WO2013093136A1 - Device and method for sensing magnetic materials - Google Patents

Device and method for sensing magnetic materials Download PDF

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Publication number
WO2013093136A1
WO2013093136A1 PCT/ES2012/000313 ES2012000313W WO2013093136A1 WO 2013093136 A1 WO2013093136 A1 WO 2013093136A1 ES 2012000313 W ES2012000313 W ES 2012000313W WO 2013093136 A1 WO2013093136 A1 WO 2013093136A1
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Prior art keywords
magnet
magnetic
magnetic field
levitating
levitating magnet
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PCT/ES2012/000313
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Spanish (es)
French (fr)
Inventor
Javier SESÉ MONCLÚS
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Universidad De Zaragoza
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Publication of WO2013093136A1 publication Critical patent/WO2013093136A1/en

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/12—Measuring magnetic properties of articles or specimens of solids or fluids
    • G01R33/1261—Measuring magnetic properties of articles or specimens of solids or fluids using levitation techniques

Definitions

  • the present invention refers to a device and method based on diamagnetic levitation, preferably intended for sensing samples of magnetic materials.
  • magnetometers such as those based on SERF devices (in English, “spin exchange relaxation-free devices”, devices based on spin exchange without relaxation) also allow measuring very weak magnetic fields, without resorting to conditions Cryogenic, although they can only operate in practically null fields, without the possibility of measuring fields of greater intensity, and their conditions of use are also technically demanding, since they require the previous heating of an alkali metal vapor, as well as a means for such an end associated with the magnetometer, which again significantly increases the costs of production and sale of these devices.
  • the present invention is oriented to satisfy said need.
  • the present invention is intended to obtain precision magnetometers for the measurement of weak magnetic fields associated with samples under study. Said objective is achieved by a material sensing device based on the principles of diamagnetic levitation, which comprises:
  • fixed referring to a position or a difference between elements of the device according to the invention, must be interpreted as that position or distance that does not vary in relation to said elements.
  • levitant in stable equilibrium is to be interpreted herein as a state of suspension in space that remains stable, even in the presence of small external disturbances.
  • a device of great sensitivity to the magnetic properties of the samples under study is achieved, comparable to that of the SQUID or SERF detectors, and which have a greater simplicity in the design of their components, as they do not require conditions of superconductivity in its operation (with the requirement of low temperature that entails) and without the need for a previous heating of sensing steam of SERF devices.
  • the device comprises a coil for controlling the position of the second levitating magnet. This achieves greater precision in the sensing conditions, being able, by generating a magnetic field induced in the coil, to modify the distance between the levitating magnet and the magnetic sample under study according to the needs of the user.
  • the sensing device comprises a current generator configured to generate, through its connection to I to coil, a variable magnetic field of frequency equal to I at the mechanical resonance frequency of the second levitating magnet.
  • the magnetic field sensor is a Hall effect sensor. An effective means for detecting the magnetic field to which the second levitating magnet is subjected is achieved.
  • the position sensor of the second levitating magnet is an optical sensor. This achieves an alternative to the Hall sensor that also provides great effectiveness in measuring the position and magnetic field of the levitating magnet.
  • the magnetic field sensor comprises a v oltmeter that records the variations in the measurement of the sensor. This achieves a means to estimate the magnetic properties of the sample by means of the maximum variation recorded in said sensor by the presence of the magnetic elements of the device.
  • the diamagnetic element is in the form of an amine. This achieves great stability in the position of the levitating magnet.
  • the sensing device comprises two diamagnetic elements. This achieves a configuration that provides great stability in the equilibrium configuration of the position of the levitating magnet.
  • the second levitating magnet and the sample of magnetic material under study are located at a distance preferably between 1 and 10 mm. Is achieved with this a sufficient measurement sensitivity so that the magnetic field sensor can detect the presence of the sample.
  • Another object of the present invention is a method of sensing magnetic materials comprising the use of a device according to any of previously described embodiments, wherein said device is configured in a stable equilibrium position of the second levitating magnet, and wherein said position has a displacement in front of I to the equilibrium position that the second levitating magnet would present in the absence of the sample of magnetic material.
  • the displacement of I to position of the second levitating magnet is measured by the position sensor or the magnetic field sensor.
  • a sensitive means is thus obtained to determine, through said displacement, the magnetic field generated by the magnetic sample under study.
  • the levitating magnet is oscillated at a frequency equal to its mechanical resonance frequency.
  • the method comprises comparing the magnetic field measured in the levitating magnet without the presence of I a sample of magnetic material, with the magnetic field measured in the presence of said sample of magnetic material, the second levitating magnet also being subjected to a variable magnetic field of frequency equal to its mechanical resonance frequency.
  • the present invention thus provides a new solution to the technical problem of measuring very small quantities of magnetic materials.
  • the following can be mentioned:
  • the device Since the device is capable of measuring very small forces, it could also be applied to the measurement of molecular forces, for example chemical or antigen-antibody recognition links, etc.
  • Figure 1 shows a schematic representation of an embodiment of the device of the invention, showing its configuration in a steady equilibrium state of the levitating magnet.
  • Figure 2 shows a perspective view of an embodiment of the device of the invention comprising a coil to vary the magnetic field to which the magnet system is subjected, showing a configuration of the device in stable steady state of the levitating magnet.
  • Figure 3 shows a measurement of the Hall sensor output signal in phase (X) and counter phase (Y), in volts, as a function of frequency (in Hz), said measurement obtained through an embodiment of the device the invention, where the amplitude of the signal exhibits a resonance behavior.
  • Figure 4 shows the signal of the measurement shown in Figure 3, represented as a module (in V) and a phase (in degrees), and where the resonance behavior of the signal is also observed.
  • Figure 5 shows the test results for different samples of magnetic material (a cobalt sheet, a pyrolytic graphite sheet and an aluminum foil sheet), in a preferred embodiment of the invention.
  • the results are represented as the electrical signal in module ( ⁇ ') and phase ( ⁇ '), measured in volts with the Hall sensor, as a function of time (in seconds).
  • the present invention relates to a device for sensing magnetic fields based on the principle of diamagnetic avoidance.
  • Said principle comprises the stabilization of I by force of attraction between two or more permanent magnets, by using diamagnetic materials (such as, for example, pyrolytic graphite, bismuth or others), achieving a stable equilibrium configuration of the set of forces that act between these magnets.
  • the principle of diamagnetic levitation can be illustrated with the following example: it is based on a levitating magnet (understood the term "levitating" as suspended in space) subjected to the magnetic force of another magnet whose position is fixed in the space (where the levitating magnet is preferably located above or below the fixed magnet, depending on the magnetic force, respectively, repulsive or attractive).
  • This situation without adding additional elements, leads, in principle, to a state of unstable equilibrium of the levitating magnet, at the point where the magnetic force to which it is subjected takes the same value as the force of attack exerted by the gravity.
  • This configuration of forces, therefore, being unstable, is unrealizable in practice, since any small disturbance deflects the system from its equilibrium position and the system loses its configuration without the possibility of returning to it.
  • Diamagnetism is the weakest magnetic response we find in natural materials.
  • One way to quantify this property is, for example, through I to magnetic susceptibility, which in the International System is a dimensionless magnitude.
  • levitation can be achieved without the need to introduce any additional active element, without providing rotational movement to the system (as occurs in levitation devices such as the so-called Levitron) and without the need to operate at low temperatures (as in the case of superconducting devices).
