Abstract:
The RFID system is for automatic recognition of each one or all of a plurality of objects located within an interrogation zone. It is applicable for stock-taking or control of goods such as food. The objects provided with tags having transponders carrying RFID codes individually are sequentially scanned and activated one by one. Interrogation signals are transmitted to the tags based on the reader antennas and the configurations and locations of the tags. Signals returned from the transponders of the tags are processed for recognizing the locations of the selected tags and the electronic contents of the tags. The operation continues until the recognition and location of all tags in the entire interrogation zone have been completed.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     This invention relates to systems of maintaining the inventory of objects provided with radio-frequency transducers such as tags or transponders containing electronic codes for their recognition. Such devices are commonly known as radio frequency identification devices (RFID). More specifically, this invention relates to radio-frequency methods of spatial resolution of tags, RFID tag and tag activation device. A RFID consists of a reader and transponders; the latter are affixed on objects which are subject to inventory and are located in a storage such as a warehouse.  
         [0003]     2. Description of Prior Art  
         [0004]     RFID methods and systems provide the recognition of objects with identification tags affixed thereon. The process of tag recognition must be accomplished at high speed and with minimum error. In this process it is necessary to determine the tag location or direction relative to a reader.  
         [0005]     Each RFID consists of a reader and a transponder with the latter affixed on the object subject to inventory. Readers are provided for primarily reading tag codes and, some of them, searching for tag direction only. The reader transmits a tag activation signal for all tags in the interrogation zone simultaneously, and adjusts the activation signal which has been sent in advance to the tags with known codes. Tags activated in such a manner transmit response signals which carry information of tag electronic codes. These signals reach the reader practically simultaneously. For a small number of tags, for example, from one to five, because of the differences in electronic circuit parameters, tags are activated in an insignificant time lag, which allows a reader to read codes by activating tags repeatedly in order to increase the probability of codes recognition. When a larger number of tags are to be read by the readers, tag signals reach the reader practically simultaneously, which may result in failure to recognize the objects with adequate accuracy.  
         [0006]     It is also very important to authenticate the tags in reading the memory content of each tag when a plurality of tags are located in the tag interrogation zone simultaneously. The RFID HANDBOOK by Klaus Finkenzeller, Carl Hansen Verlag, Munich/FRG, 1999 outlines four methods of solving the problem of space, frequency, code and time discriminations in RFID. U.S. Pat. No. 6,600,443 and U.S. Pat. No. 6,476,756 both to J. A Landt, and U.S. Pat. No. 6,069,564 to R. Hatano et al illustrate methods and systems of tag reading and determination of its direction. Both U.S. Pat. No. 6,600,443 and No. 6,476,756 to J. A. Landt illustrate a method of tag signal structure analysis while U.S. Pat. No. 6,069,564 by R. Hatano et al proposes a multi-directional RFID antennae for this purpose.  
         [0007]     U.S. Pat. No. 6,034,603 to W. E. Steeves and U.S. Pat. No. 6,354,493 to J. Mon show technical solutions for reducing the probability of recognition error on the basis of selecting RFID tag search criteria, generation feedback signals according to the ratio of RFID tags matching the search criteria to the total number of RFID tags received.  
         [0008]     U.S. Pat. No. 2,452,351 to H. L. Bloxom et al and Canadian Patent No. 2,437,888 describe tag reader systems and tag control and reading algorithms of signal processing for one or several readers.  
         [0009]     Canadian patents No. 2,447.975 to P. M. Eisenberg et al, and No. 2,399,092, and No. 2,450,189 both to P. A. Sevcik et al describe aspects of collection and use of data obtained by RFID tag interrogation, in particular, by comparing information obtained through interrogation of tags with the data recorded during repeated interrogations.  
