WO2016015369A1 - 一种直流激励磁场下的非侵入式快速温度变化的测量方法 - Google Patents

一种直流激励磁场下的非侵入式快速温度变化的测量方法 Download PDF

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WO2016015369A1
WO2016015369A1 PCT/CN2014/086283 CN2014086283W WO2016015369A1 WO 2016015369 A1 WO2016015369 A1 WO 2016015369A1 CN 2014086283 W CN2014086283 W CN 2014086283W WO 2016015369 A1 WO2016015369 A1 WO 2016015369A1
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temperature
change
magnetization
ferromagnetic particles
ferromagnetic
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PCT/CN2014/086283
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French (fr)
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刘文中
张朴
阮楚良
徐文彪
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华中科技大学
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Priority to US14/766,111 priority Critical patent/US9958342B2/en
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
    • G01K7/00—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements
    • G01K7/36—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements using magnetic elements, e.g. magnets, coils
    • G01K7/38—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements using magnetic elements, e.g. magnets, coils the variations of temperature influencing the magnetic permeability
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
    • G01K7/00—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements
    • G01K7/36—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements using magnetic elements, e.g. magnets, coils
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/02—Measuring direction or magnitude of magnetic fields or magnetic flux
    • G01R33/0213—Measuring direction or magnitude of magnetic fields or magnetic flux using deviation of charged particles by the magnetic field

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  • the invention belongs to the field of fast and accurate temperature measurement technology, and more particularly to a non-intrusive rapid temperature change measurement method under a DC excitation magnetic field, and more particularly to a ferromagnetic particle saturation magnetization under a DC excitation magnetic field.
  • Temperature is one of the most basic physical quantities of matter in nature.
  • the measurement of temperature is of great significance to the understanding of the nature of matter in nature.
  • the rapid temperature measurement method using ferromagnetic particles is a new, non-intrusive, ultra-fast (nanosecond), high-precision temperature measurement method. It mainly calculates the temperature information through a certain model relationship by measuring the varying magnetization of ferromagnetic particles.
  • the ferromagnetic particle temperature measurement method has non-invasive and fast characteristics, which makes it have broad application prospects in the fields of laser heating, metal rapid solidification, and engine temperature measurement.
  • thermo measurement problems such as measurement of the flame pulsation temperature of the engine combustion chamber of the aircraft, temperature measurement of the high temperature furnace, high frequency heating welding, casting, etc.
  • the traditional temperature measurement method can not solve these problems well.
  • the temperature measuring device should have the characteristics of fast response speed and high temperature measurement accuracy.
  • Non-intrusive rapid temperature using ferromagnetic particles Measurements combined with temperature conduction can also meet this requirement. Therefore, non-intrusive fast and accurate measurement technology is still an urgent problem in these areas.
  • the present invention provides a non-invasive high time and temperature resolution temperature measurement method based on a ferromagnetic particle saturation magnetization-temperature relationship under a DC excitation magnetic field, the purpose of which is A fast and accurate temperature measurement is achieved in a non-intrusive situation, thereby solving the technical problems of slow temperature measurement and low precision.
  • the present invention provides a non-intrusive rapid temperature change measurement method under a DC excitation magnetic field, comprising:
  • the step (1) is specifically:
  • the ferromagnetic particles are placed inside the object to be tested or applied to the surface of the object to be tested.
  • step (3) is specifically:
  • thermocouple or a fiber optic temperature sensor steady state temperature of the object to be measured under the normal temperature T 1
  • the ferromagnetic particles according to the "saturation magnetization - temperature curve” is calculated as an initial temperature of the spontaneous magnetization of the ferromagnetic particles 1 T M 1 .
  • calculating the changed temperature T 2 according to the amplitude A of the magnetization change signal in the step (4) specifically includes:
  • a is the proportional coefficient of the magnetization change amount ⁇ B and the spontaneous magnetization ⁇ M
  • ⁇ is the amplification factor of the detection circuit
  • N is the number of turns of the inductor coil
  • S is the internal area of the inductor coil
  • ⁇ t is the time of the temperature change
  • s is the parameter of the thermal demagnetization curve of the ferromagnetic material
  • T c is the Curie temperature of the ferromagnetic particles
  • M 1 is the initial spontaneous magnetization of the ferromagnetic particles at a temperature of T 1 .
  • the amplitude A of the magnetization change signal of the ferromagnetic particles after the temperature change is measured in the step (4), and specifically includes:
  • two identical single-layer coils as sensors to detect the magnetization change signal of the ferromagnetic particles in the area to be tested, wherein one of the inductors ⁇ acts as a detection coil, and the object to be tested is included therein, so that the coil can be detected Measuring all the magnetic induction intensity change signals of the object, and the other electromagnetic coil ⁇ is placed in a symmetrical position in the DC excitation magnetic field as a reference coil, which does not receive the sensing signal of the object to be tested, and only receives noise in the environment;
  • the magnetization intensity signal of the ferromagnetic particle change is collected by the inductance coil ⁇ , and the measurement signal of the coil ⁇ is subjected to a conditioning circuit such as differential amplification, and the output amplitude A of each time the magnetization change signal passes through the processing circuit is detected.
