A Concentric Cone-shaped TEM Indoor Conductor Support Structure and Its Reliability Analysis Method

Abstract

The present invention provides a concentric conical TEM indoor conductor support structure and a reliability analysis method thereof. The support structure includes a first support member located between the inner conductor and the outer conductor; the first support member has an annular structure with a hollow middle part; the outer side wall of the first support member is fixedly attached to the inner wall of the outer conductor; the inner side wall of the first support member is fixedly attached to the outer wall of the inner conductor; the material of the first support member is PMI foam material. This support structure improves the reliability and stability of the concentric conical TEM chamber.

Description

Technical Field

[0001] The present invention relates to the field of radio measurement technology. More specifically, it relates to a concentric conical TEM indoor conductor support structure and a reliability analysis method thereof. Background Art

[0002] A TEM cell is a field strength generating device based on the standard field method. The operating frequencies of current TEM cells and GTEM cells on the market are related to their sizes. For example, a 3-meter-long TEM cell has an operating frequency band of DC - 150 MHz, a 1-meter-long TEM cell has an operating frequency band of DC - 500 MHz, and the highest operating frequency of a GTEM cell is only DC - 18 GHz. Therefore, a single TEM cell cannot meet the metrology requirements of broadband field strength probes in the DC - 40 GHz range. A concentric conical TEM cell can generate an electromagnetic field with a wide frequency band from DC to 40 GHz, and can be used to establish a broadband field strength calibration system to meet the full-frequency band and broadband sweep calibration requirements of field strength probes. The concentric cone TEM cell, similar to a coaxial transmission line, is a two-conductor transmission line with an axisymmetric structure, and is composed of several parts such as coaxial feeding, impedance matching section, transmission section, terminal load, and absorbing material. The coaxial feeding provides input power for the concentric conical TEM cell, the impedance matching section transforms the characteristic impedance of the coaxial wire of 50 Ω to the characteristic impedance of the transmission section, and the terminal load and absorbing material are used to absorb electromagnetic waves to reduce the standing wave loss of the entire system. Finally, a uniform TEM wave is generated in the cavity between the two metal concentric cones to form a calculable standard field strength. Summary of the Invention

[0003] In view of the above problems, the present invention provides a concentric conical TEM indoor conductor support structure and a reliability analysis method thereof, which improve the reliability of the concentric cone TEM cell.

[0004] To achieve the above object, the present invention adopts the following technical solutions:

[0005] The present invention provides a concentric conical TEM indoor conductor support structure, including:

[0006] A first support member located between the inner conductor and the outer conductor;

[0007] The first support member has an annular structure with a hollow middle part; the outer side wall of the first support member is fixedly attached to the inner wall of the outer conductor; the inner side wall of the first support member is fixedly attached to the outer wall of the inner conductor;

[0008] The material of the first support member is PMI foam material.

[0009] In addition, preferably, along the axial direction of the inner conductor, the thickness of the first support member is 53 mm.

[0010] In addition, a preferred solution is that the support mechanism further includes a second support member, a third support member, a fourth support member, and a fifth support member;

[0011] The first support member, the second support member, the third support member, the fourth support member, and the fifth support member are arranged along the axial direction of the inner conductor.

[0012] In addition, a preferred solution is that the second support member, the third support member, the fourth support member, and the fifth support member are all in a ring structure with a hollow middle part.

[0013] In addition, a preferred solution is that the second support member is attached to the third support member; the fourth support member is attached to the fifth support member.

[0014] In addition, a preferred solution is that the materials of the second support member, the third support member, the fourth support member, and the fifth support member are all PMI foam materials.

[0015] In addition, a preferred solution is that the plane where the upper end face or the lower end face of the first support member is located is parallel to the plane where the upper end face or the lower end face of the inner and outer conductors is located.

[0016] The present invention also provides a reliability analysis method for the concentric conical TEM chamber inner conductor support structure as described above, including the following steps:

[0017] Establish a finite element model of the first support member and perform finite element analysis to obtain the deformation amount and stress distribution of the first support member;

[0018] Design and obtain the safety factor, reliability, and reliability coefficient of the first support member;

[0019] Design and obtain the reliability safety factor and failure rate of the first support member;

[0020] Analyze the obtained results of the deformation amount, stress distribution, safety factor, reliability, reliability coefficient, reliability safety factor, and failure rate of the first support member.

[0021] In addition, a preferred solution is that according to the part strength checking method, when the strength corresponding to the material of the first support member is greater than the maximum stress it bears and the safety factor obtained by dividing the two is greater than the set safety factor, it can be determined that the strength of the first support member meets the requirements; thus, setting the strength corresponding to the material of the first support member as [σ], the maximum stress received as σ, and the safety factor f 0 Can be calculated according to Formula 1 to obtain the safety factor of the first support member;

[0022]

[0023] According to the stress-strength interference theory, when the mean and standard deviation of the strength and stress of the first support in the normal distribution are known, the structural reliability of the first support is calculated using Equation 2;

[0024]

[0025] where R is the reliability; Z is called the reliability coefficient or probability safety margin and can be calculated using Equation 3;

[0026]

[0027] where μ S and σ S are the mean and standard deviation of the comprehensive strength of the part respectively; μ L and σ L are the mean and standard deviation of the comprehensive stress of the part respectively.

