A thin film material electromagnetic characteristic testing device based on a reentrant coaxial resonant cavity

Abstract

The purpose of this invention is to provide a testing device for the electromagnetic properties of thin film materials based on a re-entrant coaxial resonant cavity, belonging to the field of electromagnetic parameter testing technology for microwave and millimeter-wave materials. The device comprises three parts: a re-entrant coaxial resonant cavity, a sample fixture, and a support base. By placing samples at the locations of strongest electric and magnetic field intensity within the resonant cavity, the complex permittivity and permeability of the thin film material can be measured. The testing of the complex permittivity and permeability of the sample is completed using only one device. Simultaneously, the sample placement gap does not interrupt the electric field lines, thus not affecting the field distribution within the cavity. This allows the device to maintain the high quality factor of the resonant cavity while reducing the cavity volume, concentrating the electric field within the resonant cavity mainly in the capacitively loaded region, improving the testing bandwidth, sensitivity, and accuracy, and reducing the requirements for sample size.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic parameter testing technology for microwave and millimeter-wave materials, specifically relating to a device for testing the electromagnetic properties of thin film materials based on a re-entrant coaxial resonant cavity. Background Technology

[0002] With the rapid development of electronic technology, thin film materials are widely used in various fields such as integrated circuits, aerospace, and radar. In the microwave and millimeter-wave fields, the research and use of thin film materials require accurate testing of their electromagnetic properties.

[0003] Currently, the main testing method for the electromagnetic properties of thin film materials is the resonance method. The resonance method involves placing the material in a resonant cavity at the point of strongest electric field to test the complex permittivity, or at the point of strongest magnetic field to test the permeability. The principle of the resonance method is to measure the resonant frequency and quality factor of the cavity before and after placing the sample, and then calculate the electromagnetic parameters of the material based on the changes in these parameters. In testing thin film materials, considering the characteristics of the field distribution and ease of sample placement, rectangular or split resonant cavities are typically used. However, in the low-frequency range, the required cavity and sample sizes are too large, leading to inconvenient sample placement and high processing costs. Furthermore, because thin film materials are very thin, when the sample and cavity sizes are too large, the disturbance before and after placement is relatively small, resulting in insignificant changes in the resonant frequency and quality factor of the resonant cavity, leading to certain errors in the test results.

[0004] Reentrant coaxial resonators are widely used due to their concentrated electric field distribution and high testing sensitivity. Furthermore, their resonant frequency depends only on the longitudinal length and is independent of the transverse dimension, allowing them to operate at lower frequencies compared to rectangular and split resonators of the same cavity size. In 2011, Zhou Yang et al. developed a reentrant coaxial cavity with a movable piston at the bottom end face operating in the 400MHz–5200MHz range and tested it on PTFE and quartz samples. In 2016, Yu Chengyong of the University of Electronic Science and Technology of China designed a reentrant coaxial cavity with an operating frequency band of 0.6GHz–13GHz. By opening longitudinal slits around the cavity, he cut off the stray mode current lines, thereby suppressing stray modes. He also used the perturbation method to accurately calculate the complex permittivity of PTFE and high-purity quartz. Currently, in re-entry resonant cavity testing schemes, cylindrical solid samples are often used as test samples due to considerations of the field distribution characteristics of the coaxial cavity and the ease of sample placement. However, for thin film materials, the difficulty of sample placement and the limitations of the cavity's own structure restrict the application of re-entry coaxial resonant cavities in thin film electromagnetic parameter testing. Furthermore, existing electromagnetic parameter testing devices generally can only test one specific electromagnetic parameter. Therefore, how to utilize a single testing device to test multiple electromagnetic parameters has become one of the starting points for device design. Summary of the Invention

