Method and device for measuring center frequency of ultrasonic longitudinal wave probe

Abstract

The invention discloses a method and device for measuring the center frequency of an ultrasonic longitudinal wave probe, and belongs to the technical field of ultrasonic detection. The method comprises the specific steps that an isotropic metal test block containing a specific flat-bottomed hole and a transverse through hole is manufactured, and the flat-bottomed hole and the transverse through hole are both located in a probe far-field region; by measuring the echo height (Hf) and time (tf) of a flat-bottom hole and the echo height (Hs) of a transverse through hole and combining the positions and sizes of the flat-bottom hole and the transverse through hole, the center frequency (f) of the probe is calculated based on a formula. According to the method, the sound field characteristic difference of the double reflectors is creatively used for counteracting the machining precision interference, the operation process is simplified, and the problems that a traditional method is high in equipment cost, complex in operation and limited in applicability are solved. The test block also supports multi-material adaptation (steel, aluminum, titanium alloy and the like) and is suitable for industrial sites and laboratory environments, and the detection efficiency and economical efficiency are remarkably improved.

Description

Technical Field

[0001] The present invention belongs to the field of ultrasonic nondestructive testing, and in particular relates to a method and device for measuring the center frequency of an ultrasonic longitudinal wave probe. Background Art

[0002] The ultrasonic probe is a core component in ultrasonic testing. Its function is to transmit and receive ultrasonic signals and convert electrical signals into ultrasonic signals. Ultrasonic probes utilize the piezoelectric effect to convert electrical energy into acoustic energy. The piezoelectric chip inside the probe generates an ultrasonic signal under voltage excitation and transmits it to the object being tested. Simultaneously, the probe converts the received ultrasonic signal into an electrical signal, which is then transmitted to processing equipment for analysis.

[0003] The center frequency of an ultrasonic probe is one of the core parameters of ultrasonic testing, directly affecting detection resolution and sensitivity. Currently, commonly used methods for measuring probe center frequency include spectrum analysis and echo pulse period analysis.

[0004] The spectrum analysis method uses an ultrasonic probe to transmit a pulse signal, then uses a spectrum analyzer to capture the spectral distribution of the echo signal, selecting the frequency band with the most concentrated energy as the center frequency. This method offers high theoretical accuracy, but relies on high-precision spectrum analysis equipment, which is expensive. It also requires specialized personnel for debugging, making it complex to operate. It is also susceptible to signal noise and probe damping characteristics, resulting in poor repeatability.

[0005] The echo pulse period analysis method calculates the probe's center frequency by measuring the period of the echo pulse. This method is simple to use, but requires an ultrasonic flaw detector capable of measuring the probe's echo period, placing high demands on the equipment. Summary of the Invention

[0006] The purpose of the present invention is to provide a method and device for measuring the center frequency of an ultrasonic longitudinal wave probe, aiming to overcome the problems of high equipment requirements, complex operation, and poor repeatability in existing ultrasonic probe center frequency measurement technologies. By reducing equipment costs, simplifying operating procedures, and adopting the principle of mutual error compensation, the method significantly reduces dependence on equipment and the environment while ensuring measurement accuracy, providing a more efficient solution for ultrasonic probe frequency calibration.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] The present invention provides a method for measuring the center frequency of an ultrasonic longitudinal wave probe, comprising the following steps:

[0009] (1) Make a test block of known thickness:

[0010] The thickness of the test block is T. The upper and lower surfaces of the test block are parallel. A hole with a depth of t and a diameter of d is machined on the lower surface of the test block. fA flat bottom hole with a diameter of d is machined on the side of the test block. s The distance between the center of the horizontal through hole and the upper surface of the test block is a;

[0011] (2) Obtain ultrasonic echo and record wave height:

[0012] Use an ultrasonic longitudinal wave probe coupled to the upper surface of the test block, move the probe to the top of the flat bottom hole and the cross-drilled hole respectively, and find the highest echo respectively. Record the flat bottom hole echo height H at the same gain. f and the single-pass echo time t in the test block f , and the SDH echo height H s ;