[0028] In addition, the preferred solution is that the statistical safety factor defined by "strength mean μ S / stress mean μ L " is called the reliability safety factor. When the strength and stress follow a normal distribution, the reliability safety factor of the first support structure is calculated using Equation 4;

[0029]

[0030] where f 0 is the reliability safety factor of the mechanical structure; C VS is the strength variation coefficient; C VL is the stress variation coefficient, C VS and C VL are calculated using Equation 5 and Equation 6 respectively;

[0031]

[0032]

[0033] where μ S and σ S are the mean and standard deviation of the comprehensive strength of the part respectively; μ L and σ L are the mean and standard deviation of the comprehensive stress of the part respectively;

[0034] When the mean and standard deviation of the strength and stress of the first support in the normal distribution are known, the failure rate function is calculated using Equation 7;

[0035]

[0036] Among them, Z is the reliability coefficient; λ(t) is the failure rate function, f(t) is the failure probability density function, and R(t) is the reliability function.

[0037] The beneficial effects of the present invention are as follows:

[0038] The support structure provided by the present invention has sufficient strength to support the weight of the inner conductor; and can ensure the concentricity of the inner and outer conductors and stabilize the specific relative position relationship between the inner and outer conductors; in the auxiliary uniform region test, the support structure can also support the probe under test; selecting a PMI foam material with a high density can further increase the strength and reliability of the support structure, thereby improving the stability of the concentric cone TEM cell. Description of the Drawings

[0039] The following further details the specific embodiments of the present invention with reference to the drawings.

[0040] Figure 1 It is a schematic diagram of the overall structure of the present invention, where (a) is a schematic diagram of the overall structure of the cone of the concentric cone TEM cell, and (b) is an enlarged view of part A in (a).

[0041] Figure 2 It is a cross-sectional schematic diagram of the first support member of the present invention.

[0042] Figure 3 It is a schematic diagram of the terminal load of the present invention.

[0043] Figure 4 It is an axonometric view of the terminal load of the present invention.

[0044] Figure 5 It is a schematic diagram of the structure of the first support member of the present invention.

[0045] Figure 6 It is a schematic diagram of the structure of the second support member of the present invention.

[0046] Figure 7 It is a schematic diagram of the structure of the third support member of the present invention.

[0047] Figure 8 It is a schematic diagram of the structure of the fourth support member of the present invention.

[0048] Figure 9 It is a schematic diagram of the structure of the fifth support member of the present invention.

[0049] Figure 10 It is a finite element model diagram of the mesh division of the fifth support member of the present invention.

[0050] Figure 11 It is a displacement deformation diagram of the fifth support member of the present invention under loading condition A.

[0051] Figure 12 It is the part stress distribution diagram of the fifth support member of the present invention under loading condition A.

[0052] Figure 13 It is the displacement deformation diagram of the fifth support member of the present invention under loading condition B.

[0053] Figure 14 It is the part stress distribution diagram of the fifth support member of the present invention under loading condition B.

[0054] Figure 15 It is the finite element model diagram of the mesh division of the fourth support member of the present invention.

[0055] Figure 16 It is the displacement deformation diagram of the fourth support member of the present invention under loading condition A.

[0056] Figure 17 It is the part stress distribution diagram of the fourth support member of the present invention under loading condition A.

[0057] Figure 18 It is the displacement deformation diagram of the fourth support member of the present invention under loading condition B.

[0058] Figure 19 It is the part stress distribution diagram of the fourth support member of the present invention under loading condition B.

[0059] Figure 20 It is the finite element model diagram of the mesh division of the third support member of the present invention.

[0060] Figure 21 It is the displacement deformation diagram of the third support member of the present invention under loading condition A.

[0061] Figure 22 It is the part stress distribution diagram of the third support member of the present invention under loading condition A.

[0062] Figure 23 It is the displacement deformation diagram of the third support member of the present invention under loading condition B.

[0063] Figure 24 It is the part stress distribution diagram of the third support member of the present invention under loading condition B.

[0064] Figure 25 It is the finite element model diagram of the mesh division of the second support member of the present invention.

[0065] Figure 26 It is the displacement deformation diagram of the second support member of the present invention under loading condition A.

[0066] Figure 27 It is the part stress distribution diagram of the second support member of the present invention under loading condition A.

[0067] Figure 28 It is the displacement deformation diagram of the second support member of the present invention under loading condition B.

[0068] Figure 29 It is the component stress distribution diagram of the second support member of the present invention under loading condition B.

