A single-tooth electromagnetic bandgap resonant cavity for thickness-direction dielectric property testing

Abstract

This invention discloses a single-tooth electromagnetic bandgap resonant cavity for testing dielectric properties in the thickness direction, belonging to the technical field of dielectric property testing for microwave and millimeter-wave materials. The single-tooth electromagnetic bandgap resonant cavity constructed by this method uses the TE test mode. 10n The electric field direction within the cavity is perpendicular to the material thickness direction, enabling the testing of dielectric properties along the Z-axis. This cavity allows for multi-frequency testing, meeting testing requirements within the 2.5GHz to 110GHz frequency range. With a quality factor greater than 3000, it offers higher testing accuracy when measuring dielectric loss. Compared to a double-tooth electromagnetic bandgap resonant cavity, a single-tooth electromagnetic bandgap resonant cavity is simpler, solving the positioning difficulties caused by the need for strict symmetry in the electromagnetic bandgap structure between the two half-cavities, while also reducing manufacturing costs. Furthermore, one side of the single-tooth electromagnetic bandgap resonant cavity is a smooth metal plate, making sample insertion through the gap more convenient.

Description

Technical Field

[0001] This invention belongs to the field of microwave and millimeter-wave material dielectric property testing technology, and particularly relates to a precise testing method for the dielectric properties of materials. Background Technology

[0002] With the development and application of 5G, the operating frequency band of printed circuit boards has been upgraded from centimeter waves to millimeter waves. Due to the structural characteristics of printed circuit board materials, there are significant differences in the dielectric properties of the materials in the XY plane and the Z-axis (thickness) direction. The circuit board industry usually refers to the relative permittivity in the Z-axis direction. Therefore, the accurate testing of dielectric properties in the Z-axis direction in the millimeter wave band has become a current focus of attention.

[0003] Existing Z-axis testing methods eliminate the influence of air gaps by tightly clamping the sample and electrodes. These primarily include the stripline resonator method specified in IPC TM-650 2.5.5.5 and the balanced disk resonator (BCDR) method specified in IEC 63185-2020. However, due to the influence of air gaps, residual air in the test fixture (with an ε value of approximately 1) can cause the measured dielectric constant to be slightly lower than the material's intrinsic dielectric constant. The stripline resonator method requires fabricating a microstrip circuit from the material under test, limiting its application to easily fabricated materials, and its testing frequency is limited to 12 GHz. The balanced disk resonator method requires fabricating two identical circular sheet samples of the material under test before testing, which is difficult and unsuitable for fragile materials and copper-clad laminates with retained copper electrodes. Both of these methods are complex to operate, have low quality factors, and are limited in sample preparation and testing frequency, failing to meet the requirements for high-precision Z-axis dielectric performance testing.

[0004] When testing dielectric properties along the Z-axis, an electric field perpendicular to the dielectric plane is required. This perpendicular electric field is extremely sensitive to horizontal air gaps; if the gap is too large, the electric field will become discontinuous, preventing the generation of normal resonant modes. To avoid the influence of air gaps, an electromagnetic bandgap structure is introduced into the resonant cavity design. A non-contact structure prevents electromagnetic signals from leaking through the central gap, ensuring the electromagnetic field remains continuous even with the gap open, thus enabling open-slit testing of dielectric properties along the Z-axis. However, this electromagnetic bandgap resonant cavity design requires a strictly symmetrical distribution of the electromagnetic bandgap structure between the two half-cavities, presenting challenges in fabrication and installation. Furthermore, in actual operation, inserting the sample through the double-toothed gap with facing tooth surfaces is difficult, easily scratching the sample surface and affecting the test results. Summary of the Invention

[0005] To overcome the shortcomings of the existing technology, this invention proposes a single-tooth electromagnetic bandgap resonant cavity for testing dielectric properties in the thickness direction, providing a practical solution for high-precision testing of the Z-axis properties of microwave materials.