[0013] (3) Calculate the central wavelength λ of the ultrasonic longitudinal wave probe:

[0014] The central wavelength of the ultrasonic longitudinal wave probe is calculated by formula (1):

[0015]

[0016] Where, d f is the diameter of the flat bottom hole, d s is the diameter of the cross-hole, T is the thickness of the test block, t is the depth of the flat-bottom hole, a is the distance between the center of the cross-hole and the upper surface of the test block, H f is the flat bottom hole echo height, H s is the SDH echo height;

[0017] (4) Calculate the center frequency f of the ultrasonic longitudinal wave probe:

[0018] The center frequency of the ultrasonic longitudinal wave probe is calculated by formula (2):

[0019]

[0020] Where, t f It is the single-pass echo time of the flat-bottom hole in the test block. If it is water immersion ultrasound, the single-pass echo time in water is subtracted.

[0021] A further improvement of the present invention is that the measuring test block of known thickness in step (1) is made of an isotropic metal material.

[0022] A further improvement of the present invention is that the measuring test block is in the shape of a cuboid.

[0023] A further improvement of the present invention is that the measuring test block is in the shape of a cylinder.

[0024] A further improvement of the present invention is that the diameter d of the flat bottom hole of the measuring block is f and the diameter of the horizontal through hole d s All are not less than 4mm.

[0025] A further improvement of the present invention is that the distances between the bottom surface of the flat-bottom hole and the center and the upper surface of the transverse through hole of the measuring test block are all greater than three times the near-field length of the probe.

[0026] A further improvement of the present invention is that the length of the transverse through hole of the measuring test block is greater than the beam cross-sectional size of the ultrasonic longitudinal wave probe at that position.

[0027] A further improvement of the present invention is that the coupling mode of the ultrasonic longitudinal wave probe is selected from direct coupling or water immersion coupling.

[0028] A further improvement of the present invention is that when direct coupling is selected, a probe pressing block is used to maintain stable and uniform coupling at all positions.

[0029] The present invention also provides an ultrasonic longitudinal wave probe center frequency measuring device, comprising:

[0030] Make a measuring block unit with known thickness: the thickness of the measuring block is T, the upper and lower surfaces of the block are parallel, and a depth of t and diameter d is machined on the lower surface of the block. f A flat bottom hole with a diameter of d is machined on the side of the test block. s The distance between the center of the horizontal through hole and the upper surface of the test block is a;

[0031] Obtain ultrasonic echo and record wave height unit: Use ultrasonic longitudinal wave probe to couple to the upper surface of the test block, move the probe to the top of the flat bottom hole and the cross-drilled hole respectively and find the highest echo respectively, and record the flat bottom hole echo height H at the same gain. f and the single-pass echo time t in the test block f , and the SDH echo height H s ;

[0032] Calculate the central wavelength λ of the ultrasonic longitudinal wave probe: The central wavelength of the ultrasonic longitudinal wave probe is calculated by formula (1):

[0033]

[0034] Where, d f is the diameter of the flat bottom hole, d s is the diameter of the cross-hole, T is the thickness of the test block, t is the depth of the flat-bottom hole, a is the distance between the center of the cross-hole and the upper surface of the test block, H f is the flat bottom hole echo height, H s is the SDH echo height;

[0035] Calculate the center frequency f of the ultrasonic longitudinal wave probe: The center frequency of the ultrasonic longitudinal wave probe is calculated by formula (2):

[0036]

[0037] Where, t f It is the single-pass echo time of the flat-bottom hole in the test block. If it is water immersion ultrasound, the single-pass echo time in water is subtracted.

