High-sensitivity electrocaloric effect measuring device and measuring method

Abstract

The invention discloses a high-sensitivity electrocaloric effect measuring device and measuring method, and relates to the technical field of electrocaloric effect measurement. The device comprises a constant-temperature cavity, a heat preservation cavity, a front signal amplifier, an oscilloscope, a heat dissipation substrate, a heat flow sensor, a gold electrode, a to-be-tested ceramic chip, a signal generator and a high-voltage amplifier. According to the measurement method, based on the signal response characteristics of the heat flow sensor, accurate measurement of the electrocaloric effect is achieved through reference calibration and integral calculation. The method solves the problems that in the prior art, the measurement period is long, the heat loss influence is large, and the intrinsic electrocaloric effect is underestimated, has the advantages of being high in measurement speed, high in sensitivity and high in accuracy, and can efficiently provide data support for high electrocaloric material design.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrocaloric effect measurement, and in particular to a high-sensitivity electrocaloric effect measurement device and a measurement method. BACKGROUND

[0002] Currently, the indirect method is generally used to evaluate the electrocaloric effect, that is, the electric hysteresis loop at different temperatures is obtained, the polarization value at different temperatures and different electric fields is obtained, and the electrocaloric effect under the indirect method is calculated by using the Maxwell relationship. wherein represents the specific heat capacity, represents the ceramic density, represents the temperature. Affected by many non-essential factors such as dielectric ceramic leakage current, test frequency and polarization unsaturation, the error of the method for evaluating the electrocaloric effect is large.

[0003] Currently, researchers have developed a direct method for measuring the electrocaloric effect based on the Pt100 thermal resistance method (Patent No. CN111855736 B), which mainly uses the Pt100 thermal resistance to collect the temperature signal of the ferroelectric ceramic under the application / removal of voltage. Since the temperature and the resistance value of Pt100 present a one-to-one correspondence, the corresponding temperature change can be obtained. Since the Pt100 thermal resistance has an Al2O3 support layer at the bottom, this fixed restriction will cause serious heat loss and response lag (the electrocaloric response time is in the microsecond level), and the intrinsic electrocaloric effect of the measured ceramic is seriously underestimated. In addition, this method also needs to be vacuumized, and the temperature balance time is long. Therefore, how to quickly and accurately measure the electrocaloric effect is a problem that needs to be solved at present. SUMMARY

[0004] In view of the above problems, the present application provides a high-sensitivity electrocaloric effect measurement device and a measurement method, which focuses on how to quickly and accurately detect the electrocaloric effect of ferroelectric ceramics. It is an attempt to accurately obtain the intrinsic electrocaloric effect of ceramics and provide strong guidance for researchers in the design of high electrocaloric materials.

[0005] To solve the above problems, the technical solution adopted by the present application is: A high-sensitivity electrocaloric effect measurement device, comprising: A constant-temperature cavity for providing a variable temperature environment of 10-130℃, with a temperature rise and fall rate of 5℃ / min to ensure stable cavity temperature before testing; A heat preservation cavity installed in the constant-temperature cavity for blocking the heat flow interference of the constant-temperature cavity and shielding external clutter signals; A heat dissipation substrate installed at the bottom of the heat preservation cavity, made of high-thermal-conductivity inorganic material; A heat flow sensor is mounted above the heat dissipation substrate to sense the heat flow signal generated by the ceramic sheet under test. The gold electrode consists of two layers of reference electrodes, one above the heat flow sensor. The ceramic sheet to be tested is attached between the gold electrodes; The signal generator has a first interface, a second interface, and a third interface. The first and third interfaces are used to output a small voltage to the reference electrode, and the second and third interfaces are used to output signals with different waveforms. A high-voltage amplifier with a maximum output voltage of 10,000V is connected to the second interface of the signal generator to receive signals and apply them to the ceramic sheet under test. A preamplifier is used to amplify the microvolt-level voltage signal output by the heat flow sensor to the millivolt level. An oscilloscope, connected to a preamplifier, is used to acquire amplified voltage signals.

