FR3122496A1 - Sample holder intended for the characterization of the dielectric and/or magnetic properties of a sample - Google Patents

Abstract

The invention relates to a sample holder (10) comprising: - a main body (20) which extends from a first face (21) towards a second face (22) and coaxially surrounds a cavity (30); - two side plates called, respectively, first (40) and second (50) plate, pressed against, respectively, the first face (21) and the second face (22) so as to close the cavity (30), the first ( 40) and the second (50) plate each comprising, on one of their faces, a waveguide called, respectively, first (41) and second (51) guide, each terminated by an end called the coupling end (41a, 51a) in alignment with the guide axis (XX') so that an electromagnetic wave guided by one of the waveguides is transmitted from the coupling end of said waveguide to the coupling end of the other waveguide via the cavity (30). Figure 1

Description

Sample holder intended for the characterization of the dielectric and/or magnetic properties of a sample

FIELD OF THE INVENTION

The present invention relates to the field of measurements of dielectric and/or magnetic characteristics.

In particular, the present invention relates to a sample holder which makes it possible to accommodate a sample for which it is desired to know the dielectric and/or magnetic characteristics.

The sample holder is in particular compact, and easy to assemble compared to the sample holders known to the state of the art.

TECHNOLOGICAL BACKGROUND OF THE INVENTION

A technique known to those skilled in the art for characterizing the dielectric and/or magnetic properties of a material is based on measuring the interaction between said material and an electromagnetic wave.

In practice, the measurement is carried out by means of a guided structure provided with a cavity in which is housed a sample of the material whose dielectric and/or magnetic properties are to be characterized. The guided structure is, moreover, coupled, for example by means of one or two coaxial cables, with a network analyzer, in particular a vector network analyzer. The two coaxial cables are arranged to allow the network analyzer to measure the phases and amplitudes of a transmitted wave and a wave reflected by the sample. Modeling or an analytical calculation then makes it possible, from measurements of phases and amplitudes, to determine the dielectric permittivity and/or the magnetic permeability of the material considered.

Document [1] cited at the end of the description discloses a guided structure in this respect. This guided structure comprises a coaxial line formed of a conductive core and a tubular casing, one end of which, called the first end, is arranged to house a sample of annular shape. In particular, the sample is in frictional contact via its outer periphery with an inner surface of the tubular casing and via its inner periphery with the conductive core. The guided structure further comprises two coaxial connectors making it possible to connect each of the ends of the coaxial line on the one hand to an incident electromagnetic wave generator and on the other hand to an electromagnetic wave receiver.

However, this structure is not satisfactory.

Indeed, this structure requires a relatively delicate preparation of the sample, in particular a precise control of the thickness of the latter.

Furthermore, the assembly of the sample in the guided structure remains complicated.

In addition, this guided structure is unsuitable for measuring the dielectric and/or magnetic characteristics of fluidic samples (in particular liquid or gaseous).

Another guided structure making it possible to overcome these drawbacks is described in document [2] cited at the end of the description. The latter comprises in particular a sample holder provided with an annular cavity intended to house the sample. More particularly, the sample holder comprises a main body of generally tubular shape coaxially surrounding the cavity along a reference axis. The cavity is also closed by side walls located on either side of the cavity, transversely to the reference axis.

This optimized structure is easier to use than that described in document [1] and opens the way to the characterization of liquid samples.

There are nevertheless situations for which it may be necessary to optimize the compactness of the guided structure.

An object of the present invention is therefore to provide a sample holder that is more compact than the sample holders known from the state of the art.

BRIEF DESCRIPTION OF THE INVENTION

The object of the invention is achieved by a sample holder intended for the characterization of the dielectric and/or magnetic properties of a sample, the sample holder comprising:

- a main body of generally tubular shape which extends, along a guide axis, from a first face to a second face and surrounds a cavity coaxially with the guide axis;

- two side plates called, respectively, first and second plate, pressed against, respectively, the first face and the second face so as to close the cavity, the first and the second plate each comprising, on one of their faces, a guide 'wave said, respectively, first and second guide, each terminated by an end called coupling end in alignment with the guide axis so that an electromagnetic wave guided by one of the waveguides is transmitted from the coupling end of said waveguide to the coupling end of the other waveguide via the cavity.