  • a conditioning circuit such as differential amplification
  • the non-invasive measurement can be realized by the method of the invention, the intrusive temperature measurement method is simple, and the temperature is monitored directly and accurately in real time, but the trauma is large, the probe is easy to change or interfere with the property of the object to be tested; Temperature measurement can be physically isolated from the object being measured At the same time, it can provide high-precision temperature measurement.
  • the measuring speed of the method of the invention is fast: the prior art can not meet the temperature measurement below the microsecond level, since the theoretical hysteresis of the spontaneous magnetization of the ferromagnetic particles with temperature is very small, about 10 picoseconds, so for this time Temperature measurement can be achieved by changing the heat transfer temperature at the scale.
  • the measurement accuracy of the method of the invention is high: since the measurement signal of the measurement method corresponds to the variation of the magnetization intensity, the integral operation can well suppress the noise during the measurement process in the process of solving the temperature, so that the method can obtain Higher temperature resolution.
  • 1 is a flow chart of a method for measuring rapid temperature change of the present invention
  • Figure 2 is a graph showing saturation magnetization-temperature of ferromagnetic particles in an embodiment of the present invention
  • Figure 5 is a single laser pulse response measured by a photovoltaic power diode in accordance with an embodiment of the present invention
  • FIG. 6 is a waveform diagram of a single thermal impulse response detected by a coil in an embodiment of the present invention.
  • FIG. 7 is a waveform diagram of a 1 ms thermal change response detected by a coil in an embodiment of the present invention.
  • Figure 8 is a temperature diagram of a 1 ms thermal change detected by a thermocouple in an embodiment of the present invention.
  • Figure 9 is a 1 ms temperature diagram calculated by the method of the present invention in an embodiment of the present invention.
  • Figure 10 is a 1 ms temperature comparison chart measured by the method of the present invention and a thermocouple
  • Figure 11 is a 1 ms temperature error plot measured by the method of the present invention and a thermocouple.
  • the ferromagnetism is converted to paramagnetism.
  • a particle paramagnetic, its magnetic properties are described by the Langevin function: Where M S is the saturation magnetic moment of the magnetic nanoparticles, m is the average magnetic moment of the magnetic nanoparticles, ⁇ is the mass of the magnetic nanoparticles (the number of magnetic nanoparticles), k is the Boltzmann constant, and H is added Excitation magnetic field, T is absolute temperature.
  • M S is the saturation magnetic moment of the magnetic nanoparticles
  • m is the average magnetic moment of the magnetic nanoparticles (the number of magnetic nanoparticles)
  • k is the Boltzmann constant
  • H added Excitation magnetic field
  • T absolute temperature.
  • the Taylor expansion can be performed on the Langevin function, and the temperature is solved by measuring the harmonics under the AC model.
  • the macroscopic magnetization is composed of the internal magnetic domain spontaneous magnetization distribution, which can be described by the following formula: Where ⁇ i is the angle between the i-th spontaneous magnetization and the external field, and M s is the spontaneous magnetization.
  • the present invention proposes a ferromagnetic based on a DC excitation magnetic field.
  • a small amount of ferromagnetic particles are placed inside the object to be tested or applied to the surface of the object to be tested by a certain method, so that the appearance and normal working state of the object to be tested are not affected.
  • the steady temperature T 1 at room temperature of the object to be tested is obtained by using a thermocouple or a fiber optic temperature sensor, and the "saturation magnetization-temperature curve" of the ferromagnetic particles is as shown in FIG. 2, in the case where the ferromagnetic particles are saturated with magnetization.
  • the spontaneous magnetization has a one-to-one correspondence with the temperature, so the initial spontaneous magnetization M 1 of the ferromagnetic particles at a temperature of T 1 can be calculated.
  • the temperature T 2 after the change can be calculated by using the spontaneous magnetization M 2 after the temperature change, but the M 2 cannot be directly detected, and the amplitude A of the magnetization change signal and the corresponding change time ⁇ t are detected. Thereby deriving M 2 .
  • the rapid temperature measurement is reflected in the time resolution, and a temperature change of nanoseconds is applied to the object to be tested, and then the amplitude and duration of the response signal are detected by the detection system.
  • the magnetization change signal of the ferromagnetic particles in the region to be tested is detected by using two identical single-layer coils as sensors.
  • One of the inductors ⁇ acts as a detecting coil, and the object to be tested is included therein, so that the coil can detect all the magnetic induction intensity change signals of the object to be tested, and the other inductor coil ⁇ is placed in a symmetrical position in the DC excitation magnetic field as a reference coil. It does not receive the sensing signal of the object to be tested, and only receives noise in the environment.
  • the high-frequency equivalent model of the inductor coil is shown in Figure 3.
  • the inductor coil can be regarded as an inductor in series with the resistor, and connected in parallel with a capacitor.
  • the resonant frequency is around 1.2MHz.
  • the change time is below 1us. That is, the temperature change signal with a frequency characteristic above 1 MHz generates unavoidable interference, so the resonant frequency of the inductor coil is increased to increase the normal working range of the fast temperature measurement.
