SK500622021A3 - Device for measuring the magneto-dielectric properties of thin dielectric layers and a system containing this device - Google Patents

Abstract

The device for measuring the magneto-dielectric properties of thin dielectric layers is characterized by the fact that it contains: an electromagnet (2) containing: two E-shaped ferromagnetic cores (1), arranged with the outer posts close to each other, where the central posts of both ferromagnetic cores (1) are shorter as outer posts such that a slot (3) of thickness h is formed between the ends of the middle posts to receive the flat carrier (6) with the measured sample, where the thickness h must be less than 1/8 of the smallest cross-sectional dimension of the middle post and greater than 1mm; at least one coil (4) wound on at least part of at least one column of at least one E-shaped ferromagnetic core (1), where the coil contains contacts for connection to a current source (7), and a flat carrier (6) made of electro-insulating material, adapted to be inserted into slots (3), and containing at least two electrodes for connecting the measuring device (8), for measuring the magneto-dielectric properties of the measured sample, and where a space is created between the electrodes to receive the measured sample. The invention also relates to a measuring system containing such a device.

Description

The invention relates to a device for testing the magneto-dielectric properties of thin dielectric layers. The invention relates to the field of monitoring and measuring technology in electrical engineering.

Current state of the art

To measure the dielectric response of liquid dielectrics in external magnetic fields, capacitors embedded in various magnetic field sources are often used [1]. This type of testing is necessary especially when it comes to liquid dielectrics enriched with magnetic additives (magnetic liquids) [2,3]. In industrial and laboratory conditions, the liquid dielectric is poured into a specialized container in which the electrodes, mainly made of diamagnetic material, are placed. The container is then inserted between two flat permanent magnets, between which a static magnetic field is created [4]. In these conditions, it is possible to monitor the dielectric response of the dielectric by measuring its dielectric permittivity, which is a key property of dielectric materials. The intensity of the external magnetic field between the permanent magnets can only be changed discretely by layering several magnets or by changing their mutual distance. The disadvantage of this method is the considerable inhomogeneity of the magnetic field in the volume of the tested dielectric. The inhomogeneity is related to the strong scattering field at the edges of the magnets, which increases with the distance between the magnets. A homogeneous magnetic field of a permanent magnet with one stable value can be achieved in a Halbach cylinder, which is composed of segments of permanent magnets with appropriately arranged magnetic moments [5]. However, the space of this cylinder, in which the capacitor with the studied dielectric can be inserted, is limited to only one value of the magnetic field intensity. Electromagnets can be used to generate a magnetic field with adjustable intensity while maintaining the distribution of the magnetic field. Among the most available is the solenoid, which creates a homogeneous magnetic field in the direction of its axis in the majority of its internal space [6]. For currently used containers for testing liquid dielectrics, a larger working space provided by Helmholtz coils [7] is desirable. These are two circular coils with the same radius placed coaxially at a distance equal to their radius. Another device for generating a magnetic field with adjustable intensity is an electromagnet with pole extensions, between which a test container with a dielectric can be inserted [8]. Thanks to the ferromagnetic properties of the pole extensions, it is possible to achieve a magnetic field of higher intensity.

The mentioned methods represent structurally robust solutions and require a powerful current source. Such solutions are not suitable especially if it is desirable to test thin dielectric layers, whether liquid or solid.

The aim of this invention is to create a structurally simple, reliable and energy-efficient device for measuring the magneto-dielectric properties of thin dielectric layers as well as a measurement system.

The essence of the invention

The device for measuring the magneto-dielectric properties of thin dielectric layers according to the present invention includes:

- an electromagnet that contains:

by two E-shaped ferromagnetic cores with a relative permeability of min. 10,000, arranged with outer posts close to each other, where the middle posts of both electromagnets are shorter than the outer posts so that a gap of thickness h is formed between the ends of the middle posts to receive the carrier with the measured sample, where the thickness h must be less than 1/8 of the smallest cross-sectional dimension of the middle column and greater than 1 mm;

o at least one coil wound on at least part of at least one column of at least one E-shaped ferromagnetic core, where the coil contains contacts for connection to a current source; a

- a flat carrier made of electro-insulating material, adapted to be inserted into the slot, and containing at least two electrodes for connecting the measuring device, for measuring the magneto-dielectric properties of the measured sample, and where a space is created between the electrodes to receive the measured sample.

