The present invention relates to the field of antennas and in particular it relates to a circular polarization antenna for radio frequency energy harvesting applications.

More specifically, said antenna is dimensioned and shaped to be positioned on an end portion of a fastening element, in particular a threaded fastening element, i.e. a fastening element having a threaded portion (such as the head of a screw or the head of a stud) and designed to have greater gain, greater efficiency and pick up a greater amount of energy from an electromagnetic wave than a antenna of a known type.

The present invention also refers to a system for storing electrical energy comprising said antenna or said antenna in combination with a fastening element, as well as an impedance adapter, a rectifier for transforming an alternating electric current (generated when the antenna resonates with a frequency of an electromagnetic wave) in a direct electric current, and energy storage means for storing an electric energy.

The energy stored in said energy storage means can be used to power any electrical device and/or electronic device.

A plurality of embodiments of said system are possible.

In fact, the components mentioned above, i.e. the impedance adapter, the rectifier and the storage means, can all be arranged in a cavity formed in the antenna or all in a further cavity formed in an end portion of said fastening element (on which the antenna is positioned) or one or more components can be arranged inside a cavity formed in the antenna and the remaining components can be arranged inside a further cavity formed in the end portion of the fastening element.

Prior art Currently, several antennas are known.

An antenna of known type used in radio frequency energy harvesting applications is an antenna called a spiral antenna.

Said antenna comprises a substrate, a layer of metallic material having the shape of a spiral, positioned on a face of the substrate.

However, said antenna of known type has some disadvantages.

A first disadvantage is given by the fact that the dimensions of said antenna of known type do not allow the antenna itself to be positioned on an end portion of a fastening element, such as for example the head of a screw or the head of a stud.

A second disadvantage is given by the fact that it is necessary to reach a compromise between the gain of said antenna, the frequency band in which said antenna is used and the dimensions of said antenna in order to maximize the amount of energy to be picked up.

However, a compromise between gain, frequency band and dimensions makes it more difficult to position the antenna on an end portion of a fastening element, if not impossible, as the dimensions of the antenna would not be the only technical feature to be to take into account.

A further disadvantage is given by the fact that said antenna of known type is provided with a ground plane of significant dimensions to optimize the gain and the frequency band and the presence of said ground plane causes an increase in the dimensions of the antenna, thus that the antenna is difficult to position on an end portion of a fastening element.

Aim of the invention

Aim of the present invention is to overcome said disadvantages by providing a circular polarization antenna for radio frequency energy harvesting applications which has reduced dimensions (in the order of millimeters), and is shaped to be applied on an end portion of a fastening element, in particular a threaded fastening element (such as the head of a screw or the head of a stud), and allows to maximize the gain and efficiency of the antenna, as well as to pick up a greater amount of energy from a wave electromagnetic with a frequency greater than or equal to 2,4GHz and less than or equal to 2,5GHz, compared to an antenna of known type.

Object of the invention

It is object of the invention a circular polarization antenna configured to pick up an electromagnetic wave with a frequency between greater than or equal to 2,4GHz and less than or equal to 2,5GHz, and resonate at the frequency of said electromagnetic wave and comprises:

- a substrate comprising a first face and a second face, opposite to said first face, and

- a first layer of metallic material arranged on said first face.

In particular, said substrate is made of a ceramic material having an isotropic dielectric constant greater than or equal to 11 and less than or equal to 14, and has a cavity arranged centrally with respect to said second face.

Preferred embodiments of the circular polarization antenna are disclosed in the dependent claims

The present invention relates also to a system for storing electrical energy comprising said circular polarization antenna.

Figure list

The present invention will be now described, for illustrative, but not limitative purposes, according to its embodiment, making particular reference to the enclosed figures, wherein:

Figure 1 is a perspective view showing a screw on whose head a circular polarization antenna, according to the invention, is applied;

Figure 2 is a top view of the screw of Figure 1 ;

Figure 3 is a perspective view of the circular polarization antenna, object of the invention;

Figure 4 is a bottom view of the circular polarization antenna of Figure 3

Figure 5 is a top view of the circular polarization antenna of Figure 3;

Figure 6A is a cross-sectional view of the circular polarization antenna of figure 5 along the line A-A

Figure 6B is a sectional perspective view of the circular polarization antenna of Figure 5 along the line A-A

Figure 7 is a schematic view of a system for storing electrical energy comprising the antenna of Figure 3, an impedance adapter, a rectifier and energy storage means;

Figure 8 is a longitudinal section of a first embodiment of a system for storing electrical energy comprising the antenna of Figure 3 and a screw, wherein the antenna comprises inside an impedance adapter, a rectifier and energy storage means;

