Temperature measurement method and device based on faraday magneto-optical effect of magnetic nanoparticles

Abstract

The application discloses a temperature measuring method and device based on a Faraday magneto-optical effect of magnetic nanoparticles, and belongs to the technical field of nano material testing. The method comprises the following steps: placing a magnetic nanoparticle sample in a target area, and making the magnetic nanoparticles generate a magnetization response through an applied direct current excitation magnetic field; adopting a polarized light to irradiate the magnetic nanoparticles in the coaxial direction of the magnetic field, so that the Faraday magneto-optical effect occurs between the magnetic nanoparticles and the sample; taking a sample without adding magnetic nanoparticles as a control group, applying an excitation magnetic field with the same amplitude and opposite direction to the applied direct current excitation magnetic field to the sample, and detecting the emergent light; calculating the Faraday rotation angle generated by the magnetic nanoparticles according to the detected emergent light; and performing nonlinear fitting on the Faraday rotation angle generated by the magnetic nanoparticles and the applied direct current excitation magnetic field by using a Lenz function, so as to obtain the temperature of the magnetic nanoparticles in the target area. The application can realize remote and non-invasive in-vivo temperature measurement.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of nanomaterial testing, and more particularly relates to a temperature measurement method and device based on the Faraday magneto-optical effect of magnetic nanoparticles. BACKGROUND

[0002] Temperature is an important indicator reflecting the state of life activities. Cells can only maintain activity and normal metabolism at a suitable temperature. Meanwhile, temperature is a tool for describing physical phenomena, and its essence is the intensity of molecular or atomic motion. In addition, temperature is also a catalytic condition for chemical reactions, and elements have different chemical properties at different temperatures. Our daily life is closely related to temperature, so obtaining temperature information is a very worthy problem. At present, the main temperature measurement methods include thermometer, infrared imaging, thermochromic method, etc., but these methods can basically only reflect the surface temperature of an object, and it is difficult to obtain the internal temperature of the object without invasive, which has certain limitations.

[0003] The temperature measurement method based on the magnetization response of magnetic nanoparticles has been developed in the past decade. By injecting magnetic nanoparticles into the target area, the temperature information can be converted into the magnetization response of the particles under an external excitation magnetic field. According to Faraday's law of electromagnetic induction, the magnetization response of the magnetic nanoparticles is directly detected by using a detection coil or a magnetic resistance sensor, and the relationship between temperature and the magnetization response of the magnetic nanoparticles can be established to inversely calculate the temperature of the target area inside the object.

[0004] However, the magnetic nanoparticles are equivalent to a small magnetic dipole, and it is required that the effective area of the magnetic sensor is large enough or the distance between the magnetic nanoparticles and the sensor is very close to measure a signal with a high enough signal-to-noise ratio. Therefore, the signal coupling between the magnetic nanoparticles and the sensor is the bottleneck that limits the resolution of the temperature measurement of the magnetic nanoparticles. At the same time, directly measuring the magnetic signal will also be affected by electromagnetic interference, which will eventually bring errors to the temperature measurement. SUMMARY

[0005] In view of the above defects or improvement needs of the prior art, the present application provides a temperature measurement method and device based on the Faraday magneto-optical effect of magnetic nanoparticles, which aims to improve the accuracy of the temperature measurement of the magnetic nanoparticles.

[0006] To achieve the above-mentioned purpose, according to one aspect of the present application, a temperature measurement method based on the Faraday magneto-optical effect of magnetic nanoparticles is provided, comprising:

[0007] Placing a magnetic nanoparticle sample in a target area, and making the magnetic nanoparticles produce a magnetization response through an external direct-current excitation magnetic field;

[0008] Irradiating the magnetic nanoparticles with polarized light in the coaxial direction of the magnetic field to cause the Faraday magneto-optical effect with the sample.

[0009] The sample without adding magnetic nanoparticles is taken as a control group, an excitation magnetic field with the same amplitude and opposite direction of the applied DC excitation magnetic field is applied to the sample, and the outgoing light is detected;

[0010] The Faraday rotation angle generated by the magnetic nanoparticles is calculated according to the detected outgoing light;

[0011] The Faraday rotation angle generated by the magnetic nanoparticles is nonlinearly fitted with the applied DC excitation magnetic field by using the Lorentz function, and the temperature of the magnetic nanoparticles in the target region is obtained.

