JPH0340439B2 - - Google Patents

Description

Claim 1: Flat substrates 14, 42, 62 made of dielectric material.
a tuned circuit formed in the shape of a planar circuit on the substrate and resonating at a frequency for detecting a marker circuit within a predetermined range; and a conductive part on the substrate, which corresponds approximately to both opposing surfaces of the substrate. conductive parts 10, 12; 22, 24 located at and forming capacitors of said tuning circuit;
46,50;66,74;10a,12a;22
a, 28a and a deactivation region between some of the conductive portions, the deactivation region being capable of causing dielectric breakdown when the tuned circuit is exposed to an electromagnetic field at a deactivation frequency of sufficient energy. in an electronically detectable deactivatable sign that generates a resonant characteristic of the tuned circuit at the detection frequency, the deactivation region being between the several conductive parts; It consists of a dielectric material part that insulates the several conductive parts from each other, and this dielectric material part is
forming a discharge path along which an arc discharge occurs, the arc discharge occurring between the several conductive parts through the dielectric material in response to the electromagnetic field at the deactivation frequency; , an electronically detectable deactivatable marker characterized in that the sensing frequency destroys or alters the resonant characteristics of the tuned circuit.

2. The deactivation region is at least one of the several conductive parts 12; 24; 50; 72; 28
Recessed portion 20; 32; 56; 82; 2 provided in a
4a, and the several conductive parts (1
0,12:22,24;40,50;10a,1
2a; the distance between 22a and 28a at the recessed portion is
2. The electronically detectable and deactivable sign of claim 1, wherein the distance is short compared to the distance at a location other than the recess.

3. The arc discharge may occur in some of the conductive parts 1.
2; 24; 50; and 70 and the tuning circuit, and the shapes of the several conductive parts are formed so that the resonance characteristics of the tuning circuit are destroyed or changed at the detection frequency. An electronically detectable deactivatable marker according to claim 1 or 2, characterized in that:

4. The arc discharge may occur in some of the conductive parts 1.
12a; 22a; 28a to create a short circuit along a desired discharge path between 0a; 12a; 22a; 28a, destroying or changing the resonant characteristics of the tuned circuit at the sensing frequency 3. An electronically detectable and deactivable sign according to claim 1 or claim 2, characterized in that:

5 the deactivation frequency is equal to or close to the sensing frequency or within the predetermined range and has a higher energy level than the sensing frequency, and the tuned circuit has a single resonant sensing/deactivating frequency; circuit L ₁ , 10, 12; 40, 46, 5
0; L ₁ , 10a, and 12a, the arc discharge being operative to destroy or alter the sensing/deactivation circuit in response to the electromagnetic field at the deactivation frequency. 5. An electronically detectable and deactivable marker according to any one of claims 1 to 4.

6. The conductive portion includes a first conductive path on one surface of the substrate and a pair of conductive plate-shaped conductive portions 10, 12 at corresponding positions on both opposing surfaces of the substrate;
0; 10a, 12a and a connecting part are formed, and the first conductive path forms an inductor _L1 , 40,
The pair of conductive plate-forming conductive parts form a capacitor, the connecting part electronically connects the dielectric plate-forming conductive part to the dielectric at a predetermined location to form the tuned circuit, and the inactivation region is a portion of the substrate between the pair of conductive plate-forming conductive parts 10a and 12a, or one of the conductive plate-forming conductive parts 10; 4
6 and one connection part 18; 52 connected to the other conductive plate-forming conductive part 12; 50.
Electronically detectable and deactivable markings as described in Section.

7 a detection circuit L ₁ , 10, 12; 60, 66, 74 in which the deactivation frequency is outside the predetermined range and the tuned circuit resonates at the detection frequency;
L ₁ , 10b, 12b and a deactivation circuit L ₂ , 22, 24 that resonates at the deactivation frequency; 68, 6
4,72 _; 5. An electronically detectable and deactivable marker according to any one of claims 1 to 4, characterized in that it acts as a deactivator.

