DE2065828C3 - Marking element with high magnetic permeability for object detection by generating harmonics when interrogated by an alternating magnetic field - Google Patents

Description

a) an elongated strip or wire (854-860: 876, 880) with a ratio of length to the square root of the cross-sectional area of at least 150,

b) through a layer of a normally sticky, very strong self-adhesive on at least one side of the strip or wire,

c) by a peelable carrier material which is attached to the adhesive layer, the adhesive layer after removal of the carrier material serves to attach the strip or wire to the object (31; 850; 862) and the combination of shape and magnetic properties of the so formed Marking element (33; fl52; 86S) is such that at a maximum change speed v> of the applied magnetic * i alternating field

of more than 24,000 - per second that in the ro ^r

generated pulse contained signal includes a frequency band, the lowest limit is above the 16th harmonic of the predetermined frequency and its width is at least is ten times the predetermined frequency.

2. Marking element according to claim 1, characterized by /! Strips or wires (854-860; 876; 880), where π is an integer greater than 1 and the strips or wires are chosen so that they are after a change of direction of the field of action reverse their magnetization in sequence at equal time intervals, each time interval

equal to or less than - with T equal to the period of the

Effective field is, in such a way that a magnetic pulse is generated with each Ummagnetisiemng which occurs with a characteristic frequency that is determined by a simple device (Fig. 1) is clearly detectable.

3. Marking element according to claim 2, characterized by a coding by number and μ dimensioning of the strips or wires (854-860; 876; 880), which are assigned to each object (31; 850; 882) and from a corresponding device ( Fig. 1), and by means of decrypting and recording this b5 encoding.

4. Marking element according to claim 1, 2 or 3, characterized by at least one SteuercJement

(878, 882, 884) made of ferromagnetic material.

whose coercive force is at least -400 -,

and that with a remanent magnetization

static external magnetic field of at least 60 -

generated on at least a part of the strip (876; 880), the amplitude and the time characteristic one of the signals generated by the strip under the action of the effect field clearly differs from differs from the corresponding signal when the control element is demagnetized.

5. Marking element according to claim 4, characterized in that the control element (878) over the entire length of the strip (876) a static external magnetic field with a value of

at least 60 - generated
m

6. Marking element according to claim 4, characterized in that each of a plurality of control elements (882, 884) generates a static magnetic field on a different part of the strip (880)

7. Marking element according to claim 6, characterized characterized in that the control elements (882, 884) have different coercive forces.

8. Marking element according to one of claims 4, 6 and 7, characterized in that at least one control element (884) is arranged substantially shorter than the strip (880) and in the vicinity of the central part of the strip, the remanent magnetization of the control element causing that the parts of the strip which are not in the vicinity of the at least one control element behave as independent strips in which the ratio of the length to the square root of the cross section is less than necessary to generate the characteristic impulse.

The invention relates to a marking element for use in a device for detecting a Object in an interrogation zone, in which the object is a periodically changing electromagnetic Field is exposed, with a section made of a material of high magnetic permeability, whose magnetic properties are such that in the presence of a marking element carrying Object in the interrogation zone with a created alternating magnetic field of a predetermined frequency reverses the magnetization of the element is used to generate an external magnetic pulse, the harmonic of a predetermined frequency contains.

From FR-PS 7 63 681 a device emerges in which dynamic magnetic phenomena to determine the presence of an object, eg. A book carried through the door of a library. This known device is based on the discovery that the action of a sinusoidal alternating magnetic field on a piece of metal induces a voltage which is characteristic of the metal composition and which is induced in two balanced coils in the vicinity of the generated magnetic field. An analysis of this characteristic voltage therefore enables a classification of the generated magnetic field.

hen metal. A book can therefore be identified η to which a piece of metal of a special class has been brought

From FR-PS 7 63 681 there is a class of metals in which a magnetic saturation . a strong magnetic field must be generated. The voltage induced by a metal from the class mentioned Besides a basic component, there is a certain number of harmonic components, namely ought Such a metal, namely iron, can produce a voltage ^ which has a third harmonic and a 'Contains a small proportion of the fifth harmonic

Furthermore, highly permeable metals, e.g. such Metals that saturate in a weak magnetic field induce a voltage that, in contrast to the voltage induced by iron contains higher order harmonics A highly permeable metal "According to FR-PS 7 63 681 Permalloy (according to Webster | Permalloy has approx. 80% Ni, 20% Fe and is light magnetizable and demagnetizable) and contains the characteristic voltage induced by Permalloy as components harmonics of the ninth and eleventh order in contrast to metals like Krofer, B iron or aluminum, which is practically no harmonip see produce such a high order.

U Only the composition of a metal should be; | Determine the order of the harmonics that are present in the if characteristic voltage. Furthermore, the size of the metal piece and its external shape should proportionally influence the amplitudes of the harmonics. Accordingly, the ratio of the two would be f; 3 individual harmonics for a particular metal, the U same regardless of the size and shape of the Ρ Metallsiückes. Furthermore, the ratio of at least jq between selected components should be characteristically different for different js ti metals, but M the size of the t-1 metal piece to be used as a marking element should be important not only for determining κ; the order of the present harmonics, but rather ψ for the generation of a signal that is strong enough for the% determination

pj FR-PS 7 63 681 shows that jijji metals with a high permeability and in • || Permalloy particular from other classes magnetic 0, sierbarer metals are distinguished by NEN kön- Φ that harmonics of the ninth and eleventh-order i '. \. exist, and through the relationship of some characteristic harmonic components to one another. Perj'l malloy is therefore a suitable material for inserting a special metal mark into '; Books in a library, since normally hardly anyone carries such a metal with them.

In the FR-PS 7 63 681 are different facilities for generating an electromagnetic field. One of these institutions has a : 8-shaped spool on. The field generated by such a coil has only one direction at one point "i on while the total number of directions only 'is part of all possible directions. Another device is equipped with two coils, the bo

are excited at the same time, but none of them. There is phase equality, so that a rotating field <V is generated. At different times, such a field has a different direction, which different <\ directions always form only a part of all possible bs : \ directions, furthermore the size of such a rotating field is small compared to the size of the coil. fj By creating a field with a large

Intensity, in contrast to a minimum intensity, can reduce the unreliability that As a result, there is no field in some directions. Such a strong field would result in more vector components with sufficient intensity than a field with a minimum intensity A field with a minimum intensity is a field that supplies a marking element with sufficient energy, when the latter is "geared towards the greatest sensitivity"

Here, the directions are increased, which in the Field are possible. However, as the intensity of the field increases, the cost of the the field generating means and increases the risk that the use of other facilities is hindered or is disturbed.

With the devices of the above type can only be achieved with difficulty that each Marking element receives enough energy when entering an interrogation zone, although "energy" one Function of the Siit and the Intensity is, shall hereafter to simplify the description,,;? £ with the The expression "energy" only means that the intensity is reduced. The energy received by a marking element at one point in a zone depends on both the field intensity at this point as well as the orientation of the marking element in relation to the Direction of the field at this point. For the definition of the orientation of a marking element suitably the plane, axis or length of a marking element uses known marking elements indicate a flat receiving coil, an axial electric dipole or a piece usually in the form of an elongated strip of isotropic magnetizable material which has at least one long dimension The orientation of such geometric features (plane, Axis, length) in relation to the direction of the field generally determines the proportion of the energy of the field at this point, which is determined by the marking device Will be received. With the expression "direction or" used in the present description Intensity of the field «is intended to denote the direction or the intensity of the field at a point and this location is usually the location at which a marking element is located Marking element that has only one such geometric feature, there is an orientation in which the Marker receives the most energy. Any other alignment will produce a smaller amount of energy receive. The orientation at which the greatest amount of energy is received is the "orientation of the greatest sensitivity «. In general, orientation is the greatest sensitivity of a receiving coil or another flat receiving means, the orientation in which the direction of the field, perpendicular to the plane of the coil or of the receiver, and is at an axial electrical dipole it is the orientation in which the direction of the field is parallel to the axis of the dipole, while in the case of a magnetizable metal piece, it is the orientation of the metal piece in which the direction of the Field runs parallel to the longest straight line dimension of the metal piece. With »alignment or Direction of a marking element «should be the direction of the geometric feature of the marking element used to define the orientation at the greatest sensitivity.

In some cases the direction of a marker in a zone can be quite random, or the direction changes as the marker is moved through the zone. This applies to those cases in which theft should be prevented. In most areas of use, a Marking element take every possible direction, which can also change constantly. Is located for example a marking element on an object conveyed on a conveyor belt, so it is very likely that the marking element only takes a few of all possible directions and this does not change when running through the zone. These considerations and the one desired in the establishment Reliability are important factors in determining field requirements; H. to the Determine whether there is a field component along each direction at any location in the zone, along each Direction in some places in the zone or along only certain directions in one or most of them Places in the zone must be provided. The term “field component” naturally means a vector component, the intensity of which supplies the marking element with “sufficient” energy.