         [0010]     U.S. Pat. No. 6,317,028 to C. Valinlis, U.S. Pat. No. 5,822,714 to R. T. Cato, U.S. Pat. No. 6,034,603 to W. E. Steeves and Canadian patent No. 2,447,975 to P. M. Eisenberg et al show RFID systems of tag recognition for the case of a plurality of radio frequency identification tags. To effectively recognise tags, a number of other technical solutions assume a tags&#39; data base as previously known and perform its current status control through comparison of the read current values with the data of a base as shown in U.S. Pat. No. 5,822,714 to R. T. Cato. U.S. Pat. No. 6,034,603 to W. E. Steeves also shows such a method and system of tag construction with improved tag interference avoidance in which a tag includes both a receiver module and a processor, while the generation of a signal is decided as a result of analysis of radio frequency activity.  
         [0011]     All of the above prior art patents fail to teach, or even suggest, any RFID method and system possessing features which can perform a recognition and locating functions in case of a plurality of objects, and reading the codes and locating tags of both single decoding or working simultaneously with large numbers of articles, under conditions of locating the inventory objects on the plane or in the random volume with minimization of errors caused by reflection of signals from surrounding surfaces.  
       SUMMARY OF THE INVENTION  
       [0012]     The principal object of the present invention is to provide recognition systems with radio frequency identification devices (RFID) and, more specifically, to provide radio frequency methods of three-dimensional tag selection, creation of tag activation devices and their algorithms as well as tag design.  
         [0013]     The read range of the reader is determined according to dimensions of an interrogation zone and a search starting point, the tag&#39;s possible location is selected in the form of a small spatial domain namely a local interrogation zone. The reader starts transmitting tag activating signals through three spatially separated omnidirectional antennae. The time of each signal transmission is calculated in accordance with the tag&#39;s assumed location, which is being entered into the reader&#39;s memory. The signals are received by each of the tags, and only the tag for which the reader signals are calculated and transmitted according to the specific formulas, will be activated. The activated tag emits its own identification signal which carries the information about the individual tag code. This identification signal is received by the reader and a tag code is selected and entered into the reader&#39;s memory according to the preliminarily calculated tag location. Following the tag&#39;s assumed location having been selected, calculated, and entered into the readers&#39; memory, the next signal sequence transmission will be calculated and the signals are transmitted through the reader&#39;s antennae, etc. The entire sequence is repeated for scanning the entire interrogation zone.  
         [0014]     The invention possesses numerous benefits and advantages over known RFID systems. In particular, the invention permits the reduction of the time of search and recognition of tags when there are large numbers of tags to be recognized within an interrogation zone. It can locate each one of a plurality of objects and increases the probability of reading the codes without error. Noise immunity is increased due to the elimination of false responses when receiving signals are reflected from random surfaces such as the warehouse walls, shelves, adjacent articles, container surfaces, etc. One embodiment of the invention can be used with existing tags by providing only minor modifications of the input stages of the existing transponders. It may be used in a single-channel, or two-channel, or multi-channel systems. The universal character of the system allows it to be used as a mobile or a stationary device, as well as a two-dimensional or a three-dimensional space version.  
         [0015]     As a whole, the present invention resolves the complex problem in object location and recognition both in cases of a single decoding, as well as with a large number of articles simultaneously located in an inventory object location in diverse conditions; and it is applicable in a wide variety of fields in manufacturing, shipping or storage.  
         [0016]     The RFID method and system of the present invention are based on the implementation of a Tag Activator for creating specific signals which perform tag interrogation zone multi-step scanning, selected transponder activation, and processing the transponder signal by the reader for:  
         [0017]     Determination of the total interrogation zone coordinates and writing them into the reader memory; 
        Determination of local interrogation zone start point coordinates and writing them into the reader memory;     Calculation of activation signal parameters for each reader antennae for assumed tag location, i.e. local interrogation zone;     Creating signals for tag activation—a tag activator coder;     Transmitting of signals by reader antennas;     Receiving of activation signals for processing by the tag activator decoder and making a decision if this tag supposed to be activated or not;     Creation a control signal by the tag activator decoder to activate transponder transmitter and transfer the electronic code of the tag to a reader;     The selected tag signal has been received by a reader, then the tag electronic code is retrieved from a signal and memorized by the reader, and the reader&#39;s memory keeps the tag coordinates, which are in fact the location of the object with a tag;     If in the course of time determined by search area range no response signal has been received, then the following step of search is performed by shifting the local interrogation zone on the coordinate off one step, which is determined by tag activator resolution;     Procedure of activation signals creation, transmitting and processing, tag signal receiving is repeated until the total interrogation zone is completely examined;     Tag electronic codes, their location and other tag information are indicated on the reader&#39;s data base and monitor.       