Electromagnet cores can be made of solid ferromagnetic material or layered from sheet metal. The material of the cores must be made of a material with a relative permeability of at least 10,000. Preferably, the cores can be made of a magnetically soft alloy of iron and nickel (permalloy) with a relative permeability greater than 50,000, preferably greater than 100,000, most preferably greater than or equal to 500,000, optionally, the cores can be made of ferrite (an alloy of iron and carbon) with a relative permeability greater than 10,000, preferably greater than 15

SK 50062-2021 A3

000, most preferably greater than or equal to 20,000. The cores may also be made of a cobalt-iron alloy with a relative permeability greater than 10,000, more preferably greater than 15,000 and most preferably greater than or equal to 18,000.

According to a preferred embodiment, the E-shaped ferromagnetic cores are arranged above each other so that the slot is placed horizontally - the longitudinal axis of the slot is horizontal.

According to another preferred embodiment, the E-shaped ferromagnetic cores are identical, i.e. j. of the same shape, dimensions and material.

The dimensions of one E-shaped core (stored with the columns up) can be advantageously e.g. length: 65 mm, width: 26 mm, height (of end posts) 23 mm, where the height of the middle post is 22 mm, the thickness of the middle post is 19 mm, and where the thickness of the end posts is 9 mm. Values obtained by multiplying the above values by a coefficient in the interval from 0.3 to 3 belong to the range of values of advantageous core dimensions.

E-shaped ferromagnetic core posts are preferably square, rectangular or circular in cross-section. It is preferable to construct the middle column in a circular cross-section due to higher homogeneity of the magnetic field. The most advantageous diameter of the circular column is 20 mm. Values from 6 mm to 60 mm belong to the range of advantageous values for the diameter of the circular post.

A scattering (inhomogeneous) field is created in the gap near the edges of the columns. The degree of this inhomogeneity increases with the thickness of the gap. To ensure sufficient homogeneity of the magnetic field in the slot, the thickness of the slot must be less than 1/8 of the smallest cross-sectional dimension of the middle post. The thickness of the slot must also be greater than the thickness of the flat carrier. From a structural point of view, the thickness of the slot must be at least 1 mm. Preferably, the thickness of the slot is 2 mm.

The above-mentioned structural arrangement of the electromagnet cores enables the relatively small dimensions and weight of the device according to the invention and the resulting simple way of transporting the device according to the invention, as well as the small power required to achieve a usable magnetic field. This means that such a device does not need a robust current source for its function. Also, this design ensures a homogeneous distribution of the magnetic field in the slot without unwanted stray (edge) fields. Another advantage of the device according to the invention is its simple construction and low procurement costs.

Due to the small thickness of the slot, it is also possible to achieve larger values of magnetic induction even when a smaller electric current is flowing. Due to the use of small values of electric current, significant heating of the coil and the entire electromagnet does not occur. In this way, unwanted heating of the carrier with the sample from the electromagnet can be avoided.

Thanks to the small current and weight, higher safety and less risk of injury are ensured. Such a device can therefore also be suitable for school conditions or for the popularization of science and technology.

According to a preferred embodiment, to ensure the mechanical strength and geometrical stability of the electromagnet, the coil can be wound on a thermally and electrically insulating core, and the core is mounted on at least part of at least one column of at least one E-shaped ferromagnetic core. The core defines the shape of the cavity of the electromagnet, and must fit on core column E.

The shell can be made of Teflon, polyethylene or fiberglass with an insulation resistance of more than 100 ΜΩ. The coil winding should consist of an insulated electrical conductor with a high electrical conductivity, at least 57 x 10 ⁶ S/m.

According to a preferred embodiment, the body with the coil is fitted around the central pillar of the E-shaped ferromagnetic core, along the entire length of the pillar.

