A test device and method for measuring the dielectric constant of liquid crystal based on reflection phase difference

Abstract

The present invention is a test device and method for measuring the dielectric constant of liquid crystal based on reflection phase difference. The test device includes an upper substrate, a liquid crystal layer and a lower substrate. The radiation patch is printed below the upper substrate, the metal ground is printed above the lower substrate, the first orientation layer is spin-coated below the upper substrate, the second orientation layer is spin-coated above the lower substrate, the metal ground, the upper substrate, the gasket arranged between the metal ground and the radiation patch and the liquid crystal to be tested constitute the liquid crystal layer, and the positive and negative poles of the DC voltage signal are respectively applied to the radiation patch and the metal ground, which is used to bias the liquid crystal injected into the liquid crystal layer. The test method is to prepare a test device including a measuring liquid crystal, connect the positive and negative poles of the DC voltage source to the radiation patch and the metal ground, connect the device to the waveguide copper axis converter, and the upper substrate surface of the device is correspondingly connected to the waveguide port. The test device is applied to the measurement of the dielectric constant of liquid crystal, and has a simple structure and high measurement accuracy.

Description

Technical Field

[0001] The invention belongs to the technical field of liquid crystal devices, and in particular relates to a testing device and method for measuring a dielectric constant of liquid crystal based on a reflection phase difference. Background Art

[0002] By applying a bias voltage to the liquid crystal, the liquid crystal molecules can be rotated, so that the dielectric constant of the liquid crystal exhibits an adjustable characteristic. Different liquid crystal materials have different adjustable ranges of dielectric constant Δε. The formula Δε=ε || -ε ⊥ (1), where ε || is the dielectric constant of the liquid crystal when the long axis of the liquid crystal molecule is parallel to the direction of the electric field, ε ⊥ It is the dielectric constant of liquid crystal when the long axis of liquid crystal molecules is perpendicular to the direction of electric field. The dielectric constant tuning of liquid crystal material is closely related to the operating frequency. Due to its adjustable dielectric constant, it has become an ideal tuning material for adjustable microwave devices. Traditional mechanical tuning is bulky and inefficient, and the operating frequency based on electronic component tuning is limited. The use of liquid crystal materials solves the problems of the above two tuning technologies, making the device more portable and suitable for high frequency bands. Since the change of liquid crystal dielectric constant is continuous rather than discrete under external bias, the characteristic change of microwave devices is also continuous.

[0003] With the continuous development of microwave devices and communication technology, the demand for high-precision microwave devices is also increasing. This makes the use of liquid crystal materials no longer satisfied with knowing the approximate adjustable range of the dielectric constant over a wide frequency band, but tends to know the precise range of variation of the liquid crystal dielectric constant under a specific frequency or frequency band. The traditional method of measuring the dielectric constant of liquid crystal is the resonance method, which simulates the resonant frequency of the device under different dielectric constants to obtain the resonant frequency and dielectric constant curve of the device, and then obtains the resonant frequency of the device under different voltages through testing, and finally obtains the approximate adjustable range of the dielectric constant of the liquid crystal in this frequency band through fitting. Summary of the invention

[0004] In order to solve the above problems, the present invention provides a testing device and method for measuring the dielectric constant of liquid crystal based on reflection phase difference, so as to measure the dielectric constant of liquid crystal at a specific frequency or frequency band with a simple testing device.

[0005] In order to achieve the above object, the present invention is achieved through the following technical solutions:

[0006] The invention discloses a testing device for measuring the dielectric constant of liquid crystal based on reflection phase difference, comprising an upper substrate, a liquid crystal layer and a lower substrate, wherein a radiation patch is printed below the upper substrate, a metal ground is printed above the lower substrate, a first orientation layer is spin-coated below the upper substrate, and a second orientation layer is spin-coated above the lower substrate, the first orientation layer and the second orientation layer are used for the initial orientation of the liquid crystal, the metal ground, the upper substrate, a gasket arranged between the metal ground and the radiation patch and the liquid crystal to be tested constitute a liquid crystal layer, the positive and negative poles of a direct current voltage signal are respectively applied to the radiation patch and the metal ground, and are used to bias the liquid crystal poured into the liquid crystal layer, the device is connected to a waveguide copper axis converter, and the upper substrate surface of the device is connected to a waveguide port correspondingly, and if the device size is different from the waveguide inner diameter of the waveguide copper axis converter, a gradient waveguide can be connected.