8 The conductive portion is a first conductive portion on one surface of the substrate;
Second conductive path and multiple pairs of conductive plate forming conductive parts 10 and 12, 22 and 24; 66 and 74; 64 and 72; 1
0a and 12b, 22a and 24a, and a connecting portion are formed, and the first and second conductive paths form a first inductor L ₁ , 60 and a second inductor (L ₂ ; 68), respectively. , each pair of the conductive parts forming the conductive plate are located at corresponding positions on both opposing surfaces of the substrate to form a capacitor, and the connecting part electronically connects the conductive part forming the conductive plate to the conductive path at a predetermined location. are connected to form a tuning detection deactivation circuit, and the deactivation region includes one pair 22a of the plurality of pairs of conductive plate-forming conductive parts;
a connecting portion 30 connected to a portion of the substrate between 24a or one of the pair of conductive plate-forming conductive parts 22;64 and the other of the same pair of conductive plate-forming conductive parts 24, 72; 8. The electronically detectable deactivable marker of claim 7, wherein the electronically detectable deactivatable marker is located on a portion of the substrate between the substrate and the substrate.

9. An electronic safety device comprising a sign consisting of a resonant marker circuit with a capacitor plate on each side of the substrate, and an electronic device that detects the tuned circuit of the sign and electronically deactivates the resonant characteristics of the marker circuit. In the apparatus, the electronic device includes: a transmitter that generates an electromagnetic field at a detection frequency that is swept within a predetermined range; a detection device 94 that detects a resonance characteristic of the marker circuit within the predetermined range; Deactivation device 10 for deactivation
0, said deactivation device 10 generates an electromagnetic field at the resonant frequency of said beacon circuit of sufficient energy when the presence of a resonant beacon circuit is detected to cause said deactivation device 10 to disturb said beacon across the capacitor plates or conductive parts thereof. An electronic safety device that causes an arc discharge through the circuit board to destroy or change the resonant characteristics of the marker circuit at the detection frequency.

10. The electronic device deactivation device 100 is characterized in that it causes a short circuit between the capacitor plates of the indicator circuit or its conductive parts to destroy or change the resonance characteristics of the indicator circuit. An electronic safety device according to claim 9.

11. The device according to claim 9, wherein the electronic device deactivation device 100 vaporizes one conductive part of the marker circuit to destroy or change the resonance characteristics of the marker circuit. Electronic safety equipment.

12. Claims characterized in that the electronic device includes an indicator 96 that indicates the presence or absence of a resonant indicator circuit, and an indicator 98 that indicates that the resonance characteristic of the indicator circuit has been deactivated. The electronic safety device according to any one of paragraphs 9 to 11.

13. a threshold detector 162 in which the deactivation device 100 operates during operation of the deactivation device to detect arcing occurring between the capacitor plates or conductive parts thereof and to emit a signal indicative thereof; and a timer 164 responsive to the signal to determine a time interval during which the deactivation device 100 remains activated after the arc occurs. The electronic safety device according to any of Item 12.

FIELD OF THE INVENTION This invention relates to electronic safety devices for detecting resonant beacon circuits in controlled areas, and more particularly to beacon circuits and devices for electronically disabling the beacon circuits.

BACKGROUND OF THE INVENTION Electronic security devices for detecting unauthorized removal of items are known. Such devices are particularly used to prevent theft of merchandise from stores and books from libraries. Electronic safety devices of this type generally contain an electromagnetic field, which is located in a controlled area through which the goods must pass when being removed from the protected area. By attaching a resonant tag circuit to each item,
A receiving device detects whether or not this marker circuit is in a controlled area, and is notified of illegal removal of items.

Authorized personnel will properly remove this marking circuit from items exiting the premises and allow the items to pass through the controlled area without activating the alarm. Also,
Devices are also known for electronically deactivating resonant circuits without having to remove the deactivation circuit from the goods that are properly removed from the premises.

One such device is the U.S. patent no.
No. 3624631. In this device,
A fuse link is placed in series with an inductor and is broken by a high power radio frequency transmitter.A resonant circuit is interrogated by a sweeping radio frequency, and if this circuit is located in a controlled area, energy will be absorbed at the resonant frequency. , this is detected by the receiving device and an alarm is activated. However, applying a sweep frequency of higher energy than the energy used for sensing destroys the fuse link of the resonant circuit, rendering the tuned circuit inoperable and thus making sensing impossible. Therefore, deactivation of such circuits must be accomplished by swept frequency transmitters operating at sufficiently low radiation levels to meet Federal Communications Commission regulations.
For this reason, the fuse link must be extremely small and must be made from a material that melts at low current levels. This small fuse link has a high resistance placed in series with the inductor of the resonant circuit. The series resistor reduces the Q of the resonant circuit, thereby reducing the sensitivity of the circuit being sensed.
The current level that melts the fuse link is determined by the fuse link geometry and the thermal conductive properties of the material surrounding the fuse link. Therefore, the fusing current is greatly influenced by the material covering and supporting the fuse link.

