MXPA99008744A - Apparatus for magnetically decoupling an rfid tag - Google Patents

Abstract

A resonant circuit tag (12) includes an integrated circuit (18) for storing data and an antenna circuit (22) for generating a first local field and resonating at a first predetermined radio frequency. A second circuit including an inductive coil (30) selectively generates a second local field such that a sum of the first and second local fields approaches zero. The second circuit thus allows the resonant tag (12) to be selectively decoupled from its environment.

Description

BASIS FOR MAGNETICALLY DISCOVERING A FREQUENCY IDENTIFICATION LABEL BACKGROUND OF THE INVENTION The methods of applying labels on articles for purposes of identification and / or protection against theft are known. For example, many items are identified using a bar code comprising coded information that is read by passing the bar code in view of an optical reader. Many articles also include a resonant tag to be used in the detection and prevention of thefts. In recent times, passive resonant labels have been developed that return unique or semi-unique identification codes. These labels typically include an integrated circuit that stores the identification code. Such "smart" labels provide information referred to an article or person with whom the label is related, such information being detected in the area of an interrogating device or reader. Labels are desirable since they can be interrogated quickly and from a distance. The North American patents bearing Nos. 5,446,447 (Carney et al.), 5,430,441 (Bickley et al.) And 5,437,263 (Carroll et al.) Describe three examples of such smart tags. Labels or resonance frequency identification cards include a resonant antenna circuit electrically connected to the integrated circuit. The integrated circuit essentially consists of a programmable memory for storing digitally encoded information. The interrogating device (transmitting antenna) creates an electromagnetic field that resonates at the frequency of the smart tag. When the tag is placed in the field of the interrogating device, an alternating current voltage is induced in the resonant antenna circuit of the tag, which is rectified by the integrated circuit in order to provide the internal circuit with an internal DC voltage. As the label moves within the field of the interrogating device, the induced voltage increases. When the internal DC voltage reaches a level that ensures proper operation of the integrated circuit, the output of the latter provides its stored data. To provide its data, the integrated circuit creates a series of data pulses by switching an extra capacitor through the antenna circuit for the duration of the pulse, which changes the resonance frequency of the label, setting it outside the operating frequency . That is, the label creates data pulses by getting out of sync, which changes the amount of energy consumed by the label. The interrogating device detects the energy consumption in its field and interprets the changes considering them as data impulses. Although such labels or smart cards are known, technical difficulties and limitations still exist in the functioning thereof. In the situation in which multiple smart tags are attempted to be read within an interrogation zone of the interrogating device, the problem arises that more than one tag may be activated by the interrogating device at about the same time. When such tags are close to each other, the fields generated by one tag may disturb the fields generated by another tag. This problem of mutual inductance is especially important in smart labels that transmit their information by getting out of sync, as mentioned above. As a consequence, the effective reading distance suffers a decrease and the modulation of the tag may be completely ineffective due to the fact that such modulation depends on the fact that the tag remains in resonance (or in proximity to it). In that way, such a disin- sony caused by other labels can make the reading of stored information almost or impossible. Yet another problem frequently encountered in reading labels or smart cards is a wide variation in the energy received, for example, when the label approaches the energy transmitting antenna of the interrogating device. As this approximation occurs, the received energy increases, which can cause problems due to excessive tension or energy dissipation and, due to a decrease in the Q value of the label, the impossibility of modulating the label with sufficient the data used the aforementioned resort of the dyno. Such problems of dithering or modulation increase the difficulty of correctly reading the label. There is therefore a need to have a method to prevent resonant frequency identification tags or smart tags from generating fields that disturb or affect other labels or resonant cards that are nearby. There is also the need to have a smart card or label whose operation is not affected by large variations of the received energy. The present invention satisfies these needs.