[0007] The radiation patch should cover the upper surface of the liquid crystal layer as much as possible to reduce the maximum dielectric constant of the measured liquid crystal slightly smaller than the actual ε of the measured liquid crystal due to the fact that the liquid crystal to be measured in the liquid crystal layer after the bias is applied cannot be evenly affected by the electric field. || The result of the value.

[0008] A further improvement of the present invention is that the radiation patch is a resonant structure having a rectangular structure, a circular structure, a cross structure, a ring structure, a square ring structure, or an open ring, or the radiation patch is a multi-resonance structure patch composed of a plurality of resonant structures, and different sizes or shapes of two radiation patches provide different electromagnetic wave reflection phases.

[0009] The present invention is a test method for measuring the dielectric constant of liquid crystal based on reflection phase difference, comprising the following steps:

[0010] Step 1: Prepare a test device with a measuring liquid crystal, connect the positive and negative electrodes of the DC voltage source to the radiation patch and the metal ground, connect the test device to the waveguide copper axis converter, and connect the upper substrate surface of the test device to the waveguide port.

[0011] Step 2: Using a vector network analyzer, connect the input end of the vector network analyzer to the waveguide copper axis converter in step 1;

[0012] Step 3: Adjust the voltage value of the DC voltage source to 0V and record the reflection phase value of the required frequency on the screen of the vector network analyzer;

[0013] Step 4: adjust the voltage value of the DC voltage source to be greater than or equal to the saturation voltage value of the measured liquid crystal, and record the required frequency reflection phase value on the screen of the vector network analyzer;

[0014] Step 5: Subtract the reflection phase values ​​corresponding to the voltage values ​​in step 3 and step 4 to obtain the reflection phase difference of the test device at the required frequency;

[0015] Step 6: adjusting the voltage value of the DC voltage source to obtain the reflection phase corresponding to each voltage of the required frequency between 0V and the saturation voltage, thereby obtaining a reflection phase and voltage change curve;

[0016] Step 7: Changing the size or structure of the radiation patch of the test device to obtain a test device with different radiation patches;

[0017] Step 8: Repeat steps 1-6 to obtain the reflection phase difference and corresponding reflection phase and voltage change curves of the test devices of multiple groups of different radiation patches at the same required frequency;

[0018] Step 9: Use simulation method to obtain the liquid crystal dielectric constant and reflection phase curve of the test device with different radiation patches at the same required frequency, and then compare it with the reflection phase difference of multiple groups of test devices with different radiation patches at the same required frequency, find the liquid crystal dielectric constant and reflection phase curve segment that meets all reflection phase difference values, find the minimum value of the liquid crystal dielectric constant corresponding to the curve segment as the dielectric constant in the short axis direction of the liquid crystal, and the liquid crystal dielectric constant corresponding to the maximum value as the dielectric constant in the long axis direction of the liquid crystal, thereby determining the minimum value of the dielectric constant of the liquid crystal to be tested, and the dielectric constant values ​​corresponding to each voltage between 0V and the saturation voltage can also be determined according to the reflection phase difference.

[0019] Based on the above technical solution, a test device model is established using radio frequency simulation software, and waveguide simulation method (waveport, symmetric boundary) is used for simulation to obtain the reflection phase and dielectric constant change curves of the test device.

[0020] The beneficial effects of the present invention are:

[0021] 1. The testing device of the present invention can more accurately measure the dielectric constant of liquid crystal at a specific frequency or frequency band.

[0022] 2. The testing device provided by the present invention can be realized through conventional semiconductor processes, has a simple structure, and is easy to operate.

[0023] 3. The present invention can improve the accuracy and reliability of the dielectric constant of liquid crystal by appropriately increasing the number of simulation and test data sets. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a side view of the testing device provided by the embodiment of the present invention.

[0025] Figure 2 It is a radiation patch diagram of the test device provided in an embodiment of the present invention.

[0026] Figure 3It is an ideal variation curve of reflection phase and applied bias voltage at 28 GHz assumed by the test device for different radiation patch sizes provided by the embodiment of the present invention;

[0027] Figure 4 It is a simulation curve of the liquid crystal dielectric constant and reflection phase at 28 GHz of the different radiation patch size test devices provided by the embodiment of the present invention.

