Miniaturized conical coaxial probe

Abstract

A measuring head is arranged on a metal inner conductor, a dielectric material layer is wrapped on the metal inner conductor, a metal outer conductor is wrapped on the dielectric material layer, the measuring head extends out of the metal outer conductor, a plurality of grooves which are arranged at intervals are arranged on the metal outer conductor and close to the measuring head, and the measuring head is arranged in the grooves. And the groove is used for exposing the dielectric material layer at the corresponding position. According to the invention, the traditional layout of the coaxial probe structure is changed by protruding the inner conductor and the dielectric material layer outwards, and the dielectric material of the coaxial probe is elongated to form a cone shape, so that the stability of the probe structure is ensured while the inner conductor is extended, and the protruding dielectric material layer is covered by the outer conductor, so that the reliability of the probe structure is improved. And by designing the structure of the covered outer conductor, the exposed area of the dielectric material in the external environment is reduced, so that the material loss caused by direct contact or environmental factors is reduced.

Description

Technical Field

[0001] The invention relates to a miniaturized conical coaxial probe. Background Art

[0002] The dielectric constant is one of the important parameters to characterize the electrical properties of materials. When an external electric field is applied to a medium, induced charges are generated to weaken the electric field. The induced charges form an induced electric field inside the medium. The ratio of the external electric field to the induced electric field in the medium is the dielectric constant, and its value is related to the frequency. The dielectric constant is a physical coefficient that characterizes the insulation ability of a material. The study of the dielectric constant of liquids has important theoretical significance and application value.

[0003] The commonly used methods for measuring dielectric constants include parallel plate capacitance method, resonant cavity method, free space method, transmission reflection method, open coaxial probe method, etc.

[0004] Through comparative studies on the advantages and disadvantages of various methods for testing electromagnetic parameters, it is found that although the classical measurement methods such as the resonant cavity method and the transmission reflection method are mature in technology, the measurement equipment is complex and the measured medium samples are difficult to process. Compared with other measurement methods, the open coaxial probe method has simple sample preparation and a wide applicable frequency band. It can accurately measure the dielectric constant near the probe terminal opening without destroying the sample components. The most important point is that it will not cause damage to the measured sample, and can meet the requirements of real-time measurement and non-destructive measurement to a certain extent. And because of its open structure, strong versatility, and simple test equipment (only reflection device is required), it is particularly suitable for non-destructive on-site online (on-line), in-vivo, and in-situ testing. So far, it has been developed to measure the dielectric constant of liquid and semi-fluid dielectric materials. However, it also has the disadvantage of low test accuracy.

[0005] The main principle of the open coaxial probe method is to use the measured reflection coefficient to extract the electromagnetic parameters of the medium to be measured. Known research shows that the research on the open coaxial line method began in the 1980s, and has been widely used in biology, rock physics, chemical engineering and other fields in the past two decades. According to different application characteristics, the open coaxial probe method has been continuously improved and optimized. In the coaxial probe, not only the number of coaxial probes is increased, but also flanges and short-circuit plates are provided on the original basis, or the head port is changed to an oblique cut, or a protective film is added to the measuring part. Therefore, it can be seen that the coaxial probe structure should be optimized to improve its measurement sensitivity, thereby improving the current low test accuracy of the open coaxial probe method.

[0006] In view of this, the present invention provides a miniaturized conical coaxial probe, which changes the structure of the coaxial probe by protruding the inner conductor and dielectric material outward, and partially covers the protruding dielectric material layer with the outer conductor, thereby reducing the exposure and loss of the dielectric material layer, thereby enhancing the test sensitivity of the probe and extending the use time. Summary of the invention

[0007] The present invention provides a miniaturized conical coaxial probe in order to solve the problems existing in the prior art.

[0008] The technical solutions adopted in the present invention are:

[0009] A miniaturized conical coaxial probe comprises a metal outer conductor, a dielectric material layer and a metal inner conductor, wherein a measuring head is arranged on the metal inner conductor, the dielectric material layer is wrapped on the metal inner conductor, the metal outer conductor is wrapped on the dielectric material layer, and the measuring head extends out of the metal outer conductor, and a plurality of slots arranged at intervals are arranged on the metal outer conductor and close to the measuring head, and the slots are used to expose the dielectric material layer at corresponding positions.

[0010] Furthermore, the metal outer conductor and the dielectric material layer both include a conical portion and a cylindrical portion, the conical portion of the metal outer conductor is wrapped around the conical portion of the dielectric material layer, and the end surface of the conical portion in the metal outer conductor is flush with the end surface of the conical portion in the dielectric material layer, and the groove is arranged on the conical portion of the metal outer conductor.