Another electronic safety device is shown in US Pat. No. 3,810,147 by the inventor of the present invention. In this patent, a resonant circuit with two different frequencies is used. One is for detection and the other is for deactivation. Although the deactivation circuit uses a small fuse link, it also includes a second capacitor that provides another deactivation resonant frequency.

The resonant circuit may have a resonant frequency that varies within manufacturing tolerances. The deactivation frequency is fixed at a constant frequency, so the resonant circuit may not be precisely tuned to this fixed deactivation frequency. The series impedance of the inductor and capacitor at this predetermined deactivation frequency must be as small as possible to allow maximum current to flow through the fuse link and cause it to rupture. Therefore, the value of the capacitor must be as large as possible and the value of the inductor must be as small as possible. For this reason, the structure is such that the inductor is wound once, and the plate forming the capacitor is so large that it reaches the economical and physical limits of the marker circuit. Larger capacitors increase the cost and size of the overall resonant circuit.

SUMMARY OF THE INVENTION The present invention provides a resonant beacon circuit having at least one resonant frequency for operation within an electronic safety device. This electronic safety device senses the beacon circuit, electronically deactivates it, and destroys or changes the resonance characteristics of the beacon circuit at the detection frequency. The resonant marker circuit is electronically deactivated by a dielectric breakdown mechanism operating within the marker's resonant structure, requiring no fuse links and does not affect or reduce the Q of the resonant circuit.

Therefore, the present invention provides a flat substrate 14; 42; 62 made of a dielectric material, a tuning circuit formed in the shape of a planar circuit on the substrate and resonating at a frequency for detecting a marker circuit within a predetermined range, and a tuning circuit on the substrate. a conductive part 1 which is located substantially corresponding to both opposing surfaces of the substrate and forms a capacitor of the tuning circuit;
0,12;22,24;46,50;66,7
4; 10a; an electronically detectable deactivatable sign that causes a dielectric breakdown when the sensing frequency destroys the resonant characteristics of the tuned circuit at the sensing frequency, wherein the deactivation region is located between the several conductive parts; It consists of a dielectric material part that is located between and insulates the several conductive parts from each other, and this dielectric material part is
forming a discharge path along which an arc discharge occurs, the arc discharge occurring between the several conductive parts through the dielectric material in response to the electromagnetic field at the deactivation frequency; Thereby, an electronically detectable and deactivatable marker is provided which is characterized in that the sensing frequency destroys or alters the resonant properties of the tuning circuit.

Further, the present invention provides an electronic safety device comprising the sign and an electronic device that detects a tuned circuit of the sign and electronically deactivates the resonance characteristic of the tuned circuit, wherein the electronic device is configured to operate within a predetermined range. a transmitter for generating an electromagnetic field at a detection frequency swept within the range; a sensing device 94 for detecting the resonant properties of the beacon circuit within the range; and a deactivation device 10 for deactivating the beacon circuit.
0, the deactivation device detects the presence of a resonant beacon circuit and generates an electromagnetic field at the resonant frequency of the beacon circuit of sufficient energy to cause an arc discharge between the several conductive parts. , provides an electronic safety device that destroys or changes the resonant characteristics of a marker circuit.

In one embodiment, the resonant beacon circuit is planar and includes a flat helix formed on the surface of a thin plastic substrate layer and a capacitor on each opposing surface of the substrate. at least one capacitor formed by a plate. The beacon circuit is excited at or near the resonant frequency to cause a dielectric breakdown through the substrate layer between the two capacitor plates.
The resonant structure is provided with means to ensure that dielectric breakdown almost always occurs at a predetermined location between the two capacitor plates. When a sufficient amount of energy is applied, an electric arc is correspondingly formed through the substrate layers and vaporizes surrounding or adjacent conductive parts, thereby destroying the resonant properties of the marker circuit. Ru. Alternatively, a plasma can be formed by dielectric breakdown through the substrate layer, depositing metal along the discharge path between the two capacitor plates, thereby creating a permanent short path between the two capacitor plates. can also be formed to destroy the resonant properties of the circuit.

