CN109541319B - Liquid dielectric constant measuring method - Google Patents
Liquid dielectric constant measuring method Download PDFInfo
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- CN109541319B CN109541319B CN201811218620.7A CN201811218620A CN109541319B CN 109541319 B CN109541319 B CN 109541319B CN 201811218620 A CN201811218620 A CN 201811218620A CN 109541319 B CN109541319 B CN 109541319B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
- G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
- G01R27/26—Measuring inductance or capacitance; Measuring quality factor, e.g. by using the resonance method; Measuring loss factor; Measuring dielectric constants ; Measuring impedance or related variables
- G01R27/2617—Measuring dielectric properties, e.g. constants
- G01R27/2635—Sample holders, electrodes or excitation arrangements, e.g. sensors or measuring cells
- G01R27/2658—Cavities, resonators, free space arrangements, reflexion or interference arrangements
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
- Y02A90/00—Technologies having an indirect contribution to adaptation to climate change
- Y02A90/30—Assessment of water resources
Abstract
The invention relates to the field of material research, in particular to a liquid dielectric constant measuring method, which comprises the steps of adding a liquid sample to be measured into a sample tank, and immersing all through holes on the side wall of the lower part of an outer conductor of a resonator into the liquid sample; starting a high-voltage direct-current power supply, enabling the high-voltage direct-current power supply to output voltage to a high-voltage switch through a charging resistor, a charging wire and a pulse forming cable, wherein the typical voltage range is 1.2kV to 2.0kV, and adjusting the output voltage of the high-voltage direct-current power supply to enable the high-voltage switch to be closed; monitoring the voltage waveform of the output end of the high-voltage switch through an oscilloscope; generating a voltage difference between the core wire of the transmission line II and the sample tank shell in the closing time of the high-voltage switch, and applying the voltage difference to the liquid sample; the vector network analyzer outputs microwave signals and enters the resonator through the SMA connector, and the vector network analyzer records the resonance frequency of the liquid sample; the data collected by the vector network analyzer is input into a computer, the computer processes the data to obtain a reflection spectrum, and the dielectric constant of the liquid sample is obtained through calculation.
Description
Technical Field
The invention relates to the field of material research, in particular to a liquid dielectric constant measuring method capable of measuring the dielectric constant of a liquid sample after high voltage application.
Background
Many chemical and biological applications require precise measurement of the dielectric constant of a liquid, the prior art uses refractive index sensors which are not linear in their refractive index response, requiring cumbersome calibration procedures, and the refractive index sensors are very sensitive to bending and therefore collect interfering signals in the refractive measured characteristic spectrum, and the prior art uses reflective refractometers which are fragile, costly to manufacture and complex in process, and whose two reflective surfaces must be precisely machined to remain parallel, which affects their performance in practical applications. In an experiment for researching a liquid after high voltage application, a voltage pulse with a certain amplitude and duration needs to be applied to the liquid, however, the device in the prior art has large volume and inconvenient operation, and the liquid dielectric constant measuring method can solve the problem.
Disclosure of Invention
In order to solve the problems, the invention adopts a method of combining a pulse forming cable with a high-voltage switch to generate voltage pulses and apply the voltage pulses to a liquid sample, and adopts a method of combining a specially designed resonator with a vector network analyzer to measure the dielectric constant of the liquid.
