Sheet material oriented thermal conductivity measurement system and method based on 3omega harmonic detection

Abstract

The invention provides a sheet material oriented thermal conductivity measurement system and method based on 3 omega harmonic detection, and belongs to the technical field of thermal conductivity measurement, the system comprises a PCB, an electrode, a lock-in amplifier subsystem and a vacuum constant temperature cabin subsystem, the PCB is arranged in the vacuum constant temperature cabin subsystem, the PCB is provided with a hollow area, the two ends of the electrode are in lap joint with the PCB, and the two ends of the electrode are in lap joint with the vacuum constant temperature cabin subsystem. The middle area of the electrode is located above the hollowed-out area, a sheet material to be detected is arranged on the electrode, and the electrode is connected with the phase-locked amplifier subsystem located outside the vacuum constant-temperature cabin subsystem. The method comprises the following steps: placing a to-be-measured sheet material on an electrode, controlling the vacuum constant-temperature cabin subsystem to reach a preset temperature and a preset vacuum degree, obtaining a frequency tripling voltage through the lock-in amplifier subsystem, and obtaining the thermal conductivity of the to-be-measured sheet material through a calculation formula based on the frequency tripling voltage. According to the invention, the measurement error is reduced, the accuracy of the measurement result is improved, and the types of measurement materials are widened.

Description

Technical Field

[0001] The present application relates to the technical field of thermal conductivity measurement, and in particular to a system and method for measuring the thermal conductivity of a thin sheet material based on 3ω harmonic detection. Background Art

[0002] As current equipment and instruments are developing towards miniaturization and precision, the heat concentration and thermal effect problems they bring are becoming more and more serious, such as heat dissipation problems and interface thermal resistance problems between materials, which have become the main factors for improving the key performance of equipment. With the rapid development of modern synthesis and manufacturing processes, many new materials have emerged in an endless stream, especially one-dimensional tubular and two-dimensional film materials. The research on their thermal conductivity and thermal diffusion performance is urgently needed. Therefore, the exploration and testing of the thermal conductivity of new micro / nano film materials and fiber materials by thermal property measurement technology is crucial to the development of optoelectronic devices, energy utilization, and aerospace technology. At present, the measurement technology for macro-scale materials has become increasingly complete. For example, commercial instruments such as NETZSCH, Hot Disk, and C-Thermal can be used for the measurement of bulk, powder and liquid, and even for films of moderate thickness and fiber materials with larger diameters. However, these commercial instruments are powerless to characterize the thermal properties of micro / nano materials, especially for the measurement of the axial thermal conductivity of micro / nano film materials and single fibers. The development of technology suitable for characterizing the thermal properties of new micro-nanostructured material devices has become a key means of studying micro-nanoscale heat transfer at home and abroad.

[0003] The methods currently developed for testing the heat transfer and storage characteristics of micro-nanoscale material structures include Raman spectroscopy, H method, T-type method, thermal conductivity method, 3ω method, femtosecond laser method and DC heating method. The 3ω method stands out among these measurement methods because of its relatively rich types of detection sensors, many test parameters, and a wide range of applicable materials and devices.

[0004] However, when measuring the directional thermal conductivity of thin films with a length of more than a millimeter and a thickness of microns or less, the 3ω method requires the roughness of the film surface to be less than 100 nanometers, so that a metal detector can be deposited on the surface of the film to measure the directional thermal conductivity. If the roughness of the material surface is more than 100 nanometers, the deposited 100-nanometer thick metal electrode cannot be reliably laid flat on the surface of the film, which makes it impossible to measure using the 3ω method. Other optical methods also require the film surface to have a good roughness so that the reflected optical information can be captured for measurement. Moreover, the current synthesis of materials, especially carbon-based materials, generally has a high surface roughness after synthesis, and the surface of some materials cannot be well polished, such as thermoelectric materials.

[0005] In addition, existing thermal conductivity measuring instruments mainly include heat flux thermal conductivity analyzers used for bulk thermal conductivity measurement, which have high requirements on sample dimensions and large measurement errors. Summary of the invention

[0006] In view of this, the embodiments of the present application provide a system and method for measuring the oriented thermal conductivity of thin sheet materials based on 3ω harmonic detection, which at least partially solves the problem in the prior art that the oriented thermal conductivity measurement method of thin sheet materials has high requirements on the roughness of the material and large measurement errors.

