A device and method for testing the millimeter wave dielectric properties of liquid crystal materials under electrical orientation

Abstract

The purpose of the present invention is to provide a device and method for testing the millimeter wave dielectric properties of liquid crystal materials under electrical orientation, which belongs to the field of microwave testing technology. In the dielectric constant test of liquid crystal materials, the present invention designs a liquid crystal box composed of multiple layers of dielectrics, and innovatively uses multiple layers of dielectrics to form a top-bottom symmetrical TM 0n0 The mode double-sided circular patch resonator, and the electric field distribution inside it passes through the multi-layer medium to be tested and is perpendicular to the metal disc. Therefore, by utilizing its internal field distribution characteristics, the structure can use a mode with a higher resonant frequency, greatly broadening the test frequency range, and the test frequency can reach 110GHz. Therefore, the dielectric property test device of the present invention can realize the wide-band dielectric property test of liquid crystal materials in the millimeter wave frequency band, and the test device is simple and easy to implement.

Description

Technical Field

[0001] The invention belongs to the technical field of microwave testing, and in particular relates to a device and method for testing the millimeter wave dielectric properties of liquid crystal materials under electrical orientation. Background Art

[0002] Liquid crystal is a highly structured liquid whose constituent molecules have orientation order and spatial order. Due to the anisotropy of liquid crystal materials, the arrangement direction of liquid crystal molecules will change in an orderly manner with the magnitude of the external electric field, so that its equivalent dielectric constant will also change accordingly. In recent years, microwave communication devices based on liquid crystal materials have developed rapidly. For example, liquid crystal materials are used as microwave device substrates, and the aforementioned characteristics are used to realize electrically controlled linear adjustable phase shifters. By changing the magnitude of the external electric field, the reflection phase value of the phase-controlled unit is affected to achieve the purpose of phase control; and the dielectric constant and dielectric loss under different voltages become one of the key factors affecting the development of devices. Therefore, how to accurately test the dielectric properties of liquid crystal materials in the microwave frequency band has become one of the important research directions in the field of microwave testing technology for dielectric properties.

[0003] There are many methods for testing dielectric constants. For example, in reference [1], Toshihisa et al. filled liquid crystal in a coaxial line and changed the molecular order by adding bias voltage, that is, used the coaxial transmission line method to measure the dielectric properties and dielectric anisotropy of liquid crystal in the 100MHz to 40GHz band. This method is simple and easy to implement, but the test frequency is not high, and the loss tangent test error for low-loss dielectric materials is large. In reference [2], the dielectric properties of nematic liquid crystal materials at 9GHz and 35GHz were measured by the resonant cavity perturbation method. In reference [3], Mani et al. measured the dielectric anisotropy of liquid crystal material E7 as 0.42 using a patch resonator. Compared with the transmission / reflection method, the resonance method has higher sensitivity and measurement accuracy and can be used for high-frequency measurement, but it can only be measured at a single frequency point or a series of discrete frequency points, and is not suitable for broadband measurement. In addition, the higher the measurement frequency, the higher the requirements for the test sample, the smaller the sample size, and the more difficult it is to process.

[0004] [1]. Moessinger A, Dieter S, Menzel W, et al. Realization and characterization of a 77GHz reconfigurable liquid crystal reflectarray [C]. Paris: 13th Intemational Symposium on Antenna Technology and Applied Electromagnetics And the Canadian Radio Sciences Meeting, 2009.

[0005] [2]. Penischke Andreas, Muller Stefan, Scheele Patrick, et al. Cavityrturbation method for characterization of liquid crystals up to 35GHz [C]. London, United Kingdom: Conf-erence Proceedings-34th European Microwave Conference, 2004.

[0006] [3].Yaxdlanpanahi M,Bulja S,Mirshekar-Syahkal D,et al.Measurement of dielectric constants of nematic liquid crystals at mm-wave frequencies usingpatch resonator[J].IEEET ransactions on Instrumentation and Measurement,2010,59(12):3079-3085. Summary of the invention

[0007] In view of the problem that the prior art cannot accurately test the dielectric properties of liquid crystal materials at high frequencies, the present invention aims to provide a millimeter wave dielectric properties test device for liquid crystal materials under electrical orientation. The test device innovatively uses a top-bottom symmetrical TM 0n0mode double-sided circular patch resonator, this structure can use more high-order modes and greatly broaden the test frequency range; at the same time, a liquid crystal box loaded with liquid crystal material is designed, and by applying an electric field to the double-sided circular patch resonator, the dielectric properties of the liquid crystal material are tested in the high-frequency millimeter wave band with high test accuracy.

