Method and system for measuring dielectric constant of material

Abstract

The invention discloses a method and system for measuring the dielectric constant of a material, and the method comprises the steps: enabling a terahertz pulse signal to flow through a transmission line and generate reflection through growing a coplanar waveguide transmission line on the surfaces of an electro-optical crystal and a measured material; after femtosecond laser is processed, a terahertz signal is sampled, an optical polarization state analysis system reproduces an electric signal and extracts a peak moment, and a relative dielectric constant is calculated by combining transmission line structure parameters and a formula. According to the invention, electro-optical sampling and time domain reflection technologies are combined, high time resolution and structure adaptability are realized, and accurate measurement of the dielectric constant of the material is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of dielectric constant measurement, and in particular to a method and system for measuring the dielectric constant of a material. Background Art

[0002] The dielectric constant is a key parameter for characterizing the electromagnetic properties of materials, and its precise measurement is of great significance in fields such as materials science, microwave engineering, and terahertz technology. Among existing technologies, electro-optical sampling uses femtosecond pulsed lasers to achieve equivalent sampling of electrical signals. Based on the electro-optic effect of electro-optic crystals, it can reproduce electrical signals by analyzing changes in the laser's polarization state, offering the advantage of high temporal resolution. Time-domain reflectometry, on the other hand, utilizes the reflection characteristics of electromagnetic waves in transmission media. By analyzing parameters such as the amplitude and time of the reflected signal, it can analyze the structure and properties of the transmission medium, and is widely used in dielectric property testing.

[0003] However, single electro-optical sampling technology or time-domain reflection technology has limitations in measuring the dielectric constant of materials: although electro-optical sampling technology can accurately capture electrical signals, it is difficult to directly correlate the signals with the dielectric properties of the material; although time-domain reflection technology can analyze the properties of the medium through the reflected signal, it lacks high-resolution signal sampling means. Summary of the Invention

[0004] In view of the deficiencies in the prior art, the present invention provides a method and system for measuring the dielectric constant of a material.

[0005] The present invention discloses a method for measuring the dielectric constant of a material, comprising:

[0006] Coplanar waveguide transmission lines are grown on the surface of the electro-optical crystal and the material under test respectively;

[0007] Driving the terahertz pulse signal to flow through the coplanar waveguide transmission line on the surface of the electro-optical crystal and the coplanar waveguide transmission line on the surface of the material to be measured in sequence, and generating reflection signals at the starting and ending positions of the coplanar waveguide transmission line on the surface of the material to be measured respectively;

[0008] Synchronously driving a femtosecond pulse laser to pass through the gap between the signal line and the ground line of the coplanar waveguide transmission line on the surface of the electro-optical crystal after beam shaping, beam delay and beam convergence processing, so as to perform equivalent sampling of the terahertz pulse signal;

[0009] Detecting the polarization state change of the femtosecond pulse laser passing through the electro-optical crystal, reproducing the electrical signal on the coplanar waveguide transmission line between the electro-optical crystal and the surface of the material being tested, and extracting the peak moment of the reflected signal;

[0010] The relative dielectric constant of the material under test is calculated based on the obtained peak moment and the structural parameters of the coplanar waveguide transmission line on the surface of the material under test.

[0011] As a further improvement of the present invention, the coplanar waveguide transmission line includes a signal line and ground lines spaced apart on both sides of the signal line.

[0012] As a further improvement of the present invention, the terahertz pulse signal is an impulse-like electrical signal, whose effective bandwidth covers the terahertz level and whose transition duration is less than 10 ps.

[0013] As a further improvement of the present invention, the pulse width of the femtosecond pulse laser is less than 200 fs.

[0014] As a further improvement of the present invention, the relative dielectric constant of the material being measured is calculated, specifically including:

[0015] Based on the obtained peak moment and the length parameter of the coplanar waveguide transmission line on the surface of the measured material, the equivalent dielectric constant of the measured material with the coplanar waveguide transmission line is calculated using the equivalent dielectric constant calculation formula;

[0016] Based on the obtained equivalent dielectric constant, the relative dielectric constant of the measured material is calculated using the relative dielectric constant calculation formula.

