ITUD20100174A1 - ELECTROMAGNETIC ENERGY CONVERSION DEVICE FOR RADIOFREQUENCY - Google Patents

Description

Description of the invention having as title:

"DEVICE FOR THE CONVERSION OF ELECTROMAGNETIC ENERGY FROM RADIOFREQUENCY"

FIELD OF APPLICATION

The present invention relates to a device for converting electromagnetic energy from radiofrequency to convert the electromagnetic field to radiofrequency, generated by transmission units, such as mobile phones, wireless connection devices or others, into electrical energy in direct voltage for power supply of electronic utilities with low or very low consumption.

In particular, the conversion device according to the present invention finds application in the field of wireless distributed sensors, or Wireless Sensor Networks, for powering electronic units of the wearable type, such as sensors directly incorporated in garments, such as uniforms, jackets or others.

STATE OF THE TECHNIQUE

Devices for the conversion of radio-frequency electromagnetic energy, or radio-frequency "energy harvesting" devices, are known, which convert radio-frequency electromagnetic energy present in the environment into direct voltage electrical energy to power an electronic circuit. Such known conversion devices normally comprise an antenna for receiving the incident electromagnetic field, which is subsequently converted, by means of a suitable rectifier, or rectification circuit, into direct voltage electrical energy. The receiving antenna and the rectifier are also known as "rectenna" (Rectifying Antenna).

The quantity of useful electrical energy that can be obtained is therefore determined by the electrical and electromagnetic characteristics, which can be defined in the design, in relation to the signal of the electromagnetic field, the receiving antenna, the rectifier circuit and their coupling. However, the properties of the radiofrequency sources present in the environment, such as frequency, signal polarization, angle of incidence on the rectenna, distance of the radiofrequency source, which contribute to determining the intensity of the electromagnetic field incident on the conversion device, do not are known a priori.

Furthermore, the electromagnetic energy available is often limited with respect to the energy typically required by a low-consumption electronic device, such as, for example, a sensor node of a wireless network (Wireless Sensor Node). Moreover, the electromagnetic energy available may vary over time, depending on the type of source, such as for example the electromagnetic energy radiated in transmission by a mobile phone.

Therefore, in order to satisfy the users' requests, the devices for the conversion of electromagnetic energy to radiofrequency must be made to obtain maximum efficiency in more than a predetermined frequency band, i.e. in the bands where it is assumed that there is an available electromagnetic field of the operating environment, each band corresponding to potential sources of radio frequency electromagnetic field.

Patent WO / 2007/048052 describes a radiofrequency electromagnetic energy conversion device, which comprises an array of rectennas, each of which is designed and sized for a specific frequency band. The geometric arrangement of the rectennas in the array allows the reception with high efficiency of an electromagnetic field with any polarization, and incident at any angle, on the rectenne array itself.

A drawback of this known device is that the overall size of the rectenne array is rather large; for example, in the frequency spectrum from 900MHz to 2500Mhz the overall footprint required by the rectenne array is about 500 cm <3>. Furthermore, this system provides for a control circuit for the electrical connection, for the activation and for the power supply between the rectennas and, consequently, for an increase in the relative circuit complexity, consumption and costs.

Furthermore, the use of a device for the conversion of electromagnetic energy from radiofrequency that must be used in wearable applications determines further manufacturing constraints. In fact, from the mechanical point of view the conversion device must be flexible and sufficiently strong to follow the deformations of the body and of the garment in which it is mounted or integrated. This flexibility, in addition to being of the static type, that is of shaping and curvilinear conformation according to a predetermined profile, must also be of a dynamic type during its normal use. Therefore, it is necessary that the device is able to withstand an unlimited number of bending without deformation, for a maximum angle of curvature according to a specific area of the reference body in correspondence with which the device is positioned.

A radiofrequency electromagnetic energy conversion device which can be integrated into garments or garments is described in patent JP2003258539. This device comprises a "microstrip patch" type rectenna with single band with linear polarization, which therefore has a limited conversion efficiency, due both to the single band and to the impossibility of receiving signals with polarization different from the linear one.

Further devices for converting electromagnetic energy from radiofrequency are described in patents US2007285324 and US7193573B2, which describe a multilayer structure that can be integrated into a garment or garment. However, these devices have quite large dimensions and are specifically designed to operate efficiently in a single frequency band.