According to another advantageous embodiment, the electromagnet contains two coils wound on a body, where each coil is mounted on one outer column of the E-shaped ferromagnetic core. In the case of two coils, it is possible to obtain a magnetic field with a higher intensity when a smaller current flows in both coils. On the other hand, when using two coils, one can be powered by direct current and the other by alternating current. This results in a combined (superimposed) magnetic field in the slot, which is the result of the sum of the vector of the alternating component of the magnetic field and the vector of the direct component of the magnetic field. From the point of view of providing experimental possibilities, this implementation is more advantageous.

The flat carrier for the measured sample is made of electro-insulating material. The flat carrier must have dimensions suitable for insertion into the slot. The flat carrier contains an active or measurement area, which is the area for depositing the sample in the form of a thin layer. Basically it is the space/area between the electrodes.

The dimensions of the active area of the flat carrier are preferably in the range of 90% to 10% of the area (cross-section) of the central pillar of the electromagnet core, more preferably smaller than 85% of the area of the central pillar of the electromagnet and most preferably smaller than 80% of the area of the central pillar of the electromagnet.

Preferably, the flat carrier has such dimensions that it can be completely inserted into the slot, that means that after being placed in the slot, no part of it protrudes from the slot. The flat carrier contains at least two, possibly more electrodes, between which a space is created to receive the tested sample.

SK 50062-2021 A3

According to another advantageous embodiment, the active surface of the flat carrier has such dimensions that, after inserting the flat carrier into the slot, the cross-section of the central column overlaps the entire active surface of the carrier, so that the sample does not protrude beyond the edge of the column. This will ensure that the entire measured sample will be placed in a homogeneous mag. field and the measurement will be more accurate. The size of the sample can also be adapted to the cross-section of the column.

According to a preferred embodiment, the flat carrier is made of two glass plates with an applied electrically conductive layer, e.g. made of ITO (Indium Tin Oxide) material, in the function of electrode and contact for connection to the measuring device.

According to another advantageous embodiment, the flat carrier is in the form of a planar capacitor with an air gap, where the gap forms a space for receiving the measured sample, or with a thin layer of dielectric that forms the measured sample.

According to another advantageous embodiment, the flat carrier is a slide for the measured sample. The corresponding electrodes are steamed on the slide in the form of parallel strips or in the form of two concentric circles with conductive leads for connection to the measuring device. That part of the thin layer of the sample adhering (poured) to the slide, which is located between the vaporized electrodes, is in contact with the electrodes, and thus also exposed to the electric field and the measurement of magneto-dielectric properties.

In some cases, the experiment does not require direct contact of the electrodes with the sample. In that case, the electrodes can be further apart so that the sample between them does not touch them. The electrodes can also advantageously be vaporized on the bottom side of the glass slide and the sample placed on the top side of the glass slide.

The flat carrier preferably includes a handle for inserting into and out of the slot.

With the device according to the invention, it is possible to measure samples that are in the form of a thin layer of 1 pm to 3 mm of liquid or solid dielectric. A layer of biological material is also considered a dielectric in this case.

Another aspect of this invention is also a measurement system containing a measurement device according to the invention, a current source connected to the contacts of the coil as well as one or more measuring devices connected to the contacts of the flat carrier.

The measuring device can be a capacitive bridge, an impedance analyzer, an LCR meter or another device that allows you to measure the frequency dependence of the complex impedance and its individual components (capacitance, inductance, resistance).

As a current source, a controllable current source with ultra-low emissions (where the total harmonic distortion (THD) of the current is less than or equal to 0.1%, preferably 0.05% and most preferably 0.01%) is preferably used to achieve the desired magnetic field. It is preferable to use a current source with a power of 100 W - 500 W to achieve a magnetic field with an induction of 100 pT - 100 mT.

The measuring wires ensuring the connection of the electrodes to the measuring device are advantageously made with technology that eliminates the influence of electromagnetic interference from the environment.

Subsequently, the method of operation of the device and system according to the present invention will be described:

The coil/coils placed on the ferromagnetic core are connected to a current source. By passing an electric current through the coil, a magnetic field is generated, the flow of which is led by the connected E-shaped ferromagnetic cores. Thanks to the created gap, a free space with a quasi-homogeneous induction of the magnetic field was created, which can be used to insert a carrier with a sample whose magneto-dielectric properties are to be measured. The amount of magnetic induction is regulated by changing the amount of current flowing through the coil.

