System for measuring critical current density of high-temperature superconducting film

Abstract

The invention discloses a measuring system for critical current density of a high-temperature superconducting film. The measuring system comprises a signal generator 1, a power amplifier 2, a protective resistor 3, a sampling resistor 4, a digital multimeter 5, an excitation coil 6, a detection coil 7, a lock-in amplifier 8 and a controller 9, the lock-in amplifier 8 comprises a signal generator 1, a reference signal REF interface, an interface A and an interface B; the signal generator 1 is connected with the input end of the power amplifier 2, and the output end of the power amplifier 2 is connected with one end of the protective resistor 3; the other end of the sampling resistor 4 and the other end of the digital multimeter 5 are connected with the detection coil 7. A sample is arranged between the excitation coil 6 and the detection coil 7; the controller 9 is connected with the lock-in amplifier 8, and the lock-in amplifier 8 collects voltage signals of the detection coil 7 and carries out frequency locking filtering. The measured signal-to-noise ratio is high, and the accuracy of a measurement result is improved.

Description

Technical Field

[0001] This invention relates to the field of measuring the critical current density of high-temperature superconducting thin films, and more particularly to a measurement system for the critical current density of high-temperature superconducting thin films. Background Technology

[0002] For measuring the critical current density of high-temperature superconducting thin films, the existing technology of direct measurement using the four-wire electric transport method is complex to process, time-consuming, and not conducive to sample reuse. The traditional indirect measurement method has high signal noise, low signal-to-noise ratio, and large measurement error.

[0003] In the field of measuring the critical current density of high-temperature superconducting thin films, the four-wire electric transport method, which involves direct measurement, provides data that is direct and highly accurate. However, the microbridge etching and ohmic contact processes involved in the four-wire electric transport measurement may damage some parts of the film on the substrate and degrade the performance of the remaining parts, hindering subsequent sample processing and reuse. Furthermore, the four-wire method is time-consuming and relatively complex, often requiring high-power constant current sources for measuring high-critical-current superconducting samples, making it unsuitable for quality control of high-temperature superconducting thin films during routine preparation processes. While the traditional indirect induction method is non-destructive, the close spatial distribution of the excitation and detection coils leads to constant current noise induced in the detection coil from the excitation coil, resulting in high measurement noise, low signal-to-noise ratio, and large measurement errors, which is detrimental to the quality assessment of large-scale high-temperature superconducting thin films. Summary of the Invention

[0004] In view of the above problems, the present invention is proposed to provide a measurement system for the critical current density of high-temperature superconducting thin films that overcomes or at least partially solves the above problems.

[0005] According to one aspect of the present invention, a measurement system for the critical current density of a high-temperature superconducting thin film is provided, the measurement system comprising:

[0006] Signal generator 1, power amplifier 2, protection resistor 3, sampling resistor 4, digital multimeter 5, excitation coil 6, detection coil 7, lock-in amplifier 8, and controller 9;

[0007] The lock-in amplifier 8 includes a signal generator 1, a reference signal REF interface, an A interface, and a B interface;

[0008] The signal generator 1 is connected to the input terminal of the power amplifier 2, the output terminal of the power amplifier 2 is connected to one end of the protection resistor 3, and the other end of the protection resistor 3 is connected to one end of the sampling resistor 4 and the digital multimeter 5 respectively.

[0009] The other end of the sampling resistor 4 and the digital multimeter 5 are both connected to the detection coil 7;

[0010] The reference signal REF interface is connected to the input terminal of the power amplifier 2;

[0011] The A interface is connected to the digital multimeter 5;

[0012] The B interface is connected to the excitation coil 6;

[0013] A sample is placed between the excitation coil 6 and the detection coil 7;

[0014] The controller 9 is connected to the lock-in amplifier 8, which acquires the voltage signal of the detection coil 7 and performs frequency locking and filtering.

[0015] Optionally, the signal generator 1 has the function of generating a 100Hz to 20kHz frequency-converted AC signal for adjusting the amplitude and phase of the signal.

[0016] Optionally, the power amplifier 2 amplifies the output electrical signal power of the signal generator 1.

[0017] Optionally, the sampling resistor 4 is set according to the measurement sampling voltage requirements.

[0018] Optionally, the excitation coil 6 has a current-carrying capacity, and the AC signal amplified by the power amplifier 2 excites the magnetic field.