A further device of the type discussed is described in US7429959, which comprises a plurality of single-band or "single-band" wearable antennas arranged in correspondence with different areas of the body. Each antenna is selectively activated manually or according to its specific radiant properties, depending on the known signal to be transmitted / received. However, this known device has a large overall surface space and a high complexity determined by the presence of a circuit component for selecting the antenna to be used, and therefore for the power supply, which makes this device difficult to use in a wearable type application.

Also known are devices for the conversion of electromagnetic energy to radiofrequency of the wearable type provided with a "dual band" circular polarization antenna, however having an efficiency limited to a few dB in a single preferential band.

An object of the present invention is to provide a device for converting electromagnetic energy from radiofrequency which has a high conversion efficiency for signals having a polarization not known a priori and in several frequency bands.

A further object of the present invention is to provide a device for converting electromagnetic energy from radiofrequency which has small overall dimensions and dimensions to be integrated in an article of clothing.

A further object of the present invention is to provide an article of clothing, or a garment, comprising at least one device for converting electromagnetic energy from radiofrequency which has low manufacturing costs.

In order to obviate the drawbacks of the known art and to obtain these and further objects and advantages, the Applicant has studied, tested and implemented the present invention.

EXPOSURE OF THE FOUND

The present invention is expressed and characterized in the independent claim.

The related dependent claims disclose other characteristics of the present invention, or variants of the main solution idea.

In accordance with the aforementioned purposes, a device for converting electromagnetic energy from radiofrequency, according to the present invention, comprises an antenna, advantageously of the "microstrip patch" type, and an associated rectifier circuit for powering a connected electronic user, to constitute as a whole a so-called "rectenna".

According to a characteristic aspect of the present invention, the antenna comprises a single radiating element and an associated conductive element, substantially flat, underneath the radiating element, which has the dual function of electromagnetically cooperating with the single radiating element and of shielding from irradiation the human body. The radiating element has an annular circular shape, and the underlying conductive element has a substantially polygonal shape, advantageously square or rectangular. The two elements are mutually positioned to achieve a desired geometry of the antenna, this geometry being designed and configured to simultaneously receive electromagnetic energy in at least three distinct frequency bands of the electromagnetic field.

According to a further aspect of the present invention, the radiofrequency energy conversion device further comprises a single multiband circuit for receiving the power received by the antenna, which includes a power divider circuit and a 90 ° phase shift circuit. The two circuits, divider and phase shift, are arranged upstream of the rectification circuit, and are associated with the radiating element and the conductive element to derive two distinct branches and detect, for each of said three distinct frequency bands, at least two electromagnetic field components orthogonal and out of phase by 90 ° and, therefore, detecting, in each of said at least three distinct bands, a corresponding electromagnetic field substantially with any polarization.

The use of a circular polarization antenna able to receive an electromagnetic field, and therefore to generate radio frequency power, allows to guarantee a reception of fields having any polarization, obviously receiving the components according to the directions of the circular polarization of the antenna. . In this way, the reception of the incident field is maximized however it is polarized, that is with linear, circular, elliptical polarization, etc. According to a preferential solution of the present invention, a first frequency band of said three distinct frequency bands is the primary GSM P-GSM900 transmission band from the mobile terminal to the base station ("uplink" channel) for cellular telephony. A second frequency band of said three distinct frequency bands is the GSM1750 (DCS-1800) "uplink" band for cellular telephony. A third frequency band of these three distinct frequency bands is the 2450 MHz ISM band used for wireless transmissions of local networks, such as Wi-Fi networks, Bluetooth networks, ZigBee networks or others.

Therefore, the device for converting electromagnetic energy from radiofrequency according to the present invention, by means of a single rectenna device, that is substantially by means of a single antenna and a single conversion element, efficiently converts electromagnetic energy received in different frequency bands into energy electric. Furthermore, since the device has a single conversion circuit, its overall dimensions can be considerably reduced, also simplifying the relative electrical circuitry. Furthermore, the overall dimensions of the radiating element of the antenna are substantially related to the first frequency band, at lower frequencies, and, therefore, to the external diameter of the radiating element.

According to an embodiment of the invention, the external diameter of the annular radiating element is about 71mm, to receive electromagnetic energy in the first frequency band of radio signals in relation to the fundamental mode TM11 of the primary GSM band P-GSM900 "uplink". The radiating element also comprises first means for perturbing the currents for detecting electromagnetic energy in the second frequency band of radio signals in relation to the fundamental mode TM31 of the second frequency band, that is, of the GSM1750 (DCS-1800) band. Furthermore, the radiating element comprises second current perturbation means for detecting electromagnetic energy in said third frequency band, that is, in the ISM band 2450 MHz, in relation to its upper resonant mode TM12. According to the invention, the first and second means for perturbing the currents are made in such a way as not to significantly modify the behavior in the other two bands.