[0007] In a first aspect, an embodiment of the present application provides a thin sheet material oriented thermal conductivity measurement system based on 3ω harmonic detection, the system comprising a PCB board, an electrode, a phase-locked amplifier subsystem and a vacuum constant temperature chamber subsystem, the PCB board is arranged in the vacuum constant temperature chamber subsystem, a hollow area is provided on the PCB board, a plurality of electrodes are provided, both ends of the electrode are overlapped on the PCB board, a middle area of ​​the electrode is located above the hollow area, the thin sheet material to be measured is arranged on the middle area of ​​the electrode located in the hollow area, and one end of the electrode is connected to the phase-locked amplifier subsystem located outside the vacuum constant temperature chamber subsystem through a wire.

[0008] According to a specific implementation method of an embodiment of the present application, the phase-locked amplifier subsystem includes a first operational amplifier, a second operational amplifier, a preamplifier, a phase-locked amplifier, an adjustable resistor and a data acquisition component. The output end of the first operational amplifier and the output end of the second operational amplifier are respectively connected to the input end of the preamplifier, the output end of the preamplifier is connected to the input end of the phase-locked amplifier, the output end of the phase-locked amplifier is connected to the data acquisition component, one end of the adjustable resistor is connected to the data acquisition component, the other end of the adjustable resistor and the input end of the second operational amplifier are respectively connected to electrodes, and the input end of the first operational amplifier is connected in parallel to both ends of the adjustable resistor.

[0009] According to a specific implementation method of an embodiment of the present application, the multiple electrodes include a first electrode, a second electrode, a third electrode and a fourth electrode arranged in parallel, the thin sheet material to be tested is in contact with each electrode, one end of the first electrode is connected to the other end of the adjustable resistor, one end of the second electrode and one end of the third electrode are respectively connected to the input end of the second operational amplifier, and one end of the fourth electrode is grounded.

[0010] According to a specific implementation of the embodiment of the present application, the distance between two adjacent electrodes is set to 3-5 mm.

[0011] According to a specific implementation of the embodiment of the present application, the width of each electrode is set to 2-3 mm.

[0012] According to a specific implementation of the embodiment of the present application, the length of each electrode is set to 5-10 mm.

[0013] According to a specific implementation method of an embodiment of the present application, the vacuum constant temperature chamber subsystem includes a mechanical pump, a molecular pump, a constant temperature control component and a chamber body, the PCB board is arranged in the chamber body, the mechanical pump and the molecular pump are used to control the vacuum environment, and the constant temperature control component is used to control the temperature inside the chamber body.

[0014] According to a specific implementation of the embodiment of the present application, the temperature of the vacuum constant temperature chamber subsystem is set to a range from room temperature to 250°C.

[0015] In a second aspect, an embodiment of the present application further provides a measurement method for a thin sheet material oriented thermal conductivity measurement system based on 3ω harmonic detection according to any embodiment of the first aspect, the method comprising:

[0016] Place the thin sheet material to be tested on the electrode, with the length direction of the thin sheet material to be tested being perpendicular to the length direction of the electrode;

[0017] Control the vacuum constant temperature chamber subsystem to reach the preset temperature and preset vacuum degree;

[0018] The test data is collected through the lock-in amplifier subsystem to extract the triple frequency voltage;

[0019] Based on the extracted triple frequency voltage, the thermal conductivity of the thin film material to be tested is obtained through a calculation formula.

[0020] According to a specific implementation of the embodiment of the present application, the thermal conductivity of the thin sheet material to be tested is obtained by a calculation formula based on the extracted triple frequency voltage, including:

[0021] Construct a coordinate system, where the length direction of the thin sheet material to be measured is the x-axis, and the width direction of the thin sheet material to be measured is the y-axis;

[0022] Construct a two-dimensional unsteady heat conduction differential equation with an internal heat source:

[0023]

[0024] Where ρ is the density of the thin sheet material to be tested, C p is the specific heat capacity of the thin sheet material to be tested, k is the thermal conductivity of the thin sheet material to be tested, I0sintωt is the phase-locked alternating current supplied to the material, L is the distance between the two electrodes in the middle, a is the half-width of the thin sheet material to be tested, S is the cross-sectional area of ​​the thin sheet material to be tested along the x-axis direction, R0 is the original resistance of the thin sheet material to be tested, α CR is the temperature coefficient of resistance of the thin sheet material to be tested, T0 is the initial temperature;

