WO2015171058A1

WO2015171058A1 - Registering of a transponder tag via an alternating electromagnetic field

Info

Publication number: WO2015171058A1
Application number: PCT/SE2015/050494
Authority: WO
Inventors: Anders Rosengren
Original assignee: Delaval Holding Ab
Priority date: 2014-05-06
Filing date: 2015-05-05
Publication date: 2015-11-12
Also published as: CN207051913U

Abstract

A transmitter circuit (TX) in an apparatus (A) generates an electric source signal (Ss) and emits corresponding alternating electromagnetic field (ΕΜ_TX) via a transmitter antenna (TA). A receiver antenna (RA) registers a detection signal (SD) representing the alternating electromagnetic field (EM_TX) and any modifications thereof (EM_GX) resulting from a tag unit (GX) being present within a range of operation from the apparatus (A). An auxiliary antenna (SWA) receives a signal (Sa) representing a primary portion of the emitted alternating electromagnetic field (ΕΜ_TX) that reaches the apparatus essentially unmodified irrespective of whether or not a tag unit (GX) is present within the range of operation. A processing unit (PU) in the apparatus discriminates the identification data (GXid) of the tag unit (GX) based on the electric detection signal (Sd) and the signal (Sa) representing the primary portion of the emitted alternating electromagnetic field ( EM_TX).

Description

Registering of a Transponder Tag via an Alternating

Electromagnetic Field

THE BACKGROU N D OF THE I NVENTION AND PRIOR ART

The present invention relates to solutions for reading out data contactlessly from identification (ID) tag units.

Traditionally, data from transponder tags have been registered via transmitter-receiver equipment, where the signal from the tag is demodulated based on envelope detection, i.e. by an approach involving amplitude demodulation. Although the compo- nents required thereby can be made relatively uncomplicated, the technology is fairly inefficient in terms of power consumption.

US 4,260,990 discloses an antenna system having a transmitting antenna with at least one loop lying in a plane, and a recei- ving antenna having at least two twisted loops lying in a common plane with each loop being twisted 1 80 degrees and in phase opposition with each adjacent loop. The transmitting and receiving antennas are disposed in spaced substantially parallel relationship across an aisle or passage through which a reso- nant tag circuit must pass for detection. Hence, the transmitter and receiver are physically separated from one another by a distance given by the width of the aisle/passage for passing the resonant tag circuit through the emitted radio field .

EP 608 961 and EP 646 984 show examples of electromagnetic detection systems for detecting or identifying labels containing at least one resonant circuit, where a label's resonance frequency is indicative of its identity.

WO 94/1 9781 describes a system for identifying an electronic transponder, where the system includes a transmitter unit and at least one transmitting antenna coupled thereto for generating an electromagnetic interrogation field. A detection unit in the system detects signals emitted by the transponders when they are located in the interrogation field. To this aim, the detection unit has a means for detecting signals coming from different transponders on the basis of strength differences between these signals. In one embodiment, in order to tune the receiver unit to frequency band of the interrogation field emitted by the transmitter unit, a signal representing the frequency or frequencies of the interrogation field is supplied from the transmitter to the receiver unit through an interconnecting wire line.

PROBLEMS ASSOCIATED WITH TH E PRIOR ART The above documents present different solutions for reading out data from tag units in a contactless manner. Nevertheless, the radio technology is here comparatively inefficient with respect to energy consumption. Therefore, these solutions are not optimal for low-power implementations, such as general I D tags for ani- mals, where also robustness and simplicity are important factors.

SUMMARY OF TH E I NVENTION

The object of the present invention is to solve the above problem, and thus offer an improved remote registering of tag units.

According to one aspect of the invention, the object is achieved by an apparatus according to the preamble of claim 1 , which comprises an auxiliary antenna configured to receive a signal representing a primary portion of the emitted alternating electromagnetic field, and wherein the processing unit is configured to discriminate the identification data based on the signal representing the primary portion of the emitted alternating electromagnetic field.

This design is advantageous because the combined transmitter- receiver apparatus enables a very power efficient detection of low-complexity tag units. Consequently, data from such tag units may be read out from relatively long distances via an apparatus having moderate energy consumption . According to one preferred embodiment of this aspect of the invention , the transmitter antenna contains at least one loop delimiting a first area and the receiver antenna contains at least one loop delimiting a second area. The transmitter and receiver antennas are further arranged relative to one another such that the second area overlaps a portion of the first area. This design of the apparatus is advantageous because it enables a very power efficient detection of low-complexity tag units. Namely, if the overlap is such that the electromagnetic field picked up by the second area overlapping the first area is equal to the electromagnetic field picked up by the non-overlapping part of the second area, however in reverse polarity, the energy emitted from the transmitter antenna is cancelled out in the receiver antenna. Consequently, tag unit data may be read out from relatively long distances while only consuming a moderate amount of energy in the apparatus.