BRIEF DESCRIPTION OF THE INVENTION Briefly, in a first embodiment the present invention is an intelligent radio frequency device that when interrogated returns a response. The intelligent device includes an integrated circuit for storing data and an inductor or coil electrically connected to the integrated circuit. The inductor includes a first coil electrically connected to a second coil. A resonant capacitor is electrically connected to an integrated circuit to at least one of the coils of the pair formed by the first and second coils, so that the resonant capacitor and at least one connected coil resonate at a first predetermined sequence. A switch is provided having a first position and a second position to selectively allow the flow of current through the second coil. When the switch is in the first position, the exposure of the intelligent device to an external field that resonates at said first frequency induces a voltage in the inductor and causes a first current to flow through the inductor in a first direction, thereby generating a local field When the switch is in the second position, the exposure of the intelligent device to an external field that accurately or roughly resonates at the first frequency causes a voltage to be induced in the inductor and a first current to flow through the first coil in a first sense thereby generating a first local field, and that a second current flows through the second coil in a second sense or opposite direction, thereby generating a second local field. The sum of the first and second local fields has a result that approaches zero. In a second embodiment, the present invention is an intelligent radio frequency device comprising an integrated circuit for storing data, and an antenna circuit. The antenna circuit consists of a first coil and a resonant capacitor having a predetermined resonance frequency and which is electrically connected to the integrated circuit to supply power to it and to make the data stored in the integrated circuit be transmitted to a reading device . The exposure of the intelligent device to an external field that resonates at a predetermined frequency causes a first current to flow through the antenna circuit in a first direction, thereby producing a first local field that couples the intelligent device to its environment. The intelligent device further comprises pair means selectively generating a second local field, in which a sum of the first and second local fields has a result close to zero, in order to selectively decouple the intelligent device from its environment. In a third embodiment, the present invention consists of an intelligent resonant tag consisting of an integrated circuit for storing data and a first antenna circuit electrically connected to the integrated circuit. The exposure of the first antenna circuit to an electromagnetic field that resonates at a first radio frequency induces therein a voltage, which produces a current flowing in a first direction therethrough, thus producing a first local field. The induced voltage also supplies power to the integrated circuit, so that the data stored in said circuits is extracted from it and transmitted to a second predetermined radio frequency. The tag also comprises means for generating a second local field, which at least partially cancels the first local field generated by the first antenna circuit.

BRIEF DESCRIPTION OF THE DRAWINGS The aforesaid summary, as well as the following detailed description of preferred embodiments of the invention, may be better understood if they are interpreted with reference to the appended claims. For the purposes illustrated in the invention, embodiments which are presently preferred are shown in the drawings. Nevertheless, it should be understood that the invention is not limited to the exact arrangements and instrumentation shown. In the drawings: Figure 1 is an equivalent electrical circuit that schematically shows an interrogator device and a resonance frequency identification device according to a first embodiment of the present invention. Figure 2A is an equivalent electrical circuit schematically showing an alternative embodiment of an intelligent tag according to the present invention; Fig. 2B is a schematic representation of the equivalent electric circuit of Fig. 2A and shown in an active state, and Fig. 2C is a schematic representation of the equivalent electric circuit of the smart tag of Fig. 2A shown in an inactive state.