[0008] To achieve the above object, the technical solution of the present invention is as follows:

[0009] A millimeter wave dielectric property test device for liquid crystal materials under electrical orientation, comprising a double-sided circular patch resonator, a microwave cable, a power supply device, a vector network analyzer and a computer;

[0010] The double-sided circular patch resonator comprises three metal plates, two coupling probes, an insulating dielectric layer, a metal disc and two liquid crystal boxes; wherein the first metal plate, the first liquid crystal box, the metal disc, the second liquid crystal box, the second metal plate, the insulating dielectric layer and the third metal plate are arranged in sequence, through holes are arranged at the center positions of the first metal plate, the second metal plate and the third metal plate, the first metal plate and the third metal plate extend outwardly along the depth direction of the through holes to form coupling holes, the two coupling probes are respectively arranged in the two coupling holes, and the coupling probes are fixedly connected to the metal plates through flanges; the double-sided circular patch resonator is axially symmetrical about the straight line where the two through holes are located;

[0011] The liquid crystal box includes two upper and lower rectangular quartz plates, a plurality of support columns and packaging strips; the support columns are arranged between the upper and lower quartz plates at equal intervals to form a plurality of quartz spaces, each of which is filled with the liquid crystal material to be tested and the orientation agent, and a circle of packaging strips is arranged between the rectangular quartz plates to package the liquid crystal material to be tested;

[0012] The coupling probe is connected to the vector network analyzer through a microwave cable, and the vector network analyzer is connected to the computer through a communication cable; the power supply device is used to apply an external voltage to the first metal plate and the third metal plate; the external electric field and the orientation agent act together on the liquid crystal material to be tested, causing it to deflect and thereby obtaining two extreme states of the liquid crystal material molecules.

[0013] Furthermore, the two extreme states of the liquid crystal molecules are the parallel state and the perpendicular state; in the parallel state, an external electrostatic field acts on the liquid crystal material molecules, causing them to deflect and thereby making the long axis of the liquid crystal molecules parallel to the electric field; in the perpendicular state, when the power supply device is not supplying power, the orientation agent makes the long axis of the liquid crystal molecules perpendicular to the long axis of the liquid crystal molecules in the parallel state.

[0014] Furthermore, the diameter of the through hole provided at the center of the metal plate matches the coupling probe, so that the coupling amount can be adjusted by adjusting the depth of the coupling probe in the coupling hole to achieve a weak coupling state.

[0015] Furthermore, the coupling strength of the weak coupling is less than -40 dB.

[0016] Furthermore, before testing, the double-sided circular patch resonator needs to be pressurized using a fixture to remove the air remaining between the layers of the double-sided circular patch resonator.

[0017] Furthermore, the metal disc uses an unoxidized copper metal sheet, and the edge burrs are minimized.

[0018] Furthermore, the diameter of the metal disc, the thickness of the liquid crystal box and the test frequency are related; the higher the test frequency, the smaller the diameter of the metal disc and the thinner the thickness of the liquid crystal box.

[0019] The present invention also provides a testing method based on the above dielectric properties testing device, comprising the following steps:

[0020] Step 1: Load the liquid crystal material to be tested and the orientation agent in the liquid crystal box, and then fix the first metal plate, the first liquid crystal box, the metal disc, the second liquid crystal box, the second metal plate, the insulating medium layer and the third metal plate in order from top to bottom to obtain a double-sided circular patch resonator; wherein the center of the metal disc should coincide with the center of the metal plate and the liquid crystal box;

[0021] Step 2: Use a fixture to pressurize the double-sided circular patch resonator to remove the residual air between the layers of the double-sided circular patch resonator;

[0022] Step 3: Connect the first metal plate of the double-sided circular patch resonator pressurized in step 2 to the positive electrode of the power supply device, connect the third metal plate to the negative electrode of the power supply device, and then connect the coupling probe and the vector network analyzer 7 to obtain the above-mentioned dielectric performance test device;