[0012] Further, the light intensity I out satisfies:

[0013] I out =I0cos 2 (θ S +α)

[0014] Where I0 is the light intensity of the incident light, alpha is the angle between the polarizer and the analyzer optical axis, theta S is the outgoing light polarization angle generated by the magnetic nanoparticles, and theta S =VLvM, V is the Verdet constant, L is the length of the light passing through the medium, and v is the exchange coefficient of the magnetization response M.

[0015] Further, the angle between the polarizer and the analyzer optical axis of the generated polarized light is 45°.

[0016] Further, the Faraday rotation angle theta S generated by the magnetic nanoparticles, the applied DC excitation magnetic field H and the temperature T satisfy the relationship:

[0017]

[0018] mu0 is the vacuum permeability, k B is the Boltzmann constant, N is the number of magnetic nanoparticles per unit volume, and m s is the saturation magnetic moment of the magnetic nanoparticles.

[0019] The application also provides a temperature measurement method based on the Faraday magneto-optical effect of magnetic nanoparticles, comprising:

[0020] Placing the magnetic nanoparticle sample in the target region, and generating a magnetization response of the magnetic nanoparticles by applying an external AC excitation magnetic field;

[0021] Irradiating the magnetic nanoparticles with polarized light in the coaxial direction of the magnetic field, generating a Faraday magneto-optical effect with the sample, and detecting the outgoing light;

[0022] According to the detected outgoing light, the Faraday rotation angle generated by the magnetic nano-particles is calculated.

[0023] The Faraday rotation angle generated by the sample is nonlinearly fitted with the applied excitation magnetic field by using the Langevin function, so that the temperature of the magnetic nano-particles in the target area is obtained.

[0024] The application further provides a temperature measuring device based on the Faraday magneto-optical effect of magnetic nano-particles, which comprises a laser, a polarizer, a first coil, a second coil, a detection polarizer, a photodiode and a fitting module.

[0025] The first coil is used for applying a direct-current excitation magnetic field to the magnetic nano-particle sample placed in the target area, so that the magnetic nano-particles generate a magnetization response.

[0026] The laser and the polarizer are used together for generating polarized light in the coaxial direction of the magnetic field, irradiating the magnetic nano-particles and generating the Faraday magneto-optical effect with the sample.

[0027] The second coil is used for applying an excitation magnetic field with the same magnitude and opposite direction to the control group as the applied direct-current excitation magnetic field; the control group is a sample without magnetic nano-particles, which is placed behind the magnetic nano-particle sample.

[0028] The detection polarizer and the photodiode are used together for detecting the outgoing light intensity through the control group.

[0029] The fitting module is used for calculating the Faraday rotation angle generated by the magnetic nano-particles according to the detected outgoing light, and nonlinearly fitting the Faraday rotation angle generated by the magnetic nano-particles with the applied direct-current excitation magnetic field by using the Langevin function, so that the temperature of the magnetic nano-particles in the target area is obtained.

[0030] The application further provides a temperature measuring device based on the Faraday magneto-optical effect of magnetic nano-particles, which comprises a laser, a polarizer, a third coil, a detection polarizer, a photodiode and a fitting module.

[0031] The laser and the polarizer are used together for generating polarized light in the coaxial direction of the magnetic field, irradiating the magnetic nano-particle sample and generating the Faraday magneto-optical effect with the sample.

[0032] The third coil is used for applying an alternating-current excitation magnetic field to the magnetic nano-particle sample placed in the target area, so that the magnetic nano-particles generate a magnetization response.

[0033] The detection polarizer and the photodiode are used together for detecting the outgoing light intensity through the sample.

[0034] The fitting module is used for calculating the Faraday rotation angle generated by the magnetic nano-particles according to the detected outgoing light; and the Faraday rotation angle generated by the sample is nonlinearly fitted with the applied excitation magnetic field by using the Larmor function to obtain the temperature of the magnetic nano-particles in the target region.

[0035] Compared with the prior art, the above technical scheme conceived by the present application can achieve the following beneficial effects.