[0011] Furthermore, the metal inner conductor is a variable diameter structure, with a first cylindrical portion of constant size and a measuring head of a conical structure at both ends, and a second conical portion, a third conical portion, a fourth conical portion and a second cylindrical portion arranged in sequence between the first cylindrical portion and the measuring head.

[0012] Furthermore, the large circular end of the second conical portion is equal in diameter to the first cylindrical portion, the small circular end of the second conical portion is equal in diameter to the small circular end of the third conical portion, the large circular end of the third conical portion is equal in diameter to the large circular end of the fourth conical portion, and the small circular end of the fourth conical portion is equal in diameter to the second cylindrical portion.

[0013] Furthermore, the first cylindrical portion and the second conical portion are disposed in a cylindrical portion in the dielectric material layer.

[0014] Furthermore, the large round end of the measuring head is fitted with the small round end of the tapered portion in the dielectric material layer and has the same diameter.

[0015] Furthermore, the metal outer conductor and the metal inner conductor are both made of copper, and the dielectric material layer is made of polytetrafluoroethylene.

[0016] The present invention has the following beneficial effects:

[0017] The present invention changes the traditional layout of the coaxial probe structure by protruding the inner conductor and the dielectric material layer outward, and by stretching the dielectric material of the coaxial probe to form a cone, the inner conductor is extended while ensuring the stability of the probe structure. The protruding dielectric material layer is covered with an outer conductor, and the exposed area of ​​the dielectric material in the external environment is reduced by designing the structure of the covered outer conductor, thereby reducing material loss caused by direct contact or environmental factors. The overall structure of the probe is shorter and the diameter is thicker than that of the commonly used probes, so it is not easy to deform. Only the conical part needs to be immersed in the solution, and the volume of the solution to be tested is small. The integrity of the overall probe structure is maintained. The improvement not only improves the sensitivity of the test, but also extends the use time of the probe due to the reduction in dielectric material loss. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a structural diagram of the present invention.

[0019] Figure 2 It is a structural diagram of the metal inner conductor in the present invention.

[0020] Figure 3 It is a structural diagram of the dielectric material layer in the present invention.

[0021] Figure 4 It is a structural diagram of the metal outer conductor in the present invention.

[0022] Figure 5 The figure is a frequency response curve diagram of the reflection parameter (S11) of the probe structure of a certain size simulated under vacuum of the present invention.

[0023] Figure 6 It is a frequency response curve diagram of the probe structure of the present invention to the simulated reflection parameter (S11) in the liquid dielectric material. DETAILED DESCRIPTION

[0024] The present invention will be further described below in conjunction with the accompanying drawings.

[0025] like Figures 1 to 4 The present invention discloses a miniaturized conical coaxial probe, comprising a metal outer conductor 1, a dielectric material layer 2 and a metal inner conductor 3, wherein a measuring head 36 is provided on the metal inner conductor 3, the dielectric material layer 2 is wrapped on the metal inner conductor 3, the metal outer conductor 1 is wrapped on the dielectric material layer 2, and the measuring head 36 extends out of the metal outer conductor 1, and a plurality of slots 11 arranged at intervals are provided on the metal outer conductor 1 and close to the measuring head 36, and the slots 11 are used to expose the dielectric material layer 2 at corresponding positions.

[0026] The metal outer conductor 1 and the dielectric material layer 2 both include a tapered portion and a cylindrical portion, that is, the sizes of the metal outer conductor 1 and the dielectric material layer 2 remain unchanged at first, with the outer diameter of the metal outer conductor 1 being 8 mm and the outer diameter of the dielectric material layer 2 being 6.6 mm, and then gradually decrease, with the outer diameter of the metal outer conductor 1 first decreasing while the inner diameter remaining unchanged, and then gradually decreasing together with the outer diameter of the dielectric material layer 2, and in the portion where the sizes of the metal outer conductor 1 and the dielectric material layer 2 decrease together, the metal outer conductor 1 is wrapped and covered on the surface of the dielectric material layer 2 with a thickness of 0.01 mm, that is, the tapered portion of the metal outer conductor 1 is wrapped on the tapered portion of the dielectric material layer 2.

[0027] The end of the metal outer conductor 1 and the end of the dielectric material layer 2 are on the same horizontal plane, that is, the end surface of the tapered portion of the metal outer conductor 1 is flush with the end surface of the tapered portion of the dielectric material layer 2. The size of the end of the dielectric material layer 2 is equal to the size of the large round end of the measuring head 36 of the metal inner conductor 3, and its diameter is 1 mm.