[0038] Compared with the prior art, the present invention has at least the following beneficial technical effects:

[0039] The present invention provides a method and device for measuring the center frequency of an ultrasonic longitudinal wave probe. Through dual-reflector combined measurement, it solves several bottleneck technical problems in traditional ultrasonic probe center frequency measurement technology. The wavelength is calculated by comparing the echo heights of flat-bottom holes and cross-drilled holes, offsetting common-mode interference such as uneven coupling agent thickness and variations in test block surface roughness, thereby reducing system errors. Only a conventional ultrasonic detector is required (no spectrum analyzer or high-precision time measurement equipment is required), and the same test block can be adapted to different frequency probes, eliminating the need to customize multiple sets of test blocks for specific frequencies, saving equipment and processing costs. Flat-bottom hole and cross-drilled hole echo data can be obtained simultaneously through a single coupling and scanning operation. The method is suitable for on-site testing environments, simplifying the operating process and enhancing on-site applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0041] Figure 1 The present invention is a flow chart of a method for measuring the center frequency of an ultrasonic longitudinal wave probe.

[0042] Figure 2 This is a schematic diagram of the structure of a rectangular parallelepiped measurement test block for the center frequency of an ultrasonic longitudinal wave probe of the present invention.

[0043] Figure 3 for Figure 2 Top view of .

[0044] Figure 4 This is a schematic structural diagram of a cylindrical measurement test block for a center frequency ultrasonic longitudinal wave probe of the present invention.

[0045] Figure 5 for Figure 4 Top view of .

[0046] Figure 6 This is a schematic diagram of the dimensions and relative position identification of a test block for measuring the center frequency of an ultrasonic longitudinal wave probe according to the present invention.

[0047] Figure 7 for Figure 6 Top view of .

[0048] Figure 8 This is a structural block diagram of a device for measuring the center frequency of an ultrasonic longitudinal wave probe according to the present invention.

[0049] Among them, d f is the diameter of the flat bottom hole, d s is the diameter of the cross-hole, T is the thickness of the test block, t is the depth of the flat-bottom hole, and a is the distance between the center of the cross-hole and the upper surface of the test block. DETAILED DESCRIPTION

[0050] Hereinafter, only certain exemplary embodiments are briefly described. As will be appreciated by those skilled in the art, the described embodiments may be modified in various ways without departing from the spirit or scope of the present invention. Therefore, the drawings and description are to be considered as illustrative in nature and not restrictive.

[0051] In the description of the present invention, it should be understood that when used in this specification and the appended claims, the terms "include" and "comprises" indicate the presence of described features, wholes, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or collections thereof.

[0052] It should also be understood that the terms used in the present specification are only for the purpose of describing particular embodiments and are not intended to limit the present invention. As used in the present specification and the appended claims, the singular forms "a", "an", and "the" are intended to include the plural forms unless the context clearly indicates otherwise.

[0053] It should be further understood that the term "and / or" used in the present description and the appended claims refers to and includes any and all possible combinations of one or more of the associated listed items.

[0054] The accompanying drawings illustrate various schematic diagrams of structures according to embodiments disclosed herein. These figures are not drawn to scale; for clarity, some details are exaggerated and some details may be omitted. The shapes of the various regions and layers shown in the figures, as well as their relative sizes and positional relationships, are merely exemplary and may deviate in practice due to manufacturing tolerances or technical limitations. Those skilled in the art may design regions / layers with different shapes, sizes, and relative positions as needed.

[0055] The embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0056] Example 1

[0057] like Figure 1 As shown, the present invention provides a method for measuring the center frequency of an ultrasonic longitudinal wave probe, comprising the following steps:

[0058] 1. Make a test block of known thickness

[0059] Use isotropic metal material to make a measuring test block with a thickness of T. The upper and lower surfaces of the test block are parallel, and a hole with a depth of t and a diameter of d is machined on the lower surface of the test block. f A flat bottom hole with a diameter of d is machined on the side of the test block. s The distance between the center of the horizontal through hole and the upper surface of the test block is a.

[0060] The shape of the measuring block is a cuboid or a cylinder. The diameter d of the flat bottom hole of the measuring block is f and the diameter of the horizontal through hole d s The distances between the bottom surface of the flat-bottom hole and the center and top surface of the transverse through hole of the measurement block are all greater than three times the near-field length of the probe. The length of the transverse through hole of the measurement block is greater than the beam cross-sectional size of the ultrasonic longitudinal wave probe at that location.