[0006] Preferably, the material of the heat-insulating cavity is one of stainless steel, aluminum alloy or copper.

[0007] Preferably, the heat dissipation substrate is made of one of aluminum oxide, aluminum nitride, silicon nitride, silicon carbide, or boron nitride.

[0008] Preferably, the signal generator can output signals with different waveforms such as rectangular waves and triangular waves.

[0009] Preferably, the acquisition rate of the preamplifier is 100-5000 S / s.

[0010] Preferably, the ceramic sheet to be tested has a thickness of 0.2-0.4 mm and a smooth surface.

[0011] Preferably, thermal grease is applied between the lower reference electrode and the heat flow sensor, and between the heat flow sensor and the heat dissipation substrate, and the wires leading out from the first interface and the third interface are silver wires.

[0012] This invention also provides a high-sensitivity electrocaloric effect measurement method, comprising the following steps: S1: Install the ceramic sheet to be tested between the gold electrodes, ensuring that all components fit tightly, and turn on the constant temperature chamber to the target temperature and keep it stable. S2: A small voltage is output to the reference electrode through the first and third interfaces of the signal generator to record the response signal generated by the heat flow sensor. After being amplified by the preamplifier, the signal is acquired by an oscilloscope to calculate the integral area of ​​the signal. ; S3: According to Joule's law, the standard resistance of the reference electrode... Low voltage applied And the energizing time t, calculate the baseline heat. This leads to the proportionality constant. ; S4: A signal with a specified waveform is output through the second and third interfaces of the signal generator. After being amplified by a high-voltage amplifier, it is applied to the ceramic sheet under test. Then, the voltage is removed, and the response signal of the heat flow sensor is recorded. After amplification and acquisition, the integrated area is calculated. ; S5: According to the formula Calculate the heat generated by the caloric effect, and then, based on the isothermal assumption, use the formula... Calculate the entropy change to complete the measurement of the electrocaloric effect.

[0013] Preferably, the duration of the complete measurement cycle of applying and removing voltage in step S4 is 30 seconds.

[0014] Preferably, the thermodynamic temperature T in step S5 is the test environment temperature of the constant temperature cavity.

[0015] The beneficial effects of this invention are as follows: 1. The heat flow method enables rapid and accurate measurement of the electrocaloric effect. Traditional Pt100 temperature change detection requires vacuuming, and a single cycle of applying / removing voltage takes approximately 600 seconds. In contrast, the heat flow method requires only 30 seconds per cycle, significantly reducing the measurement time.

[0016] 2. The heat flow method uses a reference resistor signal as a reference and uses the ratio of the ceramic plate electrocaloric signal to the reference resistor to obtain the electrocaloric effect, which can significantly reduce the impact of heat loss on the electrocaloric effect. Attached Figure Description

[0017] Fig. 1 This is a schematic diagram of the device structure of the present invention; Fig. 2 This is a diagram of the heat flow signal of the reference electrode in this invention (black line). Fig. 3 This is a heat flow signal diagram (black line) for the ceramic sheet of the present invention.

[0018] In the figure: 1. Constant temperature chamber, 2. Insulated chamber, 3. Preamplifier, 4. Oscilloscope, 5. Heat dissipation substrate, 6. Heat flow sensor, 7. Gold electrode, 8. Ceramic plate under test, 9. Signal generator, 10. High voltage amplifier, 11. First interface, 12. Second interface, 13. Third interface. Detailed Implementation

[0019] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0020] Reference Figs. 1-3 A high-sensitivity electrocardiogram effect measurement device includes a constant temperature chamber 1, a heat preservation chamber 2, a preamplifier 3, an oscilloscope 4, a heat dissipation substrate 5, a heat flow sensor 6, a gold electrode 7, a ceramic sheet under test 8, a signal generator 9, and a high-voltage amplifier 10. The connection relationship and function of each component are as follows: Thermostatic Chamber 1: Provides a controllable temperature environment of 10-130℃, with a heating and cooling rate of 5℃ / minute, ensuring temperature stability during testing and meeting the requirements for electrocaloric effect measurement at different temperatures.