The alternate end of the field to requirements depend 2> further from the outer shape of the marking element from. These requirements are less strict for a "multi-dimensional" marking element than for a "one-dimensional" one. The multidimensional marking element has two or more geometric features, each of which has a different direction. One-dimensional marking elements are flat coils, foils and electrical dipoles. Because of the cost and the possibility of damage, one-dimensional marking elements are generally preferable to multi-dimensional marking elements. In some applications, other considerations make one-dimensional markers highly desirable, such as, e.g. B. if such marking elements for -in anti-theft are to be arranged hidden.

In a very reliable system for detecting an object by generating fields in several directions need the peak intensities 4-> of the field can be selected so that a field component sufficient to activate a marking element is generated in almost every direction. The fields are generated as a train of pulses, each pulse in the train having a different direction v>

To detect an object in an interrogation zone, e.g. B. at the exit of a library, must be at everyone to be detected object a marking element are attached, which consists of a ferromagnetic Material with a total magnetic saturation moment of at least 0.1 electromagnetic Units. The marking element is chosen so that its magnetization in an orientation for the highest sensitivity with respect to a 60 Hz test magnetic field changing sinusoidally with a predetermined peak intensity of

less than about 1600 - each time the

TTt

Test field is reversed.

Strictly speaking, it is a complete reversal of magnetization from one to the other Opposite polarity saturation state not required. With reversal of magnetization is This means a periodic change in magnetization of at least 0.2 electromagnetic units per cm ³ with a change in the acting field.

An alternating electromagnetic field is generated in the interrogation zone, at least the one mentioned above has a predetermined peak intensity and is substantially free of frequency components that exceed a predetermined frequency of at least 1000 Hz. If an object provided with a marking element is placed in the generated field introduced, and the marking element and a vector component of the generated field are oriented, the magnetization of the marking element mentes reversed with each change of field. Every time the magnetization is reversed, there is a pulse generated by the external polar magnetic field. Means are provided with which to close the A whole band of frequency components of the magnetic flux can be monitored in the detection zone. the The lower limit frequency of this Bafidci is higher than that predetermined frequency, while the bandwidth is at least 600 Hz. There are means of determining a signal is provided which corresponds to a polar magnetic field pulse, and which is used to detect the Object is used, the amplitude and the line characteristic of at least one of the signals is determined.

For a specific marking element, this is the predetermined peak intensity of the test field Minimum field that can reverse the magnetization of the marking agent.

The object of the invention is to provide a marking element according to the type mentioned with a combination of shape and magnetic properties create which, if the marking element is suitably fastened to an object, at the same time a reliable detection of the latter in a query zone enables !.

According to the invention, this object is achieved by

a) an elongated strip or wire with a length to square root ratio the cross-sectional area of at least 150,

b) by a layer of normally tacky, very strong, self-adhesive on at least one side of the strip or wire,

c) by a removable backing material attached to the Adhesive layer is attached, the adhesive layer after removal of the carrier material for Attachment of the strip or wire to the object is used and the combination of shape and magnetic properties of the marking element thus formed is such. that at one; maximum rate of change of the applied alternating magnetic field of more than

24,000 per second that in the generated pulse -. m. ^;

containing signal comprises a frequency band. ' whose lowest limit is above the 16th harmonic of the predetermined frequency and whose ΐ Width is at least 10 times the predetermined frequency.

With ferromagnetic materials, both K =

conductive as well as non-conductive materials meant, %

where z. B. as conductive materials iron and its ^

Alloys with nickel and as non-conductive materia- Ji

lien the ferrites are to be named. {5

Conductive materials are generally preferable because they have ten times the strength of external magnetic fields than the non-conductive materials. A lean agent jus conductive material can therefore be dimensioned smaller than from a non-conductive -, Material. Small markers are also cheaper and can be hidden away. This is especially important in preventing theft.

It has been found that an elongated strip u> made of a ferromagnetic material, if this is sufficiently thin in relation to the dimension thereof "Geometric characteristic" is measured, a characteristic impulse of an external polar magnetic field generated when its magnetization is reversed, is reversed under the influence of an alternating field,

the rate of change of which exceeds 24,000 per second. In contrast to the marking element According to FR-PS 7 63 681 this can do one thing: o Marking element according to the invention having elongated strips cannot be reliably distinguished are by means of a single frequency or a ratio of two frequencies to each other. It has it has been shown that the amplitude of a certain> ·> Harmonics depend on the amplitude and frequency of the acting field as well as on the orientation of the marking element in relation to this field. With a selected band of suitable frequencies However, a signal can be generated with a marking element according to the invention, the distinguishing signal Has features which are essentially independent of the orientation of the marking element as well as the amplitude and the frequency of the acting field. The marker according to the invention rungselcmcnt is frequency-independent up to the extent that that it generates the signal that is characteristic of it, unless another, / ... e.g. a pulsed field is used instead of a sinusoidal oath.

If a sinusoidal field acts on the elongated strip, an external polar impulse is generated which is distinguishable by the total flux components in a band whose lower limit (the predetermined frequency) exceeds 1000 Hz and whose width is at least ten times the 4- , Field frequencies /. so that a statistically representative group of frequencies is obtained with certainty. A signal indicative of the total change over time of the flux components within the band, e.g. B. corresponds to the voltage induced in a coil linked to the flux κ , is very narrow and is less than 0.1 ms at half the amplitude.

The signal generated by the elongated strip has yet another distinguishable feature, namely, for a certain composition and for a certain size and shape of the material, the amplitude peak of the signal occurs a predetermined time after each when exposed to an alternating field with a certain waveform Change of field to. This characteristic of the signal m> can also be defined by the absolute instantaneous value of the acting field at the point in time at which the net magnetization of the elongated strip has the value zero. _{According to the hypothesis, the h} 5 "reversal" of the magnetization takes place at this point in time, which corresponds to the peak point of the magnetization reversal signal depends not only on the magnetic properties of the material, but also on the waveform of the applied field. However, this expression is found to be useful in comparing the response of different elongated strips subject to the action of the same field.

The elongated strip of the marking element according to the invention can consist of a thin strip or a wire of a ferromagnetic material with a magnetic moment of at least 0.1 electromagnetic unit. At ratios below the value of the ratio of the length to the square root of the cross-sectional area of at least 150, the internal self-demagnetizing field effects in highly magnetic materials can produce the acting field> 1600 ^A. increase addition. at

below ratios below 150, the amplitude of the magnetization reversal signal drops sharply and becomes noticeably dependent on the orientation of the elongated strip in the acting field.

The corresponding criterion for a thin flat disk made of a ferromagnetic material would be a Ratio of the geometric characteristic dimension to the thickness of at least 6000. or disk-shaped marking elements should have a thickness of approximately 0.1 to 130 μm, while wire-shaped conductive marking elements should have a diameter of 10 to 300 μm. at larger dimensions, the amplitude of the magnetization reversal signal decreases, and so does the width becomes larger at half the amplitude and can ultimately no longer be distinguished from inversion signals, generated by ferromagnetic metal objects that people may be with them wear.

A thin, flat and narrow marking element is particularly suitable for books in libraries, because the marking element is inserted into the spine of the book or inserted between two book pages can be and thus remains hidden. A book generally comes with two pairs of flyleaves which are connected to one another by a fold running over the entire length. These Folds are usually wider than an open strip, so that there is a marking element in this fold can be easily hidden. If the marking element is on both sides with a Klebitoff covering and provided with an underlay so that it can be close to the bandage between two sides can be used.

The preferred number and relative orientations of the geometric characteristic dimensions of the marking element depend on the characteristics of the active field in a still to explanatory manner. An idealized marking element has a single main dimension, while a marking means with two mutually perpendicular main dimensions. e.g. in the form of a »L«, »T«, »+«, and a marking element with three mutually perpendicular main dimensions are common are.

The elongated strip can voükoniffien be inorganic or consist of a ferromagnetic laminate bonded with an organic adhesive

is held together, or the strip can also consist of a dispersion of ferromagnetic particles in an organic binder, e.g. B. vinyl chloride exist. The marking element can also be made from consist of several ferromagnetic strips separated from one another at a small distance, the position of which is fixed to each other, or which are embedded in a non-magnetic material, e.g. B. as very fine Wire threads or ribbons in a piece of paper.

Another embodiment of the invention-Ben The marking element consists of two or more elongated strips with different alternating current coercive forces, which are used as a unit. Even if such united, elongated Strips are in contact with each other, they do not influence each other magnetically so strongly, that each stripe can generate its own characteristic impulse.