  • Reducing the number of turns of the inductor coil can increase its resonant frequency, but at the same time reduce the distributed capacitance and inductance of the coil, and reduce the response of the induced signal. Therefore, in the case of ensuring the size of the output signal, a single layer coil can be used simultaneously. Resonant frequency and the amplitude of the induced signal.
  • the single-layer coil has a high resonance frequency, but the response is small, susceptible to environmental noise, and the signal-to-noise ratio is relatively low, which is inconvenient for the extraction of useful signals.
  • a high-speed instrumentation amplifier is used to differentially amplify the two signals, which can better suppress common-mode interference and increase the signal-to-noise ratio.
  • high-speed data acquisition devices are also used.
  • a magnetization change signal of the ferromagnetic particle reagent in the region to be tested is collected. Without a heat source, The output signals of the system are all circuit noise and interference in space.
  • the heat source When the temperature starts to change, the heat source generates a short time ⁇ t heat change on the ferromagnetic particle reagent, and the magnetization intensity signal of the ferromagnetic particle is collected by the inductor ⁇ , and the coil
  • the measurement signal of ⁇ is collected by a data acquisition card after being subjected to a differential amplification circuit, and then stored in a computer for subsequent data processing to obtain a magnetization change-time curve and a response signal waveform of the ferromagnetic particles, and each magnetization change is detected.
  • Reducing the amplitude A of the acquired signal to the induced electromotive force ⁇ , ie ⁇ is the magnification of the conditioning circuit.
  • Faraday's law of electromagnetic induction Where ⁇ is the induced electromotive force, N is the number of turns of the inductor, ⁇ is the amount of flux change, and ⁇ t is the time taken to change.
  • the spontaneous magnetization change value ⁇ M of the ferromagnetic particles is obtained, and the edge-optimized median filtering is performed on the spontaneous magnetization change value ⁇ M, and the spontaneous magnetization change correction value ⁇ M c which attenuates the deviation due to the DC drift of the coil is obtained.
  • m( ⁇ ) [1-s ⁇ 3/2 -(1-s) ⁇ p ] 1/3
  • t n is the time of the nth sampling point
  • M(t 0 ) is calculated from the initial temperature
  • s is the parameter of the thermal demagnetization curve of the ferromagnetic material
  • the magnetization, T c is the Curie temperature of the ferromagnetic particles
  • A is the amplitude of the magnetization change signal after the temperature change detected by the coil
  • T 2 is the measured change temperature
  • a is the proportional coefficient of the magnetization change amount ⁇ B and the spontaneous magnetization ⁇ M
  • ⁇ is the detection circuit
  • N is the number of turns of the inductor
  • S is the internal area of the inductor
  • ⁇ t is the time of temperature change
  • s is ferromagnetic
  • T c is the Curie temperature of the ferromagnetic particles
  • M 1 is the ferromagnetic particle when the temperature is T 1 Initial spontaneous magnetization.
  • the change time of the rapid temperature change is ⁇ t, which can be directly measured by the detection system. If the temperature is changed multiple times, the temperature change is multiple times.
  • thermocouple As a thermocouple.
  • the temperature reference device is placed in the same temperature environment as the object to be tested.
  • a fiber laser or other heat source is used to provide a temperature change state (ie, a temperature change environment) with a length of time t (nanoseconds) and a power level of P.
  • the fiber laser used in the experiment can generate a pulsed laser beam with a power range of 0 to 20 W, a pulse width of 200 ns, a rise time of 130 ns, and a frequency of 23.3 kHz.
  • the output energy density is huge. Due to the Curie temperature of the ferromagnetic particles itself, the output is in an unfocused form.
  • the spot diameter is about 6 mm, and the surface to be measured can be uniformly heated.
  • the response waveform of a single laser pulse is shown in Fig. 5. This is detected by the photoelectric power diode.
  • the response waveform of the ferromagnetic particles detected by the detection coil for a single heat pulse is shown in Fig. 6. Comparing the two figures can be It can be seen that the rise time among them is substantially the same as the standard rise time of the laser output laser of 130 ns, that is, the detection system can clearly distinguish the temperature change of at least 130 ns.
  • the response waveform measured by the detection system is shown in Figure 7.
  • the total time range is 2ms. It can be seen that there are more than 20 laser pulse responses, and the amplitude of each response pulse can reflect the response.
  • the power of the laser pulse that is, the temperature change caused by the laser, the difference in the amplitude of the first and last response pulses is caused by the instability of the power when the laser is switched.
  • Figure 8 shows the temperature change measured by the corresponding thermocouple. It can be seen that the temperature has changed by about 0.03 °C, and the temperature change caused by each pulsed laser can not be resolved at all, but only the total temperature change of 1 ms is reflected.
  • FIG. 9 is a magnetic measurement temperature change after the response information measured by the detection system is analyzed by a signal processing algorithm
  • FIG. 10 is a comparison chart with the thermocouple measurement. It can be easily seen that the total temperature change values measured by the two are almost identical, but In the magnetic temperature measurement, the temperature change of each laser pulse can be clearly distinguished, that is, the magnetic measurement is far stronger than the thermocouple in temperature resolution and time resolution.