DETAILED DESCRIPTION OF THE INVENTION In the following description a certain technology is used for certain reasons of convenience and it should not be considered as a limitation imposed in the present invention. In the drawings, the same reference numbers are used to designate the same elements in the various figures. The present invention provides an intelligent tag for the identification of resonance frequency and in which a net field is produced by currents flowing through it and which are caused by stresses induced on the label by an externally applied field and which Selective approach approaches zero. In accordance with the present invention, an antenna of the intelligent device comprises two coils or inductors and a switch. When the switch is in one position, currents flow through the two inductors in opposite directions, so that the field generated by the currents flowing through one of the inductors is essentially bypassed by the field generated by the current flowing through the other. inductor. When the switch is in another position, the configuration of the device circuit or smart tag is device 12 and allow it to operate according to its intended purpose, as will be described in detail below. The interrogating device 10 can be physically considered as a pair of showy pedestals (not shown) as an optical reader carried manually and intended for resonance frequency identification (not shown) or in some other way. The interrogation signal generated by the device 10 is preferably a generally continuous signal, unlike a periodic or pulsating signal. The interrogation zone is the area within which the electromagnetic field in which a voltage is induced in the label or intelligent device 12 is sufficient to feed the latter. In that way, the size of the interrogation zone is defined by the intensity of the electromagnetic field. The interrogating device 10 can detect transmissions from a plurality of intelligent devices 12 (and therefore of the articles in which such devices or tags are applied) that are within the interrogation zone. Smart tags or transmitting devices that respond when interrogated are generally known and applicable to a wide variety of uses. In US Patent No. 5,430,441 an intelligent tag is disclosed that transmits a digitally encoded signal in response to an interrogation signal. The aforementioned label comprises a rigid substrate constructed from a plurality of dielectric layers and conductive layers, and includes an integrated circuit fully embedded within an aperture of the substrate and a traced label made with a very thin sheet of conductive material. The intelligent device 12 day present invention comprises an antenna circuit 20 electrically connected to an integrated circuit 18.

Preferably, the antenna circuit 20 comprises a circuit that resonates at a predetermined radio frequency and changing, so that no annunciating current flows through one of the inductors, so that no canceling field is generated. In this way, the label can selectively be decoupled from its environment. When in such condition the label does not generate fields that interfere with the operation of any resonant label that is nearby. Turning next to the consideration of Figure 1, there is shown schematically an electrical circuit of an interrogator device or reader 12 and a device 10 for resonant frequency identification constructed in accordance with the present invention. The interrogating device 10 includes at least one voltage source 14, electrically connected to a transmitting antenna or coil 16 to generate an electromagnetic field. The interrogating device 10 and the intelligent device 12 communicate by means of an inductive coupling. Interrogating devices that communicate with an intelligent device or resonant tag by means of inductive coupling are well known in the art. For exampleinterrogating devices are described in the North American patents bearing Nos. 3,752,960, 3,816,780 and 4,580,041, all granted in the name of Walton et al., which are incorporated by reference in their entirety to the present application. . Accordingly, the interrogating device 10 is not shown or described in detail.

Suffice it to say that the interrogating device 10 establishes a field that accurately or roughly resonates with the frequency of the intelligent device 12. When the intelligent device 12 is sufficiently close to the interrogating device 10, as to be within the electromagnetic field, in the device 12 a tension is induced. As the device 12 moves within the field created by the interrogator 10, the induced voltage increases until it reaches a sufficient level to feed the one corresponding to a resonant frequency of the interrogating device 10, as will be explained in detail later. The antenna circuit 20 may comprise one or more inductive elements electrically connected to one or more capacitive elements. In a preferred embodiment, the antenna circuit 20 is formed by the combination of a single inductive element, inductor or coil 22 electrically connected in parallel with a capacitive element or resonant capacitor 24. As is well known those of ordinary