[0006] The single-tooth electromagnetic bandgap resonant cavity constructed in this invention uses the TE test mode. 10n The electric field direction within the cavity is perpendicular to the material thickness direction, enabling the testing of dielectric properties along the Z-axis. This cavity allows for multi-frequency testing, meeting testing requirements within the 2.5GHz to 110GHz frequency range. With a quality factor greater than 3000, it offers higher testing accuracy when measuring dielectric loss. Compared to a double-tooth electromagnetic bandgap resonant cavity, a single-tooth electromagnetic bandgap resonant cavity is simpler, solving the positioning difficulties caused by the need for strict symmetry in the electromagnetic bandgap structure between the two half-cavities, while also reducing manufacturing costs. Furthermore, one side of the single-tooth electromagnetic bandgap resonant cavity is a smooth metal plate, making sample insertion through the gap more convenient.

[0007] To achieve the above objectives, the present invention employs the following technology:

[0008] A single-tooth electromagnetic bandgap resonant cavity for thickness-direction dielectric property testing is disclosed. The cavity comprises an upper cavity, a lower cavity, a side support frame, and a coupling device. The upper cavity consists of a series of periodically arranged metal pillars arranged around a rectangular resonant cavity on the inner side of a metal plate, forming a non-contact electromagnetic bandgap structure. The lower cavity is a smooth metal plate. The side support frame positions the upper cavity; positioning holes are provided at corresponding positions on the side support frame and the cavity side, and screws are used for fixing, forming a fixed gap of a certain thickness between the upper and lower cavities. The coupling device consists of two coupling holes located at the center of the upper cavity, parallel to the side support frame. The single-tooth electromagnetic bandgap resonant cavity uses the TE test mode. 10n The direction of the electric field inside the cavity is perpendicular to the material thickness direction, which can be used to test the dielectric properties in the Z-axis direction.

[0009] The rectangular resonant cavity formed in the central region inside the upper cavity has a length of a and a width of b. Generally, the value of a / b ranges from 1 to 5, and the specific values ​​of a and b are determined by the design frequency of the resonant cavity.

[0010] A series of k rings of periodically distributed metal pillars are arranged around the rectangular resonant cavity. Generally, k is greater than or equal to 2, which can meet the design requirements of the microwave frequency band.

[0011] The toothed cross-section of a metal column can be rectangular, circular, triangular, or polygonal.

[0012] The metal columns are arranged periodically at equal intervals, forming a tooth pitch of p, where the value of p ranges from 1 mm to 15 mm.

[0013] Each metal pillar in the cavity must be designed identically, including its shape and size. Taking a rectangular tooth shape as an example, the cross-sectional size of each metal pillar is w*w, where w ranges from 0.2mm to 5mm; the height of each metal pillar is h, where h ranges from 0.5mm to 8mm.

[0014] The lower cavity is made of a smooth metal plate, and its size and material are the same as those of the upper cavity. The surface of the resonant cavity is made of silver or gold.

[0015] The upper cavity and the lower cavity are separated by a fixed gap of thickness D through a mechanical structure. The value of D ranges from 0.2 mm to 3 mm.

[0016] During testing, the sample to be tested is horizontally inserted from the side of the fixed gap. The sample material must be a thin sheet with uniform thickness, flat surface, and capable of covering the rectangular resonant cavity.

[0017] The relative permittivity of the material under test is applicable in the range of 2.5 GHz to 110 GHz, and the loss tangent is applicable in the range of 0.0001 to 0.01.

[0018] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are as follows:

[0019] 1. The single-tooth electromagnetic bandgap resonant cavity proposed in this invention achieves electromagnetic field continuity along the Z-axis using a non-contact physical structure, thereby enabling open-slit testing of dielectric properties along the Z-axis. The test mode used by this method is TE. 10n The mode enables testing at multiple frequency points, meeting the dielectric performance testing requirements within the frequency range of 2.5GHz to 110GHz.

