JP2009543441A - Resonant circuit tuning system using magnetic field combined with reactance element - Google Patents

Abstract

Resonant circuit tuning systems and methods for tuning are provided. The resonant circuit tuning system may include an LCR circuit and a reactance element that is magnetically coupled to the LCR circuit.

Description

  The present invention relates generally to electronic tuning circuits, and more particularly to tuning systems that use a magnetic field coupled to a reactance element.

  Magnetic fields are used in many electronic systems such as Electronic Article Surveillance (EAS), Radio Frequency Identification (RFID), metal detectors, magnetic imaging systems, remote sensing, communications, etc. Used for various purposes. In these various electronic systems, the magnetic coil is used as either a transmitter or a receiver. As a transmitter, the coil is typically used to launch a magnetic field to the desired sensing area. As a receiver, the coil is placed in an area to receive signals or to detect the presence of tags, metal objects, and the like.

  Particularly in the case of a transmitter, a very efficient method of generating a magnetic field involves the use of a series resonant LCR circuit that presents a low impedance to the transmitter at the transmit frequency. In order to achieve a high magnetic field level from the transmitter antenna, it is desirable for the transmitter to send a high current to the antenna coil. Therefore, it is desirable to maximize the current sent from the transmitter to the coil to achieve high performance. One way to maximize the current sent from the transmitter is to use an LCR circuit with a high Q factor. This may be accomplished by increasing the inductance of the antenna coil and by reducing the total series resistance of the LCR circuit.

  In the case of a receiver, different types of tuned resonant circuits are typically used that use a parallel arrangement of inductors, capacitors and resistors to form a parallel resonant LCR circuit. This circuit format is used, for example, in applications that require high impedance of the coil at resonance, such as EAS systems, RFID tag or RFID antenna receiver inputs, and magnetic field sensing inputs. In order to achieve high sensitivity at the receiver antenna using a magnetic coil, it is desirable for the receiver to exhibit a high impedance at the receiver input and thereby send a high voltage signal to the receiver input. One way to achieve this high sensitivity is to increase the Q of the antenna to make it more sensitive to the desired frequency. As in the case of series LCR circuits, it is desirable to have a high Q LCR circuit to take advantage of higher performance.

  There are practical limitations to the use of high Q LCR circuits. In many applications, the resonant frequency or tuning of the LCR circuit will be different from ideal due to design changes, changes in the installation environment, such as door frames, floors, etc., or dynamic changes in the operating environment. For example, design tolerance variations in tuning are caused by variations in antenna coil assembly and resonant capacitor assembly, thereby affecting the inductance and resistance of the LCR circuit. These variations in assembly affect tuning and performance. In addition, some types of antenna coils use permeable magnetic material to concentrate or form the magnetic field from the transmitting antenna or to increase the sensitivity of the receiver antenna to external magnetic fields. use. Many of these materials have a wide tolerance for permeability and material loss. Furthermore, these material properties change according to changes in the flux density, operating temperature, mechanical stress, etc. of the operating magnetic field. Certain materials also change over time during the lifetime of the system. All these changes in material properties affect the inductance and loss of the LCR circuit and affect tuning and performance.

  Further, in some applications, the antenna coil may be a magnetically permeable or conductive material that may be mounted near the material that changes the magnetic field around the antenna. Changing the magnetic field may change both the inductance of the coil and the effective resistance of the LCR circuit, thereby affecting the tuning and performance of the LCR circuit. In other use cases, during normal operation, the antenna's magnetic field may be dynamically altered by a permeable or conductive material moving near the antenna. As a result, this dynamically changes the inductance or effective resistance of the antenna and consequently affects the tuning and performance of the LCR circuit. In addition, some magnetically coupled antennas may be used by systems that dynamically change the direction of the magnetic field vector generated by the transmit antenna or detected by the receiver antenna in the sensing area. This dynamic change is realized by changing the relative phase relationship of the currents in the various antenna coils and may change the inductance of individual antennas due to the mutual inductance or coupling coefficient between the coils. As a result, the effective resonant frequency of the coil varies dynamically with changes in the relative phase of the current in the magnetically coupled coils.