[0069] Figure 30 It is the finite element model diagram of the mesh division of the first support member of the present invention.

[0070] Figure 31 It is the displacement deformation diagram of the first support member of the present invention under loading condition A.

[0071] Figure 32 It is the component stress distribution diagram of the first support member of the present invention under loading condition A.

[0072] Figure 33 It is the displacement deformation diagram of the first support member of the present invention under loading condition B.

[0073] Figure 34 It is the component stress distribution diagram of the first support member of the present invention under loading condition B.

[0074] Figure 35 It is the finite element model diagram of the mesh division of the terminal load of the present invention.

[0075] Figure 36 It is the cross-sectional schematic diagram of the terminal load of the present invention.

[0076] Figure 37 It is the displacement deformation diagram of the terminal load of the present invention under loading condition A.

[0077] Figure 38 It is the component stress distribution diagram of the terminal load of the present invention under loading condition A.

[0078] Figure 39 It is the displacement deformation diagram of the terminal load of the present invention under loading condition B.

[0079] Figure 40 It is the component stress distribution diagram of the terminal load of the present invention under loading condition B. Detailed implementation manners

[0080] Various exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It should be noted that: Unless otherwise specifically stated, the relative arrangements of components and steps, numerical expressions, and numerical values set forth in these embodiments do not limit the scope of the present invention.

[0081] The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way a limitation on the present invention or its application or use.

[0082] Technologies and devices known to those of ordinary skill in the relevant art may not be discussed in detail, but where appropriate, such technologies and devices shall be regarded as part of the specification.

[0083] In all the examples shown and discussed herein, any specific values should be construed as merely exemplary and not as a limitation. Thus, other examples of the exemplary embodiments may have different values.

[0084] It should be noted that like reference numerals and letters denote like items in the following figures, and thus, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0085] To solve the problem of poor stability of the existing concentric cone TEM chamber. The present invention provides a support structure for the inner conductor in a concentric cone TEM chamber and a reliability analysis method thereof. In combination with Figures 1 to 40 As shown, specifically, the support structure for the inner conductor in the concentric cone TEM chamber includes: a first support member located between the inner conductor and the outer conductor; the first support member is in a ring structure with a hollow middle; the outer side wall of the first support member is fixedly attached to the inner wall of the outer conductor; the inner side wall of the first support member is fixedly attached to the outer wall of the inner conductor; the material of the first support member is PMI foam material.

[0086] The support mechanism provided by the present invention can support and bear the weight of the inner conductor of 20 kg, and has sufficient strength; it can ensure the concentricity of the inner and outer conductors and maintain a specific relative positional relationship between the inner and outer conductors; it can also support the probe under test during the auxiliary uniform zone test.

[0087] The first support member plays a main load-bearing role and can place the uniform zone test bracket and the probe under test. The thickness of the first support member is 53 mm. On the one hand, it can reduce its attenuation of electromagnetic waves, and on the other hand, it can change the thickness-wavelength ratio. The theory shows that the more integer this value is, the greater the impact on the field, especially at high frequencies. The thickness-wavelength ratio data before and after improvement are shown in Table 1. It can be seen from Table 1 that the thickness-length ratio of the 53-mm thick foam material is not an integer at each frequency point.

[0088] Table 1:

[0089]

[0090]

[0091] In a specific embodiment, the support mechanism further includes a second support member, a third support member, a fourth support member, and a fifth support member; the first support member, the second support member, the third support member, the fourth support member, and the fifth support member are arranged along the axial direction of the inner conductor; the concentric conical TEM cell includes a terminal load for connecting and fixing the inner conductor and the outer conductor, the terminal load is located at the upper part of the concentric conical TEM cell, and the first support member is close to the terminal load.

[0092] Further, the second support member, the third support member, the fourth support member, and the fifth support member are all in a ring structure with a hollow middle part.

[0093] More specifically, the second support member is attached to the third support member; the fourth support member is attached to the fifth support member; the second support member, the third support member, the fourth support member, and the fifth support member are all made of PMI foam material. The second support member, the third support member, the fourth support member, and the fifth support member are designed in sequence at the segmented part of the inner and outer conductors from the first support member downwards to support and position the lower part of the inner conductor, playing an auxiliary role in support and positioning.

[0094] For facilitating the assembly of the support structure and the rework matching when there are dimensional errors, the plane where the upper end face or the lower end face of the first support member is located is parallel to the plane where the upper end face or the lower end face of the inner and outer conductors is located, and the upper end face or the lower end face of the inner and outer conductors serves as the reference plane during assembly; similarly, the plane where the upper end face or the lower end face of the second support member, the third support member, the fourth support member, and the fifth support member is located is also parallel to the plane where the upper end face or the lower end face of the inner and outer conductors is located.