[0020] 2. The single-tooth electromagnetic bandgap resonant cavity proposed in this invention is simpler in design than the double-tooth electromagnetic bandgap resonant cavity, which simplifies the cavity structure, significantly reduces the processing cost, and solves the problem of difficult positioning during processing and installation caused by the strict symmetry of the electromagnetic bandgap structure between the two half-cavities of the double-tooth electromagnetic bandgap resonant cavity.

[0021] 3. Compared with the double-tooth electromagnetic bandgap resonant cavity, the single-tooth electromagnetic bandgap structure resonant cavity proposed in this invention has a larger fixed gap D and a wider range of test sample thickness. One side of the single-tooth electromagnetic bandgap structure is a smooth metal plate, which makes it easy to pick up and put in samples and solves the problem of difficulty in inserting samples from the double-tooth gap with the tooth surfaces facing each other.

[0022] 4. The single-tooth electromagnetic bandgap resonant cavity proposed in this invention concentrates most of the electric field energy in the central region when used for dielectric property testing, effectively improving the resonant cavity's testing sensitivity to samples. The quality factor is greater than 3000, which is higher than the traditional z-axis testing method. Attached Figure Description

[0023] Figure 1 Top sectional view illustrating the design of a single-tooth electromagnetic bandgap resonant cavity;

[0024] Figure 2 Side view sectional view illustrating the design of a single-tooth electromagnetic bandgap resonant cavity;

[0025] Figure 3 The electric field distribution diagram is shown for a single-tooth electromagnetic bandgap resonant cavity.

[0026] Figure 4 A schematic diagram of a single-tooth electromagnetic bandgap resonant cavity testing system;

[0027] Figure 5 This is a top cross-sectional view of the 10GHz single-tooth electromagnetic bandgap resonant cavity in Example 1;

[0028] Figure 6 This is a side cross-sectional view of the 10GHz single-tooth electromagnetic bandgap resonant cavity in Example 1;

[0029] Figure 7 This is a top cross-sectional view of the 28GHz single-tooth electromagnetic bandgap resonant cavity in Example 2;

[0030] Figure 8 This is a side cross-sectional view of the 28GHz single-tooth electromagnetic bandgap resonant cavity in Example 2;

[0031] Figure 9 This is a top cross-sectional view of the 56GHz single-tooth electromagnetic bandgap resonant cavity in Example 3;

[0032] Figure 10 This is a side cross-sectional view of the 56GHz single-tooth electromagnetic bandgap resonant cavity in Example 3.

[0033] Reference numerals: 1 is the upper cavity of the electromagnetic bandgap structure, 2 is the lower cavity of the electromagnetic bandgap structure, 3 is the side support frame of the cavity, 4 is the positioning hole, 5 is the coupling device, 6 is the microwave coaxial cable, and 7 is the vector network analyzer. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings.

[0035] A single-tooth electromagnetic bandgap resonant cavity used for dielectric property testing in the thickness direction is shown in the top and side cross-sectional views as follows. Figure 1 and Figure 2 As shown. The test mode used for this cavity is TE. 10n The electric field distribution diagram is as follows Figure 3 As shown. A schematic diagram of the test system built using this cavity is shown below. Figure 4 As shown, the electromagnetic bandgap resonant cavity is connected to the network analyzer via a coaxial cable.

[0036] Example 1

[0037] This embodiment provides a single-tooth electromagnetic bandgap resonant cavity for thickness-direction dielectric property testing at a test frequency of 10 GHz. Specifically, the top and side cross-sectional views of the single-tooth electromagnetic bandgap resonant cavity are shown below. Figure 5 and Figure 6 As shown, the design parameters are as follows: the rectangular resonant cavity formed in the central region has dimensions a of 21 mm and b of 21 mm. Four rings of periodically distributed metal pillars are set around the rectangular resonant cavity. The side length w of the metal pillars is 3.5 mm, the height h is 3.45 mm, the spacing p of the metal pillars is 8.1 mm, and the gap thickness D is 1.6 mm.