  Therefore, it is necessary or desirable to use a high-Q antenna that achieves the high performance of the antenna LCR circuit. However, high Q antennas are susceptible to tuning problems. Therefore, for example, it is necessary or desirable to adjust either the tuning of the LCR circuit or Q in response to changes in the operating environment. For example, a certain interference signal is generated by a system connected to the LCR circuit or an external system device. Also, depending on the interference signal, it may be necessary to change the antenna tuning or to reduce the Q of the LCR circuit. Means for tuning and dynamically adjusting the Q of the LCR circuit to respond to these changes in the operating environment are necessary or desirable.

  Known systems and methods, such as tuning LCR antenna circuits, are typically not always satisfactory for providing what is needed or desired for tuning, increasing the cost of the system. There are no controls and other parts to add. For example, it is provided as a set of capacitors arranged in parallel or in series with a switch that is opened and closed to adjust the effective capacitance of the capacitor bank. However, as the Q of the LCR circuit increases, this method requires more tuning capacitors and tuning switches in the capacitor bank to provide fine tuning capability. In addition, as the Q of the LCR circuit increases, the voltage maintained in the capacitor bank increases, so a tuning capacitor and tuning switch rating, rated for high voltage operation, is required. Finally, since the capacitor bank is connected in series with the transmitter, the tuning capacitor and tuning switch need to be able to take advantage of the high current. Therefore, as the Q of the LCR circuit increases, the voltage and current increase as well. It requires tuning capacitors and tuning switches to be rated for high voltage and high current operation.

  It is further known to provide an LCR tuning system that reduces the magnetic field of the inductor by the presence of one or more single loop windings located near the inductor. Switchable shorted turns are used to change the magnetic field to finely tune the inductance, which eliminates the need for a capacitor tuning bank. However, closing the switch to short each of the single loop windings may only reduce the inductor magnetic field, resulting in a decrease in inductance. This only allows the resonant frequency of the LCR circuit to be adjusted higher than the original LCR frequency. Furthermore, the current induced in the single loop winding flows through conductors and switches with limited conductivity as well as switch junction voltages. In many use cases, the induced current may dramatically reduce the Q of the LCR circuit. In addition, since the current flowing in the shorted turn flows in the opposite direction as the main inductor winding, the effective magnetic field is reduced and, depending on the use case, the antenna performance may be reduced.

  Thus, the known methods often result in a decrease in the Q value of the LCR circuit Q, and even a decrease in the effective magnetic field. These reductions result in a decrease in system performance, for example, a decrease in system antenna performance.

  In one embodiment, a resonant circuit tuning system is provided that includes an LCR circuit and a reactance element that is magnetically coupled to the LCR circuit.

  In another embodiment, an electronic merchandise monitoring (EAS) system is provided that includes at least one of a transmitter and a receiver, and at least one antenna connected to the transmitter or the receiver. The EAS system may further comprise a tuning circuit configured to tune with at least one antenna. The tuning circuit may comprise at least one reactance element that is magnetically coupled to the antenna.

  In yet another embodiment, a method for tuning an LCR circuit is provided. The method may comprise coupling a reactance element magnetically to an inductor of the LCR circuit and using the reactance element to control a resonance frequency of the LCR circuit.

  For a better understanding of the present invention, together with other objects, objects, features and advantages, reference should be made to the following detailed description of the invention, taken in conjunction with the drawings in which: In the following, the same reference numerals represent the same parts.

