WO2012042348A2 - Device to convert radio frequency electromagnetic energy - Google Patents

Device to convert radio frequency electromagnetic energy Download PDF

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Publication number
WO2012042348A2
WO2012042348A2 PCT/IB2011/002253 IB2011002253W WO2012042348A2 WO 2012042348 A2 WO2012042348 A2 WO 2012042348A2 IB 2011002253 W IB2011002253 W IB 2011002253W WO 2012042348 A2 WO2012042348 A2 WO 2012042348A2
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WO
WIPO (PCT)
Prior art keywords
circuit
radiant element
antenna
band
electromagnetic energy
Prior art date
Application number
PCT/IB2011/002253
Other languages
French (fr)
Other versions
WO2012042348A3 (en
Inventor
Alessandra Costanzo
Diego Masotti
Francesco Donzelli
Stefano Adami
Original Assignee
Eurotech Spa
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Eurotech Spa filed Critical Eurotech Spa
Publication of WO2012042348A2 publication Critical patent/WO2012042348A2/en
Publication of WO2012042348A3 publication Critical patent/WO2012042348A3/en

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q1/00—Details of, or arrangements associated with, antennas
    • H01Q1/12—Supports; Mounting means
    • H01Q1/22—Supports; Mounting means by structural association with other equipment or articles
    • H01Q1/24—Supports; Mounting means by structural association with other equipment or articles with receiving set
    • H01Q1/248—Supports; Mounting means by structural association with other equipment or articles with receiving set provided with an AC/DC converting device, e.g. rectennas
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q1/00—Details of, or arrangements associated with, antennas
    • H01Q1/27—Adaptation for use in or on movable bodies
    • H01Q1/273—Adaptation for carrying or wearing by persons or animals
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q23/00—Antennas with active circuits or circuit elements integrated within them or attached to them
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q5/00—Arrangements for simultaneous operation of antennas on two or more different wavebands, e.g. dual-band or multi-band arrangements
    • H01Q5/30—Arrangements for providing operation on different wavebands
    • H01Q5/307—Individual or coupled radiating elements, each element being fed in an unspecified way
    • H01Q5/342—Individual or coupled radiating elements, each element being fed in an unspecified way for different propagation modes
    • H01Q5/357—Individual or coupled radiating elements, each element being fed in an unspecified way for different propagation modes using a single feed point
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q9/00—Electrically-short antennas having dimensions not more than twice the operating wavelength and consisting of conductive active radiating elements
    • H01Q9/04—Resonant antennas
    • H01Q9/0407—Substantially flat resonant element parallel to ground plane, e.g. patch antenna
    • H01Q9/045—Substantially flat resonant element parallel to ground plane, e.g. patch antenna with particular feeding means
    • H01Q9/0457—Substantially flat resonant element parallel to ground plane, e.g. patch antenna with particular feeding means electromagnetically coupled to the feed line
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q9/00—Electrically-short antennas having dimensions not more than twice the operating wavelength and consisting of conductive active radiating elements
    • H01Q9/04—Resonant antennas
    • H01Q9/0407—Substantially flat resonant element parallel to ground plane, e.g. patch antenna
    • H01Q9/0464—Annular ring patch

Definitions

  • the present invention concerns a device to convert radio frequency electromagnetic energy, to convert the radio frequency electromagnetic field generated by transmission units, such as mobile phones, wireless connection devices or other, into continuous tension electric energy in order to feed electronic user devices having low or very low consumption.
  • the conversion device according to the present invention is applied in the field of wireless sensor networks, to feed electronic units of the type that can be worn, such as sensors directly incorporated into articles of clothing, such as uniforms, jackets or others.
  • Devices for the conversion of electromagnetic energy of radio frequency signals, or energy harvesting devices, from radio frequency signals, which convert radio frequency electromagnetic energy present in the environment into continuous tension electric energy in order to feed an electronic circuit.
  • These known conversion devices normally comprise an antenna to receive the incident electromagnetic field, which is subsequently converted by means of a suitable rectification circuit into continuous tension electric energy.
  • the receiving antenna and the rectifier are also known as "rectenna" or rectifying antenna.
  • the quantity of usable electric energy obtainable is therefore determined by the electric and electromagnetic characteristics definable during the design stage, in relation to the signal of the electromagnetic field, of the receiving antenna, of the rectification circuit and their coupling.
  • the properties of the radio frequency sources present in the environment such as frequency, polarization of the signal, angle of incidence on the rectenna, distance from the radio frequency source, which contribute to determine the intensity of the electromagnetic field incident on the conversion device, are not known in advance.
  • the electromagnetic energy available is often limited with respect to the energy typically required by a low-consumption electronic user device, such as for example a wireless sensor node.
  • the electromagnetic energy available may vary over time, depending on the type of source, such as for example the electromagnetic energy irradiated in transmission from a mobile phone.
  • devices for converting radio frequency electromagnetic energy must be made to obtain a maximum efficiency in more than one predetermined band of frequencies, that is, in the bands where it is presumed that an available electromagnetic field of the operating environment exists, each band corresponding to potential sources of a radio frequency electromagnetic field.
  • the patent WO/A-2007/048052 describes a device for converting radio frequency electromagnetic energy which comprises an array of rectennas, each of which is designed and sized for a specific frequency band.
  • the geometric disposition of the rectennas in the array allows reception with great efficiency of an electromagnetic field with any polarization, and incident with any angle whatsoever on the array of rectennas.
  • the use of a device for converting radio frequency electromagnetic energy that must be used in wearable applications entails other production constraints. Indeed, from the mechanical point of view the conversion device must be flexible and robust enough to follow the deformations of the body and of the garment in which it is mounted or integrated. This flexibility must not only be of the static type, that is, with a curvilinear shaping and conformation according to a predetermined profile, but must also be of the dynamic type during normal use. Therefore, it is necessary that the device is able to support an unlimited number of bends without deforming, for a maximum angle of curvature depending on the specific zone of the body in correspondence with which the device is positioned.
  • a device for converting radio frequency electromagnetic energy that can be integrated into garments or articles of clothing is described in the patent JP-A- 2003258539.
  • This device comprises a rectenna of the microstrip patch type, single band and linear polarization, which therefore has a limited conversion efficiency, due both to the single band and also to the impossibility of receiving signals having a polarization other than linear.
  • Devices are also known for converting radio frequency electromagnetic energy of the wearable type provided with a dual band circular polarization antenna; however, these have an efficiency limited to a few dB in a single preferential band.
  • One purpose of the present invention is to obtain a device for converting radio frequency electromagnetic energy which has a great conversion efficiency for signals having a polarization not known in advance and in several frequency bands.
  • Another purpose of the present invention is to obtain a device for converting radio frequency electromagnetic energy which has limited bulk and sizes, to be integrated into an article of clothing.
  • Another purpose of the present invention is to obtain an article of clothing or garment comprising at least one device for converting radio frequency electromagnetic energy which has low production costs.
  • the Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.
  • a device for converting electromagnetic energy starting from a radio frequency signal comprises an antenna, advantageously of the microstrip patch type, and an associated adapted multi-band rectifier circuit formed by a rectification circuit and a circuit to adapt the impedance of the load in the desired frequency bands, or multi-band adaptation circuit, in order to feed a connected electronic user device, so as to constitute, in its entirety, a so-called rectenna.
  • the antenna comprises a single radiant element and an associated conductive element, substantially flat, below the radiant element, which has the double function of cooperating electromagnetically with the single radiant element and of shielding the human body from irradiation.
  • the radiant element has an annular circular shape, and the conductive element below it has a substantially polygonal shape, advantageously square or rectangular.
  • the two elements are reciprocally positioned to obtain a desired geometry of the antenna, said geometry being designed and configured to receive simultaneously electromagnetic energy in at least three different frequency bands of the electromagnetic field.
  • the three different frequency bands constitute three different resonant modes of the structure of the antenna.
  • a first frequency is the fundamental resonant mode of the structure, whereas the other two frequencies are other resonant modes of the structure, in particular higher resonant modes.