[0025] Let Δ(x, y, t) = T(x, y, t) - T0, solve the two-dimensional unsteady heat conduction differential equation, and obtain the temperature relationship Δ(x, y, t):

[0026]

[0027] Where, cotθ=2ωγ / (L 2 m 2 +a 2 n 2 ),

[0028] According to the temperature relationship, solve the resistance relationship δR:

[0029]

[0030] According to the resistance relationship, solve the voltage relationship V:

[0031] V=I0sinωt(R0+δR),

[0032]

[0033] According to the voltage relationship, take n = 1, m = 1, and get the triple frequency voltage V 3ω :

[0034]

[0035] The extracted tripled frequency voltage is combined with the tripled frequency voltage V 3ω The thermal conductivity k of the thin sheet material to be tested is obtained using the formula.

[0036] Beneficial effects:

[0037] The thin sheet material facing thermal conductivity measurement system and method based on 3ω harmonic detection in the embodiment of the present application, after the sample to be tested is transferred to the electrode, the sample to be tested can be fixedly connected to the electrode by conductive silver glue or solder, thereby reducing the influence of contact resistance and contact thermal resistance; placing the sample and the electrode in a medium-high temperature vacuum chamber reduces the influence of air convection heat loss, reduces measurement errors, and improves the accuracy of the measurement results. At the same time, through the derivation of the equation, the measurement method of the thin sheet facing thermal conductivity applicable to the 3ω harmonic detection method is calculated, which can solve the problem of this method in measuring such materials, and can be applied to thin film materials with higher roughness, broadening the types of materials measured by the 3ω method, and enriching the means of characterizing materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0039] Figure 1 It is a schematic structural diagram of a thin-sheet material oriented thermal conductivity measurement system based on 3ω harmonic detection according to an embodiment of the present invention;

[0040] Figure 2 is a schematic diagram of the arrangement of the sheet material to be tested according to an embodiment of the present invention;

[0041] Figure 3 FIG. 4 is a measurement principle diagram of a thin-sheet material oriented thermal conductivity measurement system based on 3ω harmonic detection according to an embodiment of the present invention.

[0042] In the figure: 1. PCB board; 2. Thin sheet material to be tested; 3. Electrode; 31. First electrode; 32. Second electrode; 33. Third electrode; 34. Fourth electrode; 4. Vacuum constant temperature chamber subsystem; 5. First operational amplifier; 6. Second operational amplifier; 7. Preamplifier; 8. Adjustable resistor; 9. Lock-in amplifier; 10. Data acquisition component; 11. Hollow area. DETAILED DESCRIPTION

[0043] The embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0044] The following describes the implementation methods of the present application through specific examples, and those skilled in the art can easily understand other advantages and effects of the present application from the contents disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The present application can also be implemented or applied through other different specific implementation methods, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present application. It should be noted that, in the absence of conflict, the following embodiments and the features in the embodiments can be combined with each other. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without making creative work belong to the scope of protection of the present application.

[0045] It should be noted that various aspects of the embodiments within the scope of the appended claims are described below. It should be apparent that the aspects described herein can be embodied in a wide variety of forms, and any specific structure and / or function described herein is merely illustrative. Based on the present application, it should be understood by those skilled in the art that an aspect described herein can be implemented independently of any other aspect, and two or more of these aspects can be combined in various ways. For example, any number of aspects described herein can be used to implement the device and / or practice the method. In addition, other structures and / or functionalities other than one or more of the aspects described herein can be used to implement this device and / or practice this method.

[0046] It should also be noted that the illustrations provided in the following embodiments are only schematic illustrations of the basic concept of the present application. The illustrations only show the components related to the present application rather than being drawn according to the number, shape and size of the components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed at will, and the component layout may also be more complicated.

[0047] Additionally, in the following description, specific details are provided to facilitate a thorough understanding of the examples. However, it will be understood by those skilled in the art that the aspects described may be practiced without these specific details.