[0028] The size of the metal inner conductor 3 is unchanged at first, and its diameter is 2 mm (i.e., the diameter of the first cylindrical portion 31), which forms a fixed ratio with the maximum inner diameter of the metal outer conductor 1, so as to match the 50 ohm impedance of the connected coaxial line. Then, the size of the metal inner conductor 3 decreases with the outer diameter of the metal outer conductor 1 to a diameter of 0.8 mm (i.e., the second conical portion 32 is obtained), so that the reflection information of the probe structure is concentrated in a range, so that the reflection parameters of the probe are enhanced. When the outer diameter of the metal outer conductor 1 and the dielectric material layer 2 gradually decrease, the size of the metal inner conductor 3 begins to gradually increase to the original size, forming the third conical portion 33, so that the reflection parameters of the more concentrated area are further enhanced, so that the reflection coefficient S11 in the concentrated range is less than -15dB. Before reaching the right end of the metal outer conductor 1, the size of the third conical portion 33 is gradually reduced to a diameter of 0.8 mm, thereby forming a fourth conical portion 34, so that the overall reflection coefficient S11 in the concentrated range is less likely to be close to -15 dB, and the range of reflection coefficient S11 less than -15 dB is no longer continuous due to external factors. When reaching the first groove 11 on the left side of the metal outer conductor 1, the size of the metal inner conductor 3 no longer changes, forming a second cylindrical portion 35 with a constant inner conductor size, corresponding to the groove 11 of the metal outer conductor 1, and its size is unchanged so that the existing concentrated range of reflection coefficient S11 less than -15 dB no longer fluctuates, until the end of the metal outer conductor 1 and the end of the dielectric material layer 2 are at the same horizontal plane, the size of the metal inner conductor 3 becomes its tip structure, that is, the size of the large round end of the measuring head 36, with a diameter of 1 mm and a tip height of 3 mm.

[0029] The gradual change structure of the metal outer conductor 1, the dielectric material layer 2 and the metal inner conductor 3 is a conical gradual change structure, and the metal outer conductor 1, the dielectric material layer 2 and the metal inner conductor 3 are sequentially wrapped from the outside to the inside without gaps.

[0030] The probe is connected to the port of the vector network analyzer (VNA) via a coaxial cable. The characteristic impedance formula of the coaxial cable is related to the ratio of the inner diameter of its metal outer conductor (1) to the outer diameter of the metal inner conductor (3). The impedance is generally 50 ohms or 75 ohms. The characteristic impedance formula is as follows:

[0031]

[0032] Where Z0 is the impedance, ε r is the relative dielectric constant of the dielectric material, b is the maximum inner diameter of the metal outer conductor 1, and a is the maximum diameter of the metal inner conductor 3.

[0033] In the present invention, the ratio of the inner diameter of the metal outer conductor 1 to the outer diameter of the metal inner conductor 3 follows the formula result that the impedance of the coaxial line is 50 ohms. The maximum outer diameter of the metal outer conductor of the probe is 8 mm, and the maximum inner diameter is 6.6 mm. Its terminal structure has 7 layers of annular vacant gap structures, the length of which is 3 mm, and the width of each layer of gap is 0.05 mm. The minimum outer diameter of the terminal end is 1.02 mm, and the minimum inner diameter is 1 mm.

[0034] The outer diameter of the dielectric material layer 2 is 6.6 mm, the inner diameter is 2 mm, and the diameter of the end opening is 1 mm.

[0035] The diameter of the metal inner conductor 3 is 2 mm, which gradually decreases to 0.8 mm, then gradually increases to the original diameter, and then gradually decreases to 0.8 mm. The bottom diameter of the measuring head is 1 mm, and the length is 3 mm. The length of the conical part of the probe is 23 mm.

[0036] The metal outer conductor 1 and the metal inner conductor 3 are made of copper, and the dielectric material layer 2 is made of polytetrafluoroethylene, whose relative dielectric constant is 2.08.

[0037] The coaxial probe method is used for measurement. The test process is roughly divided into three steps: the first step is to measure the reflection coefficient of the medium under test. The opening of the open coaxial probe terminal is partially immersed in the liquid. The other end of the coaxial probe is connected to the vector network analyzer. The reflection coefficient of the sample under test is obtained based on the vector network analyzer; the second step is to establish a theoretical model between the complex dielectric constant and the reflection coefficient of the medium under test; the third step is to obtain the complex dielectric constant of the medium under test through iterative inversion.