  • the device for converting energy from a radio frequency signal also comprises a single multi- band circuit for the reception of the power received by the antenna, which includes a power divisor circuit and a 90° phase shifter circuit.
  • the two circuits, divisor and shifter are disposed upstream of the rectification circuit, and are associated with the radiant element and the conductive element in order to derive two distinct branches and to detect, for each of the three different frequency bands, at least two components of electromagnetic field, orthogonal and shifted by 90°, and therefore to detect in each of said at least three different bands, a corresponding electromagnetic field substantially with any polarization.
  • a first frequency band of said three different frequency bands is the primary band GSM P-GSM900 for transmission from the mobile terminal to the base station (uplink channel) for mobile phones.
  • a second frequency band of said three different frequency bands is the band GSM1750 (DCS-1800), uplink channel for mobile phones.
  • a third frequency band of said three different frequency bands is the band ISM 2450 MHz used for wireless transmissions of local networks, such as Wi-Fi, Bluetooth, ZigBee or others.
  • the device for converting radio frequency electromagnetic energy by means of a single rectenna unit, that is, substantially by means of a single antenna and a single conversion element, efficiently converts electromagnetic energy received in different frequency bands into electric energy. Furthermore, given that the device has a single conversion circuit, its bulk can be considerably reduced, also simplifying the relative electric circuitry. Moreover, the overall bulk of the radiant element of the antenna is substantially correlated to the first frequency band, at lower frequencies, and hence to the external diameter of the radiant element.
  • the external diameter of the annular radiant element is about 71 mm, to receive electromagnetic energy in the first frequency band of radio signals in relation to the fundamental mode of resonance TM1 1 of the primary uplink band GSM P- GSM900.
  • the radiant element also comprises first means for perturbing the currents in order to detect electromagnetic energy in the second frequency band of radio signals in relation to the higher resonant mode TM31 of the second frequency band (which constitutes the 3 rd frequency of resonance), that is, band GSM 1750 (DCS- 1800).
  • the radiant element comprises second means for perturbing the currents in order to detect electromagnetic energy in the third frequency band, that is, in the ISM 2450 MHz band, in relation to its higher resonant mode TM12 (which constitutes the 5 th frequency of resonance).
  • the first and second means for perturbing the currents are made in such a way that they do not significantly modify the behavior in the other two bands.
  • said first means for perturbing the currents comprise four rectangular slots made annularly between the external diameter and the internal diameter of the radiant 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 the reference direction and two opposite slots orthogonal to the reference direction, disposed substantially annularly between the external diameter and the internal diameter and at the same distance from the center of the first slots.
  • the conductive element comprises non-conductive portions, shaped and positioned to cooperate with the phase shifter circuit and to excite the radiant element.
  • the conversion device is made in a structure with flexible overlapping layers, in which an upper layer of the structure comprises the radiant element, a lower layer comprises the conductive element and at least a layer of electrically insulating material, also substantially flexible, is interposed between the upper layer and the lower layer, so that the whole structure of the rectenna is flexible.
  • the radiant element is made of non-woven fabric of the conductive type.
  • the non-woven fabric is made of Global EMC Ag/Cu/Ni. It also comes within the scope of the present invention to provide that the conductive element, the rectification circuit, the power divisor circuit and the phase shifter circuit are made on a flexible type support.
  • the flexible support is a printed circuit or flexible pcb, with a polyimide base and two conductive surface layers, with an overall thickness of some hundreds of micrometers (for example using the commercial product Dupont PyraluxAP AP8545).
  • the flexible support is made of neoprene screen-printed with silver on both sides.
  • the present invention also concerns an article of clothing or garment, comprising at least one device for converting radio frequency electromagnetic energy as described above.
  • - fig. 1 is a block diagram of a device for converting radio frequency electromagnetic energy according to the present invention
  • - fig. 2 is a circuit diagram of a rectifier of the device for converting radio frequency electromagnetic energy in fig. 1 ;
  • - fig. 3 is a view from above of a circuit of the device in fig. 1 ;
  • - fig. 4 is the radiation surface of an antenna of the device in fig. 1 relating to a first frequency band used;
  • - fig. 5 is the radiation surface of the antenna of the device in fig. 1 relating to a second frequency band used;
  • - fig. 6 is the radiation diagram relating to a second frequency band used
  • - fig. 7 is the radiation surface of the antenna of the device in fig. 1 relating to a third frequency band used;
  • - fig. 8 is a diagram relating to the reflection coefficient of the antenna of the device in fig. 1 ;
  • - fig. 9 is a transparent view of two layers of a printed circuit of the conversion device in fig. 1 ;
  • - fig. 10 is a top side view of the printed circuit in fig. 9; - fig. 1 1 is a schematic view in lateral section of the device for converting radio frequency electromagnetic energy according to the present invention integrated into an article of clothing;
  • - fig. 12 is an exploded front perspective view from above of the device for converting radio frequency electromagnetic energy in fig. 1 1 ;
  • - fig. 13 is an exploded front perspective view from below of the device for converting radio frequency electromagnetic energy in fig. 1 1 ;
  • - fig. 14 is a view from above of a detail in fig. 1 1 ;
  • - fig. 15 is a view of an article of clothing in which two devices for converting radio frequency electromagnetic energy are integrated.
  • a device 10 for converting radio frequency electromagnetic energy comprises a multi-band antenna 12, of the microstrip patch type, and wide band in each of the functioning bands, a rectification circuit or rectifier 31, connected to the outlet of the antenna 12 through a circuit 32 to adapt the load impedance in the frequency bands involved, or multi-band adaptation circuit.
  • the circuit obtained by connecting the adaptation circuit 32 to the rectification circuit or rectifier 31 is indicated hereafter by the overall name of adapted multi-band rectifier circuit.
  • the device 10, as will be described in more detail hereafter, is made in a layered structure which allows it to be integrated into an article of clothing 50, as shown for example in fig. 15.
  • the device 10 is used to feed an electronic user device 40 such as for example, but not restrictively, a node of a wireless sensor network, in its turn integrated into the article of clothing 50.
  • the electronic user device 40 is provided in particular with an energy feed and storage circuit 41 , connected to the outlet of the device 10, and a microcontrol unit 42, for example a microcontroller, provided with a suitable RF interface, not indicated, and with an associated RF transceiver antenna 43.
  • the antenna 12 (fig. 3) comprises a single annular radiant element 13, circular in shape, which has an external diameter Dl and an internal diameter D2 to define a circular crown made of conductive material.
  • the diameters Dl , D2 together with specific radial slots which will be described hereafter, define the specific reception properties in the radio frequency bands desired from which environmental electromagnetic energy is taken.
  • the circuit diagram that obtains the rectification in the rectifier circuit 31, of a known type, is the whole wave rectification type.
  • a possible form of embodiment is shown in fig. 2, where the specific parameters are sized as a function of the load and the frequencies used.
  • the high efficiency rectification on the specific bands concerned is obtained with a specific circuit for 90° shifting and power division, which guarantee circular polarization to all functioning bands.
  • the adaptation circuit 32 obtains the impedance adaptation between the rectifier circuit 31 with concentrated constants and the antenna's inlet port, which coincides with the port of the power divisor.
  • this has an equivalent inlet impedance with a high reactive component, due to the capacities used.
  • the adaptation of the impedance of the antenna in several bands is mainly obtained with a structure of constants distributed with discontinuous impedance which allows to annul the reactive component in all working frequencies and for the whole band width concerned.
  • the radiant element 13 also has four first rectangular slots 16 and four second rectangular slots 18, which act as current perturbation means or elements, able to generate a perturbation effect on the current passing through the radiant element 13, to obtain the desired reception performance in the three different bands of the radio frequency.
  • the first slots 16 are made annularly on the conductive material of the radiant element 13, and are inclined by ⁇ 45° with respect to a reference direction, for example horizontal, indicated in the drawings by "x".
  • the first slots 16 are substantially tangent in correspondence with their central portion to an ideal circumference of intermediate diameter between the external diameter Dl and internal diameter D2.
