SE534420C2 - An apparatus for identification purposes - Google Patents

Abstract

A device for identifying an object, comprising a magnetic element (12, 22, 32) attached to the object. The magnetic element has a permeability which is dependent on a magnetic field exposed on the magnetic element. In addition, there is an enoscillator, the output of which is connected to the ends of the magnetic element to pass a single-current current through the magnetic element. A microwave transmitter (16) exposes the magnetic element to microwaves and a microwave receiver (17) receives the microwaves, which are reflected and / or retransmitted from the magnetic element and which are modulated alternating current. The magnetic element consists of a magnetic material, such as an amorphous nanocrystalline wire, the length of which corresponds to half the wavelength of the microwaves. (Fig. 1 must be published with the summary)

Description

534 420 The resonant frequency of said resonant circuit is affected by the peneability of said element of magnetic material. In addition, the element of magnetic material is exposed to an outer and spatially heterogeneous magnetic bias field through which the permeability of said element of magnetic material is controlled.

Document WO 99 / 66466A2 describes a method for remote detection of objects, each object being provided with a sensor comprising at least two magnetic elements arranged in a predetermined mutual relationship representing an identity of the sensor. Electromagnetic signals are generated to excite the sensor elements to generate the electromagnetic response signal ”. An amplitude of the electromagnetic response signal from each sensor element is modulated with a first magnetic field, which has a magnitude variant and a magnitude invariant component. A second magnetic field is generated with a rotating field vector. A fi-sequence shift is detected in a component of said response signal, when a magnitude-invariant component of said second magnetic field balances the magnitude-invariant component of said first magnetic field, each sensor element being momentarily exposed to a resulting magnetic field with substantially no magnitude invariant. component. An orientation of the respective sensor element is determined from the orientation of the magnitude-invariant component of said second magnetic field, when said frequency shift takes place.

All of the above systems require the tag to enter a magnetic field with certain properties. The effect of the magnetic field on a magnetic element in the tag is monitored, for example with a microwave system. The monitoring can take place at a long distance of fl tens of meters and even 100 meters, but the magnetic field cannot be generated at such a distance. If the system is to be made functional at a greater distance, large magnets are required.

There is a need in the art for a system that can detect a tag at a great distance. In addition, the system must be able to detect tags that are coded with information so that a large number of different articles can be provided with tags with separate identities.

The tags can be active, ie include a power source on board, or passive, ie function without any power source on board.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to remedy, avoid or eliminate one or more of the above-mentioned shortcomings or disadvantages, alone or in any combination.

According to one aspect of the invention, there is provided an apparatus for identifying an object, comprising a magnetic element attached to the object; a source of an alternating magnetic field for exposing said magnetic element; and a microwave transmitter for exposing said microwave magnetic elements and a microwave receiver for receiving microwaves re-reflected and / or retransmitted from said magnetic elements and modulated with said alternating magnetic field; said magnetic element having a permeability which is dependent on a magnetic field exposed on the magnetic element; and that said source of an alternating magnetic field is arranged on board the object; and that said source of an alternating magnetic field comprises an oscillator circuit, each output of which is connected to the ends of the magnetic element to drive an electric alternating current through the magnetic element.

The source of the alternating magnetic field may be powered by an energy source, such as a battery. Alternatively, the energy can be transmitted wirelessly to the object, and consists of electromagnetic radiation, ultrasound or induction.

According to one embodiment, the oscillator circuit may be arranged to generate several discrete frequencies in a sequence of times, which frequencies form an identity for the object. The magnetic element may be an amorphous or nanocrystalline magnetic wire, the magnetic wire being half the wavelength of the microwaves.

BRIEF DESCRIPTION OF THE DRAWINGS Further objects, features and advantages of the invention will become apparent from the following detailed description of embodiments of the invention with reference to the drawings, in which: Fig. 1 is a schematic diagram of an embodiment of the invention.