 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0028]      FIG. 1  is a layout of tags location and two antennae transmitting the activating signals relating to concept of tag activation according to an embodiment of the present invention.  
         [0029]      FIG. 2  is the signals emitted by two antennae of tag activator coder and received them by a tag relating to a concept of tag activation according to an embodiment of the present invention.  
         [0030]      FIG. 3  is a block diagram of tag location decoder for a case referring to according to an embodiment of the present invention.  
         [0031]      FIG. 4  is a layout of activated and non-activated tags and antennae of tag activator coder according to an embodiment of the present invention.  
         [0032]      FIG. 5  is the signals transmitted by three antennae of tag activator coder and received by tag activator decoder operating according to concept of comparison of single pulses of the present invention according to an embodiment of the present invention.  
         [0033]      FIG. 6  is a block diagram of tag activator decoder operating in accordance with the concept of comparison of single pulses according to an embodiment of the present invention.  
         [0034]      FIG. 7  shows a principle of localization and activation of tags in total interrogation zone in two-dimensional Cartesian coordinates according to an embodiment of the present invention.  
         [0035]      FIG. 8  shows a principle of localization and activation of tags in three-dimensional Cartesian coordinates according to an embodiment of the present invention.  
         [0036]      FIG. 9  is the activating signals and tag activator decoder pulse trains operating according to concept of comparison of time intervals according to an embodiment of the present invention.  
         [0037]      FIG. 10  shows the activating signals with different frequency carrier according to an embodiment of the present invention.  
         [0038]      FIG. 11  is a block diagram of tag activator coder for activating signals with different carrier according to an embodiment of the present invention.  
         [0039]      FIG. 12  is pulse train of activating signals according to an embodiment of the present invention.  
         [0040]      FIG. 13  is the activating signals for a case of tag activation by pulses with randomized envelope according to an embodiment of the present invention.  
         [0041]      FIG. 14 . is a block diagram of tag activator decoder for a case of tag activation by pulse train according to an embodiment of the present invention.  
         [0042]      FIG. 15 . is a block diagram of tag activator decoder for a case of tag activation by pulses with randomized envelope according to an embodiment of the present invention.  
         [0043]      FIG. 16  is the signals transmitted by tag activator coder with electronic access key according to an embodiment of the present invention.  
         [0044]      FIG. 17 . is a block diagram of tag activator decoder with electronic access key according to an embodiment of the present invention.  
         [0045]      FIG. 18  is a flow chart of a tag activator coder and reader according to an embodiment of the present invention.  
         [0046]      FIG. 19  is a block diagram of RFID Transponder with build-in tag activator decoder according to an embodiment of the present invention.  
         [0047]      FIG. 20  is a block diagram of RFID reader with build-in tag activator coder according to an embodiment of the present invention.  
         [0048]      FIG. 21  is a block diagram of Amplitude Shift Keying RFID transponder with build-in tag activator decoder according to an embodiment of the present invention.  
         [0049]      FIG. 22  is a block diagram of Amplitude Shift Keying RFID reader with build-in tag activator decoder according to an embodiment of the present invention.  
         [0050]      FIG. 23  is a block diagram of Amplitude Frequency Shift Keying tag with build-in tag activator decoder according to an embodiment of the present invention.  
         [0051]      FIG. 24  is a block diagram of Amplitude Frequency Shift Keying RFID reader with build-in tag activator coder according to an embodiment of the present invention.  
         [0052]      FIG. 25  is a block diagram of RFID transponder with build-in ultrasound tag activator decoder according to an embodiment of the present invention  
         [0053]      FIG. 26  is a block diagram of RFID reader with build-in ultrasound tag activator coder according to an embodiment of the present invention  
         [0054]      FIG. 27  is a block diagram of RFID transponder with build-in light activated tag activator decoder according to an embodiment of the present invention  
         [0055]      FIG. 28  is a block diagram of RFID transponder with build-in light activated tag activator decoder according to an embodiment of the present invention.  