Figure 9 is a longitudinal section of a second embodiment of a system for storing electrical energy comprising the antenna of Figure 3 and a screw, wherein the antenna comprises inside an impedance adapter and a rectifier, and the head of the screw comprises energy storage means;

Figure 10 is a longitudinal section of a third embodiment of a system for storing electrical energy comprising the antenna of Figure 3 and a screw, wherein the antenna comprises inside energy storage means and the head of the screw comprises inside an impedance adapter and a rectifier;

Figure 11 is a longitudinal section of a fourth embodiment of a system for storing electrical energy comprising the antenna of Figure 3 and a screw, wherein the head of the screw comprises inside an impedance adapter, a rectifier and energy storage means.

Detailed description of the invention

With reference to Figure 1 to 6B, a circular polarization antenna 1 , according to the invention, adapted to be installed on a fastening element, in particular a threaded fastening element, is disclosed.

Threaded fastening element means a fastening element having a threaded portion.

In particular, the antenna 1 is configured to pick up an electromagnetic wave with a frequency between 0,8GHz and 5,8GHz.

More particularly, in the embodiment being disclosed, the antenna 1 is configured to pick up an electromagnetic wave with a frequency greater than or equal to 2,4GHz and less than or equal to 2,5GHz.

Figures 1 and 2 show the antenna 1 object of the invention applied on an end portion of a threaded fastening element.

In the example being disclosed, said threaded fastening element is a screw indicated with the reference 100 and said end portion is the head 101 of said screw.

Although not shown in Figures, the antenna 1 can be installed on an end portion of any further fastening element, different from a screw, such as stud.

Furthermore, although not shown in Figures, the antenna 1 can be installed on an end portion opposite to the head of a fastening element.

In general, the fastening element is made of a metallic material and consequently the antenna 1 is positioned on metallic surface.

Below, the description will refer to the screw 100 which comprises the head 101 , as well as a body 102.

The head 101 of the screw 100 comprises a first surface 111 and a second surface 112, opposite to the first surface 111 , connected to the body 102.

The body 102 comprises a threaded portion 102A.

As shown in Figures from 3 to 6B, the antenna 1 comprises:

- a substrate 2 comprising a first face 21 and a second face 22, opposite to the first face 21 , and

- a first layer or upper layer 3 made of a metallic material, arranged on said first face 21 .

In particular, when the antenna 1 is installed on the head 101 of the screw 100, the second face 22 of the substrate 2 of the antenna 1 is arranged on the first surface 111 of the head 101 of said screw 100.

With particular reference to the substrate 2, said substrate 2 is made of a ceramic material.

In particular, said ceramic material has an isotropic dielectric constant greater than or equal to 11 and less than or equal to 14.

In the embodiment being disclosed, the isotropic dielectric constant of said ceramic material is equal to 12,2.

In particular, in the embodiment being disclosed, the ceramic material is Rogers TMM® 13i.

The substrate 2 has a height between 5mm and 20mm.

In the embodiment being disclosed, the substrate 2 has a height equal to 10mm.

Furthermore, said substrate 2 has a cylindrical shape. The diameter of the substrate 2 is between 16mm and 32mm.

In the embodiment being disclosed, the substrate 2 has a diameter equal to 20mm.

The dimensions of the height and diameter of the substrate 2 are such that the antenna 1 can be applied to an end portion of a fastening element, in particular a threaded fastening element.

In other words, the dimensions of the height and diameter of the substrate 2 are such that the antenna 1 can be applied on the head 101 of a screw 100 as shown in Figures 1 and 2.

Furthermore, said substrate 2 has a cavity 20.

The term cavity can also be understood as a blind hole.

Said cavity 20 is shaped and dimensioned to maximize the gain and efficiency of the antenna 1 .

In particular, said cavity 20 has a height between 3 mm and 14mm. In the embodiment being disclosed, the height of said cavity 20 is equal to 7mm.

The diameter of said cavity 20 is between 6mm and 14mm.

In the embodiment being disclosed, the cavity 20 has a cylindrical shape and the diameter of the cavity 20 is equal to 8mm.

Although not shown in Figures, said cavity 20 can be have a truncated cone shape, without departing from the invention.

Also when the cavity 20 has a truncated cone shape, the height can be between 3 mm and 14mm and the diameter can be 6mm and 14mm.

Regardless of the shape and dimensions of the cavity 20, such cavity 20 is arranged centrally with respect to the second face 22 of the substrate 2.

The fact that the substrate 2 is made of a ceramic material having a high isotropic dielectric constant (i.e. between 11 e 14) offers the possibility of reducing the dimensions of the antenna 1 .

