FR2489988A1 - Magnetic responsive circuit for identification - comprises coil with special core oscillating in characteristic manner in response to applied magnetic field - Google Patents

Abstract

The magnetically actuated signal generator includes a magnetic wire (21) formed of an alloy of cobalt. For example the wire may be 48.3% cobalt, 48.6% iron, 2.75% vanadium, and 0.35% manganese. The wire (21) is formed with a diameter of 0.5 mm and a sample 20 mm long is used. After manufacture, the wire is wound around a cylinder to give it a gentle curvature. This sample is then placed in a rigid tube (22) of non-magnetic material, such as glass or alumina, with an internal diameter of 1 mm. A winding (23) is formed around the tube. When the device is placed in a varying magnetic field (H), the core oscillates and provides a characteristic induced current pulse output in the winding. This output is largely independent of the nature of the applied field and may be used for identification purposes.

Description

 The invention relates to answering devices capable of emitting coded signals in response to a variation in magnetic field. These devices are used in particular in systems for detecting, identifying or sorting objects.

 There are many types of devices that transmit coded signals in response to an interrogative magnetic field. The invention relates to the types of devices whose transmitter is supplied with electrical energy. In known devices, electrical energy supplying the signal transmitter is supplied either by the network, which limits their use, in space, at the places where they can be connected to the network, or by cells or batteries, this which limits their use, over time, to the lifespan of these batteries or these batteries.

 However, it is known to generate, by means of certain magnetic materials treated, electrical pulses capable of supplying electronic circuits. This is obtained by using the magnetostrictive effect in certain magnetic materials to create an easy magnetization axis there. Along this axis, the magnetization switches from one direction to the other, suddenly, by application of an external magnetic field. This sudden tilting creates a variation in the induction flux which results, at the terminals of an electrical winding surrounding a bar of this material, by an electric pulse whose characteristics are almost independent of the external magnetic field above a threshold value and of the way it is applied.

 This provides a magnetic generator of electrical pulses, powered only by a variation of the magnetic field. It is completely independent of any source of electrical energy, and is capable of emitting calibrated electrical pulses when it is subjected to any variations in magnetic field, greater than a threshold value.

 According to the invention, it is proposed to use this magnetic generator of electric pulses as a source of energy to power a transmitter of coded signals, and thus to constitute a very reliable answering device, easy to make and to use, completely autonomous and independent of any conventional electrical energy source.

 The subject of the invention is precisely a responder device with magnetic control, comprising means for transmitting coded signals and electrical means for supplying these transmission means, and intended for transmitting coded signals when it is subjected a variation of the magnetic field, characterized in that these electrical supply means comprise at least one magnetic generator of electrical pulses, this magnetic generator of electrical pulses comprising a magnetic core having two stable magnetization states, and a sensitive electrical winding to the variation in flux produced by the passage of this magnetic core from one to the other of these stable states; the tilting speed of the magnetization of this core being independent of the characteristics of the variation of the magnetic control field.

The invention will be better understood using the following description, illustrated by the appended figures, the content of which is as follows:
- Figure 1 is a diagram of the device according to the invention;
- Figure 2 shows a magnetic generator of electrical pulses;
- Figure 3 shows the electrical pulse produced by this generator;
- Figure 4 is an example of a device according to the invention comprising a sound transmitter;
- Figure 5 shows the response signal from this device;
- Figures 6 and 7 are variants of this device with sound transmitter;
- Figure 8 is an example of a device according to the invention comprising an electric radio transmitter;
- Figure 9 is a series of explanatory diagrams;
- Figure 10 shows schematically an application of the device;
- Figure 11 shows a variant of the answering device;
- Figure 12 is an electrical diagram of a responder device with radio transmitter.

 According to the invention, we wanted to make an inexpensive answering device, simple structure and space-saving, and safe and easy to use. This device essentially comprises a signal transmitter and the means for supplying power to this transmitter. The invention does not lie in the nature of the signals transmitted, which can be light, sound, radio, etc., but in the way in which the electrical supply to the transmitter is ensured.