The technical scheme adopted by the invention is as follows:
the liquid dielectric constant measuring device comprises a high-voltage direct current power supply, a charging resistor, a charging wire, a pulse forming cable, a circulating water machine, a high-voltage switch, a power distributor, an attenuator, a transmission line I, an impedance matching circuit, an oscilloscope, a transmission line II, a sample tank, a resonator, a vector network analyzer and a computer, wherein the output voltage of the high-voltage direct current power supply is typically 1.2kV to 2.0kV, the high-voltage switch is provided with an input end and an output end, the power distributor is provided with the input end, the output end I and the output end II, the input ends of the high-voltage direct current power supply, the charging resistor, the charging wire, the pulse forming cable, the high-voltage switch and the power distributor are sequentially connected in a cable manner, the output end I of the power distributor is sequentially connected with the transmission line II and the sample tank in a cable manner, a core wire of the transmission line II is insulated from a shell of the sample tank, the shell of the sample tank is grounded, the output end II of the power distributor is sequentially connected with the attenuator, the transmission line I, the impedance matching circuit and the oscilloscope, and the resonator is positioned in the sample tank; the pulse forming cable comprises a shell, a stainless steel bar, an insulating cylinder, a water inlet and a water outlet, wherein the stainless steel bar and the insulating cylinder are both positioned in the shell, the stainless steel bar is spirally wound on the insulating cylinder, two ends of the stainless steel bar are respectively connected with a charging wire and an input end of a high-voltage switch, the shell is cylindrical barrel-shaped, deionized water is filled between the shell and the insulating cylinder, the conductivity of the deionized water is 0.1uS/cm, and the shell is provided with the water inlet and the water outlet and is respectively connected with a circulating water machine; the high-voltage switch comprises an ordinary opening film, a metal layer I, an insulating layer, a metal layer II and a Schottky diode, wherein the ordinary opening film, the metal layer I, the insulating layer and the metal layer II are sequentially deposited and prepared from bottom to top; the resonator comprises an outer conductor, an inner conductor, a sealing ring, a resonant cavity, a metal sheet and an SMA connector, wherein the SMA connector is coaxially connected with a vector network analyzer, the vector network analyzer is connected with a computer, the outer conductor and the inner conductor are both made of stainless steel, the outer conductor is a hollow cylinder, the inner conductor is a cylinder, the inner conductor is coaxially fixed in the outer conductor, the SMA connector is hermetically connected on the upper surface of the outer conductor, the metal sheet is welded below the outer conductor, the sealing ring is positioned in the middle position in the outer conductor, the inner conductor penetrates through the sealing ring, the sealing ring divides the inner part of the outer conductor into an upper part and a lower part, air tightness is arranged between the upper part and the lower part, the upper part is filled with air, the lower part forms the resonant cavity, a through hole is formed in the side wall of the lower part, and the through hole is completely immersed in a liquid sample; the diameter of the stainless steel bar is 2 mm, the diameter of the insulating cylinder is 40 mm, the length of the insulating cylinder is 200 mm, and the spiral pitch of the stainless steel bar wound on the insulating cylinder is 15 mm; the length of the shell is 300 mm, and the inner diameter is 100 mm; the thickness of the insulating layer is 12 micrometers; the length of the outer conductor is 20 cm, the inner diameter is 15 mm, the outer diameter is 20 mm, the length of the inner conductor is 20 cm, and the diameter is 5 mm; the diameter of the through hole on the side wall of the lower part of the outer conductor is 10 mm, and the distance between the upper edge of the through hole and the sealing ring is 3 mm.
The resonator works in the following manner:
during operation, through holes on the side wall of the lower part of the outer conductor of the resonator are all immersed in the liquid sample, a small amount of residual air is arranged below the sealing ring, a gas-liquid interface is formed on the contact surface of the residual air and the liquid sample, and the gas-liquid interface has larger impedance mismatch, so that the gas-liquid interface can be used as a reflector with high reflectivity, a metal sheet is used as another reflector, the liquid sample forms Fabry-Perot resonance between the sealing ring and the metal sheet, the movement of the resonance spectrum is monitored through a vector network analyzer, and the dielectric constant of the liquid sample can be obtained through measurement and corresponding calculation.
The microwave signal output by the vector network analyzer is input into the resonator through the SMA connector, forms a waveform between the outer conductor and the inner conductor, and is retransmitted along the negative y-axis direction, a majority of the microwave signal is reflected by the gas-liquid interface, defined as a first reflected signal, a minority of the microwave signal passes through the gas-liquid interface to reach the metal sheet, defined as a first transmitted signal, and most of the energy of the first transmitted signal is reflected by the metal sheet, so that multiple reflection and multiple interference are generated in the resonant cavity. The phase delay of the first reflected signal and the first transmitted signal at the gas-liquid interface is(formula one), wherein lambda and f are the wavelength and frequency of the microwave signal, respectively, d is the internal length of the resonant cavity in the y-axis direction, ε r Is the absolute dielectric constant of the liquid sample, c is the speed of light in vacuum, and when the phase delay delta=2mpi, a resonance pattern can be obtained in the reflection spectrum of the frequency domain, wherein m is an integer, called the resonance coefficient, and the resonance frequency in the reflection spectrum is(formula II), the interval between two adjacent minima in the reflection spectrum, defined as the free spectral range, is denoted +.>(formula III) when the permittivity of the liquid sample is changed to cause a shift in the reflectance spectrum, the shift in the resonance frequency is expressed as +.>(formula IV) in this way, the change in the dielectric constant of the liquid sample in the resonant cavity can be determined by monitoring the change in the resonant frequency under the condition that d is fixed, and is derived from the above formula: the liquid dielectric constant of the resonator has a measurement sensitivity of +.>Proportional to the resonance coefficient m, inversely proportional to d and the absolute dielectric constant ε of the liquid r Adopts->The change in the dielectric constant of the liquid is measured, not the absolute value, and if the change is small, the change can be regarded as linear. />(formula three) is used to measure the absolute value of the dielectric constant of the liquid, i.e. d is kept constant, by deriving the free spectral range from the recorded reflectance spectrum.