1 is a block diagram of a resonant circuit tuning system configured in accordance with an embodiment of the present invention having a reactance element. FIG. 1 is a block diagram of a resonant circuit tuning system configured in accordance with an embodiment of the present invention having a resistive element and a capacitive element. FIG. 1 is a block diagram of a resonant circuit tuning system configured in accordance with an embodiment of the present invention having a resistive element and an inductive element. FIG. 1 is a block diagram of a resonant circuit tuning system configured in accordance with an embodiment of the present invention having multiple reactance elements. FIG. 1 is a block diagram of a resonant circuit tuning system configured in accordance with an embodiment of the present invention having a reactance element and a plurality of taps. FIG. 1 is a block diagram of a resonant circuit tuning system configured in accordance with an embodiment of the present invention having multiple reactance elements and multiple magnetically coupled windings. FIG. 1 is a block diagram of a resonant circuit tuning system constructed in accordance with an embodiment of the present invention having a reactance element magnetically coupled to a winding of an LCR circuit. FIG. 1 is a block diagram of a resonant circuit tuning system configured in accordance with an embodiment of the present invention having a variable inductive element. FIG. 1 is a block diagram of a resonant circuit tuning system configured in accordance with an embodiment of the present invention having a variable capacitive element. FIG. 1 is a block diagram of a resonant circuit tuning system configured in accordance with an embodiment of the present invention having a variable capacitive element and a variable resistance element. FIG. 1 is a block diagram of a resonant circuit tuning system configured in accordance with an embodiment of the present invention having a variable inductive element and a variable resistance element. FIG.

  To simplify and facilitate the description of the invention, the invention will now be described in connection with various embodiments thereof. However, one of ordinary skill in the art should appreciate that the features and advantages of each embodiment of the invention may be implemented in a variety of ways. Accordingly, it is to be understood that the embodiments described herein are set forth as specific examples rather than limiting the present invention.

  Various embodiments of the present invention provide systems and methods for tuning an LCR circuit using one or more magnetically coupled reactance elements and / or resistance elements. The tuning system and method may be used in connection with any type of electronic system, for example, in an electronic system that uses a coil as either a transmitter or a receiver. The tuning system and method is further used in different types of applications such as electronic goods surveillance (EAS), radio frequency identification (RFID), metal detectors, magnetic imaging systems, remote sensing, communications, etc. May be used. However, various embodiments may be implemented in different applications for applications having different electronic devices as desired.

  FIG. 1 illustrates a resonant circuit tuning system 30 configured in accordance with one embodiment of the present invention, comprising a magnetically coupled winding 36 and an LCR circuit 32 that is magnetically coupled to a reactance element 34. The LCR circuit 32 may be configured as a transmission or reception antenna, for example, as an antenna for an EAS antenna pedestal. Further, the magnetically coupled winding 36 may be any type of magnetically coupled element, such as any type of magnetic field coupled element. Further, the reactance element 34 may be any type of element that provides reactance, such as one or more capacitive elements and / or one or more inductive elements.

  The LCR circuit may be a parallel and / or series circuit, and in one embodiment, a first capacitive element 38 provided in series for the parallel combination of the second capacitive element 40 and the inductive element 42. You may have. Magnetically coupled winding 36 has one or more turns that are magnetically coupled to inductive element 42 of LCR circuit 32, and reactance element 34 is connected to magnetically coupled winding 36. To do.

  Where a capacitive element, inductive element, resistive element or another element is mentioned herein, these elements may comprise equivalent elements, may be modified with equivalent elements, or may be equivalent It may be replaced with an element. For example, where an embodiment with capacitive elements is shown, this may include one or more capacitors or elements that provide capacitance. Similarly, for example, where an embodiment with inductive elements is shown, this may include one or more inductors or elements that provide inductance. Similarly, for example, where an embodiment is shown having a resistive element, this includes one or more resistors or elements that provide resistance.

  The resonant circuit tuning system 30 may also include a controller 44 connected to the reactance element 34 by a switch 46. The controller 44 is configured to control the switch 46 and, in particular, is configured to switch between an on state (connected state) and an off state (disconnected state) in order to load the LCR circuit 32 with a reactance. . For example, switching of the switch 46 by the controller 44 may be manual, eg, controlled by an operator or user, or the switching may be automatic, eg, controlled by a system controller or system program . The switch 46 may be any kind of switching element such as a switching transistor.

