Patent Application
20100265143
The present invention belongs to the field of electromagnetic antennas. More precisely, the invention relates to an antenna that is reconfigurable by electrowetting.
Conventionally, an electromagnetic antenna is composed of a radiating element, a dielectric and a ground plane. The radiating element and the ground plane are most commonly metal. They are of very diverse shapes and dimensions.
In radio systems of the software radio type, such as SDR (for Software Defined Radio in English) or SR (for Software Radio), the terminals and/or communicating objects are limited in size and weight and have a poor energy autonomy. These terminals and/or communicating objects require antennas which are miniaturized, on the one hand, and that, on the other, can satisfy a set of constraints associated with the radio system. For example, these antennas must be able to simultaneously cover all the frequencies of a wide frequency band or, as a minimum, these antennas must be very flexible in frequency in order to be able to scan a wide spectrum of frequencies.
In order to satisfy this set of constraints, antennas referred to as “reconfigurable” have been designed.
At least three types of reconfigurable antennas are currently available as presented hereinbelow.
Antenna Reconfigurable in Frequency:
The antenna is then called frequency-flexible. The antenna can thus scan a wide spectrum of frequencies. Such antennas are used in mobile terminals which can be compatible with several communications standards such as the GSM standard (for Global System for Mobile Communications in English) which relates to a frequency band around 900 MHz and the UMTS standard (for Universal Mobile Telecommunications System in English) which relates to a frequency band around 1800 MHz.
Antenna Reconfigurable in Polarization:
The antenna is then referred to as polarization-flexible. For a linear polarization, this polarization may be horizontal or vertical, and for a circular polarization, this may be left or right. Such antennas provide a better signal-to-noise ratio and are particularly advantageous in locations where the propagation of electromagnetic waves encounters numerous obstacles, such as for example inside buildings.
Antenna Reconfigurable in Radiation Pattern:
The antenna is then capable of modifying its radiation pattern in order, for example, to adapt to a change in the propagation environment.
In the current prior art, in view of the dimensional constraints, the reconfiguration of an antenna is not achieved by a mechanical or geometric deformation of the antenna or of the elements composing it.
In fact, the reconfiguration of an antenna is currently achieved by switching certain elements within the radiating element, the dielectric and the ground plane that compose it, or by varying impedances connected to certain points on the antenna.
These two modes of reconfiguration present certain drawbacks.
In the case where elements of the antenna are switched, a discontinuous variation of the characteristics that it is desired to reconfigure (frequency, directivity of the radiation) is obtained.
In the case where impedances connected to certain points on the antenna are varied, a continuous variation in frequency is obtained but limited by the ranges of variation of the impedances used. For the same reasons, the continuous variations of the radiation pattern are limited.
The combination of the two types of reconfiguration (by switching of elements and by variation of impedances) allows variations of the physical characteristics in question to be obtained over wider ranges but with an increased complexity that tends to be incompatible with the design constraints (dimensions, weight, energy autonomy) of the terminals and/or the communicating objects in question.
Furthermore, the elements (switches and impedances) enabling the reconfiguration exhibit intrinsic losses which affect the efficiency of the antenna.
There is therefore a real need for a technique for reconfiguring an electromagnetic antenna which does not exhibit the aforementioned drawbacks of the known reconfiguration techniques.
Thus, according to a first aspect, the present invention relates to an electromagnetic antenna that is noteworthy in that it comprises a radiating element composed of a first, electrically conducting, fluid substance sitting on a first element and of a second fluid substance sitting on a second element, the first fluid substance being in contact with the second fluid substance, said fluid substances being immiscible and said first and second elements being electrically conducting and electrically isolated from one another.
The antenna according to the invention has the advantage of comprising a radiating element which, instead of being made of metal, is composed of a fluid substance being deformable by nature.
According to a preferred feature, the first fluid substance is a substance made electrically conducting by the introduction into this substance of particles or of fragments of a conducting element or by the introduction into this substance of a conducting substance.
The introduction into the fluid substance of fragments of a conducting element endows the radiating element (fluid substance and fragments) with particular electromagnetic properties. Thus, the resonant frequency is no longer necessarily fixed by the dimensions and the volume of the fluid substance but can equally depend on potential folding effects of the fragments whose deployed lengths may be very significant. This thus allows operation of the antenna in frequency bands that are much lower than in the case of a simple fluid substance.
According to a preferred feature, the second element is composed of an assembly of sub-elements electrically isolated from one another.