DESCRIPTION OF THE DRAWINGS The invention will be better understood from the following detailed description and accompanying drawings.

FIG. 1 is a schematic diagram of a resonant beacon circuit according to the present invention; FIG. 2 is a schematic diagram of a dual frequency resonant beacon circuit according to the present invention; FIGS. Figures 5 and 6 are views showing the front and back sides of the resonant indicator circuit in Figure 2, Figure 7 is a block diagram of an electronic safety device using this invention, Figure 8 is a single FIG. 9 is a schematic diagram showing another embodiment of a dual frequency resonant beacon circuit; FIGS. A schematic diagram of the electrical breakdown mechanism used; Figure 13 is a schematic diagram of an electronic device for measuring the resonant frequency of the marker circuit to be deactivated; Figures 14 and 15 are diagrams of the device shown in Figure 13; Figure 16 is a block diagram of an electronic deactivation system that provides deactivation energy over a predetermined period of time.

[Detailed description of the invention]

In FIG. 1, a resonant beacon circuit is shown schematically. This resonant beacon circuit consists of a capacitor C1 formed by capacitor plates 10 and 12 provided on opposite sides of a substrate 14 made of a dielectric or electrically insulating material, and a single capacitor _C1 connected in series with this capacitor. and an inductor _L1 that supplies a resonant frequency. The inductor is connected at one end to a capacitor plate 10 and at the other end to an electrical path 16 via a substrate 14. The electrical path 16 is connected to the capacitor plate 12 via a guide path 18. The inductor and capacitor plate 10 are integrally formed on one side of the substrate. A typical shape of the dielectric formed on the substrate surface is a flat rectangular screw shape. Similarly, a capacitor plate 12 and a connecting path connected thereto are integrally formed on the other side of the substrate. The structure of the planar marker will be explained below.

The portion 20 of the guideway 18 facing the capacitor plate 10 is recessed or otherwise formed such that the distance to the capacitor plate 10 is shorter than the distance between the capacitor plates 10,12. When sufficient electrical energy is transferred to the beacon circuit at and near its resonant frequency,
The voltage between the capacitor plates 10, 12 increases until dielectric breakdown occurs at the break point of the dielectric path recess 20. Since the distance between the capacitor plates 10, 12 is at its shortest in this recess, dielectric breakdown always occurs at this point. The electric arc formed by the dielectric breakdown is sustained by energy being continuously transferred to the resonant circuit from an external power source. Electric arc is in recess 2
The metal is vaporized near zero, destroying the conductive path 18 and thus permanently destroying the resonant characteristics of the marker circuit.

Another embodiment of a resonant beacon circuit is shown in FIG. In this embodiment, the beacon circuit emits two resonant frequencies. In addition to the capacitor C ₁ and inductor L ₁ formed by capacitor plates 10 and 12, the circuit of FIG. 2 includes a second capacitor C ₂ and an inductor L ₂ formed by capacitor plates 22 and 24. It is equipped. The connection between the dielectrics L ₁ and L ₂ is connected to the capacitor plate 22 . The other end of inductor L ₂ is connected to a connection 26 passing through the substrate, and connection 26 is connected to capacitor plate 24 via a conductive path 28 . A conductive path 30 interconnects capacitor plates 24 and 12. Also,
The conductive path 30 has a break point (recess) 32 facing the capacitor plate 22 .

One resonant frequency is used to detect the sign by the electronic safety device and the other resonant frequency is used to deactivate the sign. The mark deactivation frequency is typically one of the frequencies within the Industrial, Scientific, and Medical (ISM) band assigned by the Federal Communications Commission (FCC). Accordingly, the energy emitted to deactivate the sign can be relatively high in power without special federal approval. The detection frequency is typically selected from one of the frequency bands assigned to the field disturbance sensor. A typical detection frequency is 8.2MHz.

