A dielectric property testing system and method based on split-off sectorial resonant cavity

Abstract

The application provides a dielectric property testing system and method based on a split fan-shaped resonant cavity, and belongs to the technical field of microwave testing. Different from the structure of an existing split cylindrical resonator, the application adopts a split fan-shaped cylindrical resonant cavity, and cuts a slit on the edges of two surfaces of the split resonator to suppress a spurious mode, so that complete suppression of the spurious mode near the working mode is realized, a relatively pure TE 0n1 mode spectrum is obtained in a wide frequency range, and the single resonant cavity can realize measurement of TE 011 -TE 081 eight modes. In addition, the sample testing area of the resonant cavity is less than one fifth of a traditional cylindrical cavity, so the size of the corresponding sample to be tested is also reduced by less than one fifth, and the processing cost of the sample to be tested can be effectively reduced.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of microwave testing, and particularly relates to a dielectric property testing system and method based on a split fan-shaped resonant cavity. BACKGROUND

[0002] Accurate measurement of complex permittivity is essential for the synthesis, development and application in microwave circuit and device design of materials. With the rapid development of high-frequency electronic information technology, the demand for materials such as low-loss, low-cost sheets and films applied in a wide frequency range has increased significantly, and accurate measurement of the complex permittivity of sheets and films has become crucial to their practical application. Over the past few decades, various methods for measuring the dielectric constant, such as transmission / reflection and resonance, have been well developed. Among them, the split cylindrical resonant cavity (SCR) method with high Q value is often used to measure sheets and films due to its high accuracy. According to the ratio of the diameter to the height of the SCR, it can be simply divided into TE 01p mode SCR and TE 0n1 mode SCR, because the latter has higher sensitivity, making it more suitable for measuring sheets and films than the former. The TE 0n1 mode SCR shows higher sensitivity, partly because the sample volume occupies a larger proportion, and partly because the electric field distribution of the TE 0n1 mode is more concentrated in the center region of the sample.

[0003] The working mode of the SCR is TE 0n1 , not the fundamental mode, and is usually accompanied by some interfering modes near its frequency, mainly the degenerate mode TM 1n1 and the non-zero azimuthal mode TE mn1 (m≠0) mode. In recent years, a lot of research has been done on how to separate the interfering modes in the split cylindrical resonator at home and abroad. For example, Takashi Shimizu and others in Japan proposed a method of opening a groove at both ends of the cavity of the SCR, which can shift the degenerate TM 1n1 mode to a lower frequency band and separate it from the TE 0n1 mode. Koichi Hirayama and others in Japan proposed replacing the groove with a protrusion; the presence of the protrusion can move the TM 111 mode to a higher frequency band, while the groove moves the TM 111 mode to a lower frequency band, thus increasing the measurement range of the TE 011 mode. However, these methods only separate the degenerate mode from the main mode and do not weaken it, and only work at a single frequency point, so when measuring in a wide frequency band, multiple resonant cavities need to be designed to cover it, which will result in high cost and different sample sizes.

[0004] Therefore, how to design the separated resonant cavity so that it can effectively suppress the interference mode and a single resonant cavity can realize multi-mode operation has become the current research focus. SUMMARY

[0005] In view of the problems existing in the background art, the purpose of the present application is to provide a dielectric property test system and method based on a separated fan-shaped resonant cavity. The cavity innovatively adopts a separated fan-shaped cavity, and a circular arc gap is provided on the upper and lower interfaces of the cavity, thereby realizing complete suppression of the interference mode near the working mode, obtaining a relatively "pure" TE 0n1 mode spectrum in a wide frequency range, and a single resonant cavity can realize measurement of TE 011 ~ TE 081 eight modes.

[0006] To achieve the above-mentioned purpose, the technical scheme of the present application is as follows:

[0007] A dielectric property test system based on a separated fan-shaped resonant cavity, comprising a fan-shaped separated resonant cavity, a coupling device, a height adjusting device, a support component, a vector network analyzer and a computer;