Fig. 2 is a circuit diagram of an oscillator intended for use in the embodiment of Fig. 1.

Fig. 3 is a circuit diagram of an oscillator intended for use in the embodiment of Fig. 1.

DETAILED DESCRIPTION OF EMBODIMENTS Hereinafter, your embodiments of the invention will be described with reference to the drawings. These embodiments are described for illustrative purposes in order to enable one skilled in the art to practice the invention and to describe the best mode of operation.

However, these embodiments do not limit the invention. In addition, other combinations of the various features are possible within the scope of the invention.

Document WO 99 / 66466A2, as mentioned above, describes that the magnetic element is very sensitive to the applied magnetic field. An oscillating magnetic field with a field strength equal to or less than the earth's magnetic field will cause a change in the permeability of the magnetic element, which is detectable by the microwave system.

The term "permeability" is defined as the degree of magnetization of the material corresponding to an applied magnetic field. Magnetic permeability is usually represented by the Greek letter u. The permeability of magnetic material directly affects the reactivity of the magnetic material when exposed to electromagnetic radiation, such as microwaves.

Thus, a variation in the permeability of the material will cause an amplitude modulation of the microwaves which are reflected or returned from the magnetic material.

Fig. 1 shows an embodiment of the invention, which comprises a tag 11 with a magnetic element 12, similar to the tag shown in WO 93 / 14478. In addition, the embodiment comprises a source or oscillator 15 for an alternating current or voltage, which is electrically connected with the ends of the magnetic element 12 by means of contacts 33 and 34.

The voltage source 15 is arranged to generate an alternating current with a low frequency. When alternating current is applied to the magnetic element 12, a modulation of the permeability of the magnetic element takes place with said low frequency.

A microwave transmitter 16 transmits microwaves to the magnetic element and receives microwaves reflected by the magnetic element 12 with a microwave receiver 17.

Instead of causing the magnetic field to vary from a distance, as described in WO 93/14478, the tag itself comprises a circuit 15 on board to produce an alternating magnetic field of the magnetic element 12. Another difference in relation to WO 93/14478 is that in the present embodiment, the magnetic element is monitored by a microwave transceiver 16, 17.

It has been found that the embodiment according to fi g 1 is very sensitive. A very weak voltage source 15 is sufficient to modulate the magnetic element 12. The microwave transmitter 16 and the receiver 17 may be arranged at a distance of tens of meters, or even 100 meters from the tag, and will still be able to detect the low frequency modulation of the reflected microwaves. Thus, a low energy oscillator 15 can be used in the tag, making the tag easy and inexpensive.

In the embodiment according to ñgl, an alternating voltage source 15 is shown. Such a voltage source may be driven by a very small battery arranged on the tag.

The AC voltage can be obtained with a conventional oscillator circuit, such as a Hartley oscillator, a Colpitt oscillator, a Arnstrong oscillator, etc.

Fig. 2 shows a conventional Hartley oscillator comprising a FET transistor 18 and a battery 19. A switch 28 is provided in the battery circuit and normally prevents current from passing out of the battery 19. The switch 28 comprises an insulating material 29 normally arranged between two contacts . When the insulating material 29 is removed, the switch is closed and the circuit begins to oscillate at a frequency determined by an inductance 13 and a capacitor 14.

The circuit oscillates until the battery energy runs out or the switch opens.

If the tag 11 is used in a store for billing purposes, the material 29 can be removed, for example manually, when the goods are taken from the shelf. If the battery life is sufficient for 6 hours, there is plenty of time for the buyer to pass the cost charging system. The insulating material 29 can be removed in many different ways. The material may comprise a substance which absorbs energy as it passes through an induction field, so that the material melts. The material can be an optical material that conducts current when exposed to light.

The material can be removed manually, etc.

The magnetic element 12 should have certain properties.