The decomposition of the second element into sub-elements facilitates and allows an improved control of the deformation of the assembly. It is possible to obtain an asymmetric deformation.
According to a preferred feature, the contact surfaces of the first and of the second element with the first and the second fluid substance, respectively, are planar or concave or convex.
The shape adopted by the contact surface of the elements with the fluid substances, in particular when the latter is concave, allows the effects due to the weight of the fluid substance (gravity effects) to be compensated, the size of the antenna to be increased and hence enables the use thereof in lower frequency bands.
According to a preferred feature, at least one of the contact surfaces of the first and of the second element with the first and the second fluid substance, respectively, is coated with a layer of insulating material.
Thus, the introduction of a layer of insulating material allows the fluid substances to be isolated and chemical reactions between the fluid substances and the contact surfaces of the elements with the fluid substances to be avoided.
A greater flexibility in the choice of the materials forming the first and second elements is also obtained.
According to a preferred feature, the contours and the volume of the first fluid substance are deformed in a reversible manner by application of a potential difference between the first and the second element.
The deformation of the contours and of the volume of the first fluid substance can be slow and progressive. In view of the flexibility of the substances forming the antenna, this deformation is reversible. Since the deformation is continuous, the reconfiguration of the antenna is also continuous, progressive and reversible. These features greatly enhance the adaptability of the antenna.
According to a preferred feature, the contours and the volume of the first fluid substance are deformed by application of a plurality of potential differences between the first element and each of the sub-elements of the second element.
Since the second element can be decomposed into sub-elements, the deformation of the contours and of the volume of the first fluid substance can be asymmetric. The reconfiguration of the antenna, in particular in polarization and in radiation pattern, is greatly improved.
According to a preferred feature, the antenna according to the invention comprises a protection cover enclosing the first element, the second element, the first fluid substance and the second fluid substance.
The invention also relates to a method for reconfiguring an antenna such as previously described, said method comprising an operation for deforming the contours and the volume of the first fluid substance by application of at least one potential difference between the first and the second element.
A method for reconfiguration of an antenna according to the invention has the advantage of being continuous, progressive and reversible.
The invention also relates to a radiocommunications terminal comprising an antenna such as described hereinabove.
Other features and advantages of the invention will become apparent upon reading preferred embodiments, described with reference to the appended figures in which:
a and 7b illustrate other examples of application of the reconfiguration method according to the invention,
a illustrates another example of application of the reconfiguration method according to the invention,
b illustrates, according to a transverse cross-sectional view through the plane P, the example of application of the reconfiguration method according to the invention in
a and 9b illustrate other examples of application of the reconfiguration method according to the invention,
The antenna shown in
The RF port is connected to a first electrically conducting element S1.
In the same plane P, the element S1 is surrounded by an insulating element S3 which separates it from a second electrically conducting element S2, the element S2 surrounding the element S3.
A first highly electrically conducting fluid substance F1 sits on the element S1. As shown in
The fluid substance F1 has a surface tension comparable with that of oil. By way of example, the fluid substance F1 can be a liquid, a body in a solid-liquid transition phase or else a soft and flowing material, of the polymer type.
The volume of the fluid substance F1 is small and may, by way of example, be similar to that of a droplet.
A second fluid substance F2 sits on the element S2. As is shown in
The fluid substance F2 has a surface tension comparable with that of water. By way of example, the fluid substance F2 can be water or a liquid having properties comparable with those of water.
The fluid substances F1 and F2 are immiscible.
The fluid substances F1 and F2 are in contact via a contact surface Sc. In the particular embodiment of the invention shown in
According to a variant embodiment shown in
According to another variant embodiment not shown, the fluid substance F1 is made electrically conducting by the introduction of a conducting fluid substance mixed with the fluid substance F1.
Other shapes may however be envisioned for the elements S1, S2 and S3.
The surface formed by the surfaces of the elements S1, S2 and S3 in contact with the fluid substances F1 and F2 can be planar such as those shown in
When the surface formed by the surfaces of the elements S1, S2 and S3 in contact with the fluid substances F1 and F2 is convex, the radius of curvature must be less than a certain threshold. If this threshold is exceeded, the effects of gravity acting on the fluid substances may cause the outer “envelope” of these fluid substances to tear. The fluid substances are transformed into droplets at the contact with the convex surface formed from the surfaces of the elements S1, S2 and S3.
When the surface formed by the surfaces of the elements S1, S2 and S3 in contact with the fluid substances F1 and F2 is concave, the volume and the dimensions of the fluid substances are increased, in particular the dimension of the contact surface Sc. In addition, the effects of gravity are compensated, thus limiting the impact of the weight of the fluid substance on its behavior.