[0017] As a further improvement of the present invention, the equivalent dielectric constant calculation formula is:

[0018]

[0019] Where L2 is the length of the coplanar waveguide transmission line grown on the surface of the material under test; t1 and t2 are the peak moments corresponding to the reflected signals at the starting and ending positions of the coplanar waveguide transmission line on the surface of the material under test, respectively; c is the speed of light; ε e is the equivalent dielectric constant of the material under test with a coplanar waveguide transmission line.

[0020] As a further improvement of the present invention, the relative dielectric constant calculation formula is:

[0021]

[0022] Where, ε e is the equivalent dielectric constant of the material under test with the coplanar waveguide transmission line; K(k) is the complete elliptic integral of the first kind, where k refers to k0, k1, k′0, and k′1 respectively; ε r is the relative dielectric constant of the material being tested.

[0023] As a further improvement of the present invention, the specific calculation formulas of k0, k1, k′0, and k′1 are:

[0024]

[0025]

[0026] Where s2 is the width of the signal line in the coplanar waveguide transmission line grown on the surface of the material under test, w2 is the gap width between the signal line and the ground line in the coplanar waveguide transmission line grown on the surface of the material under test, and H2 is the thickness of the material under test.

[0027] The present invention discloses a system for measuring the dielectric constant of a material, which is applied to the above-mentioned method for measuring the dielectric constant of a material, comprising:

[0028] A terahertz pulse source, which is used to provide a terahertz pulse signal;

[0029] A femtosecond laser for providing femtosecond pulsed laser light;

[0030] an electro-optical crystal having a first coplanar waveguide transmission line grown on its surface;

[0031] A material under test has a second coplanar waveguide transmission line grown on its surface;

[0032] A beam processing module, which is used to perform beam shaping, beam delay and beam convergence on femtosecond pulse lasers;

[0033] The optical polarization state analysis module is used to detect the polarization state change of the femtosecond pulse laser after passing through the electro-optical crystal, so as to reproduce the electrical signal on the coplanar waveguide transmission line between the electro-optical crystal and the surface of the material being tested;

[0034] The dielectric constant calculation module is used to calculate the relative dielectric constant of the material being tested.

[0035] As a further improvement of the present invention, the beam processing module includes a beam shaping unit, a beam delay unit and a beam converging unit which are arranged in sequence.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] The present invention combines electro-optical sampling technology with time-domain reflection technology, utilizes the reflection characteristics of terahertz pulse signals in the coplanar waveguide transmission line on the surface of the material being measured, and cooperates with the high-resolution equivalent sampling and polarization state analysis of femtosecond pulse laser to accurately reproduce electrical signals and extract key parameters. Finally, the relative dielectric constant of the material being measured is obtained through the dielectric constant calculation formula, realizing the effective measurement of the core parameters of the material's electromagnetic properties.

[0038] The present invention uses femtosecond pulse laser for equivalent sampling, inheriting the high time resolution advantage of electro-optical sampling technology, and can capture the details of terahertz pulse signals with transition duration less than 10ps; at the same time, by generating coplanar waveguide transmission lines (with a structure of ground line-signal line-ground line) on the surface of the electro-optical crystal and the material being measured, it ensures stable transmission of terahertz pulse signals and effective generation of reflected signals, adapting to measurement scenarios of different materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 A flow chart of a method for measuring the dielectric constant of a material disclosed in one embodiment of the present invention;

[0040] Figure 2 A schematic diagram of the signal transmission, acquisition, and coplanar waveguide transmission line structure of a method for measuring the dielectric constant of a material disclosed in one embodiment of the present invention;

[0041] Figure 3 This is a structural diagram of a system for measuring the dielectric constant of a material disclosed in one embodiment of the present invention.

[0042] In the picture:

[0043] 1. Terahertz pulse source; 2. Femtosecond laser; 3. Electro-optical crystal; 4. Material to be measured; 5. Beam shaping unit; 6. Beam delay unit; 7. Beam convergence unit; 8. Optical polarization state analysis module; 9. Femtosecond pulse laser spot; 10. First coplanar waveguide transmission line; 11. Second coplanar waveguide transmission line; 111. Signal line; 112. Ground line. DETAILED DESCRIPTION

[0044] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0045] In the description of the present invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate and simplify the description of the present invention. They are not intended to indicate or imply that the devices or components referred to must have, be constructed, or operate in a specific orientation, and therefore should not be construed as limitations on the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0046] In the description of the present invention, it should also be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood broadly. For example, they may refer to fixed, detachable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0047] The present invention is described in further detail below with reference to the accompanying drawings:

[0048] Example:

[0049] like Figure 1 As shown, a method for measuring the dielectric constant of a material provided by the present invention includes:

[0050] Coplanar waveguide transmission lines are grown on the surfaces of the electro-optical crystal 3 and the material to be tested 4 respectively;

[0051] Driving the terahertz pulse signal to flow through the coplanar waveguide transmission line on the surface of the electro-optical crystal 3 and the coplanar waveguide transmission line on the surface of the material to be measured in sequence, and generating reflection signals at the starting and ending positions of the coplanar waveguide transmission line on the surface of the material to be measured 4 respectively;

[0052] Synchronously drive the femtosecond pulse laser to pass through the gap between the signal line and the ground line of the coplanar waveguide transmission line on the surface of the electro-optical crystal 3 after beam shaping, beam delay and beam convergence processing, so as to perform equivalent sampling of the terahertz pulse signal;

[0053] Detect the polarization state change of the femtosecond pulse laser passing through the electro-optical crystal 3, reproduce the electrical signal on the coplanar waveguide transmission line on the surface of the electro-optical crystal 3 and the material under test 4, and extract the peak moment of the reflected signal;

[0054] Based on the obtained peak moment and the structural parameters of the coplanar waveguide transmission line on the surface of the material 4 under test, the relative dielectric constant of the material 4 under test is calculated.

[0055] Specifically:

[0056] like Figure 2 As shown, in the above embodiment, preferably, a first coplanar waveguide transmission line 10 is grown on the surface of the electro-optical crystal 3. The effective bandwidth of the first coplanar waveguide transmission line 10 is greater than the effective bandwidth of the terahertz pulse signal. The parameters of the first coplanar waveguide transmission line 10 include: length L1, thickness h1, signal line width s1, gap w1 between the signal line and the ground line, and ground line width g1. The material of the first coplanar waveguide transmission line 10 is gold, and the structure is "ground line-signal line-ground line".

[0057] In the above embodiment, preferably, a second coplanar waveguide transmission line 11 is grown on the surface of the material under test 4. The parameters of the second coplanar waveguide transmission line 111 include: length L2, thickness h2, width s2 of the signal line 111, gap w2 between the signal line 111 and the ground line 112, and width g2 of the ground line 112. The material of the second coplanar waveguide transmission line 111 is gold, and the structure is "ground line 112 - signal line 111 - ground line 112."

[0058] In the above embodiment, preferably, the terahertz pulse signal is an impulse-like electrical signal, whose effective bandwidth covers the terahertz level and whose transition duration is less than 10 ps.

[0059] In the above embodiment, preferably, during the material dielectric constant measurement process, the terahertz pulse signal first passes through a first coplanar waveguide transmission line 10 grown on the surface of the electro-optical crystal 3, and then passes through a second coplanar waveguide transmission line 11 grown on the surface of the material under test 4. During the transmission of the terahertz pulse signal on the second coplanar waveguide transmission line 11, signal reflections may occur at locations where impedance mismatches or impedance changes occur. Figure 2 In the figure, "Position 1" is the starting position of the second coplanar waveguide transmission line 11 grown on the surface of the test material 4, and "Position 2" is the ending position of the second coplanar waveguide transmission line 11 grown on the surface of the test material 4. The terahertz pulse signal generates reflection signals at "Position 1" and "Position 2". The reflection signal at "Position 1" is calibrated as "Signal 1", and the reflection signal at "Position 2" is calibrated as "Signal 2".

[0060] In the above embodiment, preferably, since the terahertz pulse signal may generate loss during transmission, the amplitude of signal 2 is smaller than that of signal 1.

[0061] In the above embodiment, preferably, the pulse width of the femtosecond pulse laser is less than 200 fs. Figure 2 The black dot in the middle is the femtosecond pulse laser spot.

[0062] In the above embodiment, preferably, calculating the relative dielectric constant of the material 4 under test specifically includes:

[0063] Based on the obtained peak moment and the length parameters of the coplanar waveguide transmission line on the surface of the measured material 4, the equivalent dielectric constant of the measured material 4 with the coplanar waveguide transmission line is calculated using the equivalent dielectric constant calculation formula;

[0064] Based on the obtained equivalent dielectric constant, the relative dielectric constant of the measured material 4 is calculated using the relative dielectric constant calculation formula.