To this end, a magnetic generator of electrical pulses is used, capable of emitting electrical pulses when, and only when, it is subjected to variations in the magnetic field. The characteristics of these pulses are practically independent of the characteristics of the variations in magnetic field which cause them, and which constitute
Interrogation of the device.

 Schematically, this responder is shown in FIG. 1. On a support 1, the shape of which does not matter, are arranged the magnetic generator of electrical pulses 2, and the transmitter 5, powered by this generator 2.

 The generator 2 is schematically represented by the fundamental elements which constitute it, namely a core 3 made of magnetic material, surrounded by an electrical winding 4.

The core 3, which is generally in the form of a bar or a wire, is made of a magnetic material which has undergone a special treatment. This special treatment is intended to create in this wire two magnetization zones of different character one with strong coercive field, the other with weak coercive field. When a magnetic polarization field is applied to the wire, a magnetization is created which remains after removal of the polarization field. There is then creation of a demagnetizing field which, if it is greater than the weak coercive field, but less than the strong coercive field, leads to a resultant magnetization of different direction in the two magnetization zones of the wire. wire is subjected to an external magnetic field greater than the demagnetizing field, the magnetization of the zone with weak coercive field rocks. When this external field disappears,
The magnetization switches back in the other direction.

 The passage of the magnetization from one direction to the other induces a rapid variation of the flux which generates an electrical impulse in a coil surrounding this wire.

 The characteristics of this electrical pulse are independent of the speed of variation of the magnetic field and of its amplitude, beyond a certain operating threshold. By way of example, two examples of magnetic pulse generator structures are given below.

A first type of structure consists of a nickel alloy wire
Iron (permalloy). Its special properties are given to it by a treatment consisting in stretching it then twisting it a certain number of times by fixing one end and turning the other end first in one direction, then in the other direction. Following this treatment, a strong coercive field is created in the area where the wire has been very stressed, that is to say at the periphery of the wire, the coercive field at the heart of the wire being much less.

 When this wire is subjected to the action of an external magnetic field, the magnetization of the heart switches which generates an electrical impulse at the terminals. of the coil surrounding the wire. When this external field disappears, the magnetization swings back in the other direction, which creates a second electric pulse.

 In this type of yarn, this twist treatment can be supplemented or replaced by an appropriate heat treatment.

 Another type of magnetic generator structure is shown in FIG. 2. It comprises a magnetic wire 21, formed from an alloy with a high cobalt content, for example 48.3% cobalt, 48.6% iron, 2 , 75% vanadium and 0.35% manganese. In an exemplary embodiment, this wire has a diameter of 0.5 mm and a length of 20 mm. After manufacture, this initially linear wire is wound on a cylinder so as to bend it, the deformation obtained, which is bending, being permanent. A piece of this wire is then cut to the desired length and introduced into a rigid tube 22 forming a sheath, formed of a non-magnetic material such as glass, alumina, etc. For example, a wire of 0.5 mm in diameter and 20 mm in length is introduced into a tube whose internal diameter is equal to 1 mm. Under these conditions, the wire placed in the tube is subjected to stresses, its two ends coming to bear on the internal face of the tube due to the permanent curvature which has been imposed on it previously, as shown in FIG. 2. The set is placed inside a winding 23 of conductive wire.

 Due to the treatment undergone by the wire, experience shows that, in one zone of the wire, an easy direction of magnetization is created along the longitudinal axis. The application of a magnetic field parallel to this axis, as shown at H in FIG. 2, causes the magnetization domains to tilt in this zone, this tilting corresponding to a variation in magnetic flux which induces an electrical signal at the terminals of the detection coil 23..When this magnetic field changes direction, the magnetization switches back and induces another variation in flux, hence another signal across the coil 23. The pulses are shown in FIG. 3 detected at the terminals of the coil 23 and corresponding to two variations in the opposite direction of the magnetic field. In this case, these two pulses are not identical, and it is advantageous that, at each interrogation, the transmitter is supplied by the same impulse. The structure described above can be mounted with compensation elements making it possible to make the two pulses identical, or to delete one of them. We can also use the structure with an interrogation comprising two variations in the opposite direction of the magnetic field, one will be called "arming", the other "trigger".