[0095] The present invention also provides a design method for the inner conductor support structure of the concentric conical TEM cell as described above. The method includes the following steps: According to the inner diameter of the outer conductor at different height segments and the outer diameter of the inner conductor at different height segments, design the size of the first support member so that the outer side wall of the first support member can be attached to the inner wall of the outer conductor, and the inner side wall of the first support member can be attached to the outer wall of the inner conductor; provide PMI foam material, and process the PMI foam material according to the obtained size of the first support member to obtain the first support member in a ring structure; through the above method, the second support member, the third support member, the fourth support member, and the fifth support member can also be obtained, and the five support members are arranged in the concentric conical TEM cell to realize the stable support of the inner and outer conductors. Further, the thickness of the first support member is designed to be 53 mm.

[0096] The present invention also provides a reliability analysis method based on the inner conductor support structure of the concentric conical TEM cell as described above, including the following steps:

[0097] Establish a finite element model of the first support member and conduct finite element analysis to obtain the deformation and stress distribution of the first support member. Specifically, establish a finite element model of the first support member and perform finite element analysis in MSC.PATRAN / NASTRAN software to obtain the deformation and stress distribution of the first support member. Design and obtain the safety factor, reliability, and reliability coefficient of the first support member. Design and obtain the reliability safety factor and failure rate of the first support member. Analyze the obtained results of the deformation, stress distribution, safety factor, reliability, reliability coefficient, reliability safety factor, and failure rate of the first support member.

[0098] Further, according to the part strength checking method, when the strength of the material corresponding to the first support member is greater than the maximum stress it bears and the safety factor obtained by dividing the two is greater than the set safety factor, it can be determined that the strength of the first support member meets the requirements. Thus, let the strength of the material corresponding to the first support member be [σ], the maximum stress it bears be σ, and the safety factor be f 0 It can be calculated according to Formula 1 to obtain the safety factor of the first support member;

[0099]

[0100] According to the stress-strength interference theory, when the mean and standard deviation of the strength and stress of the first support member in the normal distribution are known, the structural reliability of the first support member is calculated using Formula 2;

[0101]

[0102] Among them, R is the reliability; Z is called the reliability coefficient or probability safety margin and can be calculated by Formula 3;

[0103]

[0104] Among them, μ S and σ S are the mean and standard deviation of the comprehensive strength of the part respectively; μ L and σ L are the mean and standard deviation of the comprehensive stress of the part respectively.

[0105] Even further, the statistical safety factor defined as "strength mean μ S / stress mean μ L " is called the reliability safety factor. When the strength and stress follow a normal distribution, the structural reliability safety factor of the first support member is calculated by Formula 4;

[0106]

[0107] Among them, f 0 is the reliability safety factor of the mechanical structure; CVS is the coefficient of variation of strength; C VL is the coefficient of variation of stress, C VS and C VL are calculated by Formula Five and Formula Six respectively;

[0108]

[0109]

[0110] wherein, μ S and σ S are the mean value and standard deviation of the comprehensive strength of the parts respectively; μ L and σ L are the mean value and standard deviation of the comprehensive stress of the parts respectively;

[0111] When the mean value and standard deviation of the strength and stress of the first support in the normal distribution are known, the failure rate function is calculated by Formula Seven;

[0112]

[0113] wherein, Z is the reliability coefficient; λ(t) is the failure rate function, f(t) is the failure probability density function, and R(t) is the reliability function.

[0114] Specifically, before the machining and assembly of the coaxial cone TEM chamber, according to its functional requirements, structural characteristics and force requirements, the stiffness and strength of the inner conductor support material are analyzed, which is the key to determining the mechanics and reliability of the coaxial cone TEM chamber.

[0115] The overall structure of the cone is as Figure 1 shown. The force and deformation of the 6 support parts inside the cone after assembly are mainly analyzed, and their strength and reliability are analyzed. The analysis steps are as follows:

[0116] The force analysis of the 6 foam support materials between the inner and outer conductors is carried out. The 6 support parts are respectively named "terminal load" and "the first support, the second support, the third support, the fourth support and the fifth support". The weight of the inner conductor is mainly borne by the "terminal load", and at the same time, it is supported and positioned by the five support parts at different positions, forming a situation where multiple contacts jointly bear the gravity of the inner conductor. It is known that the inner conductor material is 6061 aluminum alloy, and its mass of about 17.86 kg can be obtained from the 3D design drawing. According to Figure 1 the internal structure shown, in order to obtain the force conditions of each part, the analysis is carried out from the following two loading conditions.

[0117] Loading condition A: Assume that the gravity of the aluminum alloy inner conductor is evenly distributed on the 6 support parts, and each support part bears the gravity load from the inner conductor.

[0118] At this time, the pressure borne by each supporting part is determined by the projected area of the contact surface between each part and the inner conductor on the horizontal plane. The force on each part can be expressed by the following formula:

[0119]

[0120] In the above formula, F i (i = 1 to 6) is the force on the i-th part, G is the gravity of the inner conductor, and S i is the projected area of the contact surface between the i-th part and the inner conductor on the horizontal plane. Thus, the inner conical surface of the "first support part" in contact with the inner conductor is its contact force-bearing surface, as Figure 2 shown. The contact force-bearing surface of the "terminal load" part is as Figure 3 shown.