Such a sample holder is compact and otherwise easy to assemble.

The sample holder is also removable, and can therefore be reused after each measurement or series of measurements.

According to one mode of implementation, for each waveguide of a given side plate comprises a metal strip which extends over one face of said side plate in a direction essentially perpendicular to the guide direction.

According to one mode of implementation, said sample holder comprises a conductive core arranged in the cavity and surrounded coaxially along the guide axis by the main body.

According to one mode of implementation, the conductive core comprises a first end and a second end engaged by embedding, respectively, in the first plate and the second plate.

According to one mode of implementation, first fixing means and second fixing means hold, respectively, the first plate at the first end and the second plate at the second end, the first fixing means and the second fixing means advantageously comprise a thread formed on one and the other of the first and the second end as well as a clamping means cooperating with said thread.

According to one mode of implementation, the conductive core comprises two shoulders in abutment with, respectively, a face of the first plate and a face of the second plate.

According to one embodiment, said sample holder comprises at least one conductive core centering element intended to keep said conductive core aligned parallel to the guide axis.

According to one mode of implementation, the waveguide of each terminal plate comprises another end, opposite the coupling end, and arranged to be coupled with a coaxial waveguide.

According to one mode of implementation, the other end is arranged to allow coupling with the coaxial waveguide by a slice of the terminal plate considered.

According to one mode of implementation, the sample holder comprises arrangements allowing the characterization of fluidic sample in circulation.

By "fluidic" is meant liquid or gaseous.

According to one mode of implementation, the arrangements allowing the characterization of fluidic sample in circulation comprise through-openings made in one or the other of the two end plates.

According to one mode of implementation, said sample holder comprises circulation ducts cooperating with the arrangements allowing the characterization of fluidic sample in circulation.

According to one mode of implementation, one and the other of the first and the second face comprise means for positioning the first and the second end plate.

The invention also relates to a measurement system which comprises a sample holder according to the present invention, and a network analyzer, advantageously a vector network analyzer connected to one and the other of the two waveguides by means of waveguides coaxial waves.

Other characteristics and advantages of the invention will emerge from the detailed description which follows with reference to the appended figures in which:

The is a schematic representation, according to a perspective view, of a sample holder according to the terms of the present invention;

The is a schematic representation, according to a side view, of a main body capable of being implemented within the scope of the present invention;

The is a representation of the sample holder, according to a cutting plane passing through the guide axis and the elongation axis of the waveguides, according to the terms of the present invention, this representation makes it possible in particular to observe the inside the cavity as well as the conductive core when it is implemented;

The is a representation in perspective of the sample holder according to the terms of the present invention, in this representation the first plate is omitted in order to allow observation of the interior of the cavity;

The is a representation of an end plate by its guide face capable of being implemented within the scope of the present invention, this view notably makes it possible to observe the waveguide;

The is a representation of an end plate, by its contact face, and capable of being implemented within the scope of the present invention, this view makes it possible in particular to observe the contact zone;

The is a representation of a terminal plate according to a transverse section plane making it possible to observe the metallic vias connecting the first metallic layer and the second metallic layer;

The is a photograph of the sample holder according to the present invention;

The is a schematic representation, according to a perspective view, of a sample holder and on which are represented the openings allowing the circulation of a fluidic sample;

The is a representation of the specimen holder connected with a fluid circulation system.

DETAILED DESCRIPTION OF THE INVENTION

It is understood that the various figures presented in relation to this description are given for illustration purposes only and do not limit the invention in any way. It is particularly clear that relative scales or dimensions may not be respected.

The present invention relates to a removable sample holder intended to be used to characterize the dielectric and/or magnetic properties of a sample. In particular, the sample holder is arranged to allow the measurement of the transmission and the reflection of an electromagnetic wave to which said sample is subjected.