 For example, in the case shown in Figure 3, it is interesting to use the second pulse.

 Typically, for the numerical values indicated above, and with a coil having approximately 15000 turns, on a load resistance of 1 M the detected signal comprises a useful pulse of about thirty volts of amplitude and whose duration is of l 'order of 50 / us. Depending on the wire used, the amplitude variations of these pulses do not exceed 10 to 15%, whatever the value of the magnetic field applied, provided that this value is greater than a threshold value necessary for the tilting of the magnetization, and whatever the speed of application of this magnetic field.

 This property is particularly advantageous because it leads to extremely easy use of the answering device: an interrogating magnetic field of any amplitude greater than a certain threshold can be used, ie an alternating field of any frequency, however less than about 1 MHz, and in particular an alternating field of frequency 50 Hz, ie a continuous magnetic field, the magnetic field and the device being movable relative to each other.

 The second fundamental component of the responder device according to the invention is the signal transmitter. Any type of transmitter which can be supplied by a pulse of the type which can be supplied by the generator which has just been described, can be used to constitute this answering device.

 By way of example, two variants of this device are described, one using a sound signal transmitter, the other a radio signal transmitter.

 FIG. 4 schematically represents a responder device equipped with a buzzer type sound transmitter.

 In this example, the coil 4 of the pulse generator 2 is directly connected to a buzzer 41. This buzzer consists of a piezoelectric ceramic disc 42, mounted on a metal disc 43. The face of the ceramic disc opposite the metal disc carries metallization 44.

The buzzer used here is a conventional component, of small dimension, whose diameter varies from 1 to 2 cl. The outputs of the coil 4 are electrically connected to the metallization 44 for one and to the metal disc 43 for the other.

 Since the supply signal is a pulse, no switching circuit is necessary. Such a device is therefore very simple to produce. The charge of the pulse generator is in this case essentially the capacity of the buzzer which is of the order of 20 nF.

 When this device is placed in a variable magnetic field, the generator 2 emits a pulse which feeds the buzzer, which emits a sound vibration whose frequency is characteristic of the buzzer used. This signal can be picked up by a microphone placed nearby and processed in any way possible.

 FIG. 5 represents, on diagram 51, the pulse generated by the magnetic generator 2 and transmitted to the buzzer 41, and on diagram 52 the signal collected by a microphone placed near the buzzer. The frequency of the sound signal emitted by the answering device depends only on the characteristics of the buzzer, and not at all on the way in which the interrogating magnetic field is applied. This answering device can therefore constitute an identification card for an object which would be provided with it, the code being the natural frequency of the buzzer mounted in the device.

 It is possible to increase the possibilities of coding the signal emitted by this device, by equipping it with several buzzers of different frequencies, each one being associated with a switch. We can then mass produce identical devices, equip the objects that we want to identify or differentiate during subsequent processing, and operate the coding by opening or forming certain determined switches.

 Several types of mounting are possible.

 FIG. 6 shows an example of a device in which several buzzers 61, 62, 63 ... of frequencies fl, f2, f3 ... are connected in parallel, each one being associated with a switch, respectively 65 , 66, 67 ....

 FIG. 7 represents a device where three buzzers 71, 72, 73 of frequencies f'l, f'2, f'3 have been mounted in the same case 70, each being supplied by a generator 2, via d 'a switch 75. One can imagine many other combinations of these elements.

 When this device is subjected to a variation of magnetic field, the buzzers connected to the pulse generator 2 via a closed switch start to vibrate at their natural frequency, and the answering device emits a signal composed of waves of several frequencies, translating the code imposed on the answering device.

 This signal can then be collected, analyzed and exploited by appropriate means.

 However, it seems difficult to produce, practically, a responder device comprising a large number of buzzers, so that the coding possibilities remain limited.

 If more complex coding is required, a radio transmitter can be used instead of the sound transmitter. With a radio transmitter, the coding possibilities are much greater.