  • levitation devices such as the so-called Levitron
  • superconducting devices there are other sensing devices based on diamagnetic levitation in the state of the art (whose purpose is, for example, obtaining precision balances), none of them is intended for the measurement of magnetic properties, such as The case of this invention. That is why the present device is, preferably, not intended for mass measurement, but for magnetic sensing.
  • Figure 1 of this document shows the levitation configuration for an embodiment of the present invention.
  • Said embodiment comprises a first magnet (1) located in a fixed position, a second levitating magnet (2), suspended under the effect of the magnetic field of the first magnet (1) and at least one diamagnetic element (3), located at a fixed distance of the first magnet (1), said diamagnetic element (3) being under the action of the magnetic field of the first magnet (1) and the second levitating magnet (2).
  • the position of the levitating magnet (2) is situated at the point of equilibrium of forces to which said magnet is subjected (preferably, a magnetic force of attraction towards the fixed magnet, directed upwards, and the gravitational force, directed towards below), and where said equilibrium point, which would be in principle unstable, is stabilized by the presence of the diamagnetic element (3), said element configured, preferably, as a sheet (so that the stability is obtained in a two-dimensional space ). It is also possible, in other embodiments of the invention, to use more than one diamagnetic element (3), for example by placing two diamagnetic surfaces in regions above and below the second levitating magnet (2). This allows different equilibrium configurations to be obtained as required in each type of measurement.
  • the presence of, for example, two diamagnetic elements (3) contributes to improve the stabilization of the second levitating magnet (2), by previously adjusting the distance between said diamagnetic elements (3), as well as their distance to the first fixed magnet (1), so that a potential energy well is obtained that provides a sufficient stability band to keep the second levitating magnet (2) in balance.
  • the sensing achievable by the device of the invention comprises the use of a sample of magnetic material (5) that is located at a fixed distance in the vicinity of the second levitating magnet (2) (this proximity is understood as a sufficient distance so that the magnetic fields of the sample (5) and the second levitating magnet (2) can interact with each other).
  • the presence of the magnetic field of the sample (5) alters the equilibrium position of the second levitating magnet (2).
  • the device of the invention comprises one or more sensors (4) of the magnetic field to which the first magnet (1), the second levitating magnet (2), the diamagnetic element (3) is subjected. and / or the magnetic material sample (5), configured to convert said field into an electrical signal that can be measured, for example, by a voltmeter (6).
  • the magnetic field sensor (4) is a Hall effect sensor. It is also possible to use, in another embodiment of the invention, an optical position sensor, configured to measure the displacement of the equilibrium position of the second levitating magnet (2) in the presence of the sample of magnetic material (5).
  • the device comprises, in addition to the aforementioned elements, a coil (7) that provides, by means of a current generator, the ability to displace the second levitating magnet (2) of shape controlled, through the induction of a magnetic field in said coil (7) that interacts with the second levitating magnet (2).
  • a coil (7) that provides, by means of a current generator, the ability to displace the second levitating magnet (2) of shape controlled, through the induction of a magnetic field in said coil (7) that interacts with the second levitating magnet (2).
  • an equal frequency is used to the mechanical resonance of the second levitating magnet (2) without the presence of a magnetic sample (5) and the electrical signal is recorded in module ( ⁇ ') and phase ( ⁇ ').
  • Figure 5 shows the changes in said signal by placing different materials in the device. It is also worth mentioning how the phase signal ( ⁇ '), in the case of pyrolytic graphite, is negative, which is consistent with the magnetic susceptibility of said material, which is also negative, while the signal is positive when a sheet approaches 10 nm of cobalt (positive susceptibility).
  • the distance between the sample of magnetic material (5) under study and the second levitating magnet (2) is preferably between 1 and 10 mm.
  • the intensity of the magnetic field of interaction between the two is significantly reduced, with the consequent loss of sensitivity in the sensing.
  • Another aspect of the present invention relates to a method of characterizing magnetic materials based on the device described above.
  • a balancing configuration of the second levitating magnet (2) it is possible to approximate a magnetic sample to it, producing a shift in its equilibrium position.
  • a sensor of displacement or of the magnetic field for example a Hall sensor
  • the second levitating magnet (2) is oscillated, by means of a magnetic field induced in a coil (7), at a frequency equal to the mechanical resonance frequency (by generating a induced magnetic field of said frequency with the coil (7)).
  • the measurement method of the invention comprises comparing a reference signal (without the presence of the magnetic sample) with the signal in the presence of the sample, which allows to derive the magnetic properties (for example, the magnetic susceptibility) of the same.

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  • Physics & Mathematics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Investigating Or Analyzing Materials By The Use Of Magnetic Means (AREA)

Abstract

The invention relates to a device and to a method for sensing magnetic materials based on the principle of diamagnetic levitation. The device comprises a system of permanent magnets in which at least one magnet is in a stable equilibrium levitating position by means of the presence of at least one diamagnetic element and in which a magnetic study specimen is subjected to the action of the system of magnets of the device. The method of the invention allows precise measurement of weak magnetic fields using a device that is less complex than the magnetometers that exist in the prior art and one which, furthermore, involves lower production costs.

Description

DISPOSITIVO Y MÉTODO DE SENSADO DE MATERIALES MAGNÉTICOS  DEVICE AND METHOD OF SENSATING MAGNETIC MATERIALS
CAMPO DE LA INVENCIÓN FIELD OF THE INVENTION
La presente invención hace referencia a un dispositivo y a un método basados en levitación diamagnética, destinados preferentemente al sensado de muestras de materiales magnéticos. ANTECEDENTES DE LA INVENCIÓN The present invention refers to a device and method based on diamagnetic levitation, preferably intended for sensing samples of magnetic materials. BACKGROUND OF THE INVENTION
Dentro del campo perteneciente a la medición de c antidades muy pequeñas de materiales magnéticos, hoy en día existen diversos aparatos capaces de medir con precisión campos magnéticos débiles presentes en muestras bajo estudio. Principalmente, dichos aparatos se basan en l a tecnología de s istemas SQUID (del inglés "superconducting quantum interference devices", o di spositivos superconductores de interferencia cuántica), que permiten medir muestras con campos magnéticos de hasta 10"18 Tesla, siendo hoy en di a los magnetómetros más sensibles conocidos. Within the field belonging to the measurement of very small quantities of magnetic materials, today there are several devices capable of accurately measuring weak magnetic fields present in samples under study. Mainly, these devices are based on the technology of SQUID systems (of the English "superconducting quantum interference devices", or superconducting devices of quantum interference), which allow to measure samples with magnetic fields of up to 10 "18 Tesla, being today in di to the most sensitive magnetometers known.
Si bien los citados dispositivos SQUID presentan una gran precisión en la medida de campos magnéticos, su utilización se realiza en condiciones técnicas muy exigentes, ya que, para su correcto funcionamiento, necesitan incorporar un sistema de refrigeración criogénico asociado, lo que aumenta notablemente los costes de adquisición de este tipo de aparatos, que actualmente se aproxima los 300.000€ por dispositivo.  Although the aforementioned SQUID devices have great precision in the measurement of magnetic fields, their use is carried out under very demanding technical conditions, since, for their correct operation, they need to incorporate an associated cryogenic cooling system, which significantly increases costs for the acquisition of this type of device, which is currently approaching € 300,000 per device.