More particularly, the sample holder comprises a main body of generally tubular shape which extends, along a guide axis, from a first face towards a second face and surrounds, coaxially with the guide axis, a cavity.

The sample holder further comprises two side plates called, respectively, first and second plate, pressed against, respectively, the first face and the second face so as to close the cavity.

The first and the second plate each comprise, on one of their faces, a waveguide called, respectively, first and second guide, each terminated by an end called the coupling end in alignment with the guide axis so that an electromagnetic wave guided by one of the waveguides is transmitted from the coupling end of said waveguide to the coupling end of the other waveguide via the cavity.

The represents a sample holder 10 according to the terms of the present invention.

The sample holder 10 notably comprises a main body 20.

The main body 20 has a generally tubular shape and extends, along a guide axis XX', from a first face 21 to a second face 22 ( ). The main body 20 also comprises an outer surface 23 and an inner surface 24 connected on either side of said body by the first face 21 and the second face 22.

The length of the main body 20, measured in the direction imposed by the guide axis XX', can be between 14 mm and 38 mm, for example be equal to 20 mm.

The diameter of the cylinder formed by the internal surface 24 can be between 7 mm and 150 mm, and for example be equal to 13 mm, 25.4 mm, 50 mm or even 100 mm.

The thickness of the main body (corresponding to the distance between the outer surface 23 and the inner surface 24) can be between 5 mm and 15 mm, for example equal to 8 mm.

The dimensions specified above are given for information only. Indeed, as taught in document [4] cited at the end of the description, these dimensions are adjusted in order to meet particular specifications in terms of impedance. In particular, as specified in the rest of the statement, the sample holder must have an impedance adapted to that of the measurement equipment (for example a network analyzer) with which it is coupled or to a reference impedance d a system for calibrating said sample holder.

The inventors have chosen to size the sample holder so that the latter has an impedance of 50 Ohm. Nevertheless, those skilled in the art will be able to adjust this impedance so as to make the sample holder compatible with other types of measurement and/or calibration equipment.

The main body 20 may comprise brass. However, the present invention should not be limited to this single material and those skilled in the art may consider any other material likely to have properties suitable for its implementation in the context of the present invention. In particular, it could be considered a main body made of steel or even copper.

By "generally tubular shape" is meant a hollow body which has rotational symmetry along the guide axis XX'. More particularly, the hollow body comprises a channel, which extends from the first face towards the second face, and which also has a symmetry of revolution along the guide axis XX'.

The main body 20 surrounds, coaxially with the guide axis XX ', a cavity 30. It is understood, without it being necessary to specify it, that the cavity 30 also has a symmetry of revolution according to the guide axis XX'.

The sample holder 10 also comprises two end plates called, respectively, first plate 40 and second plate 50. The first plate 40 is, in this respect, kept pressed against the first face 21, while the second plate 50 is kept pressed against the second face 22 so as to close the cavity 30.

Thus, the cavity 30 is delimited, laterally, by the internal surface 24 (also of rotational symmetry around the guide axis XX') of the main body, and by the end plates at the level of the first face and the second face.

Each terminal plate comprises, on one of its faces called the guide face, a waveguide. A terminal plate, according to the terms of the present invention, can be formed of a printed circuit (“PCB” or “Printed Circuit Board” according to Anglo-Saxon terminology).

A terminal plate may have a length L of between 20 mm and 50 mm and a width of between 20 mm and 40 mm.

Each of the terminal plates comprises a substrate provided with two parallel faces and on each of which is formed a layer of metallization. In particular, the substrate has a known thickness and permittivity. In particular, and as illustrated in , the guide face of an end plate comprises a first layer of metallization CM1. The waveguide is formed (is drawn) in the first layer of metallization. Furthermore, a contour C, of a width Wc, devoid of metal, separates the waveguide from the rest of the first metallization layer CM1. This contour C ensures in particular the guiding (confinement) of an electromagnetic wave by the waveguide.