  • the second slots 18 are made annularly on the conductive material of the radiant element 13, and are disposed in pairs respectively parallel and orthogonal to said reference direction "x".
  • the second slots 18 are substantially tangent in correspondence with their central portion to said ideal circumference, so as to be at the same distance from the center of the radiant element 13 as the first slots 16, and each of them is interposed along the ideal circumference between two first slots 16.
  • the antenna 12 also comprises a conductive element 14, substantially flat, below the radiant element 13, with a polygonal shape, advantageously square or rectangular.
  • the conductive element 14 (figs. 1 1, 12) comprises layers 48a, 49, as described hereafter, and a first side, or top side, of a printed circuit of the flexible type, or pcb 28. The whole of these layers functions as a mass plane for the antenna 12, as the layer 48a and the top side of the pcb are reciprocally glued together by means of a radio frequency conductive adhesive material.
  • the radiant element 13 is fed by electromagnetic coupling by two branches 25 of a 90° phase shifter 24, below the radiant element 13. The cooperation between the conductive elements, that is, the feed branches 25 and respective slots 20 made in the mass plane defined by the conductive element 14, determine the electromagnetic coupling with the radiant 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 widened square portions at the respective ends.
  • the slots 20 are disposed orthogonal to each other, and their shape is specifically designed to:
  • each slot 20 shown transparently in fig. 3, is disposed respectively parallel to a corresponding second slot 18, outside the ideal circumference.
  • the longitudinal extension of each slot 20 is such that the relative square portions are near to corresponding ends of respective first slots 16.
  • 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 relating to the sizes of the patch type radiant element 13 relates to the fundamental frequency of resonance, whereas other resonance frequencies can be obtained by using the same antenna sizes, that is, sizes of the radiant element 13.
  • the antenna 12 is also provided with a power divisor circuit 22 and the 90° phase shifter circuit 24, both made on a second side of the pcb 28 and which determine the circular polarization of the electromagnetic field with the same accuracy on all functioning bands.
  • Two feed branches 25 of the radiant element 13 are connected to the power divisor circuit 22 and the phase shifter circuit 24, so as to generate two components of electromagnetic field shifted out of phase by 90° and therefore, due to the reciprocity of the antenna behavior, to receive a signal with any polarization whatsoever.
  • the excitation of the radiant element 13 of the antenna 12, as we said before, is obtained by electromagnetic coupling through two slots 20 made on the mass conductive element 14 and the feed branches 25 made on the second side of the pcb 28 below the patch type radiant element 13 (figs. 3, 9 and 10), according to a known method, not described here.
  • the device 10 converts radio frequency electromagnetic energy in three different frequency bands, corresponding to different modes of resonance of the structure, one fundamental, the other two higher, relating to the frequencies assigned to mobile phones and wireless networks as now summarized:
  • a first band is the primary frequency band GSM P-GSM900, uplink for mobile phones having about 25 MHz band width;
  • a second band is the frequency band GSM 1750 (DCS- 1800), uplink for mobile phones having about 75 MHz band width;
  • a third band is the frequency band ISM 2450 MHz, used for wireless transmissions on local networks, such as the Wi-Fi networks, Bluetooth, ZigBee or others, having about 50 MHz band width.
  • the uplink bands are considered, that is, the transmission bands from the mobile phone, since the radio frequency signal usable in terms of intensity of the electromagnetic energy detectable by the antenna 12 is the transmission signal to the base station of the cells of the telephone network.
  • the fundamental resonance mode TM1 1 is used.
  • the use of the radiant element 13 with a circular ring patch structure, given the same resonance frequency, allows to have a smaller ring bulk, as for example described in "A broad-band annular-ring microstrip Antenna", Antennas & Propagation AP-30, n° 5, 1982 in the name of Weng Cho Chew.
  • the radiation lobe obtained is the broadside type (fig. 4), typical of a patch antenna.
  • the external radius relating to the diameter Dl of the ring is about 71 mm.
  • a maximum antenna gain is obtained of about 4dB, also including the adaptation to the rectifier circuit 31.
  • the upper resonance mode (3 rd frequency of resonance) TM31 is used.
  • the maximum gain obtained by the antenna 12 of the device 10 is about 5 dB.
  • the upper resonance mode (5 th frequency of resonance) TM12 is used.
  • the electromagnetic fields that irradiate the device 10 have a reduced intensity with respect to the one generated by mobile devices for mobile phones.
  • the antenna 12 Depending on the specific standard of wireless connectivity used, it is possible to have maximum powers incident on the antenna 12 of lOmW against the 300-500mW for GSM cellular transmission. Therefore, the antenna 12 must be very efficient in this band, keeping unchanged its behavior in the other two bands used.
  • the upper resonance mode TM12 is used, with maximum irradiance for ring patch antennas, so that the relative frequency of resonance is exactly as desired. Therefore, the second symmetrical horizontal and vertical slots 18 (fig. 13 on the right) determine a predetermined perturbation of the path of the currents on the radiant element 13 for mode TM12. The conformation of the second slots 18 is also sized according to the variations in behavior of the radiant element 13 as introduced by the first slots 16, which in turn are affected by the second slots 18.
  • the internal radius of the ring in relation to the diameter D2, is about 21 mm.
  • the radiation diagram obtained is the more directive broadside type, with a maximum gain of more than 9.0 dB in a direction perpendicular to the plane on which the radiant element 13 lies, that is, in the direction of the axis "Z" (fig. 7).
  • Fig. 8 shows the development of the reflection coefficient of the antenna 12 as a function of frequency: from this it is possible to see the adaptation of the antenna 12 to the specific and desired three different frequency bands in which electromagnetic energy is received.
  • a single feed antenna is obtained, the sizes of which are substantially within the overall bulk of the radiant element 13 of the antenna 12 and which operates with the desired efficiency in three different frequency bands and for the whole band width assigned for the wireless communication standards considered.
  • the area needed for the adapted multi-band rectification circuit (adaptation circuit 32 connected to the rectifier circuit 31), the power divisor circuit 22, the phase shifter circuit 24 and the slots 20 for coupling to the radiant element 13, is about 140x140 mm.
  • Fig. 3 shows the transparent view of the elements of the antenna 12 on the lying plane xy. The position of the radiant element 13 is determined by the coupling of the radiant element 13 and the slots 20, and is translated and asymmetrical with respect to the conductive element 14.
  • the minimum bulk on the plane xy is about 175x165 mm, or about 190x190 mm if the overall size of the conductive element 14 has a symmetrical distribution. These bulks also take into account aspects connected to the assembly of the different layers that make up the antenna 12, as will be described in more detail hereafter.
  • the device 10 is compatible with production in flexible materials for working fabrics or garments.
  • making the radiant element 13 and the slots 20 on the top side of the pcb requires a cutting precision of about 100 ⁇ , which is compatible with laser cutting methods for conductive non- woven fabrics.
  • the requirement of alignment with the lying plane xy between the layers that make up the antenna 12 is also about 100 ⁇ , compatible with normal assembly techniques in the textile field.
  • the antenna 12 of the device 10 according to the present invention can also be used as a transmission antenna of the electronic user device 40, as a sensor connected to it. In this case, it is possible to provide an alternate functioning at intervals of time, in which the antenna 12 is alternately used to collect RF energy or to transmit detection data of the sensor, that is, of the user device 40.
  • the antenna 12 itself can be used as a transmission antenna in said specific frequency band, which is in fact unused for the conversion of radio frequency energy.
  • the device 10 to convert radio frequency electromagnetic energy is incorporated into an article of clothing 50, integrated into the fabric itself.
  • the device 10 is made in a layered structure and has a structure of superimposed layers as shown in figs. 1 1-13.
  • the device 10 comprises the following functional layers (in order from the outside toward the user's body):
  • thermo-adhesive layer 46a shaped in the same way as the radiant element 13, and by means of which the radiant element 13 is attached to the lower layers,
  • thermo-adhesive layer 46b a second insulating thermo-adhesive layer 46b
  • thermo-adhesive layer 46c a third insulating thermo-adhesive layer 46c
  • thermo-adhesive fabric 46d a fourth layer of insulating thermo-adhesive fabric 46d
  • the second insulating thermo-adhesive layer 46b and the first layer of conductive fabric 48a are worked so as to have a first, substantially square aperture 45, with sizes slightly smaller than the sizes of the pcb 28, on the edges of which the conductive bi-adhesive frame 49 is applied.