Another embodiment of the marking element according to the invention has one or more elongated strips and at least one control element made of ferromagnetic material, the

Coercive force is at least 400 - and that at remanent magnetization has a static exterior

Magnetic field of at least 60 - on at least one

Part of the stripe is generated, the amplitude and time characteristic of one of the stripes being below Effect of the field of action generated signal clearly differs from the corresponding signal, when the control is demagnetized.

A possibility to prevent or change the magnetization reversal of the marking element thus consists in effectively preloading the field acting on the elongated strip by that a remanently magnetizable material is used as the control element. With the retentive Magnetization acts on the field of controls! alternately reinforcing or weakening the acting field in successive half-periods. If a sufficiently strong remanent field is generated on an elongated strip, then it is sufficient the net field at the half-perturbation in which the remanent field counteracts the external field is not out to a reversal of the magnetization of the elongated strip in the characteristic Way to effect. The inversion of the magnetization of the elongated strip for each change the alternating field need not be completely prevented. Rather, it suffices to do the reverse change so that the resulting signal is not characteristic of a marking element. Accordingly such a magnetic control element does not need the area of the elongated strip to cover completely. For example, a magnetized control only affects one in the center located part of the elongated strip that the segments on either side are roughly like two behave independent strips. The part in the middle should therefore be big enough and so be arranged so that none of the segments meets the aforementioned ratio criterion.

The remanent magnetization of the control element need not be uniform, and indeed are unevenly magnetized controls are generally desirable because they are less of a use is costly

For example, a non-uniformly magnetizable control has a number of retentive bands Magnetization, with adjacent bands being oppositely polarized. About internal demagnetization effects should be kept low and to generate a strong external magnetic field the directions of magnetization of the bands of such a magnetized control element parallel to the length of the Control element run.

To demagnetize the marking element, the control element can be used in the conventional manner be magnetized. For example, in order to magnetize the control element evenly, the element could exposed to the action of the field of a strong permanent magnet. For a ribbon-like Uneven magnetization of the control element could be the element of exposure to a number of Permanent magnets are exposed, adjacent permanent magnets are polarized in opposite directions. Care must be taken in removing the magnetizing magnets. One Movement of the magnetizing magnets along an axis parallel to the magnetic poles would result in a Change of the desired magnetization lead with the consequence that the magnetic influence of the control element is reduced to the extent smaller than that to demagnetize the elongate Strip required extent. When using a single pulsed magnetic field, its field distribution is similar to the field distribution generated by permanent magnets, for magnetizing marking means, the difficulties mentioned could be avoided, since in this case none are controlled Movement between the marker and the magnetization source is required. Executions for generating such errors are known per se. As an example, the "overdamped" discharge becomes a Capacitor led by a coil.

To sensitize the Markicrungsclemen'.es can a conventional degaussing device can be used with which on the marking element relatively high-frequency magnetic field with decreasing amplitude is brought into action. It can e.g. B. a device can be used that causes an "underdamped" discharge of a capacitor through a coil, d. H. an interconnection a coil with a capacitor like the circuit used to magnetize a control element is used, but which has a high (? -Wcri (Goodness). On the other hand, a degaussing device with a number of permanent magnets can also be used which are polarized in opposite directions can be used. Becomes a control in relation to a such degaussing device is moved along a coordinate common to the row of magnets, an alternating magnetic field acts on the control element. By suitable choice and arrangement the magnet can be in the degaussing device a field with decreasing amplitude can be generated. Will be magnets with different strengths used and arranged so that their fields are sequentially gradual in the direction of movement become weaker, the amplitude of the magnetic field apparently disappears when the arrangement is over Control is passed away. The same result could also be achieved by doing this, albeit the same powerful magnets in the shape of a whip or inclined Plane so that the amplitude of the

Il

Z. \ J

Magnetic field gradually becomes smaller.

Since the external magnetic field of a control element can vary depending on the pattern of magnetization, demagnetization of the control element is generally not necessary in the strictest sense, but the magnetic influence of the control element only needs to be reduced to the extent that this acting field can unmagnetize the elongated strip.
"To simplify manufacture, the control element can consist of a thin, magnetic and uniform coating of a gamma iron oxide powder in a vinyl chloride binder on one side of the stretched strip.

With other types of magnetization, the Elongated strips are deformed or torn so that its resulting longest linear section is smaller than the length required for the said ratio of length to square root of the cross section. That iMarkicrungseiemeni can also be aucii uauuicii eiUrnäignetisiert be that the elongate strip is stretched to its magnetic response change. The elongated strip can e.g. B. together with a heat-sensitive bimetal strip or used as an element of such a bimetal strip.

If the marking element is passed through the field of action, it must be influenced in at least one and preferably at several points during movement through the interrogation zone in such a way that the elongated strip of the marking element is re-magnetized. Absolutely secure orientation would be achieved with a one-dimensional field of action together with a marking element with three main dimensions perpendicular to one another, the strength of the field of action at every point in the interrogation zone being at least 1.4 times the sound field of the marking element. A one-dimensional field is a field in which all magnetic lines of force in the interrogation zone run parallel to one another.
■■ A one-dimensional field has two mutually perpendicular directions, which also run perpendicular to the direction of the field, in which directions there are actually no components of the effective field. Likewise, a two-dimensional field has only one direction in which no components of the effective field actually run, while in a three-dimensional field no field components run in any direction. From this it can be seen that with a combination of a marking element having one main dimension with a three-dimensional field and also a marking element having two mutually perpendicular main dimensions with a two-dimensional field and a marking element having three mutually perpendicular dimensions with a one-dimensional field, an absolute orientation at every point in the query / .one will be reached with certainty.
% i In such combinations the way of ISiiarkierungsclementes ^ jirz and only slightly longer can access as an elongate through the interrogation zone much. If the path is lengthened, such a combination is not necessary, in which an orientation of the marking element is achieved with certainty at every point in the interrogation zone. To 'iti see that when an elongated strip is moved through the interrogation zone over a relatively

moderately long distance at least one remagnecization & takes place, it is only necessary that the vectors of the magnetic field components are greater than the switching field of the marking element in each direction at some points in the interrogation zone.

This condition can be fulfilled by sequentially at each point in the Query zone three one-dimensional fields are generated, each field after another Coordinate axis is oriented in space. On the other hand, the required condition can also thereby be fulfilled that several districts are provided in the trajectory through the interrogation zone, in which the orientation of the field of action does not change, while the fields in successive However, districts have a different orientation.

In addition to the length of the zone through which the elongate strip is to move, there are Building a particular facility still further

; <»Important and interdependent variables, with which is assured that upon movement of the elongate strip through the interrogation zone at least one magnetization reversal takes place. These variables are the speed of the long-stretched one Strip, the number and orientation of the characteristic geometric dimensions of the elongated strip, the frequency of the effective alternating field, the peak intensity of the field, and the Vector components of the field at any point in the interrogation zone at any point in time.

The alternating magnetic field can be generated by a conventional method, for example by supplying an air core coil or the coil of an electromagnet with alternating current and through Moving a permanent magnet in such a way that its magnetic field changes polarity in the interrogation zone.

A flux monitor and a detector circuit can serve to detect the changes in magnetic flux in the interrogation zone, and the changes in magnetic flux produced by the marker to be distinguished from all external changes in the magnetic flux. Outer flow changes include that Acting field, a noise generated by electric motors, which when an off switch is pressed ^ generated noises etc., whereby the effect on the flow monitoring device depends largely on the strength the actions and the distance from the interrogation zone. There are monitoring facilities for the magnetic flux, which directly indicate the frequency of the change in the field, and others Devices that display the current strength of the field, from which display the alternating frequency can be derived. The latter devices include magnetoresistive devices in which the Hall effect is exploited, and magnetic diode sensors. Both types of facilities can be used to Improving sensitivity along with flow collection devices to be used. In such a device at least one coil is provided, with which the magnetic flux is determined inductively. It can be a large coil with a few turns can be used and even with only a single turn, or several small coils can be used can be used, of which each coil has relatively more turns. Wise small coils have the merit of being less sensitive to magnetic noise generated by electric motors and Power cut-off is caused. On the other hand, speaks

a large spool more evenly on the marker at different locations in the interrogation zone on, as individual small coils. It can be any number of opposing coils are provided, so that a magnetic noise from a remote source can be kept low, while a marker is detected, the closer to one coil than to another. When using several coils, these can be used with individual detectors are provided, or the coils ι ο are connected in sequence to a common detector.