[0048] The 3ω harmonic detection technology was first proposed by Cahill in 1990, and the thermal conductivity of semi-infinite dielectric materials was measured. The basic principle of the 3ω method is: an AC signal with an angular frequency of 1ω is applied to both ends of the micro heater. Due to the Joule effect, the detector will produce a temperature fluctuation with an angular frequency of 2ω. Since there is a linear relationship between the resistance and temperature of the detector, the resistance of the detector will also produce a 2ω fluctuation. The AC current with a frequency of 1ω and the resistance fluctuation with a frequency of 2ω obtain a voltage signal with an angular frequency of 3ω at both ends of the electrode, which contains the thermophysical parameters of the sample. The thermophysical properties of the sample can be obtained by extracting and analyzing the voltage signal. The advantage of the 3ω method is that it has a wide spatial scale for measuring materials and is applicable to many types of materials, thus attracting the attention of scholars from all over the world. This method is applicable to a wide range of sample types, including micro-nano film materials, filamentary materials, anisotropic materials, gases and nanofluids. There are many measurement parameters, including thermal conductivity, thermal diffusion coefficient and specific heat. Moreover, the measurement scale is wide, applicable from nanoscale to macroscale.

[0049] The applicant found that in 2012, Zheng Xinghua et al. used 3ω harmonic detection technology to measure the equivalent thermal conductivity of urea-formaldehyde resin-paraffin phase change microcapsules. This method provides an experimental basis for the study of the heat transfer mechanism of phase change microcapsules. In 2013, Gauthier et al. used the 3ω method to measure the thermal conductivity of nitrogen, helium and carbon dioxide at room temperature. In 2014, Qiu Lin et al. proposed the use of 3ω technology to measure the thermal conductivity and thermal diffusivity of macroscopic fibers curled from single-walled carbon nanotube films, and discussed the influence of the number of curling layers on the results and the idea of ​​estimating the surface thermal conductivity and thermal diffusivity of the film. In 2015, Qiu Lin et al. proposed a measurement structure that can be used to experimentally characterize the thermal conductivity of bismuth telluride oriented nano-columnar films using the 3ω method, and obtained the thermal conductivity and thermal diffusivity values ​​of nano-columnar films. In 2015, Yue Peng et al. designed a 3ω independent linear heat source detector based on an artificial sapphire substrate, which can be used for non-destructive measurement of the thermal conductivity of solids and liquids. In 2016, Cao Yuntao et al. applied the basic principle of the 3ω asymmetric model to develop a new type of micro-detector, and analyzed the influence of the detector metal strip width, harmonic signal frequency range, and different contact media on the measurement of the thermal conductivity of solid materials. In 2017, Bogner et al. used the 3ω method to measure the thermal conductivity of aluminum nitride films on and within the surface. In 2018, Zheng Xinghua et al. developed a flexible independent detector with film hot pressing packaging and an independent detector based on a sapphire substrate, which can be used to measure the thermal conductivity of bulk, powder and fluid.

[0050] At present, the traditional 3ω method is used to measure thin film materials with macroscopic size and thickness of microns and below. It is necessary to use a mask to deposit metal electrodes on the surface of the material. At this time, the roughness of the film surface needs to be less than 100 nanometers, so that a metal detector can be deposited on the surface of the film to measure the oriented thermal conductivity. If the roughness of the material surface is above 100 nanometers, the deposited 100-nanometer thick metal electrode cannot be reliably laid flat on the surface of the film, which makes it impossible to measure using the 3ω method. To this end, the present application proposes a method based on the 3ω method for measuring the oriented thermal conductivity of rough or non-rough surface sheet materials, which fills the gap in the 3ω method in the measurement of these materials and enriches the characterization methods of materials.

[0051] In the first aspect, the present application provides a thin-film material oriented thermal conductivity measurement system based on 3ω harmonic detection, which is used to solve the current situation that the 3ω method is difficult to measure the thermal conductivity of thin-film materials with macroscopic size, thickness of micrometers or less, and high surface roughness. Figure 1 and Figure 2 Describe in detail.

[0052] In one embodiment, a sheet material oriented thermal conductivity measurement system based on 3ω harmonic detection includes a PCB board, electrodes, a phase-locked amplifier subsystem and a vacuum constant temperature chamber subsystem, the PCB board is arranged in the vacuum constant temperature chamber subsystem, a hollow area is provided on the PCB board, a plurality of electrodes are provided, two ends of the electrode are overlapped on the PCB board, a middle area of ​​the electrode is located above the hollow area, the sheet material to be measured is arranged on the middle area of ​​the electrode located in the hollow area, and one end of the electrode is connected to the phase-locked amplifier subsystem located outside the vacuum constant temperature chamber subsystem through a wire.

