A dielectric constant measurement device and method based on oblique incidence light reflection difference technology

Abstract

This invention provides a method for measuring dielectric constant based on oblique incidence light reflection difference technology. The probe light emitted by the laser 1 is converted into p-polarized light by the polarizer 2, and then modulated into p-polarized light and s-polarized light by the photoelastic modulator 3. The p-polarized light and s-polarized light are emitted alternately at a frequency of 50 kHz, and after passing through the phase shifter 4, a fixed phase difference is generated. Then, the light is focused by the first lens 5 and obliquely incident on the surface of the sample 6 to be tested, with the incident range between 50° and 60°. The signal light reflected from the surface of the sample 6 to be tested is incident on the analyzer 9 after passing through the second lens 8. The analyzer 9 is used to zero the fundamental frequency signal of the system. The signal light after passing through the analyzer 9 is absorbed by the photodetector 10 and converted into an electrical signal. The electrical signal is demodulated by the first lock-in amplifier 11 and the second lock-in amplifier 12 into a DC signal, a fundamental frequency signal I (Ω), and a harmonic signal I (2Ω). The demodulated signal is acquired and processed by the data acquisition and processing unit 13.

Description

Technical Field

[0001] This invention relates to the field of optoelectronic technology, and more particularly to optical sensing and photoelectric detection technology. Background Technology

[0002] In the field of dielectric science and engineering, the dielectric constant is an important parameter for measuring the dielectric properties of dielectric materials. For liquid dielectrics, measuring the dielectric constant is of great significance for understanding their electrical properties, optimizing their application performance, and developing new dielectric materials.

[0003] Traditional methods for measuring dielectric constant mainly include the parallel-plate capacitance method, the bridge method, and the resonant cavity method. These methods all suffer from problems to varying degrees, such as low measurement accuracy, high sample requirements, and cumbersome operation. Taking patent application number CN116773915A as an example, this patent uses air-coupled ultrasonic testing technology to measure the dielectric constant. By adjusting the aligned length and width of the upper and lower plates of a capacitor, the capacitance value between the upper and lower plates is changed. A dual-channel signal generator generates two continuous sinusoidal signals. A digital oscilloscope generates a Lissajous image based on the electrical signal received by the air-coupled ultrasonic transducer and the continuous sinusoidal signals. The capacitance meter records multiple capacitance values ​​between the upper and lower plates of the capacitor based on the changing characteristics of the Lissajous image and calculates the dielectric constant using the changes in these capacitance values.

[0004] This method is suitable for measuring the dielectric constant of the analyte when it remains constant over a certain period of time, but it cannot obtain data on the real-time change of the dielectric constant. In reality, the dielectric constant is difficult to keep constant, and the dielectric constant obtained by traditional methods has a certain lag. Therefore, developing a real-time dielectric constant measurement method to improve the accuracy and applicability of the measurement is a current technological development requirement. Summary of the Invention

[0005] This invention mainly addresses the technical problems of existing dielectric constant measurement methods, such as complex operation and inability to measure in real time, and proposes a dielectric constant measurement method based on oblique incident light reflection difference technology.

[0006] The dielectric constant measurement method based on oblique incident light reflection difference technology of the present invention completes the measurement process by using a dielectric constant measurement device based on oblique incident light reflection difference technology and a data acquisition and processing unit 13 connected to it.

[0007] The dielectric constant measurement device based on oblique incidence light reflection difference technology includes: laser 1, polarizer 2, photoelastic modulator 3, phase shifter 4, first lens 5, sample stage 7, second lens 8, analyzer 9, photodetector 10, first lock-in amplifier 11, and second lock-in amplifier 12.

[0008] The probe light emitted by the laser 1 is converted into p-polarized light by the polarizer 2, and then modulated into p-polarized light and s-polarized light by the photoelastic modulator 3. The p-polarized light and s-polarized light are emitted alternately at a frequency of 50 kHz, and after passing through the phase shifter 4, a fixed phase difference is generated. Then, the light is focused by the first lens 5 and obliquely incident on the surface of the sample 6 to be tested, with the incident range between 50° and 60°.