The signal detector assigned to the flow monitoring device shows in the simplest embodiment the Presence of the marking element in the interrogation zone by determining the time and the amplitude features. Each of a signal corresponding to a single magnetization reversal of the marking element As already stated, the marking element according to the invention generates an unusually narrow signal and a signal that occurs for a specific field of action, while the marking field with a certain AC coercive force. Signal generated at a predetermined point in time after a change in the field of action By determining Signals that occur within a predetermined interval and have a minimum amplitude, and which start and end during a minimum interval, the detector distinguishes between noise, the signals generated by the marking element and external signals from other objects that respond to a address the alternating magnetic field.

The predetermination of the point in time at which the characteristic signals generated by the marking element occur also enables the Detek- ji to equip gate switching a bit more extensive as a safety factor against false alarms. The reference means for measuring successive signals can be a previous signal, phase or time of the field of action and may suitably be for -in the changing points of the field of action are used for this purpose. Furthermore, in the query zone a Marking element are permanently arranged, which generates the reference signal. The time intervals between the signals and the individual signal characteristics 4-. therefore reliably indicate the detection of the marker. If both options are provided, a system free from false alarms can be be achieved.

In the case of a system to prevent theft, a prescribed measure must be initiated as soon as an apparently stolen item is discovered. The special ones to be met Measures are related to the operation of the marking element according to the invention. The- v ~> These measures can consist of photographing the person in the interrogation zone, or an automatic device for opening the doors is put out of operation.

The determination device can consist of a circuit t> n exist that responds to at least one signal that has a minimum amplitude and a width less than the maximum. The formwork can additionally monitor the time of occurrence of the detected signal in relation to the time characteristic of either the active magnetic field or to a reference signal which correlates with the magnetic field signal. The same circuit can be used for both a marking element with one or more elongated strips without a control element as well as for a marker element with one or more elongated strips and one or more control elements. As stated, the signals generated by an elongated strip when an associated control element is demagnetized have essentially the same amplitude and width as the signals generated by a strip which has no control element. If, however, j the control element is magnetized, the shape, s the amplitude and the time of occurrence of the signals] are changed, which are generated by the elongated strip. The detector circuit can therefore essential in determining i chen, the magnetization of the control. *

If the marking element according to the invention ^ to prevent the theft of books from ί | a library, the use of a marking element with at least one control element proves to be suitable, the latter being demagnetized during an inspection so that the book can be removed from the library Book, the control element M can be magnetized, so that an unauthorized removal M of the book from the library is prevented. ü

In the case of such magnetization and demagnetization, the exact installation location of the marking element does not need to be known per se. By a clever and hidden arrangement of one or more marking elements on an object can a theft of the object or a ?. '] impermissible removal of the marking element can be safely avoided. yyy

The invention will now be described in detail. ■ ;;, In the drawings, the p

F i g. 1 an overview of an attachment to the '=.' Preventing theft or an impermissible Hl removal of objects from a building; wherein the plant at the outputs of the building; is arranged, fe;

F i g. 2 is a representation of two long, straight and '^; parallel conductors and the lines of force generated by a current flowing in ^ the conductors, |

F i g. 3 shows a representation of four long, straight and -; parallel conductors and the lines of force leading from the in; current flowing through the conductors is generated, z]

F i g. 4,501 is a schematic representation of two; i generally rectangular "o" coils, and 503 cincS diagrammatic representation of 501 and a zone in which the field lines of the coils run almost at right angles to ^one another,!,;

Fig. 5 505 a representation of one of three each other:., overlying coils formed by a grid consisting of two; generally rectangular "8" coils and consists of a generally rectangular "o" coil, 507,509 and 511 a representation of each of the coils of the grid 505,

F i g. 6 502 a representation of two coils after the ' Fig. 5 and a cross-section through a zone in which ;, vectors represent the fields which are caused by the »horizontal, · right "sections of the in FIG. 5, t coils shown in FIG. 5 are generated, 504 a representation of the in FIG. F i g. 5, which is not shown in 502, '.. and a cross-section through a zone in which vectors "! represent the field from the" vertical "central section of an" 8 "coil shown in FIG. is generated, * '■

F i g. 7 shows a front view of a preferred embodiment of one in the device according to FIG. 1

1!

the field generating device used,

F i g. 8 is a schematic representation of the windings of part of the FIG. 7 shown fine-generating Facility,

Fig. 9 and 10 each show a representation of the magnetic fields, that of the device shown in Figure 7 be generated,

Fi g. 11 shows the superposition of two Groups of magnetic field lines which are determined by the one shown in FIG. 7 are generated,

Fig. 12 is a circuit diagram for a device with which " a plurality of electromagnetic field generating devices in sequence with electrical energy to be taken care of,

Figure 13 is a circuit diagram for a preferred embodiment the magnetic flux monitoring device and the signal detector in the system after Fig. I,

F i g. 14 is a perspective view of a book with a marking element according to the invention and

15 is a perspective view of a book; where a part of the outer cover is above the The spine of the book has been removed for the purpose of showing the otherwise hidden masking element according to the invention

A preferred embodiment of the marking element according to the invention, which can be used in particular to protect the books in a library, consists of an elongated strip of annealed permalloy tape with a composition of 4% molybdenum, 79% nickel and 1% ice and a thickness of 25 µm, a length of 18 cm and a width of 0.6 cm. A gamma iron oxide strip control element is provided, which is the same width and length as the open strip. A solcnes control can ^ in the manner are generated by first 100 Ccwichistcile a gamma Eiscnoxidpigmentcs used for tapes and 2 Gcwichtsieile a wetting agent in a solvent toluene are dispcrgicrt as to give a 25% solids included- <n of the mixture is prepared. To this mixture, 50 parts of a resin composition are added, e.g. B. 75% of a copolymer of 89 parts vinyl chloride and 11 parts vinyl acetate (VYHH) and 25% diociylphihalai. To prepare a solution that can be applied in the form of a fourth layer, a small amount of a mixture of equal parts of methyl ethyl ketone and toluene can be added as required. The solution is applied at least with a doctor blade to a removable paper sheet-like base coated with silicone -, π. After the solution has dried, the base is peeled off, and strips with a uniform thickness of 230 μm are produced for weeks of use as a SicueVclemcni. If the thickness of the elongated strip is more than 230 μπι. so the v, elongated strip can be descnsibilisicrt if the control element is magnetized by a magnetron magnet with a gap of 25.4 mm. These controls are then layered together to form the elongated strip. For the production in large quantities _h o the mixture to the elongated strip to be applied to a wide film of the material from which film then 0.6 cm wide strips are cut out.

FIG. I shows three units 10A lOßund IOC, the _h <, are arranged so that they form two output paths, wherein the intermediate spaces between the gegenüberstehrnrirn l-'inheiten 10/4 and ioss between 10 and /? and IOCje form an interrogation zone.

The unit 10A is partially cut open so that two electromagnets 12A and 125, an air coil 14 and four smaller coils 16A, 165, 16C and 16J3 can be seen referred to), which is connected to the ungrounded (hot) conductor 18 of a filtered AC power source, and to an "output contact" which is connected via the conductors 22, 24 and 26 to a field sequence circuit 20, of which only the one with the unit 10A connected conductors 22A, 24A and 26A are shown. The units 10A and IOC have the same structure, while the unit 105 differs from the other units in that it is not equipped with the four smaller coils. These smaller coils each have 900 turns of enamelled wire with a diameter of 0.1 mm have a diameter of 10 cm and form a magnetic flux monitoring device labeled 29. These coils are connected in series with a RG 58 A / U coaxial cable, placed in separate locations on one side of the surveillance zone and carefully oriented to filter out as much of the magnetic noise generated by the field generating device and other sources as possible will. In the illustrated embodiment, the upper coils 16A and 165 are oriented vertically, while the lower coils 16C and \% D are oriented horizontally. Each coil is covered with a 12.7 μm thick aluminum foil, not shown, which shields against electrostatic noise, but allows magnetic signals to pass through. These shielding foils are connected to the shielding of the connecting coaxial cable.

A coaxial cable 28 is connected to the magnetic flux monitoring device a signal detector 32A is connected to the unit 10A, and a similar signal detector 32ϋ is connected to the magnetic flux monitoring device via a coaxial cable 30 the unit IOC in connection. A book 31 provided with a sensitized marking element 33 becomes through the field of action carried through in an interrogation zone, the marking element is umagnetisierl with each change of the effective field and generates a pulse of a external polar magnetic field. The flow monitor in this zone responds to this change of the magnetic flux in the zone and generates a signal that corresponds to the pulse and associated with it Detector circuit 32 is conducted. The detector circuit cr / .et'gt due to the special amplitude and A signal which sets an alarm and display circuit 34 in operation.

The F i g. I shows in general the spatial arrangement of the field generating device and the flow monitoring device, which devices form surveillance zones which are arranged in a library, whose books are traced with a marking element of the invention are equipped- The field generating device can, for. B. also from a grid-like or another arrangement of conductors exist, one arrangement of which is shown in Fig.2 to generally to show the field created by long straight conductors.