[0061] 2. Obtain ultrasonic echo and record wave height

[0062] Use an ultrasonic longitudinal wave probe coupled to the upper surface of the test block, move the probe to the top of the flat bottom hole and the cross-drilled hole respectively, and find the highest echo respectively. Record the flat bottom hole echo height H at the same gain. f and the single-pass echo time t in the test block f , and the SDH echo height H s .

[0063] The ultrasonic longitudinal wave probe coupling mode is selected from direct coupling or immersion coupling. When direct coupling is selected, a probe pressing block is used to maintain stable and uniform coupling at all positions.

[0064] 3. Calculate the central wavelength λ of the ultrasonic longitudinal wave probe

[0065] The central wavelength of the ultrasonic longitudinal wave probe is calculated by formula (1):

[0066]

[0067] Where, d f is the diameter of the flat bottom hole, d s is the diameter of the cross-hole, T is the thickness of the test block, t is the depth of the flat-bottom hole, a is the distance between the center of the cross-hole and the upper surface of the test block, H f is the flat bottom hole echo height, H s is the SDH echo height.

[0068] 4. Calculate the center frequency f of the ultrasonic longitudinal wave probe

[0069] The center frequency of the ultrasonic longitudinal wave probe is calculated by formula (2):

[0070]

[0071] Where, t f It is the single-pass echo time of the flat-bottom hole in the test block (if it is water immersion ultrasound, the single-pass echo time in water needs to be subtracted).

[0072] Among them, the ultrasonic longitudinal wave probe is one of the commonly used probe types in ultrasonic testing. It is mainly used to transmit and receive longitudinal waves (compression waves) to detect defects inside the material or measure material properties. Longitudinal waves are mechanical waves in which the direction of particle vibration is consistent with the direction of wave propagation, and can propagate in solids, liquids and gases. The core of the longitudinal wave probe is the piezoelectric chip, which converts electrical energy into mechanical vibrations through the inverse piezoelectric effect to generate longitudinal waves; and then converts the received longitudinal waves into electrical signals through the direct piezoelectric effect. The probe is usually composed of a piezoelectric chip, a damping block, a protective film, a casing and a cable. The piezoelectric chip is a key component, and commonly used materials include lead zirconate titanate (PZT) and the like.

[0073] Longitudinal wave probes are classified into the following categories: Straight probes: The wafer is perpendicular to the surface being inspected and are suitable for detecting defects parallel to the inspection surface, such as internal defects in plates, forgings, and castings (such as pores, inclusions, cracks, etc.). Oblique-incidence longitudinal wave probes: The longitudinal wave is incident at a certain angle into the inspected material through an inclined wedge. This is suitable for detecting defects in a specific direction or measuring material thickness.

[0074] Example 2: Measuring the 5MHz probe center frequency with a steel test block

[0075] like Figure 1 、 Figure 2 、 Figure 3 、 Figure 6 and Figure 7 As shown, the present invention provides a method for measuring the center frequency of an ultrasonic longitudinal wave probe, comprising:

[0076] 1. Test Block Preparation

[0077] Material: 45# steel; 45# steel is a high-quality carbon structural steel. Its carbon content, approximately 0.42% to 0.50%, is the primary element affecting the steel's strength and hardness. Silicon and manganese contribute to the steel's strength and hardness, while phosphorus and sulfur are impurities, and excessive amounts can degrade the steel's performance. 45# steel may also contain certain amounts of chromium (Cr), nickel (Ni), and molybdenum (Mo), which enhance its corrosion resistance and high-temperature strength, but these concentrations are typically low. 45# steel exhibits excellent mechanical properties, including high tensile strength, yield strength, elongation, and reduction of area. According to the GB / T 699-1999 standard, 45# steel must have a tensile strength of no less than 600 MPa, a yield strength of no less than 355 MPa, an elongation of no less than 16%, and a reduction of area of ​​no less than 40%. 45# steel also exhibits good impact toughness and machinability.