[0053] The system of this embodiment is suitable for measuring the oriented thermal conductivity of rough or non-rough surface sheet materials. By solving the two-dimensional non-steady-state thermal conductivity differential equation containing an internal heat source, the relationship between the triple frequency voltage extracted by phase locking and the thermal conductivity can be finally obtained to solve the thermal conductivity of the material to be measured. The preparation of the measurement system can be realized through the process of printed circuit boards.

[0054] In specific implementation, after the sample to be tested is transferred to the electrode, in order to avoid poor contact between the thin sheet to be tested and the electrode, a colloid with good conductivity, such as conductive silver glue, solder, etc., can be added between the two to reduce the influence of contact resistance and contact thermal resistance, thereby reducing the measurement error. In order to reduce the influence of convection heat dissipation on the results, the PCB board is placed in a vacuum environment for measurement to reduce the measurement error. In addition, the contact between the thin sheet material to be tested and the substrate can be reduced by setting the hollow area, mainly because the temperature rise of the sample heated by the electrode is not high, generally less than a few degrees, so it is necessary to reduce the contact with the substrate (PCB board).

[0055] For the selection of electrode materials, conductive copper sheets, or nickel sheets, silver sheets, stainless steel sheets, etc. with equivalent conductive properties can be used. The electrodes can be deposited on the PCB board by deposition.

[0056] In one embodiment, the phase-locked amplifier subsystem includes a first operational amplifier, a second operational amplifier, a preamplifier, a phase-locked amplifier, an adjustable resistor and a data acquisition component. The output end of the first operational amplifier and the output end of the second operational amplifier are respectively connected to the input end of the preamplifier, the output end of the preamplifier is connected to the input end of the phase-locked amplifier, the output end of the phase-locked amplifier is connected to the data acquisition component, one end of the adjustable resistor is connected to the data acquisition component, the other end of the adjustable resistor and the input end of the second operational amplifier are respectively connected to the electrodes, and the input end of the first operational amplifier is connected in parallel to both ends of the adjustable resistor.

[0057] In this embodiment, a phase-locked amplifier subsystem is used to test thermal conductivity based on the 3ω method harmonic. The phase-locked amplifier can provide a single-frequency voltage to obtain a triple-frequency voltage containing a sample thermal signal. The thermal conductivity can be calculated using the relationship between the triple-frequency voltage and the thermal conductivity.

[0058] Specifically, the multiple electrodes include a first electrode, a second electrode, a third electrode and a fourth electrode arranged in parallel, the thin sheet material to be tested is in contact with each electrode, one end of the first electrode is connected to the other end of the adjustable resistor, one end of the second electrode and one end of the third electrode are respectively connected to the input end of the second operational amplifier, and one end of the fourth electrode is grounded.

[0059] In one embodiment, regarding the size setting of the electrodes, since there will be measurement loss if the size of the thin sheet material to be measured is too large, the length of the thin sheet material to be measured is generally made in the order of millimeters, so the size of the electrodes is also in the order of millimeters. Specifically, the spacing between two adjacent electrodes is set to 3-5 mm, the width of each electrode is set to 2-3 mm, and the length of each electrode is set to 5-10 mm.

[0060] In one embodiment, the vacuum constant temperature chamber subsystem includes a mechanical pump, a molecular pump, a constant temperature control component and a chamber body, the PCB board is arranged in the chamber body, the mechanical pump and the molecular pump are used to control the vacuum environment, and the constant temperature control component is used to control the temperature in the chamber body.

[0061] In one embodiment, the temperature of the vacuum constant temperature chamber subsystem is set to be between room temperature and 250° C. By placing the sample and the electrode in a medium-high temperature vacuum chamber, the influence of air convection heat loss is reduced.