According to a variant, said first means for perturbing the currents comprise four rectangular slits formed annularly between the external diameter and the internal diameter of the radiating element, and inclined by ± 45 ° with respect to a reference direction. The second means for perturbing the currents comprise four rectangular slots, respectively two opposite slots parallel to said reference direction and two opposed slots orthogonal to said reference direction, arranged substantially in an annular manner between said external diameter and said internal diameter and at the same distance from the center of said first cracks.

According to a further aspect of the present invention, the conductive element comprises non-conductive portions, shaped and positioned to cooperate with said phase shift circuit and cause the excitation of the radiating element.

According to a further aspect of the invention, the conversion device is made according to a structure with flexible superimposed layers, in which an upper layer of said structure comprises said radiating element, a lower layer comprises said conductive element and at least one layer of electrically insulating material , also substantially flexible, is interposed between said upper layer and said lower layer, so that the entire structure of the rectenna has characteristics of flexibility.

According to a further aspect of the present invention, the radiating element is made of conductive non-woven fabric.

In one solution, said non-woven fabric is made of Global EMC Ag / Cu / Nl.

The present invention also includes the provision that the conductive element, the rectification circuit, the power divider circuit and the phase shifter circuit are made on a flexible type support.

In one solution, said flexible support is a printed circuit, or flexible pcb, based on Polyimide and two conductive surface layers, with a total thickness of a few hundred micrometers (for example using the commercial product Dupont PyraluxAP AP8545).

In another solution, said flexible support is a silkscreened neoprene support with silver on both sides.

The present invention also relates to an article, or article of clothing, comprising at least one device for converting electromagnetic energy from radiofrequency as previously described.

ILLUSTRATION OF DRAWINGS

These and other characteristics of the present invention will become clear from the following description of a preferential embodiment, given by way of non-limiting example, with reference to the attached drawings in which:

- fig. 1 is a block diagram of a radiofrequency electromagnetic energy conversion device according to the present invention;

fig. 2 is a circuit diagram of a rectifier of the radiofrequency electromagnetic energy conversion device of fig. 1;

fig. 3 is a top view of a circuit embodiment of the device of fig. 1;

fig. 4 is the radiation surface of an antenna of the device of fig. 1 relating to a first frequency band of use;

fig. 5 is the radiation surface of the antenna of the device of fig. 1 relating to a second frequency band of use;

fig. 6 is the radiation diagram relating to a second frequency band of use;

fig. 7 is the radiation surface of the antenna of the device of fig. 1 relating to a third frequency band of use;

fig. 8 is a diagram relating to the reflection coefficient of the antenna of the device of fig.

- fig. 9 is a transparency view of two layers of a printed circuit of the conversion device of fig. 1; - fig. 10 is a top side view of the printed circuit of fig. 9;

- fig. 11 is a schematic side sectional view of the radiofrequency energy conversion device according to the present invention integrated in an article of clothing;

- fig. 12 is an exploded top front perspective view of the radiofrequency energy conversion device of fig. 11;

- fig. 13 is an exploded bottom front perspective view of the radiofrequency energy conversion device of fig. 11;

- fig. 14 is a top view of a detail of fig. 11;

- fig. 15 is a view of a garment in which two radiofrequency energy conversion devices are integrated.

To facilitate understanding, identical reference numbers have been used wherever possible to identify identical common elements in the figures. It should be understood that elements and features of one embodiment can be conveniently incorporated into other embodiments without further specification.

DESCRIPTION OF A PREFERENTIAL FORM OF

REALIZATION

With reference to the attached figures, a radiofrequency energy conversion device 10 according to the present invention comprises a multiband antenna 12 of the "microstrip patch" type, and broadband in each of the operating bands, a rectification circuit 31 multiband, directly connected to the output of the antenna 12, and a load matching circuit 32, connected in turn to the output of the multiband rectification circuit 31. The device 10, as will be better described below, is made according to a layered structure which allows its integration into an article of clothing 50, as illustrated in an example in fig. 15.