The other face of a terminal plate, called the contact face, and opposite the guide face, also comprises a second layer of metallization CM2 ( ). This second metallization layer CM2 comprises an opening, called active zone ZA, and devoid of metal. This active zone ZA is generally circular in shape.

The first metal layer CM1 and the second metal layer CM2 are arranged to be at the same electric potential. In this respect, a terminal plate may comprise metal vias VM passing through said plate from its guide face to its contact face and electrically connecting the first metal layer CM1 with the second metal layer CM2 ( ). The two metallic layers CM1 and CM2 together form an isolated ground plane of the waveguide carried by the terminal plate considered.

Thus, the first plate 40 comprises, on its side of the guide, a waveguide called the first guide 41.

Equivalently, the second plate 50 also comprises on its guide face a waveguide called second waveguide 51.

According to the terms of the present invention, a waveguide is intended to guide, by confinement, an electromagnetic field along a path defined by said waveguide. In the context of the present invention, the waveguide may comprise a strip, in particular a metal strip, of a width Wg and a thickness T, and formed by etching a metal layer. The waveguide notably forms a transmission line. This waveguide can in particular be formed by deposition of a metallic layer on one face of the terminal plate, followed by a photolithography/etching step intended to define the waveguide. The photolithography/etching step can be limited to the withdrawal of a contour C of a width Wg delimiting the waveguide. The metallic species forming the waveguide may comprise copper.

The width Wg of the waveguide can be between 0.5 mm and 3 mm.

The thickness T of the waveguide can be between 0.5 mm and 3 mm.

It is understood that the dimensions and geometric characteristics of the waveguide give it a particular impedance, which, like the sample holder, is adjusted in order to meet particular specifications, and in particular the adaptation criterion of 'impedance.

The inventors have chosen to size the waveguide so that it has an impedance of 50 Ohm. Nevertheless, those skilled in the art will be able to adjust this impedance differently so as to make the waveguide compatible with other types of measurement and/or calibration equipment.

The waveguide can be adapted to guide an electromagnetic wave belonging to the microwave range and in particular having a frequency between 1 MHz and 3 GHz.

The first guide 41 and the second guide 51 are each terminated by one end, called coupling ends.

In particular, the first guide 41 comprises a first coupling end 41a and the second guide 51 comprises a second coupling end 51a.

In particular, the first plate 41 and the second plate 51 are arranged on, respectively, the first face 21 and the second face 22 so that the first coupling end 41a and the second coupling end 51a are in alignment with the axis guide XX'. The active zones ZA are also facing each other and delimit with the internal surface 24 the cavity 30.

It is understood, without it being necessary to specify, that the first plate 40 bears against the first face by its contact face. Equivalently, the second plate 50 bears against the second face via its contact face.

According to this arrangement, an electromagnetic wave guided by one of the waveguides is capable of being transmitted from the coupling end of said waveguide to the coupling end of the other waveguide via the cavity.

More generally, an electromagnetic wave guided by one of the waveguides is likely to be transmitted into the cavity 30 from the coupling end of the waveguide considered. Conversely, an electromagnetic wave propagating in the cavity towards a coupling end of one of the waveguides will be coupled to said waveguide.

This arrangement is particularly advantageous insofar as it makes it possible to observe the response of a sample present in the cavity to the action of an electromagnetic field.

More particularly, an electromagnetic wave, called an incident wave, propagating in one of the waveguides, for example the first guide, can be transmitted into the cavity and interact with the sample. During this interaction, the incident wave can be reflected and/or transmitted by the sample to form, respectively, a reflected wave and a transmitted wave.

The reflected wave and the transmitted wave are, at least in part, injected into the first guide and the second guide respectively.

The analysis in terms of phase and amplitude of the reflected and transmitted waves makes it possible to determine the dielectric and magnetic characteristics of the sample.

This analysis can in particular be carried out by means of an analysis device arranged to collect the transmitted and reflected waves. This analysis device can comprise an electromagnetic wave generator and a radio frequency vector signal analyzer, more particularly a vector network analyzer or an RFID reader operating in a range of frequencies of interest.