[0009] The signal light reflected from the surface of the sample 6 is incident on the analyzer 9 after passing through the second lens 8. The analyzer 9 is used to zero the fundamental frequency signal of the system. The signal light after passing through the analyzer 9 is absorbed by the photodetector 10 and converted into an electrical signal. The electrical signal is demodulated by the first lock-in amplifier 11 and the second lock-in amplifier 12 into a DC signal, a fundamental frequency signal I (Ω), and a harmonic signal I (2Ω). The demodulated signal is acquired and processed by the data acquisition and processing unit 13, and finally processed by:

[0010]

[0011]

[0012]

[0013] The dielectric constant ε of the sample under test was calculated by inversion.

[0014] in

[0015]

[0016]

[0017]

[0018]

[0019]

[0020]

[0021]

[0022]

[0023]

[0024]

[0025]

[0026]

[0027]

[0028]

[0029] The angle of incidence is denoted as .

[0030] Furthermore, the sample to be tested 6 is placed on a precision three-dimensional moving platform, which can be quantitatively and directionally moved.

[0031] Furthermore, the polarizer 2 is used to ensure that the emitted light is linearly polarized and that its polarization direction is in the same direction as the optical axis of the polarizer 2; by rotating the polarizer 2, the emitted linearly polarized light is incident in the p-polarization direction, which refers to the direction parallel to the incident surface formed by the incident light and the interface normal.

[0032] Furthermore, the photoelastic modulator 3 is used to modulate the polarization state of the incident light, so that the polarization state switches back and forth between the p-polarization state and the s-polarization state at 50 kHz.

[0033] Furthermore, the phase shifter 4 introduces a fixed phase difference between the p-polarization component and the s-polarization component to achieve background zeroing operation of the oblique incident light reflection difference signal.

[0034] Furthermore, the first lens 5 is used to focus the incident beam, and the second lens 8 is used to collect the signal light reflected by the sample 6 under test; the focal length of the first lens 5 is exactly equal to the distance from the first lens 5 to the laser incident point on the surface of the sample 6 under test, so that the detection spot reaching the sample 6 under test is minimized; the distance from the second lens 8 to the laser reflection point on the surface of the sample 6 under test is greater than one focal length of the second lens 8 but less than twice its focal length, so that the imaging point will be outside twice the focal length of the second lens 8, and the imaging point after reflection by the sample 6 under test is on the photodetector 10 outside the second lens 8.

[0035] Furthermore, the photodetector 10 is used to convert optical signals into electrical signals, and its core part is a PN junction, the magnitude of which is proportional to the intensity of the incident light.

[0036] Furthermore, the first lock-in amplifier 11 and the second lock-in amplifier 12 are used to amplify the electrical signal and extract the DC signal, the fundamental frequency signal I (Ω) and the multiplier signal I (2Ω) and send them to the acquisition card. The acquisition card converts the analog signal output by the lock-in amplifier into a digital signal according to the sampling theorem and acquires it to the data acquisition and processing unit 13.

[0037] Furthermore, the data acquisition and processing unit 13 saves the acquired data signals in txt format on the computer, reads the saved data, and calculates the dielectric constant of the sample 6 to be tested.

[0038] The present invention also provides a dielectric constant measurement device based on oblique incident light reflection difference technology. The device includes: a laser 1, a polarizer 2, a photoelastic modulator 3, a phase shifter 4, a first lens 5, a sample stage 7, a second lens 8, an analyzer 9, a photodetector 10, a first lock-in amplifier 11, and a second lock-in amplifier 12.

[0039] The probe light emitted by the laser 1 is converted into p-polarized light by the polarizer 2, and then modulated into p-polarized light and s-polarized light by the photoelastic modulator 3. The p-polarized light and s-polarized light are emitted alternately at a frequency of 50kHz, and after passing through the phase shifter 4, a fixed phase difference is generated. Then, the light is focused by the first lens 5 and obliquely incident on the surface of the sample 6 to be tested, with the incident angle ranging from 50° to 60°.