In the present case (fig. 1), the device 10 is used to power an electronic user 40 such as, for example, but not limited to, a node of a wireless sensor network, which in turn is integrated in said item of clothing 50 . The electronic user 40, in particular, is provided with an energy supply and storage circuit 41, connected to the output of the device 10, and a microcontroller unit 42, for example a microcontroller, equipped with a suitable RF interface , not indicated, and an associated RF transceiver antenna 43.

The antenna 12 (Fig. 3) comprises a single annular radiating element 13 of circular shape, which has an external diameter Di and an internal diameter D2 to define a circular crown made of conductive material. In particular, said diameters Di, D2, together with specific radial slots, which will be described below, define the specific reception properties in the desired radiofrequency bands from which to take environmental electromagnetic energy.

The circuit diagram which carries out the rectification in the multiband rectification circuit 31, per se known, is of the full wave rectification type. One possible realization of it is illustrated in fig. 2, in which the specific parameters are sized according to the load and frequency of use.

The high efficiency rectification on the specific bands of interest is obtained with a specific circuit for the 90 ° phase shift and the power division, which guarantee circular polarization for all operating bands. Furthermore, a specific circuit element, not explicitly indicated in the figures, which carries out the impedance matching between the lumped constant rectifier circuit and the input port of the antenna, which coincides with the port of the power divider. In particular, due to the circuit structure of the rectifier, this has an equivalent input impedance with a high reactive component, due to the capacities used.

The adaptation of the impedance of the multiband antenna is mainly obtained with a structure with distributed constants at jump impedance which allows to cancel this reactive component in all the working frequencies and for the whole bandwidth of interest.

The radiating element 13 also has first four rectangular slots 16 and second four rectangular slots 18, which act as current perturbation elements to obtain the desired reception performance in the three distinct radio frequency bands.

The first slots 16 are formed annularly on the conductive material of the radiating element 13, and are inclined by ± 45 ° with respect to a reference direction, for example horizontal, indicated in the figures with "x". These first slots 16 are substantially tangent at their central portion to an ideal circumference of intermediate diameter between the external diameter Di and the internal diameter D2. The second slots 18 are formed annularly on the conductive material of the radiating element 13, and are arranged two by two, respectively parallel and orthogonal to said reference direction "x". The second slots 18 are substantially tangent at their central portion to said ideal circumference, so as to be at the same distance from the center of the radiating element 13 as the first slots 16, and each of them is interposed along said ideal circumference between two first cracks 16.

The antenna 12 also comprises a conductive element 14, substantially flat, underneath the radiating element 13, of polygonal shape, advantageously square or rectangular. The conductive element 14 (figs. 11, 12) comprises layers 48a, 49, as described below, and a first side, or top side, of a printed circuit of the flexible type, or pcb 28. The set of these layers acts as a ground plane for the antenna 12, the layer 48a and the top side of the pcb being mutually bonded by means of a radio-frequency conductive adhesive material. In particular, the radiating element 13 is powered by electromagnetic coupling from two branches 25 of a 90 ° phase shifter circuit 24, or phase shifter, underneath the radiating element 13. The cooperation between these conductive elements, i.e. power supply 25, and respective slots 20 made in the ground plane defined by the conductive element 14, determine the electromagnetic coupling with the radiating element 13.

The pcb 28 has two non-conductive portions, in this case two slots 20, which have an oblong rectangular central portion and two substantially square widened portions, at the respective ends. The 20 slots are arranged orthogonal to each other, and their shape is specifically designed to:

- guaranteeing the excitation functionality of the radiant element 13 so as to generate a circular electromagnetic field polarization component in all the frequency bands used;

- guaranteeing at the same time the best decoupling between the two power supply branches 25 and therefore the maximum power transfer in radiofrequency.

The printed circuit, or pcb 28, is arranged in such a way that each slot 20, illustrated transparently in fig. 3, is respectively arranged parallel to a corresponding second slot 18, externally to said ideal circumference. The longitudinal extension of each slot 20 is such that the relative square portions are close to corresponding ends of respective first slots 16.

Advantageously, the antenna 12 of the device 10 uses, in particular, higher resonant modes of the microstrip patch type antennas for the higher frequency bands that are used. Therefore, the constraint relative to the dimensions of the patched radiant element 13 is relative to the fundamental resonance frequency, while further resonant frequencies can be obtained using the same dimensions of the antenna, that is, of the radiant element 13.