[0121] Loading condition B: Considering the extreme force-bearing situation of each part, the 6 support parts are set to separately bear the gravity of the inner conductor, that is, each support part separately bears all the gravity of the inner conductor on its contact surface with the inner conductor.

[0122] In this extreme loading situation, the force-bearing contact surface of each part remains unchanged, but its force-bearing situation, including deformation and stress, will change.

[0123] The parts of the "first support part" to the "fifth support part" and the "terminal load" part are as Figures 4 to 9 shown.

[0124] Mechanical analysis and results of the inner conductor support component

[0125] Separate finite element models of the 6 support parts are established and finite element analysis is carried out in the MSC.PATRAN / NASTRAN software to obtain the deformation amount and stress distribution of each part.

[0126] The 6 support parts in contact with the inner and outer conductors are loaded according to their force-bearing areas for calculation. First, after obtaining the maximum diameter Φ 1 and the minimum diameter Φ 2 of the maximum diameter of each support foam conical hole, the force-bearing area S converted to the horizontal plane is calculated, and further the percentage of the bearing force of each support part in the weight of the inner conductor and the load borne are calculated, as shown in Table 2. The strength, reliability, safety, etc. of these 6 support parts directly affect the safety and reliability of the entire system and belong to key components.

[0127] Table 2 Structural parameters and loading conditions of each part

[0128]

[0129] The first to fifth support members and the "terminal load" part are meshed using a tetrahedral eight-node mesh type, and the parameters of the meshing results are shown in Table 3.

[0130] Table 3 Meshing results of each part

[0131]

[0132] Thus, the finite element model diagram of the meshing of the fifth support member is as shown in Figure 10 Shown.

[0133] (1) Finite element analysis of the "fifth support member" part

[0134] The "fifth support member" part is analyzed according to loading condition A, and the displacement deformation and stress nephograms of its finite element analysis are as shown in Figure 11 And Figure 12 Shown.

[0135] From Figure 11 And Figure 12 It can be seen that the maximum deformation of the part under loading condition a is 1.28×10 -5 mm, occurring at the lower edge of the inner conical hole of the part; the maximum stress of the part is 325 Pa, occurring at the lower edge of the outer conical surface of the part.

[0136] The displacement deformation and stress nephograms of the finite element analysis of the fifth support member under loading condition B are as shown in Figure 13 And Figure 14 Shown.

[0137] From Figure 13 And Figure 14 It can be seen that the maximum deformation of the part is 2.87×10 -2 mm, occurring at the lower edge of the inner conical hole of the part; the maximum stress of the part is 0.683 MPa, occurring at the lower edge of the outer conical surface of the part.

[0138] (2) Finite element analysis of the "fourth support member" part

[0139] The finite element model diagram of the meshing of the "fourth support member" part is as shown in Figure 15 Shown. The "fourth support member" part is analyzed by finite element according to loading condition A, and the displacement deformation and stress obtained are respectively as shown in Figure 16 And Figure 17 Shown.

[0140] From Figure 16 And Figure 17 It can be seen that the maximum deformation of the part is 1.51×10 -5 mm, occurring at the lower edge of the inner conical hole of the part; the maximum stress of the part is 309 Pa, occurring at the lower edge of the outer conical surface of the part.

[0141] The displacement deformation and stress nephogram obtained by performing a finite element analysis on the fourth support member according to loading condition B are as shown in Figure 18 and Figure 19 shown.

[0142] From Figure 18 and Figure 19 it can be seen that the maximum deformation of this part is 3.29×10 -2 mm, which occurs at the lower edge of the inner tapered hole of the part; the maximum stress of the part is 0.673 MPa, which occurs at the lower edge of the outer tapered surface of the part.

[0143] (3) Finite element analysis of the "third support member" part

[0144] The finite element model diagram of the mesh division of the "third support member" part is as shown in Figure 20 shown. The "third support member" part is subjected to a finite element analysis according to loading condition A, and the displacement deformation and stress obtained are as shown in Figure 21 and Figure 22 shown.

[0145] From Figure 21 and Figure 22 it can be seen that the maximum deformation of the part is 2.43×10 -4 mm, which occurs at the lower edge of the inner tapered hole of the part; the maximum stress of the part is 699 Pa, which occurs at the lower edge of the outer tapered surface of the part.

[0146] The "third support member" part is subjected to a finite element analysis according to the situation of loading condition B, and the displacement deformation and stress nephogram obtained are as shown in Figure 23 and Figure 24 shown.

[0147] From Figure 23 and Figure 24 it can be seen that the maximum deformation of the "third support member" part is 3.88×10 -2 mm, which occurs at the lower edge of the inner tapered hole of the part; the maximum stress of the part is 68.6 KPa, which occurs at the lower edge of the inner tapered hole of the part.