[0040] The signal light reflected from the surface of the sample 6 is incident on the analyzer 9 after passing through the second lens 8. The analyzer 9 is used to zero the fundamental frequency signal of the system. The signal light after passing through the analyzer 9 is absorbed by the photodetector 10 and converted into an electrical signal. The electrical signal is demodulated by the first lock-in amplifier 11 and the second lock-in amplifier 12 into a DC signal, a fundamental frequency signal I (Ω), and a harmonic signal I (2Ω). The demodulated signal is acquired and processed by the data acquisition and processing unit 13, and finally processed by:

[0041]

[0042]

[0043]

[0044] The dielectric constant ε of the sample under test was calculated by inversion.

[0045] in

[0046]

[0047]

[0048]

[0049]

[0050]

[0051]

[0052]

[0053]

[0054]

[0055]

[0056]

[0057]

[0058]

[0059]

[0060] The angle of incidence is given. Compared with the prior art, the present invention has the following advantages:

[0061] Non-destructive measurement: This method uses optical measurement techniques, which is a non-contact and non-destructive measurement method. It does not require physical contact or sampling, so it can maintain the integrity of the sample, making it particularly suitable for sensitive or expensive samples.

[0062] Real-time monitoring: This method uses optical means, and the reflected light that records sample information is received by the data acquisition and processing unit. The data acquisition and processing unit automatically calculates the dielectric constant of the liquid based on the received DC, fundamental frequency, and harmonic signals, which can calculate the dielectric constant of the current sample in real time, achieving the purpose of real-time detection.

[0063] High accuracy: Employing the oblique incidence light reflection difference method avoids the accuracy degradation issue encountered by the perpendicular incidence light method in measuring certain highly absorbent liquid samples, thus improving measurement accuracy. Furthermore, high-precision measurements can be achieved through precise control of components such as the light source module, reflector module, and angle sensor.

[0064] High flexibility: The design of this system allows it to adjust parameters such as optical path and reflection angle according to different needs, giving it high flexibility. Attached Figure Description

[0065] Figure 1 This is a schematic diagram of the OIRD detection device provided by the present invention;

[0066] Figure 2 This is a schematic diagram of the LabVIEW rear panel noise reduction module provided by the present invention;

[0067] Figure 3 This is a schematic diagram of the LabVIEW back panel data recording module provided by the present invention;

[0068] Figure 4 This is a schematic diagram of the LabVIEW front panel provided by the present invention;

[0069] Figure 5This is a process flow diagram of the real-time measurement method of liquid dielectric constant based on oblique incidence light reflection difference technology provided by the present invention;

[0070] Figure 6 This invention provides a comparison and error diagram of the dielectric constants of sucrose solution and sodium chloride solution.

[0071] Reference numerals in the attached figures: 1. Laser; 2. Polarizer; 3. Photoelastic modulator; 4. Phase shifter; 5. First lens; 6. Sample to be tested; 7. Sample stage; 8. Second lens; 9. Analyzer; 10. Photodetector; 11. First lock-in amplifier; 12. Second lock-in amplifier; 13. Data acquisition and processing unit. Detailed Implementation

[0072] To make the technical problems solved by this invention, the technical solutions adopted, and the technical effects achieved clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, only the parts relevant to the invention are shown in the accompanying drawings, not all of them.

[0073] The oblique incident light reflection difference method (OIRD) of this embodiment is a novel, non-destructive, real-time online method for detecting changes in samples. It reflects changes in interface characteristics by measuring the change in the difference between the p-ray and s-ray components of the reflected light obliquely incident on the interface.