The magnetic material may be an amorphous or nanocrystalline magnetic wire, as described, for example, in WO 97 / 24734A1, the contents of which are incorporated herein by reference. This material can exhibit Giant Magnetoresistive properties or even Colossal Magnetoresistive properties, which may explain why such a small magnetic field can cause such a large change in permeability.

The material may be, for example, an amorphous magnetic wire comprising a metallic amorphous core having a diameter in the range between 5 and 25 μm and having a composition based on Co containing 20 atomic% or less of Si, 7 up to 35 atomic% B and Atomic% or less of one or more metals selected from the group Fe, Ni, Cr, Ta, Nb, V, Cu, Al, Mo, Mn, W, Zr, Hf and a glass shell with a thickness in the range between 1 and 15 μm, for example an alloy with the composition Co70Fe5Bl 5Si10.

The wire may be thin, such as less than 25 microns, and may have a length adapted to the microwave frequency, such as about 49 mm for a microwave frequency of 2.45 GHz, which corresponds to half the wavelength of the microwaves. In another embodiment, the length may be selected to correspond to the entire wavelength or any length between the entire wavelength and half the wavelength.

The oscillator that generates the alternating voltage can be operated in other ways than with a battery. Other ways to generate an AC voltage without using a battery on board would be to arrange a piezoelectric crystal tuned to a frequency well above the audible range such as about 100 kHz. An ultrasonic source with the same frequency is directed at the tag and is captured by the piezoelectric crystal which acts as a microphone. The sound energy is converted into an electrical voltage, which is used as the AC power source 15 or as a battery source.

Similar energy transfer can be performed by other wireless methods, such as infrared light, induction, etc. The on-board voltage source may include a capacitor, which is charged from a distance and then forms a voltage source when needed.

Awakening circuits are known in the art for generating an oscillating signal when activated by an electromagnetic signal.

The embodiments of the invention can be used in many applications.

The frequency of the voltage source 15 can be set to a predetermined value, which constitutes an indication of the tag. Thus, the frequency can be selected according to the following formula: 534 420 f = n * 1000Hz where n is a number between 1 and 1000, which gives 1000 identities. By using two such circuits on the same tag, 10 ^ 6 different identities can be coded.

In some cases, it may be inappropriate to use low frequencies below 20 kHz, for example if an ultrasonic transmitter is used. In such a case, frequencies in the range of 100 kHz to 1100 kHz may be used.

The circuit 15 can be arranged to generate a series of frequencies, which are repeated until the energy of the battery is consumed. These frequencies can form the identity for the tag. The tag may be initiated to start the generation of said series of frequencies of an external signal, for example as mentioned above in connection with Fig. 2.

The oscillator can be an unstable multivibrator with several capacitors connected one after the other in sequence in order to generate fl your frequencies one after the other. Such a circuit is shown in Fig. 3.

The circuit in fl g 3 is built around a circuit 61, a so-called 555-IC, which is well known.

This 555-IC generates a square wave output signal with a frequency defined by a capacitor at its input. In the circuit according to fi g 3, there are three capacitors 62, 63 and 64, which can be connected to the circuit 61. A first capacitor 62 is always connected to the circuit 61. When this capacitor 61 is connected, the circuit generates a square wave signal at an output 67, which has a high frequency, determined by the value of the capacitor.