  • Figure 11 shows the error between the magnetic temperature measurement and the thermocouple temperature measurement. The maximum temperature error is 0.01 °C.

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  • General Physics & Mathematics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
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  • Measuring Magnetic Variables (AREA)

Abstract

一种直流激励磁场下的非侵入式快速温度变化测量方法，包括：（1）将铁磁性粒子置于待测对象处；（2）对所述铁磁性粒子所在区域施加直流磁场使所述铁磁性粒子达到饱和磁化状态；（3）获得待测对象在常温下的稳态温度T1，根据所述稳态温度T1计算出铁磁性粒子的初始自发磁化强度M1；（4）当待测对象发生温度变化后，测量铁磁性粒子在温度变化后的磁化强度变化信号的幅值A，根据所述磁化强度变化信号的幅值A计算得到变化后的温度T2；（5）根据变化后的温度T2以及稳态温度T1，计算得到温度变化值ΔT＝T2-T1。所述测量方法能够在非侵入的情况下实现快速精确的温度测量，由此解决测温速度慢、精度低的技术问题。

Description

一种直流激励磁场下的非侵入式快速温度变化的测量方法 【技术领域】
本发明属于快速精确测温技术领域，更具体地，涉及一种直流激励磁场下的非侵入式快速温度变化测量方法，更具体地说，涉及一种直流激励磁场下的基于铁磁性粒子饱和磁化强度-温度关系的非侵入式高时间和温度分辨率的温度测量方法。
【背景技术】
温度是自然界中物质最基本的物理量之一，温度的测量对认知自然界中物质的本质具有重要的意义。利用铁磁性粒子的快速测温方法，是一种全新的、非侵入式的、超快速的(纳秒级)、高精度的温度测量方法。它主要通过测量铁磁性粒子的变化磁化强度，通过一定的模型关系计算出温度信息。铁磁性粒子温度测量方法具有非侵入与快速特性，使其在激光加热、金属快速凝固、发动机测温等领域具有广泛的应用前景。
随着工程技术的发展，带来了许多热作用时间极短、瞬时热流密度极高、温度变化极为迅速的热传导问题。传统的傅立叶定律不再适用于这些超常规、超急速的热传导。这些超常热传递条件下出现的不遵循傅立叶定律的热传导效应被人们称为非傅立叶导热效应。遗憾的是现有的技术和设备很难精确测量到如此短时间内的温度变化，利用铁磁性粒子进行非侵入式快速温度测量可以克服作用时间极短的问题，对此温度变化过程进行监控以便更好的研究。
航空航天领域经常会出现一些特殊测温问题，如飞机发动机燃烧室的火焰脉动温度的测量、热加工高温炉，高频加热焊接、铸造等的温度测量。采用传统的测温方法不能很好的解决这些问题，对此，测温装置应该具有响应速度快、测温精度高等特点。利用铁磁性粒子进行非侵入式快速温度 测量与温度传导相结合的方法也可以满足这种要求。因此非侵入式的快速精确测量技术，仍然是这些领域亟需解决的问题。
【发明内容】
针对现有技术的以上缺陷或改进需求，本发明提供了一种直流激励磁场下的基于铁磁性粒子饱和磁化强度-温度关系的非侵入式高时间和温度分辨率的温度测量方法，其目的在于非侵入的情况下实现快速精确的温度测量，由此解决测温速度慢、精度低等的技术问题。
为实现上述目的，本发明提供了一种直流激励磁场下的非侵入式快速温度变化测量方法，包括：
(1)将铁磁性粒子置于待测对象处；
(2)对所述铁磁性粒子所在区域施加直流磁场使所述铁磁性粒子达到饱和磁化状态；
(3)获得待测对象在常温下的稳态温度T1，根据所述稳态温度T1计算出铁磁性粒子的初始自发磁化强度M1；
(4)当待测对象发生温度变化后，测量铁磁性粒子在温度变化后的磁化强度变化信号的幅值A，根据所述磁化强度变化信号的幅值A计算得到变化后的温度T2；
(5)根据变化后的温度T2以及稳态温度T1，计算得到温度变化值ΔT＝T2-T1。
在本发明的一个实施例中，所述步骤(1)具体为：
将铁磁性粒子置于待测对象内部或涂覆于待测对象表面。
在本发明的一个实施例中，所述步骤(3)具体为：
使用热电偶或者光纤温度传感器获得待测对象常温下的稳态温度T1，根据铁磁性粒子的“饱和磁化强度-温度曲线”，计算出温度为T1时铁磁性粒子的初始自发磁化强度M1。