Capacitor C ₂ and inductor L ₂ are the main components forming a resonant tuned circuit at the beacon deactivation frequency. On the other hand, capacitor C ₁ and inductor L ₁ are the main components forming a resonant tuned circuit at the sensing frequency. All these components are interconnected and thus interact to provide accurate sensing and deactivation frequencies. When enough energy is transferred to the beacon circuit at the deactivation frequency, the voltage increases between the capacitor plates 22, 24 until the substrate layer breaks down at break point 32. In this case as well, dielectric breakdown always occurs at this break point 3.
Occurs in 2. This is because this breaking point 32
This is because the distance between the capacitor plates 22 and 24 becomes the shortest. The electrical arc created by the breakdown is sustained by energy transferred to the resonant circuit from an external power source, and the arc vaporizes metal near the breakdown region, including adjacent portions of conductive path 30. When the external energy is interrupted, the electric arc is extinguished. The resonant properties of the marker at the detection frequency are permanently destroyed. This is because there is no longer an electrical connection between capacitor plates 24 and 22.

Since the resonant circuit of FIGS. 1 and 2 does not require the use of small, narrow fuses, no resistor is added in series with the inductor and capacitor plates of the circuit. Therefore, the Q of the resonant circuit does not decrease. Furthermore, since the electric arc occurs between the capacitor plates and not at their surfaces, the ability of the electric arc to In other words, the ability of the arc to vaporize metal in the vicinity of the arc does not change significantly. To maximize the voltage developed between the capacitor plates 22, 24, the capacitance of the capacitor C ₂ should be as small as possible and the isductance of the inductor L ₂ should be as large as possible so that it resonates at the predetermined deactivation frequency. Do it like this. Since capacitor C ₂ can be physically made very small, it does not significantly increase the size and cost of the dual frequency beacon circuit of FIG.

A typical structure of the resonant beacon circuit of FIG. 1 is shown in FIGS. 3 and 4. Figures 3 and 4 show each of the opposite sides of the sign. In FIG. 3, the inductor L ₁ is connected to a thin plastic layer substrate 4
It is formed as a flat screw-shaped object 40 on the surface of 2. This plastic layer serves as a dielectric for the parallel capacitor plates and as a supporting substrate for the circuit. The spiral shaped object 40 is the outer conductive part 4
4 and the inner conductive portion 46 . The inner conductive portion 46 acts as a capacitor plate 10. As shown in FIG. 4, the opposite side of the sign has a conductive portion 48.
and 50 are provided at positions corresponding to the conductive parts 44 and 46, respectively, and are connected to each other by a conductive path 52. The conductive part 50 acts as a capacitor plate 12, so that the conductive parts 46, 50 facing each other form a capacitor _C1 . Conductive connection portion 54 connects conductive portions 44 and 48
are connected to complete the marker circuit. Conductive part 50
A recess 51 is provided therein. This depression is close to the joint between the conductive portion 50 and the conductive path 52. A recess 56 is provided in this joint portion and forms a conductive portion of the conductive path 52. This conductive part faces the conductive part 46, and the distance from this conductive part to the conductive part 46 is the same as the conductive part 46, 50.
shorter than the distance between. This recess 56 becomes a breaking point where dielectric breakdown occurs. Dielectric breakdown occurs at the beacon circuit's resonant frequency in response to the application of energy from an external power source of sufficient magnitude to cause dielectric breakdown.

The typical structure of the dual frequency beacon circuit shown in Figure 2 is:
This is illustrated by Figures 5 and 6, which show both opposing planes of the marker. Inductor L ₁ is formed by a flat thread on the surface of plastic layer 62, which thread extends between conductive portions 64 and 66. Electrical conductor _L2 extends between flat threads 64 and 70 on the surface of the plastic layer. On the opposite side of the layered substrate shown in FIG.
4 and 76 are conductive parts 64 and 6 on the other substrate surface.
6 and 70, respectively. Conductive parts 72 and 74 are connected to each other via conductive path 78, and conductive parts 72 and 76 are connected to conductive path 8.
They are connected to each other via 0. A recess is formed in a portion 82 of the conductive path 78 facing the conductive portion 64 to serve as a breaking point. Capacitor C ₁ in Figure 2
consists of conductive parts 66 and 74, and capacitor _C2 consists of conductive parts 64 and 72. Further, a conductive connection portion 84 for connecting conductive portions 70 and 76 to each other is provided through the substrate layer to complete the marker circuit. The circuit operates in the manner described above to destroy the resonant characteristics of the beacon circuit at the sensing frequency by burning out or vaporizing the conductive path near break point 82 in response to the electric arc.