skill in the art , the operating frequency of the antenna circuit 20 depends on the values of the inductor 22 and the resonant capacitor 24. The values of the inductor 22 and the capacitor 24 are determined on the basis of the desired resonant frequency of the antenna circuit 20. In a embodiment of the invention, the intelligent device 12 is constructed to operate at a frequency of 13.56 MHz. While it is preferred to resonate at said frequency, it is preferred that the device 12 be constructed to resonate at other frequencies, and the exact value of such Frequency should not be construed as limiting the present invention. In this way, it will be eminent for those of ordinary skill in the art that the antenna circuit 20 can operate at frequencies that are not of the indicated value, and certainly those of other bands, such as, for example, the microwave frequencies. Connected in series with the first inductor 22 is a resistor 26, which represents an equivalent series resistance of the inductor 22 due to energy losses. Further, while the antenna circuit 20 comprises a single inductive element 22 and a single capacitor 24, multiple inductor and capacitor elements can also be employed. For example, multiple element resonant circuits are known in the specialty of electronic security and surveillance means such as those described in US Patent No. 5,103,210, entitled "Activatable / Deactivatable Security Label to be Used with an Electronic Disposition of Security ", which is included in the present application as a reference. Although a preferred antenna is described, it will be apparent to those of ordinary skill in the art that any means for establishing the power coupling can be used with respect to the integrated circuit 18. In comparison with such known deactivatable devices, which include a switch to deactivate the resonant circuit of a resonant tag, according to the present invention the antenna circuit 20 is never deactivated. On the contrary, the circuit 20 continues to resonate but the field created by the first inductor 22 is effectively neutralized by means of a nulling field created by a second inductor, as will be explained in detail below. Preferably, the integrated circuit 18, provided for storing data, is a passive device that is powered by the voltage induced in the antenna circuit 20 by the interrogating device 10. That is, when the intelligent device 12 is sufficiently close to the interrogating device 10. so as to be within the electromagnetic field, the voltage induced in the inductor 22 supplies power to the integrated circuit in the antenna input of said circuit. The integrated circuit 18 internally rectifies the alternating current voltage induced at the antenna input, in order to provide an internal power supply that provides DC voltage. When the internal DC voltage reaches a level which ensures proper operation of the integrated circuit 18, this circuit functions to supply a digital value stored in the programmable memory of the modulation output of the integrated circuit 18. A method with the help of which the data stored in the integrated circuit can be transmitted to a reading device (not shown) consists in the use of a modulation capacitor 28 connected to the modulation output of the integrated circuit 18 and to the antenna circuit 20. According to this method, in the modulation output switch the data output alternately place the modulation capacitor 28 in the antenna circuit 20 and remove it from said circuit by closing and opening ground connections, so that the overall capacitance of the antenna circuit 20 is changed according to the stored data, which in turn changes the resonance frequency of the circuit 20, putting it out of tune with respect to the first predetermined resonant frequency and bringing it to a predetermined higher frequency. In that way, the data pulses of the intelligent device 12 are created by tuning and detuning the resonant antenna circuit 20, so that, instead of returning a single and simple frequency response signal, the antenna circuit 20 returns a signal that contains a packet of information previously programmed. Of course, as will be understood by those of ordinary skill in the art, other suitable modulation means may be used with the present invention. In addition, while these means for transmitting data to the reading device work properly, the present invention uses different means, as will be explained in detail below, with the help of which the stored data is transmitted to the reading device. The information packet (data pulses) is received and processed by a set of receiver circuits (not shown) generally associated with the interrogating device 10. That is, such a set of receiver circuits detects the changes that occur in the energy consumed within the receiver. electromagnetic field of the interrogating device 10, to determine the digital data value that appears at the output of the integrated circuit 18. If necessary, the data is decoded by the interrogating device or a set of circuits associated therewith, to provide identification and another information referred to an article is a person