[0005] To address the problems existing in the background technology, the present invention aims to provide a thin film material electromagnetic property testing device based on a re-entrant coaxial resonant cavity. This device comprises three parts: a re-entrant coaxial resonant cavity, a sample fixture, and a support base. By placing samples at the locations of strongest electric and magnetic field strengths within the resonant cavity, the complex permittivity and permeability of the thin film material can be measured. The complex permittivity and permeability of the sample are tested using only one device. Simultaneously, the sample placement gap does not interrupt the electric field lines, thus not affecting the field distribution within the cavity. This allows the device to maintain the high quality factor of the resonant cavity while reducing the cavity volume, concentrating the electric field within the resonant cavity mainly in the capacitively loaded region, improving the test bandwidth, sensitivity, and accuracy, and reducing the requirements for sample size.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] A thin film material electromagnetic property testing device based on a re-entrant coaxial resonant cavity includes a re-entrant coaxial resonant cavity (1), a sample holder (2), and a support base (3).

[0008] The re-entry coaxial resonant cavity (1) includes an inner conductor (4), an outer conductor (5), a coupling excitation device (6-1), and a coupling receiving device (6-2); wherein, the outer conductor (5) is a hollow cylinder with only an upper top surface, and a gap is provided at the center of the upper top surface, and a gap corresponding to the position of the gap on the upper top surface is provided on the side wall near the lower bottom surface; the inner conductor (4) includes a conductor post (4-1) and a base (4-2), the conductor post (4-1) is a solid metal cylinder, and gaps are provided at the center of both the upper top surface and the lower bottom surface, and the gap on the lower bottom surface extends into the cylinder; the base is a metal disc, and a through-hole is provided at its center. The gaps are fixed at the center of the base; the top surface of the conductor (4-1) and the top surface of the conductor (5) outside the resonant cavity do not contact each other; the gaps set on the conductor (4) inside the resonant cavity and the conductor (5) outside the resonant cavity are coplanar; the gap (5-2) on the top surface of the conductor (5) outside the resonant cavity and the gap (4-3) on the top surface of the conductor (4-1) together serve as the test channel for the complex permittivity of the thin film material; the gap (5-3) on the side wall near the bottom surface of the conductor (5) outside the resonant cavity and the gap (4-4) on the bottom surface of the conductor (4-1) and the gap on the base of the conductor (4) inside the resonant cavity together serve as the test channel for the magnetic permeability of the thin film material;

[0009] The coupling excitation device (6-1) and the coupling receiving device (6-2) are symmetrically fixed on the side wall of the outer conductor (5) of the resonant cavity near the bottom surface by means of device fixing parts, and the line connecting the positions of the coupling excitation device (6-1) and the coupling receiving device (6-2) is perpendicular to the gap (5-2) on the top surface of the outer conductor (5) of the resonant cavity.

[0010] The re-entry coaxial resonant cavity (1) is placed horizontally on the support base (3), and the sample holders (2) to be tested are respectively set on the left and right sides of the support base (3); wherein, the sample holder (2) to be tested consists of two "U-shaped" thin plates, the thin film to be tested is placed between the two thin plates and located in the recess, the two thin plates are fixed and clamped by screws, and the sides of the thin plates are fixed on the support base (3) by a micrometer head; the depth of the thin film to be tested in the complex permittivity test channel and the permeability test channel is moved by adjusting the micrometer head.

[0011] Furthermore, the distance between the top surface of the conductor pillar (4-1) and the top surface of the inner wall of the resonant cavity conductor (5) is d, the radius of the conductor pillar (4-1) is a, the radius of the inner wall of the resonant cavity conductor (5) is b, b / a=3.6, 0.25a≤d≤2a.

[0012] Furthermore, the height of the conductor pillar (4-1) inside the resonant cavity is λ / 4, where λ is the wavelength of the electromagnetic wave being tested.

[0013] Furthermore, the coupling excitation device (6-1) and the coupling receiving device (6-2) are magnetic coupling rings, and the plane of the ring is perpendicular to the test channel.