[0019] Optionally, the detection coil 7 receives an alternating magnetic field and induces a voltage signal according to Faraday's law of electromagnetic induction.

[0020] Optionally, the relative spatial position structure of the excitation coil 6 and the detection coil 7 includes:

[0021] Fixed bracket 10, adjusting nut 11, high temperature superconducting thin film 12 and liquid nitrogen container 13;

[0022] The fixed bracket 10 is used to fix the excitation coil 6 and the detection coil 7 in a coaxial position;

[0023] The adjusting nut 11 is made of non-magnetic insulating material and is used to adjust the coaxial distance between the excitation coil 6 and the detection coil 7 so as to place a high-temperature superconducting thin film sample between the excitation coil 6 and the detection coil 7, and to adjust the excitation coil 6 and the detection coil 7 to the measurement position.

[0024] A high-temperature superconducting thin film 12 is placed between the excitation coil 6 and the detection coil 7;

[0025] The excitation coil 6, the detection coil 7, and the high-temperature superconducting thin film 12 are immersed together in the liquid nitrogen container 13.

[0026] This invention provides a measurement system for the critical current density of high-temperature superconducting thin films. The measurement system includes: a signal generator 1, a power amplifier 2, a protective resistor 3, a sampling resistor 4, a digital multimeter 5, an excitation coil 6, a detection coil 7, a lock-in amplifier 8, and a controller 9. The lock-in amplifier 8 includes the signal generator 1, a reference signal REF interface, an A interface, and a B interface. The signal generator 1 is connected to the input terminal of the power amplifier 2, and the output terminal of the power amplifier 2 is connected to one end of the protective resistor 3. The other end of the protective resistor 3 is connected to one end of the sampling resistor 4 and the digital multimeter 5. The other ends of the sampling resistor 4 and the digital multimeter 5 are both connected to the detection coil 7. The reference signal REF interface is connected to the input terminal of the power amplifier 2. The A interface is connected to the digital multimeter 5. The B interface is connected to the excitation coil 6. A sample is placed between the excitation coil 6 and the detection coil 7. The controller 9 is connected to the lock-in amplifier 8, and the lock-in amplifier 8 acquires the voltage signal of the detection coil 7 and performs frequency locking and filtering. The high signal-to-noise ratio of the measurement improves the accuracy of the measurement results.

[0027] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, and in order to make the above and other objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described below. Attached Figure Description

[0028] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 A schematic diagram of the measurement circuit of a measurement system for the critical current density of a high-temperature superconducting thin film provided in an embodiment of the present invention;

[0030] Figure 2 A schematic diagram of the relative spatial positions of the excitation coil and the detection coil in a measurement system for the critical current density of a high-temperature superconducting thin film provided in an embodiment of the present invention;

[0031] Figure 3 Experiments and results of a measurement system for the critical current density of a high-temperature superconducting thin film provided in an embodiment of the present invention;

[0032] Figure 4Signal-to-noise ratio analysis of a measurement system for the critical current density of a high-temperature superconducting thin film provided in an embodiment of the present invention. Detailed Implementation

[0033] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0034] The terms "comprising" and "having," and any variations thereof, in the specification, embodiments, claims, and drawings of this invention are intended to cover non-exclusive inclusion, such as including a series of steps or units.

[0035] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0036] like Figure 1 As shown, a measurement system for the critical current density of a high-temperature superconducting thin film is provided. The measurement system includes:

[0037] The system comprises a signal generator 1, a power amplifier 2, a protective resistor 3, a sampling resistor 4, a digital multimeter 5, an excitation coil 6, a detection coil 7, a lock-in amplifier 8, and a controller 9. The lock-in amplifier 8 includes the signal generator 1, a reference signal REF interface, an A interface, and a B interface. The signal generator 1 is connected to the input of the power amplifier 2. The output of the power amplifier 2 is connected to one end of the protective resistor 3. The other end of the protective resistor 3 is connected to one end of the sampling resistor 4 and the digital multimeter 5. The other ends of the sampling resistor 4 and the digital multimeter 5 are both connected to the detection coil 7. The reference signal REF interface is connected to the input of the power amplifier 2. The A interface is connected to the digital multimeter 5. The B interface is connected to the excitation coil 6. A sample is placed between the excitation coil 6 and the detection coil 7.