[0078] Test block size: rectangular parallelepiped, dimensions 100 mm (length) × 50 mm (width) × 25 mm (thickness T = 25 mm);

[0079] Flat bottom hole parameters:

[0080] Diameter d f =4mm, depth t=10mm, distance between hole bottom and upper surface Tt=15mm; length of probe near field (Probe chip diameter d = 10 mm, nominal frequency 5 MHz, estimated wavelength λ ≈ 1.2 mm) satisfies Tt = 15 mm > 3N = 9 mm.

[0081] Side through hole parameters:

[0082] Diameter d s =4mm, the distance from the center to the upper surface a = 15mm, the length of the transverse through hole L = 50mm (greater than the probe beam diameter at this depth ≈ 12mm);

[0083] Processing accuracy: hole diameter tolerance ±0.05mm, hole depth tolerance ±0.1mm.

[0084] 2. Measurement steps

[0085] Coupling mode: immersion coupling, water sound path 10mm, the probe is vertically aligned with the upper surface of the test block;

[0086] Signal acquisition: Move the probe to the top of the flat bottom hole, adjust the position to maximize the echo amplitude, and record H f =80%, single-trip echo time t of the flat-bottom hole in the test block f = 2.5μs; Similarly, obtain the maximum echo amplitude H of the SDH under the same gain s =21%.

[0087] 3. Frequency calculation

[0088] 1) Calculate the wavelength λ according to formula (1):

[0089]

[0090] 2) Calculate the center frequency f according to formula (2):

[0091]

[0092] Example 3: Measuring the 10MHz probe center frequency on an aluminum alloy test block

[0093] like Figure 1 、 Figure 4 and Figure 5 As shown, the present invention provides a method for measuring the center frequency of an ultrasonic longitudinal wave probe, comprising:

[0094] 1. Test Block Preparation

[0095] Material: 6061 aluminum alloy. 6061 aluminum alloy is a heat-treatable, hardenable aluminum alloy with magnesium and silicon as primary alloying elements. It offers medium strength, excellent processability, weldability, and corrosion resistance, making it widely used in aerospace, transportation, architectural decoration, and other fields. 6061 aluminum alloy boasts medium strength, with a yield strength exceeding 110 MPa, a tensile strength exceeding 205 MPa, an elongation exceeding 16.0%, a density of 2.75 g / cm³, and a Poisson's ratio of 0.330. While its strength cannot compare to 2XXX or 7XXX series aluminum alloys, it offers excellent processability and toughness. It exhibits excellent formability, weldability, and machinability, maintaining good workability even after annealing. It is also highly deformable and dense, defect-free after machining. It exhibits excellent corrosion resistance, particularly in terms of its lack of stress corrosion cracking tendency, and exhibits excellent corrosion resistance and cold workability. It is easy to polish and color, and oxidizes well. It can be anodized, painted, or enameled, making it suitable for architectural decoration.

[0096] Test block size: cylindrical, diameter Φ50mm×20mm (thickness T=20mm);

[0097] Flat bottom hole parameters: diameter d f =4mm, depth t=8mm, distance between hole bottom and upper surface Tt=12mm; length of probe near field zone N≈2.5mm, satisfying Tt=12mm>3N=7.5mm.

[0098] Horizontal through hole parameters: diameter d s =4mm, the distance from the center to the upper surface a = 12mm, and the length of the horizontal through hole L = 40mm.

[0099] 2. Measurement steps

[0100] Coupling method: Direct coupling, using glycerin as a coupling agent, and applying a constant pressure of 20N to the probe clamp. The main function of the coupling agent is to eliminate the air gap between the probe and the material being tested, ensuring efficient transmission of ultrasonic or sound wave energy. The air gap will cause the sound wave reflectivity to exceed 99%, significantly reducing the detection sensitivity. The coupling agent fills the gap and matches the acoustic impedance (for example, the acoustic impedance of glycerin is 2.4×10 6 kg / (m2·s), which is close to that of human tissue and metal), which can greatly improve signal transmission efficiency.

[0101] Signal acquisition: Flat bottom hole echo amplitude H f =80%, single-trip echo time t of the flat-bottom hole in the test block f =1.9μs; SDH echo amplitude H s =10%.

