CN113820033B - A temperature measurement method based on ferromagnetic resonance frequency - Google Patents

Abstract

The invention relates to a temperature measurement method based on ferromagnetic resonance frequency, comprising the following steps: applying a static magnetic field to a measured object containing a ferromagnetic nanoparticle solution to enable the ferromagnetic nanoparticle to be saturated and magnetized; applying an alternating pulsed excitation magnetic field in a direction perpendicular to said static magnetic fieldThe method comprises the steps of carrying out a first treatment on the surface of the Determining the ferromagnetic resonance frequency of the ferromagnetic nano particles when the ferromagnetic nano particles generate ferromagnetic resonance through a sweep frequency method; and calculating the temperature of the measured object according to the determined ferromagnetic resonance frequency, wherein the calculation formula is as follows:

according to the method provided by the invention, the temperature is measured through the constructed relation model of the ferromagnetic resonance frequency and the temperature, the model is simple in form, the measuring method is simple and convenient, the rapid and convenient measurement of the internal temperature of the measured object can be realized, and the measuring accuracy is very high.

Description

A temperature measurement method based on ferromagnetic resonance frequency

technical field

The invention relates to the technical field of temperature measurement, in particular to a temperature measurement method using ferromagnetic nanoparticles.

Background technique

Temperature is an important indicator reflecting the internal state of the measured object, and its accurate and fast measurement is very important in many cases. Temperature measurement methods can generally be divided into contact temperature measurement and non-contact temperature measurement. Compared with contact temperature measurement, non-contact temperature measurement can obtain more accurate temperature measurement because it will not destroy the temperature field of the measured object. result.

Due to their unique magnetic properties, ferromagnetic nanoparticles have been used in temperature measurement in many fields and occasions, and because ferromagnetic nanoparticles are nanoscale, they are suitable for non-contact temperature measurement. The principle is to add ferromagnetic nanoparticles into the measured object, such as injecting into the human body or inside the material or coating on the surface of the material, and then calculate the measured object’s temperature by measuring a certain physical quantity of the ferromagnetic nanoparticles and based on the established mathematical model. temperature information. The existing non-contact temperature measurement methods of ferromagnetic nanoparticles mainly include the following:

1. The temperature is measured based on the temperature dependence of the reciprocal of the magnetic susceptibility of ferromagnetic nanoparticles magnetized under a static magnetic field, but the measurement time of this method is long, which is difficult to meet the application requirements of rapid temperature measurement.

2. Temperature measurement is based on the temperature dependence of the magnetization of ferromagnetic nanoparticles excited by a single-frequency AC magnetic field, but this method needs to measure the higher harmonics of the magnetization response of ferromagnetic nanoparticles, which increases the difficulty of measurement.

3. Temperature measurement is based on the relationship between the homogeneous or even harmonic amplitude of the magnetization response of ferromagnetic nanoparticles and temperature, but the corresponding temperature measurement model is complex, which increases the complexity of measurement and processing.

Contents of the invention

In order to realize the simple and fast non-contact temperature measurement based on ferromagnetic nanoparticles, the invention provides a temperature measurement method based on ferromagnetic resonance frequency.

The temperature measurement method based on the ferromagnetic resonance frequency provided by the present invention includes:

Apply a static magnetic field to the measured object containing ferromagnetic nanoparticles to saturate and magnetize the ferromagnetic nanoparticles;

applying an alternating pulse excitation magnetic field along the vertical direction of the static magnetic field;

Determine the ferromagnetic resonance frequency when the ferromagnetic nanoparticles undergo ferromagnetic resonance by frequency sweep method;

Calculate the temperature of the measured object according to the determined ferromagnetic resonance frequency, the calculation formula is as follows:

Among them, f is the ferromagnetic resonance frequency in GHz, γ _e is the magnetic gyro ratio of electrons in GHz/T, k _B is Boltzmann's constant in J/K, and M is the ferromagnetic nanometer The macro-magnetization of the uncoupled free electron spins after the particles are magnetized, in A/m, θ is the nutation angle of the macro-magnetization, in rad, T is the temperature of the measured object, in is K;

The macroscopic magnetization is calculated by the following formula:

Wherein, B is the magnetic induction intensity inside the ferromagnetic nanoparticles when ferromagnetic resonance occurs, calculated by the formula 2πf= _γeB , and the unit is T, _{and H0} is the magnetic field intensity of the static magnetic field, and the unit is A/m , μ ₀ is the vacuum permeability, the unit is Tm/A.