[0014] Furthermore, the base surface of the resonant cavity conductor in contact with the conductor post has a metal boss (4-5) for good contact with the resonant cavity conductor (5).

[0015] Furthermore, the conductor pillar (4-1), the metal boss (4-5), and the inner wall (5-1) of the resonant cavity outer conductor (5) are all silver-plated.

[0016] Furthermore, the sample holder is made of a low dielectric constant material, preferably an acrylic sheet.

[0017] Furthermore, the coupling excitation device (6-1) and the coupling receiving device (6-2) adopt SMA connectors.

[0018] Furthermore, the thickness of the thin film sample to be tested should be greater than 1 μm.

[0019] The present invention also provides a testing system based on the above-mentioned reentrant coaxial cavity for testing the electromagnetic properties of thin film materials, including a vector network analyzer, testing software, and an electromagnetic property testing device; wherein, the coupling excitation device and the coupling receiving device of the electromagnetic property testing device are respectively connected to two ports of the vector network analyzer, and are used to measure the changes in resonant frequency and quality factor before and after the sample is placed in the resonant cavity; the testing software is used to calculate the resonant frequency and quality factor before and after sample placement and to provide the test results.

[0020] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0021] 1. Compared with traditional rectangular resonant cavities and split resonant cavities, the testing device of the present invention has a more concentrated electric field distribution, and the resonant frequency is only related to the longitudinal length and not to the transverse dimension. This allows the testing device of the present invention to operate at a lower frequency band, expand the testing bandwidth, reduce the cavity size, and reduce the processing cost. In addition, it also reduces the limitation on the size of thin film samples, improves the testing accuracy, and makes the measurement results more accurate.

[0022] 2. The testing device of the present invention concentrates most of the electric field energy in the cavity into the testing channel, effectively improving the testing sensitivity of the resonant cavity; at the same time, by placing the sample in the place where the electric field strength and magnetic field strength are strongest in the resonant cavity, the complex permittivity and permeability of the sample can be measured respectively. The complex permittivity and permeability of the sample are tested using only one set of devices, and the electric field lines are not cut off during the sample placement process, so as not to affect the field distribution in the cavity.

[0023] 3. The testing device of the present invention has designed a sample clamp for thin film materials to position and fix the thin film materials, so that the thin film materials remain flat in the testing channel, which solves the problem of difficult sample placement of thin film materials in traditional testing devices. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the electromagnetic property testing device for thin film materials based on a re-entry coaxial resonant cavity according to the present invention.

[0025] Figure 2 This is a schematic diagram of the coaxial resonant cavity in the electromagnetic characteristic testing device of the present invention.

[0026] Figure 3 This is a schematic diagram of the structure of the conductor inside the resonant cavity in the electromagnetic characteristic testing device of the present invention.

[0027] Figure 4 These are the front and side views of the outer conductor of the resonant cavity in the electromagnetic characteristic testing device of the present invention.

[0028] Figure 5 The electromagnetic property testing device of this invention operates in TEM. 013 Electric field distribution diagram under the model.

[0029] Figure 6 The electromagnetic property testing device of this invention operates in TEM. 013 Magnetic field distribution diagram under the model.

[0030] Figure 7 This is a schematic diagram of the thin film material electromagnetic property testing system based on a re-entry coaxial resonant cavity according to the present invention. Detailed Implementation

[0031] 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.

[0032] A schematic diagram of a thin-film material electromagnetic property testing device based on a reentrant coaxial resonant cavity is shown below. Figure 1 As shown, it includes a re-entry coaxial resonant cavity (1), a sample holder (2), and a support base (3); the re-entry coaxial resonant cavity (1) is placed horizontally on the support base (3), and the sample holders (2) are respectively set on the left and right sides of the support base (3); wherein, the sample holder (2) is composed of two "U-shaped" thin plates, the thin film to be tested is fixed between the two thin plates and located in the recess, the two thin plates are fixed and clamped by screws, and the sides of the thin plates are fixed on the support base (3) by a micrometer head; the depth of the thin film to be tested in the complex permittivity test channel and the permeability test channel is moved by adjusting the micrometer head.