  The resonant circuit tuning system 30 may be connected to and may include a communication device 48, such as a transmitter or receiver. During operation, when the reactance load is applied to the LCR circuit 32 by switching the reactance element 34, that is, the tuning reactance, the tuning of the LCR circuit 32 is adjusted. The tuning of the communication device 48 connected to the LCR circuit 32 is also adjusted thereby.

  FIG. 2 shows a resonant circuit tuning system 50 configured in accordance with another embodiment of the invention. The resonant circuit tuning system 50 includes an LCR circuit 52 that is magnetically coupled to a capacitive element 54 (C2), such as a capacitor that loads through a magnetically coupled winding 56, for example. The LCR circuit 52 is configured in series with a capacitive element 58 (C1), a resistive element 60 (R1), and an inductive element 62 (L1). Inductive element 62 is also called primary inductance, and capacitive element 58 is also called resonant capacitance. The magnetically coupled winding 56 includes an inductive element 64 (L2) and a resistive element 66 (R2). The inductive element 64 of the magnetically coupled winding 56 is coupled to the inductive element 62 of the LCR circuit 52 with a coupling coefficient k, and is magnetically coupled, for example. The LCR circuit 52 is also connected to a voltage source 68 (Vs).

方程式1をZに関して解いて、方程式1の変形された形は以下のように帰着する：

ここで：

方程式2のリアクタンスの合計が0である場合、この結合回路の共振周波数が生じる：

Here, the operation and operating characteristics of the resonant circuit tuning system 50 are described below. This description is equally applicable to various other embodiments of the resonant circuit tuning system described herein. In particular, the impedance of LCR circuit 52 at voltage source 68 is shown in Equation 1:

Solving equation 1 with respect to Z, the modified form of equation 1 results in:

here:

If the total reactance in Equation 2 is 0, the resonant frequency of this coupling circuit occurs:

  In operation, for example, the inductance of the inductive element 64 is selected to have a much lower value than the inductance of the inductive element 62. Here, inductive element 64 is a tuned winding in one embodiment. Capacitive element 54 is selected to have approximately the same size as capacitive element 58, and by tuning purpose controller (not shown), for example, by capacitive element 52 as needed for tuning purposes. Adjusted to large or small values.

When the tuning winding, ie inductive element 64, is an open circuit, the resonant frequency of the main winding, ie inductive element 62, occurs when the series winding reactance is X _series = 0. It occurs when:

そして

これが次のように変形する：

したがって、X_total=0の時に、共振が生じる。方程式の解を見つけると、次をもたらす：

および

By way of example, for a typical antenna circuit and tuning winding, capacitive element 54 dominates both the resistance of resistive element 66 and the inductive reactance of inductive element 62 as follows:

And

This transforms into the following:

Therefore, resonance occurs when X _total = 0. Finding the solution to the equation results in:

and

あるいは、相互インダクタンスと同調容量のリアクタンスに置き換えて、次のように表現される：

ここで：

および

これらの方程式から、X_C2≫X_M12の場合には、抵抗素子66からの回路への実インピーダンスの増加が、非常に小さいことが理解される。 In addition, at the new resonant frequency, the resonant impedance is:

Alternatively, it can be expressed as:

here:

and

From these equations, it is understood that in the case of X _C2 >> X _M12 , the increase in the actual impedance from the resistance element 66 to the circuit is very small.

ここで：

In another embodiment shown in FIG. 3, the resonant circuit tuning system 70 is shown similar to the resonant circuit tuning system 50 shown in FIG. 2, and therefore the same reference numerals indicate the same components. Represents. Unlike resonant circuit tuning system 50, capacitive element 54 may be replaced with inductive element 72 (L3). Using an analysis technique similar to that described above with respect to resonant circuit tuning system 50, the impedance at voltage source 68 is:

here:

また

上述したように、共振周波数に関して解くと、下記に至る：

また、共振周波数でのインピーダンスは近似的に次のようになる：

ここで、

例えば、SPICE(Simulation Program with Integrated Circuit Emphasis)、多くの製造元から市販で入手可能な製品、あるいはインピーダンスの図式解法のような回路シミュレーションソフトウェアを用いて、並列のLCR回路の共振周波数の解を評価できる。 In addition, the following assumptions are made for many applications:

Also

As mentioned above, solving for the resonant frequency leads to:

Also, the impedance at the resonant frequency is approximately as follows:

here,

For example, you can evaluate the resonance frequency solution of a parallel LCR circuit using SPICE (Simulation Program with Integrated Circuit Emphasis), products available commercially from many manufacturers, or circuit simulation software such as graphical impedance solving. .

  In another embodiment shown in FIG. 4, the resonant circuit tuning system 80 is shown similar to the resonant circuit tuning system 30 shown in FIG. 1, so that the same reference numerals indicate the same components. Represents. Unlike the resonant circuit tuning system 30, the reactance element 34 is replaced with a plurality of reactance elements 84.

  The controller 44 is configured to control a plurality of switches 82. In particular, the controller 44 switches between an on state (connected state) and an off state (disconnected state) in order to apply a reactance load to the LCR circuit 32. . The switch 82 corresponds to each reactance element 84. The switching of the switch 82 by the controller 44 is controlled by an operator or a user, for example, and may be performed manually, for example, controlled by a system program, or automatically.

  In another embodiment shown in FIG. 5, the resonant circuit tuning system 90 is shown similar to the resonant circuit tuning system 30 shown in FIG. 1, and therefore, the same reference numerals indicate the same components. Represents. Unlike the resonant circuit tuning system 30, the reactance element 34 may be connected to a plurality of taps. In particular, the reactance element 34 is connected to a plurality of taps 82 that provide tapping of the reactance element 34 to the magnetically coupled winding 36 (wire connection). This tapping makes it possible, for example, to select a different number of turns of the magnetically coupled winding 36 included in the active part of the magnetically coupled winding 36 or to select a winding. For a single winding, one or more taps 82 with corresponding switching elements are provided.

  In operation, the controller 44 connects the reactance element 34 to one or more taps 82 of the magnetically coupled winding 36. Each of the taps 82 provides a different coupling of the reactance element 34 to the LCR circuit 32. Controller 44 adjusts the tuning of LCR circuit 32 by connecting reactance element 34 to different taps 82 in magnetically coupled windings 36.

  In another embodiment shown in FIG. 6, the resonant circuit tuning system 100 is shown similar to the resonant circuit tuning system 30 shown in FIG. 1, and thus the same reference numerals indicate the same components. Represents. Unlike the resonant circuit tuning system 30, another reactance element 102 is provided, and the LCR circuit 32 is magnetically coupled to the reactance element 102 by a magnetically coupled winding 104. The controller 44 is connected to the reactance element 104 via the switch 106. In this embodiment, controller 44 is configured to control switch 46 and switch 106 to adjust the tuning of LCR circuit 32. More specifically, reactance element 34 and reactance element 102 are magnetically coupled to LCR circuit 32 via a magnetically coupled winding 36 and a magnetically coupled winding 104, respectively. Additional reactance elements may be added to the resonant circuit tuning system 100 in a similar manner.

  In another embodiment shown in FIG. 7, the resonant circuit tuning system 110 is shown similar to the resonant circuit tuning system 30 shown in FIG. 1, and thus the same reference numerals indicate the same components. Represents. Unlike the resonant circuit tuning system 30, the resonant circuit tuning system 110 includes a plurality of taps 112 on the winding 114 of the inductive element 42 of the LCR circuit 32 and no magnetically coupled winding 36. The reactance element 34 may be connected to a plurality of taps 112 that provide tapping of the reactance element 34 relative to the winding 114 of the inductive element 42. This tapping can, for example, select a different number of turns or select the winding 114 of the inductive element 42 to be included in the active portion of the resonant circuit tuning system 110.