Optionally, the nutation angle is calculated by the following formula:

θ=γ _e B ₁ T _p ,

Wherein, B ₁ is the amplitude of the magnetic induction intensity of the alternating pulse excitation magnetic field, and the unit is T, and T _p is the pulse width of the alternating pulse excitation magnetic field, and the unit is ps.

Optionally, permanent magnets, Helmholtz coils or electromagnets are used for applying the static magnetic field.

Optionally, the alternating pulse excitation magnetic field is a pulsed microwave field or a pulsed radio frequency field.

The above-mentioned temperature measurement method based on ferromagnetic resonance frequency provided by the present invention measures temperature through the constructed relationship model between ferromagnetic resonance frequency and temperature. Quick and easy measurement with high measurement accuracy.

According to the following detailed description of specific embodiments of the present invention in conjunction with the accompanying drawings, those skilled in the art will be more aware of the above and other objects, advantages and features of the present invention.

Description of drawings

Hereinafter, some specific embodiments of the present invention will be described in detail by way of illustration and not limitation with reference to the accompanying drawings. The same reference numerals in the drawings designate the same or similar parts or parts. Those skilled in the art will appreciate that the drawings are not necessarily drawn to scale. In the attached picture:

Fig. 1 is a schematic flow chart of a temperature measurement method based on a ferromagnetic resonance frequency in one embodiment of the present invention;

Fig. 2 is a schematic structural diagram of a temperature measuring device in one embodiment of the present invention;

Fig. 3 is in a simulation example of the present invention, the variation curve of ferromagnetic resonance frequency with temperature;

Fig. 4 is in the above-mentioned simulation example, the _fT2 curve and the comparison chart between the actual temperature inverted by the measured frequency;

Figure 5 is a diagram of the measurement error changing with temperature in the above simulation example.

Detailed ways

In order to enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. It should be noted that, in the case of no conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other.

Existing studies have proved that the ferromagnetic resonance frequency of ferromagnetic nanoparticles is temperature-dependent, and the ferromagnetic resonance frequency is also related to the external magnetic field. Based on this, the present invention starts from the free energy of the atomic spin system under the condition of an external static magnetic field, and builds a relationship model between ferromagnetic resonance frequency and temperature through analysis, derivation and testing. The model has a simple form and a simple and convenient measurement method. , can realize the quick and easy measurement of the internal temperature of the measured object, and has high measurement accuracy.

A specific embodiment of the ferromagnetic resonance frequency-based temperature measurement method of the present invention will be described in detail below with reference to FIGS. 1-5 . Figure 1 shows the steps of an example of the method, and Figure 2 shows the temperature measuring equipment used in the above example of the method. The temperature measuring equipment includes an electromagnet 1, a microwave source 2, a resonant cavity 3, a microwave circulator 4, a wave detector 5, a lock-in amplifier 6 and a computer processing system 7.

As shown in Figure 1, the method includes:

S01: Apply a static magnetic field to the measured object containing ferromagnetic nanoparticles to saturate and magnetize the ferromagnetic nanoparticles.

As shown in FIG. 2 , in this embodiment, the electromagnet 1 is selected as the static magnetic field applying device. In other embodiments, the static magnetic field applying device can also be a permanent magnet or a Helmholtz coil. Ferromagnetic material nanoparticles with a particle size of 5-10 nm can be selected, and the ferromagnetic material is, for example, ferrite materials such as Fe ₃ O ₄ . The method of adding ferromagnetic nanoparticles to the measured object depends on the actual situation. For example, when measuring the temperature of the human body, ferromagnetic nanoparticles can be wrapped with organic molecules to make a contrast agent and injected into the human body subcutaneously; another example is to measure the temperature of a certain material When , ferromagnetic nanoparticles can be coated on the surface of the material to be tested.

S02: Apply an alternating pulse excitation magnetic field along the vertical direction of the static magnetic field.