  • a conductive glue is used instead of the bi-adhesive frame 49.
  • the third insulating thermo-adhesive layer 46c also has a second aperture 45c, substantially square, with sizes slightly bigger than the sizes of the pcb 28.
  • the materials used were chosen to optimize the conversion performance, that is, the overall efficiency of conversion, and to guarantee mechanical flexibility of the antenna 12 during its use when integrated into the article of clothing 50.
  • the overall thickness of the device 10 must be less than 10 mm, so as to be inserted in an article of clothing such as a jacket 50, without causing defects or tension in the fabric.
  • Table 1 summarizes some possible materials that can be used for the different layers, where for simplicity the relative numerical references have been inserted into the first column relating to the layer.
  • dielectric substrate e.g. screen printed with Ag DuPont PyraluxAP
  • the most complex part for making the antenna 12 concerns the layers of the pcb 28 on which are made the adapted multi-band rectification circuit, formed as we said by the adaptation circuit 32 and the rectifier circuit 31 , the power divisor circuit 22, the phase shifter circuit 24, all multi-band, on the bottom side, and the slots 20 made as apertures on the mass plane that supply the feed by electromagnetic coupling for the radiant element 13, on the top side.
  • the thicknesses and precision required from the geometries to be made on the bottom side can vary considerably and might not be respected with the technologies available for the materials selected.
  • the overall thickness of the device 10 increases by some mm but it is possible to obtain greater flexibility and strength of the whole rectenna.
  • the production of the antenna 12 and the pcb 28 are substantially independent of each other. This allows to decide which type of pcb 28 to use: for example, with a constraint of minimum thickness and accepting a 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 ; for a solution with maximum flexibility and strength it is possible to make the pcb starting from an insulating support element made of neoprene, screen printed on the surface with conductive paint.
  • the structure of the pcb 28 is independent from the size and shape of the device 10 in its final production, therefore it is independent from production and assembly features of the whole rectenna.
  • the other layers of the device are sized and shaped according to the garment and the zone where the rectenna is positioned.
  • the conductive layer 48a which constitutes the reference mass plane of the antenna, has the aperture 45a in correspondence with the position that the pcb 28 is to assume with respect to the radiant element 13.
  • the aperture 45a has a size so as to be superimposed by 5- 10 mm above the mass plane made on the pcb 28, top side, and so as not to interfere with the two slots 20.
  • the application of a conductive adhesive element, that is, the frame 49, by radio frequency application between the second conductive layer 48a and the pcb 28 top side, allows to achieve a mass plane with maximum sizes compatible with the size and shape of the device in its final form. This allows to improve the overall conversion efficiency of the antenna 12 according to the area available on the garment for the application of the device 10.
  • the overall encapsulation of the pcb 28 in the layers of the antenna 12, and hence its attachment and protection, is obtained by gluing the second layer of fabric 47b onto the first conductive fabric 48a with the aid of the insulating thermo-adhesive layer, removed in correspondence with the whole area occupied by the pcb 28. Since the two layers of insulating fabric 47a, 47b are much thicker than the pcb 28, they are compressed in correspondence with the pcb 28, incorporating it inside them and all around.
  • the pcb 28 is made with a neoprene base with a thickness of a few millimeters, a rounded profile is obtained with a greater thickness only in correspondence with the pcb 28, whereas the rest of the surface of the antenna 12 has a uniform thickness, as already seen, of about 8mm.

Abstract

Device (10) to convert radio frequency electromagnetic energy, comprising an antenna (12), advantageously of the microstrip patch type, and an associated adapted multi-band rectifier circuit formed by a rectifier circuit (31) and by an adaption circuit (32) of the impedance of the load in the frequency bands concerned, to feed at least a connected electronic user device (40). The antenna (12) comprises a single radiant element (13), an associated conductive element (14) below the radiant element (13) and a reception circuit of the power received by the antenna (12). The radiant element (13) has an annular circular shape. The power reception circuit comprises at least a power divisor circuit (22) and a 90° phase shift circuit (24), Two feed branches (25) of the radiant element (13) are connected to the power divisor circuit (22) and the phase shift circuit (24), and are configured so as to generate two electromagnetic field components orthogonal and shifted 90° out of phase and therefore so as to receive a signal with any polarization whatsoever on at least three distinct frequency bands.

Description

"DEVICE TO CONVERT RADIO FREQUENCY ELECTROMAGNETIC
ENERGY"
FIELD OF THE INVENTION
The present invention concerns a device to convert radio frequency electromagnetic energy, to convert the radio frequency electromagnetic field generated by transmission units, such as mobile phones, wireless connection devices or other, into continuous tension electric energy in order to feed electronic user devices having low or very low consumption.
In particular, the conversion device according to the present invention is applied in the field of wireless sensor networks, to feed electronic units of the type that can be worn, such as sensors directly incorporated into articles of clothing, such as uniforms, jackets or others.
BACKGROUND OF THE INVENTION
Devices are known for the conversion of electromagnetic energy of radio frequency signals, or energy harvesting devices, from radio frequency signals, which convert radio frequency electromagnetic energy present in the environment into continuous tension electric energy in order to feed an electronic circuit. These known conversion devices normally comprise an antenna to receive the incident electromagnetic field, which is subsequently converted by means of a suitable rectification circuit into continuous tension electric energy. The receiving antenna and the rectifier are also known as "rectenna" or rectifying antenna.
The quantity of usable electric energy obtainable is therefore determined by the electric and electromagnetic characteristics definable during the design stage, in relation to the signal of the electromagnetic field, of the receiving antenna, of the rectification circuit and their coupling. However, the properties of the radio frequency sources present in the environment such as frequency, polarization of the signal, angle of incidence on the rectenna, distance from the radio frequency source, which contribute to determine the intensity of the electromagnetic field incident on the conversion device, are not known in advance.
Furthermore, the electromagnetic energy available is often limited with respect to the energy typically required by a low-consumption electronic user device, such as for example a wireless sensor node. However, the electromagnetic energy available may vary over time, depending on the type of source, such as for example the electromagnetic energy irradiated in transmission from a mobile phone.
Therefore, in order to satisfy users' requirements, devices for converting radio frequency electromagnetic energy must be made to obtain a maximum efficiency in more than one predetermined band of frequencies, that is, in the bands where it is presumed that an available electromagnetic field of the operating environment exists, each band corresponding to potential sources of a radio frequency electromagnetic field.
The patent WO/A-2007/048052 describes a device for converting radio frequency electromagnetic energy which comprises an array of rectennas, each of which is designed and sized for a specific frequency band. The geometric disposition of the rectennas in the array allows reception with great efficiency of an electromagnetic field with any polarization, and incident with any angle whatsoever on the array of rectennas.
One disadvantage of this known device is that the overall size of the array of rectennas is somewhat high; for example, in the spectrum of frequencies from 900MHz to 2500MHz, the overall bulk required by the array of rectennas is about 500 cm3. Furthermore, this system provides a control circuit of the electric connection, the activation and feed of the rectennas and consequently an increase in the overall complexity of the circuit, consumption and costs.
Moreover, the use of a device for converting radio frequency electromagnetic energy that must be used in wearable applications entails other production constraints. Indeed, from the mechanical point of view the conversion device must be flexible and robust enough to follow the deformations of the body and of the garment in which it is mounted or integrated. This flexibility must not only be of the static type, that is, with a curvilinear shaping and conformation according to a predetermined profile, but must also be of the dynamic type during normal use. Therefore, it is necessary that the device is able to support an unlimited number of bends without deforming, for a maximum angle of curvature depending on the specific zone of the body in correspondence with which the device is positioned. A device for converting radio frequency electromagnetic energy that can be integrated into garments or articles of clothing is described in the patent JP-A- 2003258539. This device comprises a rectenna of the microstrip patch type, single band and linear polarization, which therefore has a limited conversion efficiency, due both to the single band and also to the impossibility of receiving signals having a polarization other than linear.