  In operation, the controller 44 connects the reactance element 34 to one or more taps 112 of the inductive element 42. Each of the taps 112 provides a different coupling of the reactance element 34 to the LCR circuit 32. The controller 44 adjusts the tuning of the LCR circuit 32 by connecting the reactance element 34 to different taps 112 of the inductive element 42. As an example, for example, antenna windings may be used in this embodiment to magnetically couple the reactance element 34.

  In another embodiment shown in FIG. 8, the resonant circuit tuning system 120 is shown similar to the resonant circuit tuning system 30 shown in FIG. 1, so that the same reference numerals indicate the same components. Represents. In this embodiment, the reactance element is a variable inductive element, such as variable inductor 122. The controller 44 is configured to control the operation of the switch 46 and change the inductance of the variable inductor 122. For example, separate control lines that provide separate control signals may be included. In operation, the controller 44 adjusts the inductive value of the variable inductor 122 to provide variable adjustment to the tuning of the LCR circuit 32, as well as the on state (connected state) and off state (variable state) of the variable inductor 122. It may be configured to switch between (disconnected state).

  In another embodiment shown in FIG. 9, the resonant circuit tuning system 130 is shown similar to the resonant circuit tuning system 30 shown in FIG. 1, so that the same reference numerals refer to the same components. Represents. In this embodiment, the reactance element is a variable capacitive element such as a variable capacitor 132 called a varactor. In this embodiment, the controller 44 is configured to control the operation of the switch 46 and change the capacitance of the variable capacitor 132. For example, separate control lines that provide separate control signals may be included. In operation, the controller 44 adjusts the capacitive value of the variable capacitor 132 to provide variable adjustment to the tuning of the LCR circuit 32, as well as the variable capacitor on state (connected state) and off state (disconnected). It may be configured to switch between (state).

  In another embodiment shown in FIG. 10, the resonant circuit tuning system 140 is shown similar to the resonant circuit tuning system 130 shown in FIG. 9, so that the same reference numerals indicate the same components. Represents. In this embodiment, a variable resistance element such as variable resistor 142 is also provided. In this embodiment, controller 44 is configured to control the operation of switch 46 and change the capacitance of variable capacitor 132 and the resistance of variable resistor 142. For example, you may have separate control lines that provide separate control signals. In operation, the controller 44 is configured to switch between the on state (connected state) and the off state (disconnected state) of the variable capacitor 132 and the variable resistor 142. The variable capacitor 132 and the variable resistor 142 are provided in parallel connection. In addition, the controller 44 is configured to adjust the capacitive value of the variable capacitor 132 and the resistive value of the variable resistor 142 to provide adjustable adjustments to the tuning of the LCR circuit 32. Yes. Specifically, the Q, the resonance frequency, or both of the LCR circuit 32 may be adjusted.

  In another embodiment shown in FIG. 11, the resonant circuit tuning system 150 is shown similar to the resonant circuit tuning system 120 shown in FIG. 8, and therefore, the same reference numerals indicate the same components. Represents. In this embodiment, a variable resistance element such as variable resistor 152 is also provided. In this embodiment, the controller 44 is configured to control the operation of the switch 46 and to change the inductance of the variable inductor 122 and the resistance of the variable resistance element 152. For example, it includes separate control lines that provide separate control signals. In operation, the controller 44 may be configured to switch between an on state (connected state) and an off state (disconnected state) of the variable inductor 122 and variable resistor 152. The variable inductor 122 and the variable resistor 152 are provided in parallel connection. In addition, the controller 44 is configured to adjust the inductance value of the variable inductor 122 and the resistance value of the variable resistor 152 to provide adjustable adjustment to the tuning of the LCR circuit 32. Yes. Specifically, the Q, the resonance frequency, or both of the LCR circuit 32 may be adjusted.

  Accordingly, various embodiments of the invention provide a resonant circuit tuning system characterized in that one or more of a reactance element, an inductive element, and a resistive element are magnetically coupled to an LCR circuit for tuning. The coupled elements should be adjustable to provide variable adjustment of the LCR circuit's Q, resonant frequency, or both.