[0033] The structural schematic diagram of the re-entry coaxial resonator (1) is shown below. Figure 2 As shown, it includes an inner conductor (4) of the resonant cavity, an outer conductor (5) of the resonant cavity, a coupling excitation device (6-1), and a coupling receiving device (6-2). The front view (right figure) and side view (left figure) of the outer conductor (5) are shown below. Figure 4 As shown, the outer conductor of the resonant cavity is a hollow cylinder with only an upper top surface. A gap is set at the center of the upper top surface, and a gap corresponding to the position of the gap on the upper top surface is set on the side wall near the lower bottom surface. A schematic diagram of the structure of the inner conductor (4) of the resonant cavity is shown below. Figure 3 As shown, it includes a conductor post (4-1) and a base (4-2). The conductor post (4-1) is a solid metal cylinder with gaps at the center of both the top and bottom surfaces, and the gap on the bottom surface extends into the cylinder. The base is a metal disc with a gap penetrating through the base at its center. The conductor post is fixedly placed at the center of the base. The top surface of the conductor post (4-1) and the top surface of the outer conductor (5) of the resonant cavity do not contact each other. The gaps on the inner conductor (4) and the outer conductor (5) of the resonant cavity are coplanar. The gap (5-2) on the top surface of the outer conductor (5) and the gap (4-3) on the top surface of the conductor post (4-1) together serve as the test channel for the complex permittivity of the thin film material. The gap (5-3) on the side wall of the outer conductor (5) near the bottom surface, the gap (4-4) on the bottom surface of the conductor post (4-1), and the gap on the base of the inner conductor (4) of the resonant cavity together serve as the test channel for the magnetic permeability of the thin film material.

[0034] The coupling excitation device (6-1) and the coupling receiving device (6-2) are symmetrically fixed on the side wall of the outer conductor (5) of the resonant cavity near the bottom surface by means of device fixing parts (7-1, 7-2), and the line connecting the positions of the coupling excitation device (6-1) and the coupling receiving device (6-2) is perpendicular to the gap (5-2) on the top surface of the outer conductor (5) of the resonant cavity.

[0035] The coupling excitation device fixing part (7-1) and the coupling receiving device fixing part (7-2) are metal stepped structures. The area near the first side wall hole (5-4) and the second side wall hole (5-5), as well as the corresponding part of the base of the conductor in the resonant cavity, are all cut to change their outer side wall from a cylindrical surface to a plane. The coupling excitation device fixing part (7-1) and the coupling receiving device fixing part (7-2) can fit tightly against the outer side wall of the re-entry resonant cavity through this plane.

[0036] Example 1

[0037] A thin film material electromagnetic property testing device based on a re-entry coaxial resonant cavity has an inner conductor (4) with a diameter of 20 mm and a height of 230 mm. The gap (4-3) at the top of the inner conductor has a width of 1 mm and a depth of 3 mm. The gap (4-4) at the connection between the conductor post (4-1) of the inner conductor and the base part (4-2) has a width of 1 mm and a depth of 24.5 mm. The inner wall (5-1) of the outer conductor has a diameter of 70 mm and a height of 235.70 mm. The gap (5-2) at the top of the outer conductor (5) has a width of 1 mm and a depth of 14 mm. The gap (2-3) at the bottom of the outer conductor (5) has a width of 1 mm and a depth of 10.3 mm. The thin film sample to be tested is clamped between two thin acrylic plates with a thickness of 0.3 mm. The sample clamp (2) is fixed on the base (3) of the testing device by a micrometer head with a stroke of 50 mm.