Otros magnetómetros más recientes, como por ejemplo los basados en dispositivos SERF (del inglés, "spin exchange relaxation-free devices", dispositivos basados en intercambio de spin sin relajación) permiten también medir campos magnéticos muy débiles, sin recurrir a condiciones criogénicas, aunque sólo pueden operar a campos prácticamente nulos, sin posibilidad de medir campos de mayor intensidad, y sus condiciones de uso también son técnicamente exigentes, ya que requieren el calentamiento previo de un v apor de metal alcalino, así como un medio destinado a tal fin asociado al magnetómetro, lo que de nuevo incrementa notablemente los costes de producción y venta de estos aparatos. Other more recent magnetometers, such as those based on SERF devices (in English, "spin exchange relaxation-free devices", devices based on spin exchange without relaxation) also allow measuring very weak magnetic fields, without resorting to conditions Cryogenic, although they can only operate in practically null fields, without the possibility of measuring fields of greater intensity, and their conditions of use are also technically demanding, since they require the previous heating of an alkali metal vapor, as well as a means for such an end associated with the magnetometer, which again significantly increases the costs of production and sale of these devices.
A la luz de I os problemas anteriormente referidos que plantea actualmente el estado de la técnica, se hace necesario desarrollar, pues, alternativas técnicas dentro del campo de la invención, que consigan medir con precisión campos magnéticos débiles (aunque no necesariamente campos muy próximos a cero, como en el caso de l os magnetómetros SERF), cuyos requisitos de funcionamiento no lleven asociados procesos previos al sensado técnicamente complejos (como la obtención de temperaturas criogénicas o el calentamiento de los átomos de sensado), y que además impliquen costes de fabricación y adquisición bajos.  In the light of the aforementioned problems currently posed by the state of the art, it is therefore necessary to develop technical alternatives within the scope of the invention, which are able to accurately measure weak magnetic fields (although not necessarily fields very close to zero, as in the case of SERF magnetometers), whose operating requirements do not have associated processes prior to technically complex sensing (such as obtaining cryogenic temperatures or heating sensing atoms), and which also involve manufacturing costs and acquisition low.
La presente invención está orientada a satisfacer dicha necesidad. DESCRIPCIÓN BREVE DE LA INVENCIÓN  The present invention is oriented to satisfy said need. BRIEF DESCRIPTION OF THE INVENTION
La presente invención está destinada a obtener magnetómetros de precisión para la medida de campos magnéticos débiles asociados a muestras bajo estudio. Dicho objetivo se alcanza mediante un dispositivo de sensado de materiales basado en los principios de levitación diamagnética, que comprende: The present invention is intended to obtain precision magnetometers for the measurement of weak magnetic fields associated with samples under study. Said objective is achieved by a material sensing device based on the principles of diamagnetic levitation, which comprises:
- un primer imán situado en una posición fija;  - a first magnet located in a fixed position;
- un segundo imán levitante en equilibrio estable, suspendido bajo el efecto del campo magnético del primer imán, y configurado para interaccionar magnéticamente con una muestra de material magnético objeto del sensado; - al menos, un elemento diamagnético, situado a una distancia fija del primer imán, encontrándose dicho elemento diamagnético bajo la acción del campo magnético del primer imán y del segundo imán levitante; - a second levitant magnet in stable equilibrium, suspended under the effect of the magnetic field of the first magnet, and configured to interact magnetically with a sample of magnetic material subject to sensing; - at least one diamagnetic element, located at a fixed distance from the first magnet, said diamagnetic element being under the action of the magnetic field of the first magnet and the second levitating magnet;
- al menos, un sensor de la posición del segundo imán levitante y/o un sensor del campo magnético al que se encuentra sometido el segundo imán levitante.  - at least one sensor of the position of the second levitating magnet and / or a sensor of the magnetic field to which the second levitating magnet is subjected.
El término "fijo", referido a una posición o a una di stancia entre elementos del dispositivo de I a invención, ha de i nterpretarse como aquella posición o distancia que no presenta variaciones con relación a dichos elementos.  The term "fixed", referring to a position or a difference between elements of the device according to the invention, must be interpreted as that position or distance that does not vary in relation to said elements.
El término "levitante en equilibrio estable" ha de interpretarse, en el presente documento, como un estado de suspensión en el espacio que se mantiene estable, incluso bajo la presencia de peq ueñas perturbaciones externas.  The term "levitant in stable equilibrium" is to be interpreted herein as a state of suspension in space that remains stable, even in the presence of small external disturbances.
Mediante la presente invención se consigue un dispositivo de g ran sensibilidad a las propiedades magnéticas de las muestras bajo estudio, comparable a la que poseen los detectores SQUID o SERF, y que presentan una mayor simplicidad en el diseño de sus componentes, al no requerir condiciones de superconductividad en su funcionamiento (con la exigencia de baj a temperatura que ello conlleva) y sin necesidad de un calentamiento previo de vapor de sensado de los dispositivos SERF.  By means of the present invention, a device of great sensitivity to the magnetic properties of the samples under study is achieved, comparable to that of the SQUID or SERF detectors, and which have a greater simplicity in the design of their components, as they do not require conditions of superconductivity in its operation (with the requirement of low temperature that entails) and without the need for a previous heating of sensing steam of SERF devices.
En una r ealización preferente de I a invención, el dispositivo comprende una bobina para el control de la posición del segundo imán levitante. Se consigue con ello una mayor precisión en las condiciones del sensado, pudiendo, mediante la generación de un campo magnético inducido en la bobina, modificar la distancia entre el imán levitante y la muestra magnética bajo estudio según las necesidades del usuario.  In a preferred embodiment of the invention, the device comprises a coil for controlling the position of the second levitating magnet. This achieves greater precision in the sensing conditions, being able, by generating a magnetic field induced in the coil, to modify the distance between the levitating magnet and the magnetic sample under study according to the needs of the user.
En otra realización preferente de I a invención, el dispositivo de sensado comprende un generador de corriente configurado para generar, mediante su conexión a I a bobina, un c ampo magnético variable de frecuencia igual a I a frecuencia de resonancia mecánica del segundo imán levitante. Se consigue con ello un dispositivo sensible a la variación de la posición del imán levitante en función de s u frecuencia de resonancia, lo que proporciona una precisión en la detección de muestras magnéticas al menos 100 v eces superior a la sensibilidad dé l os detectores SQUID comerciales. In another preferred embodiment of I to the invention, the sensing device comprises a current generator configured to generate, through its connection to I to coil, a variable magnetic field of frequency equal to I at the mechanical resonance frequency of the second levitating magnet. This achieves a device that is sensitive to the variation of the position of the levitating magnet based on its resonance frequency, which provides an accuracy in the detection of magnetic samples at least 100 times higher than the sensitivity of commercial SQUID detectors. .
En una realización preferente adicional de la invención, el sensor del campo magnético es un sensor de efecto Hall. Se consigue con ello un medio efectivo para la detección del campo magnético al que se encuentra sometido el segundo imán levitante.  In a further preferred embodiment of the invention, the magnetic field sensor is a Hall effect sensor. An effective means for detecting the magnetic field to which the second levitating magnet is subjected is achieved.
En una realización preferente de la invención, el sensor de posición del segundo imán levitante es un sensor óptico. Se consigue con ello una alternativa al sensor Hall que también proporciona una gran efectividad en la medida de la posición y el campo magnético del imán levitante.  In a preferred embodiment of the invention, the position sensor of the second levitating magnet is an optical sensor. This achieves an alternative to the Hall sensor that also provides great effectiveness in measuring the position and magnetic field of the levitating magnet.