[0008] The fan-shaped separated resonant cavity comprises a first metal plate, an upper half cavity, a lower half cavity and a second metal plate; wherein the upper half cavity and the lower half cavity are the same in size and structure, and are provided with a fan-shaped cavity in the center in a cubic shape, the central angle of the fan shape is a, and the fan radius is b; the first metal plate is fixedly arranged on the upper surface of the upper half cavity, and the second metal plate is fixedly arranged on the lower surface of the lower half cavity; a fan-shaped through gap is arranged on the first metal plate and the second metal plate, and the outer circular arc of the gap overlaps the circular arc segment of the fan-shaped cavity in the vertical direction, and the inner circular arc is within the cavity range; the upper half cavity and the lower half cavity are separable, the upper half cavity is fixed to the other end of the support arm, and the lower half cavity is fixed to the height adjusting device; the material to be measured is placed between the upper half cavity and the lower half cavity;

[0009] The support component comprises a horizontal support base and one end of a support arm fixedly arranged on one side of the horizontal support base, and the other end of the support arm is fixedly arranged on the upper half cavity of the fan-shaped separated resonant cavity;

[0010] The coupling device comprises two coupling probe rings and a coupling amount adjusting unit, the first coupling ring is arranged on the left side of the circular arc segment of the upper half cavity, the second coupling ring is arranged on the right side of the circular arc segment of the lower half cavity, and the heights of the first coupling ring and the second coupling ring from the interface of the fan-shaped separated resonant cavity are the same, at the same time, the distances from the two coupling rings to the line connecting the center of the fan-shaped cavity and the center point of the circular arc are the same, and the coupling rings are horizontal and point to the center; the coupling amount adjusting unit is fixed to the other end of the support arm and connected to the end of the coupling ring, and is used for adjusting the depth of the coupling ring in the fan-shaped cavity to adjust the coupling amount and achieve a weak coupling state.

[0011] The height adjusting device is arranged on the horizontal supporting base, the second metal plate and the lower half cavity are placed on the upper surface of the height adjusting device, the height adjusting device is adjusted, the upper half cavity and the lower half cavity jointly form a completed fan-shaped cavity, the distance between the upper half cavity and the lower half cavity is adjusted by the height adjusting device, so that the testing of the sample with different thicknesses is realized.

[0012] The vector network analyzer is connected with the coupling device through a cable and connected with a computer through a network cable.

[0013] Further, in order to suppress the angular Mode, the fan-shaped cavity central angle α needs to avoid the angle which can be divided by 360°, and α < 90°, because α is too large, the suppression effect on the angular Mode is small, the smaller α is, the lower the quality factor will be.

[0014] Further, the fan-shaped cavity central angle α is preferably 70°.

[0015] Further, the radius b of the fan-shaped cavity is determined by the mode frequency.

[0016] Further, the conductor plane of the fan-shaped cavity is processed by brass, and the inner wall is plated with silver.

[0017] Further, the two coupling rings are coaxial line fed magnetic coupling rings.

[0018] Further, the coupling probe ring is a coaxial line fed magnetic coupling ring, and the weak coupling is that the coupling amount is less than -50dB.

[0019] Further, the sample to be measured is a thin film dielectric material, the material area should be greater than the coverage area of the upper half cavity, and the thickness range is 0.01mm-1mm.

[0020] Further, the fan-shaped gap width is preferably 0.9mm.

[0021] The application also provides a method for inverting the dielectric performance of the measured dielectric material based on the above-mentioned test system, specifically: because the two sides of the fan-shaped resonant cavity are equivalent to electric walls, the cavity is regarded as a complete cylindrical cavity wall, and because the sample has an influence on the electric wall, the correction term of the edge field of the cavity is corrected by using finite element simulation software, and then the accurate dielectric performance of the measured material is inverted according to the measured values of the resonant frequency f0 and the quality factor Q u (empty load Q factor) of the resonant cavity.

[0022] Neglecting the edge effect of the sample, the approximate values of the dielectric constant and the loss tangent of the sample are obtained based on the measured values of the resonant frequency f0 and the quality factor Q u .a and tan δ a :

[0023]

[0024] where c is the speed of light (c = 2.9979 x 10 8 m / s), M is the height of the half-cavity, t is the thickness of the medium material to be measured, X and Y are intermediate process quantities, X is the first root calculated from a given Y value, and R s is the surface resistance of the cavity conductor, specifically the formula is:

[0025]

[0026] where k0= 2πf 0 / c, k r = j' 0n / R, j' 0n is the nth root of the derivative of the zeroth order Bessel function; when k0- k r < 0, Y is approximately jY'; μ and σ are the permeability and conductivity of the cavity conductor, respectively, σ r is the relative conductivity, σ0= 5.8 x 10 7 S / m is the conductivity of standard copper; the specific formulas of constants A and B are:

[0027]

[0028] where W1 e and W2 e are the electrical energy stored in the sample region and the air region, respectively, P cy1 is the conductor loss of the sample region, P cy2 is the conductor loss of the sidewall of the air region, P end is the conductor loss of the shorted end wall, and ω is the angular frequency at each mode frequency, and the specific formula is:

[0029]

[0030] where J0is the zeroth order Bessel function.