Preferably, the auxiliary antenna contains at least one loop, which , in turn, is enclosed by the at least one loop of the transmitter antenna. This vouches for that the signal component indeed represents a primary portion of the alternating electromagnetic field emitted from the transmitting antenna.

According to yet another embodiment of this aspect of the invention, the receiver antenna contains at least one antenna coil that is arranged in a transmission path for the alternating elect- romagnetic field. Thus, the receiver antenna may pick up the emitted alternating electromagnetic field in a straightforward manner.

According to another preferred embodiment of this aspect of the invention, the processing unit is configured to derive a phase angle of the electric source signal as a function of time based on the signal representing the primary portion of the alternating electromagnetic field. Moreover, the processing unit is configured to discriminate the identification data based on phase variations of the electric detection signal relative to the phase angle of the electric source signal. Preferably, the processing unit is configured to discriminate the identification data by exclusively analyzing the electric detection signal at predetermined phase angle shifts relative to the electric source signal . Thereby, a highly efficient data-readout is enabled.

According to yet another preferred embodiment of this aspect of the invention, the apparatus contains a case covering the transmitter and receiver antennas. The case has an electromagnetic- field-transparency that is different in different directions, and the case is arranged such that a potential tag unit within the range of operation may be located on an operative side of the transmitter antenna, however is prevented from being located on a passive side of the transmitter antenna. The receiver antenna includes at least one first antenna coil arranged on the operative side. The at least one first antenna coil is located in the transmission path for the alternating electromagnetic field between the transmitter antenna and the potential tag unit within the range of operation. The at least one second antenna coil is arranged on the passive side, and is configured to provide the signal representing the primary portion of the alternating electromagnetic field to the receiver circuit. This arrangement is advantageous because it allows a reliable reception of any identification data signal from a tag unit, and at the same time, it provides a reliable reference signal. According to a further preferred embodiment of this aspect of the invention, the transmitter antenna and the receiver antenna are co-located and arranged relative to one another such that during normal operation of the apparatus a distance between the transmitter antenna and the receiver antenna is shorter than an expected distance between the tag unit and any of the transmitter antenna and the receiver antenna. This design allows a hig hly compact and small-sized apparatus.

According to another preferred embodiment of this aspect of the invention, the processing unit is configured to discriminate the identification data by exclusively analyzing the electric detection signal at time instances corresponding to phase angles where the electric source signal has zero-line passages. Namely, these instances represent optimal sampling points for the type of single sideband signal that the tag unit is presumed to produce in response to the emitted electromagnetic field.

According to a further preferred embodiment of this aspect of the invention, the processing unit contains a sampling circuit, a differential amplifier and a filter unit. The sampling circuit is configured to sample the electric detection signal at the time instances corresponding to the phase angles where the electric source signal has zero-line passages. The differential amplifier is configured to receive the sample values from the sampling circuit, and based thereon form a resultant signal containing a signal component representing the identification data. The filter unit is configured to bandpass filter the resultant signal to produce the identification data. This design is beneficial, since it enables a reliable detection of the identification data.

According to another aspect of the invention, the object is achie- ved by the method according to the preamble of claim 1 1 , wherein a signal representing a primary portion of the emitted alternating electromag netic field is received via an auxiliary antenna, and the identification data are discriminated on the further basis of the signal representing the primary portion of the emitted alternating electromagnetic field. The advantages of this method, as well as the preferred embodiments thereof, are apparent from the discussion above with reference to the proposed apparatus.

According to a further aspect of the invention the object is ac- hieved by a computer program product, which is loadable into the memory of a computer, and includes software adapted to implement the method proposed above when said program is run on a computer.

According to another aspect of the invention the object is achie- ved by a computer readable medium, having a program recorded thereon, where the program is to control a computer to perform the method proposed above when the program is loaded into the computer. Further advantages, beneficial features and applications of the present invention will be apparent from the following description and the dependent claims.