[0038] In this embodiment, the resonant cavity is modeled using classical perturbation theory. After a series of simplifications and approximations, the relationship between the electromagnetic properties of the sample under test and the resonant frequencies before and after placing the thin film sample is obtained as follows:

[0039]

[0040]

[0041] Where ω0 and ω represent the complex resonant frequencies of the resonant cavity before and after the sample is placed, respectively, and ε r It is the complex permittivity of the sample under test, μ r V is the complex permeability of the sample under test, E0 and H0 represent the electric and magnetic fields in the resonant cavity before the sample was placed, respectively. S and V C N represents the sample perturbation volume and the resonant cavity volume, respectively. e and N m These are the depolarization factors for the electric and magnetic fields, respectively, and they depend on the sample's geometry, electromagnetic properties, and the applied field.

[0042] For lossy materials, the complex resonant frequency can be split into real and imaginary parts, as shown in the following equation:

[0043]

[0044] Where f0, f, Q0, and Q represent the resonant frequency and quality factor before and after sample placement, respectively, and the complex permittivity and complex permeability of the sample can be calculated using the following four implicit expressions:

[0045]

[0046]

[0047]

[0048]

[0049] Strictly speaking, existing testing devices cannot guarantee complete independence between the electric and magnetic fields in the sample. The mutual interference between electric and magnetic fields can introduce errors into the calculations. Therefore, a typical device only measures one electromagnetic parameter. In this embodiment, a multi-state method is introduced to correct for electromagnetic interference. By inserting the sample to be tested at the top and bottom of the cavity respectively, two fully perturbation equations are constructed, as follows:

[0050]

[0051]

[0052] Where, ω t and ω b C represents the resonant frequencies after placing the sample at the top and bottom of the cavity, respectively. et C eb C ht and C hb N represents the shape factors of the electric and magnetic fields after the sample is placed at the top and bottom of the cavity, respectively. et N eb N mt and N mb Let represent the depolarization factors of the electric and magnetic fields after placing samples at the top and bottom of the cavity, respectively. Theoretically, by solving the two fully perturbation equations simultaneously, electromagnetic interference can be eliminated, as expressed below:

[0053]

[0054]

[0055] The testing device in this embodiment is in TEM. 013 The electric and magnetic field distributions under the mode are as follows Figure 5 and Figure 6 As shown in the figure, the electric and magnetic field energy within the resonant cavity is mainly concentrated in their respective test channels, which improves the sensitivity of the resonant cavity for testing thin film materials. In addition, different modes can be used for testing as needed, and the resonant frequency of the resonant cavity is different in different modes, that is, the resonant cavity can be tested at multiple frequency points as needed.

[0056] This invention also provides a testing system based on the above-mentioned re-entry coaxial cavity for testing the complex permittivity of thin film materials, the overall structure of which is shown in the schematic diagram below. Figure 7As shown, the system includes a vector network analyzer, testing software, and a thin film material electromagnetic property testing device. The coupling excitation and receiving devices of the thin film material electromagnetic property testing device are connected to two ports of the vector network analyzer, respectively, to measure the changes in resonant frequency and quality factor before and after the sample is placed in the resonant cavity. The testing software is used to calculate the resonant frequency and quality factor before and after sample placement and to provide the test results.