[0038] The controller 9 is connected to the lock-in amplifier 8, which acquires the voltage signal of the detection coil 7 and performs frequency locking and filtering.

[0039] Signal generator 1 needs to be able to generate AC signals with a frequency conversion of 100Hz to 20kHz, and adjust the amplitude and phase of the signal.

[0040] Power amplifier 2 needs to have the function of amplifying the output electrical signal power of the signal generator.

[0041] The protection resistor 3 needs to have the capability of a voltage divider protection circuit.

[0042] The sampling resistor 4 needs to meet the requirements for measuring the sampling voltage.

[0043] The digital multimeter 5 needs to have the function of measuring voltage and current amplitude and RMS value.

[0044] The excitation coil 6 has a certain current-carrying capacity, and the AC signal amplified by the power amplifier 2 can be used to generate a magnetic field.

[0045] The detection coil 7 needs to receive the alternating magnetic field and induce a voltage signal according to Faraday's law of electromagnetic induction.

[0046] The lock-in amplifier 8 has the function of acquiring the voltage signal of the detection coil and frequency locking filtering.

[0047] The controller 9 contains the control program for manipulating the lock-in amplifier 8 and also saves the processed data.

[0048] like Figure 2 As shown, the relative spatial position structure of the excitation coil and the detection coil of a high-temperature superconducting thin film critical current density measurement system includes: a fixed bracket 10, an adjusting nut 11, a high-temperature superconducting thin film 12, and a liquid nitrogen container 13.

[0049] The fixed bracket 10 is used to fix the excitation coil and the detection coil in a coaxial position.

[0050] In the adjusting nut 11, the adjusting nut is also made of non-magnetic insulating material and is used to adjust the coaxial distance between the excitation coil and the detection coil so as to place the high-temperature superconducting thin film sample between the excitation coil and the detection coil, and to adjust the excitation coil and the detection coil to the appropriate measurement position.

[0051] A high-temperature superconducting thin film 12 is placed between the excitation coil 6 and the detection coil 7;

[0052] The excitation coil 6, the detection coil 7, and the high-temperature superconducting thin film 12 are immersed together in the liquid nitrogen container 13.

[0053] According to such Figure 2 After fabricating the mounting bracket and adjusting nut as shown, fix the excitation coil and the detection coil as follows. Figure 2 At the position shown, the excitation coil and the detection coil are then connected as shown. Figure 1 The circuit diagram shown provides a measurement system for the critical current density of high-temperature superconducting thin films.

[0054] Based on their magnetization properties, superconductors can be classified into Type I and Type II superconductors. Type I superconductors are ideal superconductors, possessing only one critical magnetic field H. C When the magnetic field strength H < H C At this time, the first type of superconductor exhibits perfect diamagnetism, and the magnetic induction intensity within the superconductor is zero; when the magnetic field strength H > H CAt this point, Type I superconductors lose their superconductivity and completely transition from the superconducting state to a normal material state. Unlike Type I superconductors, Type II superconductors have two critical magnetic fields in their magnetization curves, namely the lower critical magnetic field H0. C1 and the upper critical magnetic field H C2 When the magnetic field strength H < H C1 When the magnetic field strength H > H, the superconductor exhibits perfect diamagnetism, and the magnetic field is expelled from the superconductor; when the magnetic field strength H > H C2 When the magnetic field strength H changes, the superconductor transitions from the superconducting state to all normal states; C1 <H<H C2 When the magnetic field partially enters the superconductor, the interior of the superconductor is a mixed state of normal and superconducting states, also known as the vortex state.

[0055] Using the geometric center of the high-temperature superconducting thin film surface as the origin, a planar polar coordinate system is established along the plane containing the high-temperature superconducting thin film surface. Then, a cylindrical coordinate system is established with the z-axis perpendicular to the high-temperature superconducting thin film surface. An excitation coil is placed coaxially along the high-temperature superconducting thin film. The superconducting film thickness is d, the distance between the superconducting film and the coil is Z1, the number of coil turns is N, the coil thickness is h, the inner radius of the coil is R1, the outer radius of the coil is R2, the cross-sectional area of ​​the coil is S=(R2-R1)h, and the amplitude of the excitation signal in the coil is I0 and I(t)=I0cosωt.