BRI EF DESCRI PTION OF TH E DRAWI NGS

The invention is now to be explained more closely by means of preferred embodiments, which are disclosed as examples, and with reference to the attached drawings.

Figure 1 shows a general overview of the proposed apparatus and a radio environment in which a tag unit can be detected;

Figures 2-5 show antenna arrangements according to embodiments of the invention;

Figure 6 illustrates how a tag unit produces a modified alternating electromagnetic field and how the proposed apparatus may receive a signal based thereon;

Figure 7 shows a schematic block diagram over a processing unit according to one embodiment of the invention;

Figures 8a-f represent graphs exemplifying the signal flow in the apparatus according to an embodiment of the invention which contains a processing unit as shown in Figure 7; and

Figure 9 illustrates, by means of a flow diagram, the general method according to the invention . DESCRIPTION OF PREFERRED EMBODIM ENTS OF THE INVENTION

We refer initially to Figure 1 , which shows a general overview of an apparatus A for contactless identification of a tag unit GX according to the invention .

The tag unit GX is presumed to include circuitry configured to modify an alternating electromagnetic field ΕΜ_Τχ within which the tag unit GX is located. Typically, to this aim, the tag unit GX contains at least one resonance circuit. The apparatus A includes a transmitter circuit TX, a transmitter antenna TA, a receiver circuit RX, a receiver antenna RA and a processing unit PU .

The transmitter circuit TX is configured to generate an electric source signal Ss and, via the transmitter antenna TA connected thereto, emit an alternating electromagnetic field EM_TX from the apparatus A, which alternating electromag netic field ΕΜ_Τχ corresponds to the electric source signal Ss.

The receiver antenna RA is configured to register the alternating electromagnetic field EM_TX and any modifications thereof EM_GX that are caused by the presence of a tag unit GX within a range of operation from the apparatus A. The receiver circuit RX is connected to the receiver antenna RA. Thereby, the receiver circuit RX is further configured to produce an electric detection signal Sd in response to the alternating electromagnetic field ΕΜ_Τχ and EM_Gx registered by the receiver antenna RA.

The processing unit PU is configured to receive the electric detection signal Sd. Based on the electric detection signal Sd, the processing unit PU is configured to discriminate identification data GXid of any tag unit GX having modified the alternating electromagnetic field EM_GX.

To provide a signal component Sa (i.e. a reference signal) representing a primary portion of the emitted alternating electro- magnetic field E M_TX to the processing unit P U , and thus facilitate discriminating the identification data GXid, the receiver antenna RA is arranged relative to the transmitter antenna TA and a potential tag unit GX, such that a portion of the emitted alternating electromagnetic field EM_TX always reaches the receiver antenna RA essentially unmodified, irrespective of whether or not a tag unit GX is present within the range of operation. Figures 2, 3 and 6 show different examples how this may be accomplished. Thus, more precisely, the processing unit P U is configured to discriminate the identification data GXid based on the electric detection signal Sd and by utilizing the signal component Sa representing said primary portion, i.e. a signal originating from the primary portion of the alternating electromagnetic field ΕΜ_Τχ. Referring now to Fig ure 2, we see a part of an apparatus A according to a first embodiment of the invention .

The receiver antenna RA is arranged in a transmission path for the emitted alternating electromagnetic field EM_TX between the transmitter antenna (not shown) and a potential tag unit GX within the range of operation. This means that the receiver antenna RA will register the emitted alternating electromagnetic field EMJX as well as any modifications thereof EM_GX caused by the tag unit GX.

The receiver antenna RA here has at least two loops of antenna coil , where a first loop + is twisted 180 degrees and in phase opposition with a second loop -. The first and second loops +/- are arranged in the transmission path for the emitted alternating electromagnetic field EM_TX, such that the primary portion of the emitted alternating electromagnetic field E M_TX that passes through both the first and second loops +/- is cancelled out. However, the tag unit GX is expected to be located such that the distance between the tag unit GX and the first loop + is always different from the distance between the tag unit GX and the second loop -. In other words, the apparatus A is positioned such that the tag unit GX may only be located where its distance to the receiver antenna RA is shorter than its distance to the transmitter antenna TA. I .e. , in Figure 2, the tag unit is located on the general right hand side. As a result, the modified alternating electromagnetic field EM_Gx will not cancel out in the receiver antenna, and can therefore be detected by the apparatus A.