with whom the intelligent device 12 is associated 12. Presently it is preferred to use a passive integrated circuit which is powered by the voltage induced in the antenna circuit 20. However, within the scope of the present invention other means for feeding the integrated circuit 18, such as a bat would be The integral circuit d may also include a supply voltage return or an earth output, and one or more additional inputs (not shown) that are used to program the integrated circuit 18 (i.e., store or alter the stored digital value). of the same) in a conventional manner. In the presently preferred embodiment, the integrated circuit 18 comprises 128 bits of non-volatile memory. Naturally, it will be evident to those of ordinary skill in the art that the integrated circuit 18 could have a greater or better storage capacity. When exposed to an external field, such as for example the field generated by the interrogator 10, at a frequency that exactly or approximately equals the first predetermined resonant frequency, the intelligent device 12 induces a voltage in the antenna circuit 20, causing a first current to flow through the antenna circuit 20 and in a first direction, as indicated by the arrow. The current flowing through the circuit 20 produces a first local electromagnetic field. The following abbreviations have the meanings indicated. For example, "exc" represents excitation (caused by the generated electromagnetic field): "can" represents cancellation; finally "res" represents resonance. For example, Kexc .es represents the magnetic collection coefficient established between the interrogation coil 16 and the first inductor 22. As explained above, the field generated by the current flowing through the first inductor 22 may interfere with the operation of other devices or smart tags operating in the vicinity of said device 12. Accordingly, the present invention further comprises a second canceller inductor 30. In the embodiment shown in Figure 1, the second inductor 30 is electrically connected to the first inductor 22. However , as will be apparent to those of ordinary skill in the art, it is not necessary for the second inductor 30 to be electrically connected to the first inductor 22 in order to fulfill its desired function. A resistor 32 connected in series with the second inductor 30 is shown, which represents an equivalent series resistance of the inductor 30 and due to energy losses. A switch 34 and a switch resistor 36 connect the second inductor 30 to the antenna circuit 20. The switch resistor 36 represents the equivalent series resistance of the switch 34. The second inductor 30 is connected to the antenna circuit 20 so that when the switch 34 is closed and the intelligent device 12 is arranged to the external field generated by the interrogator 10 and having a frequency that is exactly or approximately equal to the first predetermined frequency, in each of the first and second inductors, or be the inductors 22 and 30, a voltage is induced, causing the first current I2 to flow respectively through the circuit 20 in the first direction, and a second current I2 flow respectively through the second inductor 30 in a second direction opposite to the direction of the first current. as indicated by arrow l2. The current 12 flowing through the second inductor 30 produces a second local electromagnetic field. Kexc: can represents the magnetic coupling coefficient established between the interrogating inductor 16 and the second inductor 30, which is the canceller inductor. KeXC: can represents the magnetic coupling coefficient established between the first inductor 22 and the second inductor 30. Typically, KeXC: res and KeXC: can have a value of less than 0.01 and Ke? C: can have a lower value of the unit and greater than 0.4. Preferably, the first and second local magnetic fields act on each other, so that a sum of the first and second local magnetic fields has a result approaching zero. That is, a net field produced by the currents flowing through the intelligent device 12, from voltages induced in said device by the interrogator 10, has a value that selectively approaches zero. Thus, when the field next to the intelligent device 12 is measured, the measurement approaches that of the field generated by the interrogator 10, as represented by the equation: Lrl 1 + Lcl2 = = > 0 (D where Lrl? Is the magnetic flux produced by the first inductor 22, while Lc is the magnetic flux produced by the second inductor 30. Lr is the inductance of the first inductor 22, and is the inductance of the second inductor. The switch 34 preferably comprises an electronic switch connected to the second inductor 30, to either allow or prevent current from flowing therethrough The electronic switch 34 can be any suitable device, such as for example a field effect transistor and may be either a separate element of the integrated circuit 18 or a part thereof If desired, the switch 34 has a memory, so that the state of the switch 34 is maintained regardless of whether the intelligent device 12 is working or not An example of that kind of switch 34 is a field effect transistor