[0065] In the above embodiment, preferably, the equivalent dielectric constant calculation formula is:

[0066]

[0067] Where L2 is the length of the coplanar waveguide transmission line grown on the surface of the material under test; t1 and t2 are the peak moments corresponding to the reflected signals at the starting and ending positions of the coplanar waveguide transmission line on the surface of the material under test, respectively; c is the speed of light; ε e is the equivalent dielectric constant of the material under test with a coplanar waveguide transmission line.

[0068] In the above embodiment, preferably, the relative dielectric constant calculation formula is:

[0069]

[0070] Where, ε e is the equivalent dielectric constant of the material under test with the coplanar waveguide transmission line; K(k) is the complete elliptic integral of the first kind, where k refers to k0, k1, k′0, and k′1 respectively; ε r is the relative dielectric constant of the material being tested.

[0071] In the above embodiment, preferably, the specific calculation formulas of k0, k1, k′0, and k′1 are:

[0072]

[0073] Where s2 is the width of the signal line in the coplanar waveguide transmission line grown on the surface of the material under test, w2 is the gap width between the signal line and the ground line in the coplanar waveguide transmission line grown on the surface of the material under test, and H2 is the thickness of the material under test.

[0074] In the relative dielectric constant calculation formula, only the relative dielectric constant ε of the measured material 4 is used. r is an unknown quantity, and the remaining variables can be calculated through the structural parameters of the second coplanar waveguide transmission line 11 on the surface of the measured material 4 and the thickness of the measured material 4. Therefore, according to the equivalent dielectric constant obtained by the relative dielectric constant calculation formula, the relative dielectric constant ε of the measured material 4 can be calculated. r .

[0075] like Figure 3 As shown, a material dielectric constant measurement system provided by the present invention is applied to the above-mentioned material dielectric constant measurement method, including:

[0076] A terahertz pulse source 1, which is used to provide a terahertz pulse signal;

[0077] A femtosecond laser 2, which is used to provide femtosecond pulse laser;

[0078] an electro-optical crystal 3 having a first coplanar waveguide transmission line 10 grown on its surface;

[0079] A material under test 4, having a second coplanar waveguide transmission line 11 grown on its surface;

[0080] A beam processing module, which is used to perform beam shaping, beam delay and beam convergence on femtosecond pulse lasers;

[0081] The optical polarization state analysis module 8 is used to detect the polarization state change of the femtosecond pulse laser after passing through the electro-optical crystal 3, so as to reproduce the electrical signal on the electro-optical crystal 3 and the coplanar waveguide transmission line on the surface of the material under test;

[0082] The dielectric constant calculation module is used to execute the equivalent dielectric constant calculation formula and the relative dielectric constant calculation formula to calculate the relative dielectric constant of the material 4 under test.

[0083] In the above embodiment, preferably, the beam processing module includes a beam shaping unit 5 , a beam delay unit 6 and a beam converging unit 7 which are arranged in sequence.

[0084] In the above embodiment, preferably, the femtosecond laser 2 is synchronized with the terahertz pulse source 1 .

[0085] In the above embodiment, preferably, the femtosecond laser 2 outputs femtosecond pulse laser light, and the pulse width of the femtosecond pulse laser light is less than 200 fs.

[0086] Advantages of the present invention:

[0087] The present invention combines electro-optical sampling technology with time-domain reflection technology, utilizes the reflection characteristics of terahertz pulse signals in the coplanar waveguide transmission line on the surface of the material 4 under test, and cooperates with the high-resolution equivalent sampling and polarization state analysis of femtosecond pulse laser to accurately reproduce electrical signals and extract key parameters. Finally, the relative dielectric constant of the material 4 under test is obtained through the relative dielectric constant calculation formula, thereby realizing the effective measurement of the core parameters of the electromagnetic properties of the material 4 under test.

[0088] The present invention uses femtosecond pulse laser for equivalent sampling, inheriting the high time resolution advantage of electro-optical sampling technology, and can capture the details of terahertz pulse signals with transition duration less than 10ps; at the same time, by growing coplanar waveguide transmission lines (with a structure of ground line-signal line-ground line) on the surface of the electro-optical crystal 3 and the material to be measured 4, it ensures stable transmission of terahertz pulse signals and effective generation of reflected signals, adapting to measurement scenarios of different materials.