[0102] 3. Frequency calculation

[0103] 1) Calculate the wavelength λ according to formula (1):

[0104]

[0105] 2) Calculate the center frequency f according to formula (2):

[0106]

[0107] Example 4

[0108] like Figure 8 As shown, the present invention provides an ultrasonic longitudinal wave probe center frequency measuring device, comprising:

[0109] Make a measuring block unit with known thickness: the thickness of the measuring block is T, the upper and lower surfaces of the block are parallel, and a depth of t and diameter d is machined on the lower surface of the block. f A flat bottom hole with a diameter of d is machined on the side of the test block. s The distance between the center of the horizontal through hole and the upper surface of the test block is a;

[0110] Obtain ultrasonic echo and record wave height unit: Use ultrasonic longitudinal wave probe to couple to the upper surface of the test block, move the probe to the top of the flat bottom hole and the cross-drilled hole respectively and find the highest echo respectively, and record the flat bottom hole echo height H at the same gain. f and the single-pass echo time t in the test block f , and the SDH echo height H s ;

[0111] Calculate the central wavelength λ of the ultrasonic longitudinal wave probe: The central wavelength of the ultrasonic longitudinal wave probe is calculated by formula (1):

[0112]

[0113] Where, d f is the diameter of the flat bottom hole, d s is the diameter of the cross-hole, T is the thickness of the test block, t is the depth of the flat-bottom hole, a is the distance between the center of the cross-hole and the upper surface of the test block, H f is the flat bottom hole echo height, H s is the SDH echo height;

[0114] Calculate the center frequency f of the ultrasonic longitudinal wave probe: The center frequency of the ultrasonic longitudinal wave probe is calculated by formula (2):

[0115]

[0116] Where, t f It is the single-pass echo time of the flat-bottom hole in the test block. If it is water immersion ultrasound, the single-pass echo time in water is subtracted.

[0117] In summary, the present invention addresses the problems of high equipment requirements, complex operation, and poor repeatability in the prior art. By designing a composite test block containing flat-bottom holes and transverse through-holes, high-precision frequency measurement is achieved by combining the double-reflector echo signal joint analysis. Specifically, the present invention calculates the wavelength by the echo height ratio of the flat-bottom hole and the transverse through-hole, offsetting the common-mode interference such as uneven thickness of the coupling agent and changes in the surface roughness of the test block, thereby reducing system errors. Only a conventional ultrasonic detector is required (no spectrum analyzer or high-precision time measurement equipment is required), and the same test block can be adapted to different frequency probes, eliminating the need to customize multiple sets of test blocks for specific frequencies, saving equipment and processing costs. The echo data of the flat-bottom hole and the transverse through-hole can be obtained simultaneously through a single coupling and scanning, and is suitable for on-site detection environments, simplifying the operating process and enhancing on-site applicability.

[0118] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. It is obvious to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention. Therefore, from all points of view, the embodiments should be regarded as illustrative and non-restrictive. The scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes that fall within the meaning and range of equivalents of the claims are included in the present invention. Any reference signs in the claims should not be construed as limiting the claim to which they relate.

[0119] In addition, it should be understood that although this specification describes the embodiments, not every embodiment contains only one independent technical solution. This description is for clarity only. Those skilled in the art should consider the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art. The above content is only for the purpose of illustrating the technical concept of the present invention and cannot be used to limit the scope of protection of the present invention. Any changes made based on the technical solution in accordance with the technical concept proposed by the present invention fall within the scope of protection of the claims of the present invention.