         [0056]      FIG. 29  is a block diagram of Amplitude Shift Keying RFID transponder with build-in tag activator decoder according to an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0057]     With reference to the drawings, the procedure of the activation of tags located within an interrogation zone is shown on  FIGS. 1 and 2 . A tag can be located randomly in points, for example, from Point  1  to Point  5 , representing tags  1  to  5  locating at these points on a flat surface in a two-dimensional interrogation zone. If a tag is located at Point  1  and is transmitting a signal, the latter signal  10  reaches the antenna  11  with time delay t D  and is received by the antennae  11  and  12  with a time delay having a path length difference l 21 . This path length difference is constant for any location of tags  1 ,  2  or  3 , for example, on a hyperbolic curve  8 .  
         [0058]     Whereas in a reversed situation, namely, signals  14  and  15  are simultaneously transmitted by antennae  11  and  12  respectively, the signal  15  from antenna  12  will reach any tag located on the curve  8  with a delay of 1 21 /C relative to the signal  14 , where C is a signal propagation velocity in the given environment. But if the signal  15  is transmitted by 1 21 /C earlier than the signal  14 , then both signals will reach any tag  1 ,  2  or  3  simultaneously. Here and after only signal envelopes for radio frequency signals are shown.  
         [0059]     When two signals  14  and  15  (in the form of pulses) are being transmitted, the signal  15  will be transmitted by the delay time (t o −t 21 ) relative to signal  14 , if the path  7 &gt; the path  6 , it indicates that the tags are located on the left of the middle line  16  or with the delay (t o +t 21 ), if the path  7 &lt;the path  6 , it indicates that the tags are located on the right of the line  16 , where the paths  6  and  7  represent the distances between the tag  1  and antennae  11  and  12  respectively, wherein t o =d/C; and d is the distance  9  between the antennae, and the duration T p  the pulses  14  and  15  is selected from T p &lt;&lt;t o  for determining the system&#39;s range resolution.  
         [0060]      FIG. 2  shows the transmission of pulse signals  17  and  18  respectively from the antenna  12  for the tags  4  and  5 . In such event, if the difference between the times in which these signals are received by tags  4  and  5  is equal to t o .  
         [0061]      FIG. 3  shows the basic tag decoder in the system of the present invention, it consists of a delay device  24  and an AND circuit  25 . Signals  14  and  15  enter the first input of the tag decoder in a propagation time of t D  through the antenna  11  to the tag  1 , and then the second input through the delay device  24  to provide output signals  21  and  22  with the time delay of t o , and due to the selected temporal relations, the AND circuit  25  will create an output signal  23  at the moment when the first input has received signals  19  and  20  from the second antenna, and the second input has a signal from the first antenna with the time delay for the period t o . The output signal  23  is used as the signal for the activation of a tag located at any point of the hyperbolic curve  8 .  
         [0062]     As shown in  FIG. 2 , the tags  4  and  5  are not located on the hyperbolic curve  8 . In such instance, the AND circuit  25  will not produce the coincidence signal due to nonconformity of temporal relations between the signals and, as a result, these tags  4  and  5  will not be activated. The positions of pulses  17  and  18  for tags  4  and  5  show that it would not able to activate these tags. For the above reasons, two omni directional antennae would not provide a single-valued local activation of tags located on the flat surface. Therefore, to activate a tag located in a certain local interrogation zone  1  on the flat surface by antennae  11 ,  12  and  13  as shown in  FIG. 4 , it is necessary to use all these three antennae located along a straight line on the indicated flat surface, although generally antennae can be located randomly in a certain volume.  
         [0063]      FIG. 4  shows that a tag will be activated at point  1  of a flat surface which will the unique point of intersection of two hyperbolic curves  8  and  26 , where the curve  8  is determined by the antennas  11  and  12 , and the curve  26  is determined by the antennae  12  and  13  respectively. The temporal  
         [0000]     relations between the activating signals  14 ,  15  and  33  from antennas  11 ,  12  and  13  respectively are selected similar to the case examined above for the two antennae as shown in  FIG. 1  and  FIG. 3 .  