By passing throughAs can be seen from the formula II, the change of the resonant cavity length caused by thermal expansion causes the shift of the resonant frequency, thereby causing temperature disturbance with a temperature sensitivity of +.>Wherein alpha is 0 Is the temperature expansion coefficient of stainless steel, thereby obtaining the dielectric constant-temperature cross sensitivity of 2 epsilon r α 0 。
The working mode of the high-voltage switch is as follows:
when the voltage between the anode and cathode of the schottky diode exceeds its reverse breakdown voltage, the PN junction at the interface between the schottky diode and metal layer II produces an evaporation effect, which in turn causes a plasma to be generated and amplified, breaking down the insulating layer, causing a high voltage arc between metal layer I and metal layer II, which causes a redistribution of the metal between metal layer I and metal layer II, causing the high voltage switch to close.
The liquid dielectric constant measuring method comprises the following steps:
step 1, adding a liquid sample to be detected into a sample tank, and immersing all through holes on the side wall of the lower part of an outer conductor of a resonator into the liquid sample;
step 2, starting a high-voltage direct-current power supply, outputting voltage to a high-voltage switch through a charging resistor, a charging wire and a pulse forming cable, and adjusting the output voltage of the high-voltage direct-current power supply to enable the high-voltage switch to be closed;
step 3, monitoring the voltage waveform of the output end of the high-voltage switch through an oscilloscope;
step 4, generating a voltage difference between the core wire of the transmission line II and the sample tank shell in the closing time of the high-voltage switch, and applying the voltage difference to the liquid sample;
step 5, the vector network analyzer outputs microwave signals and enters the resonator through the SMA connector, and the vector network analyzer records the resonance frequency of the liquid sample;
and 6, inputting data acquired by the vector network analyzer into a computer, processing the data by the computer to obtain a reflection spectrum, and calculating to obtain the dielectric constant of the liquid sample.
The beneficial effects of the invention are as follows:
the method of the invention adopts a simple and compact structure to generate high-voltage pulse, is convenient to operate, and has the advantages of simple method for measuring the dielectric constant of the liquid, lower cost and higher precision of the test result.
Drawings
The following is further described in connection with the figures of the present invention:
FIG. 1 is a schematic illustration of the present invention;
FIG. 2 is an enlarged schematic diagram of a pulse-shaping cable;
FIG. 3 is an enlarged schematic diagram of a high voltage switch;
FIG. 4 is a top view of FIG. 3;
fig. 5 is an enlarged schematic view of a resonator.
In the figure, 1.high voltage DC power supply, 2.charging resistor, 3.charging wire, 4.pulse forming cable, 4-1 housing, 4-2 stainless steel strip, 4-3 insulating cylinder, 4-4 water inlet, 4-5 water outlet, 5 circulating water machine, 6.high voltage switch, 6-1 common membrane, 6-2 metal layer I,6-3 insulating layer, 6-4 metal layer II,6-5 Schottky diode, 7.power distributor, 8.attenuator, 9.transmission line I, 10.impedance matching circuit, 11.oscilloscope, 12.transmission line II, 13.sample cell, 14.resonator, 14-1 outer conductor, 14-2 inner conductor, 14-3 sealing ring, 14-4 resonant cavity, 14-5 metal sheet, 14-6 SMA joint, 15.vector network analyzer, 16.computer.