The resonant label shown in this specification is the patent number of the inventor.
It is similar to the resonant sign of No. 3810147. This marker circuit is preferably made according to the method for manufacturing planar circuits that is the subject of my patent No. 3,913,219.

FIG. 7 shows the apparatus used to deactivate the resonant characteristics of the marker circuit. The device includes an antenna 90 operative to sense the presence of a resonant beacon circuit 92. The antenna 90 is coupled to a sign detection device 94 that provides output signals to a sign presence indicator 96 and a sign deactivation indicator 98. In addition, the sign detection device 94
Sign deactivation device 10 also includes an antenna 102
0 to supply a control signal. The beacon deactivation device may also be operated by manual control 104. When the sign detection device 94 senses the presence of the sign circuit 92, it is operative to trigger the deactivation device 100 to cause electromagnetic radiation of a sufficient power level to be emitted from the antenna 102 at the resonant frequency of the sign circuit to detect the presence of the sign circuit 92. This causes dielectric breakdown at the point of break in the circuit, causing an electric arc to form. When detecting a dual frequency beacon, the deactivation device provides energy at the deactivation frequency of the beacon. The presence of the sign and the deactivation of the sign are indicated by indicators 96, 98.
may be displayed visually or otherwise.

If the beacon circuit is a single resonant circuit, such as that shown in FIG. is sent to the deactivation device 100. In response to this control signal, the deactivation device emits electromagnetic waves at its resonant frequency, which are efficiently transmitted to the beacon circuit to destroy its resonant characteristics. The sign detection device 94 includes a device for measuring the approximate resonant frequency of the sign circuit (Fig. 13).
may be provided. The sign sensing antenna 90 is driven by a voltage controlled oscillator 150. This oscillator is D/A (digital-analog)
Microcomputer 15 via converter 154
It is controlled by the second output section. The digital value stored in the microcomputer is used after being converted into an analog signal by a D/A converter 154, and the oscillator 150 is driven to sweep the frequency step by step. The antenna signal is applied to an A/D (analog-to-digital) converter 156 and the digital output is sent to a microcomputer 152 for storage.

The operation of the device shown in FIG. 13 will be described below in conjunction with the waveforms shown in FIGS. 14 and 15. The output of the voltage controlled oscillator 150 is
Shown in the figure. This output consists of step frequencies, each step occurring in response to a corresponding time or step number. FIG. 15 shows the antenna 90
shows the relationship of current through time. In the absence of a resonant circuit, the current through the antenna decreases as the oscillator frequency increases.
This is illustrated by the straight line portion of the waveform in FIG. If the resonant circuit 92 is located near the antenna 90, the ispidance of the resonant circuit will be reflected to the antenna, causing the current in the antenna to drop rapidly as shown in FIG. Antenna current is converted to A/D converter 15
6 into a digital value, and this digital value is stored in the memory of the microcomputer 152. The step number corresponding to the minimum value among the stored current values corresponds to the approximate resonant frequency of the indicator circuit. Converting the stored digital value representing the resonant frequency into an analog signal for controlling the oscillator 150 in the deactivation device 100
(FIG. 7), and destroys the resonant characteristics of the indicator circuit 92.

The deactivation energy is applied over a predetermined period of time, the predetermined period of time depending on how long the marker is scheduled to be deactivated.
After deactivation, the sign sensing device 94 is operated to sense the presence of the sign and, if the sign 92 is deactivated, the indicator 98 is energized to indicate that deactivation has occurred. show. Also, if sign detection device 94 senses that sign 92 is still operating at its resonant frequency, then
The deactivation device 100 is triggered again to perform another deactivation cycle. The deactivation cycle is repeated a predetermined number of times until deactivation occurs. If deactivation has not occurred after a predetermined number of cycles, some signal indicator may be used to indicate to the operator that the particular indicator has not been deactivated. The operator may then manually activate a deactivation device to deactivate the sign, or use other means to deactivate or destroy the sign.

Alternatively, upon detection of resonant beacon circuit 92, beacon sensing device 94 may actuate deactivation device 100 to cause antenna 102 to be activated with a relatively high power signal. The frequency of this signal is slowly swept at the resonant frequency of the resonant beacon circuit 92. The marker sensing device may be configured to periodically alternate between sensing the presence of the marker and deactivating the marker until the marker is deactivated. If a particular indicator is not deactivated, the operator is appropriately notified.