Fig. 2 shows as a section two long, straight and parallel conductors 512 and 514 with the lines of force derived from the current flowing in each conductor in different

Time intervals are generated. The circular line 513 represents only one line of force in a series, of circular ones Represent lines of force that are generated by the current flowing in the conductor 512, while the circular line 515 only a line of force. of a series of concentric and s represents circular lines of force from the im Conductor 514 flowing current can be generated. For the purpose of simplifying the illustration, FIG. 2 only the magnetic flux lines shown. For the same reasons, only the magnetic properties are shown hereinafter of the electromagnetic field

As can be seen from Fig.2, run in the the area 510 enclosed by the broken line 517 is the field lines of the two conductors 512 and 514 although curved, but essentially at right angles to one another at the crossing points. District 510 represents a cross-section through an interrogation zone and is therefore shown at right angles, since this is often the The shape of the cross-section of a passage is in which the interrogation zone generates an electromagnetic field will be SQÜ- Such a cross-section in the general entrances and exits, corridors and the like Passages on.

Assuming dimension 519 of the District 510 corresponds to the width of a passage, and that the conductors 512 and 514 are aligned vertically dimensions 519 and 521 correspond to Latitude or longitude of the query zone. The considerations in determining the actual length of the Interrogation zone have already been explained. It is well known that the intensity of the field changes directly with the Amplitude of the current flowing in the conductor and vice versa in relation to the distance from the conductor. For a special passage with the width 519, with a distance of the ladder 5 * ?. and 514 of each other, which corresponds to dimension 523, and its distance from the edge of the passage is equal to distance 525 is, and for a marking element which requires a particular sufficient energy, can be carried out by a Vector analysis of each of the fields at their intersection points at the most distant point in the district (near the Dimension 521) determine the amplitude of the current flowing in conductors 512 and 514 must have.

Figure 3 shows four long, straight and parallel conductors 516, 518, 520 and 522 and two groups of Magnetic field lines that could be generated by the current flowing in the conductors. The one group of Flow lines are shown with solid lines and the other group with broken lines. The solid lines are the lines of force that would be created when in conductors 516 and 518 currents in opposite directions with the same strength would flow while there is no current in conductors 520 and 522. Those shown with broken lines y> th field lines are generated with a reversed flow of current, i. i.e., conductors 516 and 518 are de-energized, while in the conductors 520 and 522 equally strong but oppositely directed currents flow. It it is pointed out that with the same dimension unbo gen in Fig.2 and 3 the field, in Fig.3 a greater length (521), but both fields can be generated in the same time span (in in both cases only two "field impulses" need to be generated). The analysis to determine the current b5 May the two leaders in Fig. 3 is performed generally in the same manner as with respect to FIG Fig. 2 described. If another "sentence" becomes a Such an arrangement of ladders is provided, and these two sets of ladders are combined into one closely spaced parallel planes arranged so that the conductors of the respective sets 1 run perpendicular to each other, a three-dimensional device is created. With such a Facility exists at essentially every location in district 510 at least once during each pulse sequence of the four pulse fields each of the three Magnetic fields that are almost perpendicular to each other. J The »end« -lead of the above-mentioned further ladder set I. is in FIG. 3 shown with broken lines | and denoted by 527

4 shows a two-dimensional FcIdI generating device, which is labeled 501 and J has two "o" coils 524 and 526. For purposes j an analysis, the vertical sections of the! Coils viewed as long, straight, and parallel conductors! will. Coils 524 and 526 are essentially inj located on the same level, but overlap in such a way that the distance between the neighboring and different! Sections 528 belonging to the coils and from one another are much smaller than the distance between the coils perpendicular sections of the same coil from each other! In this way the field lines between the inside vertical sections approximately the field lines shown in Figure 2. At 503 there is a from those that are unevenly spaced Coils formed zone shown, which the length 521, did Has width 519 and height 534. If the Spulcd were equidistant from each other, i. i.e. if de | Distance between the inner sections! equal to half the distance between the vertical sections would be the same coil, fields with the in de j F i g. 3 field lines shown are generated. It has been shown that with such, an unequal abstanij having coils with a length of 105 cm de vertical sections and with 120 cm long scales] right sections, which coils made of 10 turns of a wire strand No. 10 A.W.G- (like both No. 30 öW passed, an essentially two-dimensional FcI can be generated in an interrogation zone containing a Height of about 90 cm, a width of 90 cm and a length of 150 cm when through the Spulq a pulsating underdamped sinusoidal current ι an initial peak amplitude of 180A! became.

In Figure 5 is a three-dimensional Fej generating device shown. The device shown at has a grid-like ^ Structure 539, which consists of three coils. In the preferred embodiment, the coils are parallel and a small area upciscndl plains. The coils are SO at 507t? and shown individually. The grid has three perpendicular Components 540, 542 and 533 as well as five waagercelj Components 546,548,550,552 and 554. As from ι The following description of these components will be seen, each of these components consists ι at least one section of a coil, and most of these components comprise sections of several | Wash. It should be noted that those Fields are not required, the coil sections forming the components 540 and 544 be generated. However, these fields are erzej and shorten the "length" of the zone when Components 540 and 544 are sufficiently close to inventory 542. In those cases where

2U OO ÖZÖ

Component consists of a section of more than one ■ coil, only the field of one section is required. Only the required fields of the individual coils are therefore dealt with below. In FIG. 5, an upright and generally rectangular "8" coil 555 is shown at 507. The coil consists of a conductor which is wound in the shape of an "8" and forms two generally rectangular and j parts connected in series of almost the same size, generally with; 558 and 560 and which have substantially parallel top and bottom lengths. Part 558 has an upper length 572 and a lower length 574, while part 560 has an upper length 576 and a lower length 578. The lower length 574 of the loop 558 and the upper length 576 of the loop 560 together form the central portion of the "8" coil 555. The upper and lower lengths of the parts 558 and 560, the upper length 572 and the lower length 578, form the end sections of the "8" coil 555. Energy pulses can be supplied to the coil via the connection contacts 580 and 582. The arrows shown in the two loops, one of which is denoted by 584, indicate the direction of the flow of current through the various sections of the divisions with direct current. From the sub-figure 507 it can be seen that the length 572 corresponds to the horizontal component 546, that the length 572 corresponds to the horizontal component 546, that the lengths 574 and 576 correspond to the horizontal component 550, and that the length 578 corresponds to the horizontal component 554 jo corresponds. The sub-figure 509 shows an “o” -spu! e 557, the horizontal sections of which are denoted by 586 and 588, and which correspond to the horizontal components 548 and 552 of the grid 539 (sub-figure 505). The sub-figure 511 shows a j5 "8" spool turned into a rope. The lengths of the coil labeled 594 and 5% correspond to the vertical component 542 of the grid 539 (50J), while the lengths 590 and 592 correspond to the components 540 and 544, respectively.

The F i g. 6 ~ Eigi vector representations of the magnetic lines of force for the fields which are generated by the device generating a three-dimensional field (coils 555, 557 and 559 according to FIG. 5). In the sub-figure 502, field vectors are shown in a plane that is parallel to the "perpendicular" lengths (e.g. 594 and 596) of the coil as well as perpendicular to the plane of the coils, and a side view of the lengths of the coils 555 and 557 The coil 559 is not shown. A region 539 of a cross-section is shown with dashed lines. Field vectors are shown at three arbitrarily chosen points 610, 612 and 614. The vectors labeled "afc" vectors correspond to the field produced by lengths 572,574, 576, and 578 of coil 555, while vectors labeled "b" vectors correspond to the field produced by conductors 586 and 588 of the coil 557 is generated. The field vectors of the field generated by the third coil 559 are shown at 504 at points 610, 612 and 614 with the i-eld viewed in a ω) plane that is parallel to the horizontal lengths of the coils and perpendicular to the plane of the coils is located. The coils 555 and 557 are not shown. The area 510 is shown again with broken lines, and the vectors of the field (, ·> of the coil 559 are designated as "Crt vectors. The sub-figure 504 shows the lengths 594 and 5% in the middle and the end lengths 590 and 592 of the coil

559. The dimension 521 of the district 510 runs only Over part of the route from the two mistletoe sections 594 and 596 to the end conductor 590 and 592. This is a consequence of the fact that in the end conductors 590 and 592 the current in the opposite Direction flows as in conductors 594 and 596. In conductors 594 and 596 the current flows in the same Direction so that the two conductors can be treated as a single conductor. With such a "(" Coil may be the distance between conductors 594 and 596 of the middle section and end conductors 590 and 592 can be changed by changing the dimension 521. The FIGS. 6 field vector diagrams shown at 5Q2 show that coils 555 and 557 form a two-dimensional field at points 610, 612 and 614-, while the field vectors shown at 504 show that the field of coil 559 corresponds to the Field added a "third" dimension

In an embodiment of FIG. 3 used for detecting marking elements according to the invention Device according to FIG. 5 became an interrogation zone consisting of a passageway district existed, with a height of at least 150 cm 60 cm wide and 75 cm long (dimensions 534, 519 and 521). That from The grid formed by coils 555,557 and 559 had the following dimensions: the perpendicular components 540, 542 and 544 were 180 cm long, while the horizontal components 546,548,550 and 554 were one Had a length of 150 cm. The "o" coil was made around the intersection of the center sections of the "8" coils centered around, and their lengths 586 and 588 were spaced 53 cm from lengths 574 and 576 of the spool 555. All of the spools 555, 557, and 559 were made from a strand of vinyl insulated wire No. 10 (both No. 30610) The coil 555 consisted of 6 turns, the coil 557 of 10 Turns and the coil 559 of 7 turns.