[0023] Step 4: Conduct a complex dielectric constant test in the parallel direction of the liquid crystal material to be tested. The specific process is: adjust the depth of the coupling probe into the coupling hole to achieve a weak coupling state. At this time, the quality factor of the system at the resonant frequency is the largest, and the resonant frequency is recorded;

[0024] Step 5: Conduct a complex dielectric constant test in the vertical direction of the liquid crystal material to be tested. The specific process is as follows: the power supply device does not apply an external electric field, and the liquid crystal molecules to be tested are oriented vertically by relying on the effect of the orientation agent in the liquid crystal box. Then, the depth of the coupling probe into the coupling hole is adjusted to reach a weak coupling state. At this time, the quality factor of the system at the resonant frequency is the largest, and the resonant frequency is recorded.

[0025] Step 6: According to the mode matching algorithm, the complex dielectric constant of the liquid crystal material is obtained by inverting the resonance parameters obtained in steps 4 and 5.

[0026] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0027] In the dielectric constant test of liquid crystal materials, the present invention designs a liquid crystal box composed of multiple layers of dielectrics, and innovatively uses multiple layers of dielectrics to form a vertically symmetrical TM 0n0 The mode double-sided circular patch resonator, and the electric field distribution inside it passes through the multi-layer medium to be tested and is perpendicular to the metal disc. Therefore, by utilizing its internal field distribution characteristics, the structure can use a mode with a higher resonant frequency, greatly broadening the test frequency range, and the test frequency can reach 110GHz. Therefore, the dielectric property test device of the present invention can realize the wide-band dielectric property test of liquid crystal materials in the millimeter wave frequency band, and the test device is simple and easy to implement. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a structural schematic diagram of the dielectric property testing device of the present invention;

[0029] Among them, 1 is a power supply device, 2 is a metal plate, 3 is a liquid crystal box, 4 is a metal disc, 5 is a coupling probe, 6 is an insulating dielectric layer, 7 is a vector network analyzer, 8 is a computer, and 9 is a microwave cable.

[0030] Figure 2 It is a schematic diagram of the structure of the double-sided circular patch resonator of the present invention.

[0031] Figure 3 Schematic diagram of the structure of the liquid crystal box.

[0032] Figure 4 This is a system resonance parameter curve diagram obtained by measuring the liquid crystal material to be tested by the testing device of the present invention. DETAILED DESCRIPTION

[0033] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below in conjunction with the implementation modes and the accompanying drawings.

[0034] A millimeter wave dielectric property testing device for liquid crystal materials under electrical orientation, the structural schematic diagram of which is shown in FIG. Figure 1 As shown, it includes a double-sided circular patch resonator, a microwave cable 9, a power supply device 1, a vector network analyzer 7 and a computer 8;

[0035] The double-sided circular patch resonator comprises three metal plates 2, two coupling probes 5, an insulating dielectric layer 6, a metal disc 4 and two liquid crystal boxes 3; wherein the first metal plate, the first liquid crystal box, the metal disc, the second liquid crystal box, the second metal plate, the insulating dielectric layer and the third metal plate are arranged in sequence, through holes are arranged at the center positions of the first metal plate, the second metal plate and the third metal plate, the first metal plate and the third metal plate extend outwardly along the depth direction of the through holes to form coupling holes, the two coupling probes are respectively arranged in the two coupling holes, and the coupling probes are fixedly connected to the metal plates through flanges; the double-sided circular patch resonator is axially symmetrical about the straight line where the two through holes are located; the insulating dielectric layer is used to isolate the second metal plate and the third metal plate to avoid short circuit between the two metal plates;

[0036] The structural diagram of the liquid crystal cell 3 is shown in FIG. Figure 3 As shown, it includes two upper and lower rectangular quartz plates, a plurality of support columns and packaging strips; the support columns are arranged between the upper and lower quartz plates at equal intervals to form a plurality of quartz spaces, each of which is filled with a liquid crystal material to be tested and an orientation agent, and a circle of packaging strips is arranged between the rectangular quartz plates to package the liquid crystal material to be tested;

[0037] The coupling probe is connected to the vector network analyzer 7 through a microwave cable 9, and the vector network analyzer 7 is connected to the computer 8 through a communication cable; the power supply device is used to apply an external voltage to the first metal plate and the third metal plate to form an electric field, and the second metal plate is used to provide a metal surface; the external electric field and the orientation agent act together on the liquid crystal material to be tested, causing it to deflect and thereby obtaining two extreme states of the liquid crystal material molecules.