The analysis methods allowing the determination of the dielectric and/or magnetic characteristics from the collection of the reflected and transmitted waves are well known to those skilled in the art and are therefore not described in detail in the present application. Nevertheless, those skilled in the art may consult document [3] cited at the end of the description which deals with this subject.

Furthermore, each waveguide also comprises an end, opposite the coupling end, called the connection end, and flush with the edge of the terminal plate on which it is formed.

More particularly, the first guide comprises a connection end called the first connection end 41b and the second guide comprises a connection end called the second connection end 51b ( ).

Each of the connection ends may include a connector adapted to allow coupling between the waveguide and a coaxial cable. In particular, the first connection end 41b and the second connection end 51b can comprise, respectively, a first connector 41c and a second connector 51c ( and ). The connectors 41c and 51c allow in particular the connection, by means of coaxial cables, of the sample holder and of an analysis device.

The positioning of one and the other of the first plate 40 and of the second plate 50 against, respectively, the first face 21 and the second face 22 can involve positioning means.

In particular, the positioning means may comprise pins cooperating with holes. In particular the holes can be provided on the end plates while the pins can be formed on one and the other of the first face and the second face.

Thus, and as illustrated in , pawns P1 and P2 are arranged, respectively, on the first face and the second face while the first plate and the second plate comprise holes, respectively, T1 and T2.

In a particularly advantageous manner, the sample holder comprises a conductive core 60 placed in the cavity 30 and surrounded coaxially along the guide axis XX' by the main body 20.

More particularly, the conductive core comprises a first end 61 and a second end 62 engaged by embedding, respectively, in the first plate 40 and the second plate 50. It is clear that insofar as the conductive core 60 is arranged coaxially to the guide pin XX', it necessarily connects the coupling ends of the first guide and of the second guide to one another.

This arrangement, and in particular the consideration of the conductive core, facilitates the guiding of an electromagnetic wave in the cavity 30.

It is also possible to consider first fixing means and second fixing means intended to hold, respectively, the first plate 40 at the first end and the second plate at the second end.

Advantageously, the first fixing means and the second fixing means can each comprise a thread and a threaded ring.

More particularly, the first fixing means comprise a first thread 61a formed on the first end of the conductive core 60, and a first threaded ring 61b ( ).

Equivalently, the second fixing means comprise a second thread formed on the second end of the conductive core 60, and a second threaded ring.

The implementation of the first and second fixing means makes it possible to hold the first plate and the second plate tight against, respectively, the first face and the second face.

The conductive core 60 can advantageously also comprise shoulders in abutments against the faces of the first plate and of the second plate plated in contact with, respectively, the first face and the second face.

Still advantageously, the conductive core 60 can be maintained coaxially with the guide axis XX', by at least one conductive core centering element intended to maintain said conductive core aligned parallel to the axis of guidance. The centering element can advantageously comprise a washer 63, 64 ( ) in particular bearing against the internal surface of the main body 20, in which the conductive core is inserted. The inner surface may include a groove in which the washer 63, 64 is embedded.

Advantageously, the sample holder comprises arrangements allowing the characterization of liquid sample in circulation. More particularly, the first and/or the second plate comprise through openings 70 ( ).

Conduits as well as a system for activating the circulation of a liquid sample can be connected to the sample holder.

In particular, and as illustrated in , the through-openings 70 are connected, by means of tubes 80, to a reservoir 90 containing a liquid to be analyzed, and a pump 100, in particular a peristaltic pump, intended to circulate the fluid to be analyzed in the cavity 30 of the sample holder . A network analyzer 110 as well as an analysis device 120 (in the present case a computer) of the experimental data are also connected to the sample holder 10.

The sample holder 10 thus described remains compact and relatively easy to use.

Furthermore, this sample holder remains removable and can therefore be reused for different types of measurements.

The present invention also relates to a measurement system which comprises a sample holder according to the terms of the present invention, and a network analyzer, advantageously a vector network analyzer connected to one and the other of the two waveguides at the means of coaxial waveguides.