Other devices for converting radio frequency electromagnetic energy are described in the patents US-A-2007/285324 and US-B-7193573, which describe a multilayer structure able to be integrated into an article of clothing or a garment. These devices, however, are rather large and are specifically designed to operate efficiently in a single frequency band.
Another device of the type in question is described in the patent US-A- 7429959, which comprises a plurality of single-band wearable antennas, disposed in correspondence with different parts 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 bulk and great complexity, determined by the presence of a circuit component for selecting the antenna to be used, and hence of feed; this makes the device difficult to use in an application of the wearable type.
Devices are also known for converting radio frequency electromagnetic energy of the wearable type provided with a dual band circular polarization antenna; however, these have an efficiency limited to a few dB in a single preferential band.
One purpose of the present invention is to obtain a device for converting radio frequency electromagnetic energy which has a great conversion efficiency for signals having a polarization not known in advance and in several frequency bands.
Another purpose of the present invention is to obtain a device for converting radio frequency electromagnetic energy which has limited bulk and sizes, to be integrated into an article of clothing.
Another purpose of the present invention is to obtain an article of clothing or garment comprising at least one device for converting radio frequency electromagnetic energy which has low production costs. The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.
SUMMARY OF THE INVENTION
The present invention is set forth and characterized in the independent claim, while the dependent claims describe other characteristics of the invention or variants to the main inventive idea.
In accordance with the above purposes, a device for converting electromagnetic energy starting from a radio frequency signal according to the present invention comprises an antenna, advantageously of the microstrip patch type, and an associated adapted multi-band rectifier circuit formed by a rectification circuit and a circuit to adapt the impedance of the load in the desired frequency bands, or multi-band adaptation circuit, in order to feed a connected electronic user device, so as to constitute, in its entirety, a so-called rectenna. According to a characteristic feature of the present invention, the antenna comprises a single radiant element and an associated conductive element, substantially flat, below the radiant element, which has the double function of cooperating electromagnetically with the single radiant element and of shielding the human body from irradiation. In a preferential form of embodiment, the radiant element has an annular circular shape, and the conductive element below it has a substantially polygonal shape, advantageously square or rectangular. The two elements are reciprocally positioned to obtain a desired geometry of the antenna, said geometry being designed and configured to receive simultaneously electromagnetic energy in at least three different frequency bands of the electromagnetic field.
According to one characteristic of the present invention, the three different frequency bands constitute three different resonant modes of the structure of the antenna.
In a preferential solution, a first frequency is the fundamental resonant mode of the structure, whereas the other two frequencies are other resonant modes of the structure, in particular higher resonant modes.
According to another feature of the present invention, the device for converting energy from a radio frequency signal also comprises a single multi- band circuit for the reception of the power received by the antenna, which includes a power divisor circuit and a 90° phase shifter circuit. The two circuits, divisor and shifter, are disposed upstream of the rectification circuit, and are associated with the radiant element and the conductive element in order to derive two distinct branches and to detect, for each of the three different frequency bands, at least two components of electromagnetic field, orthogonal and shifted by 90°, and therefore to detect in each of said at least three different bands, a corresponding electromagnetic field substantially with any polarization.
The use of an antenna with a circular polarization able to receive an electromagnetic field, and hence to generate radio frequency power, allows to guarantee a reception of fields having any polarization whatsoever, 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 no matter how it is polarized, that is, with linear, circular, elliptical polarization etc. According to a preferential form of embodiment of the present invention, a first frequency band of said three different frequency bands is the primary band GSM P-GSM900 for transmission from the mobile terminal to the base station (uplink channel) for mobile phones. A second frequency band of said three different frequency bands is the band GSM1750 (DCS-1800), uplink channel for mobile phones. A third frequency band of said three different frequency bands is the band ISM 2450 MHz used for wireless transmissions of local networks, such as Wi-Fi, Bluetooth, ZigBee or others.
Therefore, the device for converting radio frequency electromagnetic energy according to the present invention, by means of a single rectenna unit, that is, substantially by means of a single antenna and a single conversion element, efficiently converts electromagnetic energy received in different frequency bands into electric energy. Furthermore, given that the device has a single conversion circuit, its bulk can be considerably reduced, also simplifying the relative electric circuitry. Moreover, the overall bulk of the radiant element of the antenna is substantially correlated to the first frequency band, at lower frequencies, and hence to the external diameter of the radiant element.
According to one form of embodiment of the present invention, the external diameter of the annular radiant element is about 71 mm, to receive electromagnetic energy in the first frequency band of radio signals in relation to the fundamental mode of resonance TM1 1 of the primary uplink band GSM P- GSM900. The radiant element also comprises first means for perturbing the currents in order to detect electromagnetic energy in the second frequency band of radio signals in relation to the higher resonant mode TM31 of the second frequency band (which constitutes the 3rd frequency of resonance), that is, band GSM 1750 (DCS- 1800). Moreover, the radiant element comprises second means for perturbing the currents in order to detect electromagnetic energy in the third frequency band, that is, in the ISM 2450 MHz band, in relation to its higher resonant mode TM12 (which constitutes the 5th frequency of resonance).
According to the invention, the first and second means for perturbing the currents are made in such a way that they do not significantly modify the behavior in the other two bands.
According to a variant, said first means for perturbing the currents comprise four rectangular slots made annularly between the external diameter and the internal diameter of the radiant 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 the reference direction and two opposite slots orthogonal to the reference direction, disposed substantially annularly between the external diameter and the internal diameter and at the same distance from the center of the first slots.
According to another feature of the present invention, the conductive element comprises non-conductive portions, shaped and positioned to cooperate with the phase shifter circuit and to excite the radiant element.
According to another feature of the present invention, the conversion device is made in a structure with flexible overlapping layers, in which an upper layer of the structure comprises the radiant element, a lower layer comprises the conductive element and at least a layer of electrically insulating material, also substantially flexible, is interposed between the upper layer and the lower layer, so that the whole structure of the rectenna is flexible.
According to another feature of the present invention, the radiant element is made of non-woven fabric of the conductive type.
In one solution, the non-woven fabric is made of Global EMC Ag/Cu/Ni. It also comes within the scope of the present invention to provide that the conductive element, the rectification circuit, the power divisor circuit and the phase shifter circuit are made on a flexible type support.
In one solution, the flexible support is a printed circuit or flexible pcb, with a polyimide base and two conductive surface layers, with an overall thickness of some hundreds of micrometers (for example using the commercial product Dupont PyraluxAP AP8545).
In another solution, the flexible support is made of neoprene screen-printed with silver on both sides.
The present invention also concerns an article of clothing or garment, comprising at least one device for converting radio frequency electromagnetic energy as described above.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other characteristics of the present invention will become apparent from the following description of a preferential form of embodiment, given as a non-restrictive example with reference to the attached drawings wherein:
- fig. 1 is a block diagram of a device for converting radio frequency electromagnetic energy according to the present invention;
- fig. 2 is a circuit diagram of a rectifier of the device for converting radio frequency electromagnetic energy in fig. 1 ;
- fig. 3 is a view from above of a circuit of the device in fig. 1 ;
- fig. 4 is the radiation surface of an antenna of the device in fig. 1 relating to a first frequency band used;
- fig. 5 is the radiation surface of the antenna of the device in fig. 1 relating to a second frequency band used;
- fig. 6 is the radiation diagram relating to a second frequency band used;
- fig. 7 is the radiation surface of the antenna of the device in fig. 1 relating to a third frequency band used;
- fig. 8 is a diagram relating to the reflection coefficient of the antenna of the device in fig. 1 ;
- fig. 9 is a transparent view of two layers of a printed circuit of the conversion device in fig. 1 ;
- fig. 10 is a top side view of the printed circuit in fig. 9; - fig. 1 1 is a schematic view in lateral section of the device for converting radio frequency electromagnetic energy according to the present invention integrated into an article of clothing;
- fig. 12 is an exploded front perspective view from above of the device for converting radio frequency electromagnetic energy in fig. 1 1 ;
- fig. 13 is an exploded front perspective view from below of the device for converting radio frequency electromagnetic energy in fig. 1 1 ;
- fig. 14 is a view from above of a detail in fig. 1 1 ;
- fig. 15 is a view of an article of clothing in which two devices for converting radio frequency electromagnetic energy are integrated.