En una realización más de la invención, el sensor del campo magnético comprende un v oltímetro que registra las variaciones en la medida del sensor. Se consigue con ello un m edio para estimar las propiedades magnéticas de la muestra por medio de la variación máxima registrada en dicho sensor por la presencia de los elementos magnéticos del dispositivo.  In a further embodiment of the invention, the magnetic field sensor comprises a v oltmeter that records the variations in the measurement of the sensor. This achieves a means to estimate the magnetic properties of the sample by means of the maximum variation recorded in said sensor by the presence of the magnetic elements of the device.
En otra realización preferente de la invención, el elemento diamagnético posee forma de I ámina. Se consigue con ello una gran estabilidad en la posición del imán levitante.  In another preferred embodiment of the invention, the diamagnetic element is in the form of an amine. This achieves great stability in the position of the levitating magnet.
En una realización alternativa de I a invención, el dispositivo de sensado comprende dos elementos diamagnéticos. Se consigue con ello una configuración que proporciona una gran estabilidad en la configuración de equilibrio de la posición del imán levitante.  In an alternative embodiment of the invention, the sensing device comprises two diamagnetic elements. This achieves a configuration that provides great stability in the equilibrium configuration of the position of the levitating magnet.
En otra realización de la invención, el segundo imán levitante y la muestra de material magnético bajo estudio se encuentran situados a una distancia preferentemente comprendida entre 1 y 10 mm. Se consigue con ello una sensibilidad de medida suficiente para que el sensor de campo magnético pueda detectar la presencia de la muestra. In another embodiment of the invention, the second levitating magnet and the sample of magnetic material under study are located at a distance preferably between 1 and 10 mm. Is achieved with this a sufficient measurement sensitivity so that the magnetic field sensor can detect the presence of the sample.
Otro objeto de la presente invención es un método de sensado de materiales magnéticos que comprende el uso de un dispositivo según cualquiera de realizaciones anteriormente descritas, donde dicho dispositivo está configurado en una posición de equilibro estable del segundo imán levitante, y donde dicha posición presenta un desplazamiento frente a I a posición de e quilibrio que presentaría el segundo imán levitante en ausencia de la muestra de material magnético.  Another object of the present invention is a method of sensing magnetic materials comprising the use of a device according to any of previously described embodiments, wherein said device is configured in a stable equilibrium position of the second levitating magnet, and wherein said position has a displacement in front of I to the equilibrium position that the second levitating magnet would present in the absence of the sample of magnetic material.
Se consigue con ello un método eficaz, por su alta precisión y sencillez, para la medición dé l as propiedades magnéticas de muestras bajo estudio.  This achieves an effective method, due to its high precision and simplicity, for measuring the magnetic properties of samples under study.
En una realización preferente del método de I a invención, el desplazamiento de I a posición del segundo imán levitante se mide mediante el sensor de posición o el sensor de c ampo magnético. Se consigue con ello un medio sensible para determinar, a través de dicho desplazamiento, el campo magnético generado por la muestra magnética bajo estudio.  In a preferred embodiment of the method of I to the invention, the displacement of I to position of the second levitating magnet is measured by the position sensor or the magnetic field sensor. A sensitive means is thus obtained to determine, through said displacement, the magnetic field generated by the magnetic sample under study.
En otra realización preferente del método de sensado de la invención, por medio de la generación de una corriente a través dé l a bobina, se hace oscilar el imán levitante a una frecuencia igual a su frecuencia de resonancia mecánica. Preferentemente, el método comprende la comparación del campo magnético medido en el imán levitante sin la presencia de I a muestra de material magnético, con el campo magnético medido en presencia de dicha muestra de material magnético, estando el segundo imán levitante sometido, asimismo, a un campo magnético variable de frecuencia igual su frecuencia de resonancia mecánica. Se consigue con ello una c onfiguración de estabilidad en la posición del imán levitante enormemente sensible a las propiedades magnéticas de la muestra bajo estudio, lo que dota de una precisión en las medidas obtenidas por el dispositivo mayor en al menos dos órdenes de m agnitud a la obtenida mediante detectores SQUID comerciales. In another preferred embodiment of the sensing method of the invention, by means of generating a current through the coil, the levitating magnet is oscillated at a frequency equal to its mechanical resonance frequency. Preferably, the method comprises comparing the magnetic field measured in the levitating magnet without the presence of I a sample of magnetic material, with the magnetic field measured in the presence of said sample of magnetic material, the second levitating magnet also being subjected to a variable magnetic field of frequency equal to its mechanical resonance frequency. This achieves a configuration of stability in the position of the levitating magnet that is highly sensitive to the magnetic properties of the sample under study, which provides precision in the measurements obtained by the major device in at least two orders of magnitude to that obtained by commercial SQUID detectors.
La presente invención aporta, pues, una nueva solución al problema técnico de medir cantidades muy pequeñas de materiales magnéticos. Como aplicaciones específicas del dispositivo, cabe citar las siguientes:  The present invention thus provides a new solution to the technical problem of measuring very small quantities of magnetic materials. As specific applications of the device, the following can be mentioned:
- Detección de tintas magnéticas utilizadas en bi Metes de curso legal (sector de seguridad).  - Detection of magnetic inks used in bi Metes of legal tender (security sector).
- Cuantificación de masa magnética en el caso de tests de flujo lateral basados en nanopartículas magnéticas (los tests de flujo lateral son baratos y sencillos y se utilizan en sector farmacéutico, salud, medio ambiente, etc.).  - Quantification of magnetic mass in the case of lateral flow tests based on magnetic nanoparticles (lateral flow tests are cheap and simple and are used in the pharmaceutical sector, health, environment, etc.).
- Detección de n anopartículas magnéticas en s istemas de microfluídica.  - Detection of n magnetic anoparticles in microfluidic systems.
- Caracterización de aceros inoxidables ("no magnéticos").  - Characterization of stainless steels ("non-magnetic").
- Caracterización de láminas delgadas con un espesor nanométrico de materiales magnéticos (por ejemplo, discos duros).  - Characterization of thin sheets with a nanometric thickness of magnetic materials (for example, hard drives).
- Dado que el dispositivo es capaz de m edir fuerzas muy pequeñas, también se podría aplicar a la medición de fuerzas moleculares, por ejemplo enlaces químicos o de reconocimiento antígeno- anticuerpo, etc.  - Since the device is capable of measuring very small forces, it could also be applied to the measurement of molecular forces, for example chemical or antigen-antibody recognition links, etc.
Adicionalmente a las ya planteadas, otras características y ventajas de la invención se desprenderán de la descripción que sigue, así como de las figuras que acompañan al presente documento.  In addition to those already raised, other features and advantages of the invention will be apparent from the following description, as well as from the figures accompanying this document.
DESCRIPCIÓN DE LAS FIGURAS DESCRIPTION OF THE FIGURES
La Figura 1 muestra una representación esquemática de una realización del dispositivo de la invención, mostrando su configuración en estado de equilibrio estable del imán levitante. La Figura 2 muestra una vista en perspectiva de una realización del dispositivo de la invención que comprende una bobina para variar el campo magnético al que está sometido el sistema de imanes, mostrando una configuración del dispositivo en estado de equilibrio estable del imán levitante. Figure 1 shows a schematic representation of an embodiment of the device of the invention, showing its configuration in a steady equilibrium state of the levitating magnet. Figure 2 shows a perspective view of an embodiment of the device of the invention comprising a coil to vary the magnetic field to which the magnet system is subjected, showing a configuration of the device in stable steady state of the levitating magnet.