         [0064]     The operation of the deactivator at the antenna locations shown in  FIG. 4 , is illustrated in  FIG. 5 . As shown, signals  14 ,  15  and  33  are transmitted by antennas  11 ,  12  and  13  respectively with the delay relative to signal  14  for the time period (t o −t 21 ), if the delay periods D 2 &gt;D 1 , or (t o +t 21 ), if the delay periods D 2 &lt;D 1 . Likewise signal  33  is transmitted with the delay relative to signal  14  for the time period (2 t o −t 31 ), if D 3 &gt;D 1 , or (2 t o +t 31 ) if the delay periods D 3 &lt;D 1 . The delay of signal  33  relative to signal  15  can be calculated in the same manner.  
         [0065]      FIG. 5  also shows pulse signals  34  received at point  1  in  FIG. 4  from antennas  11 ,  12  and  13 , and the pulse signals  35  delayed by a time period of t o  pulse signals  34 , and pulse signals  36  delayed by the time period of 2t o  from pulse signals  34 .  FIG. 6  shows the block diagram of the tag deactivator for processing these signals from the three antennae. The deactivator consists of an antenna  29 , a preamplifier  30 , a demodulator  31 , two time delay devices  24  which provide a time delay period of t o , and an AND circuit  32 . The pulse signals  34 ,  35  and  36  serially enter the first input, the second input and the third input of the AND circuit  32  respectively.  FIG. 5  shows these signals coincide only at the moment t a  with a resulting signal  37  appearing at the output of the AND circuit  32 . The signal  37  activates a tag transmitter of the tag located at point  1  in  FIG. 4 . The group Signal  38  consists of pulses  14 ,  15  and  33 . These pulses reach the first input of the AND circuit  32  of another tag located at point  4  in  FIG. 4 . On the other hand when group signals  39  and  40  are provided at the second and third inputs of the AND circuit  32 , the AND circuit  32  will not produce any output signal, thus, no tag will be activated. Therefore, it is possible to activate any tag in a total tag interrogation zone by changing signal delays according to a specific rule well in advance at any point on the surface bearing antennae and tags.  
         [0066]      FIG. 7  shows the reader interrogation zone in the Cartesian coordinates X and Y. To facilitate estimations, antennae  11  and  13  are placed symmetrically relative to the centre of the coordinates, at which an antenna  12  is placed. In the general case, antennae can be placed on the surface within the X and Y coordinates randomly. The search area has, for example, the shape of a rectangle defined by four points, namely point  60  (at coordinates −Rm, 0), point  53  (at coordinates −Rm, Rm), point  54  (at coordinates Rm, Rm), and point  58  (at coordinates Rm, 0), where Rm is the Read Range; X and Y are the coordinates of the present interrogation zone  57 ;          X ( 55 ),          Y ( 56 ) are the steps of scanning on coordinates X and Y respectively; d is the distance between the antennae; and l 31 ( 27 ), l 32 ( 59 ), l 21 ( 10 ) are path length differences of these signals.  
         [0067]     Scanning of the Local interrogation zone (indicated by a circle); is performed step-by-step starting from point  53  (−Rm, Rm) with the step size on X axis determined by value          X (the direction shown by pointer). For signals transmitted by a tag activator coder from reader in the form of amplitude-modulated pulse signals, for example, the dimensions of local interrogation zone are dependent on the pulse duration and it is determined by the range definition          X and          Y.  
         [0000]     Wherein          X=         Y≈Tp×C.  
         [0000]     D 1 , D 2 , D 3  are distances from the antennas to the local interrogation zone.  