The antenna 12 is also provided with a power divider circuit 22 and the 90 ° phase shifter circuit, 24, made on a second side of said pcb 28, which determine the circular polarization of the field. electromagnetic with the same accuracy on all operating bands. Two power supply branches 25 of the radiating element 13 are connected to the power divider circuit 22 and to the phase shift circuit 24 so as to generate two electromagnetic field components out of phase by 90 ° and therefore, due to the reciprocal behavior of the antenna, receive a signal with any polarization.

The excitation of the radiant element 13 of the antenna 12, as previously mentioned, is obtained by electromagnetic coupling through the two slots 20 made on the ground conductive element 14 and the power supply branches 25 made on the second side of the pcb 28 below the patch radiant element 13 (Figs. 3, 9 and 10), according to a known method and not described here.

In particular, the device 10 converts radio frequency electromagnetic energy into three different frequency bands, relating to the frequencies assigned to cellular telephony and wireless networks as summarized below:

- a first band is the GSM P-GSM900 primary "uplink" frequency band for cellular telephony having about 25 MHz of bandwidth;

- a second band is the GSM1750 (DCS-1800) "uplink" frequency band for cellular telephony of about 75 MHz of bandwidth;

- a third band is the 2450 MHz ISM frequency band used for wireless transmissions on local networks, such as Wi-Fi networks, Bluetooth networks, ZigBee networks or others with a bandwidth of about 50MHz;

As regards the first and second bands, ie the cellular telephone bands, only the "uplink" bands, ie transmission from the cellular phone, are considered, as the radiofrequency signal is useful in terms of electromagnetic energy intensity detectable by antenna 12 is that of transmission to the base station of the telephone network cells. First frequency band

In the first frequency band, for P-GSM900, the TM11 fundamental mode is used.

The use of the radiant element 13 with circular ring patch structure allows, at the same resonance frequency, to have a smaller ring size, as described for example in "A broad-Band Annular-Ring Microstrip Antenna", Antennas & Propagation AP-30, No. 5, 1982 for Weng Cho Chew. The resulting radiation lobe is of the broadside type (fig. 4), typical of a patch antenna.

In particular, the external radius, relative to the diameter D1, of the ring is approximately 71mm.

Using a real square ground plane, therefore not ideal and infinite, having dimensions of about 250x250mm and an arrangement of the radiant element 13 and of the conductive element as previously described and illustrated in figs. 12 and 13, a maximum antenna gain of about 4dB is obtained, also including adaptation to the multiband rectification circuit 31.

Second frequency band

In the second frequency band, ie in the GSM1750 band, the TM31 resonant mode is used.

In fact, I notice the behavior of a ring patch element (with thin substrate) as regards its resonant modes, as indicated for example in "Mode Chart for Microstrip Ring Resonators", Transactions on Microwave Theory and Techniques, Volume: 21, Issue : 7, 1973, to Y.S. Wu, F.J. Rosenbaum, the current perturbation method to regulate the resonant frequency of TM21 at a predetermined frequency is also known, as, for example, indicated in "Design of a dual-mode annular ring antenna with a coupling feed", Microwave and optical technology letters, Vol. 51, N ° 12, 2009, in the name of Jae Hee Kim, Dae Woong Woo and Wee Sang Park, the aforementioned arrangement of the first 16 slots capable of bringing the desired resonance frequency and with a predetermined bandwidth, without interfering with the other radiant modes used.

Given the power supply with the two elements out of phase by 90 ° and the symmetrical structure of the first slots 16 made in the radiating element 13, a radiation surface is obtained with two lobes inclined by 30 ° with respect to a "Z" axis which protrude from the plane of arrangement of the radiant element 13 itself (figs. 5 and 6).

In these conditions the maximum gain obtained by the antenna 12 of the device 10 is approximately 5 dB Third frequency band

In the third frequency band, or 2450 MHz ISM band, the TM12 upper resonant mode is used.

In this case, the electromagnetic fields that radiate the device 10 are of reduced intensity compared to that generated by mobile devices for cellular telephony. Based on the specific wireless connectivity standard used, the antenna 12 may have a maximum power of 10mW against 300-500mW relating to GSM cellular transmission. Therefore, the antenna 12 must be very efficient in this band, maintaining the behavior in the other two bands of use unchanged.

Therefore, the TM12 upper resonant mode at maximum irradiation is used for ring patch antennas, so that the relative resonance frequency is exactly that desired. Therefore, the realization of the second horizontal and vertical symmetrical slots 18 (in figure 13 on the right) cause a predetermined perturbation of the path of the currents on the radiating element 13 for the aforementioned TM12 mode. The conformation of the second slots 18 is also dimensioned on the basis of the variations in behavior of the radiating element 13 introduced by the first slots 16, which in turn are affected by the second slots 18.