[0038] Example 1

[0039] The testing method based on the above dielectric properties testing device comprises the following steps:

[0040] Step 1: Load the liquid crystal material to be tested and the orientation agent in the liquid crystal box, and then fix the first metal plate, the first liquid crystal box, the metal disc, the second liquid crystal box, the second metal plate, the insulating medium layer and the third metal plate in order from top to bottom to obtain a double-sided circular patch resonator; wherein the center of the metal disc should coincide with the center of the metal plate and the liquid crystal box; wherein the diameter of the metal disc is 30 mm and the thickness is 18 μm; the size of the upper and lower rectangular quartz plates of the liquid crystal box is 50 mm×50 mm and the thickness is 0.15 mm; the thickness of the liquid crystal material to be tested (the height of the support column) is 70 μm;

[0041] Step 2: Use a fixture to pressurize the double-sided circular patch resonator to remove the residual air between the layers of the double-sided circular patch resonator;

[0042] Step 3: Connect the first metal plate of the double-sided circular patch resonator pressurized in step 2 to the positive electrode of the power supply device, connect the third metal plate to the negative electrode of the power supply device, and then connect the coupling probe and the vector network analyzer 7 to obtain the above-mentioned dielectric performance test device;

[0043] Step 4: Conduct a complex dielectric constant test in the parallel direction of the liquid crystal material to be tested. The specific process is: adjust the depth of the coupling probe into the coupling hole to achieve a weak coupling state. At this time, the quality factor of the system at the resonant frequency is the largest, and the resonant frequency is recorded;

[0044] Step 5: Conduct a complex dielectric constant test in the vertical direction of the liquid crystal material to be tested. The specific process is as follows: the power supply device does not apply an external electric field, and the liquid crystal molecules to be tested are oriented vertically by relying on the effect of the orientation agent in the liquid crystal box. Then, the depth of the coupling probe into the coupling hole is adjusted to reach a weak coupling state. At this time, the quality factor of the system at the resonant frequency is the largest, and the resonant frequency is recorded.

[0045] Step 6: According to the mode matching algorithm, the complex dielectric constant of the liquid crystal material is obtained by inverting the resonance parameters obtained in steps 4 and 5.

[0046] The liquid crystal material to be tested is tested based on the above test device, and the test results are as follows: Figure 4 As shown in the figure, it can be seen from the test results that the system of the present invention has multiple resonance peaks with good resonance effects in the entire wide frequency range of 5 to 110G, and the complex dielectric constant of the liquid crystal material to be tested can be inverted by the resonance parameters of each resonance peak. The test results show that the test device of the present invention can realize the test of millimeter wave band liquid crystal materials under broadband, and provide a way to realize the study of the dielectric properties of liquid crystal materials under broadband millimeter wave band.

[0047] The above description is only a specific implementation mode of the present invention. Any feature disclosed in this specification, unless otherwise stated, can be replaced by other alternative features that are equivalent or have similar purposes; all the disclosed features, or all the steps in the methods or processes, except for mutually exclusive features and / or steps, can be combined in any way.