In one particular embodiment of the invention, at least one of the surfaces of the elements S1, S2 and S3 in contact with the fluid substances F1 and F2 is coated with a thin layer of an insulating material.
This thin layer allows the fluid substances F1 and F2 to be isolated and thus chemical reactions between the fluid substances F1 and F2 and the surfaces of the elements S1, S2 and S3 to be avoided.
This solution also allows a greater flexibility in the choice of the materials forming, in particular, the elements S1 and S2.
The invention also relates to a method for reconfiguring an antenna according to the invention.
In
By applying a DC voltage to the element S2, in other words a steady potential difference between the elements S1 and S2, the energy between the fluid substance F2 and the contact surface Sc is modified. The volume occupied by the fluid substance F2 is then deformed and the contours of this fluid substance F2 are displaced.
The displacement of the contours of the fluid substance F2 leads to the displacement of the contours of the fluid substance F1 with which it is in contact. The volume occupied by the fluid substance F1 is in turn then deformed. This displacement and this deformation lead to a modification of the characteristics of the fluid substance F1 from the point of view of electromagnetic radiation.
The arrows drawn in
An antenna that is reconfigurable by deformation of the contours and of a volume of a conducting fluid substance is thus obtained.
This reconfiguration is possible in frequency and in radiation pattern.
Generally speaking, the phenomenon of deformation and of displacement of the contours of a fluid substance in contact with a surface to which an electrical voltage is applied corresponds to the phenomenon referred to as “electrowetting”.
a illustrates an example of application of the reconfiguration method according to the invention. A deformation, represented by the arrows, of the contours and volumes of the two fluid substances F1 and F2 is obtained by the application of a voltage T1. In this example, the deformation produced leads to the formation of a substantial radiating length and hence to a relatively low frequency of operation.
b illustrates another example of application of the reconfiguration method according to the invention. A deformation, represented by the arrows, of the contours and volumes of the two fluid substances F1 and F2 is obtained by the application of a voltage T2 different from T1. In this new example, the deformation produced leads to the formation of a shorter radiating length than in the preceding example and hence to a higher frequency of operation.
These two examples illustrate the capacity for reconfiguration in frequency of the antenna according to the invention.
When the element S2 is composed of an assembly of n sub-elements SEi with i varying from 1 to n (embodiment shown in
a illustrates another example of application of the reconfiguration method according to the invention. In this example, an asymmetric deformation of the contours and volumes of the two fluid substances F1 and F2 is obtained by application of different voltages Ti and Tj for two sub-elements SEi and SEj, respectively, of the element S2.
b illustrates, according to a transverse cross-sectional view through the plane P, the preceding example of application of the reconfiguration method according to the invention such as illustrated in
a and 9b illustrate other examples of application of the reconfiguration method according to the invention.
a and 9b illustrate examples of application of the reconfiguration method according to the invention similar to those shown in
When the surface formed by the surfaces of the elements S1, S2 and S3 in contact with the fluid substances F1 and F2 is concave (for example, so as to form a kind of bowl), a part of this surface (that which forms the edges of the bowl and which corresponds notably to the surface of the element S2) allows the deformation of the volume of the fluid substance F2 to be mechanically controlled and the effects of gravity to be compensated, thus enhancing the quality of the antenna obtained.
The possibility of being able to vary in a continuous manner the potential difference (or differences) between the elements S1 and S2 (or the sub-elements of the element S2) enables a reversible deformation of the contours and of the volume of the fluid substance F1 and a continuous variation of the characteristics of the antenna (frequency, polarization, directivity of the radiation) to be obtained.
The protection cover provides an enclosure for the various elements composing the antenna such as the elements S1, S2 and S3 and the fluid substances F1 and F2.
The protection cover is formed from solid walls.
These walls are permeable to the radiation of electromagnetic waves by the antenna with a minimum of losses.
In one particular embodiment, such as that shown in
In one particular embodiment, the protection cover can also enclose a third fluid substance F3 which is immiscible with the fluid substances F1 and F2. This third fluid substance F3 allows the empty spaces between the walls of the protection cover and the elements that it encloses to be filled.
The invention also relates to a radiocommunications terminal or any communicating object capable of accepting an antenna according to the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0758890 | Nov 2007 | FR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/FR08/51987 | 11/4/2008 | WO | 00 | 5/5/2010 |