It should be noted that the in Fig.5 The flat structure shown can be produced without great cost and can be clad so that a Has a pleasing appearance Such a structure can easily be attached to one side of a door leading passage can be arranged. The structure described has the further advantage that the coils can easily be "balanced" in such a way that between an excited coil and the the other two unexcited coils have little or no inductance. It is therefore actually the energy generated by a coil is available for the generation of a field, which in a Query zone is in effect.

The F i g. 7 shows a front view of a field-generating and flow-monitoring device according to FIG . 5. The electromagnets 12 of the field generating means consisted of iron bars having a cross section of 5, \ cm ^2, which were surrounded by freshener. The rods were composed of sheets with a thickness of 0.457 mm of transformer steel type M-19 and had a length of 142 cm and a width. 5.1 cm. Each coil consisted of two windings with 125 turns of enamelled wire with a diameter of 0.2 cm, which were evenly distributed on the rod, as well as two further windings with 60 turns of enamelled wire with a diameter of 0.259 cm at each end the sings. The two additional windings with 60 turns each were connected to the am

60 turns at the end of the 125 turns existing windings bifilar wound. In FIG. 8 the type of winding is shown schematically.

As can be seen from Figure 8, the 60 turns of the windings 36/4 and 36S are connected to each other and with i the parallel connection of 125 windings comprising windings 38/4 and 38ß in series This combination of the coils is hereinafter referred to as "coil winding" designated, which is provided with an input contact 35 and an output contact 37. It was found that the poles of the magnets were from the ends of the rods at a distance of 7.5 cm. Two such devices, which are arranged at a distance of approximately fm from one another and have the dimensions mentioned, r, are suitable for setting up a surveillance zone with dimensions of approximately 100 cm × 200 cm × 200 cm.

The air core coil 14 consists of a simple closed loop with several turns. at the one shown in FIG. 7, the loop 14 is circular, the diameter of which is equal to the distance between the poles of the electromagnets 12, while the loop of FIG Coils of enamelled wire with a diameter: s of 2.05 mm is formed. If the electromagnets were not of the same length, the loop would curved, but designed so that the circumference of the loop is close to the poles of both magnets. the Reasons for such a measure result from the jo Relationships between the magnetic fields of the electromagnets and the air core coil, explained below.

9 and 10 show the characteristic Magnetic fields of an electromagnet and an air core coil like the coil shown in FIG. 7 in | -, free space, with the lines of force running in the plane of the drawing. According to the illustration, the Field of the vertically oriented electromagnet and perpendicular components (parallel to the V-axis) important horizontal components close to the poles (parallel to the X-axis). Likewise contains the magnetic field the air coil components that run parallel to the X-axis and parallel to the V-axis.

If the air coil is moved past the poles of the electromagnet, the two forms of the field-generating means complement each other. This can best be seen from Fig. 11, in which the superposition of two magnetic fields in free space is shown, which are generated by the devices 12Λ and 125 and 14 in a zone unit. For the sake of clarity, the fields generated by the device 12Λ are more representative. Lines are drawn uniformly dashed, while the lines representing the field generated by the device 125 are drawn by alternating short and long γ, dashes. The lines representing the field generated by the device 14 are solid. As can be seen from the illustration at 2, one group of lines of force intersects at point M and the other group of lines of force at point N. At 4, the angular relationship of the magnetic field strengths at point M and at § at point N is shown (vectors ). At 4 the components r are steep. s and t represent the strength of the magnetic fields at point M which are generated by devices 125, 14 and 12/4, while at 6 the components r ″, 5 ′ and f ′ represent the strength of the corresponding magnetic fields at point N by means of vectors As can be seen, they run Components of each group almost perpendicular to each other, although the directions of the components r, 5 and / are different from the directions of the components / · '5' and / '. It can be seen from FIG. 11 that the vector components of the points of intersection of other groups of lines of force likewise run almost perpendicular to one another. With the devices 12/4, 1B and 14, an almost exemplary field could be generated by an appropriate choice of the individual magnetic field strengths.

Are fields of not less than 1.4 times (square root of 2) the field of the elongated If the strip is generated, such fields are even at the ends of the interrogation zone at the ends of the polar ones Magnets on which the relevant directions of the fields change rapidly, almost exemplary or "Three-dimensional". An absolutely uniform three-dimensional field is not required because it is impossible is to pass a marking element through an entire zone without the Markicrungselcmcnt at least cinrns! so that a component of the active field is aligned that is larger than the switching field of the marking element.

The fields shown in FIGS. 9, 10 and 11 are generated unless there is an external magnetic influence. In the case of the one shown in FIG Arrangement with three zone units, the middle zone unit works with the two outer zone units together to form two interrogation zones, so that, in sequence, all nine fdderzcugendcn means in Operation would have to be set so that the displayed fields are generated. Because of the proportionate long distance is out of the. For reasons already explained, the generation of the nine fields in sequence not mandatory. This can be undesirable as the Peak amplitude of that flowing through the windings of the electromagnets and through the air core coil Currents and thus the cost of the circuit can be reduced in that in each zone component a field is generated at the same time.

FIG. 12 shows a circuit diagram for a device with one energy supply part 670, with three Energy transfer sections 672/4, 672S and 672C as well as with a sequence control signal generator 683. The circuit is not only limited to exactly three transmission sections 672, but this number has been increased only to simplify the description of a circuit for a field generating device with three Coils according to Fig. 5 or 7 selected. Of the transmission sections 672, there is only one section shown in detail, since all these sections have the same structure. Are the electric Features of the coils different from one another, o. H, they have different inductive properties and the energy supplied to each coil should be the same Have duration and frequency, other values can be selected for some circuit elements. Of the Power supply section 670 suitably has an AC voltage source 674. those from the conventional mains connection 617 and a conventional voltage doubler rectifier 676. This generates a DC voltage with a potential of approximately zero and minus 200 volts, which is voltage across conductors 678 and 680 Energy transfer sections 672/4, 672S and 672C is fed.

An electrical circuit is provided that is in a conductor (e.g. in the winding of the electromagnetic

ten according to the I · 'i g. 7 and 8, in the air core coil after the 7 and in the conductors of the field generating means according to FIGS. 2, 3, 4 and 5) generates an alternating current, the first half-cycle of which generates an electromagnetic field, which in turn has a characteristic which can be stimulated Signal generated. The electrical circuit therefore generates a damped one in an interrogation zone sinusoidal electromagnetic field. The circuit has a> * parallel resonance circuit, its inductive Component consists of a conductor that generates the electromagnetic field. They are means provided with which a source of electrical energy is intermittently connected to the resonant circuit, so that a predetermined amount of electrical energy is supplied to the resonance circuit. Will the If the energy source is switched off by the resonance core, free vibrations consume the resonance circuit supplied energy in the form of a damped sinusoidal current flowing in the conductor, so that subsequently cir. damped sinusoidal eleki.-cmagneticcs Field is generated. The transmitted energy can either be capacitive or inductive Component of the resonance circuit are stored. Should the energy be stored in the inductive element the time required to generate sufficiently strong currents results in much longer Pulses are generated than when the energy is stored in the capacitive element.

In a preferred embodiment, the amount of electrical transmitted to the resonant circuit Energy limited approximately to a value at which the speed of dissipation of the energy from the resonance circuit exceeds the speed at which the energy is stored in the resonance circuit will. This can be done with the help of a controllable silicon rectifier can be achieved, with which the resonance circuit is intermittently connected to the energy source will. Will mi! a suitably selected inductor in series with the rectifier and the resonance circuit switched, no further means for locking the rectifier and for switching off the Resonance circuit required by the energy source. The inductance of the inductor should be at least 4.7 times the inductance of the conductor used to generate the electromagnetic field. These Inductance should preferably be 4.7 to 25 times and ideally about 6 times the inductance of the Ladder. If the difference is less than 4.7 times c, the controllable silicon rectifier not be blocked.