The flat carrier with the sample is exposed to a homogeneous magnetic field after being inserted into the slot. In the case of using flat electrodes placed in the slot plane, the electric field intensity vector in the capacitor is parallel to the magnetic induction vector in the electromagnet slot. When using strip electrodes placed next to each other in the slot plane, it is possible to achieve a perpendicular effect of the magnetic induction vector on the electric field intensity vector between the electrodes.

By using an ultra-low or low frequency electric current source (1 uHz - 1 Hz), an ultra-low or low frequency magnetic field is generated in the slot of the electromagnet. In this way, it is possible to examine, among other things, also biological materials. By placing an inorganic or organic material in the slot of an electromagnet, it is possible to measure the electro-physical properties of materials such as electrical conductivity, resistivity, dielectric losses, permittivity, etc. in an external homogeneous magnetic field with ultra-low or low frequency.

The device and measurement system according to the present invention can be advantageously used in various areas of experimental research or industrial testing, where it is necessary to monitor the dielectric properties of thin layers of liquid or solid dielectrics under conditions of an external magnetic field.

Thanks to the small dimensions of the device, the system can be used to generate a homogeneous magnetic field for research on the magneto-dielectric properties of materials at low temperatures, for example

SK 50062-2021 A3 by immersing the entire system in liquid nitrogen.

Overview of images on drawings

Figure 1 shows a perspective view of the unfolded E-shaped ferromagnetic cores

Figure 2 shows a perspective view of the assembled electromagnet core.

Figure 3 shows a partial section through an E-shaped ferromagnetic core and a coil located on the center column of the core.

Figure 4 shows a cross-section of the ferromagnetic core in the assembled state with a flat carrier inserted into the slot.

Figure 5 shows a top view of the ferromagnetic core and frame, on which a coil is wound with leads connected to a source of electric current.

Figure 6 shows a top view of a ferromagnetic core, a frame on which a coil is wound with leads connected to a source of electric current and a measuring device connected to a planar capacitor inserted in the slot between the central posts of the cores.

Examples of implementation of the invention

Example 1

The device according to the invention contains an electromagnet 2 in the form of two cores 1 of ferrite in the shape of the letter E, arranged on top of each other with posts facing each other, so that the upper and lower outer posts are in close contact with each other, and a gap 3 with a thickness of 2 mm is created between the middle posts (as shown in Fig. 2). The dimensions of the folded core are 65 mm x 26.5 mm x 65 mm.

On the middle column of the lower core is mounted coil 4 wound on a core 5 made of insulator with dimensions of 19.5 mm x 26.5 mm x 22 mm. Coil 4 has ten layers. Each layer has 18 turns of insulated copper wire with a core diameter of 1.1 mm.

Alternatively, the device can contain two coils 4, mounted on the outer posts of the lower ferromagnetic core 1. Each coil 4 is wound on a core 5 made of insulator with dimensions of 10 mm x 26.5 x 22 mm. Each coil 4 has 10 layers, each layer has 18 turns of insulated copper wire with a core diameter of 1.1 mm.

Example 2

In this example, the system is used to investigate the effect of a magnetic field on polarization processes in a hybrid nanofluid with magnetic additives. A hybrid nanofluid is a suspension of non-magnetic and magnetic nanoparticles in a non-polar liquid, in which polarization processes occur at the nanoparticle interfaces.

A flat carrier 6 with a sample (as shown in Fig. 4) is placed in the slot 3 of the device described in Example 1 and connected to a measuring device 8, which is an impedance analyzer (as shown in Fig. 6), which tests the dielectric the response of the tested sample by measuring the capacitance of the flat carrier as a function of the frequency of the electric field. The influence of the magnetic field on the dielectric response of the tested sample is determined by measuring the capacity of the flat carrier 6 in different intensities of the magnetic field. The desired intensity of the magnetic field in the slot 3 of the electromagnet 2 is regulated by setting the value of the current using the source 7 of electric current (as shown in Fig. 6) flowing through the winding of the coil 4 wound on the body 5. The recorded polarization processes are reflected in the change of the measured capacitance and dielectric losses of the flat carrier 6.

Example 3

In this example, the system can be used to induce and detect Fréedericksz phase transitions in ferronematic liquid crystals.