[0056] The excitation coil generates an axisymmetric magnetic field:

[0057] H r (r, t)=H0cosωt=I0F1(r)cosωt (2.1)

[0058] Where H0 is the magnitude of the magnetic field strength along the polar coordinate plane, and F1(r) is the theoretical coil coefficient:

[0059]

[0060] R=(z 2 +r 2 +ρ 2 -2rρcosθ) 1 / 2 (2.3)

[0061] Obtain the extreme values ​​of the theoretical coil coefficients

[0062] F 1max (r)=F1((R1+R2) / 2) (2.4)

[0063] F1(0)=F1(∞)=0 (2.5)

[0064] That is, the maximum value of the magnetic field generated by the excitation coil on the surface of the high-temperature superconducting thin film is located at r = (R1 + R2) / 2.

[0065] When a high-temperature superconducting thin film is in the superconducting state, i.e., H0 < H C1 , I0 < I th At this time, due to the presence of diamagnetism, on the upper surface of the high-temperature superconducting thin film, the magnetic fields generated by the excitation coil and the superconducting current cancel each other out in the vertical direction and superimpose each other in the parallel direction, which can be calculated using the loop theorem of magnetic fields.

[0066] H z =0 (2.6)

[0067]

[0068] Among them, K s (r, t) is the sheet current density of the high-temperature superconducting thin film, and K s (r, t) ≤ |J c d|,

[0069] J c It is precisely the critical current density of high-temperature superconducting thin films.

[0070] Based on the magnetization curve of type II superconductors, the magnetic field excited by the excitation coil and superconducting current on the surface of the high-temperature superconducting thin film can be equivalently represented as the superposition of the magnetic fields excited by the excitation coil and its mirror image coil symmetrical about the z=0 plane.

[0071] H + =K s (r, t) = 2H r (r, t) ∝ I0cosωt (2.8)

[0072] Meanwhile, due to the presence of superconducting diamagnetism, at the lower surface of the high-temperature superconducting thin film, i.e., at z = -d,

[0073] H - =0.

[0074] The above analysis shows that when the high-temperature superconducting thin film is in the superconducting state, the magnetic field along the polar coordinate plane on the upper surface of the high-temperature superconducting thin film and the excitation coil current form a linear system, and the strength of the magnetic field is proportional to the amplitude of the excitation current.

[0075] When the amplitude of the current in the excitation coil reaches the threshold current I th At that time, the magnetic field strength in the high-temperature superconducting thin film reaches the lower critical magnetic field H. C1 At this point, the current density of the superconducting sheet reaches its maximum value J. c d. If the current in the excitation coil is further increased, the high-temperature superconducting thin film will transition from the superconducting state to the vortex state until the magnetic field strength reaches the upper critical magnetic field H. C2If the excitation current continues to increase, the high-temperature superconducting thin film will enter a normal state and no longer possess any superconducting properties. When the excitation current exceeds the threshold current I... th Throughout the continuous increase, the linear system between the excitation current and the high-temperature superconducting thin film is disrupted, and the sheet current density continuously decreases until it disappears completely.

[0076] H + =H r (r, t) + H s →H r (r, t) (2.9)

[0077] H - >0 (2.10)

[0078] Among them, H s It is the magnetic field generated by the superconducting current when the high-temperature superconducting thin film is in a vortex state.

[0079] When the current amplitude I0 < I is applied to the excitation coil th That is, H0 < H C1 When a high-temperature superconducting thin film is in a fully superconducting state, the excitation current and the high-temperature superconducting thin film form a linear system. At this time, the magnetic fields on the upper and lower surfaces of the superconducting film are respectively...

[0080] H + =K s (r, t) = 2H r (r, t) ∝ I0cosωt (2.11)

[0081] H - =0 (2.12)

[0082] Due to the perfect diamagnetism of the high-temperature superconducting thin film, the magnetic field excited by the excitation current cannot penetrate to...

[0083] In the region z < -d, and with no electrical signal applied to the detection coil, the voltage signal in the detection coil is obtained by Faraday's law of electromagnetic induction.