In another embodiment, the inductor forms the primary winding and the inductive part of the The secondary winding of a transformer. To be sure of an effective coupling of the two windings with each other, the transformer can consist of an autotransformer (autotransformer) exist. In a further alternative embodiment, instead of an inductor, there is between the connecting means and the resonance circuit switched a resistor.

As is known per se, the amount of energy supplied to a resonance circuit can thereby be determined be that either the charge on the capacitive element or in the inductive element of the resonance circuit flowing electricity is regulated.

With reference to the F i g. 12, an embodiment of an electrical circuit is described below, with which a further circuit cooperates, so that several of the first-mentioned circuits are used can to supply several field-generating means with electrical energy in sequence.

It should be noted that in the circuit according to FIG. 12 the transmitted from the energy source Energy primarily in the capacitive element and not in the inductive element of the resonance circuit is saved. The capacitive element of the resonance circuit therefore has a double function, and Firstly, the energy is transmitted from this element, and secondly, together with the inductive element formed a resonance circuit, the rest of the transmitted energy as free oscillations consumed. Because of this double function, this capacitive element is sometimes referred to as a Considered part of the resonance circuit as well as part of the energy transmission section and accordingly referred to, with the remainder of this section the means for connecting the energy source represents a mild resonance circle.

The energy transfer section 672 contains a switch in the form of a transistor 682/1, which is in the conductive state is set when the connection point 684/4 receives a control signal from the sequence control signal generator 683 is fed. If the transistor 682/1 is conductive, the section 672Λ conducts one Energy pulse to the coil of the associated field-generating device on. In Fig. 12 is the for The coil belonging to the energy transfer section 672/1 is shown schematically as an inductor 686. Is the When transistor 682 is conductive, a capacitor 688 stores an energy pulse which is used to generate the field Facility is passed on as a damped energy pulse. The circuit for charging the capacitor 688, which later conducts this charge to the field-generating device or to the inductor 686 causes an inductor 690, a controllable silicon rectifier 692 and one shown at 694 Circuitry for triggering rectifier 692. Trigger circuit 694 has a normally non-conductive type. Transistor 696, the base electrode of which is connected to one end of the two resistors 698 and 700 connected is. Resistor 698 is at the other end via blocking capacitor 704 and diode 706 connected to the collector electrode of transistor 682> t. One layer of the capacitor 704 and the cathode of the diode 706 are connected together with the one conductor of a resistor 708, the other conductor of which is connected to conductor 678 which has a reference voltage of zero volts. Is the If transistor 682 is non-conductive, the voltage across capacitor 704 is normally approximately 200 V, so that 6% no current can flow to the base electrode of the transistor, the transistor in the normal non-conductive state remains. When transistor 682 becomes conductive, capacitor 704 becomes charged, and the charging current flowing through the capacitor 704 puts the transistor 696 in the conductive state until the voltage on capacitor 704 has reached the level of 212 V The remaining part of the Trigger circuit 694 includes emitter and collector resistors 710 and 712 of transistor 696, a Capacitor charging network with a resistor 714, a Zener diode 716 and with a capacitor 718. The grid conductor of the rectifier 692 is connected to both the emitter electrode of the transistor 696 as also with the emitter resistor 710 in connection, so that at one at the other end of the resistor 710

2β

and a voltage of approximately minus 200 V at the cathode of the diode 692, the rectifier is rendered conductive or triggered, and only if the transistor 696 is conductive. Transistor 6% becomes conductive when a pulse is applied to junction 684 which forward biases transistor 682. A current flows from the emitter electrode to the collector electrode of the transistor 682 via the diode 7 (Xf *, the capacitor 704 and the resistor 693, whereby the transistor 696 is put into the conductive state. In this case, the capacitor 718 via the resistor 712 and discharge the transistor 696, so that the grid electrode of the controllable silicon rectifier 692 is supplied with a current pulse which puts the rectifier in the conductive state so that a current flows through the capacitor 688, the inductor 690 and through the rectifier 692 the consequence that energy is stored on the capacitor 688. In order for the energy to be stored sufficiently quickly, the value of the inductor 690 must be chosen so that it is no more than about 1/5 of the value of the inductor 686. Most of the therefore flow from the capacitor 688 flows through the inductor 690 and not ungefäh through the inductor 686. When charging of 2 ■> capacitor 688 r minus 200 V, the current flowing in inductor 590 has its maximum value. This current flow continues until the energy in the inductor 690 is consumed, with the result that the capacitor is charged to a voltage of approximately -300 V jn. This highest voltage depends in part on the ratio of the inductances of inductors 686 and 690 and the losses caused by the resistance in inductor 690 and other circuit elements through which the current flows. If the voltage across the capacitor 688 has reached its maximum value and no more current flows in the inductor 690, the controllable silicon rectifier 692 becomes non-conductive. The capacitor 688 is now discharged into the field-generating inductor 686, a current with a characteristic damped and sinusoidal waveform flowing in the coil. A resistor 4 ′) 691 with a very small value is connected between one end of the inductor 686 and the conductor 678, on which the reference voltage of zero volts is applied. The voltage drop across the resistor 691 is exactly proportional to the current flowing in the inductor 686 and can therefore be used as a synchronization signal for a detector device. In such a device, a detector indicates the presence of a responder if a characteristic signal is determined at a specific time in relation to the time base of the electromagnetic field.

The sequence control signal generator 683 has the task of connecting points 684A, 684B and 684C of the To supply a control signal in turn so that the coils of sections 672A, 672f and 672C generate field pulses generate, one of which is shown as an inductor 686. The generator 683 could consist of a μ Number of rnonostabüen multivibrators exist in a ring circuit, so that when switching of each multivibrator from the unstable to the stable state is a reversal of the operating states the following multivibrators in the ring circuit The outputs of the individual multivibrators would be fed to connection points 684. Another possibility is the connection points 684 to be connected to the individual stages of a simple flip-flop counter, which is controlled by a free-running Multivibrator is operated.

F i g, which consists of two drawings a and b. 13th is a circuit diagram for one of the two and the same structure having combinations of the magnetic flux monitoring device 29 with the signal detector circuits 32 of the system according to FIG. 1. As shown in FIG F i g. 13 shows the coils 16.4, 16 £, 16Γ and 16D of the magnetic flux monitoring device 29 via a coaxial cable 28 to the input of FIG Detector circuit 32 in connection.

The detector circuit 32 includes a signal shaping and amplifying section (SSAS) 128, a Signal discriminator section (SDS) 130 and an output section 132, the output of which via the conductor 134 to the alarm and display device 34 of the system according to FIG. 1 is directed.

The SSAS section 128 comprises, in turn, an input filter 136, a preamplifier 138 in FIG first stage, a preamplifier i40 in the / second stage, a preamplifier 142 in the third stage, the is connected via a coaxial cable to a further filter (144), a further amplifier 146 and a limiter stage (148), which circuit elements consist of designs known per se. the two twin T-filter elements of filler 136 have a very high transmission impedance at 60 Hz, which frequency is the frequency of the field generating Device in the embodiment according to FIG. 7 is. These filters consist of a cheap one Execution with a tolerance of 10%, do not require coordination, almost completely eliminate the very strong 60 Hz interference and weaken other interfering signals up to 1000 Hz as well. In the input filter 136, the capacitors 201, 202, 204 and 206 have one Value of 0.01 μΡ, capacitors 208 and 210 one Value of 0.022 μΡ each. the resistors 212,214, 216 and 258 has a value of 270 kfi each and the resistances 220 and 222 have a value of 120 kn each. In the Preamplifier stage 138, a transistor with very little inherent noise is used, since it is avoided it should be that in the amplified signal as; · output an additional inherent noise occurs.

The second and third amplifier stages 140 and 142 effect signal amplification with good linearity. The interposed coupling capacitors attenuate frequencies below approximately 1000 Hz. Between the preamplifiers 140 and 142 is a variable resistor 150 switched on, with which the system can be set so that no wrong Alarms are triggered by randomly occurring signals in the vicinity of the system concerned may occur frequently. The best setting is made by increasing the on the collector electrode of the transistor 152 lying AC voltage to a value at which the detector 130 a signal determined, although it is known that there is no signal characteristic of a responder in the interrogation zone has been generated. The value of this alternating voltage at the collector electrode is determined, after which the Variable resistor 150 is set so that the alternating voltage applied to the collector electrode of transistor 152 half of the determined value.