In particular, the fact that the substrate 2 is made of a ceramic material having a high isotropic dielectric constant allow the antenna 1 to resonate at the same frequency of the electromagnetic wave, regardless of whether the antenna 1 is positioned on a fastening element or not.

Consequently, the resonant effect of the antenna 1 is not affected by the presence of a fastening element (which, as previously said, is generally made of a metallic material) and therefore it is possible to maximize the amount of energy picked up by the antenna 1 .

In other words, the choice of using for the substrate 2 a ceramic material having a high isotropic dielectric constant allows to maximize the ability of the antenna 1 to pick up energy since such ability is not significantly influenced by the presence of the fixing.

Furthermore, the fact that the substrate 2 is made of a ceramic material having a high isotropic dielectric constant together with the fact the substrate 2 has a certain height (between 5mm and 20mm) and a certain diameter (between 16mm and 32mm) allow to avoid the presence of a ground plane.

The absence of a ground plane further reduces the dimensions of the antenna 1 .

Consequently, the resonant effect of the antenna 1 is guaranteed even if the antenna 1 has no ground plane.

If an antenna of known type is considered, to obtain a resonant effect with a ceramic material having a value of the isotropic dielectric constant different from the values of the isotropic dielectric constant mentioned above, it would be necessary to increase the height of a substrate and/or the diameter of said substrate or, alternatively, to add a ground plane.

However, the addition of the ground plane would increase the dimensions of the antenna of a known type and such an antenna of a known type would not be able to be positioned on a fastening element which has reduced dimensions or would render the fastening element unusable (for example when the dimensions antenna of known type are such that a peripheral portion of said antenna of known type extends beyond the perimeter of the end portion of the fixing element).

Also the presence of the cavity 20 in the substrate 2 allows to reduce the dimensions of the antenna 1 . However, the contribution offered by the cavity 20 for the reduction of the dimensions of the antenna is less significant than the contribution offered by the ceramic material.

The presence of the cavity 20 in the substrate 2 allows to maximize the gain and the efficiency of the antenna 1 .

The ceramic material of the substrate 2 also allows to maximize the gain and efficiency of the antenna. However, the contribution offered by the ceramic material to maximize the gain and efficiency of the antenna is less significant than the contribution offered by the presence of the cavity 20.

Furthermore, the fact that the antenna 1 has a substrate 2 made of a ceramic material and a cavity 20 arranged centrally with respect to the second face 22 of the substrate 2 (in which said antenna preferably has a certain shape and certain dimensions) allows the antenna 1 to pick up a greater quantity of energy from an electromagnetic wave than an antenna of a known type, considering that the antenna 1 is positioned on the head 101 of the screw 100.

With particular reference to the first layer 3 of metallic material, said metallic material is chosen from the following metals: copper, annealed copper, brass, silver, gold.

Nella forma di realizzazione che si descrive, il materiale metallico scelto per il primo Strato 3 e il rame.

In the embodiment being disclosed, the metallic material chosen for the first layer 3 is copper.

Furthermore, said first layer 3 has a double spiral shape.

Although not shown in Figures, a second layer or lower layer made of a metallic material can be arranged on the second face 22 of the substrate

2.

In terms of shape and dimensions, said second layer is different from the first layer 3 of metallic material.

In fact, said second layer has shape and dimensions such as to contact the entire second face 22 of the substrate 2.

In terms of material, the metallic material chosen for said second layer can be equal to or different from the metallic material of the first layer

3.

Consequently, the metallic material for said second layer can be copper or a further metallic material different from copper.

Similarly to the first layer 3, the metallic material for the second layer can be chosen from the following metals: copper, annealed copper, brass, silver, gold.

In particular, as shown in Figure 7, said antenna 1 can be part of an electrical energy storage system for storing electrical energy comprising an impedance adapter 5, a rectifier 6, and energy storage means 7 (such as at least one battery and/or at least one supercapacitor).

Therefore, the present invention also refers to an electrical energy storage system for storing electrical energy comprising the antenna 1 , the impedance adapter 5, connected to the first layer 3 of the antenna 1 , the rectifier 6, connected to said impedance adapter 5, and said energy storage means 7 for storing electrical energy, connected to said rectifier 6.

In particular, the impedance adapter 5 is configured to adapt the impedance of said antenna 1 to said rectifier 6, and the rectifier 6 is configured to transform an alternating electric current, generated when the antenna 1 resonates with a frequency of said electromagnetic wave, in a direct electric current.