To facilitate comprehension, the same reference numbers have been used, where possible, to identify identical common elements in the drawings. It is understood that elements and characteristics of one form of embodiment can conveniently be incorporated into other forms of embodiment without further clarifications.
DETAILED DESCRIPTION OF A PREFERENTIAL FORM OF
EMBODIMENT
With reference to the attached drawings, a device 10 for converting radio frequency electromagnetic energy according to the present invention comprises a multi-band antenna 12, of the microstrip patch type, and wide band in each of the functioning bands, a rectification circuit or rectifier 31, connected to the outlet of the antenna 12 through a circuit 32 to adapt the load impedance in the frequency bands involved, or multi-band adaptation circuit. The circuit obtained by connecting the adaptation circuit 32 to the rectification circuit or rectifier 31 is indicated hereafter by the overall name of adapted multi-band rectifier circuit. The device 10, as will be described in more detail hereafter, is made in a layered structure which allows it to be integrated into an article of clothing 50, as shown for example in fig. 15.
In this case (fig. 1), the device 10 is used to feed an electronic user device 40 such as for example, but not restrictively, a node of a wireless sensor network, in its turn integrated into the article of clothing 50. The electronic user device 40 is provided in particular with an energy feed and storage circuit 41 , connected to the outlet of the device 10, and a microcontrol unit 42, for example a microcontroller, provided with a suitable RF interface, not indicated, and with an associated RF transceiver antenna 43.
The antenna 12 (fig. 3) comprises a single annular radiant element 13, circular in shape, which has an external diameter Dl and an internal diameter D2 to define a circular crown made of conductive material. In particular, the diameters Dl , D2 together with specific radial slots which will be described hereafter, define the specific reception properties in the radio frequency bands desired from which environmental electromagnetic energy is taken.
The circuit diagram that obtains the rectification in the rectifier circuit 31, of a known type, is the whole wave rectification type. A possible form of embodiment is shown in fig. 2, where the specific parameters are sized as a function of the load and the frequencies used.
The high efficiency rectification on the specific bands concerned is obtained with a specific circuit for 90° shifting and power division, which guarantee circular polarization to all functioning bands. Furthermore, the adaptation circuit 32 obtains the impedance adaptation between the rectifier circuit 31 with concentrated constants and the antenna's inlet port, which coincides with the port of the power divisor. In particular, for the circuit structure viewed from the side of the rectifier, this has an equivalent inlet impedance with a high reactive component, due to the capacities used.
With reference to fig. 9, the adaptation of the impedance of the antenna in several bands is mainly obtained with a structure of constants distributed with discontinuous impedance which allows to annul the reactive component in all working frequencies and for the whole band width concerned.
The radiant element 13 also has four first rectangular slots 16 and four second rectangular slots 18, which act as current perturbation means or elements, able to generate a perturbation effect on the current passing through the radiant element 13, to obtain the desired reception performance in the three different bands of the radio frequency.
The first slots 16 are made annularly on the conductive material of the radiant element 13, and are inclined by ±45° with respect to a reference direction, for example horizontal, indicated in the drawings by "x". The first slots 16 are substantially tangent in correspondence with their central portion to an ideal circumference of intermediate diameter between the external diameter Dl and internal diameter D2. The second slots 18 are made annularly on the conductive material of the radiant element 13, and are disposed in pairs respectively parallel and orthogonal to said reference direction "x". The second slots 18 are substantially tangent in correspondence with their central portion to said ideal circumference, so as to be at the same distance from the center of the radiant element 13 as the first slots 16, and each of them is interposed along the ideal circumference between two first slots 16.
The antenna 12 also comprises a conductive element 14, substantially flat, below the radiant element 13, with a polygonal shape, advantageously square or rectangular. The conductive element 14 (figs. 1 1, 12) comprises layers 48a, 49, as described hereafter, and a first side, or top side, of a printed circuit of the flexible type, or pcb 28. The whole of these layers functions as a mass plane for the antenna 12, as the layer 48a and the top side of the pcb are reciprocally glued together by means of a radio frequency conductive adhesive material. In particular, the radiant element 13 is fed by electromagnetic coupling by two branches 25 of a 90° phase shifter 24, below the radiant element 13. The cooperation between the conductive elements, that is, the feed branches 25 and respective slots 20 made in the mass plane defined by the conductive element 14, determine the electromagnetic coupling with the radiant 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 widened square portions at the respective ends. The slots 20 are disposed orthogonal to each other, and their shape is specifically designed to:
- guarantee the excitation functionality of the radiant element 13 so as to generate a polarization component of a circular electromagnetic field in all the frequency bands used;
- to guarantee, at the same time, the best uncoupling of the two feed branches 25 and therefore the maximum transfer of radio frequency power.
The printed circuit or pcb 28 is disposed so that each slot 20, shown transparently in fig. 3, is disposed respectively parallel to a corresponding second slot 18, outside the ideal circumference. The longitudinal extension of each slot 20 is such that the relative square portions are near 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 relating to the sizes of the patch type radiant element 13 relates to the fundamental frequency of resonance, whereas other resonance frequencies can be obtained by using the same antenna sizes, that is, sizes of the radiant element 13.
The antenna 12 is also provided with a power divisor circuit 22 and the 90° phase shifter circuit 24, both made on a second side of the pcb 28 and which determine the circular polarization of the electromagnetic field with the same accuracy on all functioning bands. Two feed branches 25 of the radiant element 13 are connected to the power divisor circuit 22 and the phase shifter circuit 24, so as to generate two components of electromagnetic field shifted out of phase by 90° and therefore, due to the reciprocity of the antenna behavior, to receive a signal with any polarization whatsoever.
The excitation of the radiant element 13 of the antenna 12, as we said before, is obtained by electromagnetic coupling through two slots 20 made on the mass conductive element 14 and the feed branches 25 made on the second side of the pcb 28 below the patch type radiant element 13 (figs. 3, 9 and 10), according to a known method, not described here.
In particular, the device 10 converts radio frequency electromagnetic energy in three different frequency bands, corresponding to different modes of resonance of the structure, one fundamental, the other two higher, relating to the frequencies assigned to mobile phones and wireless networks as now summarized:
- a first band is the primary frequency band GSM P-GSM900, uplink for mobile phones having about 25 MHz band width;
- a second band is the frequency band GSM 1750 (DCS- 1800), uplink for mobile phones having about 75 MHz band width;
- a third band is the frequency band ISM 2450 MHz, used for wireless transmissions on local networks, such as the Wi-Fi networks, Bluetooth, ZigBee or others, having about 50 MHz band width.
As far as the first and second bands are concerned, that is, the mobile phone bands, only the uplink bands are considered, that is, the transmission bands from the mobile phone, since the radio frequency signal usable in terms of intensity of the electromagnetic energy detectable by the antenna 12 is the transmission signal to the base station of the cells of the telephone network.
First frequency band
In the first frequency band, for P-GSM900, the fundamental resonance mode TM1 1 is used.
The use of the radiant element 13 with a circular ring patch structure, given the same resonance frequency, allows to have a smaller ring bulk, as for example described in "A broad-band annular-ring microstrip Antenna", Antennas & Propagation AP-30, n° 5, 1982 in the name of Weng Cho Chew. The radiation lobe obtained is the broadside type (fig. 4), typical of a patch antenna.
In particular, the external radius relating to the diameter Dl of the ring is about 71 mm.
Using a square real mass plane, that is, not ideal and infinite, with sizes of about 250x250 mm and a disposition of the radiant element 13 and the conductive element as described above and shown in figs. 12 and 13, a maximum antenna gain is obtained of about 4dB, also including the adaptation to the rectifier circuit 31.