In the slot 3 of the device described in example 1, a flat carrier 6 (as shown in Fig. 4) is placed in the form of a liquid-crystalline cell - a planar capacitor composed of glass plates with vaporized thin conductive layers. The liquid crystal chamber is filled with a ferronematic liquid crystal (a liquid crystal doped with magnetic nanoparticles) in order to induce and detect Fréedericksz phase transitions induced by an external magnetic field. A liquid crystal cell filled with the test sample is connected to a dielectric tester (as shown in Fig. 6) which tests the dielectric response

SK 50062-2021 A3 of the tested sample by measuring the capacity of the liquid crystal cell. By exciting the electromagnet 2 with a current in the range of 100 mA to 3 A from the current source 7, a magnetic field is generated in the slot 3, which causes the arrangement of the magnetic nanoparticles in the direction of the magnetic field. This arrangement increases the susceptibility of the liquid crystal molecules to a magnetic field, resulting in a magnetic Fréedericks transition. The transition is detected by a change in the capacity of the capacitor - flat carrier 6.

Example 4

In this example, the system is used to experimentally test the effect of a magnetic field on the dielectric response of a thin layer of magnetic fluid. A magnetic liquid is a stable suspension of magnetic nanoparticles dispersed in an electro-insulating liquid. A sample of magnetic liquid in the form of a thin layer with a thickness of 10 pm is trapped between the electrodes of a planar capacitor, which is a flat carrier 6. The planar capacitor is inserted into a slot 3 of 2 mm thickness of an electromagnet 2, where it is exposed to an external homogeneous magnetic field. The electrodes of the capacitor are connected to a measuring device 8, which is an impedance analyzer, which tests the dielectric response of the magnetic liquid by measuring the capacitance of the capacitor depending on the frequency of the applied electric field. The influence of the magnetic field on the dielectric response of the magnetic liquid is determined by measuring the capacitance of the capacitor in different intensities of the magnetic field. The intensity of the magnetic field in the slot 3 of the electromagnet 2 is regulated by setting the value of the current using the source 7 of electric current flowing through the winding of the coil 4 wound on the skeleton 5. When the critical value of the magnetic field is reached, the magnetic nanoparticles in the magnetic liquid will be structured, which will be reflected in the change in the measured capacity of the capacitor .

Example 5

In this example, the system is used to generate a homogeneous magnetic field with a frequency from 1 mHz to 100 Hz in order to investigate biological materials.

A sample with a thin layer of biological material is placed in slot 3 of electromagnet 2. By using a direct current source 7 or a current source 7 with a frequency from 1 mHz to 100 Hz, a homogeneous static or ultra-low or low-frequency magnetic field is generated in the slot 3 of the electromagnet 2 by supplying current to the winding of the coil 4 wound on the body 5. By subsequent measurement of the dielectric permittivity spectra of the biological material using an impedance analyzer, the frequency response of the biological material to a static or ultra-low frequency magnetic field is investigated.

Industrial applicability

The industrial applicability is obvious. According to this invention, it is possible to easily generate relatively strong and homogeneous magnetic fields with a small input power in applications for measuring the magneto-dielectric properties of developed materials. According to this invention, it is also possible to test and examine biological materials under the conditions of an external homogeneous magnetic field.

SK 50062-2021 A3

List of relationship tags

- ferromagnetic core in the shape of the letter E

- electromagnet

3 - slot

- coil

- skeleton

- flat sample carrier

- current source

8 - measuring device

SK 50062-2021 A3

List of cited literature:

[1] A. S. Semisalova, N. S. Perov, G. V. Stepanov, E. Y. Kramarenko, and A. R. Khokhlov, Soft Matter 9, 11318 (2013).

[2] R. Sahoo, M. V. Rasna, D. Lisjak, A. Mertelj, and S. Dhara, Appl. Phys. Lett. 106, 161905 (2015).

[3] M. Rajnak, B. Dolnik, J. Kurimsky, R. Cimbala, P. Kopcansky, and M. Timko, J. Chem. Phys. 146, 014704 (2017).