 An exemplary embodiment of a responder device equipped with a radio transmitter is described below, but one can imagine very many variants.

 An explanatory diagram of such a device is shown in Figure 8.

It represents a device in which a high frequency carrier wave is modulated by a low frequency signal, coded by means of conventional electronics.

 The high frequency carrier wave, for example 27 MHz, is generated by a first oscillator 81. The low frequency signal, for example 200 kHz, is created by a second oscillator 82. The signal emitted by the oscillator 82 is coded by through the electronic coding circuit 80 comprising, for example semiconductor circuits of the CMOS type which have a very low consumption, expressed in tuW.

 Advantageously, the code can be introduced and modified on demand, for example using switches, shown diagrammatically by the arrows 84, here 8 in number for a code with 8 linear elements.

 The oscillators 81 and 82, as well as the electronic coding circuit 80, are supplied with electrical energy by the generator of electrical pulses, here by means of a circuit 86 which modifies the pulse leaving the generator, typically 30 to 40 V for a duration of 50 / us, in a pulse of 6.8 volts of amplitude for a duration of 100 / us, which is more suitable for the power supply of the radio transmitter. During this period, the available power is around 12 mW.

 The circuit 86 comprises for example a zener diode 87, in parallel with a capacitor 88 and a resistor 89.

 The coded signal is mixed with the carrier in the mixer 83, and the radio wave, transporting the coded information is transmitted by the answering device each time this device is subjected to a variation in magnetic field. The transmitted signal can be received by a detector 85, interpreted and exploited by an appropriate system.

FIG. 9 shows, by amplitude versus time diagrams, an example of coding of the radio wave emitted by the device. These different diagrams respectively represent:
diagram A: the carrier wave at the output of oscillator 81
diagram B: the low frequency signal at the output of oscillator 82
diagram C: the low frequency signal after coding by the device 83;
diagram D: the radio signal emitted by the answering device;
diagram E: the useful signal received by the detector.

 This diagram is only one example of what the radio transmitter of the answering device according to the invention can be. Many variations can be made on the number of binary elements of the coding, the types of circuits used, the frequencies, etc.

 By way of example, we have reproduced in FIG. 12 the electrical diagram of a responder device equipped with a radio transmitter at 27 MHz with which a range of 2 meters has been obtained.

 The magnetic generator 2 with its coil 4 comprising 16,000 turns supplies the various elements of this circuit, by supplying them with the voltage Vcc, as indicated in this diagram. This circuit can be divided into four subsets 120, 130, 140, 150.

 The subset 140 relates to the coding of the information. The coding is introduced manually by means of the 8 switches 141 in parallel which are left open or closed and is translated into a modulation of the low frequency signal via the parallel-serial converter 142. The low frequency signal is supplied by the oscillator represented by the sub-assembly 120.

 At the output of the converter 142, this low frequency signal modulates the high frequency carrier wave generated by the 27 MHz oscillator represented by the sub-assembly 130, carrier wave which is emitted from the device by the antenna 131.

 In this example, the serial parallel converter 142 is a shift register operating with two control signals, one being a loading signal, directly supplied by the low frequency oscillator, the other, a generated clock signal, from the low frequency signal, by the circuit represented in the sub-assembly 150.

As it appears on this electrical diagram, this transmitter is carried out starting from a small number of components:
a CMOS integrated circuit, of reference CD 4014, constituting the shift register 142.

 - a CMOS integrated circuit, reference CD 4030 containing 4 "or exclusive" operators. These 4 operators are used in 160/1, 160/2, 160/3 and 160/4 as shown in Figure 12.

 For these two integrated circuits, the different outputs are identified on the diagram with their number.

 - a reference transistor T 2N 2222 A.

 - 14 resistors: R1 to R3 of 220 ka, R9 and R1D of 10 kQ, R11 of 680 kh, R12 of 47 kQ, R13 of 4.7 kQ, R14 of 2.7 ka.

 - 6 capacities including C1 of 39 pF, C2 of 120 pF, C3 and C4 of 100 pF, C5 of 56 pF, C6 of 470 pF.

 - 1 self L1 of 18 turns.