Claims

1. A method for measuring the center frequency of an ultrasonic longitudinal wave probe, characterized in that: The following steps are involved: (1) Make a test block of known thickness: The thickness of the test block is T. The upper and lower surfaces of the test block are parallel. A hole with a depth of t and a diameter of d is machined on the lower surface of the test block. f A flat bottom hole with a diameter of d is machined on the side of the test block. s The distance between the center of the horizontal through hole and the upper surface of the test block is a; (2) Obtain ultrasonic echo and record wave height: Use an ultrasonic longitudinal wave probe coupled to the upper surface of the test block, move the probe to the top of the flat bottom hole and the cross-drilled hole respectively, and find the highest echo respectively. Record the flat bottom hole echo height H at the same gain. f and the single-pass echo time t in the test block f , and the SDH echo height H s ; (3) Calculate the central wavelength λ of the ultrasonic longitudinal wave probe: The central wavelength of the ultrasonic longitudinal wave probe is calculated by formula (1): Where, d f is the diameter of the flat bottom hole, d s is the diameter of the cross-hole, T is the thickness of the test block, t is the depth of the flat-bottom hole, a is the distance between the center of the cross-hole and the upper surface of the test block, H f is the flat bottom hole echo height, H s is the SDH echo height; (4) Calculate the center frequency f of the ultrasonic longitudinal wave probe: The center frequency of the ultrasonic longitudinal wave probe is calculated by formula (2): Where, t f It is the single-pass echo time of the flat-bottom hole in the test block. If it is water immersion ultrasound, the single-pass echo time in water is subtracted.

2. The method for measuring the center frequency of an ultrasonic longitudinal wave probe according to claim 1, wherein: Step (1) manufactures a measuring test block of known thickness using an isotropic metal material.

3. The method for measuring the center frequency of an ultrasonic longitudinal wave probe according to claim 1, wherein: The measuring test block is in the shape of a cuboid.

4. The method for measuring the center frequency of an ultrasonic longitudinal wave probe according to claim 1, wherein: The shape of the measuring test block is cylindrical.

5. The method for measuring the center frequency of an ultrasonic longitudinal wave probe according to claim 1, wherein: The diameter d of the flat bottom hole of the measuring block f and the diameter of the horizontal through hole d s All are not less than 4mm.

6. The method for measuring the center frequency of an ultrasonic longitudinal wave probe according to claim 1, wherein: The distances between the bottom surface of the flat-bottom hole and the center of the transverse through hole and the upper surface of the measuring test block are all greater than three times the near-field length of the probe.

7. The method for measuring the center frequency of an ultrasonic longitudinal wave probe according to claim 1, wherein: The length of the transverse through hole of the measuring test block is greater than the beam cross-sectional size of the ultrasonic longitudinal wave probe at that position.

8. The method for measuring the center frequency of an ultrasonic longitudinal wave probe according to claim 1, wherein: The ultrasonic longitudinal wave probe coupling mode is selected as direct coupling or water immersion coupling.

9. The method for measuring the center frequency of an ultrasonic longitudinal wave probe according to claim 8, characterized in that: When direct coupling is selected, a probe clamp is used to maintain stable and uniform coupling at all positions.

10. An ultrasonic longitudinal wave probe center frequency measuring device, characterized in that: include: Make a measuring block unit with known thickness: the thickness of the measuring block is T, the upper and lower surfaces of the block are parallel, and a depth of t and diameter d is machined on the lower surface of the block. f A flat bottom hole with a diameter of d is machined on the side of the test block. s The distance between the center of the horizontal through hole and the upper surface of the test block is a; Obtain ultrasonic echo and record wave height unit: Use ultrasonic longitudinal wave probe to couple to the upper surface of the test block, move the probe to the top of the flat bottom hole and the cross-drilled hole respectively and find the highest echo respectively, and record the flat bottom hole echo height H at the same gain. f and the single-pass echo time t in the test block f , and the SDH echo height H s ; Calculate the central wavelength λ of the ultrasonic longitudinal wave probe: The central wavelength of the ultrasonic longitudinal wave probe is calculated by formula (1): Where, d f is the diameter of the flat bottom hole, d s is the diameter of the cross-hole, T is the thickness of the test block, t is the depth of the flat-bottom hole, a is the distance between the center of the cross-hole and the upper surface of the test block, H f is the flat bottom hole echo height, H s is the SDH echo height; Calculate the center frequency f of the ultrasonic longitudinal wave probe: The center frequency of the ultrasonic longitudinal wave probe is calculated by formula (2): Where, t f It is the single-pass echo time of the flat-bottom hole in the test block. If it is water immersion ultrasound, the single-pass echo time in water is subtracted.

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