[0038] The test sample material used in this embodiment is 1mm fused silica glass (relative permittivity ε). r ′ =3.7, loss tangent tanδ = 0.0005). The measured resonant frequency of the cavity was 10.455 GHz, and the quality factor was 6267.2. Fused silica glass was horizontally placed into the fixed gap from the side along the lower cavity. The resonance peak was found using a network analyzer, and the resonant frequency after loading the sample was found to be 10.106 GHz and the quality factor was 5239.1. The dielectric properties of the material were calculated based on the resonant characteristics of the cavity before and after loading the sample, and the dielectric constant and loss tangent of the material were found to be 3.68 and 5.72 × 10⁻⁶, respectively. -4 Compared with the standard value, the test results of this system for quartz glass are within the standard range, and the accuracy of the test results meets the requirements.

[0039] Example 2

[0040] This embodiment provides a single-tooth electromagnetic bandgap resonant cavity for thickness-direction dielectric property testing at a test frequency of 28 GHz. Specifically, the top and side cross-sectional views of the single-tooth electromagnetic bandgap resonant cavity are shown below. Figure 7 and Figure 8As shown, the design parameters are as follows: the rectangular resonant cavity formed in the central region has dimensions a of 17.8 mm and b of 6.7 mm. Three rings of periodically distributed metal pillars are set around the rectangular resonant cavity. The side length w of the metal pillars is 1.5 mm, the height h is 4 mm, the spacing p of the metal pillars is 3.95 mm, and the gap thickness D is 1 mm.

[0041] The test sample material used in this embodiment is 0.6mm fused silica glass (relative permittivity ε). r ′ =3.7, loss tangent tanδ = 0.0005). The measured resonant frequency of the cavity was 28.752 GHz, and the quality factor was 4170.3. Fused silica glass was horizontally placed into the fixed gap from the side along the lower cavity. The resonance peak was found using a network analyzer, and the resonant frequency after loading the sample was found to be 27.125 GHz and the quality factor was 3791.1. The dielectric properties of the material were calculated based on the resonant characteristics of the cavity before and after loading the sample, and the dielectric constant and loss tangent of the material were found to be 3.72 and 4.8 × 10⁻⁶, respectively. -4 Compared with the standard value, the test results of this system for quartz glass are within the standard range, and the accuracy of the test results meets the requirements.

[0042] Example 3

[0043] This embodiment provides a single-tooth electromagnetic bandgap resonant cavity for thickness-direction dielectric property testing at a test frequency of 56 GHz. Specifically, the top and side cross-sectional views of the single-tooth electromagnetic bandgap resonant cavity are shown below. Figure 9 and Figure 10 As shown, the design parameters are as follows: the rectangular resonant cavity formed in the central region has dimensions a of 9.5 mm and b of 5 mm. Two rings of periodically distributed metal pillars are set around the rectangular resonant cavity. The side length w of the metal pillars is 0.5 mm, the height h is 2 mm, the spacing p between the metal pillars is 1.8 mm, and the gap thickness D is 0.5 mm.

[0044] The test sample material used in this embodiment is 0.3mm fused silica glass (relative permittivity ε). r ′ =3.7, loss tangent tanδ = 0.0005). The measured resonant frequency of the cavity was 56.427 GHz, and the quality factor was 4134.3. Fused silica glass was horizontally placed into the fixed gap from the side along the lower cavity. The resonance peak was found using a network analyzer, and the resonant frequency after loading the sample was obtained as 56.014 GHz and the quality factor as 3679.6. The dielectric properties of the material were calculated based on the resonant characteristics of the cavity before and after loading the sample, and the dielectric constant and loss tangent of the material were found to be 3.7 and 6.9 × 10⁻⁶, respectively. -4Compared with the standard value, the test results of this system for quartz glass are within the standard range, and the accuracy of the test results meets the requirements.