[0084]

[0085] When the current amplitude I0 > I is passed through the excitation coil th During this process, the high-temperature superconducting thin film transitions from a fully superconducting state through a vortex state to a normal state. In this process, the linear system consisting of the excitation current and the high-temperature superconducting thin film is disrupted, and the magnetic field H generated by the superconducting current... s The magnetic field gradually decays to zero, while the magnetic field excited by the excitation current penetrates the high-temperature superconducting film. The magnetic fields distributed on the upper and lower surfaces of the superconducting film are mainly excited by the excitation current.

[0086]

[0087] H + =H(r, z, t) + H s →H(r, 0, t) (2.15)

[0088] H - =H(r, z, t) + H s →H(r, -d, t) (2.16)

[0089] At this time, the voltage signal in the probe coil is

[0090]

[0091] When the current amplitude I0 = I is passed through the excitation coil th When, H0 = H C1 The superconducting film is precisely at the transition point to the fully superconducting state, where the superconducting current reaches its maximum value, which is also the critical current of the high-temperature superconducting thin film.

[0092]

[0093] At the same time, the loop theorem of magnetic fields and the mirror model can be used to obtain...

[0094] K s (r, t) = H + =2H r (r, t) = 2F 1max (r)I th (2.19)

[0095] Combining equations 2.18 and 2.19 above, the critical current density of high-temperature superconducting thin films can be obtained.

[0096]

[0097] like Figure 3 The figure shows the experimental results of measuring the critical current density of a high-temperature superconducting thin film sample prepared in the laboratory using a measurement system for the critical current density of a high-temperature superconducting thin film. The specific implementation steps are as follows.

[0098] Using the known critical current density J c0 Standard high-temperature superconducting thin film samples were used to obtain the threshold current I. th Substituting into Equation 2.20, the value of the experimental coil coefficient k is obtained;

[0099] The high-temperature superconducting thin film with unknown critical current density to be measured, the detection coil, and the excitation coil are placed in a position such as... Figure 1 and Figure 2 The relative positions shown in the induction circuit are fixed to the bottom of the liquid nitrogen container.

[0100] Keep the experimental environment well ventilated, pour an appropriate amount of liquid nitrogen into the liquid nitrogen container to completely immerse the high-temperature superconducting thin film with the unknown critical current density to be measured, the detection coil and the excitation coil. After the liquid nitrogen stops boiling and the surface of the liquid nitrogen tends to stabilize, proceed to the next step.

[0101] Will Figure 1 Power on all the instruments and equipment shown. Set the output signal of the signal generator to sinusoidal AC with an AC frequency of f and an initial phase of 0. Set the power amplifier to current amplification. Use the controller to open the lock-in amplifier control program, set the sampling frequency of the lock-in amplifier to a suitable range, and set the frequency of the lock-in signal to 3 times the frequency of the sinusoidal AC signal output by the signal generator.

[0102] Double-check that the circuit connection is correct, click the "output" button on the output channel of the signal generator, and adjust the output signal amplitude I0 from 0 to gradually increase it in a certain step. Repeat the next step after each increase.

[0103] The controller records the third harmonic voltage signal U3 induced in the detection coil each time the signal generator increases the amplitude of the output signal through the lock-in amplifier control program, until U3 changes from stable to a sharp increase.

[0104] The measurement region of the high-temperature superconducting thin film with unknown critical current density to be tested should be measured at least three times. The data can be saved and processed to calculate the U3 / fI0 data under the condition of excitation frequency f.

[0105] Change the output signal frequency f of the signal generator two or three times, and repeat the above steps completely.

[0106] The controller records and saves the experimental data, shuts down all instruments and equipment, and uses tweezers to remove the high-temperature superconducting thin film, detection coil and excitation coil from the liquid nitrogen container and place them in a dry place to allow them to naturally return to room temperature, while waiting for the liquid nitrogen to evaporate naturally.

[0107] The experimental threshold current I of the high-temperature superconducting thin film with unknown critical current density is obtained using the constant electric field criterion. th Substituting the remainder and k into Equation 2.20, the critical current density J of the high-temperature superconducting thin film in the measurement region, where the unknown critical current density is to be measured, can be calculated. c .

[0108] By following the specific steps described above, a measurement system and test data for the critical current density of high-temperature superconducting thin films can be obtained.

[0109] like Figure 4The figure shows the signal-to-noise ratio analysis of a measurement system for the critical current density of a high-temperature superconducting thin film according to the above laboratory standard measurement procedure, and compares it with the traditional induction method. The induction method of the present invention can improve the signal-to-noise ratio by up to about 20dB, which verifies the innovation and advancement of the present invention.