[0074] like Figure 1 As shown, the apparatus used in this method includes a laser 1, a polarizer 2, a photoelastic modulator 3, a phase shifter 4, a first lens 5, a sample stage 7, a second lens 8, an analyzer 9, a photodetector 10, a first lock-in amplifier 11, and a second lock-in amplifier 12. This method utilizes a LabVIEW program to record and process data. The LabVIEW program's back panel consists of a block diagram, as shown... Figure 2 , 3 As shown; the front panel mainly consists of controls and indicators, such as Figure 4 As shown.

[0075] Figure 5 This is a process flow diagram of the real-time measurement method of liquid dielectric constant based on oblique incidence light reflection difference technology provided by the present invention. The specific measurement method and principle are as follows:

[0076] Laser 1 is a helium-neon laser used to emit probe light with a wavelength of λ = 632.8 nm. The probe light is converted to p-polarized light by polarizer 2, and then modulated by photoelastic modulator 3 into alternately emitted p-polarized and s-polarized light. The two polarized lights emitted from photoelastic modulator 3 are then converted into a fixed phase difference by phase shifter 4. The light is then focused by the first lens 5 and obliquely incident on the surface of the sample 6 to be tested, with the incident angle equal to Brewster's angle.

[0077] The probe light reflected from the surface of the sample 6 passes through the second lens 8 and enters the analyzer 9. The signal light after passing through the analyzer 9 is absorbed by the photodetector 10 and converted into an electrical signal. The electrical signal is demodulated into a DC signal, a fundamental frequency signal, and a harmonic signal by two lock-in amplifiers. The demodulated signal is acquired and processed by the data acquisition and processing unit 13, and finally the dielectric constant of the sample is calculated.

[0078] The photoelastic modulator 3 modulates the original p-polarized light into p-light and s-light emitted alternately at a frequency of 50 kHz.

[0079] The phase shifter 4 introduces a fixed phase difference between the p-beam and the s-beam.

[0080] Both the first lens and the second lens are converging lenses. The first lens 5 converges the incident light onto the surface of the sample 6 to be tested, so that the detection spot on the sample 6 is minimized. Therefore, the distance from the sample 6 to the first lens 5 is the focal length of the first lens 5. In order to focus the reflected light onto the photodetector 10 so that the photodetector 10 can collect more sample information, the distance from the second lens 8 to the light spot on the surface of the sample 6 is greater than one focal length but less than two focal lengths.

[0081] The sample stage 7 is used to support the sample 6 to be tested. The sample stage 7 is connected to a stepper motor and has two modes: manual and automatic. In manual mode, the three-dimensional movement of the sample stage 7 is controlled by rotating different knobs under the sample stage 7; in automatic mode, the manual knob is locked, and the movement of the sample stage 7 is controlled by sending commands to the stepper motor through the computer.

[0082] The polarizer 2 and the analyzer 9 are fixed at 45 degrees. The polarizer 2 is used to convert the probe light into p light, and the analyzer 9 is used to detect the polarization state of the probe light and to zero the fundamental frequency signal of the system.

[0083] The photodetector 10 is used to convert optical signals into electrical signals, and then transmits the electrical signals to a lock-in amplifier. Its core component is a PN junction. When a photon enters the PN junction, electron-hole pairs are generated within it. These electron-hole pairs move directionally under the influence of an external electric field, thus forming a photocurrent. The magnitude of the photocurrent is proportional to the incident light intensity within a certain range. To ensure that the output electrical signal is proportional to the received optical signal, the optical signal received by the photodetector 10 cannot be too strong.

[0084] The first lock-in amplifier 11 and the second lock-in amplifier 12 separate the DC, fundamental frequency, and harmonic signals from the total intensity collected by the photodiode, and can suppress various non-reference carrier frequencies, thereby realizing signal amplification for a specific carrier frequency.

[0085] The data acquisition and processing unit 13 comprises both software and hardware. The hardware includes a computer acquisition card and connecting cables. The acquisition card receives electrical signals transmitted from the lock-in amplifier and converts them into digital signals that can be processed by the computer. The software includes data acquisition software and data processing software. The data acquisition software records and saves the acquired data to the computer, while the data processing software reads the saved data and performs calculations according to formulas.