[0148] (4) Finite element analysis of the second support member part

[0149] The finite element model diagram of the mesh division of the "second support member" part is as shown in Figure 25 shown. The second support member part is subjected to a finite element analysis according to loading condition A, and the displacement deformation and stress nephogram obtained are as shown in Figure 26 and Figure 27 shown.

[0150] From Figure 26 and Figure 27 it can be seen that the maximum deformation of the part is 3.06×10-4 mm, occurring at the lower edge of the inner tapered hole of the part; the maximum stress of the part is 790 Pa, occurring at the lower edge of the outer tapered surface of the part.

[0151] The second support part is subjected to finite element analysis according to loading condition B, and the displacement deformation and stress nephogram obtained are as Figure 28 shown in Figure 29 Figure.

[0152] It can be seen from Figure 28 and Figure 29 that the maximum deformation of the part is 2.87×10 -2 mm, occurring at the lower edge of the inner tapered hole of the part; the maximum stress of the part is 51.4 KPa, occurring at the lower edge of the inner tapered hole of the part.

[0153] (5) Finite element analysis of the first support part

[0154] The finite element model diagram of the mesh division of the first support part is as Figure 30 shown in Figure. The first support part is subjected to finite element analysis according to loading condition A, and the displacement deformation and stress nephogram obtained are as Figure 31 shown in Figure 32 Figure.

[0155] It can be seen from Figure 31 and Figure 32 that the maximum deformation of the part is 1.1×10 -3 mm, occurring at the lower edge of the inner tapered hole of the part; the maximum stress of the part is 1.47 KPa, occurring at the lower edge of the outer tapered surface of the part.

[0156] The first support part is subjected to finite element analysis according to loading condition B, and the displacement deformation and stress nephogram obtained are as Figure 33 shown in Figure 34 Figure.

[0157] It can be seen from Figure 33 and Figure 34 that the maximum deformation of the part is 1.14×10 -2 mm, occurring at the lower edge of the inner tapered hole of the part; the maximum stress of the part is 9.08 KPa, occurring at the lower edge of the outer tapered surface of the part.

[0158] (6) Finite element analysis of the "terminal load" part

[0159] The finite element model diagram of the mesh division of the "terminal load" is as Figure 35 shown in Figure, and the location of the thinnest part of the "terminal load" part is as Figure 36 shown in Figure. The "terminal load" part is subjected to finite element analysis according to loading condition A, and the displacement deformation and stress nephogram obtained are as Figure 37 shown in Figure 38 Figure.

[0160] From Figure 37 and Figure 38 it can be seen that the maximum deformation of the part is 5.51×10 -2 mm, occurring at the lower edge of the inner hole of the small end hole of the part; the maximum stress of the part is 49.5 KPa, occurring at the inner edge of the thinnest part of the part.

[0161] The displacement deformation and stress nephogram of the "terminal load" part analyzed by finite element according to loading condition B are as Figure 39 shown in Figure 40 the figure.

[0162] From Figure 39 and Figure 40 it can be seen that the maximum deformation of the part is 5.72×10 -2 mm, occurring at the lower edge of the inner hole of the small end hole of the part; the maximum stress of the part is 51.3 KPa, occurring at the lower edge of the inner hole of the small end hole of the part.

[0163] (7) Analysis results of stiffness and strength

[0164] According to the finite element analysis of the above 6 support parts made of PMI foam material, the force, deformation and stress distribution under two different loading conditions can be obtained. Therefore, the above analysis results are summarized, and the analysis data are tabulated in Table 4.

[0165] Table 4 Finite element analysis results of each part

[0166]

[0167] As can be seen from Table 4, among the 6 support parts under loading condition A and loading condition B, the deformation and maximum stress of the "terminal load" part are the largest. The maximum deformation of the "first support part - fifth support part" is less than 0.03 mm, while the maximum deformation of the "terminal load" part is less than 0.06 mm, which is difficult to affect the function of the concentric cone. That is to say, the analyzed "first support part - fifth support part" and "terminal load" parts can meet the stiffness requirements.

[0168] According to the part strength checking method, when the strength corresponding to the part material is greater than the maximum stress it bears and the safety factor obtained by dividing the two is greater than the set safety factor, it can be determined that the part strength meets the requirements. Therefore, let the strength corresponding to the part material be [σ], the maximum stress it bears be σ, and the safety factor f 0 can be calculated by the following formula.

[0169]

[0170] For the 6 support parts made of PMI foam analyzed previously, the main failure modes are tearing and fracture. Here, taking its shear strength as the part strength, we can obtain [σ] = 2.7 MPa. Combining with the finite analysis results shown in Table 4, we can take its maximum stress as the value of the variable σ. According to the above formula, the safety factors of each part under loading condition A and loading condition B can be calculated as shown in Table 5.