[0036] The present application uses the Faraday magneto-optical effect to measure the temperature, can modulate the magnetic signal of the magnetic nano-particles to the deflection angle of the light, can realize the remote and non-invasive in-vivo temperature measurement, does not need to place the sensor very close to the target, avoids the influence of direct electromagnetic coupling on the signal detection; in addition, when the coil is used to directly detect the magnetic signal in the prior art, the temperature drift of the sensor is also serious, but the influence on the photoelectric detector is smaller, so the present application can make the accuracy of the temperature measurement result higher.

[0037] Specifically, the direct current excitation magnetic field is used, the direct current field is easier to generate, a strong direct current magnetic field can be generated by a permanent magnet or an electromagnet, the generated deflection angle can be larger, and a chopper or a photoelastic modulator and the like are easy to detect; the alternating current excitation magnetic field is used, the specific detection of the magnetic nano-particles can be realized by directly using high-order harmonics, a control group does not need to be set, the use range is more extensive, and the more the high-order harmonics of the outgoing light, the higher the fitting accuracy. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 is a schematic diagram of a Faraday magneto-optical effect temperature measurement device;

[0039] Figure 2 (a) is the Faraday rotation angle θ generated by the magnetic nano-particles at different temperatures S The simulation results change with the excitation magnetic field H; (b) is the measured temperature and the Larmor fitting temperature and the measurement error;

[0040] Figure 3 is the odd harmonic of the outgoing light intensity I out when the excitation magnetic field H=H0sin(ωt);

[0041] Figure 4 is the 1st, 3rd and 5th harmonics of I out change with the excitation magnetic field H at different temperatures. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is further described in detail below with reference to the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application. In addition, the technical features involved in the various embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0043] The method of the present application comprises the following steps:

[0044] S1. Place the magnetic nanoparticle sample in the target area, and generate a magnetization response M of the magnetic nanoparticles by applying a direct current excitation magnetic field.

[0045] S2. Use a laser plus polarizer to generate a linearly polarized light, and pass the light through the magnetic nanoparticle sample along the coaxial direction of the magnetic field to produce Faraday magneto-optical effect with the sample;

[0046] According to classical electron dynamics theory, the Faraday magneto-optical effect can be intuitively described as the relationship between the electrons in the medium and the applied excitation magnetic field H and the magnetization response M, and the corresponding Faraday rotation angle θ of the sample satisfies

[0047] θ = VL(H + vM)

[0048] Where V is the Verdet constant, L is the length of the light passing through the medium, and v is the exchange coefficient of the magnetization response M.

[0049] Due to the background of the solvent and the container, the Faraday rotation angle θ B = VLH is inevitably generated, when the magnetization response of the magnetic nanoparticles is small, the influence of θ B cannot be ignored, which will have a great influence on the detection result, and θ B is not convenient to measure directly, and the present application sets up a control group to offset it.

[0050] S3. Place a container containing the same solvent behind the sample as a control group, and apply an excitation magnetic field with the same amplitude as the applied excitation magnetic field H and opposite direction. When the light after passing through the sample is transmitted to the control group again, the rotation angle θ B = VLH generated by the solvent under the applied excitation magnetic field can be offset. At this time, the polarization angle θ S of the outgoing light is completely generated by the magnetic nanoparticles, and satisfies

[0051] θ S = θ - θ B = VLvM

[0052] S4. Detect the outgoing light using a polarizer, and according to Malus' law, the light intensity I out measured at the position of the photodiode satisfies,

[0053] I out = I0cos 2 (θ S + α)

[0054] where I0is the intensity of the incident light, and α is the angle between the optical axis of the polarizer and the analyzer. When α = 45°, it satisfies and since the deflection angle θ S << 1 produced by the magnetic nanoparticles on the incident light under the excitation magnetic field, it can be approximated as At this time, the detection sensitivity of the Faraday rotation angle θ S is the largest. Thus, by detecting the outgoing light with a photodiode, the Faraday rotation angle θ S produced by the sample can be calculated, and then the magnetization response M produced by the sample can be calculated.

[0055] A specific device schematic diagram can be shown as Figure 1 , in which a reversed Helmholtz coil is used to provide equal and opposite excitation magnetic fields for the magnetic nanoparticle sample and the control group.