The above spatial relationship can be ensured by a case (or an- tenna dome) covering the transmitter and receiver antennas TA and RA respectively, where the case has an electromagnetic- field-transparency that is different in different directions and is arranged such that a potential tag unit GX within the range of operation may be located on an operative side of the transmitter antenna TA however is prevented from being located on a passive side of the transmitter antenna TA.

Moreover, according to the invention, the apparatus A has an auxiliary antenna SWA, which is configured to receive the primary portion of the emitted alternating electromagnetic field ΕΜτχ to represent the sig nal component Sa. The signal component Sa is then forwarded to the processing unit PU for use when discriminating the identification data GXid.

Figure 3 shows an apparatus A according to a second embodiment of the invention. Here, the receiver antenna RA contains at least one first antenna coil RA1 and at least one second antenna coil RA2.

The at least one first antenna coil RA1 is arranged on the operative side of the transmitter antenna TA, which in Fig ure 3, is the general right hand side. The at least one first antenna coil RA1 is further located in the transmission path for the alternating electromagnetic field between the transmitter antenna TA and a potential tag unit GX within the range of operation on the operative side of the transmitter antenna TA. Consequently, the at least one first antenna coil RA1 may receive both the primary portion of the emitted alternating electromagnetic field ΕΜ_Τχ and any modifications thereof EM_Gx due to the presence of a tag unit GX. The at least one second antenna coil RA2 is arranged on the passive side of the transmitter antenna TA, which passive side is opposite to the operative side. Thereby, the at least one second antenna coil RA2 is configured to receive the primary portion of the emitted alternating electromagnetic field EM_TX. Thus, the at least one second antenna coil RA2 can provide the signal component Sa to the receiver circuit RX.

Each of figures 4 and 5 show an apparatus A according to a preferred embodiment of the invention . Here, the transmitter antenna TA contains at least one loop and delimits a first area A1 . Analogous to the transmitter antenna TA, the receiver antenna RA contains at least one loop, and delimits a second area A2.

Due to physical constraints, since for practical reasons, the apparatus A must be relatively compact, it cannot be avoided that the receiver antenna RA is arranged in a transmission path for the alternating electromagnetic field EMTX emitted from the transmitter antenna TA. In other words, the receiver antenna RA will register the emitted alternating electromagnetic field EMTX as well as any modifications thereof EMGX caused by the tag unit GX.

To minimize the amplitude of the electromagnetic field ΕΜ_Τχ emitted from the transmitter antenna TA and picked up directly by the receiver antenna RX, the receiver and transmitter antennas RX and TX respectively should overlap one another to such an extent that the field picked up by the second area A2 overlapping the first area A1 is equal to the field picked up by the non-overlapping part of the second area A2, however in reverse polarity. I n other words, the transmitter antenna TA and the receiver antenna RA are arranged relative to one another, such that the second area A2 delimited by the at least one loop of the receiver antenna RA overlaps a particular portion of the first area A1 delimited by the at least one loop of the transmitter antenna TA. Namely, given appropriate proportions of the overlap and the areas A1 and A2, this results in that the direct wave of the electromagnetic field ΕΜ_Τχ emitted from the transmitter antenna TA is cancelled out in the receiver antenna RX. This effect can be improved by arranging the transmitter and receiver antennas TA and RA relative to one another such that the at least one loop of the transmitter antenna TA crosses the at least one loop of the receiver antenna RA at an essentially straight angle. Further, to optimize the areas A1 and A2 with respect to a largest possible sensitivity per unit size of the apparatus A, it is advantageous if the at least one loop of each of the transmitter and receiver antennas TA and RA has an overall outline of a general rectangular shape. Moreover, as shown in Figure 4, each of the general rectangular shapes may include two adjoining corners that are beveled. In this embodiment of the invention, the transmitter and receiver antennas TA and RA are specifically arranged relative to one another such that a beveled portion 41 0 and 420 of the at least one loop of the transmitter antenna TA crosses a beveled portion 430 and 440 respectively of the at least one loop of the receiver antenna RA. This is desirable because then the respective areas covered by the antennas can be made as large as possible; and at the same time, the straight-angle crossing condition for minimizing the coupling between the antennas TA and RA can be fulfilled.

Additionally, according to one embodiment of the invention , the at least one loop of the transmitter antenna TA is essentially pa- rallel to the at least one loop of the receiver antenna RA. Thereby, undesirable pick-up of electromagnetic energy directly from the transmitter antenna TA can be made relatively low.