[0028] Figure 5 It is a basic flow chart of the measurement method provided by the embodiment of the present invention. DETAILED DESCRIPTION

[0029] The following will disclose the embodiments of the present invention with drawings. For the purpose of clear description, many practical details will be described together in the following description. However, it should be understood that these practical details should not be used to limit the present invention. That is to say, in some embodiments of the present invention, these practical details are not necessary.

[0030] like Figure 1-2 As shown, the present invention is a test device for measuring the dielectric constant of liquid crystal based on reflection phase difference. The test device is a cuboid with equal length and width, and the length and width are not greater than 0.5λ, where λ is the working wavelength of the test device. The test device includes an upper substrate 1, a radiation patch 2, a gasket 3, a first orientation layer 4, a liquid crystal layer 5, a second orientation layer 6, a metal ground 7, and a lower substrate 8. The radiation patch 2 is printed below the upper substrate 1, the metal ground 7 is printed above the lower substrate 8, the first orientation layer 4 is spin-coated below the upper substrate 1, and the second orientation layer 6 is spin-coated above the lower substrate 8 for the initial orientation of the liquid crystal. The metal ground 7, the upper substrate 1, the gasket 3 arranged between the metal ground 7 and the radiation patch 2, and the liquid crystal to be tested constitute the liquid crystal layer 5, and the positive and negative poles of the DC voltage signal are respectively applied to the 2 radiation patches and the 7 metal ground, which are used to bias the liquid crystal poured into the liquid crystal layer 5. The orientation layer 4 is arranged parallel or cross relative to the upper substrate 1.

[0031] In the test device for the dielectric constant of liquid crystal, a voltage difference is introduced between the radiation patch 2 and the metal ground 7, and the positive and negative electrodes of the DC voltage source are respectively connected to the radiation patch 2 and the metal ground 7, so that the voltage difference between the upper and lower surfaces of the liquid crystal layer 5 can be adjusted by the DC voltage source. When the dielectric constant of liquid crystal in the microwave frequency band is measured by the test device, microwaves are input into the test device, and the microwaves can couple with the resonant structure of the radiation patch in the test device to generate resonance; at the same time, the voltage value of the DC voltage source is adjusted to change the equivalent dielectric constant of the liquid crystal layer 5. Different equivalent dielectric constants of the liquid crystal layer 5 will have different effects on the resonance in the resonant structure layer, and this effect can be reflected by the reflection phase of the microwave connected to the test device. Thus, by obtaining the reflection phase difference and reflection phase and voltage change curves between the two extreme states of the liquid crystal: horizontal orientation and vertical orientation, and then testing the reflection phase difference and reflection phase and voltage change curves of the test devices of multiple groups of different radiation patches 2 under the two extreme states, the dielectric constant of the liquid crystal in the short axis direction and the dielectric constant of the long axis direction can be deduced according to the reflection phase and dielectric constant change curves of the test devices of different radiation patches 2 obtained by simulation, and the dielectric constant of the liquid crystal in the microwave frequency band is measured. After determining the dielectric constant of the liquid crystal in the short axis direction, the dielectric constant values ​​corresponding to each voltage between 0V and the saturation voltage can also be deduced according to the corresponding reflection phase difference under different voltages. The test device has a simple structure and can be manufactured using standardized semiconductor processes. It does not require the subsequent precision assembly of various components. It only needs to pay attention to the infusion and packaging of the liquid crystal, so it is low in cost and highly practical.

[0032] The outer ring radius size of the first circular ring 2-3 in the radiation patch 2 is L, and the inner ring radius size is L-0.2mm; the outer ring radius size of the second circular ring 2-2 is L+0.4mm, and the inner ring radius size is L+0.2mm; the outer ring radius size of the four-way opening circular ring 2-1 is L+0.8mm, and the inner ring radius size is L+0.6mm, and the length of the four openings is 0.4mm; the cross-shaped structure 2-4 is composed of two rectangular blocks with a length and width of 1.4mm and 0.4mm respectively; the width of the external bias feed line 2-5 is 0.01mm; the simulation model thickness of the radiation patch adopts the actual processing thickness of 0.035mm. The upper and lower substrates of the reflective array unit are both Rogers4003, with a relative dielectric constant of 3.55, a length and width of 5mm, and a thickness of 1.524mm and 0.203mm respectively. The gasket 3 is Rogers4003 with a thickness of 0.203mm. When this method is actually used, a spacer as thin as possible should be used, which will improve the effectiveness of the initial orientation. The spacer thickness is selected to be thicker here, but it has no effect because it is only used as an example. The metal ground 7 covers the upper surface of the lower substrate 8 of the reflective array unit, with a thickness of 0.035mm. Both the radiation patch and the metal ground are copper.