[0031] By solving (1) ~ (12), the accurate dielectric constant ε' and loss tangent tan δ can be calculated from the measured resonance frequency f0, the Q u factor and size parameters of the resonant cavity:

[0032]

[0033] Δε', ΔA, ΔB are correction terms due to the edge field.

[0034] Further, the Δε', ΔA, ΔB are obtained by finite element numerical simulation software simulation.

[0035] In summary, due to the adoption of the technical scheme, the application has the following advantages:

[0036] The application provides a dielectric property test system based on a fan-shaped split resonant cavity. 0n1 The application adopts a fan-shaped split cylindrical resonant cavity, cuts a slit at the edge of two surfaces of the split resonant cavity to suppress a spurious mode, and finally realizes complete suppression of the spurious mode near the working mode. 011 081 In addition, the sample test area of the resonant cavity is less than one fifth of a traditional cylindrical cavity, and thus the size of the sample to be tested is also reduced by less than one fifth, so that the processing cost of the sample to be tested can be effectively reduced. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 Fig. 1 is a structural schematic diagram of the dielectric property test system based on the fan-shaped split resonant cavity.

[0038] Figure 2 Fig. 2 is a structural schematic diagram of the fan-shaped split resonant cavity in the dielectric property test device.

[0039] Figure 3 Fig. 3 is a comparison diagram of simulation results of the fan-shaped resonant cavity and the split cylindrical cavity with the same size in the dielectric property test device, which respectively correspond to TE 0n1 (n=1-8) modes.

[0040] 1 is the fan-shaped split resonant cavity, 2 is the coupling device, 3 is the height adjusting device, 4 is the support arm, 5 is the vector network analyzer, 6 is the computer, 1-1 is the upper half of the resonant cavity, 1-2 is the lower half of the resonant cavity, and 1-3 is the slit of the cavity. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical scheme and advantages of the application clearer, the application is further described in detail below in combination with the embodiments and the drawings.

[0042] A dielectric property test system based on a split fan-shaped resonant cavity has a structural schematic diagram as shown in Figure 1 Fig. 1, which comprises a fan-shaped split resonant cavity 1, a coupling device 2, a height adjusting device 3, a support component, a vector network analyzer 5 and a computer 6.

[0043] ​The structural diagram of the fan-shaped split resonant cavity 1 is shown in the figure Figure 2 As shown, it comprises a first metal plate, an upper half cavity 1-1, a lower half cavity 1-2 and a second metal plate; wherein the upper half cavity and the lower half cavity have the same structure and are both in the shape of a cube, with a fan-shaped cavity in the center, the central angle of the fan being a and the cavity radius being b; the first metal plate is fixedly arranged on the upper surface of the upper half cavity, and the second metal plate is fixedly arranged on the lower surface of the lower half cavity; a fan-shaped through slit 1-3 is arranged on the first metal plate and the second metal plate, and the outer arc of the slit overlaps the arc segment of the fan-shaped cavity in the vertical direction, and the inner arc is within the cavity range; the upper half cavity and the lower half cavity are detachable, the upper half cavity is fixed to the other end of the support arm, and the lower half cavity is fixed to the height adjusting device; the material to be tested is placed between the upper half cavity and the lower half cavity;

[0044] The support component comprises a horizontal support base and one end of a support arm 4 fixedly arranged on one side of the horizontal support base, and the upper half cavity of the fan-shaped split resonant cavity is fixedly arranged on the other end of the support arm;

[0045] The coupling device 2 comprises two coupling probe rings and a coupling amount adjusting unit, the first coupling ring is arranged on the left side of the arc segment of the upper half cavity, the second coupling ring is arranged on the right side of the arc segment of the lower half cavity, and the first coupling ring and the second coupling ring are at the same height from the interface of the fan-shaped split resonant cavity, at the same time, the distance from the two coupling rings to the center line of the fan-shaped cavity center and the arc center point is the same, and the coupling rings are horizontal and point to the center; the coupling amount adjusting unit is fixedly arranged on the other end of the support arm and connected with the end of the coupling ring, for adjusting the depth of the coupling ring in the fan-shaped cavity, adjusting the coupling amount and achieving the weak coupling state;