Figure 6 shows the apparatus A according to another embodi- ment of the invention . As described above, the apparatus A emits an alternating electromagnetic field EM_TX via a transmitting antenna TX. The alternating electromagnetic field EM_TX covers an operative range from the apparatus A. We assume that a tag unit GX is located within the operative range, and thus produces a modified alternating electromagnetic field EM_GX in response to the emitted alternating electromagnetic field EM_TX.

This modification may involve phase-shift modulating of a data signal onto the emitted alternating electromagnetic field ΕΜ_Τχ , where the data signal has a rate substantially lower than the fre- quency of the emitted alternating electromagnetic field ΕΜ_Τχ , say a factor 100 lower, and the data signal represents an identification of the tag unit GX. Nevertheless, due to a resonance circuit in the tag unit GX, the modification therein typically also results in a -90 degrees phase shift of the emitted alternating electromagnetic field EM_TX. The emitted alternating electromagnetic field EMjx may thus be regarded as a -90° phase shifted, single-side-band modulated signal propagating towards the apparatus A resulting from a reflection of the emitted alternating electromagnetic field EM_TX in the tag unit GX. The operative range is defined as the distance from the apparatus A within which a tag unit GX must be located in order to enable the apparatus A to discriminate identification data GXid from its modified alternating electromagnetic field EM_GX. Since the tag unit GX is a truly passive element, and the power level of the electromagnetic field decreases with a cubic relationship to the distance, the operative range is relatively short. Nevertheless, a power level difference of 80- 100 dBA between the EM_TX and EMQX fields is normally acceptable. This is explained by the fact that, as explained above, the emitted alternating electro- magnetic field EM_TX cancels out in the receiver antenna RA, whereas the modified alternating electromagnetic field EM_GX does not.

An auxiliary antenna SWA in the apparatus A is configured to re- ceive a signal Sa representing the primary portion of the emitted alternating electromagnetic field EM_TX and forward this signal Sa to the processing unit PU . Further, the processing unit PL) is preferably configured to derive the signal component Sa to represent a phase angle of the electric source signal Ss as a func- tion of time, and finally discriminate the identification data GXid based on the phase variations of the electric detection signal Sd relative to the phase angle of the electric source signal Ss.

Preferably, the transmitter antenna TA and the receiver antenna RA are co-located and arranged relative to one another, such that during normal operation of the apparatus A, a distance between the transmitter antenna TA and the receiver antenna RA is shorter than an expected distance between the tag unit GX and any of the transmitter antenna TA and the receiver antenna RA. As described above, this relationship between said distances can be guaranteed by placing the transmitter and receiver antennas TA and RA behind an antenna dome, where the distance from the respective antennas and the dome exceeds the distance between the transmitter antenna TA and the receiver antenna RA. Namely, thereby, any tag unit TX must always be further away from the transmitter and receiver antennas TA and RA than the distance between the two of them. Such a design is, of course, enabled by the proposed use of the signal component Sa representing the primary portion of the emitted alternating electromagnetic field EM_TX. The relatively short distance between the transmitter and receiver antennas TA and RA allows a highly compact and small-sized apparatus A, especially compared to a design where the transmitter and receiver antennas are arranged on different sides of aisle (or similar) along which individuals carrying the tag units GX proceed. Figure 7 shows a schematic block diagram of the processing unit PU according to one embodiment of the invention, and Figures 8a to 8f represent graphs illustrating the different signals in the processing unit PU . Figure 8a shows the electric source signal Ss as a function of the phase angle φ. The electric source signal Ss is fed into a sampling circuit SC of the processing unit PU . In this embodiment, the sampling circuit SC, in turn, includes a phase shifting unit PPh, which is configured to delay the electric source signal Ss so as to produce a delayed signal Sa_-90°, which corresponds to a -90 degrees phase shift of the electric source signal Ss.

The delayed signal Sa.₉₀», which is illustrated in Figure 8b as a function of time t, is fed to each of a first switch unit T1 and a second switch unit T2 in the sampling circuit SC. Both the switch units T1 and T2 receive the electric detection signal Sd from the receiver circuit RX. The first switch unit T1 is configured to be closed briefly, e.g . via a diode circuit and an associated capacitor C 1 , and thus pass through the electric detection signal Sd at time instances t-ι , t₃, t_{i (} t_n when the delayed signal Sa__g0° has its maximum positive amplitude. Figure 8c represents a signal Sa_-90°p, which reflects this operation of the first switch unit T1 as a function of time t. Analogously, the second switch unit T2 is configured to be closed briefly, e.g . via a diode circuit and an associated capacitor C2, and thus pass through the electric detection signal Sd at time instances t₂, ... , t_i+1 when the delayed signal Sa_-90° has its maximum negative amplitude. Figure 8d represents a signal Sa_-90°N , which reflects this operation of the second switch unit T2 as a function of time t.