La Figura 3 m uestra una medida de la señal de salida del sensor Hall en fase (X) y contrafase (Y), en voltios, en función de la frecuencia (en Hz), obtenida dicha medida a través de una realización del dispositivo de la invención, donde la amplitud de la señal presenta un comportamiento de resonancia.  Figure 3 shows a measurement of the Hall sensor output signal in phase (X) and counter phase (Y), in volts, as a function of frequency (in Hz), said measurement obtained through an embodiment of the device the invention, where the amplitude of the signal exhibits a resonance behavior.
La Figura 4 muestra la señal de la medida mostrada en la Figura 3, representada como un módulo (en V) y una fase (en grados), y donde se observa también el comportamiento de resonancia de la señal.  Figure 4 shows the signal of the measurement shown in Figure 3, represented as a module (in V) and a phase (in degrees), and where the resonance behavior of the signal is also observed.
La Figura 5 m uestra los resultados de s ensado para diferentes muestras de material magnético (una lámina de cobalto, una lámina de grafito pirolítico y una lámina de p apel de aluminio), en un a realización preferente de la invención. Los resultados se representan como la señal eléctrica en módulo (Χ') y fase (Υ'), medidas en voltios con el sensor Hall, en función del tiempo (en segundos).  Figure 5 shows the test results for different samples of magnetic material (a cobalt sheet, a pyrolytic graphite sheet and an aluminum foil sheet), in a preferred embodiment of the invention. The results are represented as the electrical signal in module (Χ ') and phase (Υ'), measured in volts with the Hall sensor, as a function of time (in seconds).
DESCRIPCIÓN DETALLADA DE LA INVENCIÓN DETAILED DESCRIPTION OF THE INVENTION
La presente invención se refiere a un dispositivo para el sensado de campos magnéticos basado en el principio de I evitación diamagnética. Dicho principio comprende la estabilización de I a fuerza de at racción comprendida entre dos o más imanes permanentes, mediante la utilización de m ateríales diamagnéticos (como, por ejemplo, el grafito pirolítico, el bismuto u otros), logrando una configuración de equilibrio estable del juego de fuerzas que actúan entre dichos imanes. The present invention relates to a device for sensing magnetic fields based on the principle of diamagnetic avoidance. Said principle comprises the stabilization of I by force of attraction between two or more permanent magnets, by using diamagnetic materials (such as, for example, pyrolytic graphite, bismuth or others), achieving a stable equilibrium configuration of the set of forces that act between these magnets.
El principio de levitación diamagnética se puede ilustrar con el siguiente ejemplo: se parte de un imán levitante (entendido el término "levitante" como suspendido en el espacio) sometido a la fuerza magnética de otro imán cuya posición se encuentra fijada en el espacio (donde el imán levitante se sitúa, preferentemente, encima o d ebajo del imán fijo, según la fuerza magnética sea, respectivamente, repulsiva o atractiva). Esta situación, sin añadir elementos adicionales, conduce, en principio, a un estado de equilibrio inestable del imán levitante, en el punto en que la fuerza magnética a la que se encuentra sometido toma el mismo valor que la fuerza de at racción ejercida por la gravedad. Esta configuración de fuerzas, por tanto, al ser inestable, resulta irrealizable en la práctica, ya que cualquier pequeña perturbación desvía al sistema de su posición de eq uilibrio y el sistema pierde su configuración sin posibilidad de volver a ella. The principle of diamagnetic levitation can be illustrated with the following example: it is based on a levitating magnet (understood the term "levitating" as suspended in space) subjected to the magnetic force of another magnet whose position is fixed in the space (where the levitating magnet is preferably located above or below the fixed magnet, depending on the magnetic force, respectively, repulsive or attractive). This situation, without adding additional elements, leads, in principle, to a state of unstable equilibrium of the levitating magnet, at the point where the magnetic force to which it is subjected takes the same value as the force of attack exerted by the gravity. This configuration of forces, therefore, being unstable, is unrealizable in practice, since any small disturbance deflects the system from its equilibrium position and the system loses its configuration without the possibility of returning to it.
Sin embargo, es posible generar una configuración de equilibrio estable si se añade al sistema un material diamagnético o fuertemente diamagnético, tal como, por ejemplo, el grafito pirolítico o el bismuto. El diamagnetismo es la respuesta magnética más débil que encontramos en los materiales en estado natural. Una forma de cuantificar esta propiedad es, por ejemplo, a través de I a susceptibilidad magnética, que en el Sistema Internacional es una magnitud adimensional.  However, it is possible to generate a stable equilibrium configuration if a diamagnetic or strongly diamagnetic material is added to the system, such as, for example, pyrolytic graphite or bismuth. Diamagnetism is the weakest magnetic response we find in natural materials. One way to quantify this property is, for example, through I to magnetic susceptibility, which in the International System is a dimensionless magnitude.
De esta forma, mediante la introducción de un material diamagnético en el juego de fuerzas, la levitación se puede lograr sin necesidad de introducir ningún elemento activo adicional, sin dotar de movimiento giratorio al sistema (tal y como ocurre en dispositivos de levitación como el llamado Levitrón) y sin la necesidad de operar a bajas temperaturas (como ocurre en el caso de I os dispositivos superconductores). Si bien existen, en el estado de I a técnica, otros dispositivos de sensado basados en levitación diamagnética (cuyo fin es, por ejemplo, la obtención de balanzas de precisión), ninguno de ellos está destinado a la medición de propiedades magnéticas, como es el caso de esta invención. Es por ello que el presente dispositivo está, preferentemente, no destinado a la medición de la masa, sino al sensado magnético. In this way, by introducing a diamagnetic material in the play of forces, levitation can be achieved without the need to introduce any additional active element, without providing rotational movement to the system (as occurs in levitation devices such as the so-called Levitron) and without the need to operate at low temperatures (as in the case of superconducting devices). Although there are other sensing devices based on diamagnetic levitation in the state of the art (whose purpose is, for example, obtaining precision balances), none of them is intended for the measurement of magnetic properties, such as The case of this invention. That is why the present device is, preferably, not intended for mass measurement, but for magnetic sensing.