provided with a charge storage mechanism associated with its composite electrode. rta, in the same way that it is used in a memory-only, programmable and electrically erasable memory storage cell. According to the first embodiment, the switch 34 has a first position and a second position to selectively allow a current to flow through the second inductor 30. When the first position is found, the switch 34 is open, and is not generates no canceling field when the intelligent device 12 is exposed to the external field produced by the interrogator 10. When it is in the second position the switch 34 is closed, so that it allows the second current l2 to flow through the second inductor 30 and generate the second local field when the intelligent device 12 is exposed to the external field produced by the interrogating device 10. The analysis of the circuit of the intelligent device 12 allows to appreciate that, when the switch 34 is closed, in the portions of Lr and Lc that are coupled to each other (through Kres: can) no voltage is induced by the effect of the current and l2 that they flow through them. The voltages induced in the coupled positions of each current © are equal, but of opposite sign, so that the sum of them is equal to zero. As a result, the collected portions of Lr and Lc can be considered as being absent in the next analysis step. In the first inductor 22 there is a voltage induced by the external field generated by the interrogating device 10, said induced voltage being generated through an equivalent series circuit comprising (1- Kres: can) Lr (the non-coupled portion of the inductance ) the resistor 26 and the resonant capacitor 24, since the impedances of (1 -Kres: can) Lr and the resistor 26 have a low value compared to the impedance of the resonant capacitor 24, the combined impedance of these elements in series is predominant capacitive and therefore the current flowing through this series circuit has an advance of approximately 90 ° with respect to the induced voltage. Similarly, in the second inductor 30, a voltage is induced by the effect of the external field generated by the interrogating device 10, said induced voltage being generated through an equivalent series circuit comprising (1-Kres: can) Lc, the resistor 32 and switch resistance 36. Since the series resistance of resistors 32 and 36 has a relatively low value compared to the impedance of (1-Kres: can) Lc, the combined impedance of these series elements is predominantly inductive and therefore the current 12 has a delay of approximately 90 ° with respect to the induced voltage. The result is that the currents and l2 have a phase relationship of approximately 180 °. That is, the current and I2 essentially flow in opposite directions. The relative magnitudes of the current e l2 can be adjusted by controlling the value of inductors 22 and 30 and coupling Kres an, adjusting the number, size and relative disposition of the coils of the inductor coils, as understood by those who have ordinary knowledge in the field. Naturally, when the relative magnitudes of the currents e2 are adjusted approximately, the assumption of equation (1) is true. As explained above, the smart device 12 transmits the data stored in the integrated circuit 18 by tuning and detuning the antenna circuit 20. According to the present invention, the switch 34 has one side connected to the integrated circuit modulation output and the other side connected to the ground. In that way the switch 34 is then moved between the open position and the closed position, according to the meaning of the stored data, to tune and de-tune the antenna circuit 20, so that the stored data is transmitted to the reading device . Thus, the present invention uses the switch 34 and the modified antenna circuit 20 in place of the modulation capacitor 28 to tune and detune the antenna circuit 20 and transmit data to a reading device. Turning next to Figure 2A, there is shown therein an electrical schematic representation of a second preferred embodiment of an intelligent device 40. Similar to the first embodiment, the device 40 includes an integrated circuit 18, a first inductor 22 , a second inductor 30, an equivalent resistance 26, a resonant capacitor 24, a switch 34, and a switch resistance 36. (The equivalent resistance 26 is for both inductors 22 and 30). The intelligent device 40 operates in accordance with the same basic principles as the antenna circuit 20. That is, the second inductor 32 is provided to generate a canceling field, so that a sum of the local fields produced by the currents flowing through the inductors 22 and 30 have a result that approaches zero. However, according to the second embodiment, a current always flows through the second inductor. When the switch 34 is open (Figure 2B), the intelligent device 40 comprises a series circuit that includes the inductors 22 and 30 (collectively shown as a set 42) the resistor 26, and the resonant capacitor 24. In the meantime, when the switch 34 is closed (FIG. 2C), a first current li flows through first inductor 22 and a second current l2 flows through second inductor 