Thus, the switch units T1 and T2 produce a respective series of sampled values Sd_Ps and Sd_Ns from the electric detection signal Sd. Due to the phase shift between the electric detection signal Sd) and the emitted electric source signal Ss, the time instances t₂, t₃, ti, t_i+i , t_n when the electric detection signal Sd is sampled correspond to the phase angles φ where the electric source signal Ss has zero-line passages. In other words, the processing unit PL⁾ is configured to exclusively analyze the electric detection signal Sd at predetermined phase angle shifts relative to the electric source signal Ss. As explained below, this analysis forms a basis for discriminating the identification data GXid.

More precisely, according to this embodiment of the invention, the sample values Sd_Ps and Sd_Ns are fed into a differential amplifier D, such that the values Sd_Ps from the first switch unit T1 are associated with a positive sign and the values Sd_Ns from the second switch unit T2 are associated with a negative sign. In response thereto, the differential amplifier D produces a resultant signal R, which is bandpass filtered in a filter unit BPF having a passband matched to a resonance frequency of the tag unit GX. Consequently, based on the resultant signal R, the filter unit BPF produces identification data GXid, for instance indicating identity information pertaining to an animal carrying the tag unit GX.

Preferably, the apparatus A contains, or is communicatively con- nected to, a memory unit M storing a computer program product, which contains software for controlling the apparatus A to perform the above-described actions when the computer program product is run on a processor in the processing unit PU .

In order to sum up, we will now describe the general method ac- cording to the invention with reference to the flow diagram in Figure 9.

In a first step 910, the transmitter circuit TX generates an electric source signal Ss and emits a corresponding alternating electromagnetic field ΕΜτχ from the apparatus A via a transmitter antenna TA.

A step 920, then registers the alternating electromagnetic field ΕΜτχ as well as any modifications thereof EM_Gx due to a tag unit within the range of operation from the apparatus A. In parallel with step 920, a step 930 registers a signal Sa representing a primary portion of the alternating electromagnetic field ΕΜ_Τχ.

Thereafter, a step 940 discriminates the identification data GXid from the alternating electromagnetic fields ΕΜ_Τχ and EM_Gx re- gistered in step 920 by utilizing the signal Sa derived in step 930. Subsequently, the procedure loops back to step 910.

All of the process steps, as well as any sub-sequence of steps, described with reference to Figure 9 above may be controlled by means of a programmed computer apparatus. Moreover, al- though the embodiments of the invention described above with reference to the drawings comprise computer apparatus and processes performed in computer apparatus, the invention thus also extends to computer programs, particularly computer programs on or in a carrier, adapted for putting the invention into practice. The program may be in the form of source code, object code, a code intermediate source and object code such as in partially compiled form, or in any other form suitable for use in the implementation of the process according to the invention. The program may either be a part of an operating system, or be a separate application. The carrier may be any entity or device capable of carrying the program. For example, the carrier may comprise a storage medium , such as a Flash memory, a ROM (Read Only Memory), for example a DVD (Digital Video/Versatile Disk), a CD (Compact Disc) or a semiconductor ROM, an EP- ROM (Erasable Programmable Read-Only Memory), an EEPROM (Electrically Erasable Programmable Read-Only Memory), or a magnetic recording medium, for example a floppy disc or hard disc. Further, the carrier may be a transmissible carrier such as an electrical or optical signal which may be conveyed via elect- rical or optical cable or by radio or by other means. When the program is embodied in a signal which may be conveyed directly by a cable or other device or means, the carrier may be constituted by such cable or device or means. Alternatively, the carrier may be an integrated circuit in which the program is embedded, the integrated circuit being adapted for performing , or for use in the performance of, the relevant processes.

The term "comprises/comprising" when used in this specification is taken to specify the presence of stated features, integers, steps or components. However, the term does not preclude the presence or addition of one or more additional features, integers, steps or components or groups thereof.

The invention is not restricted to the described embodiments in the figures, but may be varied freely within the scope of the claims.