[0038] The sample to be tested is a liquid material, so during simulation, the material to be tested is used to wrap and cover the conical part of the probe. The material area to be tested and the conical part of the probe present a truncated cone-shaped test area as a whole. The long diameter of this area is 12 mm, the short diameter is 3.3 mm, and the length is 25 mm.

[0039] Figure 5 The reflection parameter information of the probe structure is given, from which it can be seen that the reflection coefficient S11 of the probe is less than -15dB in the range of 4.74-10.11GHz, and the measurement sensitivity of the probe is relatively high in the range of 4.74-10.11GHz. The space occupied by the probe proposed by the present invention has a maximum diameter of 8mm and a maximum length of 71mm.

[0040] Figure 6 The relative dielectric constant ε of the probe is given r The simulation measurement result of the liquid medium material is 10. The liquid material fills the test area to ensure the close contact between the material and the probe. The information of the reflection parameter S11 caused by it is as follows Figure 6 As shown, compared Figure 5 and Figure 6 It can be seen that the measured material can cause obvious changes in the reflection parameters. The present invention obtains the dielectric constant of the measured material through this change combined with the theoretical model, numerical inversion and neural network method.

[0041] The present invention also stretches the dielectric material of the coaxial probe to form a cone, so that the inner conductor is extended while ensuring the stability of the probe structure. However, the cost is to expose a large area of ​​the dielectric material. Therefore, the outer conductor is directly used as a protective film for the dielectric material layer. Unlike the previous dielectric material layer exposed on the same plane, the new structure designed has grooves on the cone surface through the outer conductor to reduce the exposure of the dielectric material, reduce the loss of the probe component materials, and extend the use time. The overall length of the probe is shorter, and the overall diameter is larger than that of the previous commonly used probes, and it is not easy to deform. In the simulation test, the volume of the solution to be tested is small. The measuring device designed as a whole in this way can improve the measurement sensitivity when working in the range of 4.74-10.11GHz.

[0042] The above description is only a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several improvements without departing from the principle of the present invention, and these improvements should also be regarded as within the protection scope of the present invention.

Claims

1. A miniaturized conical coaxial probe, characterized in that: The invention comprises a metal outer conductor (1), a dielectric material layer (2) and a metal inner conductor (3); a measuring head (36) is provided on the metal inner conductor (3); the dielectric material layer (2) is wrapped on the metal inner conductor (3); the metal outer conductor (1) is wrapped on the dielectric material layer (2); the measuring head (36) extends out of the metal outer conductor (1); and a plurality of slots (11) arranged at intervals are provided on the metal outer conductor (1) and at positions close to the measuring head (36); the slots (11) are used to expose the dielectric material layer (2) at corresponding positions.

2. The miniaturized conical coaxial probe according to claim 1, characterized in that: The metal outer conductor (1) and the dielectric material layer (2) both comprise a conical portion and a cylindrical portion, the conical portion of the metal outer conductor (1) is wrapped around the conical portion of the dielectric material layer (2), and the end surface of the conical portion of the metal outer conductor (1) is flush with the end surface of the conical portion of the dielectric material layer (2), and the groove (11) is arranged on the conical portion of the metal outer conductor (1).

3. The miniaturized conical coaxial probe according to claim 2, characterized in that: The metal inner conductor (3) is a variable diameter structure, and its two ends are respectively a first cylindrical portion (31) of constant size and a measuring head (36) of a conical structure, and a second conical portion (32), a third conical portion (33), a fourth conical portion (34) and a second cylindrical portion (35) are arranged in sequence between the first cylindrical portion (31) and the measuring head (36).

4. The miniaturized conical coaxial probe according to claim 3, characterized in that: The large circular end of the second conical portion (32) has the same diameter as the first cylindrical portion (31), the small circular end of the second conical portion (32) has the same diameter as the small circular end of the third conical portion (33), the large circular end of the third conical portion (33) has the same diameter as the large circular end of the fourth conical portion (34), and the small circular end of the fourth conical portion (34) has the same diameter as the second cylindrical portion (35).

5. The miniaturized conical coaxial probe according to claim 4, characterized in that: The first cylindrical portion (31) and the second conical portion (32) are disposed in a cylindrical portion in the dielectric material layer (2).

6. The miniaturized conical coaxial probe according to claim 3, characterized in that: The large round end of the measuring head (36) fits with the small round end of the tapered portion in the dielectric material layer (2) and has the same diameter.

7. The miniaturized conical coaxial probe according to claim 1, characterized in that: The materials of the metal outer conductor (1) and the metal inner conductor (3) are both copper, and the material of the dielectric material layer (2) is polytetrafluoroethylene.

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