The filter 144 consists of a high-pass filter with an additional band filter whose mean value is based on the Gnmd frequency of the field of action is tuned, which last-mentioned filter consists of a twin T-Fil-

r ^ consists \, which is switched on between the high-pass filter capacitors. The twin T-filter network has a high transmission impedance at the fundamental frequency of 60 Hz of the effective field, and the high-pass filter capacitors essentially attenuate signals whose frequency is between 60 and 1000 Hz, which frequency is the predetermined one in the currently preferred embodiment Frequency is. In the filter 144, the capacitors 224 and 266 each have a value of 0.01 μΩ, the resistors 228 and 230 each have a value of 270 kilograms, the resistor 232 has a vain value of 120 kΩ and the capacitor 234 has a value of 0.022 μΩ. The amplifier 146 effects an additional amplification, while the limiting stage 148 effects a further amplification, represents a high input impedance for the amplifier 146 and supplies the signal discriminator 130 with asymmetrically cut signals.

The signal discriminator 130 generates an output signal which puts the alarm and display device 34 into operation whenever, in successive intervals of approximately 16 ² / ams, three signals with an amplitude at least twice as high as that of the noise and with a duration of less than occur approximately 0.3 ms. Each of these signals corresponds to the characteristic signal of a responder of the embodiment described above. Furthermore, the 16 ² / jms comprehensive interval corresponds to the period of a 60 Hz signal and therefore represents the reversal of magnetization of a sensitized marking element about 1.5 ms or within a time window that immediately follows a change in direction of the field of action. When such a signal is detected, a signal is fed to output section 132 via conductor 154. When three signals are received over the conductor 154 at successive intervals of 16 ^2/3 ms each, the output section 132 feeds a signal to the alarm and display device 34. After receiving a first signal, the output section 132 blocks the counter during the following 13 ^2/3 ms, and if no further signal is received in the following 6 ms, the counter is reset to the state zero.

The signal discriminator 130 has a blocking transistor 156 which, together with the trigger circuit 158. the delay timer 160 and the coercive gate 162 the passage of an output signal from the limiter 148 to the combination of a Waveform shaper 164 and a signal width discriminator 166 during most of each period prevented. In operation, the trigger circuit 158 changes its state approximately at the time when the AC line voltage exceeds zero. In this transition from the positive to the negative Value, an equal transition occurs at the output of the trigger circuit, with a pulse being generated that triggers the delay timer via a capacitor 168 and enters the monostable multivibrator unstable state. The delay timer remains in this state for approximately 4 ms, after which a shutdown takes place approximately at the point in time in which the field of action has the value zero crossed (the field of action shows a lag of slightly less than

90 ° on or about 4 ms). When the delay timer takes effect, it conducts through the capacitor / • 70 a negative going pulse which is the coercive gate triggers and puts a monostable multivibrator in the unstable state in which the multivibrator approximately 1.5 ms remains until it returns to the steady state. In the unstable state is on Resistor 172 has a low voltage so that there is no current to the base electrode of blocking transistor 156 flows. If the gate 162 is in the unstable state, the transistor 156 is therefore non-conductive, during which time the signal conditioning circuit is put into operation. At the same time, resistor 174 a high voltage is applied so that the base electrode of transistor 176 receives current and the transistor becomes conductive with the result that the signal width discriminator is put into operation. The multivibrator returns of the coercive gate returns to the stable state, the reverse is the case. At resistor 172 is a high voltage, so that the transistor 156 a current through the resistor 177 Seilet with the result, that transistor 179 is continuously conductive, the waveform shaping circuit being disabled. At the same time, the resistor 174 is supplied with a low voltage, so that the transistor 176 none Receives power and turns off the signal width discriminator. Only during the short-term unstable State of the coercive gate 162 every 60 Hz period, a signal can therefore be received. In this short time interval is followed by the characteristic signal pulse from a marking element of the invention is generated.

If such a characteristic signal is received in a timely manner by the limiting stage 148, the The state of the signal conditioning circuit changes when the level of the amplitude has a value of approximately 8 V. exceeds while transistors 179 and 181 change from the normally conductive to the non-conductive State. Here, a pulse is passed through the capacitor 178 and the diode 180, which puts the multivibrator 182 dos signal width discriminator in the unstable state.

The transistors 179 and 181 remain in their new states for as long as the received signal exceeds the value of about 6 V, which time for characteristic marker signals is less than about 03 ms. Since during this time there is no current through the collector electrode of transistor 179 flows, the transistor 184 remains blocked, which is blocked again when either one or both Transistors 176 and 186 are non-conductive. The non-conductive state of the first transistor was already described in the description of the coercive gate 162. The transistor 186 is non-conductive during the steady state of the signal width multivibrator 18X, the transistor 184 is therefore only then conductive when the coercive gate and the signal width multivibrator are in the unstable state and during a normal state of the signal shaper 164, when the collector current of transistor 179 has its base electrode with a forward bias provided. The unstable state of the multivibrator 182 must therefore last longer than the width of the characteristic signal.

If the transistor 184 is put into the conductive state by a characteristic signal, then the A negatively directed signal is supplied to the input conductor of the output section 132 via the conductor 154

The output section has a counter 188 Period timer 190, a consecutive pulse gate 192 and a count clear gate 194.

The period timer 190 simply consists of a monostable multivibrator which is connected to the input conductor 154 * and which is placed in the unstable state by a negative-going signal. At each transition of the periodic timer from the stable in the unstable state, the counter 188 is incremented by the switching transistor 196 by one step, the unstable state of the period timer takes about 132/3 ms, so that the speed of the counter to a number of step for every 13 ^2/3 ms or to approximately one count in a 60 Hz period. The counter is prevented from being cleared or reset during this 13V3 ms period of time by the forward bias voltage present at connection point 198, since transistor 200 is blocked in this case. The consecutive pulse gate 192, which consists of a further monostable multivibrator, is put into the unstable state when the period counter returns to the stable state. In the unstable state lasting approximately 6 ms, the gate 192 prevents the counter from being reset to the zero division by virtue of the base electrode of the counter clear gate 194 is supplied with a forward bias. If the period timer has not yet been reset to the unstable state when the consecutive pulse gate 192 has returned to the stable state, the counter is reset to the setting zero.

A relay driver circuit 133 generates a on conductor 134 when the counter has counted to three Output signal which sets the alarm and display device 34 into operation

The F i g. 14 shows a perspective view of a book 850 having a marker 852 with "n" individually arranged open strip members 854, 856, 858 and 860 of Ferromagnetic ™ material near the back cover of the book. At least three members 854, 858 and 860, labeled "1", "λ-1" and "n", are required to produce at least three separate magnetic pulses and to accommodate the necessarily equally spaced intervals. The element 856 shown in dashed lines is determined to represent a number by the value of "n"

Limbs used

15 shows a perspective view of a book 852 with a concealed marking element 864 in multiple states. Part of an outer cover 866 over the spine of the book is shown broken away to show the marking element 864. The marking element 264 has "a" links 868, 870, 872 and 874. The terms 868, 872 and 874 represent the numbers "1", "a - 1" and "na", respectively. The member 870 shown in dashed lines represents optional members, the number of which depends on the value of "n". The members 868, 870 and 872 are comprised of elongated strips 876 having piled thereon controls 878 which extend the entire length of each elongated strip. The member 874 consists of an elongated strip 880 on which controls 882 and 884 are stacked, each of which extends only over a portion of the open strip 880.

The arrangement and selection of the marking elements according to FIGS. 13 and 14 is arbitrary and in can be changed in any way.

The marking device according to the invention can also be used for protection against theft from libraries or from warehouses for other purposes, such as sorting Objects. The objects belonging to a class can be marked with a marking element are equipped, the elongated strips of which have a certain alternating current coercive force, while objects belonging to a different class are provided with a marking element whose elongated strips have a different AC coercive force, etc.

The marking element according to the invention could also be used as a fraud-proof closure, the integrity of which can be determined without direct contact by facilities, e.g. B. on one Railroad car driving past a checking point. Such a marking element can be made from a strong adhesive on a length of an elongated strip of ferromagnetic Material. The adhesive can be made from the US-PS Re 24 906 described embodiment exist, while the elongated strip of Permalloy with a width of 6 mm, a thickness of 25 μπι and one Length of 18 cm.

In addition 9 sheets of drawings

Claims (1)

Patent claims: 1. Marking element for use in a device for 'detecting an object in an interrogation zone in which the object is exposed to a periodically changing electromagnetic field is exposed, with a portion of a material of high magnetic permeability, the Magnetic properties are such that in the presence of the marking element supporting Object in the interrogation zone with an applied alternating magnetic field of a predetermined Frequency the magnetization of the element is reversed in order to generate a external magnetic pulse containing harmonics of a predetermined frequency, characterized by