Claims

1 . An apparatus (A) for contactless identification of a tag unit (GX) having circuitry configured to modify an alternating electromagnetic field (EMJX) within which the tag unit (GX) is located, the apparatus (A) comprising :

a transmitter circuit (TX) configured to generate an electric source signal (Ss);

a transmitter antenna (TA) connected to the transmitter circuit (TX), configured to receive the electric source signal (Ss) and based thereon emit an alternating electromagnetic field (EMJX) from the apparatus (A);

a receiver antenna (RA) configured to register the alternating electromagnetic field (EM_TX) and any modifications thereof (E M_GX) due the presence of a tag unit (GX) within a range of operation from the apparatus (A);

a receiver circuit (RX) connected to the receiver antenna (RA) and configured to produce an electric detection signal (Sd) in response to the alternating electromagnetic field (ΕΜ_Τχ, E MQX) registered by the receiver antenna (RA); and

a processing unit (PU) configured to receive the electric detection signal (Sd), and based thereon discriminate identification data (GXid) of any tag unit (GX) having modified the alternating electromagnetic field (EM_GX) , characterized in that

the apparatus comprises an auxiliary antenna (SWA, RA2) configured to receive a signal (Sa) representing a primary portion of the emitted alternating electromagnetic field (ΕΜ_Τχ), and the processing unit (PU) is configured to discriminate the identification data (GXid) based on the signal (Sa) representing the primary portion of the emitted alternating electromagnetic field (EM_TX).

2. The apparatus (A) according to claim 1 , wherein the transmitter antenna (TA) comprises at least one loop delimiting a first area (A1 ), the receiver antenna (RA) comprises at least one loop delimiting a second area (A2), and the transmitter and receiver antennas (TA, RA) are arranged relative to one another such that the second area (A2) overlaps a portion of the first area (A1 ).

3. The apparatus (A) according to claim 2, wherein the auxiliary antenna (SWA) comprises at least one loop, said at least one loop being enclosed by the at least one loop of the transmitter antenna (TA).

4. The apparatus (A) according to any one of the preceding claims, wherein the receiver antenna (RA) comprises at least one antenna coil (RA1 , RA2) arranged in a transmission path for the alternating electromagnetic field (ΕΜ_Τχ, EM_Gx).

5. The apparatus (A) according to any one of the preceding claims, wherein the processing unit (PU) is configured to:

derive a phase angle (cp) of the electric source signal (Ss) as a function of time (Sa__90°) based on the signal (Sa) represen- ting the primary portion of the alternating electromagnetic field (E M-™), and

discriminate the identification data (GXid) based on phase variations of the electric detection signal (Sd) relative to the phase angle (φ) of the electric source signal (Ss).

6. The apparatus (A) according to any one of the preceding claims, comprising a case covering the transmitter and receiver antennas (TA, RA), the case having an electromagnetic-field- transparency that is different in different directions and is arranged such that a potential tag unit (GX) within the range of operation may be located on an operative side of the transmitter antenna (TA), however is prevented from being located on a passive side of the transmitter antenna (TA), and wherein the receiver antenna (RA) comprises:

at least one first antenna coil (RA1 ) arranged on the ope- rative side, which at least one first antenna coil (RA1 ) is located in the transmission path for the alternating electromagnetic field (EMjx, EMQX) between the transmitter antenna (TA) and the potential tag unit (GX) with in the range of operation , and

at least one second antenna coil (RA2) arranged on the passive side, the at least one second antenna coil (RA2) being configured to provide the signal (Sa) representing the primary portion of the alternating electromag netic field (ΕΜ_Τχ) to the receiver circuit (RX).

7. The apparatus (A) according to claim 6 , wherein the transmitter antenna (TA) and the receiver antenna (RA) are co- located and arranged relative to one another and the electro- magnetic-field transparent case such that a potential tag un it (GX) within the range of operation may exclusively be located so that a distance between the transmitter anten na (TA) and the receiver antenna (RA) is shorter than the distance between the potential tag unit (GX) and any of the transmitter antenna (TA) and the receiver antenna (RA).

8. The apparatus (A) according to any one of the preceding claims , wherein the processing unit (PU) is config ured to discriminate the identification data (GXid) by exclusively analyzi ng the electric detection sig nal (Sd) at predetermined phase angle shifts relative to the electric source signal (Ss).