[0171] Table 5 Safety factors of the strength of each part

[0172]

[0173] As can be seen from Table 5, whether under loading condition A or loading condition B, the strength safety factors of the support parts and the terminal load are both greater than 3, which can meet the safe use of the product under static conditions.

[0174] Reliability analysis of the internal support components

[0175] In the process of traditional strength design and analysis of parts, the strength of a certain material is often regarded as a constant value, which actually does not conform to the actual situation. Due to the differences in the smelting / synthesis, production, manufacturing, heat treatment, and chemical treatment of the materials of parts, as well as the different specimen loading methods, test environments, and dimensional tolerances, the strength of various materials will show a discrete phenomenon. Similarly, in engineering practice, the stress borne by parts also has a certain degree of discreteness. The static strength of parts and the stress under static action can generally be described by a normal distribution.

[0176] (1) Calculation of the structural reliability of parts

[0177] According to the stress-strength interference theory, when the mean and standard deviation of the strength and stress in the normal distribution are known, the structural reliability of parts can be calculated by the following formula.

[0178]

[0179] Among them, R is the reliability; Z is called the reliability coefficient or probability safety margin, which can be calculated by the following formula.

[0180]

[0181] Among them, μ S and σ S are the mean and standard deviation of the comprehensive strength of the part respectively; μL and σ L are the mean and standard deviation of the comprehensive stress of the part respectively.

[0182] (2) Calculation of the reliability safety factor of parts

[0183] Taking "the mean strength μ S / Mean stress μ L The defined statistical safety factor is called the reliability safety factor. When the strength and stress follow a normal distribution, the reliability safety factor of the part structure can be calculated by the following formula.

[0184]

[0185] Among them, f 0 is the reliability safety factor of the mechanical structure. C VS is the coefficient of variation of strength, and C VL is the coefficient of variation of stress, which can be calculated by the following formula.

[0186]

[0187]

[0188] Among them, μ S and σ S are the mean and standard deviation of the comprehensive strength of the part respectively; μ L and σ L are the mean and standard deviation of the comprehensive stress of the part respectively.

[0189] (3) Failure rate calculation

[0190] Given the mean and standard deviation of the strength and stress in the normal distribution, the failure rate function can be calculated by the following formula.

[0191]

[0192] Among them, Z is the reliability coefficient, which can be obtained from the above formula; λ(t) is the failure rate function, f(t) is the failure probability density function, and R(t) is the reliability function.

[0193] (4) Reliability calculation results

[0194] Considering that in the actual working condition, the weight of the inner conductor is mainly borne by the "terminal load" part, and the "first support part - fifth support part" plays an auxiliary support role. Loading condition A is closer to its actual working condition. Considering the possible errors between the actual load and the calculated load caused by assembly, processing, and deformation, etc., the standard deviation of the load on each part under loading condition A is taken as 10% of its calculated load, that is, the coefficient of variation, and it is often taken as 5% - 10% for reliability analysis.

[0195] Perform reliability calculations on the 6 support parts made of PMI foam material analyzed above under loading condition A. Among them, the mean strength μ S of the PMI foam material is 2.7 MPa, and the standard deviation σ SThe value is 0.3 MPa. In the concentric cone structure, the mean values of the maximum stresses of each part are shown in Tables 4 and 5, and the coefficient of variation C of the stress received VL = 10%. Combining with the formula in the reliability calculation method, the reliability data of each part under loading condition A can be calculated.

[0196] Taking the reliability of the "terminal load" part as an example below, the strength reliability, reliability safety factor and failure rate are calculated.

[0197] The comprehensive strength mean value μ of the terminal load S = 2.7 MPa, the standard deviation σ S = 0.3 MPa, the comprehensive maximum stress mean value μ L = 0.0495 MPa, and its coefficient of variation C VL = 10%.

[0198] The reliability coefficient is obtained:[[]]

[0199]

[0200] The structural reliability R of it is obtained:[[]]

[0201]

[0202] From the calculation formula of the reliability safety factor, the coefficient of variation C of the strength is obtained VS :[[]]

[0203]

[0204] The coefficient of variation C of the stress VL :[[]]

[0205] C VL = 10% = 0.1

[0206] Therefore, the reliability safety factor f:[[]]

[0207]

[0208] The failure rate λ is obtained:[[]]

[0209]

[0210] Similarly, the reliability data of all parts can be calculated and are shown in Table 6.

[0211] Table 6 Reliability calculation results of each part

[0212]

[0213] When the mass of the supported inner conductor is 17.86 kg, the designed parts of "the first support member - the fifth support member" and the "terminal load" part all have high strength reliability. Considering that the concentric cone structure is static under actual working conditions, it meets the requirements of its strength reliability.

[0214] Force analysis and finite element analysis were carried out on the load-bearing part "terminal load" of the inner conductor and the auxiliary positioning parts "the first support member - the fifth support member" in two load-bearing cases. The analysis results show that the above six parts meet the strength and reliability requirements in both load-bearing cases.