Detailed Description
As shown in fig. 1, xyz is a schematic diagram of the invention, xyz is a three-dimensional space coordinate system, as shown in fig. 2, an enlarged schematic diagram of a pulse forming cable, a measuring device comprises a high-voltage direct current power supply (1), a charging resistor (2), a charging wire (3), a pulse forming cable (4), a circulating water machine (5), a high-voltage switch (6), a power distributor (7), an attenuator (8), a transmission line I (9), an impedance matching circuit (10), an oscilloscope (11), a transmission line II (12), a sample tank (13), a resonator (14), a vector network analyzer (15) and a computer (16), the output voltage of the high-voltage direct current power supply (1) is typically in the range of 1.2kV to 2.0kV, the high-voltage switch (6) is provided with an input end and an output end, the power distributor (7) is provided with an input end, an output end I and an output end II, the high-voltage direct current power supply (1), the charging resistor (2), the charging wire (3), the pulse forming cable (4), the high-voltage switch (6) and the input end of the power distributor (7) are sequentially connected through cables, the output end I (12) of the power distributor (7) is connected with a sample tank (13), the output end of the power distributor (7) is connected with a shell (13) in turn, the sample tank (13) is connected with a core wire (13), the output end II of the power distributor (7) is sequentially connected with an attenuator (8), a transmission line I (9), an impedance matching circuit (10) and an oscilloscope (11) in a cable mode, and a resonator (14) is positioned in the sample groove (13); the pulse forming cable (4) comprises a shell (4-1), a stainless steel bar (4-2), an insulating cylinder (4-3), a water inlet (4-4) and a water outlet (4-5), wherein the stainless steel bar (4-2) and the insulating cylinder (4-3) are both positioned in the shell (4-1), the stainless steel bar (4-2) is spirally wound on the insulating cylinder (4-3), two ends of the stainless steel bar (4-2) are respectively connected with a charging wire (3) and an input end of a high-voltage switch (6), the shell (4-1) is cylindrical, deionized water is filled between the shell (4-1) and the insulating cylinder (4-3), the conductivity of the deionized water is 0.1uS/cm, and the shell (4-1) is provided with the water inlet (4-4) and the water outlet (4-5) and is respectively connected with a circulating water machine (5); the diameter of the stainless steel bar (4-2) is 2 mm, the diameter of the insulating cylinder (4-3) is 40 mm, the length of the insulating cylinder is 200 mm, and the spiral pitch of the stainless steel bar (4-2) wound on the insulating cylinder (4-3) is 15 mm; the length of the outer shell (4-1) is 300 mm, and the inner diameter is 100 mm.
As shown in fig. 3, which is an enlarged schematic diagram of the high-voltage switch, as shown in fig. 4, which is a top view of fig. 3, the high-voltage switch (6) comprises an open common film (6-1), a metal layer I (6-2), an insulating layer (6-3), a metal layer II (6-4) and a schottky diode (6-5), wherein the open common film (6-1), the metal layer I (6-2), the insulating layer (6-3) and the metal layer II (6-4) are sequentially deposited from bottom to top, the anode of the schottky diode (6-5) is connected with the metal layer II (6-4), the cathode of the schottky diode (6-5) is connected with the input end of the high-voltage switch (6), the output end of the high-voltage switch (6) is connected with the metal layer I (6-2), the open common film (6-1) is square with a side length of 1 cm, the insulating layer (6-3) is made of parylene material, and the thickness of the insulating layer (6-3) is 12 micrometers; the metal layer I (6-2) is made of copper with the thickness of 50 microns, the upper surface of the metal layer I is plated with tungsten with the thickness of 5 microns, the metal layer II (6-4) is made of copper with the thickness of 35 microns, the upper surface and the lower surface of the metal layer I are plated with tungsten with the thickness of 5 microns, and the tungsten can prevent the copper from being burnt by high-temperature electric arcs generated in the switching process of the high-voltage switch (6).