[0062] In a second aspect, an embodiment of the present application further provides a measurement method for a thin sheet material oriented thermal conductivity measurement system based on 3ω harmonic detection according to any embodiment of the first aspect, the method comprising:

[0063] Place the thin sheet material to be tested on the electrode, with the length direction of the thin sheet material to be tested being perpendicular to the length direction of the electrode;

[0064] Control the vacuum constant temperature chamber subsystem to reach the preset temperature and preset vacuum degree;

[0065] The test data is collected through the lock-in amplifier subsystem to extract the triple frequency voltage;

[0066] Based on the extracted triple frequency voltage, the thermal conductivity of the thin film material to be tested is obtained through a calculation formula.

[0067] Furthermore, the thermal conductivity of the thin sheet material to be tested is obtained by a calculation formula based on the extracted triple frequency voltage, including:

[0068] Construct a coordinate system, refer to Figure 3 , the length direction of the thin sheet material to be tested is the x-axis, and the width direction of the thin sheet material to be tested is the y-axis;

[0069] Construct a two-dimensional unsteady heat conduction differential equation with an internal heat source:

[0070]

[0071] Where ρ is the density of the thin sheet material to be tested, C p is the specific heat capacity of the thin sheet material to be tested, k is the thermal conductivity of the thin sheet material to be tested, I0sintωt is the phase-locked alternating current supplied to the material, L is the distance between the two electrodes in the middle, a is the half-width of the thin sheet material to be tested, S is the cross-sectional area of ​​the thin sheet material to be tested along the x-axis direction, R0 is the original resistance of the thin sheet material to be tested, α CR is the temperature coefficient of resistance of the thin sheet material to be tested, T0 is the initial temperature;

[0072] Let Δ(x, y, t) = T(x, y, t) - T0, solve the two-dimensional unsteady heat conduction differential equation, and obtain the temperature relationship Δ(x, y, t):

[0073]

[0074] Where, cotθ=2ωy / (L 2 m 2 +a 2 n 2 ),

[0075] According to the temperature relationship, solve the resistance relationship δR:

[0076]

[0077] According to the resistance relationship, solve the voltage relationship V:

[0078] V=I0sinωt(R0+δR),

[0079]

[0080] According to the voltage relationship, take n = 1, m = 1, and get the triple frequency voltage V 3ω :

[0081]

[0082] The extracted tripled frequency voltage is combined with the tripled frequency voltage V 3ω The thermal conductivity k of the thin sheet material to be tested is obtained using the formula.

[0083] In this embodiment, the triple frequency voltage is finally extracted using a lock-in amplifier to obtain:

[0084]

[0085] It can be seen from formula (6) that the triple frequency voltage signal contains the thermal conductivity k of the thin sheet material to be tested. Therefore, the thermal conductivity of the material can be calculated by the triple frequency voltage obtained by the test.

[0086] In the embodiment provided by the present invention, after the sample to be tested is transferred to the electrode, the sample to be tested can be fixedly connected to the electrode by means of conductive silver glue or solder, thereby reducing the influence of contact resistance and contact thermal resistance; placing the sample and the electrode in a medium-high temperature vacuum chamber reduces the influence of air convection heat loss, reduces measurement errors, and improves the accuracy of the measurement results. At the same time, through the derivation of equations, the measurement method of the thin film facing thermal conductivity applicable to the 3ω harmonic detection method is calculated, which can solve the difficulty of this method in measuring such materials, and can be applied to thin film materials with higher roughness, broadening the types of materials measured by the 3ω method and enriching the means of material characterization.

[0087] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. A thin sheet material oriented thermal conductivity measurement system based on 3ω harmonic detection, characterized in that: The system includes a PCB board, electrodes, a phase-locked amplifier subsystem and a vacuum constant temperature chamber subsystem. The PCB board is arranged in the vacuum constant temperature chamber subsystem. A hollow area is arranged on the PCB board. A plurality of electrodes are provided. Two ends of the electrodes are overlapped on the PCB board. The middle area of ​​the electrodes is located above the hollow area. The sheet material to be tested is arranged on the middle area of ​​the electrodes located in the hollow area. One end of the electrode is connected to the phase-locked amplifier subsystem located outside the vacuum constant temperature chamber subsystem through a wire.