[0033] The method for testing using the above-mentioned testing device comprises the following steps:

[0034] Step 1: Prepare a test device with a measuring liquid crystal, connect the positive and negative poles of the DC voltage source to the radiation patch 2 and the metal ground 7, connect the test device to the waveguide copper axis converter, and the surface of the upper substrate 1 of the test device corresponds to the access waveguide port. If the device size is different from the waveguide inner diameter of the waveguide copper axis converter, a gradient waveguide can be connected; before the liquid crystal is poured into the liquid crystal layer 5, polyimide needs to be spin-coated on the bottom of the upper substrate 1 and above the metal ground 7 as the initial orientation layer of the liquid crystal.

[0035] Step 2: Use a vector network analyzer to connect the input interface of the vector network analyzer to the test device through a waveguide copper axis converter, and the microwave signal is coupled with the resonant structure.

[0036] Step 3: At the same time, by adjusting the voltage of the DC voltage source, a reflection phase value of 28 GHz on the screen of the vector network analyzer can be obtained when the voltage value of the DC voltage source is 0 V.

[0037] Step 4: When the voltage value of the DC voltage source is adjusted to be greater than or equal to the saturation voltage value of the measured liquid crystal, a reflection phase value of 28 GHz is obtained on the screen of the vector network analyzer.

[0038] Step 5: Subtract the reflection phase values ​​corresponding to the voltage values ​​in step 3 and step 4 to obtain the reflection phase difference of the test device at the required frequency.

[0039] Step 6: The voltage value of the DC voltage source is adjusted to be between 0V and the saturation voltage to obtain the reflection phase corresponding to each voltage of the required frequency, thereby obtaining a reflection phase and voltage variation curve.

[0040] Step 7: Change the patch size and use the above method to obtain the voltage and reflection phase change curves and reflection phase difference of four 2-radiation patch size test devices at 28GHz, L = 1.05mm, L = 1.1mm, L = 1.15mm, and L = 1.2mm. The reflection phase difference values ​​are 10°, 28°, 140°, and 118°, respectively. Figure 3 The operating frequency band of the test device in the disclosed example is 27 GHz to 31 GHz, and 28 GHz is selected as an example only for illustration. The dielectric constant of the liquid crystal at any frequency in this frequency band can actually be measured.

[0041] Step 8: Use simulation methods to obtain the liquid crystal dielectric constant and reflection phase curves of the test devices with different radiation patches at the same required frequency, and then compare them with the reflection phase differences of multiple groups of test devices with different radiation patches at the same required frequency obtained by the test, find the liquid crystal dielectric constant and reflection phase curve segments that meet all reflection phase difference values, find the minimum value of the liquid crystal dielectric constant corresponding to the curve segment as the dielectric constant in the short axis direction of the liquid crystal, and the liquid crystal dielectric constant corresponding to the maximum value as the dielectric constant in the long axis direction of the liquid crystal, thereby determining the minimum value of the dielectric constant of the liquid crystal to be tested, and the dielectric constant values ​​corresponding to each voltage between 0V and the saturation voltage can also be determined according to the reflection phase difference, specifically:

[0042] Modeling is performed in the RF simulation software, a medium is added to the liquid crystal layer of the test device 5, and the dielectric constant of the medium is set as a variable; the reflection phase and dielectric constant change curves of the above four patch size test devices are obtained by simulation using the waveguide simulation method, as shown in Figure 3 shown.

[0043] Comparing the above-mentioned ideal test phase difference data with the simulation, it is found that the dielectric constant of the liquid crystal to be tested in the hypothesis varies from 2.7 to 2.9, and only this range is satisfied. Then the ε ⊥ The value is 2.7, ε || Since the initial value of the dielectric constant of the liquid crystal is known to be 2.7, the dielectric constant values ​​corresponding to the voltages between 0V and the saturation voltage can be obtained by fitting the reflection phase corresponding to the voltage based on the reflection phase difference when the voltage is 0V and the simulation curve.