[0021] Insulation chamber 2: Made of stainless steel, aluminum alloy or copper, it is fitted inside the constant temperature chamber 1. It can block the heat flow of the constant temperature chamber 1 from diffusing inward, avoiding interference with the measurement of the card signal, and also shield external electromagnetic noise signals to ensure signal stability.

[0022] Heat dissipation substrate 5: Made of inorganic materials with high thermal conductivity such as alumina, aluminum nitride, silicon nitride, silicon carbide or boron nitride, it provides stable support for the heat flow sensor 6 and quickly conducts heat to reduce heat accumulation.

[0023] Heat flow sensor 6: Located between heat dissipation substrate 5 and gold electrode 7, it can accurately sense the heat flow changes generated by the ceramic sheet 8 under test under the action of electric field and convert them into voltage signal output.

[0024] Gold electrode 7: It consists of two layers of reference electrodes, one layer to support the ceramic sheet under test 8, and the other layer to serve as the electrode structure for reference calibration, ensuring the stability of the signal reference.

[0025] The ceramic sheet 8 to be tested has a thickness controlled between 0.2 and 0.4 mm and a flat surface to ensure good adhesion with the gold electrode 7 and reduce contact thermal resistance.

[0026] Signal generator 9: Equipped with a first interface 11, a second interface 12 and a third interface 13. The first interface 11 and the third interface 13 output a small voltage to the reference electrode to obtain the reference heat flow signal; the second interface 12 and the third interface 13 can output signals of different waveforms such as rectangular wave and triangular wave to provide input signals for the high voltage amplifier 10.

[0027] High voltage amplifier 10: The maximum output voltage can reach 10000V. After receiving the signal from the signal generator 9, it amplifies it and applies and removes the high voltage to the ceramic sheet 8 under test, causing it to generate a heat flow signal related to the electrocardiogram effect.

[0028] Preamplifier 3: Since the voltage signal output by the heat flow sensor 6 is only at the microvolt level, it cannot be directly acquired by the oscilloscope 4. Therefore, this amplifier amplifies the signal to the millivolt level. The acquisition rate can be adjusted between 100-5000S / s to adapt to measurement requirements with different response speeds.

[0029] Oscilloscope 4: Connected to preamplifier 3, it is used to accurately acquire the amplified voltage signal and provide raw data for subsequent integration calculations.

[0030] To further reduce heat loss, thermal grease is evenly applied between the lower electrode and the heat flow sensor 6, and between the heat flow sensor 6 and the heat dissipation substrate 5, to improve heat conduction efficiency; the wires leading out from the first interface 11 and the third interface 13 are made of silver wire to reduce loss and interference during signal transmission.

[0031] The measurement method using the above-mentioned device is as follows: Step S1: Device assembly and temperature calibration: Install the ceramic sheet 8 to be tested, with a thickness of 0.2-0.4mm and a flat surface, between the upper and lower gold electrodes 7, ensuring that the ceramic sheet and the electrodes are in close contact; check the connection of each component, apply thermal grease to the designated contact surface, place the entire structure in the heat preservation chamber 2, turn on the constant temperature chamber 1, set the target temperature and wait for the temperature to stabilize to ensure that the test environment temperature is constant.

[0032] Step S2: Reference Signal Acquisition and Integration Calculation: A small voltage is output to the reference electrode through the first interface 11 and the third interface 13 of the signal generator 9. The heat flow sensor 6 senses the heat flow signal generated in this process and converts it into a microvolt-level voltage signal. After being amplified to the millivolt level by the preamplifier 3, the oscilloscope 4 acquires the curve of the signal changing over time. The curve is integrated over the complete heat transfer time period to obtain the integration area. .