In this embodiment the inner radius of the ring, relative to the diameter, D2 is approximately 21mm.

The radiation pattern obtained is of the broadside type more directional, with a maximum gain of more than 9.0 dB in the direction perpendicular to the plane of the radiating element 13, that is, in the direction of the "Z" axis ( fig.

In fig. 8 the trend of the reflection coefficient of the antenna 12 is plotted as a function of the frequency, and from which it is possible to see the adaptation of the antenna 12 itself to the specific and desired three distinct frequency bands in which electromagnetic energy is received .

Therefore, a single feed antenna is obtained, the dimensions of which are substantially in the overall dimensions of the radiating element 13 of the antenna 12 and which operates with desired efficiency in three distinct frequency bands and for the entire bandwidth assigned for the wireless communication standards considered.

With reference to figs. 3, 9 and 10, the area required for the impedance matching circuit 32, the multiband rectifier circuit 31, the power divider circuit 22, the phase shifter circuit 24 and the slot 20 for coupling to the radiant element 13 Ã ̈ about 140x140mm. Fig. 3 shows the transparent view of the elements of the antenna 12 on the xy plane of position. The position of the radiating element 13 is determined by the coupling between the radiating element 13 and the slots 20, and is translated and asymmetrical with respect to the conductive element 13.

The minimum encumbrance on the xy plane is approximately 175x165mm, or approximately 190x190mm if the overall dimension of the conductive element 14 has a symmetrical distribution. These overall dimensions also take into account the aspects linked to the assembly of the different layers that make up the antenna 12, as will be better described below.

Greater efficiency can be achieved in all bands for larger dimensions of the ground plane. In particular, a significant reduction in efficiency is obtained by passing from a ground plane having a size of 250x250mm to a ground plane having the minimum size indicated above.

Device 10 is compatible with making flexible materials for fabric or garment processing. In particular, the realization of the radiant element 13 and of the slot openings 20 on the top side pcb requires a cutting precision of about 100 µm, which is compatible with laser cutting processes of conductive non-woven fabric.

The alignment requirement with the xy plane between the layers that make up the antenna 12 is also approximately 100Î1⁄4m, compatible with normal assembly techniques in the textile field.

Furthermore, the antenna 12 of the device 10 of the present invention can also be used as a transmitting antenna of the electronic user 40, such as a sensor connected thereto. In this case it is possible to provide alternating operation at time intervals in which the antenna 12 is alternatively used for the collection of RF energy or to transmit the detection data of the sensor, that is of the user 40 itself.

Furthermore, in the event that at least one of the frequency bands is not used, for example because no radio frequency source is detectable in the specific band, the antenna 12 itself can be used as a transmitting antenna in said specific frequency band, in fact not used for the conversion of radiofrequency energy.

The radiofrequency electromagnetic energy conversion device 10 is incorporated into an item of clothing 50, integrated into the fabric itself. In fact, the device 10 made according to a layered structure has a superimposed layer structure, as illustrated in figs. 11-13. In particular, the device 10 comprises the following functional layers (in order from the outside towards the user's body):

- a flexible outer layer disposed towards the outside of the article of clothing 50 and having a substantially protective function; this layer not indicated in the present figures can be, if the device 10 is internal to the garment, obtained from the outer layer of fabric 44 of which the garment is made, indicated only in fig. 11; - a flexible layer under the layer 44 which forms the antenna which in turn comprises:

- the radiating element 13 which defines a first upper layer,

- a first insulating thermoadhesive layer 46a, shaped in the same way as the radiant element 13, and by means of which the radiant element 13 is fixed to the lower layers,

- a first layer 47a of insulating fabric interposed between the radiating element 13 and the conductive element 14 which comprises the layers 48a and 49, - a second thermo-adhesive insulating layer 46b, - a first layer of conductive fabric 48a and a layer formed by a conductive double-sided adhesive frame 49 included in the conductive element 14, which define a second lower layer,

the double-layer pcb 28, fixed to the first layer of conductive fabric 48a by means of said conductive double-sided adhesive frame 49,

- a third thermo-adhesive insulating layer 46c, - a second layer of insulating fabric 47b, having the function of spacing and containing the electromagnetic field,

- a fourth layer of 46d insulating fabric,

- a second layer of conductive fabric 48b.