9. The apparatus according to claim 8, wherein the processing unit (PU) is config ured to discriminate the identification data (GXid) by exclusively analyzing the electric detection signal (Sd) at time instances (t _; t₂, t₃, tj, t_n) corresponding to phase angles (cp ) where the electric source sig nal (Ss) has zero-line passages.

1 0. The apparatus (A) according to claim 9, wherein the processing unit (P U) comprises:

a sampli ng circuit (SC) config ured to sample the electric detection signal (Sd) at the time instances (t-i , t₂, t₃, t, , t_n) corresponding to the phase angles (<p) where the electric source sig nal (Ss) has zero-line passages and thus produce sample values

a differential amplifier (D) configured to receive the sample values (Sd_Ps, Sd_Ns), and based thereon form a resultant signal (R) containing a signal component representing the identification data (GXid), and

a filter unit (BPF) configured to bandpass filter the resultant signal (R) to produce the identification data (GXid).

1 1 . A method of contactless identification of a tag unit (GX) having circuitry configured to modify an alternating electromag- netic field (EM) within which the tag unit (GX) is located, the method comprising :

generating an electric source signal (Ss);

emitting , based on the electric source signal (Ss), an alternating electromagnetic field (EM_TX) from a transmitting antenna (TA);

registering, via a receiver antenna (RA), the alternating electromagnetic field (EMJX) and any modifications thereof (E M_Gx) due the presence of a tag unit (GX) within a range of operation ; producing an electric detection signal (Sd) in response to the registered alternating electromagnetic field (EM_GX); and

discriminating identification data (GXid) of any tag unit (GX) having modified the alternating electromagnetic field (EMQX), characterized by:

receiving , via an auxiliary antenna (SWA, RA2), a signal (Sa) representing a primary portion of the emitted alternating electromagnetic field (EM_TX), and

discriminating the identification data (GXid) on the further basis of the signal (Sa) representing the primary portion of the emitted alternating electromagnetic field (EM_TX).

12. The method according to claim 1 1 , comprising :

deriving a phase angle (φ) of the electric source signal (Ss) as a function of time (Sa__90°) based on the signal (Sa) representing the primary portion of the emitted alternating electromagnetic field (EMjx); and discriminating the identification data (GXid) based on phase variations of the of the electric detection signal (Sd) relative to the phase angle (φ) of the electric source signal (Ss).

13. The method according to any one of claims 1 1 or 12 , wherein a case covers the transmitter and receiver antennas

(TA, RA), the case having an electromagnetic-field-transparency that is different in different directions, and the case is arranged such that a potential tag unit (GX) within the range of operation may be located on an operative side of the transmitter antenna (TA) however is prevented from being located on a passive side of the transmitter antenna (TA), the method comprising :

receiving the modified alternating electromagnetic field (EMGX) via at least one first antenna coil (RA1 ) arranged on an operative side of the transmitter antenna (TA), which at least one first antenna coil (RA1 ) is located in the transmission path for the alternating electromagnetic field (ΕΜ_Τχ, EM_Gx) between the transmitter antenna (TA) and a tag unit (GX) within the range of operation, and

receiving the signal (Sa) representing the primary portion of the alternating electromagnetic field (EM_TX) via at least one second antenna coil (RA2) arranged on a passive side of the transmitter antenna (TA).

14. The method according to any one of claims 1 1 -13, comprising discriminating the identification data (GXid) by exclusi- vely analyzing the electric detection signal (Sd) at predetermined phase angle shifts relative to the electric source signal (Ss).

15. The method according to claim 14, comprising discriminating the identification data (GXid) by exclusively analyzing the electric detection signal (Sd) at time instances (ti , t₂, t₃, t,, t_n) corresponding to phase angles (φ) where the electric source signal (Ss) has zero-line passages.

16. The method according to claim 1 5 , comprising : sampling the electric detection signal (Sd) at the time instances (t-i , t₂, t₃, tj, t_n) corresponding to the phase angles (cp) where the electric source signal (Ss) has zero-line passages to produce sample values (Sd_Ps, Sd_Ns),

forming, based on the sample values (Sd_Ps, Sd_Ns), a resultant signal (R) containing a signal component representing the identification data (GXid), and

bandpass filtering the resultant signal (R) to produce the identification data (GXid).

17. A computer program product loadable into the internal memory (M) of a computer, comprising software for performing the steps of any one of the claims 1 1 to 16 when the computer program product is run on the computer.

18. A computer readable medium (M), having a program recor- ded thereon, where the program is to make a computer perform the steps of any one of the claims 1 1 to 16.