A counter 68 is arranged to generate a binary signal at two output contacts connected to two switching elements 65, 66 in the form of MOSFET transistors, before adding capacitors 63, 64 to the circuit 61. The counter is arranged to generate the following sequence of signals: 00, 01, 10, 11, 00 for, for example, one second. When the output signal becomes 00, both switching elements 65, 66 are closed and only the first capacitor determines the frequency which becomes high, for example 550 kHz. When the output signal becomes 01 or omkring about 250 ms, the second capacitor 63 is connected in parallel with the first capacitor 62 and the frequency becomes lower, for example 320 kHz. When the output signal becomes 10 after another 250 ms, the third capacitor 64 is connected in parallel with the first capacitor 62 and the frequency becomes even lower, for example 260 kHz. When the output signal becomes 1 1 after another 250 ms, both the second capacitor 63 and the third capacitor 64 are connected in parallel with the first capacitor 62 and the frequency becomes even lower, for example 210 kHz. Then the sequence restarts from the beginning. In this way, four different frequencies are generated in succession. The output signal is fed to the wire 12 in Fig. 1. These four frequencies form an identity for the tag and the goods to which the tag is attached. These frequencies are detected by the microwave transceiver 16, 17. 534 420 The stability of the circuit 61 is sufficient to define, for example, 100 different frequencies, the number of combinations of four frequencies being 10 ^ 8. Additional frequencies can be added for increased number of combinations, for example 6 or 10 frequencies.

If better stability is desired, the multivibrator circuit can be based on a crystal oscillator which oscillates with a high frequency of, for example, 100 MHz and is divided by a counter into a range of 100 kHz to 1100 kHz. Such a multivibrator is very stable.

The signals supplied to the magnetic element 32, the wire 23 or the LC circuit 13, 14 may be a square wave signal or a sinusoidal signal or have some other suitable waveform, such as triangular.

- There are almost no limits to which frequencies can be used. The magnetic material will change its permeability at frequencies up to fl era MHz and down to zero Hz.

As mentioned above, the circuit may comprise devices for charging a power source located on board. When the current source has been charged, for example by means of ultrasonic energy or induction or in some other way, the circuit will generate said series of frequencies. In this way, the tag becomes self-sufficient and can work whenever energy is supplied. Although the invention has been described above with reference to specific embodiments, it is not intended to limit it to the specific embodiments set forth herein. Rather, the invention is limited only by the following claims and embodiments other than those specified above are equally possible within the scope of these appended claims.

In the claims, the terms "include / include" do not exclude the existence of more elements or steps. Even if they are specified individually, a number of devices, elements or process steps can be performed by, for example, a single unit or processor. In addition, even if individual features are included in different claims, these may possibly be combined to advantage and the inclusion in different claims does not suggest that a combination of features is not possible and / or advantageous. In addition, a single reference does not exclude a number. The expressions “one”, “one”, “first”, “second” etc do not exclude a number. Reference numerals in the claims are provided for illustrative purposes only and are not to be construed as limiting the scope of the claims in any way.

Claims (7)

1. A device for identification of an object, comprising a magnetic element (12, 22, 32) attached to the object,; a source (13, 14, 15; 25; 35) of an altemating magnetic field for exposure of saidmagnetic element; and a microwave transmitter (16) for exposing said magnetic element for microwavesand a rnicrowave receiver (17) for receiving microwaves reflected and/or retransmitted fromsaid magnetic element and modulated by said altemating magnetic field; characterized in that said magnetic element has a permeability, which is dependent on a magnetic fieldexposed to the magnetic element; said source of an altemating magnetic field is arranged on-board of the object; and said source (3 5) of an altemating magnetic field cornprises an oscillator círcuit (61),the output (67) of which is connected to the ends of the magnetic element in order to pass anelectric altemating current through the magnetic element.

2. The device according to claim 1, wherein said source (3 5) of an altematingmagnetic field is powered by an energy source.

3. The device according to claim 2, wherein said energy source is a battery.

4. The device according to claim 2, wherein said energy source is energy which hasbeen wirelessly transmitted to the object, and being electromagnetic radiation, ultrasound, orinduction.

5. The device according to any one of the previous clairns, wherein said oscillatorcírcuit is arranged to generate several discrete fiequencies in a time sequence, whichfrequencies form an identity of the object.

6. The device according to any one of the previous claims, wherein said magneticelement is an amorphous or nano-crystalline magnetic wire.

7. The device according to claim 6, wherein the length of the magnetic wire is halfthe wavelength of the niicrowaves.