The second thermoadhesive insulating layer 46b and the first layer of conductive fabric 48a are processed in such a way as to present a first substantially square opening 45 slightly smaller than the dimensions of the pcb 28, on the edges of which the conductive double-sided adhesive frame 49 is applied. another embodiment a conductive glue is used instead of the double-sided adhesive frame 49. The third thermo-adhesive insulating layer 46c also has a second opening 45c which is substantially square and slightly larger than those of the pcb 28.

The materials used have been chosen to optimize the conversion performance, i.e. the overall conversion efficiency and to ensure mechanical flexibility of the antenna 12 during its use integrated in the garment 50. Furthermore, the overall thickness of the device 10 must be less than 10mm in order to be inserted into a garment, such as a jacket 50, without generating steps or tension on the fabric.

The following table 1 summarizes some possible construction materials for the different layers, in which, for simplicity, the relative numerical references have been inserted in the first column relating to the layer.

Layer Material Description

13, Global EMC Ag / Cu / Nl Non-woven fabric

48a, 48b conductive

47a, 47b Polartech ThermalPro Pile

28 Double flexible pcb Alternative: Neoprene conductive face on screen printed Ag on both dielectric substrate faces

(eg DuPont PyraluxAP

AP8545)

46a, 46b, Thermal adhesive insulation

46c, 46d

49 3M ECATT 9707 conductive double-sided tape

Table 1

The most complex part to be made for the antenna 12 is that relating to the layers of the pcb 28 on which the multiband rectifier circuit 31 is made, the power divider circuit 22, the phase shifter circuit 24, all multiband, on the bottom side, and the slots 20 formed as openings on the ground plane which provide the power supply by electromagnetic coupling to the radiant element 13, on the top side. Based on the thickness and electromagnetic characteristics of the insulating layers of dielectric material placed between the conductive elements on the top and bottom side, the thicknesses and precision required for the geometries to be made on the bottom side can vary significantly and may not be respected with the available technologies. for the selected materials. For example, in the case in which the pcb 28 is made with a flexible electronic circuit easily available on the market, consisting of 2 copper faces of 35um and Polyimide dielectric (εr = 3.4) of 1000um, it is necessary to create conductive tracks with a thickness of 3mils, a value that is at the limit of the current processing possibilities for these materials. Otherwise, using neoprene as dielectric medium (εr in the range of values between 6 and 9) with a thickness of about 1-2 mm, it is possible to obtain the desired geometry of the antenna using a silkscreen process with conductive silver-based ink with width of the higher traces and lower required accuracy.

In this second case, the overall thickness of the device 10 increases by a few mm but it is possible to obtain greater flexibility and robustness of the entire rectenna.

Therefore, the construction of the antenna 12 and that of the pcb 28 are substantially independent of each other. This allows you to decide which type of pcb 28 to use: for example, with a minimum thickness constraint and accepting limited flexibility, it is possible to use a flexible pcb made from a flexible electronic circuit with more traditional materials as indicated in table 1; in the case of a solution with maximum flexibility and sturdiness, it is possible to make the pcb starting from an insulating support element in neoprene, surface silk-screened with conductive paint.

Furthermore, the structure of the pcb 28 is independent of the size and shape of the device 10 in its final embodiment 10, therefore, it is independent of the production and assembly aspects of the entire rectenna. The other layers of the device are sized and shaped according to the garment and the area where the rectenna is placed.

With reference to figure 11 and referring to the implementation of pcb 28 with flexible electronic circuit, the conductive layer 48a, which constitutes the reference ground plane of the antenna, has said opening 45a in correspondence with the position that pcb 28 must assume same with respect to the radiant element 13. The opening 45a has a size such as to be superimposed by 5-10mm on the ground plane made on the pcb 28, top side and not to interfere with the two slots 20. The application of an element conductive adhesive, that is of the frame 49, for radiofrequency application between the second conductive layer 48a and the pcb 28 on the top side allows to create a ground plane of maximum dimensions compatibly with the size and shape of the device in its final form. This improves the overall conversion efficiency of the antenna 12 based on the area available on the garment for the application of the rectenna 10.