La Figura 1 del presente documento muestra la configuración de levitación para una realización de la presente invención. Dicha realización comprende un primer imán (1) situado en una posición fija, un segundo imán (2) levitante, suspendido bajo el efecto del campo magnético del primer imán (1 ) y, al menos, un elemento diamagnético (3), situado a una distancia fija del primer imán (1 ), encontrándose dicho elemento diamagnético (3) bajo la acción del campo magnético del primer imán (1 ) y del segundo imán (2) levitante. La posición del imán levitante (2) se sitúa en el punto de equilibrio de f uerzas a l as que dicho imán se ve sometido (preferentemente, una fuerza magnética de atracción hacia el imán fijo, dirigida hacia arriba, y la fuerza gravitatoria, dirigida hacia abajo), y donde dicho punto de equilibrio, que resultaría en principio inestable, se ve estabilizado por la presencia del elemento diamagnético (3), configurado dicho elemento, preferentemente, como una lámina (de forma que la estabilidad se obtenga en un espacio bidimensional). También es posible, en otras realizaciones de la invención, emplear más de un el emento diamagnético (3), por ejemplo situando dos superficies diamagnéticas en regiones por encima y por debajo del segundo imán (2) levitante. Ello permite obtener diferentes configuraciones de eq uilibrio según se requiera en cada tipo de medida. La presencia de, por ejemplo, dos elementos diamagnéticos (3), contribuye a m ejorar la estabilización del segundo imán (2) levitante, mediante el ajuste previo de la distancia comprendida entre dichos elementos diamagnéticos (3), así como la distancia de los mismos al primer imán fijo (1 ), de forma que se obtenga un pozo de e nergía potencial que proporcione una banda de estabilidad suficiente para mantener el segundo imán (2) levitante en equilibrio.  Figure 1 of this document shows the levitation configuration for an embodiment of the present invention. Said embodiment comprises a first magnet (1) located in a fixed position, a second levitating magnet (2), suspended under the effect of the magnetic field of the first magnet (1) and at least one diamagnetic element (3), located at a fixed distance of the first magnet (1), said diamagnetic element (3) being under the action of the magnetic field of the first magnet (1) and the second levitating magnet (2). The position of the levitating magnet (2) is situated at the point of equilibrium of forces to which said magnet is subjected (preferably, a magnetic force of attraction towards the fixed magnet, directed upwards, and the gravitational force, directed towards below), and where said equilibrium point, which would be in principle unstable, is stabilized by the presence of the diamagnetic element (3), said element configured, preferably, as a sheet (so that the stability is obtained in a two-dimensional space ). It is also possible, in other embodiments of the invention, to use more than one diamagnetic element (3), for example by placing two diamagnetic surfaces in regions above and below the second levitating magnet (2). This allows different equilibrium configurations to be obtained as required in each type of measurement. The presence of, for example, two diamagnetic elements (3), contributes to improve the stabilization of the second levitating magnet (2), by previously adjusting the distance between said diamagnetic elements (3), as well as their distance to the first fixed magnet (1), so that a potential energy well is obtained that provides a sufficient stability band to keep the second levitating magnet (2) in balance.
El sensado realizable mediante el dispositivo de I a invención comprende el uso de una muestra de material magnético (5) que se sitúa a una distancia fija en la proximidad del segundo imán (2) levitante (entendida dicha proximidad como una distancia suficiente para que los campos magnéticos de la muestra (5) y del segundo imán (2) levitante puedan interaccionar entre sí). La presencia del campo magnético de la muestra (5) altera la posición de equilibrio del segundo imán (2) levitante. Mediante la medida de ese desplazamiento, o bien mediante la medida del campo magnético total al que se ve sometido el segundo imán (2) levitante, y su comparación con la posición de equilibrio o el campo magnético del segundo imán (2) levitante medido antes de situar la muestra (5) bajo estudio, es posible derivar la susceptibilidad magnética de dicha muestra (5). The sensing achievable by the device of the invention comprises the use of a sample of magnetic material (5) that is located at a fixed distance in the vicinity of the second levitating magnet (2) (this proximity is understood as a sufficient distance so that the magnetic fields of the sample (5) and the second levitating magnet (2) can interact with each other). The presence of the magnetic field of the sample (5) alters the equilibrium position of the second levitating magnet (2). By measuring this displacement, or by measuring the total magnetic field to which the second levitating magnet (2) is subjected, and its comparison with the equilibrium position or the magnetic field of the second levitating magnet (2) measured before If the sample is placed (5) under study, it is possible to derive the magnetic susceptibility of said sample (5).
Para realizar la medida del campo magnético, el dispositivo de la invención comprende uno o más sensores (4) del campo magnético al que se encuentra sometido el primer imán (1), el segundo imán (2) levitante, el elemento diamagnético (3) y/o la muestra de m aterial magnético (5), configurado para convertir dicho campo en una señal eléctrica que puede ser medida, por ejemplo, por un voltímetro (6). Como se ha mencionado anteriormente, mediante la colocación de una muestra magnética (5) a medir en la proximidad del segundo imán (2) levitante, se produce una variación en el campo magnético que afecta a este último, lo que conlleva una variación correspondiente en el potencial medido por el voltímetro (6), y que permite estimar las propiedades magnéticas de I a muestra, mediante la adecuada calibración del dispositivo. Preferentemente, el sensor (4) de c ampo magnético es un s ensor de efecto Hall. También es posible utilizar, en otra realización de la invención, un s ensor óptico de posición, configurado para medir el desplazamiento de la posición de equilibrio del segundo imán (2) levitante en presencia de la muestra de material magnético (5).  To measure the magnetic field, the device of the invention comprises one or more sensors (4) of the magnetic field to which the first magnet (1), the second levitating magnet (2), the diamagnetic element (3) is subjected. and / or the magnetic material sample (5), configured to convert said field into an electrical signal that can be measured, for example, by a voltmeter (6). As mentioned above, by placing a magnetic sample (5) to be measured in the vicinity of the second levitating magnet (2), there is a variation in the magnetic field that affects the latter, which implies a corresponding variation in the potential measured by the voltmeter (6), and that allows to estimate the magnetic properties of I to sample, by means of the suitable calibration of the device. Preferably, the magnetic field sensor (4) is a Hall effect sensor. It is also possible to use, in another embodiment of the invention, an optical position sensor, configured to measure the displacement of the equilibrium position of the second levitating magnet (2) in the presence of the sample of magnetic material (5).
En una realización de I a invención (Figura 2), el dispositivo comprende, además de los elementos anteriormente referidos, una bobina (7) que proporciona, mediante un generador de c orriente, la capacidad de desplazar el segundo imán (2) levitante de forma controlada, a través dé l a inducción de un campo magnético en dicha bobina (7) que interacciona con el segundo imán (2) levitante. Ello permite realizar, por ejemplo, medidas del campo magnético haciendo oscilar el segundo imán (2) levitante a una frecuencia igual a s u frecuencia de resonancia mecánica (mediante la generación de un campo magnético inducido de dicha frecuencia con la bobina (7)). Cuando el segundo imán (2) levitante se desplaza de la posición de equilibrio, se produce un comportamiento dinámico similar al que presentaría si estuviera sujeto por un muelle. Es conocido que el comportamiento dinámico de una masa m, sometida a la acción de un muelle de constante k tiene un máximo para la frecuencia F de resonancia, que viene dado por la condición 2TT- F=(/ //7I)1/2. Para observar la resonancia con la bobina (7) se crea un campo magnético de referencia y se varía la frecuencia. La señal del sensor (4) del campo magnético depende, como se ha dicho, de la posición del imán levitante. Esta señal se puede representar en función de una componente en fase (X) y una c omponente en contrafase (Y) respecto al campo magnético de referencia. En la Figura 3 se muestra una medida obtenida mediante una realización del dispositivo de I a invención, donde la amplitud de la señal presenta un comportamiento de resonancia a una frecuencia F de 7,4 Hz. In an embodiment of the invention (Figure 2), the device comprises, in addition to the aforementioned elements, a coil (7) that provides, by means of a current generator, the ability to displace the second levitating magnet (2) of shape controlled, through the induction of a magnetic field in said coil (7) that interacts with the second levitating magnet (2). This allows, for example, measurements of the magnetic field by oscillating the second levitating magnet (2) at a frequency equal to its mechanical resonance frequency (by generating an induced magnetic field of said frequency with the coil (7)). When the second levitating magnet (2) moves from the equilibrium position, a dynamic behavior similar to what it would present if it were held by a spring occurs. It is known that the dynamic behavior of a mass m, subjected to the action of a constant spring k has a maximum for the resonant frequency F, which is given by the condition 2TT-F = (/ // 7I) 1/2 . To observe the resonance with the coil (7) a magnetic reference field is created and the frequency is varied. The signal of the sensor (4) of the magnetic field depends, as has been said, on the position of the levitating magnet. This signal can be represented as a function of a phase component (X) and a counter component (Y) with respect to the reference magnetic field. A measurement obtained by an embodiment of the device of the invention is shown in Figure 3, where the amplitude of the signal has a resonance behavior at a frequency F of 7.4 Hz.