30, said currents flowing in opposite directions, so that the generated local fields are canceled, as explained above. The intelligent device 40 has an operation in accordance with the equations: ? L1 +? L2 = 1 /? C 1 (2) Q = (? L1 +? L2) / R1 (3) where L1 is the first inductor 22, L2 is the second inductor 30, C1 is the resonant capacitor 24, R1 is the series resistor 26, and? It is the resonant frequency. It should be noted in Figure 2B that the inductors 22 and 30 are in series, and are therefore represented by a single inductor 42, where L = L1 + L2. If the ratio between the number of turns of the inductors 22 and 30 is chosen so that the current I 2 flowing through the second inductor 30 produces a magnetic field whose amplitude is equal but opposite to the field produced by the current that flows through the first inductor 22, then the intelligent device 40 does not unduly influence other intelligent devices that are nearby, since it produces a net field of zero or almost zero value. This effect can be represented in the equation: = - (N1 / N2) 2 KL1L2 l2 (4) where KUL2 is the mutual inductance coupling factor, and N1 and N2 are the number of turns of the respective inductors 22 and 30. The advantage of the second embodiment compared to the first embodiment is that the value of the resonant capacitor can be lower in the second embodiment (since it is connected through both inductors 22 and 30). Preferably, switch 34 is normally open so that the tag is "active". The switch 34 can be controlled by a signal line 44 coming from the integrated circuit 18. The signal line 44 can be controlled by a sequencer disposed within the integrated circuit. For example, once the intelligent device 12 has completed the transmission of the data read from the integrated circuit, the integrated circuit then activates the signal line 44, thereby closing the switch 34 so that the intelligent device 12 is decoupled of your environment. The integrated circuit 18 may also include a timer that is used to determine the value of the signal, so that after a predetermined period, the switch 34 is open and, if the intelligent device 12 is still within the external field generated by the integrating device 10, smart device 12 relays its data message. Another means of controlling switch 34 will be apparent to those of ordinary skill in the art.

As explained above, the switch 34 is also preferably used to cause the stored (and read) data to be transmitted from the integrated circuit 18 to the reading device. That is, the switch 34 is closed and open to essentially extract energy from the field generated by the interrogating device 10 and not to perform such extraction, respectively, at rates that are equivalent to the regimes at which the data would be modulated by other means . This modulation mechanism has the result of causing the interrogating device 10 to transmit a signal that can not be distinguished from signals created using other modulation means. According to this method, once all the data have been transmitted, the switch 34 is put in the closed position, whereby the intelligent device 12 is decoupled from its environment. The switch 34 could also comprise a variable resistance element, so that the resistance of the element can be controlled from the value of approximately zero (the active resistance of the switch) to essentially an infinite value (the passive resistance of the switch) and any intermediate located between those limits. Such intermediate values are useful for the purpose of determining the amount of energy that is extracted from the external field. For example, if the value of the resistance is adjusted to a mean value (between zero and infinity), a partial decoupling of the intelligent device 12 occurs., which is advantageous for the case in which said device 12 is in the immediate adjacency of the interrogating device 10 and the external fields generated by the interrogating device are especially intense. In a conventional circuit arrangement, the energy extracted from the external field must be dissipated in the integrated circuit 18. As is known to those of ordinary skill in the art, this energy may occasionally be of sufficient magnitude to reheat the integrated circuit and destroy it. The advantage of partially uncoupling the intelligent device 12 from its medium is that it reduces the amount of energy that can be collected from the external field, and therefore limits the power dissipation requirements of the integrated circuit. Analogously, the voltages that can be induced in the intelligent device 12 are reduced to a minimum, and therefore the possibility of a rupture caused by excessively large induced voltages is reduced. Specialists in the field should recognize that in the aforementioned embodiment of the invention changes can be introduced without meaning to depart from the inventive concepts thereof. It should be understood therefore that the present invention is not limited to the described embodiments, but is intended to cover any modification that may fall within the scope and spirit of the invention as defined in the appended claims.