  It will be understood that variations and modifications of the present invention can be made without departing from the scope of the invention. Also, it should be understood that the scope of the invention should not be construed as limited to the particular embodiments, but should be read according to the appended claims, with reference to the above disclosure.

Claims (26)

With LCR circuit;
A reactance element magnetically coupled to the LCR circuit;
A resonant circuit tuning system comprising:   2. The resonant circuit tuning system according to claim 1, wherein the reactance element includes at least one of an inductive element and a capacitive element.   2. The resonant circuit tuning system according to claim 1, wherein the reactance element includes at least one of a variable inductive element and a variable capacitive element.   2. The resonant circuit tuning system according to claim 1, further comprising a resistive element magnetically coupled to the LCR circuit.   5. The resonant circuit tuning system according to claim 4, wherein the resistance element includes a variable resistance element.   2. The resonant circuit tuning system according to claim 1, wherein the LCR circuit is configured by at least one of a series arrangement and a parallel arrangement.   The resonant circuit tuning system of claim 1, further comprising at least one magnetically coupled winding coupling the reactance element to the LCR circuit.   2. The resonant circuit tuning system according to claim 1, further comprising at least one of a transmitter and a receiver connected to the LCR circuit.   The resonant circuit tuning system of claim 1, wherein the LCR circuit comprises an antenna configured to provide at least one of transmission and reception.   2. The resonant circuit tuning system of claim 1, further comprising a controller connected to the reactance element and configured to control operation of the reactance element.   11. The resonant circuit tuning system of claim 10, further comprising a switch connected to the controller to control switching of the reactance element.   11. The resonant circuit tuning system according to claim 10, further comprising a plurality of reactance elements.   11. The resonant circuit tuning system according to claim 10, further comprising a plurality of resistance elements.   2. The resonant circuit tuning system according to claim 1, further comprising a plurality of taps connecting the reactance element to at least one coil of the LCR circuit. A plurality of taps connecting the reactance element to at least one coil of the LCR circuit;
The plurality of taps were connected to an inductor winding of the LCR circuit;
The resonant circuit tuning system according to claim 1.   2. The resonant circuit tuning system according to claim 1, wherein the reactance element is magnetically coupled to an inductive winding of the LCR circuit. A resistive element magnetically coupled to the LCR circuit;
A controller configured to control at least one of a resonance frequency and a Q value of the LCR circuit using the reactance element and the resistance element;
The resonance circuit tuning system according to claim 1, further comprising:   The resonant circuit tuning system of claim 1, wherein the LCR circuit is configured to operate in connection with an electronic merchandise monitoring (EAS) system. At least one of a transmitter and a receiver;
At least one antenna connected to at least one transmitter and receiver;
A tuning circuit configured to tune with the at least one antenna;
And wherein the tuning circuit has at least one reactance element magnetically coupled to the antenna.   20. The EAS system according to claim 19, further comprising a controller configured to control at least one of (i) switching of the reactance element and (ii) changing a level of the reactance element.   The EAS system according to claim 19, wherein the tuning circuit further comprises at least one resistive element magnetically coupled to the antenna.   22. The EAS system according to claim 21, further comprising a controller configured to control at least one of (i) switching of the resistance element and (ii) changing a level of the resistance element. A method of tuning an LCR circuit;
Magnetically coupling a reactance element to the inductor of the LCR circuit;
Controlling the resonant frequency of the LCR circuit using the reactance element;
LCR circuit tuning method including the steps.   24. The LCR circuit tuning method according to claim 23, wherein the magnetic coupling step includes tapping the reactance element on a winding of the inductor of the LCR circuit.   24. The LCR circuit tuning method according to claim 23, wherein the LCR circuit further includes an antenna.   24. The LCR circuit tuning method according to claim 23, further comprising a step of magnetically coupling a resistance element to an inductor of the LCR circuit and controlling a Q value of the LCR circuit using the resistance element.

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