[0044] The testing device is applied to the measurement of the dielectric constant of liquid crystal and has a simple structure and high measurement accuracy.

[0045] The above description is only an embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A test method for measuring the dielectric constant of liquid crystal based on reflection phase difference, characterized in that: The testing method comprises the following steps: Step 1: Prepare a test device including a measuring liquid crystal, connect the positive and negative electrodes of the DC voltage source to the radiation patch (2) and the metal ground (7), connect the test device to the waveguide copper axis converter, and connect the surface of the upper substrate (1) of the test device to the waveguide port. Step 2: Using a vector network analyzer, connect the input end of the vector network analyzer to the waveguide copper axis converter in step 1; Step 3: Adjust the voltage value of the DC voltage source to 0V and record the reflection phase value of the required frequency on the screen of the vector network analyzer; Step 4: adjust the voltage value of the DC voltage source to be greater than or equal to the saturation voltage value of the measured liquid crystal, and record the required frequency reflection phase value on the screen of the vector network analyzer; Step 5: Subtract the reflection phase values ​​corresponding to the voltage values ​​in step 3 and step 4 to obtain the reflection phase difference of the test device at the required frequency; Step 6: adjusting the voltage value of the DC voltage source to obtain the reflection phase corresponding to each voltage of the required frequency between 0V and the saturation voltage, thereby obtaining a reflection phase and voltage change curve; Step 7: Changing the size or structure of the radiation patch (2) of the test device to obtain a test device with a different radiation patch (2); Step 8: Repeat steps 1-6 to obtain reflection phase differences and corresponding reflection phase and voltage change curves of test devices of multiple groups of different radiation patches (2) at the same required frequency; Step 9: Use a simulation method to obtain the liquid crystal dielectric constant and reflection phase curves of the test devices of different radiation patches (2) at the same required frequency, and then compare them with the reflection phase differences of multiple groups of test devices of different radiation patches (2) at the same required frequency obtained by the test, find the liquid crystal dielectric constant and reflection phase curve segment that meets all reflection phase difference values, find the minimum value of the liquid crystal dielectric constant corresponding to the curve segment as the dielectric constant in the short axis direction of the liquid crystal, and the liquid crystal dielectric constant corresponding to the maximum value as the dielectric constant in the long axis direction of the liquid crystal, thereby determining the minimum value of the dielectric constant of the liquid crystal to be tested, and the dielectric constant values ​​corresponding to each voltage between 0V and the saturation voltage can also be determined according to the reflection phase difference; wherein step 9: The measuring device test device in step 1 comprises an upper substrate (1), a liquid crystal layer (5) and a lower substrate (8); a radiation patch (2) is printed below the upper substrate (1); a metal ground (7) is printed above the lower substrate (8); a first orientation layer (4) is spin-coated below the upper substrate (1); a second orientation layer (6) is spin-coated above the lower substrate (8); the metal ground (7), the upper substrate (1), a gasket (3) arranged between the metal ground (7) and the radiation patch (2) and the liquid crystal to be measured constitute a liquid crystal layer (5); the positive and negative electrodes of a DC voltage signal are respectively applied to the radiation patch (2) and the metal ground (7) to bias the liquid crystal injected into the liquid crystal layer (5).

2. A test method for measuring the dielectric constant of liquid crystal based on reflection phase difference according to claim 1, characterized in that: In step 9, the steps of simulating and emulating the liquid crystal dielectric constant and reflection phase curve of the test device at the same required frequency include: Step 9-1: Establish a test model on the radio frequency simulation software, add a medium into the liquid crystal layer (5) of the test device, and set the dielectric constant of the medium as a variable; Step 9-2: Use waveguide simulation method to simulate; Step 9-3: Simulate and obtain the reflection phase and dielectric constant change curve of the test device at the required frequency.

3. A test method for measuring the dielectric constant of liquid crystal based on reflection phase difference according to claim 2, characterized in that: The required frequency is any frequency in the operating frequency band of the test device.

4. A test method for measuring the dielectric constant of liquid crystal based on reflection phase difference according to claim 3, characterized in that: The operating frequency band of the test device is determined by the size of the test device and the size or structure of the patch. The reflection phase of the test device in this frequency band varies with the dielectric constant of the liquid crystal and the variation range is large. Then this frequency band is the operating frequency band of the test device.

Images