Claims (6)

1. NOVELTY OF THE INVENTION CLAIMS 1. - An intelligent device or capable of transmitting a signal in response to an interrogation signal and to be used in radio frequency comprises: an integrated circuit for storing data; an inductor including a first coil electrically connected to a second coil; a resonant capacitor electrically connected to the integrated circuit and at least one of the first and second coils, the resonant capacitor and said at least one coil having a first predetermined resonant frequency; and a switch having a first position and a second position to selectively allow the passage of current through the second coil, so that when the switch is in the first position, the exposure of the intelligent device to an internal field to a frequency that exactly or approximately equals the first resonant sequence induces a voltage in the inductor and causes a first current to flow through the inductor in a first direction, thereby generating a local field, and when the switch is in the second position, the exposure of the intelligent device to an external field that exactly or approximately equals the first resonance frequency induces a voltage in the inductor and causes a first current to flow through the first coil in a first sense, thereby generating a first local field and a second current flowing through the second coil in a second direction or sin opposite, generating a second local field, so that a sum of the first and second local fields has a result that approaches zero.
2. 2. The intelligent device according to claim 1, wherein the voltage induced in the inductor is used to power the integrated circuit.
3. 3. The intelligent device according to claim 1, wherein the first coil and the resonant capacitor resonate at the first resonant frequency when the switch is in the first position.
4. 4. The intelligent device according to claim 1, wherein the first coil, the second coil and the resonant capacitor resonate at the first resonant frequency when the switch is in the first position.
5. 5. The intelligent device according to claim 1, wherein the switch is used as a modulation means for transmitting the stored data within the integrated circuit.
6. 6. The intelligent device according to claim 1, wherein the switch comprises an electronic switch. The intelligent device according to claim 6, wherein the switch is disposed within the integrated circuit. 8. The intelligent device according to claim 6, wherein the switch is normally in the second position. 9. - The intelligent device according to claim 1, wherein the switch comprises a variable resistance element, so that a magnitude of the second local field is variable, wherein when the second local field substantially equal and opposite to the First field, the intelligent device is not generally decoupled from its environment. 10. The intelligent device according to claim 9, wherein, when the switch is in the second position, the intelligent device is partially decoupled from its environment, thereby reducing the amount of energy collected from the external field. 1 1.- An intelligent radio frequency device comprises: an integrated circuit to store data; an antenna circuit comprising a first coil and a resonant capacitor having a predetermined resonant frequency and which is electrically connected to the integrated circuit to supply power to the integrated circuit and to make the data stored in the integrated circuit be transmitted to a reader device , in which the exposure of the intelligent device to an external field of a frequency that exactly or approximately equals the predetermined resonant frequency causes a first current to flow in the first direction in the first coil, thereby producing a first local field that collects the intelligent device with its environment; and means for selectively generating a second local field, wherein a sum of the first and second local fields has a value approaching zero, to selectively decouple the intelligent device from its environment. 12. The intelligent device according to claim 1, wherein the means for generating the second local field comprises a second coil. 13. The intelligent device according to claim 12, further comprising a sw electrically connected to the second coil to selectively prevent the second coil from generating the second local field. 14.- An intelligent resonant tag comprises: an integrated circuit for storing data; a first antenna circuit electrically connected to the integrated circuit, in which the exposure of the first antenna circuit to an electromagnetic field having a first predetermined radio frequency induces therein a voltage, which produces a current flowing in a first direction through it, thus producing a first local field, the induced voltage also provides power to the integrated circuit, so that the data stored therein is read from it and transmitted to a second predetermined radio frequency; and means for generating a second local field that at least partially cancels the first local field generated by the first antenna circuit. 15. - The resonant intelligent tag according to claim 14, further comprising means for varying the magnitude of the second local field, thereby varying a magnitude of the first field. 16. The intelligent device according to claim 15, wherein the magnitude variation means comprises a variable resistance element. 17. The intelligent resonant tag according to claim 14, further comprising a switch for selectively generating the second local field, thereby to cancel at least partially the first local field. 18. The intelligent resonant tag according to claim 14, wherein the first antenna circuit comprises a first inductive coil electrically connected to a resonant capacitor. 19. The intelligent resonant tag according to claim 18, wherein the means for generating the second local field comprises a second coil electrically connected to the first inductive coil. 20. The intelligent device according to claim 14, wherein the integrated circuit comprises a programmable and non-volatile memory.