[0056] Since the magnetic nanoparticles exhibit superparamagnetism after being subjected to an external excitation magnetic field, their magnetization response conforms to the Langevin function

[0057]

[0058] where μ0is the vacuum permeability, k B is the Boltzmann constant, N is the number of magnetic nanoparticles per unit volume, and m s is the saturation magnetic moment of the magnetic nanoparticles. Therefore

[0059]

[0060] S5. The Faraday rotation angle θ S measured for the sample and the external excitation magnetic field H are used to perform nonlinear fitting using the Langevin function, so as to calculate the temperature T of the target area magnetic nanoparticles; as shown in Figure 2 , where (a) is the simulation result of the Faraday rotation angle θ S produced by the magnetic nanoparticles at different temperatures as the excitation magnetic field H changes; and (b) is the measured temperature and the Langevin fitting temperature as well as the measurement error.

[0061] Since the generation of a direct current field is easier, a strong direct current magnetic field can be generated by a permanent magnet or an electromagnet, which can make the generated deflection angle larger and be easier to detect with a chopper or an electro-optical modulator. However, in some measurement scenarios, it is not easy to set up the same control group at the same time, and it is difficult to eliminate the Faraday rotation angle θ BTherefore, the application also provides a second embodiment, using an alternating excitation magnetic field H=H0sin(ωt) as an external excitation, the method steps specifically include:

[0062] S1. Placing a magnetic nanoparticle sample in a target area, and making the magnetic nanoparticle generate a magnetization response M through an applied alternating excitation magnetic field.

[0063] S2. Generating a linearly polarized light beam using a laser and a polarizer, and passing the light beam through the magnetic nanoparticle sample along a coaxial direction of the magnetic field, so as to generate a Faraday magneto-optical effect with the sample;

[0064] S3. Detecting the outgoing light using an analyzer,

[0065] Using an alternating excitation magnetic field H=H0sin(ωt), since the background such as a solvent and a container is paramagnetic or diamagnetic, the magnetization response thereof varies linearly with the magnetic field; while the magnetic nanoparticle is superparamagnetic, and the magnetization response M thereof is nonlinear, and M can be approximately expanded as

[0066] k is a positive integer

[0067] wherein a n is a coefficient corresponding to the nth expansion term, and thus the measured outgoing light intensity will have high-order harmonics, and satisfies

[0068] k is a positive integer

[0069] wherein θ=VL(H0+νM1)=VL(H0+νa1H0) is related to both the background and the magnetic nanoparticle; while is only related to the magnetic nanoparticle.

[0070] Therefore, under the alternating magnetic field, the high-order harmonics can be directly used to realize specific detection of the magnetic nanoparticle, and there is no need to set a control group.

[0071] Preferably, in order to facilitate calculation, the optical axis angle α between the polarizer and the analyzer is set to 45°, and since the magnetization response M of the magnetic nanoparticle is nonlinear, the outgoing light I out will generate odd-order harmonics of the excitation magnetic field frequency, as shown in Figure 3 , and has

[0072] k is a positive integer

[0073] wherein A n is a coefficient of each odd-order harmonic.

[0074] S4. The amplitude of the high-order harmonics of the outgoing light can be used to obtain θ Sn , and θ SnThe temperature can be inversed by nonlinear fitting with the AC excitation magnetic field amplitude H0.

[0075] As shown in Figure 4 It can be seen that the difference of higher harmonic is more obvious at different temperatures, which shows that the higher harmonic is more sensitive to temperature. And the experiment found that the more the measured harmonic number, the higher the fitting accuracy.

[0076] Those skilled in the art will easily understand that the above description is only the preferred embodiment of the present application, and is not used to limit the present application, any modification, equivalent replacement and improvement made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A temperature measurement method based on the Faraday magneto-optical effect of magnetic nanoparticles, characterized in that, include: The magnetic nanoparticle sample was placed in the target area, and the magnetic nanoparticles were magnetized by applying an external DC excitation magnetic field. Magnetic nanoparticles are irradiated with polarized light in a coaxial direction with a magnetic field to induce a Faraday magneto-optical effect with the sample. The sample without magnetic nanoparticles was used as a control group. An excitation magnetic field with the same amplitude but opposite direction as the applied DC excitation magnetic field was applied to it, and the emitted light was detected. The Faraday rotation angle generated by the magnetic nanoparticles is calculated based on the detected emitted light. The temperature of the magnetic nanoparticles in the target region was obtained by nonlinearly fitting the Faraday rotation angle generated by the magnetic nanoparticles with the applied DC excitation magnetic field using the Langevin function.