[0215] The reliability analysis method of the present invention provides an effective means for the reliability assessment of the concentric cone TEM cell. This reliability analysis method can also be used for the reliability assessment of equipment such as TEM cells, GTEM cells, and microwave anechoic chambers. Applying this method to the design of concentric cone TEM cells can greatly improve the reliability of concentric cone TEM cell products.

[0216] In summary, the support structure provided by the present invention has sufficient strength to support the weight of the inner conductor; and can ensure the concentricity of the inner and outer conductors and stabilize the specific relative position relationship between the inner and outer conductors; in the auxiliary uniform area test, the support structure can also support the probe under test; selecting PMI foam material with high density can further increase the strength and reliability of the support structure, thereby improving the stability of the concentric cone type TEM cell.

[0217] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, rather than limitations on the implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes or variations can be made based on the above description. It is impossible to list all the implementation manners here. Any obvious changes or variations derived from the technical solutions of the present invention still fall within the protection scope of the present invention.

Claims

1. A reliability analysis method for a concentric conical TEM indoor conductor support structure, characterized in that, the concentric conical TEM indoor conductor support structure includes: a first support member located between the inner conductor and the outer conductor; the first support member has an annular structure with a hollow middle part; the outer side wall of the first support member is fixedly attached to the inner wall of the outer conductor; the inner side wall of the first support member is fixedly attached to the outer wall of the inner conductor; the material of the first support member is PMI foam material; the reliability analysis method includes the following steps: Establish a finite element model of the first support member and perform finite element analysis to obtain the deformation amount and stress distribution of the first support member; Design and obtain the safety factor, reliability, and reliability coefficient of the first support member; Design and obtain the reliability safety factor and failure rate of the first support member; Analyze the obtained results of the deformation amount, stress distribution, safety factor, reliability, reliability coefficient, reliability safety factor, and failure rate of the first support member; According to the component strength checking method, when the strength corresponding to the material of the first support component is greater than the maximum stress it bears and the safety factor obtained by dividing the two is greater than the set safety factor, it can be determined that the strength of the first support component meets the requirements; thus, let the strength corresponding to the material of the first support component be [σ], the maximum stress it bears be σ, and the safety factor be f 0 It can be calculated according to Formula 1 to obtain the safety factor of the first support component; According to the stress-strength interference theory, when the mean and standard deviation of the strength and stress of the first support member in the normal distribution are known, the structural reliability of the first support member is calculated using Formula Two; where R is the reliability; Z is called the reliability coefficient or probability safety margin and can be calculated using Formula Three; Among them, μ S and σ S are the mean and standard deviation of the comprehensive strength of the parts respectively; μ L and σ L are the mean and standard deviation of the comprehensive stress of the parts respectively; With "mean strength μ S / mean stress μ L " defined as the statistical safety factor, it is called the reliability safety factor. When the strength and stress follow a normal distribution, the reliability safety factor of the first support structure is calculated by Equation 4; Among them, f 0 is the reliability safety factor of the mechanical structure; C VS is the strength variation coefficient; C VL is the stress variation coefficient, and C VS and C VL are calculated through Formula Five and Formula Six respectively; Among them, μ S and σ S are the mean and standard deviation of the comprehensive strength of the parts respectively; μ L and σ L are the mean and standard deviation of the comprehensive stress of the parts respectively. When the mean and standard deviation of the strength and stress of the first support member in the normal distribution are known, the failure rate function is calculated using Formula Seven; where Z is the reliability coefficient; λ(t) is the failure rate function, f(t) is the failure probability density function, and R(t) is the reliability function.

2. The reliability analysis method for a concentric conical TEM indoor conductor support structure according to claim 1, characterized in that, along the axial direction of the inner conductor, the thickness of the first support member is 53 mm.

3. The reliability analysis method for a concentric conical TEM indoor conductor support structure according to claim 1, characterized in that, the support structure further includes a second support member, a third support member, a fourth support member, and a fifth support member; the first support member, the second support member, the third support member, the fourth support member, and the fifth support member are arranged along the axial direction of the inner conductor.

4. The reliability analysis method for a concentric conical TEM indoor conductor support structure according to claim 3, characterized in that, the second support member, the third support member, the fourth support member, and the fifth support member all have an annular structure with a hollow middle part.

5. The reliability analysis method for a concentric conical TEM indoor conductor support structure according to claim 3, characterized in that, the second support member is attached to the third support member; the fourth support member is attached to the fifth support member.

6. The reliability analysis method for a concentric conical TEM indoor conductor support structure according to claim 3, characterized in that, the materials of the second support member, the third support member, the fourth support member, and the fifth support member are all PMI foam materials.

7. The reliability analysis method for a concentric conical TEM indoor conductor support structure according to claim 1, characterized in that, the plane where the upper end face or the lower end face of the first support member is located is parallel to the plane where the upper end face or the lower end face of the inner and outer conductors is located.

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