在本发明的一个实施例中，所述步骤(4)中根据所述磁化强度变化信 号的幅值A计算得到变化后的温度T2具体包括：
根据所述磁化强度变化信号的幅值A与变化后的温度T2之间的关系：
Figure PCTCN2014086283-appb-000001
利用磁化强度变化信号的幅值A计算得到变化后的温度T2；
其中：a是磁化强度变化量ΔB与自发磁化强度ΔM的比例系数，β是检测电路的放大倍数，N是电感线圈的匝数，S是电感线圈的内部面积，Δt是温度变化的时间，M(T＝0)是铁磁性粒子在绝对零度时的自发磁化强度，s为铁磁性材料热退磁曲线的参数，Tc为铁磁性粒子的居里温度，M(T＝0)和Tc对于某一确定铁磁性粒子材料其为一确定值，M1为温度为T1时铁磁性粒子的初始自发磁化强度。
在本发明的一个实施例中，所述步骤(4)中测量铁磁性粒子在温度变化后的磁化强度变化信号的幅值A，具体包括：
利用两个相同的单层线圈作为传感器，来检测待测区域内的铁磁性粒子的磁化强度变化信号，其中一个电感线圈α作为探测线圈，将待测对象包含于其中，使线圈可以检测到待测对象所有的磁感应强度变化信号，另一个电感线圈γ置于直流激励磁场中的对称位置作为参考线圈，它并不接收待测对象的感应信号，只接收环境中的噪声；
通过电感线圈α采集铁磁性粒子变化的磁化强度信号，与线圈γ的测量信号经过差分放大等调理电路，检测出每次的磁化强度变化信号通过处理电路后的输出幅值A。
总体而言，通过本发明所构思的以上技术方案与现有技术相比，具有以下有益效果：
1，通过本发明方法能够实现非侵入式测量，侵入式测温方法简单，便于直接实时高精度地监控温度，但创伤性较大，探针容易改变或者干扰被测物的性质；而非侵入式温度测量可以在几乎与被测对象物理隔离的情况 下，同时可以提供高精度的温度测量。
2，本发明方法的测量速度快：现有技术都不能满足微秒级以下温度测量，由于铁磁性粒子自发磁化强度随温度的变化的理论迟滞非常小，在10皮秒左右，所以对于此时间尺度下的传热学温度变化，都可以实现温度测量。
3，本发明方法的测量精度高：由于该测量方法的测量信号对应的是磁化强度的变化量，在求解温度的过程中，积分运算可以良好的抑制测量过程中的噪声，使该方法可以获得更高的温度分辨率。
【附图说明】
图1是本发明快速温度变化的测量方法流程图；
图2是本发明一实施例中铁磁性粒子饱和磁化强度-温度曲线图；
图3是本发明一实施例中电感线圈在高频下的等效模型；
图4是本发明一实施例中电感线圈在高频等效模型的幅频响应；
图5是本发明一实施例中光电功率二极管测量的单个激光脉冲响应；
图6是本发明一实施例中由线圈检测到的单个热脉冲响应波形图；
图7是本发明一实施例中由线圈检测到的1ms热变化响应波形图；
图8是本发明一实施例中由热电偶检测到的1ms热变化的温度图；
图9是本发明一实施例中由本发明方法所测量计算出的1ms温度图；
图10是通过本发明方法与热电偶测得的1ms温度对比图；
图11是通过本发明方法与热电偶测得的1ms温度误差图。
【具体实施方式】
为了使本发明的目的、技术方案及优点更加清楚明白，以下结合附图及实施例，对本发明进行进一步详细说明。应当理解，此处所描述的具体实施例仅仅用以解释本发明，并不用于限定本发明。此外，下面所描述的本发明各个实施方式中所涉及到的技术特征只要彼此之间未构成冲突就可以相互组合。
为了更好地说明本发明，首先对铁磁性粒子的温度测量原理进行简要介绍。
铁磁性粒子的粒径在减小到一定程度后，其铁磁性会转换为顺磁性。当粒子呈顺磁性时，其磁性特性由郎之万函数进行描述：
Figure PCTCN2014086283-appb-000002
其中，MS为磁纳米粒子的饱和磁矩，m为磁纳米粒子的平均磁矩，φ为磁纳米粒子的质量(磁纳米粒子的个数)，k为玻尔兹曼常数，H为外加激励磁场，T为绝对温度。可以对郎之万函数进行泰勒展开，在交流模型下，通过对谐波的测量对温度进行求解。但如果要进行高时间分辨率的测量，需要对顺磁粒子的交流激励磁场在不衰减磁场强度的前提下，频率足够高(如GHz)，这是难以实现的；而如果使用直流模型，顺磁粒子的响应是非常微弱，难以检测的；当粒子呈铁磁性时，其自发磁化强度与温度具有固定的关系，可以用m(τ)方程进行描述，自发磁化强度随温度的变化不存在时间迟滞，因此，选用铁磁性粒子作为温度敏感元件可以满足高时间分辨率温度测量的要求。
对于铁磁性粒子，其宏观磁化强度由其内部磁畴自发磁化强度分布构成，可以用以下公式描述：
Figure PCTCN2014086283-appb-000003
其中θi为第i个自发磁化强度与外场的夹角，Ms是自发磁化强度。