[0057] 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 device for testing the electromagnetic properties of thin film materials based on a re-entrant coaxial resonant cavity, characterized in that, It includes a re-entry coaxial resonant cavity (1), a sample holder (2), and a support base (3); The re-entry coaxial resonant cavity (1) includes an inner conductor (4), an outer conductor (5), a coupling excitation device (6-1), and a coupling receiving device (6-2); wherein, the outer conductor (5) is a hollow cylinder with only an upper top surface, and a gap is provided at the center of the upper top surface, and a gap corresponding to the position of the gap on the upper top surface is provided on the side wall near the lower bottom surface; the inner conductor (4) includes a conductor post (4-1) and a base (4-2), the conductor post (4-1) is a solid metal cylinder, and gaps are provided at the center of both the upper top surface and the lower bottom surface, and the gap on the lower bottom surface extends into the cylinder; the base is a metal disc, and a through-hole is provided at its center. The gaps are fixed at the center of the base; the top surface of the conductor (4-1) and the top surface of the conductor (5) outside the resonant cavity do not contact each other; the gaps set on the conductor (4) inside the resonant cavity and the conductor (5) outside the resonant cavity are coplanar; the gap (5-2) on the top surface of the conductor (5) outside the resonant cavity and the gap (4-3) on the top surface of the conductor (4-1) together serve as the test channel for the complex permittivity of the thin film material; the gap (5-3) on the side wall near the bottom surface of the conductor (5) outside the resonant cavity and the gap (4-4) on the bottom surface of the conductor (4-1) and the gap on the base of the conductor (4) inside the resonant cavity together serve as the test channel for the magnetic permeability of the thin film material; The coupling excitation device (6-1) and the coupling receiving device (6-2) are symmetrically fixed on the side wall of the outer conductor (5) of the resonant cavity near the bottom surface by means of device fixing parts, and the line connecting the positions of the coupling excitation device (6-1) and the coupling receiving device (6-2) is perpendicular to the gap (5-2) on the top surface of the outer conductor (5) of the resonant cavity. The re-entry coaxial resonant cavity (1) is placed horizontally on the support base (3), and the sample holders (2) to be tested are respectively set on the left and right sides of the support base (3); wherein, the sample holder (2) to be tested consists of two "U-shaped" thin plates, the thin film to be tested is placed between the two thin plates and located in the recess, the two thin plates are fixed and clamped by screws, and the sides of the thin plates are fixed on the support base (3) by a micrometer head; the depth of the thin film to be tested in the complex permittivity test channel and the permeability test channel is moved by adjusting the micrometer head.

2. The thin film material electromagnetic property testing device as described in claim 1, characterized in that, The distance between the top surface of the conductor pillar (4-1) and the top surface of the inner wall of the resonant cavity conductor (5) is d, the radius of the conductor pillar (4-1) is a, the radius of the inner wall of the resonant cavity conductor (5) is b, b / a=3.6, 0.25a≤d≤2a.

3. The thin film material electromagnetic property testing device as described in claim 1, characterized in that, The height of the conductor pillar (4-1) inside the resonant cavity is λ / 4, where λ is the wavelength of the electromagnetic wave being tested.

4. The thin film material electromagnetic property testing device as described in claim 1, characterized in that, The coupling excitation device (6-1) and coupling receiving device (6-2) are magnetic coupling rings, and the plane of the ring is perpendicular to the test channel.

5. The thin film material electromagnetic property testing device as described in claim 1, characterized in that, The base surface in contact with the conductor post has metal bosses (4-5) for connecting with the outer conductor (5) of the resonant cavity.

6. The thin film material electromagnetic property testing device as described in claim 1, characterized in that, The conductor post (4-1), the metal boss (4-5), and the inner wall (5-1) of the resonant cavity outer conductor (5) are all silver-plated.

7. The thin film material electromagnetic property testing device as described in claim 1, characterized in that, The sample holder is made of a low dielectric constant material.

8. The thin film material electromagnetic property testing device as described in claim 1, characterized in that, The coupling excitation device (6-1) and the coupling receiving device (6-2) adopt SMA connectors.

9. The thin film material electromagnetic property testing device as described in claim 1, characterized in that, The thickness of the thin film sample to be tested should be greater than 1 μm.

10. A testing system for the electromagnetic properties of thin film materials, characterized in that, The device includes a vector network analyzer, testing software, and a thin film material electromagnetic property testing apparatus as described in any one of claims 1-9; wherein, the coupling excitation device and coupling receiving device of the electromagnetic property testing apparatus are respectively connected to two ports of the vector network analyzer, and are used to measure the changes in resonant frequency and quality factor before and after the sample is placed in the resonant cavity; the testing software is used to calculate the resonant frequency and quality factor before and after sample placement and to provide the test results.

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