In a first variant of the antenna 1 , said antenna 1 comprises said impedance adapter 5 and said rectifier 6 which are arranged inside the cavity 20 of the substrate 2, while said energy storage means 7 can be arranged elsewhere.

In a second variant of the antenna 1 , said antenna 1 comprises said impedance adapter 5, said rectifier 6 and said energy storage means 7 which are arranged inside the cavity 20 of the substrate 2.

In both of the variants mentioned above, the antenna itself is an electrical energy storage system for storing electrical energy.

Figures from 8 to 11 show a respective embodiment of a system for storing electrical energy comprising the antenna 1 and the screw 100, whose head 101 has a further cavity 110 (different from the cavity 20 of the substrate 2).

The three components mentioned above, i.e. said impedance adapter 5, said rectifier 6, and said energy storage means 7 can be arranged inside the antenna 1 or inside the head 101 of the screw 100 or two components can be arranged inside the antenna 1 and one component in the head 101 of the screw 100 or two components can be arranged inside the head 101 of the screw 100 and one component inside the antenna 1 .

Figure 8 shows a first embodiment of a system for storing electrical energy.

In said first embodiment, said impedance adapter 5, said rectifier 6 and said energy storage means 7 are arranged inside the cavity 20 of the substrate 2.

In particular, the antenna 1 can be provided with a printed circuit (PCB), not shown, having a first surface and a second surface, opposite the first surface.

The impedance adapter 5, the rectifier 6 and the energy storage means 7 can be positioned on the first surface of said printed circuit.

Figure 9 shows a second embodiment of a system for storing electrical energy.

In said second embodiment, differently from the first embodiment, said impedance adaptor 5 and said rectifier 6 are arranged inside the cavity 20 of the substrate 2 and said energy storage means 7 are arranged inside the further cavity 110 of the head 101 of the screw 100.

Furthermore, differently from the first embodiment, when the antenna 1 is provided with the printed circuit, only the impedance adapter 5 and the rectifier 6 can be positioned on the first surface of said printed circuit.

With particular reference to said energy storage means 7, in a first alternative, said energy storage means 7 can be positioned on the second surface of said printed circuit.

In a second alternative, said storage energy means 7 can be positioned on a further printed circuit, different from said printed circuit and arranged inside said further cavity 110.

In this second alternative, said further printed circuit is included in the system for storing energy. ln particular, said further printed circuit has a first surface and a second surface, opposite to the first surface, and said energy storage means 7 can be positioned on the first surface of said further printed circuit.

Figure 10 shows a third embodiment of a system for storing electrical energy.

In said third embodiment, differently from the second embodiment above mentioned, said impedance adapter 5 and said rectifier 6 are arranged inside the further cavity 110 of the head 101 of the screw 100 and said energy storage means 7 are arranged inside the cavity 20 of the substrate of the antenna 1 .

Hence, when the antenna is provided with the printed circuit, only said energy storage means 7 can be positioned on the first surface of said printed circuit.

With particular reference to the impedance adapter 5 and to the rectifier 6, in a first alternative, said impedance adapter 5 and said rectifier 6 can be positioned on the second surface of said printed circuit.

In a second alternative, said impedance adapter 5 and said rectifier 6 can be positioned on the first surface of said further printed circuit (which is included in the system for storing electrical energy).

Figure 11 shows a fourth embodiment of a system for storing electrical energy.

In said fourth embodiment, said impedance adapter 5, said rectifier 6 and said energy storage means 7 are arranged inside the further cavity 110 of the head 101 of the screw 100.

In said fourth embodiment, differently from the third embodiment, the impedance adapter 5, the rectifier 6 and the energy storage means 7 can be positioned on the first surface of a further printed circuit (which is included in the system for storing electrical energy).

With reference to the four embodiments above mentioned, when the antenna 1 is provided with a printed circuit, said printed circuit can have shape and dimensions such its second surface contacts at least a portion of the head 101 of the screw 100.

In a first alternative, said printed circuit can have a shape and dimensions such that the second face 22 of the substrate 2 partially or totally contacts the first surface of said printed circuit.

In a second alternative, the printed circuit can have a shape and dimensions such that the second face 22 of the substrate 2 does not contact the first surface of said printed circuit. In other words, the printed circuit can have a shape and dimensions such as to be inside an area defined by the projection of the cavity 20 on the head 101 of the screw 100.

Furthermore, although not shown in Figures, said system for storing electrical energy can comprise one or more sensors, each of which is connected to said energy storage means 7 to be powered by said energy storage means 7 when in use.

Said one or more sensors can be arranged on the head 101 of the screw 100 or inside the screw 100 or in a supporting element arranged between the antenna 1 and the head 101 of the screw 100.