[0089] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for measuring the dielectric constant of a material, characterized in that: include: Coplanar waveguide transmission lines are grown on the surface of the electro-optical crystal and the material under test respectively; Driving the terahertz pulse signal to flow through the coplanar waveguide transmission line on the surface of the electro-optical crystal and the coplanar waveguide transmission line on the surface of the material to be measured in sequence, and generating reflection signals at the starting and ending positions of the coplanar waveguide transmission line on the surface of the material to be measured respectively; Synchronously driving a femtosecond pulse laser to pass through the gap between the signal line and the ground line of the coplanar waveguide transmission line on the surface of the electro-optical crystal after beam shaping, beam delay and beam convergence processing, so as to perform equivalent sampling of the terahertz pulse signal; Detecting the polarization state change of the femtosecond pulse laser passing through the electro-optical crystal, reproducing the electrical signal on the coplanar waveguide transmission line between the electro-optical crystal and the surface of the material being tested, and extracting the peak moment of the reflected signal; The relative dielectric constant of the material under test is calculated based on the obtained peak moment and the structural parameters of the coplanar waveguide transmission line on the surface of the material under test.

2. The method for measuring the dielectric constant of a material according to claim 1, wherein: The coplanar waveguide transmission line includes a signal line and ground lines spaced apart on both sides of the signal line.

3. The method for measuring the dielectric constant of a material according to claim 1, wherein: The terahertz pulse signal is an impulse-like electrical signal, its effective bandwidth covers the terahertz level, and its transition duration is less than 10 ps.

4. The method for measuring the dielectric constant of a material according to claim 1, wherein: The pulse width of the femtosecond pulse laser is less than 200 fs.

5. The method for measuring the dielectric constant of a material according to claim 1, wherein: Calculate the relative dielectric constant of the material being tested, including: Based on the obtained peak moment and the length parameter of the coplanar waveguide transmission line on the surface of the measured material, the equivalent dielectric constant of the measured material with the coplanar waveguide transmission line is calculated using the equivalent dielectric constant calculation formula; Based on the obtained equivalent dielectric constant, the relative dielectric constant of the measured material is calculated using the relative dielectric constant calculation formula.

6. The method for measuring the dielectric constant of a material according to claim 5, wherein: The equivalent dielectric constant calculation formula is: Where L2 is the length of the coplanar waveguide transmission line grown on the surface of the material under test; t1 and t2 are the peak moments corresponding to the reflected signals at the starting and ending positions of the coplanar waveguide transmission line on the surface of the material under test, respectively; c is the speed of light; ε e is the equivalent dielectric constant of the material under test with a coplanar waveguide transmission line.

7. The method for measuring the dielectric constant of a material according to claim 6, wherein: The relative dielectric constant calculation formula is: Where, ε e is the equivalent dielectric constant of the material under test with the coplanar waveguide transmission line; K(k) is the complete elliptic integral of the first kind, where k refers to k0, k1, k′0, and k′1 respectively; ε r is the relative dielectric constant of the material being tested.

8. The method for measuring the dielectric constant of a material according to claim 7, wherein: The specific calculation formulas for k0, k1, k′0, and k′1 are: Where s2 is the width of the signal line in the coplanar waveguide transmission line grown on the surface of the material under test, w2 is the gap width between the signal line and the ground line in the coplanar waveguide transmission line grown on the surface of the material under test, and H2 is the thickness of the material under test.

9. A system for measuring the dielectric constant of a material, applied to the method for measuring the dielectric constant of a material according to any one of claims 1 to 8, characterized in that: include: A terahertz pulse source, which is used to provide a terahertz pulse signal; A femtosecond laser for providing femtosecond pulsed laser light; an electro-optical crystal having a first coplanar waveguide transmission line grown on its surface; A material under test has a second coplanar waveguide transmission line grown on its surface; A beam processing module, which is used to perform beam shaping, beam delay and beam convergence on femtosecond pulse lasers; The optical polarization state analysis module is used to detect the polarization state change of the femtosecond pulse laser after passing through the electro-optical crystal, so as to reproduce the electrical signal on the coplanar waveguide transmission line between the electro-optical crystal and the surface of the material being tested; The dielectric constant calculation module is used to calculate the relative dielectric constant of the material being tested.

10. The material dielectric constant measurement system according to claim 9, characterized in that: The beam processing module includes a beam shaping unit, a beam delay unit and a beam converging unit which are arranged in sequence.

Images