         [0068]     To calculate parameters of the activating signals and delay times relative to each other, the following equations are used: 
 
 D 1=✓( x+d ) 2 +( y ) 2   , D 2=✓( x ) 2 +( y ) 2   , D 3=✓( x−d ) 2 +( y ) 2 ;  (1) 
 
 t   21 =( D 2 −D 1)/ C; t   31 =( D 3 −D 1)/ C; t   32 =( D 3 −D 2)/ C.   (2) 
 
         [0069]     To calculate greatest time interval of signal propagation from reader to interrogation zone borders the following equations are used: 
 
 T   R =( Rm   2   +Rm   2 )/ C=Rm✓/ 2/ C.   (3) 
 
         [0070]     To activate a tag in the three-dimensional coordinates as shown in  FIG. 8 , it is necessary to use four antennas  11 ,  12 ,  13 , and  61  while hyperbolic curves  8  and  26  determine the activated tag location in the X, Y plane, and the curve  62  determines the tag location in the three-dimensional space X, Y, and Z.  
         [0071]     The tag activation described above is based on using activating signals in the shape of pulses. For the single-valued activation of a tag, differences between other signal parameters as frequency and phase can be used.  
         [0072]     The main criteria of activation of a tag is the coincidence, at a certain moment of time, of signals transmitted by a reader, which have been previously selected according to the time, frequency or to the phase of transmitting signals. A coincidence must take place at a certain moment of time in the tag decoder.  
         [0073]     Another method is by the comparison of time intervals between signals received by tag from antennas  11  and  12 , in which the time of signal propagation between these antennas is t o .  
         [0074]     As shown in  FIG. 9 , signals  14 ,  15 , and  33  transmitted by antennas  11 ,  12 , and  13  respectively. Signal  15  is transmitted with the delay relative to signal  14  for the time (t o −t 21 ), if D 2 &gt;D 1  or (t o +t 21 ), if D 2 &lt;D 1 . Likewise signal  33  is transmitted with the delay relative to signal  14  for (2t o −t 31 ), if D 3 &gt;D 1  or (2t o +t 31 ), if D 3 &lt;D 1 ; the group signal  34  are received from antennas  11 ,  12 , and  13  at point  1  of  FIG. 4 . The group signal  50  from clock generator, filling the time interval between signals, is received by the tag, from antennas  11  and  12  in which the group signal N 1  is received at the antenna  12  and the group signal N 2  is received at the antenna  13  respectively. As shown, these group signals N 1  and N 2  coincide only for the tags located at point  1  of  FIG. 4 .  
         [0000]     Thus, this coincidence is a main criteria of proper tags activation.  
         [0075]     For other tags, such as tag  4  of  FIG. 4  for example, the interval t* between signals arriving the tag from antennas  11  and  12  is not equal to interval t** between signals arriving the tag from antennas  12  and  13 , it means the number N 1 * is not equal to number N 2 * respectively. At the same time, in order to avoid false activation, the time intervals between signals received from antennas  11  and  12 , by the tag,  12  and  13  must be compared between itself and by the interval t o  as well.  
         [0076]     Another method of tag activation when carrier frequencies of activating signals are different in shown in  FIG. 10  in which Signals  63 ,  64 , and  65  with carrier frequencies ω 1 , ω 2 , ω 3  are transmitted by antennas  11 ,  12 , and  13  respectively of  FIG. 4 . Delay times t 21 , t 31  selected according to the rule of scanning of the total interrogation zone, for example, from left to right, from up to down as shown in  FIG. 7 . Then if tag is located in previously calculated zone with coordinates X,Y. Signals with carrier frequencies ω 1 , ω 2 , ω 3  to reach the tag simultaneously will be sent to tag antenna  29  with delays t 31  for signal  63 , and (t 31 −t 21 ) for signal  64 , and without delay for signal  65  as shown in  FIG. 10 . These signals are amplified by preamplifier  30  as shown in  FIG. 11  and converted in frequency converter  66  with heterodyne frequency ω 0 . The sum of signals with new frequences ω 1 −ω 0 , ω 1 +ω 0 , ω 2 −ω 0 , ω 2 +ω 0 , ω 3 −ω 0 , ω 3 +ω 0  pass through band-pass filters  67 ,  68 , and  69  respectively tuned on frequencies ω 1 −ω 0 , ω 2 −ω 0 , ω 3 −ω 0 . Each of these signals passes through the envelope detector  70  and then is sent to the proper input of AND circuit  32 . When the signals enter the circuit  32  simultaneously, the output signal from the AND circuit will activate the tag transmitter. For the tags which are not in point to be considered the signals are not sent to their inputs simultaneously because the delays t 21  and t 31  are calculated separately for each local interrogation zone and they differ from each other. So the AND circuits  32  of tag activator decoder will not generate any activation signal and no signal will be transmitted by the transponder.  