Claims

1. A millimeter wave dielectric property testing device for liquid crystal materials under electrical orientation, characterized in that: It includes a double-sided circular patch resonator, a microwave cable, a power supply device, a vector network analyzer, and a computer; The double-sided circular patch resonator comprises three metal plates, two coupling probes, an insulating dielectric layer, a metal disc and two liquid crystal boxes; wherein the first metal plate, the first liquid crystal box, the metal disc, the second liquid crystal box, the second metal plate, the insulating dielectric layer and the third metal plate are arranged in sequence, through holes are arranged at the center positions of the first metal plate, the second metal plate and the third metal plate, the first metal plate and the third metal plate extend outwardly along the depth direction of the through holes to form coupling holes, the two coupling probes are respectively arranged in the two coupling holes, and the coupling probes are fixedly connected to the metal plates through flanges; the double-sided circular patch resonator is axially symmetrical about the straight line where the two through holes are located; The liquid crystal box includes two upper and lower rectangular quartz plates, a plurality of support columns and packaging strips; the support columns are arranged between the upper and lower quartz plates at equal intervals to form a plurality of quartz spaces, each of which is filled with the liquid crystal material to be tested and the orientation agent, and a circle of packaging strips is arranged between the rectangular quartz plates to package the liquid crystal material to be tested; The coupling probe is connected to the vector network analyzer through a microwave cable, and the vector network analyzer is connected to the computer through a communication cable; the power supply device is used to apply an external voltage to the first metal plate and the third metal plate; the external electric field and the orientation agent act together on the liquid crystal material to be tested, causing it to deflect and thereby obtaining two extreme states of the liquid crystal material molecules.

2. The millimeter wave dielectric properties testing device according to claim 1, characterized in that: The two extreme states of liquid crystal molecules are the parallel state and the perpendicular state; in the parallel state, an external electrostatic field acts on the liquid crystal material molecules, causing them to deflect and thus making the long axis of the liquid crystal molecules parallel to the electric field; in the perpendicular state, when the power supply device is not supplying power, the orientation agent makes the long axis of the liquid crystal molecules perpendicular to the long axis of the liquid crystal molecules in the parallel state.

3. The millimeter wave dielectric properties testing device according to claim 1, characterized in that: The diameter of the through hole set at the center of the metal plate matches the coupling probe, so that the coupling amount is adjusted by adjusting the depth of the coupling probe in the coupling hole to achieve a weak coupling state.

4. The millimeter wave dielectric properties testing device according to claim 3, characterized in that: The coupling strength of weak coupling is less than -40dB.

5. The millimeter wave dielectric properties testing device according to claim 1, characterized in that: Before testing the double-sided circular patch resonator, it is necessary to pressurize it using a fixture to remove the air remaining between the layers of the double-sided circular patch resonator.

6. The millimeter wave dielectric properties testing device according to claim 1, characterized in that: The metal disc uses an unoxidized copper metal sheet.

7. The millimeter wave dielectric properties testing device according to claim 1, characterized in that: The diameter of the metal disc, the thickness of the liquid crystal box and the test frequency are related; the higher the test frequency, the smaller the diameter of the metal disc and the thinner the thickness of the liquid crystal box.

8. A testing method based on the dielectric performance testing device according to any one of claims 1 to 7, characterized in that: The following steps are involved: Step 1: Load the liquid crystal material to be tested and the orientation agent in the liquid crystal box, and then fix the first metal plate, the first liquid crystal box, the metal disc, the second liquid crystal box, the second metal plate, the insulating medium layer and the third metal plate in order from top to bottom to obtain a double-sided circular patch resonator; wherein the center of the metal disc should coincide with the center of the metal plate and the liquid crystal box; Step 2: Use a fixture to pressurize the double-sided circular patch resonator to remove the residual air between the layers of the double-sided circular patch resonator; Step 3: Connect the first metal plate of the double-sided circular patch resonator pressurized in step 2 to the positive electrode of the power supply device, connect the third metal plate to the negative electrode of the power supply device, and then connect the coupling probe and the vector network analyzer to obtain a dielectric performance test device; Step 4: Conduct a complex dielectric constant test in the parallel direction of the liquid crystal material to be tested. The specific process is: adjust the depth of the coupling probe into the coupling hole to achieve a weak coupling state. At this time, the quality factor of the system at the resonant frequency is the largest, and the resonant frequency is recorded; Step 5: Conduct a complex dielectric constant test in the vertical direction of the liquid crystal material to be tested. The specific process is as follows: the power supply device does not apply an external electric field, and the liquid crystal molecules to be tested are oriented vertically by relying on the effect of the orientation agent in the liquid crystal box. Then, the depth of the coupling probe into the coupling hole is adjusted to reach a weak coupling state. At this time, the quality factor of the system at the resonant frequency is the largest, and the resonant frequency is recorded. Step 6: According to the mode matching algorithm, the complex dielectric constant of the liquid crystal material is obtained by inverting the resonance parameters obtained in steps 4 and 5.

Images