without considering the influence of the thread on the sound wave, the remaining dimensions of the bolt refer to the standard "GB / T 5783-2016 Fully Threaded Hexagonal Head Bolt". Then, the piezoelectric layer 21 and the electrode layer 22 are generated layer by layer on the top surface of the head of each bolt, and the diameters of the electrode layers 22 of different bolts are different, thereby obtaining a preload force sensor with different diameters of the electrode layer 22. Preferably, the different diameters of the electrode layers 22 of different bolts are specifically different inner electrode diameters. After placing annular masks of different diameters on the upper end surfaces of the piezoelectric layers 21 of different bolts, inner electrodes of different diameters are prepared, thereby achieving different diameters of the electrode layers 22.

[0073] Reference Figure 5 A two-dimensional axisymmetric model for determining the diameter of the preload sensor electrode layer 22, where the screw size L is 35 mm. Figure 5 A plurality of preload force sensors with different electrode layer 22 diameters are prepared according to the model, and the ultrasonic echo signal strength is determined when the excitation voltage is applied to the plurality of preload force sensors. The diameter of the electrode layer 22 at which the ultrasonic echo signal strength reaches the maximum intensity is the required diameter of the electrode layer 22.

[0074] Further optionally, the ultrasonic echo signal strengths of the plurality of preload sensors are determined in the following manner: a fixed constraint is set on the lower surface of the head, and a time domain calculation is performed after an excitation voltage is applied to the electrode layer 22 .

[0075] Specifically, refer to Figure 5The two-dimensional axisymmetric model is fixed with the lower surface of the head 11 of the bolt 1 being fixed. At this time, the remaining boundaries of the head 11 of the bolt 1 are low-reflection boundaries to simulate the preload sensor in the installed state (the lower surface of the bolt needs to be in direct contact with the workpiece). Only the propagation of the ultrasonic signal in the longitudinal direction of the preload sensor needs to be considered to ensure the accuracy of the ultrasonic echo signal detection result. Then, an excitation voltage signal is applied to the electrode layer 22, and the excitation voltage satisfies:

[0076]

[0077] Where: F(t) is the excitation voltage, f is the signal frequency, t is the signal propagation time, T is the signal period, and T=1 / f.

[0078] Finally, time domain calculation is performed, and the finite element method is used to calculate the ultrasonic echo signal strength of the preload sensor with different electrode layer 22 diameters. The diameter of the electrode layer 22 corresponding to the preload sensor with the strongest ultrasonic echo signal is the required diameter of the electrode layer 22, and is also the optimal diameter of the electrode layer 22 corresponding to the bolt of this specification.

[0079] In general, this embodiment optimizes the diameter of the electrode layer on the top surface of the bolt head and adapts it to the nominal diameter of the bolt, thereby obtaining a preload sensor that can accurately measure the bolt preload. The size difference between the bolt head and the screw has little effect on the ultrasonic signal strength. The ultrasonic echo signal strength of the preload sensor when the excitation voltage is applied can reach the maximum intensity, which can solve the effect of the size difference between the bolt head and the screw of the preload sensor and the size of the electrode layer on the preload detection accuracy, thereby achieving accurate measurement of the bolt preload.

[0080] The above is only a preferred embodiment of the present invention, and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment, it is not used to limit the present invention. Any technician familiar with this patent can make some changes or modify the technical contents suggested above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the solution of the present invention.

Claims

1. A method for improving the directivity of ultrasonic longitudinal wave signal propagation, applied to a preload sensor, the preload sensor comprising a bolt and a thin film sensor, the bolt comprising a head and a screw with threads, the thin film sensor comprising a piezoelectric layer and an electrode layer, the piezoelectric layer and the electrode layer are in-situ grown layer by layer from inside to outside on the top surface of the head, characterized in that: The method comprises: The directivity of ultrasonic longitudinal wave signal propagation is improved by optimizing the diameter of the electrode layer on the top end surface of the head and making it match the nominal diameter of the bolt.

2. The method according to claim 1, characterized in that The electrode layer includes an inner electrode and an outer electrode, and optimizing the diameter of the electrode layer on the top surface of the head is to optimize the diameter of the inner electrode on the top surface of the head.

3. The method according to claim 2, characterized in that The method comprises: The diameter of the inner electrode at the top end surface of the head is designed to be smaller than or equal to the nominal diameter of the bolt and larger than or equal to a minimum threshold.

4. The method according to claim 2, characterized in that: Different nominal diameter ranges of the bolts correspond to different inner electrode diameters, and a larger nominal diameter range corresponds to a larger inner electrode diameter.

5. A preload force sensor, characterized in that: It adopts the method described in any one of claims 1 to 4 to improve the directivity of ultrasonic longitudinal wave signal propagation; The preload force sensor includes a bolt and a thin film sensor, the bolt includes a head and a screw with a thread, the thin film sensor includes a piezoelectric layer and an electrode layer, the piezoelectric layer and the electrode layer are in-situ grown layer by layer from the inside to the outside on the top surface of the head, the electrode layer includes an inner electrode and an outer electrode, and the diameter of the inner electrode on the top surface of the head is designed to be less than or equal to the nominal diameter of the bolt and greater than or equal to a minimum threshold.

6. The preload force sensor according to claim 5, characterized in that: The inner electrode diameter of the preload force sensor corresponding to the bolt with a nominal diameter of 4 mm to 20 mm is 2 mm to 4 mm.

7. The preload force sensor according to claim 6, characterized in that: The inner electrode diameter of the preload force sensor corresponding to the nominal diameter of the bolt is 8mm is 4mm.

8. A method for determining the diameter of an electrode layer of a preload sensor, the method being used to determine the diameter of the electrode layer of the preload sensor according to any one of claims 5 to 7 on the top surface of the head, the method comprising: Select multiple bolts with different nominal diameters; Generating piezoelectric layers and electrode layers respectively on the end faces of the heads of the plurality of bolts from the inside to the outside to form a plurality of preload sensors, wherein the electrode layers of the plurality of preload sensors have different diameters; Under the state of applying the excitation voltage, the ultrasonic echo signal strengths of the plurality of preload force sensors are determined, and the electrode layer diameter corresponding to the preload force sensor with the largest ultrasonic echo signal strength is the required electrode layer diameter.

9. The method for determining the electrode layer diameter of the preload sensor according to claim 8, characterized in that: The ultrasonic echo signal strength of multiple preload sensors is determined in the following manner: Setting a fixed constraint on the lower surface of the head; Performing time domain calculation after applying an excitation voltage signal to the electrode layer; The excitation voltage satisfies: Where: F(t) is the excitation voltage signal, f is the signal frequency, t is the signal propagation time, T is the signal period, and T=1 / f.

10. The method for determining the electrode layer diameter of the preload sensor according to claim 8, characterized in that: The bolts include a screw rod, and the screw rods of the plurality of bolts have the same length.

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