如果利用剩余磁化强度与温度的关系来进行温度测量，则对于不同晶系的晶体而言，剩余磁化强度和自发磁化强度的关系如下表所示：
单轴晶系的多晶体 Mr＝0.5Ms
三轴晶系的多晶体(K1>0) Mr＝0.832Ms
四轴晶系的多晶体(K1<0) Mr＝0.866Ms
上述剩余磁化强度是在饱和磁化强度状态下将激励磁场缓慢减小至0时得到，在实际工作状态下，多晶体会工作在第二象限的退磁曲线上，这 样使得剩余磁化强度与温度的关系更加复杂；而在饱和磁场下，自发磁化强度的方向都指向外场方向，此时宏观的磁化强度就是自发磁化强度的线性叠加，即：M＝Ms。因此，在进行高时间分辨率温度测量时，首先对铁磁性粒子施加一个外磁场，使之达到饱和，然后在通过再测量由于温度变化带来的磁响应，从而得到温度变化。
自发磁化强度Ms是铁磁性物质最基本的性质，人们在上个世纪耗费了很多精力在理论描述自发磁化强渡Ms关于温度的函数，温度范围在绝对零度到居里温度之间。现在，只能解决评估T＝0时的饱和磁化强度0<τ<1的问题，即基于密度泛函理论计算出的M0与实际实验得到的M0最匹配。还有一些采用基于经典海森堡模型的密度泛函理论与郎之万的旋转动力学理论计算距离温度Tc的研究。经典的(s＝∞)近似方法也被证明不适用，特别是对于居里温度Tc的计算。对于m(τ)方程，在半个世纪以来，还没有一个完全基于实验的m(τ)方程可以有效的描述所有的铁磁性物质(即相应状态定律)。但是一个基于分子场的理论对此作出了解释：m(τ)仅仅依赖于一个无量纲参数。
以往，除了在τ→0与τ→1时，还没有一个一般的解析表达式在分子近似场上来描述m(τ)方程，但是最近发表了一个由两个或三个简单能量定理推出的对于m(τ)方程在0<τ<1的精确表达式，即m(τ)＝[1-sτ3/2-(1-s)τp]1/3，其中，m为归一化自发磁化强度
Figure PCTCN2014086283-appb-000004
Ms为自发磁化强度，M0为温度在绝对零度时的自发磁化强度，即M0＝Ms(T＝0)，τ为归一化温度
Figure PCTCN2014086283-appb-000005
Tc为居里温度，s和p为参数系数，p>3/2，s>0。此方程在低温区域遵循Bloch的3/2能量定律，由Heisenberg模型的临界状态可推知，当τ→0时，
Figure PCTCN2014086283-appb-000006
而在临界区，即τ→1时，m≈(1-τ)1/3。
基于上述技术思路，本发明提出了一种直流激励磁场下的基于铁磁性 粒子饱和磁化强度-温度关系的非侵入式高时间和温度分辨率的温度测量方法，如图1所示，所述方法具体为：
(1)将铁磁性粒子置于待测对象处；
将少量铁磁性粒子通过一定方法置于待测对象内部或涂覆于待测对象表面，这样不会影响待测对象的外观与正常工作状态。
(2)对所述铁磁性粒子所在区域施加直流磁场使所述铁磁性粒子达到饱和磁化状态；
向铁磁性粒子所在区域施加恒定直流磁场Hdc＝b使其达到饱和磁化状态，针对不同材料，使其饱和磁化的外加直流激励磁场的幅值大小不同。
(3)获得待测对象在常温下的稳态温度T1，根据所述稳态温度T1计算出铁磁性粒子的初始自发磁化强度M1；
使用热电偶或者光纤温度传感器等设备获得待测对象常温下的稳态温度T1，铁磁性粒子的“饱和磁化强度-温度曲线”如图2所示，在铁磁性粒子被饱和磁化的情况下，其自发磁化强度与温度一一对应，所以可以计算出温度为T1时铁磁性粒子的初始自发磁化强度M1。
(4)当待测对象发生温度变化后，测量铁磁性粒子在温度变化后的磁化强度变化信号的幅值A，根据所述磁化强度变化信号的幅值A计算得到变化后的温度T2；
当粒子呈铁磁性时，其自发磁化强度与温度具有固定的关系，即m(τ)方程，m(τ)＝[1-sτ3/2-(1-s)τp]1/3，求解相关方程即可确定待测对象温度T，其中，m为归一化自发磁化强度
Figure PCTCN2014086283-appb-000007
Ms为自发磁化强度，M0为温度在绝对零度时的自发磁化强度，即M0＝Ms(T＝0)，τ为归一化温度
Figure PCTCN2014086283-appb-000008
Tc为居里温度，s和p为参数系数，p>3/2，s>0。此方程在低温区域遵循Bloch的3/2能量定律，由Heisenberg模型的临界状态可推知，当τ→0时，
Figure PCTCN2014086283-appb-000009
而在临界区，即τ→1时，m≈(1-τ)1/3。
所以利用温度变化后的自发磁化强度M2，即可计算出变化后的温度T2，但是M2不能直接检测到，要通过检测出磁化强度变化信号的幅值A与相应的变化时间Δt，从而推导出M2。