When using a dual frequency marker circuit, the marker detection device 94 senses the marker's resonant frequency while the deactivator 100 emits energy at the marker's resonant deactivation frequency. A device for sensing and deactivating dual-frequency signs is disclosed in the inventor's patent no.
Described in No. 3938044.

Another configuration of the resonant circuit is shown in FIGS. 8 and 9. Both are similar to the circuits of FIGS. 1 and 2, respectively. In the embodiments of FIGS. 8 and 9, a recess is provided at a point or points on one or both of the capacitor plates, and the thickness of the dielectric layer is reduced at the point where the recess is provided. This reduces the voltage required to generate an arc between the capacitor plates. In the embodiment of FIG. 8, the recess is provided in the capacitor plate 12a. In the embodiment of FIG. 9, the recess is provided in the capacitor plate 24. In the embodiment of FIG. When energy is applied at a sign resonant frequency of sufficient magnitude, dielectric breakdown occurs in the recess through the dielectric layer. The arc continues because energy is continuously being sent to the sign.
A plasma is formed between both capacitor plates. Due to the Q of the resonant circuit, energy is dissipated very little in the resonant circuit itself and in the arc formed between both capacitor plates. The plasma is rapidly heated by the energy of the arc,
The metal forming the capacitor plate is vaporized.
The vaporized metal causes the arc to become a conductor, shorting out the capacitor plates. This temporarily destroys the resonant characteristics of the beacon circuit, causing the current through the arc and the voltage across it to decay rapidly. The arc thus cools and deposits the previously vaporized metal between the capacitor plates.

If a short circuit occurs, the sign will be permanently destroyed. If no short circuit occurs, a voltage is again developed between both capacitor plates in response to the applied energy and the process is repeated. The plastic layer has already been destroyed and weakened at the point of failure.
Normally, the arc will form again at this same break point, and more metal will vaporize and deposit until a permanent short circuit occurs. The process of deactivation is the 10th
It is shown in Figure-12. FIG. 10 shows a plastic layer 110 between capacitor plates 112 and 114.
The onset of voltage breakdown through is shown. FIG. 11 shows the formation of the plasma after arc discharge, and FIG. 12 shows the final deposition of metal along the discharge path shorting the capacitor plates. If the deactivation power is too high, a portion of the capacitor plate may be burned out without creating a short circuit between the two capacitors. When this happens, the resonant frequency changes slightly each time an arc is formed or wanes until no arc is formed, even though the sign still emits one resonant frequency. Therefore, the deactivation power must be accurately controlled, ie, the deactivation process must be electronically monitored to shut down the deactivation device immediately after the first arc is formed. The deactivation device may be repeatedly energized periodically as described above until a permanent short circuit is formed between both capacitor plates. Since the antenna of the deactivator is coupled to the beacon circuit, the impedance of the beacon circuit is reflected back to the antenna. When an arc forms, the impedance of the resonant circuit changes suddenly. This change is reflected directly back to the deactivation device's antenna and can be detected by the deactivation device and used to precisely control the device. Thus, upon detecting a sudden change in the deactivation antenna current caused by a change in impedance in the resonant beacon circuit in response to an arc breakdown, the deactivation device is shut down and The resonant characteristics of the beacon circuit can be controlled by periodic reactivation to form an arc and deposit metal along the discharge path between the capacitor plates.

The deactivation device 100 can be controlled as shown in FIG. The beacon detection device 94 provides a beacon signal in response to a sweeping high frequency signal passing through the resonant frequency of the beacon circuit, which beacon signal is sent to a sharp cut high pass filter 160. This filter 160 filters out the modulation component and substantially all components of the spectrum of the beacon signal. Once an arc is formed between the capacitor plates, a relatively large change in current through antenna 90 occurs. Then, a signal representing it passes through a high-pass filter 160 and is sent to a threshold value detector 162. The detector sends a signal to trigger a timer 164;
This timer determines the operating time of the deactivation device 100 after arc formation. This deactivation cycle step may be repeated as many times as necessary to deactivate the resonant characteristics of the beacon circuit.