[0045] 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 features or steps in the disclosed methods or processes may be combined in any way, except for mutually exclusive features and / or steps.

Claims

1. A single-tooth electromagnetic bandgap resonant cavity for testing dielectric properties in the thickness direction, characterized in that, The single-tooth electromagnetic bandgap resonant cavity includes an upper cavity, a lower cavity, a side support frame, and a coupling device. The upper cavity is formed by a series of periodically arranged metal pillars around a rectangular resonant cavity on the inner side of a metal plate, creating a non-contact electromagnetic bandgap structure. The lower cavity is a smooth metal plate. The side support frame is used to position the upper cavity; positioning holes are provided at corresponding positions on the side support frame and the cavity side, and screws are used for fixing, forming a fixed gap of a certain thickness between the upper and lower cavities. The coupling device consists of two coupling holes located at the center of the upper cavity, parallel to the side support frame. The test mode used for the single-tooth electromagnetic bandgap resonant cavity is... The direction of the electric field inside the cavity is perpendicular to the material thickness direction, which enables the testing of... Z Dielectric properties in the axial direction.

2. The single-tooth electromagnetic bandgap resonant cavity for thickness-direction dielectric property testing as described in claim 1, characterized in that, The rectangular resonant cavity formed in the central region inside the upper cavity has a length of a , width is b , a / b The value range is 1 to 5. a and b The specific value is determined by the design frequency of the resonant cavity.

3. The single-tooth electromagnetic bandgap resonant cavity for thickness-direction dielectric property testing as described in claim 1, characterized in that, Set around the rectangular resonant cavity k Metal columns arranged in a periodic pattern. k A value greater than or equal to 2 can meet the design requirements of the microwave frequency band.

4. The single-tooth electromagnetic bandgap resonant cavity for thickness-direction dielectric property testing as described in claim 1, characterized in that, The toothed cross-section of the metal column is circular or polygonal.

5. The single-tooth electromagnetic bandgap resonant cavity for thickness-direction dielectric property testing as described in claim 1, characterized in that, The metal columns are arranged periodically at equal intervals, forming a tooth pitch of... p , p The value range is 1mm to 15mm.

6. The single-tooth electromagnetic bandgap resonant cavity for thickness-direction dielectric property testing as described in claim 1, characterized in that, Each metal pillar in the cavity must be designed identically, including its shape and size. When the teeth of the metal pillars are rectangular, the cross-sectional size of each metal pillar is... w * w , w The value range is 0.2mm to 5mm; the height of each metal column is... h , h The value range is 0.5mm to 8mm.

7. The single-tooth electromagnetic bandgap resonant cavity for thickness-direction dielectric property testing as described in claim 1, characterized in that, The lower cavity is made of a smooth metal plate, and its size and material are the same as those of the upper cavity. The surface of the resonant cavity is made of silver or gold.

8. The single-tooth electromagnetic bandgap resonant cavity for thickness-direction dielectric property testing as described in claim 1, characterized in that, The upper and lower cavities are separated by a mechanical structure with a thickness of [missing information]. D Fixed gap, D The value range is 0.2mm to 3mm.

9. The single-tooth electromagnetic bandgap resonant cavity for thickness-direction dielectric property testing as described in claim 1, characterized in that, During testing, the sample to be tested is horizontally inserted from the side of the fixed gap. The sample material must be a thin sheet with uniform thickness, flat surface, and capable of covering the rectangular resonant cavity.

10. The single-tooth electromagnetic bandgap resonant cavity for thickness-direction dielectric property testing as described in claim 1, characterized in that, The relative permittivity of the material under test is applicable in the range of 2.5 GHz to 110 GHz, and the loss tangent is applicable in the range of 0.0001 to 0.01.

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