[4] P. Kopčanský, L. Tomčo, K. Marton, M. Koneracká, M. Timko, and I. Potočová, in J. Magn. Magn. Mater. (North-Holland, 2005), pp. 415-418.

[5] J.S. Choi and J. Yoo, IEEE Trans. Magn. 44, 2361 (2008).

[6] B. D. Cullity and C. D. Graham, Introduction to Magnetic Materials (John Wiley & Sons, Inc., 2008).

[7] S. R. Trout, IEEE Trans. Magn. 24, 2108 (1988).

[8] N. Davy, London, Edinburgh, Dublin Philos. Mag. J. Sci. 33, 575 (1942).

Claims (14)

1. A device for measuring the magneto-dielectric properties of thin dielectric layers, that it contains: An electromagnet (2) containing: two E-shaped ferromagnetic cores (1), arranged with outer posts close to each other, where the middle posts of both ferromagnetic cores (1 ) are shorter than the outer posts so that a slot (3) of thickness h is formed between the ends of the middle posts to receive the flat carrier (6) with the measured sample, where the thickness h must be less than 1/8 of the smallest cross-sectional dimension of the middle post and greater than 1 mm; at least one coil (4) wound on at least part of at least one column of at least one E-shaped ferromagnetic core (1), where the coil contains contacts for connection to a current source (7); flat carrier (6) made of electro-insulating material, adapted to be inserted into the slot (3), and containing at least two electrodes for connecting the measuring device (8), for measuring the magneto-dielectric properties of the measured sample, and where a space is created between the electrodes for acceptance of the measured sample. 2. Device according to claim 1, characterized in that the coil (4) is wound on a thermally and electrically insulating shell (5), which is fitted around the middle column of the E-shaped ferromagnetic core (1), along the entire length of the column. 3. Device according to claim 1, characterized in that the electromagnet (2) contains two coils (4) wound on thermally and electrically insulating coils (5), where each coil (5) is mounted on one outer ferromagnetic column E-shaped cores (1). 4. Device according to any of the preceding claims, characterized in that the ferromagnetic cores (1) in the E-shaped electromagnet are made of permalloy - an alloy of iron and nickel - with a relative permeability greater than 50,000 or ferrite with a relative permeability greater than 10 000. 5. Device according to any of the preceding claims, characterized in that the flat carrier (6) is a planar capacitor with an air gap, where the gap forms a space for receiving the measured sample, or a capacitor with a dielectric layer that forms the measured sample. 6. Device according to any one of the preceding claims, characterized in that the electromagnet (2) is arranged in such a way that the E-shaped ferromagnetic cores (1) are placed one above the other and the longitudinal axis of the slot (3) is horizontal. 7. Device according to claim 6, characterized in that the flat carrier (6) is a glass slide with vaporized electrodes in the form of parallel strips or concentric circles, between which there is a place for storing the measured sample. 8. Device according to any one of the preceding claims, characterized in that the flat carrier (6) contains an active surface for receiving the measured sample in the form of a thin layer, and where the dimensions of the flat carrier (6) and the active surface are such that after inserting the flat carrier (6) into the slot (3), the cross-section of the middle column covers the entire active surface of the flat carrier (6). 9. Device according to any one of claims 1 to 7, characterized by the dimensions of the flat carrier (6) being such that it can be fully inserted into the slot (3). 10. The device according to any one of the preceding claims, wherein the flat carrier (6) contains a handle for insertion and removal from the slot (3). 11. The device according to any one of the preceding claims, characterized in that the ferromagnetic cores (1) of the E shape are identical. 12. System, characterized in that it contains a device according to any of the previous claims, a current source (7) connected to the contacts of the coil (4) and at least one measuring device (8) for measuring the magneto-dielectric properties of the measured sample connected to flat carrier electrodes (6). 13. System according to claim 10, characterized in that the measuring device (8) is a capacitance bridge, impedance analyzer, LCR meter or other device that allows measuring complex impedance and its individual components - resistance, inductance, capacity - depending on the frequency of the attached electric field. 14. The system according to claim 13 or 14, characterized in that the current source (7) is a controllable source of electric current with ultra-low emissions, where the total harmonic distortion of the current THD is less than or equal to 0.1%, more preferably 0, 05% and most preferably 0.01%.