Es posible, también, representar la señal medida por el voltímetro como un módulo igual a (X2 + Y2)1/2 y una fase igual a arctan(Y/X). El resultado obtenido para una realización de la invención se representa en la Figura 4 ( para la misma muestra utilizada en la Figura 3), donde se observa, de nuev o, cómo la amplitud del movimiento tiene un pico de resonancia muy estrecho. It is also possible to represent the signal measured by the voltmeter as a module equal to (X 2 + Y 2 ) 1/2 and a phase equal to arctan (Y / X). The result obtained for an embodiment of the invention is represented in Figure 4 (for the same sample used in Figure 3), where it is observed, again, how the amplitude of the movement has a very narrow resonance peak.
Como ejemplo del funcionamiento del dispositivo de sensado de la presente invención para el sensado de diferentes muestras de material magnético (5) (una lámina de cobalto, una lámina de g rafito pirolítico y una lámina de papel de aluminio), se utiliza una frecuencia igual a la de resonancia mecánica del segundo imán (2) levitante sin la presencia de una muestra magnética (5) y se registra la señal eléctrica en módulo (Χ') y fase (Υ'). En la Figura 5 se muestran los cambios en dicha señal al situar diferentes materiales en el dispositivo. Cabe mencionar también cómo la señal de fase (Υ'), en el caso del grafito pirolítico, es negativa, lo que concuerda con la susceptibilidad magnética de dicho material, que también es negativa, mientras que la señal es positiva cuando se acerca una lámina de 10 nm de cobalto (susceptibilidad positiva). La detección de dicha lámina de 10 nm de cobalto, en la representación de resultados de la Figura 5, se realizó para una distancia entre la muestra (5) y el segundo imán (2) levitante de 6 mm. Teniendo en cuenta que la sensibilidad depende fuertemente con la distancia (el campo magnético va como 1/cf3, siendo d la distancia), la conclusión es que se trata de un método extremadamente sensible. Trabajando a una distancia de 1 mm, por ejemplo, la sensibilidad sería 100 veces mejor. Estos resultados representan una mejora frente a los dispositivos SQUID estimada en, aproximadamente, 2 órdenes de magnitud, lo que representa una considerable mejora frente al estado de I a técnica, que lleva consigo, además, una importante simplificación en las exigencias técnicas para la realización del sensado (no comprende condiciones criogénicas ni de calentamiento de átomos de sensado), con la reducción de costes que, en consecuencia, ello implica. As an example of the operation of the sensing device of the present invention for the sensing of different samples of magnetic material (5) (a cobalt sheet, a pyrolytic graphite sheet and an aluminum foil sheet), an equal frequency is used to the mechanical resonance of the second levitating magnet (2) without the presence of a magnetic sample (5) and the electrical signal is recorded in module (Χ ') and phase (Υ'). Figure 5 shows the changes in said signal by placing different materials in the device. It is also worth mentioning how the phase signal (Υ '), in the case of pyrolytic graphite, is negative, which is consistent with the magnetic susceptibility of said material, which is also negative, while the signal is positive when a sheet approaches 10 nm of cobalt (positive susceptibility). The detection of said 10 nm cobalt sheet, in the representation of results of Figure 5, was performed for a distance between the sample (5) and the second levitating magnet (2) of 6 mm. Taking into account that the sensitivity depends strongly on the distance (the magnetic field goes like 1 / cf 3 , d being the distance), the conclusion is that it is an extremely sensitive method. Working at a distance of 1 mm, for example, the sensitivity would be 100 times better. These results represent an improvement over SQUID devices estimated at approximately 2 orders of magnitude, which represents a considerable improvement over the state of the art, which also entails a significant simplification in the technical requirements for the realization of the sensing (does not include cryogenic conditions or heating of sensing atoms), with the reduction of costs that, consequently, implies.
Para un correcto sensado mediante el dispositivo de la invención, la distancia comprendida entre la muestra de material magnético (5) bajo estudio y el segundo imán (2) levitante está, preferentemente, comprendida entre 1 y 10 mm. Para distancias mayores, la intensidad del campo magnético de interacción entre ambas se reduce notablemente, con la consiguiente pérdida de sensibilidad en el sensado.  For correct sensing by the device of the invention, the distance between the sample of magnetic material (5) under study and the second levitating magnet (2) is preferably between 1 and 10 mm. For greater distances, the intensity of the magnetic field of interaction between the two is significantly reduced, with the consequent loss of sensitivity in the sensing.
Otro aspecto de l a presente invención se refiere a un método de caracterización de materiales magnéticos basado en el dispositivo anteriormente descrito. Mediante una configuración de equilibro del segundo imán (2) levitante, es posible aproximar una muestra magnética al mismo, produciéndose un desplazamiento de su posición de equilibrio. Mediante un s ensor de desplazamiento o del campo magnético (por ejemplo un sensor Hall), es posible medir la variación en la configuración de equilibrio del dispositivo y derivar, mediante una adecuada calibración previa, las propiedades magnéticas de la muestra utilizada. Another aspect of the present invention relates to a method of characterizing magnetic materials based on the device described above. By means of a balancing configuration of the second levitating magnet (2), it is possible to approximate a magnetic sample to it, producing a shift in its equilibrium position. By means of a sensor of displacement or of the magnetic field (for example a Hall sensor), it is possible to measure the variation in the equilibrium configuration of the device and derive, by a suitable prior calibration, the magnetic properties of the sample used.
En una realización del método de la invención, se hace oscilar el segundo imán (2) levitante, por medio de un campo magnético inducido en una bobina (7), a una frecuencia igual a la frecuencia de resonancia mecánica (mediante la generación de un campo magnético inducido de dicha frecuencia con la bobina (7)). Cuando el segundo imán (2) levitante se desplaza de la posición de equilibrio, como consecuencia de I a colocación de una muestra de material magnético (5) en el dispositivo, se produce una variación en la señal detectada por el sensor (4) de campo magnético o el sensor de posición del segundo imán (2) levitante. El método de medida de la invención comprende la comparación de una señal de referencia (sin la presencia de la muestra magnética) con la señal en presencia de la muestra, lo que permite derivar las propiedades magnéticas (por ejemplo, la susceptibilidad magnética) de la misma.  In an embodiment of the method of the invention, the second levitating magnet (2) is oscillated, by means of a magnetic field induced in a coil (7), at a frequency equal to the mechanical resonance frequency (by generating a induced magnetic field of said frequency with the coil (7)). When the second levitating magnet (2) moves from the equilibrium position, as a result of the placement of a sample of magnetic material (5) in the device, there is a variation in the signal detected by the sensor (4) of magnetic field or the position sensor of the second levitating magnet (2). The measurement method of the invention comprises comparing a reference signal (without the presence of the magnetic sample) with the signal in the presence of the sample, which allows to derive the magnetic properties (for example, the magnetic susceptibility) of the same.