[0033] Step S3: Reference proportional constant calibration. Given the standard resistance Rr of the reference electrode, according to Joule's law... (in Calculate the reference heat (where the applied low voltage is used and t is the energizing time). Combined with the integral area obtained in step S2 Through formula Calculate the proportionality constant between heat and integral area. .

[0034] Step S4: Electrocardiogram signal acquisition and integration calculation. A signal with a specified waveform is output through the second interface 12 and the third interface 13 of the signal generator 9. This signal is amplified to a set high voltage by the high-voltage amplifier 10 and applied to the ceramic sheet 8 under test. After the high voltage is removed, the ceramic sheet 8 experiences a change in heat flow due to the electrocardiogram effect. The heat flow sensor 6 converts this heat flow change into a voltage signal, which is amplified and acquired by the oscilloscope 4. The integrated area of ​​this signal over the complete heat transfer time period is calculated. .

[0035] Step S5: Calculation of the electrical card effect. Based on the proportionality constant obtained in step S3. Combined with formula Calculate the heat generated by the caloric effect Based on the isothermal assumption, taking the test environment temperature T of the constant-temperature cavity 1 as the thermodynamic temperature, and using the entropy change formula... The entropy change of the ceramic piece 8 under test was calculated, and the electrocaloric effect was measured.

[0036] Working principle: The integral area of ​​the output signal of the heat flux sensor is linearly proportional to the amount of heat absorbed / released. When heat passes through the sensor, it is distributed as heat flux (the amount of heat passing through a unit area per unit time, denoted as heat flow). Changes produce a response, and the output is the same as... proportional voltage signal heat flux density With instantaneous heat The relationship is: ( (Effective area of ​​the electrode) (Formula 1) Substituting the voltage signal relationship, we can obtain: (Formula 2) (Formula 3) Output voltage signal Integrating over time yields the area of ​​integration: (Formula 4) Combining with Formula 3 from the previous step, for time... arrive Integral total heat (over the entire time period of heat transfer): (Formula 5) Due to the electrodes It is a fixed parameter, therefore the total heat With integral area Exhibits a strictly linear proportional relationship (k is a proportionality constant) (Formula 6) Standard resistor on the sample Apply low voltage The reference heat is obtained from Joule's law. : (Formula 7) Simultaneously record the integral area of ​​the heat flow signal corresponding to this heat. Formula 6 forms the baseline ratio of "heat-area": (Formula 8) Applying high voltage generates an electrothermal effect; the integral area of ​​its heat flow signal is recorded. Using the above baseline ratio, the heat can be calculated. : (Formula 9) entropy( Temperature is a physical quantity that describes the degree of disorder in a system. In an isothermal process, temperature... (Constantly), the entropy change of the system is equal to the ratio of "heat absorbed / released during the reversible process" to "thermodynamic temperature", that is: (Formula 10) During this process, the heat transfer of the sample is approximately adiabatic, but the calculation of entropy change must be based on the "isothermal assumption" (using the ambient temperature of the test environment). (Based on the standard). At this time, the heat generated by the electrothermal effect This can be approximated as the reversible heat of the system during an isothermal process: (Formula 11) Fig. 2 and Fig. 3 The heat flow signals of the reference electrode and the ceramic sheet are respectively represented. The ratio of the shaded areas of the two is obtained by integration, and the electrocaloric effect can be obtained according to formula 9-11.