2. The temperature measurement method based on the Faraday magneto-optical effect of magnetic nanoparticles according to claim 1, characterized in that, The emitted light intensity I of the control group out satisfy: I out =I0cos 2 (i S +a) Where I0 is the intensity of the incident light, α is the angle between the optical axes of the polarizer and the analyzer, and θ is the angle between the optical axes of the polarizer and the analyzer. S θ is the polarization angle of the emitted light generated by the magnetic nanoparticles. S =VLvM, where V is the Feld constant, L is the length of the light passing through the medium, and v is the exchange interaction coefficient of the magnetization response M.

3. The temperature measurement method based on the Faraday magneto-optical effect of magnetic nanoparticles according to claim 2, characterized in that, The angle between the polarizer and the analyzer optical axis that generate polarized light is 45°.

4. The temperature measurement method based on the Faraday magneto-optical effect of magnetic nanoparticles according to claim 2, characterized in that, Faraday rotation angle θ generated by magnetic nanoparticles S The relationship between the applied DC excitation magnetic field H and the temperature T satisfies the following equation: μ0 is the free permeability, k B Where is the Boltzmann constant, N is the number of magnetic nanoparticles per unit volume, and m s This represents the saturation magnetic moment of the magnetic nanoparticles.

5. A temperature measurement method based on the Faraday magneto-optical effect of magnetic nanoparticles, characterized in that, include: The magnetic nanoparticle sample was placed in the target area, and the magnetic nanoparticles were magnetized by applying an external AC excitation magnetic field. Magnetic nanoparticles are irradiated with polarized light in the same direction as the magnetic field to induce the Faraday magneto-optical effect with the sample, and the emitted light is detected. The Faraday rotation angle generated by the magnetic nanoparticles is calculated based on the detected emitted light. The temperature of the magnetic nanoparticles in the target region was obtained by nonlinear fitting of the Faraday rotation angle generated by the sample and the applied excitation magnetic field using the Langevin function.

6. A temperature measuring device based on the Faraday magneto-optical effect of magnetic nanoparticles, characterized in that, include: Laser, polarizer, first coil, second coil, analyzer, photodiode, and fitting module; The first coil is used to apply a DC excitation magnetic field to the magnetic nanoparticle sample placed in the target area, so that the magnetic nanoparticles generate a magnetization response. The laser and polarizer are used together to generate polarized light that is coaxial with the magnetic field, which irradiates the magnetic nanoparticles and causes the Faraday magneto-optical effect to occur with the sample. The second coil is used to apply an excitation magnetic field with the same amplitude but opposite direction to the external DC excitation magnetic field to the control group; the control group is a sample without magnetic nanoparticles, placed behind the magnetic nanoparticle sample; The analyzer and photodiode are used together to detect the intensity of the emitted light passing through the control group; The fitting module is used to calculate the Faraday rotation angle generated by the magnetic nanoparticles based on the detected outgoing light, and to perform nonlinear fitting between the Faraday rotation angle generated by the magnetic nanoparticles and the applied DC excitation magnetic field using the Langevin function to obtain the temperature of the magnetic nanoparticles in the target region.

7. A temperature measuring device based on the Faraday magneto-optical effect of magnetic nanoparticles, characterized in that, include: Laser, polarizer, third coil, analyzer, photodiode, and fitting module; The laser and polarizer are used together to generate polarized light that is coaxial with the magnetic field, which irradiates the magnetic nanoparticle sample and causes the Faraday magneto-optical effect to occur with the sample. The third coil is used to apply an alternating excitation magnetic field to the magnetic nanoparticle sample placed in the target area, so that the magnetic nanoparticles generate a magnetization response. The analyzer and photodiode work together to detect the intensity of the emitted light passing through the sample; The fitting module is used to calculate the Faraday rotation angle generated by the magnetic nanoparticles based on the detected outgoing light; and to perform nonlinear fitting of the Faraday rotation angle generated by the sample with the applied excitation magnetic field using the Langevin function to obtain the temperature of the magnetic nanoparticles in the target region.

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