As shown in fig. 5, which is an enlarged schematic view of the resonator, the resonator (14) comprises an outer conductor (14-1), an inner conductor (14-2), a sealing ring (14-3), a resonant cavity (14-4), a metal sheet (14-5), an SMA joint (14-6), a vector network analyzer (15) connected with the SMA joint (14-6) and a vector network analyzer (15), the vector network analyzer (15) is connected with a computer (16), the outer conductor (14-1) and the inner conductor (14-2) are both made of stainless steel, the outer conductor (14-1) is a hollow cylinder, the inner conductor (14-2) is a cylinder, the inner conductor (14-2) is coaxially fixed in the outer conductor (14-1), the length of the outer conductor (14-1) is 20 cm, the inner diameter is 15 mm, the outer diameter is 20 mm, the length of the inner conductor (14-2) is 20 cm, the diameter is 5 mm, the upper surface of the outer conductor (14-1) is hermetically connected with the SMA joint (14-6), the lower surface is welded with the metal sheet (14-5), the sealing ring (14-3) is positioned in the middle position of the inner conductor (14-1), the inner conductor (14-1) is positioned in the middle position of the outer conductor (14-1), the inner conductor (14-1) is a part of the sealing ring (14-3), and the inner conductor (14-1) is a part penetrates through the sealing ring (14-3), the upper part and the lower part are airtight, the upper part is filled with air, the lower part forms a resonant cavity (14-4), the side wall of the lower part is provided with a through hole, the through hole is completely immersed in a liquid sample, the diameter of the through hole on the side wall of the lower part of the outer conductor (14-1) is 10 mm, and the distance between the upper edge of the through hole and the sealing ring (14-3) is 3 mm.
The liquid dielectric constant measuring device comprises a high-voltage direct current power supply (1), a charging resistor (2), a charging wire (3), a pulse forming cable (4), a circulating water machine (5), a high-voltage switch (6), a power distributor (7), an attenuator (8), a transmission wire I (9), an impedance matching circuit (10), an oscilloscope (11), a transmission wire II (12), a sample tank (13), a resonator (14), a vector network analyzer (15) and a computer (16), wherein the output voltage of the high-voltage direct current power supply (1) is typically in the range of 1.2kV to 2.0kV, the high-voltage switch (6) is provided with an input end and an output end, the power distributor (7) is provided with an input end, an output end I and an output end II, the high-voltage direct current power supply (1), the charging resistor (2), the attenuator (3), the pulse forming cable (4), the high-voltage switch (6) and the input end of the power distributor (7) are sequentially connected through cables, the output end I of the power distributor (7) is sequentially connected with the transmission wire II (12) and the sample tank (13), the output end I of the transmission wire II (12) is sequentially connected with the sample tank (13), the shell (13) is sequentially connected with the shell (13) of the power distributor (7) through the cable, and the output end I is sequentially connected with the output end of the power distributor (7) through the cable (13) through the cable An impedance matching circuit (10) and an oscilloscope (11), wherein a resonator (14) is positioned in a sample tank (13); the pulse forming cable (4) comprises a shell (4-1), a stainless steel bar (4-2), an insulating cylinder (4-3), a water inlet (4-4) and a water outlet (4-5), wherein the stainless steel bar (4-2) and the insulating cylinder (4-3) are both positioned in the shell (4-1), the stainless steel bar (4-2) is spirally wound on the insulating cylinder (4-3), two ends of the stainless steel bar (4-2) are respectively connected with a charging wire (3) and an input end of a high-voltage switch (6), the shell (4-1) is cylindrical, deionized water is filled between the shell (4-1) and the insulating cylinder (4-3), the conductivity of the deionized water is 0.1uS/cm, and the shell (4-1) is provided with the water inlet (4-4) and the water outlet (4-5) and is respectively connected with a circulating water machine (5); the high-voltage switch (6) comprises an ordinary film (6-1), a metal layer I (6-2), an insulating layer (6-3), a metal layer II (6-4) and a Schottky diode (6-5), wherein the ordinary film (6-1), the metal layer I (6-2), the insulating layer (6-3) and the metal layer II (6-4) are sequentially deposited from bottom to top, the anode of the Schottky diode (6-5) is connected with the metal layer II (6-4), the cathode of the Schottky diode (6-5) is connected with the input end of the high-voltage switch (6), the output end of the high-voltage switch (6) is connected with the metal layer I (6-2), the ordinary film (6-1) is square with the side length of 1 cm, the insulating layer (6-3) is made of a parylene material, the metal layer I (6-2) is made of copper with the thickness of 50 microns, the upper surface is plated with tungsten with the thickness of 5 microns, the metal layer II (6-4) is made of copper with the thickness of 35 microns, the upper surface and the lower surface is plated with tungsten with the thickness of 5 microns, and the tungsten can be prevented from being burnt out in the high-temperature process; the resonator (14) comprises an outer conductor (14-1), an inner conductor (14-2), a sealing ring (14-3), a resonant cavity (14-4), a metal sheet (14-5) and an SMA connector (14-6), wherein the SMA connector (14-6) is connected with a vector network analyzer (15), the vector network analyzer (15) is connected with a computer (16), the outer conductor (14-1) and the inner conductor (14-2) are both made of stainless steel, the outer conductor (14-1) is a hollow cylinder, the inner conductor (14-2) is a cylinder, the inner conductor (14-2) is coaxially fixed in the outer conductor (14-1), the SMA connector (14-6) is hermetically connected on the outer conductor (14-1), the metal sheet (14-5) is welded below, the sealing ring (14-3) is positioned at the middle position in the outer conductor (14-1), the inner conductor (14-2) penetrates through the sealing ring (14-3), the sealing ring (14-3) divides the inner part of the outer conductor (14-1) into an upper part and a lower part, the upper part and the lower part are airtight, the upper part is filled with air, the lower part forms a resonant cavity (14-4), a through hole is formed in the side wall of the lower part, and all the through holes are immersed in the liquid sample; the diameter of the stainless steel bar (4-2) is 2 mm, the diameter of the insulating cylinder (4-3) is 40 mm, the length of the insulating cylinder is 200 mm, the spiral distance between the stainless steel bar (4-2) and the insulating cylinder (4-3) is 15 mm, the length of the shell (4-1) is 300 mm, the inner diameter of the shell is 100 mm, the thickness of the insulating layer (6-3) is 12 microns, the length of the outer conductor (14-1) is 20 cm, the inner diameter of the outer conductor is 15 mm, the outer diameter of the outer conductor is 20 mm, the length of the inner conductor (14-2) is 20 cm, the diameter of the through hole on the side wall of the lower portion of the outer conductor (14-1) is 10 mm, and the distance between the upper edge of the through hole and the sealing ring (14-3) is 3 mm.
The resonator (14) operates in the following manner:
in operation, the through holes in the side walls of the lower part of the outer conductor (14-1) of the resonator (14) are all immersed in the liquid sample, a small amount of residual air is arranged below the sealing ring (14-3), the contact surface of the residual air and the liquid sample forms a gas-liquid interface, and the gas-liquid interface has larger impedance mismatch, so that the gas-liquid interface can be used as a reflector with high reflectivity, the metal sheet (14-5) is used as another reflector, the liquid sample forms Fabry-Perot resonance between the sealing ring (14-3) and the metal sheet (14-5), the movement of the resonance spectrum is monitored through the vector network analyzer (15), and the dielectric constant of the liquid sample can be obtained through measurement and corresponding calculation.
Microwave signals output by the vector network analyzer (15) are input into the resonator (14) through the SMA connector (14-6), waveforms are formed between the outer conductor (14-1) and the inner conductor (14-2), and are retransmitted along the negative y-axis direction, a majority of the microwave signals are reflected by the gas-liquid interface, defined as first reflected signals, a minority of the microwave signals reach the metal sheet (14-5) through the gas-liquid interface, defined as first transmitted signals, and a majority of the energy of the first transmitted signals is reflected by the metal sheet (14-5), so that multiple reflections and multiple interferences are generated in the resonant cavity (14-4). The phase delay of the first reflected signal and the first transmitted signal at the gas-liquid interface is(formula one), wherein lambda and f are the wavelength and frequency of the microwave signal, respectively, d is the internal length of the resonant cavity (14-4) in the y-axis direction, epsilon r Is the absolute dielectric constant of the liquid sample, c is the speed of light in vacuum, when the phase delay delta=2mpi, the resonance pattern can be obtained in the reflection spectrum of the frequency domain, wherein m is an integer, called resonance coefficient, the resonance frequency in the reflection spectrum is +.>(formula II), the interval between two adjacent minima in the reflection spectrum, defined as the free spectral range, is denoted +.>(formula III) when the permittivity of the liquid sample is changed to cause a shift in the reflectance spectrum, the shift in the resonance frequency is expressed as +.>(formula four) so that the change in the dielectric constant of the liquid sample in the resonant cavity (14-4) can be determined by monitoring the change in the resonant frequency with d fixed, from the above formula: the liquid dielectric constant of the resonator (14) has a measurement sensitivity of +>Proportional to the resonance coefficient m, inversely proportional to d and the absolute dielectric constant ε of the liquid r Adopts->The change in the dielectric constant of the liquid is measured, not the absolute value, and if the change is small, the change can be regarded as linear. />(formula three) is used to measure the absolute value of the dielectric constant of the liquid, i.e. d is kept constant, by deriving the free spectral range from the recorded reflectance spectrum.