Of course, the invention is not limited to the embodiments described and variant embodiments can be added without departing from the scope of the invention as defined by the claims.

REFERENCES

[1] FR2619223;

[2] EP2715378;

[3] AM Nicolson and GF Ross, “ Measurement of the Intrinsic Properties of Materials by Time-Domain Techniques ” IEEE Trans. Instruments. Meas, vol. 19, no.4, pp. 377-382, 1970 and W. Weir, " Automatic measurement of complex dielectric constant and permeability at microwave frequencies " Proceedings of the IEEE vol. 62, no. 1, p. 33-36, 1974;

[4] “transmission line theory, coaxial line”, Microwave engineering, David M. Pozar, 4th edition, Wiley, Chapter 2: Transmission Line Theory, Page 56, and Chapter 3: Transmission Lines and Waveguides, Page 130.

Claims (14)

Sample holder (10) intended for the characterization of the dielectric and/or magnetic properties of a sample, the sample holder (10) comprising:
- a main body (20) of generally tubular shape which extends, along a guide axis (XX'), from a first face (21) to a second face (22) and surrounds coaxially with the guide axis (XX') a cavity (30);
- two side plates called, respectively, first (40) and second (50) plate, pressed against, respectively, the first face (21) and the second face (22) so as to close the cavity (30), the first ( 40) and the second (50) plate each comprising, on one of their faces, a waveguide called, respectively, first (41) and second (51) guide, each terminated by an end called the coupling end (41a, 51a) in alignment with the guide axis (XX') so that an electromagnetic wave guided by one of the waveguides is transmitted from the coupling end of said waveguide to the coupling end of the other waveguide via the cavity (30). A sample holder (10) according to claim 1, wherein for each waveguide (41, 51) of a given side plate (40, 50) comprises a metal strip extending over one face of said side plate in a direction essentially perpendicular to the guide axis. Specimen holder (10) according to claim 2, wherein said specimen holder (10) comprises a conductive core (60) disposed in the cavity (30) and coaxially surrounded along the guide axis (XX') by the main body (20). Sample holder (10) according to Claim 3, in which the conductive core (60) comprises a first end (61) and a second end (62) engaged by embedding, respectively, in the first plate (40) and the second plate (50). Specimen holder (10) according to claim 4, wherein first fixing means and second fixing means hold, respectively, the first plate at the first end and the second plate at the second end, the first fixing means and the second fixing means advantageously comprise a thread formed on one and the other of the first and the second end as well as a clamping means cooperating with said thread. Sample holder (10) according to one of Claims 3 to 5, in which the conductive core (60) comprises two shoulders in abutment with, respectively, one face of the first plate and one face of the second plate. A specimen holder (10) according to one of claims 3 to 6, wherein said specimen holder (10) includes at least one core conductor centering member (60) for maintaining said core conductor (60) aligned parallel to the guide axis (XX'). Sample holder (10) according to one of Claims 1 to 7, in which the waveguide of each terminal plate comprises another end, opposite the coupling end, and arranged to be coupled with a waveguide coaxial wave. Sample holder (10) according to claim 8, in which the other end is arranged to allow coupling with the coaxial waveguide by a slice of the terminal plate in question. Sample holder (10) according to one of Claims 1 to 9, in which the sample holder (10) comprises arrangements allowing the characterization of a liquid sample in circulation. Sample holder (10) according to Claim 10, in which the arrangements allowing the characterization of the liquid sample in circulation comprise through-openings made in one and/or the other of the two end plates. A sample holder (10) according to claim 10 or 11, wherein said sample holder (10) comprises flow conduits cooperating with arrangements allowing the characterization of flowing fluid samples. Sample holder (10) according to one of Claims 1 to 12, in which both of the first and of the second faces (22) comprise means for positioning the first and of the second end plate . Measurement system which comprises a sample holder according to one of claims 1 to 13, and a network analyzer, advantageously a vector network analyzer connected to one and the other of the two waveguides by means of waveguides coaxial waves.