[0037] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-sensitivity electrocaloric effect measurement apparatus, characterized by, The application relates to a ceramic sheet thermal conductivity testing device, which comprises the following parts: a constant-temperature cavity (1) for providing a variable temperature environment of 10-130 DEG C, the temperature rising and falling rate being 5 DEG C / min, and the cavity temperature being stable before testing; a heat-insulating cavity (2) installed in the constant-temperature cavity (1) for blocking the heat flow interference of the constant-temperature cavity (1) and shielding external disorder signals; a heat-dissipating substrate (5) installed at the bottom of the heat-insulating cavity (2) and made of high-thermal-conductivity inorganic material; a heat flow sensor (6) arranged above the heat-dissipating substrate (5) and used for sensing the heat flow signal generated by a ceramic sheet (8) to be tested; gold electrodes (7) divided into upper and lower reference electrodes and arranged above the heat flow sensor (6); the ceramic sheet (8) to be tested which is attached between the gold electrodes (7); a signal generator (9) provided with a first interface (11), a second interface (12) and a third interface (13), the first interface (11) and the third interface (13) are used for outputting a small voltage to the reference electrodes, and the second interface (12) and the third interface (13) are used for outputting signals of different waveforms; a high-voltage amplifier (10) with a maximum output voltage of 10000V, which is connected with the second interface (12) of the signal generator (9), receives signals and applies the signals to the ceramic sheet (8) to be tested; a preamplifier (3) used for amplifying the micro-volt-level voltage signal output by the heat flow sensor (6) to a millivolt level; an oscilloscope (4) connected with the preamplifier (3) and used for collecting the amplified voltage signal.

2. The high sensitivity electrocaloric effect measurement device of claim 1, wherein, The material of the heat-insulating cavity (2) is one of stainless steel, aluminum alloy and copper.

3. The high sensitivity electrocaloric effect measurement device of claim 1, wherein, The material of the heat-dissipating substrate (5) is one of alumina, aluminum nitride, silicon nitride, silicon carbide and boron nitride.

4. The high sensitivity electrocaloric effect measurement device of claim 1, wherein, The signal generator (9) can output signals of different waveforms such as rectangular waves and triangular waves.

5. The high sensitivity electrocaloric effect measurement device of claim 1, wherein, The collection rate of the preamplifier (3) is 100-5000 S / s.

6. The high sensitivity electrocaloric effect measurement device of claim 1, wherein, The ceramic sheet (8) to be tested has a thickness of 0.2-0.4 mm and a smooth surface.

7. The high sensitivity electrocaloric effect measurement device of claim 1, wherein, The lower reference electrode and the heat flow sensor (6) are coated with heat-conducting silicone grease, and the lead wires led out from the first interface (11) and the third interface (13) are silver wires.

8. A high-sensitivity electrocaloric effect measurement method based on the device of claim 1, characterized in that, The application further discloses a ceramic sheet thermal conductivity testing method, which comprises the following steps: S1: installing the ceramic sheet (8) to be tested between the gold electrodes (7), ensuring that all parts are tightly attached, turning on the constant-temperature cavity (1) to the target temperature and keeping the temperature stable; S2: output a small voltage to the reference electrode through the first interface (11) and the third interface (13) of the signal generator (9), record the response signal generated by the heat flow sensor (6), which is amplified by the preamplifier (3) and collected by the oscilloscope (4), and calculate the integral area of the signal ; S3: Calculate the reference heat Qref from the standard resistance of the reference electrode, the applied low voltage, and the current-on time t according to Joule's law ;​​​ S4: output the signal of the specified waveform through the second interface (12) and the third interface (13) of the signal generator (9), amplify it through the high-voltage amplifier (10), and then apply it to the ceramic sheet (8) to be tested, then remove the voltage, record the response signal of the heat flow sensor (6), and calculate the integral area after amplification and collection ; S5: Calculate the heat generated by the electrocaloric effect and, based on the isothermal assumption, calculate the entropy change from the formula S5: Calculate the heat generated by the electrocaloric effect and, based on the isothermal assumption, calculate the entropy change from the formula S5: Calculate the heat generated by the electrocaloric effect and, based on the isothermal assumption, calculate the entropy change from the 9. The method of claim 8, wherein the high sensitivity electrocaloric effect measurement method is characterized by, The complete measurement cycle time of the voltage application and removal in step S4 is 30 seconds.

10. The method of claim 8, wherein the high sensitivity electrocaloric effect measurement method is characterized by, The thermodynamic temperature T in step S5 is the testing environment temperature of the constant-temperature cavity (1).

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