Second frequency band
In the second frequency band, that is, GSM1750, the upper resonance mode (3rd frequency of resonance) TM31 is used.
In fact, since the behavior of a ring type patch element (with thin substrate) is known, as far as its resonant modes are concerned, as indicated for example in "Mode Chart for Microstrip Ring Resonators", Transactions on Microwave Theory and Techniques, Volume: 21, Issue: 7, 1973, in the name of Y.S. Wu, F.J. Rosenbaum, and since the current perturbation method for regulating the resonant frequency of TM21 at a determinate frequency is also known, as indicated for example 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, we designed the aforesaid disposition of the first slots 16 able to lead to the desired resonance frequency and with a predetermined band width, without interfering with the other radiant modes used. Given the feed with two elements shifted out of phase by 90° and the symmetrical structure of the first slots 16 made in the radiant element 13, we obtain a radiation surface with two lobes inclined by 30° with respect to an axis "Z" that protrude from the plane on which the radiant element 13 itself lies (figs. 5 and 6).
In these conditions, the maximum gain obtained by the antenna 12 of the device 10 is about 5 dB.
Third frequency band
In the third frequency band, or ISM 2450 MHz band, the upper resonance mode (5th frequency of resonance) TM12 is used.
In this case the electromagnetic fields that irradiate the device 10 have a reduced intensity with respect to the one generated by mobile devices for mobile phones. Depending on the specific standard of wireless connectivity used, it is possible to have maximum powers incident on the antenna 12 of lOmW against the 300-500mW for GSM cellular transmission. Therefore, the antenna 12 must be very efficient in this band, keeping unchanged its behavior in the other two bands used.
Therefore, the upper resonance mode TM12 is used, with maximum irradiance for ring patch antennas, so that the relative frequency of resonance is exactly as desired. Therefore, the second symmetrical horizontal and vertical slots 18 (fig. 13 on the right) determine a predetermined perturbation of the path of the currents on the radiant element 13 for mode TM12. The conformation of the second slots 18 is also sized according to the variations in behavior of the radiant element 13 as introduced by the first slots 16, which in turn are affected by the second slots 18.
In this form of embodiment the internal radius of the ring, in relation to the diameter D2, is about 21 mm.
The radiation diagram obtained is the more directive broadside type, with a maximum gain of more than 9.0 dB in a direction perpendicular to the plane on which the radiant element 13 lies, that is, in the direction of the axis "Z" (fig. 7).
Fig. 8 shows the development of the reflection coefficient of the antenna 12 as a function of frequency: from this it is possible to see the adaptation of the antenna 12 to the specific and desired three different frequency bands in which electromagnetic energy is received.
Therefore, a single feed antenna is obtained, the sizes of which are substantially within the overall bulk of the radiant element 13 of the antenna 12 and which operates with the desired efficiency in three different frequency bands and for the whole band width assigned for the wireless communication standards considered.
With reference to figs. 3, 9 and 10, the area needed for the adapted multi-band rectification circuit (adaptation circuit 32 connected to the rectifier circuit 31), the power divisor circuit 22, the phase shifter circuit 24 and the slots 20 for coupling to the radiant element 13, is about 140x140 mm. Fig. 3 shows the transparent view of the elements of the antenna 12 on the lying plane xy. The position of the radiant element 13 is determined by the coupling of the radiant element 13 and the slots 20, and is translated and asymmetrical with respect to the conductive element 14.
The minimum bulk on the plane xy is about 175x165 mm, or about 190x190 mm if the overall size of the conductive element 14 has a symmetrical distribution. These bulks also take into account aspects connected to the assembly of the different layers that make up the antenna 12, as will be described in more detail hereafter.
It is possible to obtain a greater efficiency in all bands for greater sizes of the mass plane. In particular a significant reduction in efficiency is obtained by passing from a mass plane sized 250x250 mm to a mass plane with the minimum size as indicated previously.
The device 10 is compatible with production in flexible materials for working fabrics or garments. In particular, making the radiant element 13 and the slots 20 on the top side of the pcb requires a cutting precision of about 100 μηι, which is compatible with laser cutting methods for conductive non- woven fabrics.
The requirement of alignment with the lying plane xy between the layers that make up the antenna 12 is also about 100 μιη, compatible with normal assembly techniques in the textile field.
Furthermore, the antenna 12 of the device 10 according to the present invention can also be used as a transmission antenna of the electronic user device 40, as a sensor connected to it. In this case, it is possible to provide an alternate functioning at intervals of time, in which the antenna 12 is alternately used to collect RF energy or to transmit detection data of the sensor, that is, of the user device 40.
Moreover, if at least one of the frequency bands is not used, for example because no radio frequency source can be detected in the specific band, the antenna 12 itself can be used as a transmission antenna in said specific frequency band, which is in fact unused for the conversion of radio frequency energy.
The device 10 to convert radio frequency electromagnetic energy is incorporated into an article of clothing 50, integrated into the fabric itself. The device 10 is made in a layered structure and has a structure of superimposed layers as shown in figs. 1 1-13. In particular, the device 10 comprises the following functional layers (in order from the outside toward the user's body):
- a flexible external layer disposed toward the outside of the article of clothing 50 and having a substantially protective function; this layer, not indicated in the attached drawings, can be obtained, if the device 10 is inside the garment, from the outer layer of fabric 44 which makes up the garment, indicated only in fig.
1 1 ;
- a flexible layer below layer 44 which obtains the antenna which in turn comprises:
- the radiant element 13 that defines a first upper layer,
- a first insulating thermo-adhesive layer 46a, shaped in the same way as the radiant element 13, and by means of which the radiant element 13 is attached to the lower layers,
- a first layer 47a of insulating fabric interposed between the radiant element 13 and the conductive element 14 which comprises layers 48a and 49,
- a second insulating thermo-adhesive layer 46b,
- a first layer of conductive fabric 48a and a layer formed by a conductive bi- adhesive frame 49 comprised in the conductive element 14, which define a second lower layer,
- the double-layer pcb 28, attached to the first layer of conductive fabric 48a by means of said conductive bi-adhesive frame 49,
- a third insulating thermo-adhesive layer 46c,
- a second layer of insulating fabric 47b, with the function of distancing and containing the electromagnetic field,
- a fourth layer of insulating thermo-adhesive fabric 46d,
- a second layer of conductive fabric 48b.
The second insulating thermo-adhesive layer 46b and the first layer of conductive fabric 48a are worked so as to have a first, substantially square aperture 45, with sizes slightly smaller than the sizes of the pcb 28, on the edges of which the conductive bi-adhesive frame 49 is applied. In another form of embodiment a conductive glue is used instead of the bi-adhesive frame 49. The third insulating thermo-adhesive layer 46c also has a second aperture 45c, substantially square, with sizes slightly bigger than the sizes of the pcb 28.
The materials used were chosen to optimize the conversion performance, that is, the overall efficiency of conversion, and to guarantee mechanical flexibility of the antenna 12 during its use when integrated into the article of clothing 50. Moreover, the overall thickness of the device 10 must be less than 10 mm, so as to be inserted in an article of clothing such as a jacket 50, without causing defects or tension in the fabric.
Table 1 summarizes some possible materials that can be used for the different layers, where for simplicity the relative numerical references have been inserted into the first column relating to the layer.