 - 8 switches 141.

 You can also use this magnetic generator of electrical pulses to power a light wave transmitter.

 An example of the application of this answering device is described below.

It is a system for identifying and sorting objects of any shape, such as mail bags, capable of being handled and sorted several times.

 These objects are each provided with a responder device of the type with radio transmitter. The code translating the information that the object must transmit is written on this device which then constitutes an identification label of the object.

 Whenever it is necessary to sort or identify the objects provided with their labels, the system provides for them to be scrolled, on a conveyor belt for example, in front of an interrogation station capable of locally imposing a variation of magnetic field and of collecting and d '' exploit the signal sent in response, by the responder device constituting the label of the object.

 A diagram of such a system is shown in FIG. 10. Objects 101 provided with their label 102 and placed on a conveyor belt 103 moving in the direction of the arrow, scroll past the interrogation station 104. This station provides a field magnetic alternator located in the area inside the induction loop 105 crossed by the treadmill.

The use of the alternating magnetic field ensures arming and triggering of the answering device.

 One can also have on the path of the objects two zones of permanent and opposite magnetic fields, which also ensures the arming and the triggering of the answering device when the object provided with this device crosses these zones.

 The detector 106 with which the station 104 is equipped receives the signals and transmits them to a processing system enabling them to be used.

 As the way in which the interrogating magnetic field is applied does not influence the characteristics of the response of the object, the object and consequently the label can appear in any position, and this is an advantage certain compared to known systems.

 However, the interrogating magnetic field must be substantially parallel to the direction of the magnetic wire, or at least the component of this field, parallel to this direction must be greater than the operating threshold. We can therefore improve the sensitivity of the device occurring in any position by arranging, to produce the pulse, not one, but three generators, in three orthogonal directions, as shown in FIG. 11. The three identical generators represented by the sheaths 111, surrounded by the windings 112 are arranged in the three directions x, y, z. The two ends of each winding are connected respectively to terminals 113 and 114 from which the power connectors of the transmitter circuit leave.

Claims (8)

 1. Magnetically-controlled answering device, comprising means (5) for transmitting coded signals and electrical means - for supplying these transmitting means and intended for emitting coded signals when it is subjected to a variation of magnetic field, characterized in that these electrical supply means comprise at least one magnetic generator (2) of electrical pulses, this magnetic generator (2) of electrical pulses comprising a magnetic core (3) having two states of 'stable magnetization, and an electrical winding (4) sensitive to the flux variation produced by the passage of this magnetic core (3) from one to the other of these stable states; the tilting speed of the magnetization of this core being independent of the characteristics of the variation of the magnetic control field.  2. Responder device according to claim 1, characterized in that the transmission means (5) of coded signals comprise at least one transmitter of sound signals.  3 answering device according to claim 2, characterized in that it comprises a transmitter of sound signals of the buzzer type (41).  4. Responder device according to claim 2, characterized in that it comprises a set of buzzers of different frequencies mounted in parallel on a magnetic generator (2) of electrical pulses, each buzzer being associated with a switch.  5. Responder device according to claim 2, characterized in that it comprises several transmitter assemblies, each assembly comprising a buzzer, a switch and a pulse generator; all buzzers with different frequencies.  6. Responder device according to claim 1, characterized in that the transmission means (5) of coded signals consist of a transmitter of modulated radio waves.  7. Responder device according to claim 6, characterized in that the coding is introduced in a non-definitive manner by switches and that it can be modified for reuse of the device.  3. Responder device according to claim 1, characterized in that the transmission means (5) of coded signals consist of a light wave transmitter.  9. Responder device according to any one of claims 1 to 8, characterized in that it comprises several magnetic generators of electrical pulses arranged along orthogonal axes.  10. System for identifying and sorting objects provided with answering devices according to any one of claims 1 to 9, characterized in that it comprises a conveyor belt on which these objects pass, and an interrogation station in front of which these objects one by one, and which comprises means making it possible to subject these responder devices to a variable magnetic field, and means making it possible to collect, analyze and exploit the signals emitted by these responder devices.