In particular, said one or more sensors can be chosen between the following sensors:

- a temperature sensor for detecting a temperature of said screw 100,

- an ultrasonic sensor for detecting a length of said screw 100,

- a strain gauge sensor for detecting an elongation of said screw 100,

- a torsion sensor for detecting a degree of torsion of said screw 100,

- an angular position sensor for detecting a position of said screw 100,

- a rotation sensor for detecting an angle that corresponds to the rotation angle of said screw 100,

- an accelerometer sensor for detecting an acceleration of said screw 100,

- a vibration sensor for detecting a vibration of said screw 100. For example, in a first variant, said system for storing electrical energy can comprise a temperature sensor for measuring the temperature of the screw 100 and an ultrasonic sensor for measuring the length of the screw 100.

In particular, said temperature sensor and said ultrasonic sensor are connected to said energy storage means 7 to be powered by said energy storage means 7 when in use.

Said temperature sensor and said ultrasonic sensor can be arranged on the head 101 of the screw 100 or inside said screw 100 or in a supporting element arranged between said antenna 1 and the head 101 of the screw 100.

In a second variant, said system for storing electrical energy can comprise a temperature sensor for measuring the temperature of the screw 100 and a strain gauge sensor for measuring an elongation of the screw 100.

Said temperature sensor and said strain gauge sensor can be arranged on the head 101 of the screw 100 or inside the screw 100 or in a supporting element arranged between said antenna 1 and the head 101 of the screw 100.

Regardless of the variant, the ultrasonic sensor and the strain gauge sensor are two examples of sensors that allow an indirect measurement of the load exerted by the screw 100 on the structure in which the screw 100 is used.

In a third variant, the system for storing electrical energy can comprise the temperature sensor, the ultrasonic sensor and the strain gauge sensor, without departing from the invention.

Furthermore, further variants are possible in which the system for storing electrical energy can comprise alternatively or in combination with the sensors of the variants described above one or more further sensors among the remaining sensors mentioned above (i.e. a torsion sensor, an angular position sensor, a rotation sensor, an accelerometer sensor, a vibration sensor).

Advantages

An advantage of the antenna object of the invention is given by the fact that said antenna is designed to be installed on the end portion of a fastening element, in particular a threaded fastening element, and to resonate with a frequency of an electromagnetic wave greater than or equal to 2,4GHz and less than or equal to 2,5GHz.

Furthermore, by means of the antenna object of the invention, it is possible to obtain a greater gain and efficiency compared to antennas of a known type, as well as a resonant effect at a frequency of an electromagnetic wave to pick up a greater quantity of energy from an electromagnetic wave (despite the antenna in use is positioned on an end portion of a fastening element which is generally a fastening element made of metallic material), avoiding the presence of a ground plane.

The possibility of picking up a greater quantity of energy from an electromagnetic wave with respect to an antenna of known type allows to generate a greater quantity of electrical energy than the amount of electrical energy generated by an antenna of known type.

Consequently, it is possible to store a greater amount of electrical energy to be used to power one or more electrical devices and/or one or more electronic devices.

The present invention has been described for illustrative, but not limitative purposes, according to its preferred embodiment, but it is to be understood that variations and/or modifications can be carried out by a skilled in the art, without departing from the scope thereof, as defined according to enclosed claims. CLAIMS

1. Circular polarization antenna (1 ) configured to pick up an electromagnetic wave with a frequency between greater than or equal to 2,4GHz and less than or equal to 2,5GHz, and resonate at the frequency of said electromagnetic wave and comprising:

- a substrate (2) comprising a first face (21 ) and a second face (22), opposite to said first face (21 ),

- a first layer (3) of metallic material arranged on said first face (21 ), wherein said substrate (2) is made of a ceramic material having an isotropic dielectric constant greater than or equal to 11 and less than or equal to 14, and has a cavity (20) arranged centrally with respect to said second face (22).

2. Circular polarization antenna (1 ) according to the previous claim, wherein said substrate (2) has a height between 5mm and 20mm, a cylindrical shape and a diameter between 16mm e 32mm.

3. Circular polarization antenna (1 ) according to any one of the previous claims, wherein said cavity (20) has a height between 3mm and 14mm, a cylindrical o truncated cone shape and a diameter between 6mm and 14mm.

4. Circular polarization antenna (1 ) according to any one of the previous claims, wherein said isotropic dielectric constant is equal to 12,2.

5. Circular polarization antenna (1 ) according to any one of the previous claims, wherein said ceramic material is Rogers TMM® 13i.

6. Circular polarization antenna (1 ) according to any one of the