By passing throughAs can be seen from the formula II, the change in the length of the resonant cavity (14-4) caused by thermal expansion causes a shift in the resonant frequency, resulting in temperature disturbance, and the temperature sensitivity is +.>Wherein alpha is 0 Is the temperature expansion coefficient of stainless steel, thereby obtaining the dielectric constant-temperature cross sensitivity of 2 epsilon r α 0 。
The working mode of the high-voltage switch (6) is as follows:
when the voltage between the anode and cathode of the schottky diode (6-5) exceeds its reverse breakdown voltage, the PN junction at the interface between the schottky diode (6-5) and the metal layer II (6-4) produces an evaporation effect, which in turn causes plasma to be generated and amplified, breaking through the insulating layer (6-3) such that a high voltage arc is generated between the metal layer I (6-2) and the metal layer II (6-4), which causes a redistribution of the metal between the metal layer I (6-2) and the metal layer II (6-4), thereby causing the high voltage switch (6) to close.
The liquid dielectric constant measuring method comprises the following steps:
step 1, adding a liquid sample to be detected into a sample tank (13), and immersing all through holes on the side wall of the lower part of an outer conductor (14-1) of a resonator (14) into the liquid sample;
step 2, starting a high-voltage direct-current power supply (1), outputting voltage to a high-voltage switch (6) through a charging resistor (2), a charging wire (3) and a pulse forming cable (4), and adjusting the output voltage of the high-voltage direct-current power supply (1) to enable the high-voltage switch (6) to be closed;
step 3, monitoring the voltage waveform of the output end of the high-voltage switch (6) through an oscilloscope (11);
step 4, generating a voltage difference between the core wire of the transmission line II (12) and the shell of the sample tank (13) in the closing time of the high-voltage switch (6), and applying the voltage difference to the liquid sample;
step 5, a vector network analyzer (15) outputs microwave signals and enters a resonator (14) through an SMA connector (14-6), and the vector network analyzer (15) records the resonance frequency of the liquid sample;
and 6, inputting data acquired by the vector network analyzer (15) into a computer (16), processing the data by the computer (16) to obtain a reflection spectrum, and calculating to obtain the dielectric constant of the liquid sample.
The invention adopts a method of combining a pulse forming cable with a high-voltage switch to generate voltage pulse so as to apply high voltage to a liquid sample, and adopts a resonator based on the Fabry-Perot resonance principle to measure the dielectric constant of the liquid.
Claims (1)
1. The liquid dielectric constant measuring method comprises a high-voltage direct-current power supply (1), a charging resistor (2), a charging wire (3), a pulse forming cable (4), a circulating water machine (5), a high-voltage switch (6), a power distributor (7), an attenuator (8), a transmission line I (9), an impedance matching circuit (10), an oscilloscope (11), a transmission line II (12), a sample tank (13), a resonator (14), a vector network analyzer (15) and a computer (16), wherein the typical output voltage of the high-voltage direct-current power supply (1) is in the range of 1.2kV to 2.0kV, the high-voltage switch (6) is provided with an input end and an output end, the power distributor (7) is provided with an input end, an output end I and an output end II, the high-voltage direct-current power supply (1), the charging resistor (2), the charging wire (3), the pulse forming cable (4), the high-voltage switch (6) and the input end cable of the power distributor (7) are connected, the output end I of the power distributor (7) is sequentially connected with the transmission line II (12) and the sample tank (13), the output end of the high-voltage direct-current power supply (6) is sequentially connected with the sample tank (13), the sample tank (13) is sequentially connected with the sample tank (13), and the sample tank (7) is sequentially connected with the sample tank and the sample tank, A transmission line I (9), an impedance matching circuit (10) and an oscilloscope (11), wherein a resonator (14) is positioned in a sample tank (13); the pulse forming cable (4) comprises a shell (4-1), a stainless steel bar (4-2), an insulating cylinder (4-3), a water inlet (4-4) and a water outlet (4-5), wherein the stainless steel bar (4-2) and the insulating cylinder (4-3) are both positioned in the shell (4-1), the stainless steel bar (4-2) is spirally wound on the insulating cylinder (4-3), two ends of the stainless steel bar (4-2) are respectively connected with a charging wire (3) and an input end of a high-voltage switch (6), the shell (4-1) is cylindrical, deionized water is filled