The overall encapsulation of the pcb 28 in the layers of the antenna 12, and therefore its fixing and protection, is obtained by gluing the second layer of fabric 47b on the first conductive fabric 48a with the aid of the thermo-adhesive insulating layer, removed in correspondence with the whole the area occupied by the pcb 28. Since the two layers of insulating fabric 47a, 47b have a much greater thickness than the pcb 28, they compress in correspondence with the pcb 28 itself, incorporating it inside and all around them. In particular, if the pcb 28 is made of neoprene with a thickness of a few millimeters, a thicker rounded profile is obtained only in correspondence with the pcb 28 while the rest of the surface of the antenna 12 has a uniform thickness, as already seen in about 8mm.

It is clear that modifications and / or additions of parts can be made to the device 10 for converting electromagnetic energy from radiofrequency described up to now, without departing from the scope of the present invention.

It is also clear that, although the present invention has been described with reference to some specific examples, a person skilled in the art will certainly be able to realize many other equivalent forms of device 10 for converting electromagnetic energy from radiofrequency, having the characteristics expressed in the claims and therefore all fall within the scope of protection defined by them.

Claims (13)

CLAIMS 1.Device for converting electromagnetic energy from radiofrequency comprising an antenna (12), advantageously of the "microstrip patch" type, and an associated multiband rectifier circuit (31) for powering at least one connected electronic user (40), characterized by the fact that the antenna (12) comprises a single radiating element (13), an associated conductive element (14) underlying the radiating element (13) and a circuit for receiving the power received from the antenna (12), in which the radiating element (13) has an annular circular shape, in which said power receiving circuit comprises at least one power divider circuit (22) and a 90 ° phase shift circuit (24), in which the power divider circuit (22) and to the phase shift circuit (24) are connected two power supply branches (25) of the radiating element (13) configured so as to generate two electromagnetic field components orthogonal and out of phase by 90 ° and therefore to receive a signal le with any polarization on at least three distinct frequency bands. 2. Device as in claim 1, characterized in that the radiating element (13) comprises at least first and second current perturbation means (16, 18), configured so as to detect electromagnetic energy in respective second and third frequency bands distinct from a first main frequency band corresponding to the received electromagnetic field not perturbed. 3. Device as claimed in claim 2, characterized in that said first and second current perturbation means (16, 18) are made in such a way as not to significantly modify the behavior of at least the radiating element (13) in the other two bands. 4. Device as in claim 2 or 3, characterized in that the first means for perturbing the currents comprise four first rectangular slots (16) formed annularly between an external diameter (DI) and an internal diameter (D2) of the radiating element ( 13), and inclined by ± 45 ° with respect to a reference direction (x), and that the second means for perturbing the currents comprise four second rectangular slots (18), respectively two opposite slots parallel to said reference direction (x) and two opposite slots orthogonal to said reference direction (x), arranged substantially annularly between said external diameter (DI) and said internal diameter (D2) at the same distance from the center of the radiating element of said first slots (16). 5. Device as in one or the other of the preceding claims, characterized in that said at least three frequency bands comprise frequency bands for cellular telephony and at least one ISM 2450 band. 6. Device as in claims 3 and 5, characterized in that the external diameter (Di) of the annular radiating element (13) is dimensioned to approximately 7Imm, to detect electromagnetic energy in said first frequency band of radio signals in relation to the fundamental mode TMll of the primary GSM P-GSM900 "uplink" band. 7. Device as in any one of the preceding claims, characterized in that it is made according to a structure with flexible superimposed layers, in which a first upper layer of said structure comprises said radiating element (13), a second lower layer comprises said element conductive (14), and at least one layer (47a) of electrically insulating material is interposed between said first upper layer and said second lower layer. 8. Device as in claim 7, characterized in that the radiating element (13) is made of conductive non-woven fabric. 9. Device as in claim 1, characterized in that at least part of the conductive element (14), the rectifier circuit (31), the power divider circuit (22) and the 90 ° phase shifter circuit (24) are made on a support (28) of the flexible type. 10. Device as in claim 9, characterized in that said flexible support is a printed circuit, or pcb (28), with at least two conductive layers separated by a dielectric layer. 11. Device as in claim 10, characterized in that said flexible support (28) is a neoprene support silkscreened with silver on both sides. 12. Device as claimed in claim 10 or 11, characterized in that the flexible support (28) has non-conductive portions (20), arranged substantially orthogonal to each other, and specifically designed to ensure the excitation functionality of the radiant element (13) so as to generate a circular electromagnetic field polarization component in all the frequency bands used and at the same time guarantee the decoupling between the two power supply branches (25) and therefore the maximum radio frequency power transfer. Article of clothing comprising at least one radio frequency electromagnetic energy conversion device (10) as in any one of claims 1 to 12.