[0086] The principle of the data processing software is as follows:

[0087] As can be seen from matrix optics, the total light intensity received by the photodetector is

[0088] I photodiode =I dc +I(Ω)sinΩt+I(2Ω)cos2Ωt, where:

[0089] DC signal

[0090] fundamental frequency signal

[0091] Frequency multiplication signal

[0092] I0 is the initial intensity of the emitted light. I(Ω) and I(2Ω) are the fundamental and harmonic frequencies measured by the lock-in amplifier of the OIRD. J0(A), J1(A), and J2(A) are the zeroth, first, and second order Bessel functions, respectively. The DC component is I. dc , The phase difference introduced by the phase shifter, Ω = 50kHz is the modulation frequency of the photoelastic modulator, and rp and rs are the surface reflectivities for P- and S-polarized light, respectively. and It is the phase difference between rp and rs. Before the experiment, the analyzer was adjusted to... The baseband signal will be modulated to zero.

[0093] From Fresnel's formula:

[0094]

[0095]

[0096] Calculated

[0097]

[0098] in

[0099]

[0100]

[0101]

[0102]

[0103]

[0104]

[0105]

[0106]

[0107] in

[0108]

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[0110]

[0111]

[0112]

[0113]

[0114]

[0115]

[0116] The initial light intensity and incident angle of the system can be determined, and the final DC, fundamental, and harmonic signals are only related to the dielectric constant of the sample. After measuring the DC, fundamental, and harmonic signals of the sample, they can be substituted into the formula to obtain the dielectric constant.

[0117] Figure 6 The circle represents the dielectric constant calculated using this method, and the triangle represents the dielectric constant measured using a network analyzer. The error between the calculated and measured values ​​of the dielectric constant at each concentration is less than 0.3, indicating that this method has high accuracy.

[0118] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications to the technical solutions described in the foregoing embodiments, or equivalent substitutions for some or all of the technical features, do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for measuring dielectric constant based on oblique incidence light reflection difference technology, comprising a dielectric constant measuring device based on oblique incidence light reflection difference technology and a data acquisition and processing unit (13) connected thereto to complete the measurement process, characterized in that, The dielectric constant measurement device based on oblique incident light reflection difference technology includes: a laser (1), a polarizer (2), a photoelastic modulator (3), a phase shifter (4), a first lens (5), a sample stage (7), a second lens (8), an analyzer (9), a photodetector (10), a first lock-in amplifier (11), and a second lock-in amplifier (12). The probe light emitted by the laser (1) is converted into p-polarized light by the polarizer (2), and then modulated into p-polarized light and s-polarized light by the photoelastic modulator (3). The p-polarized light and s-polarized light are emitted alternately at a frequency of 50 kHz, and after passing through the phase shifter (4), a fixed phase difference is generated. Then, the light is focused by the first lens (5) and obliquely incident on the surface of the sample to be tested (6). The incident range is between 50° and 60°. The signal light reflected from the surface of the sample (6) passes through the second lens (8) and enters the analyzer (9). The analyzer (9) is used to zero the fundamental frequency signal of the system. The signal light after passing through the analyzer (9) is absorbed by the photodetector (10) and converted into an electrical signal. The electrical signal is demodulated by the first lock-in amplifier (11) and the second lock-in amplifier (12) into a DC signal, a fundamental frequency signal I (Ω), and a harmonic signal I (2Ω). The demodulated signal is acquired and processed by the data acquisition and processing unit (13), and finally processed by: ； The dielectric constant of the sample under test is calculated by inversion. ; in ； The angle of incidence is denoted as .

2. The method for measuring dielectric constant based on oblique incidence light reflection difference technology according to claim 1, characterized in that, The sample to be tested (6) is placed on a precision three-dimensional moving platform, which can be quantitatively and directionally moved.

3. The method for measuring dielectric constant based on oblique incidence light reflection difference technology according to claim 1, characterized in that, The polarizer (2) is used to ensure that the emitted light is linearly polarized and that its polarization direction is in the same direction as the optical axis of the polarizer (2); by rotating the polarizer (2), the emitted linearly polarized light is incident in the p-polarization direction, which refers to the direction parallel to the incident surface formed by the incident light and the interface normal.