between the shell (4-I) and the insulating cylinder (4-3), the conductivity of the deionized water is 0.1uS/cm, and the shell (4-1) is provided with the water inlet (4-4) and the water outlet (4-5) and is respectively connected with a circulating water machine (5); the high-voltage switch (6) comprises an ordinary film (6-1), a metal layer I (6-2), an insulating layer (6-3), a metal layer II (6-4) and a Schottky diode (6-5), wherein the ordinary film (6-1), the metal layer I (6-2), the insulating layer (6-3) and the metal layer II (6-4) are sequentially deposited from bottom to top, the anode of the Schottky diode (6-5) is connected with the metal layer II (6-4), the cathode of the Schottky diode (6-5) is connected with the input end of the high-voltage switch (6), the output end of the high-voltage switch (6) is connected with the metal layer I (6-2), the ordinary film (6-1) is square with the side length of 1 cm, the insulating layer (6-3) is made of a parylene material, the metal layer I (6-2) is made of copper with the thickness of 50 microns, the upper surface is plated with tungsten with the thickness of 5 microns, the metal layer II (6-4) is made of copper with the thickness of 35 microns, the upper surface and the lower surface is plated with tungsten with the thickness of 5 microns, and the tungsten can be prevented from being burnt out in the high-temperature process; the resonator (14) comprises an outer conductor (14-1), an inner conductor (14-2), a sealing ring (14-3), a resonant cavity (14-4), a metal sheet (14-5) and an SMA connector (14-6), wherein the SMA connector (14-6) is connected with a vector network analyzer (15), the vector network analyzer (15) is connected with a computer (16), the outer conductor (14-1) and the inner conductor (14-2) are both made of stainless steel, the outer conductor (14-1) is a hollow cylinder, the inner conductor (14-2) is a cylinder, the inner conductor (14-2) is coaxially fixed in the outer conductor (14-1), the SMA connector (14-6) is hermetically connected on the outer conductor (14-1), the metal sheet (14-5) is welded below, the sealing ring (14-3) is positioned at the middle position in the outer conductor (14-1), the inner conductor (14-2) penetrates through the sealing ring (14-3), the sealing ring (14-3) divides the inner part of the outer conductor (14-1) into an upper part and a lower part, the upper part and the lower part are airtight, the upper part is filled with air, the lower part forms a resonant cavity (14-4), a through hole is formed in the side wall of the lower part, and all the through holes are immersed in the liquid sample; the diameter of the stainless steel bar (4-2) is 2 mm, the diameter of the insulating cylinder (4-3) is 40 mm, the length of the insulating cylinder is 200 mm, and the spiral pitch of the stainless steel bar (4-2) wound on the insulating cylinder (4-3) is 15 mm; the length of the shell (4-1) is 300 mm, and the inner diameter is 100 mm; the thickness of the insulating layer (6-3) is 12 micrometers; the length of the outer conductor (14-1) is 20 cm, the inner diameter is 15 mm, the outer diameter is 20 mm, the length of the inner conductor (14-2) is 20 cm, and the diameter is 5 mm; the diameter of the through hole on the side wall of the lower part of the outer conductor (14-1) is 10 mm, the distance between the upper edge of the through hole and the sealing ring (14-3) is 3 mm,
the method is characterized in that: the liquid dielectric constant measuring method comprises the following steps:
step 1, adding a liquid sample to be detected into a sample tank (13), and immersing all through holes on the side wall of the lower part of an outer conductor (14-1) of a resonator (14) into the liquid sample;
step 2, starting a high-voltage direct-current power supply (1), outputting voltage to a high-voltage switch (6) through a charging resistor (2), a charging wire (3) and a pulse forming cable (4), and adjusting the output voltage of the high-voltage direct-current power supply (1) to enable the high-voltage switch (6) to be closed;
step 3, monitoring the voltage waveform of the output end of the high-voltage switch (6) through an oscilloscope (11);
step 4, generating a voltage difference between the core wire of the transmission line II (12) and the shell of the sample tank (13) in the closing time of the high-voltage switch (6), and applying the voltage difference to the liquid sample;
step 5, a vector network analyzer (15) outputs microwave signals and enters a resonator (14) through an SMA connector (14-6), and the vector network analyzer (15) records the resonance frequency of the liquid sample;
and 6, inputting data acquired by the vector network analyzer (15) into a computer (16), processing the data by the computer (16) to obtain a reflection spectrum, and calculating to obtain the dielectric constant of the liquid sample.
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