[0046] The height adjusting device 3 is arranged on the horizontal support base, and the second metal plate and the lower half cavity are placed on the upper surface of the height adjusting device; the height adjusting device is adjusted to make the upper half cavity and the lower half cavity together form a complete fan-shaped cavity; the distance between the upper half cavity and the lower half cavity is adjusted by using the height adjusting device, so as to realize the test of different thicknesses of the material to be tested;

[0047] The vector network analyzer 5 is connected with the coupling device 2 through a cable and connected to the computer 6 through a network cable.

[0048] Example 1

[0049] The central angle a of the fan-shaped cavity is 70°, the cavity radius b is 40 mm, the height of the upper half cavity and the lower half cavity is 8.4 mm; the width of the fan-shaped slit is 0.9 mm;

[0050] The coupling ring is a coaxial feeding magnetic coupling ring, which is arranged on the side of the resonant cavity arc and perpendicular to the arc surface; the two coupling rings point to the center of the circle, and the included angle between the center of the arc and the center of the circle is 35°, and the height of each coupling ring from the interface of the cavity is 0.6mm.

[0051] Based on the test device of example 1, the resonant frequency f0 and the quality factor Q of the resonant cavity are obtained u Then the dielectric constant of the material to be measured is obtained by inversion, and the specific process is as follows:

[0052] Ignoring the edge effect of the sample, based on the measured values of the resonant frequency f0 and the quality factor Q u , the approximate values of the dielectric constant and the loss tangent of the sample are obtained ε' a and tanδ a :

[0053]

[0054] Wherein, c is the speed of light (c=2.9979×10 8 m / s), M is the length of the half cavity, t is the thickness of the medium material to be measured, X is the first root calculated according to the given Y value, R s is the surface resistance of the cavity conductor, and the specific formula is:

[0055]

[0056] Wherein, k0=2πf 0 / c, k r =j' 0n / R, j' 0n is the nth root of the derivative of the zero-order Bessel function; when k0-k r <0, Y is approximately jY'; μ and σ are the magnetic permeability and electrical conductivity of the cavity conductor respectively, σ r is the relative electrical conductivity, σ0=5.8×10 7 S / m is the electrical conductivity of standard copper; the specific formula of constants A and B is:

[0057]

[0058]

[0059] Wherein, and are the electrical energy stored in the sample area and the air area respectively, P cy1 is the conductor loss of the sample area, P cy2 is the conductor loss of the side wall of the air area, P end is the conductor loss of the short-circuit end wall, and ω is the angular frequency at each mode frequency, and the specific formula is:

[0060]

[0061] Where J0 is the zeroth-order Bessel function;

[0062] By solving (1) to (12), the measured resonant frequency f0 and the Q of the resonant cavity are obtained. u The accurate dielectric constant ε' and loss tangent tanδ of the dielectric material under test can be calculated from the dimensional parameters:

[0063]

[0064] Δε', ΔA, and ΔB are correction terms generated by the edge field, which can be obtained through finite element numerical simulation software.

[0065] A schematic diagram of the dielectric constant testing device based on a sector-shaped split resonant cavity in this embodiment is shown below. Figure 3 As shown, a comparison is made with the schematic diagram of a traditional split cylindrical resonant cavity dielectric constant testing device. Figure 3 The comparison results show that the dielectric constant testing device based on the sector-shaped split resonant cavity described in this invention can completely suppress interference modes near the operating mode and obtain a relatively "pure" TE0n1 mode spectrum over a wide frequency range.

[0066] The above description is merely a specific embodiment of the present invention. Any feature disclosed in this specification may be replaced by other equivalent or similar features unless otherwise specified. All disclosed features, or steps in all methods or processes, may be combined in any way except for mutually exclusive features and / or steps.