4. The dielectric constant measurement method based on oblique incidence light reflection difference technology according to claim 1, characterized in that, The photoelastic modulator (3) is used to modulate the polarization state of the incident light, so that the polarization state changes back and forth between the p-polarization state and the s-polarization state at 50 kHz.

5. The method for measuring dielectric constant based on oblique incidence light reflection difference technology according to claim 1, characterized in that, The phase shifter (4) introduces a fixed phase difference between the p-polarization component and the s-polarization component to achieve background zeroing of the oblique incident light reflection difference signal.

6. The method for measuring dielectric constant based on oblique incidence light reflection difference technology according to claim 1, characterized in that, The first lens (5) is used to focus the incident beam, and the second lens (8) is used to collect the signal light reflected by the sample (6) to be tested. The focal length of the first lens (5) is exactly equal to the distance from the first lens (5) to the laser incident point on the surface of the sample (6) to be tested, so that the detection spot on the sample (6) to be tested is minimized. The distance from the second lens (8) to the laser reflection point on the surface of the sample (6) to be tested is greater than one focal length of the second lens (8) and less than twice its focal length, so that the imaging point will be outside twice the focal length of the second lens (8), so that the imaging point after reflection by the sample (6) to be tested is on the photodetector (10) outside the second lens (8).

7. The method for measuring dielectric constant based on oblique incidence light reflection difference technology according to claim 1, characterized in that, The photodetector (10) is used to convert optical signals into electrical signals. Its core part is a PN junction, and the magnitude of the photocurrent is proportional to the intensity of the incident light.

8. The method for measuring dielectric constant based on oblique incidence light reflection difference technology according to claim 1, characterized in that, The first lock-in amplifier (11) and the second lock-in amplifier (12) are used to amplify the electrical signal and extract the DC signal, the fundamental frequency signal I (Ω) and the multiplier signal I (2Ω) and send them to the acquisition card. The acquisition card converts the analog signal output by the lock-in amplifier into a digital signal according to the sampling theorem and acquires it to the data acquisition and processing unit (13).

9. The method for measuring dielectric constant based on oblique incidence light reflection difference technology according to claim 1, characterized in that, The data acquisition and processing unit (13) saves the acquired data signals in txt format on the computer, reads the saved data and calculates the dielectric constant of the sample (6) to be tested.

10. A dielectric constant measuring device based on oblique incidence light reflection difference technology, characterized in that, The device includes: a laser (1), a polarizer (2), a photoelastic modulator (3), a phase shifter (4), a first lens (5), a sample stage (7), a second lens (8), a polarizer (9), a photodetector (10), a first lock-in amplifier (11), and a second lock-in amplifier (12). The probe light emitted by the laser (1) is converted into p-polarized light by the polarizer (2), and then modulated into p-polarized light and s-polarized light by the photoelastic modulator (3). The p-polarized light and s-polarized light are emitted alternately at a frequency of 50 kHz, and after passing through the phase shifter (4), a fixed phase difference is generated. Then, the light is focused by the first lens (5) and obliquely incident on the surface of the sample to be tested (6). The incident angle range is between 50° and 60°. The signal light reflected from the surface of the sample (6) passes through the second lens (8) and enters the analyzer (9). The analyzer (9) is used to zero the fundamental frequency signal of the system. The signal light after passing through the analyzer (9) is absorbed by the photodetector (10) and converted into an electrical signal. The electrical signal is demodulated by the first lock-in amplifier (11) and the second lock-in amplifier (12) into a DC signal, a fundamental frequency signal I (Ω), and a harmonic signal I (2Ω). The demodulated signal is acquired and processed by the data acquisition and processing unit (13), and finally processed by: ； The dielectric constant of the sample under test is calculated by inversion. , in, ； The angle of incidence is denoted as .

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