Una vez descrita la presente invención y algunas de s us realizaciones preferentes, junto con sus principales ventajas sobre el estado de la técnica, cabe resaltar, de nuevo, que su aplicación no ha de ser entendida como limitada necesariamente a una configuración determinada de los elementos del dispositivo, ni a los materiales referidos en los ejemplos de realizaciones de I a invención, sino que resulta aplicable también a otro tipo de configuraciones y muestras, mediante las adecuadas variaciones en sus elementos, siempre que dichas variaciones no alteren la esencia de la invención, así como el objeto de la misma.  Once the present invention and some of its preferred embodiments have been described, together with its main advantages over the state of the art, it should be noted again that its application should not be understood as necessarily limited to a particular configuration of the elements of the device, nor to the materials referred to in the examples of embodiments of I to the invention, but it is also applicable to other types of configurations and samples, by means of the appropriate variations in its elements, provided that said variations do not alter the essence of the invention , as well as the object of it.

Claims

REIVINDICACIONES
1. - Dispositivo de s ensado de materiales magnéticos caracterizado porque comprende: 1. - Device for testing magnetic materials characterized in that it comprises:
- un primer imán (1 ) situado en una posición fija;  - a first magnet (1) located in a fixed position;
- un segundo imán (2) levitante en equilibrio estable, suspendido bajo el efecto del campo magnético del primer imán (1 ), y configurado para ¡nteraccionar magnéticamente con una muestra de material magnético (5) objeto del sensado;  - a second levitating magnet (2) in stable equilibrium, suspended under the effect of the magnetic field of the first magnet (1), and configured to magnetically interact with a sample of magnetic material (5) object of sensing;
- al menos, un elemento diamagnético (3), situado a una distancia fija del primer imán (1 ), encontrándose dicho elemento diamagnético (3) bajo la acción del campo magnético del primer imán (1 ) y del segundo imán (2);  - at least one diamagnetic element (3), located at a fixed distance from the first magnet (1), said diamagnetic element (3) being under the action of the magnetic field of the first magnet (1) and the second magnet (2);
- al menos, un s ensor (4) de la posición del segundo imán (2) levitante y/o del campo magnético al que se encuentra sometido el segundo imán (2) levitante.  - at least one sensor (4) of the position of the second levitating magnet (2) and / or of the magnetic field to which the second levitating magnet (2) is subjected.
2. - Dispositivo según la reivindicación 1 , que comprende una bobina (7) para el control de la posición del segundo imán (2) levitante. 2. - Device according to claim 1, comprising a coil (7) for controlling the position of the second levitating magnet (2).
3. - Dispositivo según la reivindicación 2 q ue comprende un generador de corriente configurado para generar, mediante su conexión a la bobina (7), un campo magnético variable de frecuencia igual a I a frecuencia de resonancia mecánica del segundo imán levitante (2). 3. - Device according to claim 2 which comprises a current generator configured to generate, by connecting to the coil (7), a variable magnetic field of frequency equal to I to mechanical resonance frequency of the second levitating magnet (2) .
4. - Dispositivo según cualquiera de las reivindicaciones 1-3, donde el sensor (4) del campo magnético es un sensor de efecto Hall. 4. - Device according to any of claims 1-3, wherein the magnetic field sensor (4) is a Hall effect sensor.
5. - Dispositivo según cualquiera de las reivindicaciones 1-4, donde el sensor de posición del segundo imán (2) levitante es un sensor óptico. 5. - Device according to any of claims 1-4, wherein the position sensor of the second levitating magnet (2) is an optical sensor.
6.- Dispositivo según cualquiera de las reivindicaciones 1-5, donde el sensor (4) del campo magnético o el sensor de posición están conectados a un voltímetro (6). 6. Device according to any of claims 1-5, wherein the magnetic field sensor (4) or the position sensor is connected to a voltmeter (6).
7.- Dispositivo según cualquiera de las reivindicaciones 1-6, donde el elemento diamagnético (3) posee forma de lámina. 7. Device according to any of claims 1-6, wherein the diamagnetic element (3) has a sheet shape.
8. - Dispositivo según cualquiera dé l as reivindicaciones 1-7, que comprende dos elementos diamagnéticos (3). 8. - Device according to any one of claims 1-7, comprising two diamagnetic elements (3).
9. - Dispositivo según cualquiera de las reivindicaciones 1-8, donde al menos un elemento diamagnético (3) comprende grafito pirolítico. 9. - Device according to any of claims 1-8, wherein at least one diamagnetic element (3) comprises pyrolytic graphite.
10. - Dispositivo según cualquiera de las reivindicaciones 1-9, donde el segundo imán (2) levitante y la muestra de material magnético (5) bajo estudio se encuentran situados a una distancia comprendida entre 1 y 10 mm. 10. - Device according to any of claims 1-9, wherein the second levitating magnet (2) and the sample of magnetic material (5) under study are located at a distance between 1 and 10 mm.
11. - Método de sensado de materiales magnéticos que comprende el uso de un di spositivo según cualquiera dé l as reivindicaciones 1-10, estando el dispositivo configurado en una posición de equilibro estable del segundo imán (2) levitante, y donde d ¡cha posición presenta un desplazamiento frente a I a posición de e quilibrio que presentaría el segundo imán (2) levitante en aus encía de la muestra de material magnético (5). 11. - Method of sensing magnetic materials comprising the use of a device according to any of claims 1-10, the device being configured in a stable equilibrium position of the second levitating magnet (2), and where right The position presents a displacement in front of I to the equilibrium position that would be presented by the second levitating magnet (2) in the absence of the magnetic material sample (5).
12. - Método según la reivindicación 11 , donde el desplazamiento de la posición del segundo imán (2) levitante se mide mediante el sensor de posición o el sensor (4) de campo magnético. 12. - Method according to claim 11, wherein the displacement of the position of the second levitating magnet (2) is measured by the position sensor or the magnetic field sensor (4).
13. - Método de sensado de materiales magnéticos que comprende el uso de un dispositivo según cualquiera de las reivindicaciones 2-3, donde, por medio de la generación de una corriente a través de la bobina (7) se hace oscilar el segundo imán (2) levitante a una frecuencia igual a su frecuencia de resonancia mecánica. 13. - Method of sensing magnetic materials comprising the use of a device according to any of claims 2-3, wherein, by means of generating a current through the coil (7) the second magnet is oscillated ( 2) levitant at a frequency equal to its mechanical resonance frequency.
14. - Método de sensado según la reivindicación 13, donde se compara el campo magnético medido en el segundo imán (2) levitante sin la presencia de la muestra de material magnético (5) con el campo magnético en presencia de dicha muestra de material magnético (5), estando el segundo imán levitante sometido a un campo magnético variable de frecuencia igual su frecuencia de resonancia mecánica. 14. - Sensing method according to claim 13, wherein the magnetic field measured in the second levitating magnet (2) without the presence of the sample of magnetic material (5) is compared with the magnetic field in the presence of said sample of magnetic material (5), the second levitating magnet being subjected to a variable magnetic field of equal frequency its mechanical resonance frequency.
15. - Método según cualquiera de las reivindicaciones 11-14, donde la distancia comprendida entre el segundo imán (2) levitante y la muestra de material magnético (5) bajo estudio se encuentran situados a una distancia comprendida entre 1 y 10 mm. 15. - Method according to any of claims 11-14, wherein the distance between the second levitating magnet (2) and the sample of magnetic material (5) under study are located at a distance between 1 and 10 mm.
PCT/ES2012/000313 2011-12-23 2012-12-14 Device and method for sensing magnetic materials WO2013093136A1 (en)

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