Table 1
Table 1
Layer Material Description
13, 48a, 48b Global EMC Ag/Cu Ni Conductive non-woven fabric
47a, 47b Polartech ThermalPro Pile
28 Conductive double face flexible Alternative: neoprene
Pcb on dielectric substrate (e.g. screen printed with Ag DuPont PyraluxAP) on both faces
AP8545
46a,46b,46c,46d Insulating thermo-adhesive
49 Conductive bi-adhesive 3M ECATT 9707
The most complex part for making the antenna 12 concerns the layers of the pcb 28 on which are made the adapted multi-band rectification circuit, formed as we said by the adaptation circuit 32 and the rectifier circuit 31 , the power divisor circuit 22, the phase shifter circuit 24, all multi-band, on the bottom side, and the slots 20 made as apertures on the mass plane that supply the feed by electromagnetic coupling for the radiant element 13, on the top side. Depending on the thickness and the electromagnetic characteristics of the insulating layers of dielectric material positioned between the conductive elements on the top and bottom side, the thicknesses and precision required from the geometries to be made on the bottom side can vary considerably and might not be respected with the technologies available for the materials selected. For example, if the pcb 28 is made with a flexible electronic circuit easily found on the market, consisting of 2 faces of 35um copper and lOOum Polyimide dielectric (er=3.4) , it is necessary to make conductive tracks with a thickness of 3 mils, which value is at the limit of possibilities for the current working of these materials. Otherwise, using neoprene as the dielectric mean (er 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 screen printing process with a silver based conductive ink with a greater track width and less accuracy required.
In this second case, the overall thickness of the device 10 increases by some mm but it is possible to obtain greater flexibility and strength of the whole rectenna.
Therefore, the production of the antenna 12 and the pcb 28 are substantially independent of each other. This allows to decide which type of pcb 28 to use: for example, with a constraint of minimum thickness and accepting a 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 ; for a solution with maximum flexibility and strength it is possible to make the pcb starting from an insulating support element made of neoprene, screen printed on the surface with conductive paint.
Furthermore, the structure of the pcb 28 is independent from the size and shape of the device 10 in its final production, therefore it is independent from production and assembly features of the whole rectenna. The other layers of the device are sized and shaped according to the garment and the zone where the rectenna is positioned.
With reference to fig. 1 1 and to the implementation of the pcb 28 with a flexible electronic circuit, the conductive layer 48a, which constitutes the reference mass plane of the antenna, has the aperture 45a in correspondence with the position that the pcb 28 is to assume with respect to the radiant element 13. The aperture 45a has a size so as to be superimposed by 5- 10 mm above the mass plane made on the pcb 28, top side, and so as not to interfere with the two slots 20. The application of a conductive adhesive element, that is, the frame 49, by radio frequency application between the second conductive layer 48a and the pcb 28 top side, allows to achieve a mass plane with maximum sizes compatible with the size and shape of the device in its final form. This allows to improve the overall conversion efficiency of the antenna 12 according to the area available on the garment for the application of the device 10.
The overall encapsulation of the pcb 28 in the layers of the antenna 12, and hence its attachment and protection, is obtained by gluing the second layer of fabric 47b onto the first conductive fabric 48a with the aid of the insulating thermo-adhesive layer, removed in correspondence with the whole area occupied by the pcb 28. Since the two layers of insulating fabric 47a, 47b are much thicker than the pcb 28, they are compressed in correspondence with the pcb 28, incorporating it inside them and all around. In particular, if the pcb 28 is made with a neoprene base with a thickness of a few millimeters, a rounded profile is obtained with a greater thickness only in correspondence with the pcb 28, whereas the rest of the surface of the antenna 12 has a uniform thickness, as already seen, of about 8mm.
It is clear that modifications and/or additions of parts may be made to the device 10 for converting radio frequency electromagnetic energy as described heretofore, without departing from the field and 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 of skill in the art shall certainly be able to achieve many other equivalent forms of device 10 for converting radio frequency electromagnetic energy, having the characteristics as set forth in the claims and hence all coming within the field of protection defined thereby.

Claims

1. Device to convert electromagnetic energy of a radio frequency signal, comprising an antenna (12), in particular of the microstrip patch type, and an associated adapted multi-band rectifier circuit formed by a rectifier circuit (31) and by an adaption circuit (32) of the impedance of the load in the frequency bands concerned, to feed at least a connected electronic user device (40), characterized in that the antenna (12) comprises a single radiant element (13), an associated conductive element (14) below the radiant element (13) and a reception circuit of the power received by the antenna (12), in which the radiant element (13) has an annular circular shape, in which said power reception circuit comprises at least a power divisor circuit (22) and a 90° phase shift circuit (24), in which two feed branches (25) of the radiant element (13) are connected to the power divisor circuit (22) and the phase shift circuit (24), said feed branches (25) being configured so as to generate two electromagnetic field components orthogonal and shifted 90° out of phase and therefore so as to receive a signal with any polarization whatsoever on at least three distinct frequency bands, in which said three frequency bands comprise at least the fundamental resonant mode of the antenna and two different resonance modes.
2. Device as in claim 1, characterized in that said different resonance modes are higher resonance modes.
3. Device as in claim 1, characterized in that the radiant element (13) comprises at least first and second perturbation means (16, 18), able to generate a perturbation effect on the current passing through the radiant element, said perturbation means (16, 18) being configured so as to detect electromagnetic energy in respective second and third frequency bands distinct from a first main frequency band.
4. Device as in claim 3, characterized in that said first and second current perturbation means (16, 18) are made so as not to significantly modify the behavior at least of the radiant element (13) in the other two bands.
5. Device as in claim 3 or 4, characterized in that the first current perturbation means comprise four first rectangular slots (16) made annularly between an external diameter (Dl) and an internal diameter (D2) of the radiant element (13), and inclined by ±45° with respect to a reference direction (x), and in that the second current perturbation means 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), disposed substantially in an annular manner between said external diameter (Dl) and said internal diameter (D2) at the same distance from the center of the radiant element as said first slots (16).
6. Device as in any claim hereinbefore, characterized in that said at least three frequency bands comprise frequency bands for mobile phones and at least an ISM 2450 band.
7. Device as in claim 4 and 6, characterized in that the external diameter (Dl ) of the annular radiant element (13) is sized at about 71 mm, in order to detect electromagnetic energy in said first frequency band of radio signals in relation to the fundamental TM1 1 mode of the primary band GSM P-GSM900 uplink.
8. Device as in any claim hereinbefore, characterized in that it is made as a structure of overlapping flexible layers, in which a first upper layer of said structure comprises said radiant element (13), a second bottom layer comprises said conductive element (14), and at least a layer (47a) of electric insulating material is interposed between said first upper layer and said second bottom layer.
9. Device as in claim 8, characterized in that the radiant element (13) is made of non-woven fabric of the conductive type.
10. Device as in claim 1, characterized in that at least part of the conductive element (14), the adaptation circuit (32), the rectifier circuit (31 ), the power divisor circuit (22) and the 90° phase shifter circuit (24) are made on a support (28) of the flexible type.
1 1. Device as in claim 10, characterized in that said flexible support is a printed circuit or pcb (28), with at least two conductive layers separated by a dielectric layer.
12. Device as in claim 1 1, characterized in that said flexible support (28) is a neoprene support screen printed with silver on both sides.
13. Device as in claim 1 1 or 12, characterized in that the flexible support (28) has non-conductive portions (20), disposed substantially orthogonal to each other, and specifically designed to guarantee the excitation functionality of the radiant element (13) so as to generate a polarization component of a circular electromagnetic field in all the frequency bands used and to guarantee, at the same time, the uncoupling of the two feed branches (25) and therefore the maximum radio frequency power transfer.
14. Article of clothing comprising at least a device (10) to convert radio frequency electromagnetic energy as in any claim from 1 to 12.
PCT/IB2011/002253 2010-09-27 2011-09-27 Device to convert radio frequency electromagnetic energy WO2012042348A2 (en)

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ITUD2010A000174A IT1402247B1 (en) 2010-09-27 2010-09-27 ELECTROMAGNETIC ENERGY CONVERSION DEVICE FOR RADIOFREQUENCY
ITUD2010A000174 2010-09-27

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US10014730B2 (en) 2013-07-08 2018-07-03 Utc Fire & Security Americas Corporation, Inc. Radio frequency harvester assembly
CN111129759A (en) * 2020-01-14 2020-05-08 山西大学 Integrated broadband circularly polarized rectifying antenna capable of being conformal
CN111916903A (en) * 2020-06-29 2020-11-10 四川大学 Double-channel communication rectification multifunctional antenna based on asymmetric coupler
CN111916903B (en) * 2020-06-29 2022-07-05 四川大学 Double-channel communication rectification multifunctional antenna based on asymmetric coupler

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