The alternating pulse excitation magnetic field is generated by an electromagnetic wave source. In this embodiment, the alternating pulse excitation magnetic field is a pulse microwave field, which is generated by the microwave source 2 . The resonant cavity 3 is placed between the two poles of the electromagnet 1 , and the measured object is placed in the resonant cavity 3 . The pulsed microwave generated by the microwave source 2 is applied to the measured object in the direction perpendicular to the static magnetic field through the microwave circulator 4, that is, the direction of the alternating pulse excitation magnetic field is perpendicular to the direction of the static magnetic field. In other embodiments, a pulsed radio frequency field may be used instead of a pulsed microwave field as the alternating pulsed excitation magnetic field.

S03: Determine the ferromagnetic resonance frequency when the ferromagnetic nanoparticles undergo ferromagnetic resonance by frequency sweep method.

Specifically, in this step, when the applied static magnetic field remains constant, the microwave frequency is changed, and the reflected power in the resonant cavity 3 enters the detector 5 through the microwave circulator 4. When ferromagnetic resonance occurs, the ferromagnetic The nanoparticles will absorb part of the microwave power, resulting in a decrease in the reflected power. The detector 5 detects the amplitude signal of the reflected power corresponding to each microwave frequency during the frequency scanning process, and converts it into a DC voltage signal. After the DC voltage signal is amplified by the lock-in amplifier 6, it is recorded in the computer processing system 7. Because when ferromagnetic resonance occurs, the absorption of microwave reaches the maximum, so when the amplitude of DC voltage drops to the minimum, the corresponding microwave frequency is the ferromagnetic resonance frequency. Since the detection of the ferromagnetic resonance frequency by the scanning method belongs to the prior art, it is only an example and a brief description here.

S04: Calculate the temperature of the measured object according to the determined ferromagnetic resonance frequency, the calculation formula is as follows:

Among them, f is the ferromagnetic resonance frequency in GHz, γ _e is the magnetic gyro ratio of electrons in GHz/T, k _B is the Boltzmann constant in J/K, M is the ferromagnetic nanoparticle The macroscopic magnetization of the uncoupled free electron spins after magnetization is calculated by ferromagnetic resonance frequency, and the unit is A/m. θ is the nutation angle of the macroscopic magnetization. Value and pulse width calculated in rad (radians). It can be seen that the above parameters are all known, and the absolute temperature T inside the measured object in K can be calculated through the above formula.

The macroscopic magnetization is calculated by the following formula:

Among them, B is the magnetic induction intensity inside the ferromagnetic nanoparticles when the ferromagnetic resonance occurs, which is determined by the external static magnetic field and the alternating pulse excitation magnetic field, and can be calculated by the ferromagnetic resonance condition, that is, 2πf=γ _e B, and the unit is T, H ₀ is the magnetic field strength of the external static magnetic field, the unit is A/m, μ ₀ is the vacuum permeability, the unit is Tm/A.

In this embodiment, the nutation angle is calculated by the following formula:

θ=γ _e B ₁ T _p

Among them, B ₁ is the amplitude of the magnetic induction intensity of the alternating pulse excitation magnetic field, and the unit is T, and T _p is the pulse width of the alternating pulse excitation magnetic field, and the unit is ps (picosecond).

Simulation example

In order to verify the feasibility of the above-mentioned temperature measurement method based on ferromagnetic resonance frequency, the inventor designed a simulation experiment according to the content of the invention to repeatedly verify the method. A specific example is used to illustrate:

The measured object added with ferromagnetic nanoparticles is placed in a static magnetic field with a magnetic induction intensity of μ ₀ H ₀ =2T.

A microwave pulse excitation with a certain magnetic induction intensity amplitude μ ₀ H ₁ =10 ^-4 T is generated by a microwave source, and the pulse width T _p is controlled at 1.5 ps. The microwave pulse excitation is applied in a direction perpendicular to the static magnetic field through a microwave circulator. Under the condition that the magnitude of the static magnetic field strength _H0 is constant, the microwave frequency f is constantly changed, and the resonant absorption signal is detected by the detector, and the ferromagnetic resonance frequency f of ferromagnetic nanoparticles is detected when ferromagnetic resonance occurs. The gyromagnetic ratio γ _e of the electron can be calculated by the following formula:

Wherein, g is the Landes factor, here g=2, m _e is the mass of the electron, e is the charge of the electron, here γ _e =1.76×10 ⁷ rad/(s·Oe)=176GHz/T.