Claims

1. A dielectric property testing system based on a split-type sector resonant cavity, characterized in that, It includes a fan-shaped split resonant cavity, coupling device, height adjustment device, support components, vector network analyzer, and computer; The fan-shaped split resonant cavity includes a first metal plate, an upper cavity, a lower cavity, and a second metal plate. The upper and lower cavities are identical in size and structure, forming a cube with a centrally located fan-shaped cavity. The central angle of the fan is α, and the radius of the fan is b. The first metal plate is fixedly mounted on the upper surface of the upper cavity, and the second metal plate is fixedly mounted on the lower surface of the lower cavity. Both the first and second metal plates have fan-shaped through-slits, with the outer arc of the slits overlapping the arc of the fan-shaped cavity in the vertical direction, and the inner arc within the cavity. The upper and lower cavities are separable; the upper cavity is fixed to the other end of a support arm, and the lower cavity is fixed to a height adjustment device. The material to be tested is placed between the upper and lower cavities. The support component includes a horizontal support base and a support arm fixedly installed on one side of the horizontal support base, with the upper cavity fixedly installed on the other end of the support arm; The coupling device includes two coupling probe rings and a coupling amount adjustment unit. The first coupling ring is located on the left side of the upper half-cavity arc segment, and the second coupling ring is located on the right side of the lower half-cavity arc segment. The first and second coupling rings are at the same height from the interface of the sector-shaped split resonant cavity. At the same time, the two coupling rings are equidistant from the line connecting the center of the sector-shaped cavity and the center point of the arc. The coupling rings are horizontal and point towards the center. The coupling amount adjustment unit is fixed to the other end of the support arm and connected to the end of the coupling ring. It is used to adjust the depth of the coupling ring in the sector-shaped cavity to adjust the coupling amount and achieve a weak coupling state. The height adjustment device is set on a horizontal support base. The second metal plate and the lower half cavity are placed on the upper surface of the height adjustment device. The height adjustment device is adjusted so that the upper half cavity and the lower half cavity together form a complete fan-shaped cavity. The distance between the upper half cavity and the lower half cavity is adjusted by the height adjustment device, so as to realize the testing of samples of different thicknesses. The vector network analyzer is connected to the coupling device via a cable and to the computer via a network cable.

2. The dielectric performance testing system as described in claim 1, characterized in that, The central angle α of the sector cavity should avoid angles divisible by 360°, and α < 90°.

3. The dielectric performance testing system as described in claim 2, characterized in that, The central angle α of the sector-shaped cavity is 70°.

4. The dielectric performance testing system as described in claim 1, characterized in that, The radius b of the sector cavity is determined by the mode frequency.

5. The dielectric performance testing system as described in claim 1, characterized in that, The conductor plane of the fan-shaped cavity is made of brass, and the inner wall is plated with silver.

6. The dielectric performance testing system as described in claim 1, characterized in that, The two coupling rings are coaxially fed magnetic coupling rings; weak coupling is defined as coupling amount less than -50dB.

7. The dielectric performance testing system as described in claim 1, characterized in that, The sample to be tested is a thin film dielectric material, the material area should be larger than the coverage area of ​​the upper cavity, and the thickness range is 0.01mm~1mm.

8. The dielectric performance testing system as described in claim 1, characterized in that, The width of the fan-shaped gap is 0.9mm.

9. A test method based on the dielectric performance test system as described in any one of claims 1-8, characterized in that, The specific process is as follows: Step 1. Place the sample to be tested on the upper surface of the lower cavity, and then adjust the height adjustment device so that the sample is in contact with the lower surface of the upper cavity. Measure the resonant frequency f0 and the quality factor Q at this point. u ; Step 2. Based on the resonant frequency f0 and the quality factor Q u The approximate dielectric constant of the sample under test is obtained by inverting the measured values. Approximate value of loss tangent : （1） （2） Where c is the speed of light, M is the height of the half-cavity, t is the thickness of the medium material being measured, X is the first root calculated based on the given Y value, and R... s It is the surface resistance of the hollow conductor, and the specific formula is: (3) (4) , (5) in, , , It is the nth root of the derivative of the 0th-order Bessel function; and These are the magnetic permeability and electrical conductivity of the cavity conductor, respectively. It is the relative conductivity. This is the conductivity of standard copper; the specific formulas for constants A and B are: (6) (7) in, and These are the electrical energy stored in the sample region and the air region, respectively. For the conductor loss in the sample region, For conductor losses on the sidewalls of the air region, For conductor loss at the short-circuit end wall, The specific formula for the angular frequency at each mode frequency is: (8) (9) (10) (11) (12) in, It is a zero-order Bessel function; The accurate dielectric constant can be calculated by solving (1)~(12). and loss tangent : （13） （14） , , This is a correction term generated by the edge field.

10. The test method as described in claim 9, characterized in that, , , The results were obtained through simulation using finite element numerical simulation software.

Images