2. The thin sheet material oriented thermal conductivity measurement system based on 3ω harmonic detection according to claim 1 is characterized in that: The phase-locked amplifier subsystem includes a first operational amplifier, a second operational amplifier, a preamplifier, a phase-locked amplifier, an adjustable resistor and a data acquisition component. The output end of the first operational amplifier and the output end of the second operational amplifier are respectively connected to the input end of the preamplifier, the output end of the preamplifier is connected to the input end of the phase-locked amplifier, the output end of the phase-locked amplifier is connected to the data acquisition component, one end of the adjustable resistor is connected to the data acquisition component, the other end of the adjustable resistor and the input end of the second operational amplifier are respectively connected to the electrodes, and the input end of the first operational amplifier is connected in parallel to both ends of the adjustable resistor.

3. The thin sheet material oriented thermal conductivity measurement system based on 3ω harmonic detection according to claim 2 is characterized in that: The multiple electrodes include a first electrode, a second electrode, a third electrode and a fourth electrode arranged in parallel. The thin sheet material to be tested contacts each electrode. One end of the first electrode is connected to the other end of the adjustable resistor, one end of the second electrode and one end of the third electrode are respectively connected to the input end of the second operational amplifier, and one end of the fourth electrode is grounded.

4. The thin sheet material oriented thermal conductivity measurement system based on 3ω harmonic detection according to claim 1, characterized in that: The distance between two adjacent electrodes is set to 3-5 mm.

5. The thin sheet material oriented thermal conductivity measurement system based on 3ω harmonic detection according to claim 1, characterized in that: The width of each electrode is set to 2-3 mm.

6. The thin sheet material oriented thermal conductivity measurement system based on 3ω harmonic detection according to claim 1, characterized in that: The length of each electrode is set to 5-10 mm.

7. The thin-sheet material oriented thermal conductivity measurement system based on 3ω harmonic detection according to claim 1, characterized in that: The vacuum constant temperature chamber subsystem includes a mechanical pump, a molecular pump, a constant temperature control component and a chamber body. The PCB board is arranged in the chamber body. The mechanical pump and the molecular pump are used to control the vacuum environment, and the constant temperature control component is used to control the temperature in the chamber body.

8. The thin sheet material oriented thermal conductivity measurement system based on 3ω harmonic detection according to claim 1, characterized in that: The temperature of the vacuum constant temperature chamber subsystem is set to range from room temperature to 250°C.

9. A measurement method based on the thin-sheet material oriented thermal conductivity measurement system based on 3ω harmonic detection as described in any one of claims 1 to 8, characterized in that: The method comprises: Place the thin sheet material to be tested on the electrode, with the length direction of the thin sheet material to be tested being perpendicular to the length direction of the electrode; Control the vacuum constant temperature chamber subsystem to reach the preset temperature and preset vacuum degree; The test data is collected through the lock-in amplifier subsystem to extract the triple frequency voltage; Based on the extracted triple frequency voltage, the thermal conductivity of the thin film material to be tested is obtained through a calculation formula.

10. The measuring method according to claim 9, characterized in that: The method of obtaining the thermal conductivity of the thin sheet material to be measured by a calculation formula based on the extracted triple frequency voltage includes: Construct a coordinate system, where the length direction of the thin sheet material to be measured is the x-axis, and the width direction of the thin sheet material to be measured is the y-axis; Construct a two-dimensional unsteady heat conduction differential equation with an internal heat source: Where ρ is the density of the thin sheet material to be tested, C p is the specific heat capacity of the thin sheet material to be tested, k is the thermal conductivity of the thin sheet material to be tested, I0sintωt is the phase-locked alternating current supplied to the material, L is the distance between the two electrodes in the middle, a is the half-width of the thin sheet material to be tested, S is the cross-sectional area of ​​the thin sheet material to be tested along the x-axis direction, R0 is the original resistance of the thin sheet material to be tested, α CR is the temperature coefficient of resistance of the thin sheet material to be tested, T0 is the initial temperature; Let Δ(x, y, t) = T(x, y, t) - T0, solve the two-dimensional unsteady heat conduction differential equation, and obtain the temperature relationship Δ(x, y, t): Where, cotθ=2ωy / (L 2 m 2 +a 2 n 2 ), According to the temperature relationship, solve the resistance relationship δR: According to the resistance relationship, solve the voltage relationship V: V=I0sinωt(R0+δR), According to the voltage relationship, take n = 1, m = 1, and get the triple frequency voltage V 3ω : The extracted tripled frequency voltage is combined with the tripled frequency voltage V 3ω The thermal conductivity k of the thin sheet material to be tested is obtained using the formula.

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