Then take μ ₀ =1.26×10 ^-6 Tm/A to calculate the value of M.

Take k _B = 1.38×10 ^-23 J/K, θ is calculated from the amplitude of microwave magnetic induction intensity μ ₀ H ₁ and pulse width T _p , the temperature of the measured object is raised to 373K, then cooled naturally, and recorded by the temperature sensitive sensor in real time When the temperature T of the measured object drops by 5K, adjust the microwave frequency to make it reach ferromagnetic resonance, and record the ferromagnetic resonance frequency f until the temperature drops to 260K; The temperature T ₂ of each frequency, according to these obtained points, draw the curve of the ferromagnetic resonance frequency f with the temperature T, as shown in Figure 3, and the inverted fT ₂ curve, as shown in Figure 4, compare T ₂ with the standard temperature T For comparison, the error ε=|T ₂ -T| can be obtained, as shown in Figure 5, it can be seen that the absolute error of the model is less than 0.05K.

It can be seen from the above-mentioned embodiments and simulation examples provided by the present invention that the present invention provides a new idea and new method for non-contact temperature measurement using ferromagnetic nanoparticles. Compared with the previous temperature measurement model, the present invention starts from The temperature model established from the perspective of ferromagnetic resonance frequency is simple in form, and the temperature of the measured object can be calculated only by measuring the ferromagnetic resonance frequency. The measurement method is simple and easy to implement. It has been verified that the temperature measurement model adopted in the present invention has high temperature measurement accuracy, and has good anti-noise performance when the signal-to-noise ratio is above 90 decibels.

The above is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed in the present invention can easily think of changes or Replacement should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be determined by the protection scope of the claims.

Claims (4)

1. A method of temperature measurement based on ferromagnetic resonance frequency, comprising:

applying a static magnetic field to a measured object containing ferromagnetic nanoparticles to enable the ferromagnetic nanoparticles to be saturated and magnetized;

applying an alternating pulsed excitation magnetic field in a perpendicular direction to the static magnetic field;

determining the ferromagnetic resonance frequency of the ferromagnetic nano particles when the ferromagnetic nano particles generate ferromagnetic resonance through a sweep frequency method;

and calculating the temperature of the measured object according to the determined ferromagnetic resonance frequency, wherein the calculation formula is as follows:

wherein f is the ferromagnetic resonance frequency in GHz gamma _e Is the magnetic rotation ratio of electrons, and has the unit of GHz/T and k _B Is the Boltzmann constant, the unit is J/K, M is the macroscopic magnetization intensity of uncoupled free electron spin after the ferromagnetic nano-particles are magnetized, the unit is A/M, θ is the nutation angle of the macroscopic magnetization intensity, the unit is rad, T is the temperature of the measured object, and the unit is K;

the macroscopic magnetization is calculated from the following formula:

wherein B is the magnetic induction inside the ferromagnetic nanoparticle when ferromagnetic resonance occurs, and is represented by the formula 2pi f=γ _e B is calculated to be T, H ₀ Is the magnetic field intensity of the static magnetic field, the unit is A/m and mu ₀ Vacuum permeability in Tm/A.

2. The ferromagnetic resonance frequency based temperature measurement method of claim 1, wherein:

the nutation angle is calculated from the following formula:

θ＝γ _e B ₁ T _p ，

wherein B is ₁ Is the amplitude of the magnetic induction intensity of the alternating pulse excitation magnetic field, and the unit is T and T _p Is the pulse width of the alternating pulse excitation magnetic field, and the unit is ps.

3. The ferromagnetic resonance frequency based temperature measurement method of claim 1, wherein:

the static magnetic field is applied by a permanent magnet, a Helmholtz coil or an electromagnet.

4. The ferromagnetic resonance frequency based temperature measurement method of claim 1, wherein:

the alternating pulse excitation magnetic field is a pulse microwave field or a pulse radio frequency field.

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