[0110] In summary, based on the perfect diamagnetism of superconductivity, a measurement system for the critical current density of high-temperature superconducting thin films was designed after theoretical analysis. Through circuit analysis and instrument selection, a measurement system for the critical current density of high-temperature superconducting thin films was constructed. The critical current density of the measurement region of the high-temperature superconducting thin film with an unknown critical current density was obtained through standard procedure testing. Signal-to-noise ratio analysis confirmed that the measurement system for the critical current density of high-temperature superconducting thin films can indeed improve the measurement signal-to-noise ratio. Finally, a measurement system for the critical current density of high-temperature superconducting thin films was designed.

[0111] Beneficial effects: The measurement of the critical current density of a high-temperature superconducting thin film is a non-destructive measurement, which does not require sample processing and reduces sample damage; the measurement circuit is simplified and the measurement process is simple, which greatly reduces the economic and time costs of measurement; the measurement has a high signal-to-noise ratio, which greatly improves the accuracy of the measurement results.

[0112] The above specific embodiments further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A measurement system for the critical current density of a high-temperature superconducting thin film, characterized in that, The measurement system includes: Signal generator 1, power amplifier 2, protection resistor 3, sampling resistor 4, digital multimeter 5, excitation coil 6, detection coil 7, lock-in amplifier 8, and controller 9; The lock-in amplifier 8 includes a signal generator 1, a reference signal REF interface, an A interface, and a B interface; The signal generator 1 is connected to the input terminal of the power amplifier 2, the output terminal of the power amplifier 2 is connected to one end of the protection resistor 3, and the other end of the protection resistor 3 is connected to one end of the sampling resistor 4 and the digital multimeter 5 respectively. The other end of the sampling resistor 4 and the digital multimeter 5 are both connected to the detection coil 7; The reference signal REF interface is connected to the input terminal of the power amplifier 2; The A interface is connected to the digital multimeter 5; The B interface is connected to the excitation coil 6; A sample is placed between the excitation coil 6 and the detection coil 7; The controller 9 is connected to the lock-in amplifier 8, which acquires the voltage signal of the detection coil 7 and performs frequency locking and filtering.

2. The measurement system for the critical current density of a high-temperature superconducting thin film according to claim 1, characterized in that, The signal generator 1 has the function of generating a frequency-converted AC signal from 100Hz to 20kHz, which is used to adjust the amplitude and phase of the signal.

3. The measurement system for the critical current density of a high-temperature superconducting thin film according to claim 1, characterized in that, The power amplifier 2 amplifies the output electrical signal power of the signal generator 1.

4. The measurement system for the critical current density of a high-temperature superconducting thin film according to claim 1, characterized in that, The sampling resistor 4 is set according to the measurement sampling voltage requirements.

5. The measurement system for the critical current density of a high-temperature superconducting thin film according to claim 1, characterized in that, The excitation coil 6 has current-carrying capacity, and the AC signal amplified by the power amplifier 2 excites the magnetic field.

6. The measurement system for the critical current density of a high-temperature superconducting thin film according to claim 1, characterized in that, The detection coil 7 receives the alternating magnetic field and induces a voltage signal according to Faraday's law of electromagnetic induction.

7. The measurement system for the critical current density of a high-temperature superconducting thin film according to claim 1, characterized in that, The relative spatial position structure of the excitation coil 6 and the detection coil 7 includes: Fixed bracket 10, adjusting nut 11, high temperature superconducting thin film 12 and liquid nitrogen container 13; The fixed bracket 10 is used to fix the excitation coil 6 and the detection coil 7 in a coaxial position; The adjusting nut 11 is made of non-magnetic insulating material and is used to adjust the coaxial distance between the excitation coil 6 and the detection coil 7 so as to place a high-temperature superconducting thin film sample between the excitation coil 6 and the detection coil 7, and to adjust the excitation coil 6 and the detection coil 7 to the measurement position. A high-temperature superconducting thin film 12 is placed between the excitation coil 6 and the detection coil 7; The excitation coil 6, the detection coil 7, and the high-temperature superconducting thin film 12 are immersed together in the liquid nitrogen container 13.

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