快速温度测量体现在时间分辨率上，在待测对象上施加纳秒级变化时长的温度变化，然后通过检测系统检测其响应信号的幅值和持续时间。
利用两个相同的单层线圈作为传感器，来检测待测区域内的铁磁性粒子的磁化强度变化信号。其中一个电感线圈α作为探测线圈，将待测对象包含于其中，使线圈可以检测到待测对象所有的磁感应强度变化信号，另一个电感线圈γ置于直流激励磁场中的对称位置作为参考线圈，它并不接收待测对象的感应信号，只接收环境中的噪声。
电感线圈的高频等效模型如图3示，即可把电感线圈看作电感与电阻串联后，与一个电容并联，其传递函数为
Figure PCTCN2014086283-appb-000010
现给定参数为R＝5Ω，L＝800μH，C＝20pF的电感线圈，幅频响应如图4所示，其谐振频率在1.2MHz左右，对于快速温度测量，特别是变化时间在1us以下，即频率特征在1MHz以上的温度变化信号产生不可避免的干扰，所以要提高电感线圈谐振频率来增大快速测温的正常工作范围。降低电感线圈的匝数可以增大其谐振频率，但是会同时减小线圈的分布电容以及电感，而使感应信号响应减小，所以在保证输出信号大小的情况下，使用单层线圈可以同时满足谐振频率与感应信号幅值的要求。
单层线圈谐振频率高，但是响应较小，易受环境噪声影响，信噪比较低，不便于有用信号的提取。在这里使用高速的仪表放大器，将两个信号进行差分放大，可以较好的抑制共模干扰，增大信噪比，相应的也要使用高速数据采集装置。
采集待测区域铁磁性粒子试剂的磁化强度变化信号。无热源情况下， 系统输出信号全部为电路噪声与空间中的干扰，开始变温时，热源在铁磁性粒子试剂上产生1次短时间Δt的热量变化，通过电感线圈α采集铁磁性粒子变化的磁化强度信号，与线圈γ的测量信号经过差分放大等调理电路后被数据采集卡采集并存储于计算机以便后续的数据处理，获得铁磁性粒子的磁化强度变化-时间曲线和响应信号波形，检测出每次的磁化强度变化信号通过处理电路后的输出幅值A与相应的变化时间Δt。
将所采集信号的幅值A还原为感应电动势ε，即
Figure PCTCN2014086283-appb-000011
β是调理电路的放大倍数。根据法拉第电磁感应定律
Figure PCTCN2014086283-appb-000012
其中，ε为感应电动势，N为电感线圈的匝数，ΔΦ是磁通变化量，Δt是发生变化所用时间。可以计算出变化的磁通量ΔΦ，又ΔΦ＝ΔB*S，ΔB＝a*ΔM其中，ΔB是磁化强度变化量，S是面积，a是比例系数，ΔM是自发磁化强渡变化量。进而得到铁磁性粒子的自发磁化强度变化值ΔM，对该自发磁化强度变化值ΔM进行边缘优化的中值滤波，得到减弱由于线圈直流漂移而导致的偏离的自发磁化强度变化修正值ΔMc，得到铁磁性粒子自发磁化强度随温度变化后的瞬态值M2＝M1+ΔMc。
进而根据m(τ)方程，m(τ)＝[1-sτ3/2-(1-s)τp]1/3，推出关系式
Figure PCTCN2014086283-appb-000013
反演得到温度值T2，变化的温度ΔT＝T2-T1。其中tn是第n个采样点的时间，M(t0)由初始温度计算得到，s为铁磁性材料热退磁曲线的参数，M(T＝0)是铁磁性粒子在绝对零度时的自发磁化强度，Tc为铁磁性粒子的居里温度，M(T＝0)和Tc对于某一确定材料其为一确定值。所以推出M2与T2的关系式
Figure PCTCN2014086283-appb-000014
综合以上推导，可以推变化温度与检测信号幅值关系式，
Figure PCTCN2014086283-appb-000015
其中A是线圈检测到的温度变化后的磁化强度变化信号的幅值，T2是所测的变化后的温度，a是磁化强度变化量ΔB与自发磁化强度ΔM的比例系数，β是检测电路的放大倍数，N是电感线圈的匝数，S是电感线圈的内部面积，Δt是温度变化的时间，M(T＝0)是铁磁性粒子在绝对零度时的自发磁化强度，s为铁磁性材料热退磁曲线的参数，Tc为铁磁性粒子的居里温度，M(T＝0)和Tc对于某一确定材料其为一确定值，M1为温度为T1时铁磁性粒子的初始自发磁化强度。
(5)根据变化后的温度T2以及稳态温度T1，计算得到温度变化值ΔT＝T2-T1。
快速变温的变化时间为Δt可以由检测系统直接测量得到，若多次变温，则温度变化为多次叠加。
在实验测量中，由于自然环境中少有纳秒级或以下的温度变化情况，所以在工程上使用光纤激光器产生热脉冲击打于待测对象上，来产生快速温度变化，同时使用热电偶作为温度参照设备与待测对象置于相同的温度环境中。
使用光纤激光器或其他热源提供温度变化状态(即变温环境)，时间长度为t(纳秒级)，功率大小为P。
实验所用光纤激光器可以产生脉冲激光束，功率范围0～20W，脉冲宽度200ns，上升时间130ns，频率23.3kHz。激光器通过透镜聚焦输出时，输出能量密度巨大，由于铁磁性粒子本身居里温度所限，所以采用非聚焦形式输出，光斑直径约6mm，可以对待测对象进行表面均匀加热。
单次激光脉冲的响应波形如图5所示，这是由光电功率二极管检测得到的，由探测线圈检测到的铁磁性粒子对于单个热脉冲的响应波形如图6所示，比较两个图可以看到，它们中的上升时间与激光器输出激光的标准上升时间130ns基本相同，即检测系统可以清晰分辨至少130ns的温度变化。
对于1ms的连续激光变温，检测系统所测响应波形如图7所示，总时间范围是2ms，可以看到其中有二十多道激光脉冲响应，每个响应脉冲的幅值即可反映响应的激光脉冲的功率大小，也就是激光所导致的变温大小，首尾几个响应脉冲幅值差异是激光器开关时功率不稳定造成的。图8是对应的热电偶测量得到的温度变化，可以看到温度变化了约0.03℃，且完全不能分辨出每一次脉冲激光带来的温度变化，而只能反映出1ms时间的总温度变化。图9是检测系统测得的响应信息通过信号处理算法解析后的磁测量温度变化，图10是其与热电偶测量的对比图，可以轻易看出二者测量的总温度变化值几乎一致，但是磁测温中可以清晰分辨每一次激光脉冲的温度变化情况，即磁测量在温度分辨率以及时间分辨率上远强于热电偶。图11是二者磁测温与热电偶测温的误差，最大温度误差在0.01℃。
本领域的技术人员容易理解，以上所述仅为本发明的较佳实施例而已，并不用以限制本发明，凡在本发明的精神和原则之内所作的任何修改、等同替换和改进等，均应包含在本发明的保护范围之内。

Claims (6)

  1. 一种直流激励磁场下的非侵入式快速温度变化测量方法，其特征在于，所述方法包括：
    (1)将铁磁性粒子置于待测对象处；
    (2)对所述铁磁性粒子所在区域施加直流磁场使所述铁磁性粒子达到饱和磁化状态；
    (3)获得待测对象在常温下的稳态温度T1，根据所述稳态温度T1计算出铁磁性粒子的初始自发磁化强度M1；
    (4)当待测对象发生温度变化后，测量铁磁性粒子在温度变化后的磁化强度变化信号的幅值A，根据所述磁化强度变化信号的幅值A计算得到变化后的温度T2；
    (5)根据变化后的温度T2以及稳态温度T1，计算得到温度变化值ΔT＝T2-T1。
  2. 如权利要求1所述的方法，其特征在于，所述步骤(1)具体为：
    将铁磁性粒子置于待测对象内部或涂覆于待测对象表面。
  3. 如权利要求1或所述的方法，其特征在于，所述步骤(2)具体为：所述步骤(2)中采用亥姆霍茨线圈对所述铁磁性粒子所在区域施加直流磁场。
  4. 如权利要求1或2所述的方法，其特征在于，所述步骤(3)具体为：
    使用热电偶或者光纤温度传感器获得待测对象常温下的稳态温度T1，根据铁磁性粒子的“饱和磁化强度-温度曲线”，计算出温度为T1时铁磁性粒子的初始自发磁化强度M1。
  5. 如权利要求1或2所述的方法，其特征在于，所述步骤(4)中根据所述磁化强度变化信号的幅值A计算得到变化后的温度T2具体包括：
    根据所述磁化强度变化信号的幅值A与变化后的温度T2之间的关系：
    Figure PCTCN2014086283-appb-100001
    利用磁化强度变化信号的幅值A计算得到变化后的温度T2；
    其中：a是磁化强度变化量ΔB与自发磁化强度ΔM的比例系数，β是检测电路的放大倍数，N是电感线圈的匝数，S是电感线圈的内部面积，Δt是温度变化的时间，M(T＝0)是铁磁性粒子在绝对零度时的自发磁化强度，s为铁磁性材料热退磁曲线的参数，Tc为铁磁性粒子的居里温度，M(T＝0)和Tc对于某一确定铁磁性粒子材料其为一确定值，M1为温度为T1时铁磁性粒子的初始自发磁化强度。
  6. 如权利要求1或2所述的方法，其特征在于，所述步骤(4)中测量铁磁性粒子在温度变化后的磁化强度变化信号的幅值A，具体包括：
    利用两个相同的单层线圈作为传感器，来检测待测区域内的铁磁性粒子的磁化强度变化信号，其中一个电感线圈α作为探测线圈，将待测对象包含于其中，使线圈可以检测到待测对象所有的磁感应强度变化信号，另一个电感线圈γ置于直流激励磁场中的对称位置作为参考线圈，它并不接收待测对象的感应信号，只接收环境中的噪声；
    通过电感线圈α采集铁磁性粒子变化的磁化强度信号，与线圈γ的测量信号经过差分放大等调理电路，检测出磁化强度变化信号通过处理电路后的输出幅值A。
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