         [0077]     In some cases it is necessary to use transponders protected from unauthorized access. The modification of such systems is the method described above. This is the way of tag activation using differences in carrier frequency of activating signals transmitting by reader antennae. The other possible options of similar system are RFID systems with activating signals in the form of pulse train or quasi-random signals. Similar systems possess the larger reader range and interference protection because of increasing signal/noise ratio in comparison with single pulse systems.  FIG. 12  shows signals in the system with the transmission of the activating signals in the form of a pulse sequence. The activating signal  14  consists, for example, of four pulses with the same or different duration and transmitted by the first antenna  11  of  FIG. 1 . Signal  15  represents a copy of the first signal shifted for time (t o −t 21 ) and transmitted by antenna  12 . Signals  19  and  20  represent the sum of signals from antennas  11  and  12  received by tag activator decoder. This signal is sent to the direct input of the AND circuit  25  of  FIG. 3  and then sent to the second input of AND circuit as well but delayed for time t o . Four pulses will appear in serially in the output of AND circuit  25  of  FIG. 3 . A block diagram of tag activator decoder for RFID system with activating signals in the form of pulses train is shown in  FIG. 14 . This block diagram is the development of tag activator decoder of  FIG. 6  and differs from it by the introduction of a pulse counter  71 . If number of pulses calculated by a counter in the output of AND circuit  32  concurs with the numbers of activating pulses from the tag activator coder, then the transponder control circuit  108  will create a signal to initialize the tag transmitter.  
         [0078]      FIG. 13  shows signals in the RFID system with the activating signals in the form of quasi-random signals. The activating signal  14  represents, for example, harmonic signal modulated by randomized amplitude of limited duration and transmitted by the first antenna  11  of  FIG. 1  in which only signal envelopes are shown. Signal  15  represents a copy of the first signal displaced for time (t o −t 21 ) and transmitted by antenna  12 . Signals  19  and  20  represent a sum of signals from antennas  11  and  12  received by a tag activator decoder. Referring to  FIG. 15 a  block diagram of tag activator decoder for RFID system with quasi-random signals is illustrated. This tag activator decoder is similar to that shown  FIG. 6  and differs from with the addition of the controller  74  and correlator  75 . Signals  19  and  20  enter the input of signal processor  73  of  FIG. 15 . The signal processor  73  performs an analog-to-digital conversion of the input signals, and then transfers them to the first input of the controller  74  which transfers signals  19  and  20  to the first input of the correlator  75 . Signals  21  and  22  are similar to signals  19  and  20  but delayed for a time period of t o  to be sent to the second input of the correlator  75 . A correlation function  76  as shown in  FIG. 13  will appear from the output of the correlator  75  after the signals  19 ,  20 ,  21  and  22  have been processed. The function  76  has a maximum time of t m  which corresponds to time (t R −t L )/2 in which t R  and t L  are upper and lower borders of the time interval between the end of signal  20  and the beginning of signal  21 . Signals  19  and  20  enter interrogation zone with a time delay of t o  between signals  19  and  20 , and signals  21  and  22  are coincided respectively. The correlator  75  of  FIG. 15  evaluates the position of the maximum value of the correlation function  76  and sends a signal to the transponder control circuit  108  to initiate the tag transmitter. If a tag is located outside of the interrogation zone then the maximum of the the correlation function  76  will be shifted to the left or to the right depending on the tag position and the correlator  75  will not create and send signal to initialize the tag transmitter.  
         [0079]     Another embodiment of the present system is the provision for protection from unauthorized access of the system with an electronic key. An electronic access key is realized as as a system that transmitting a specific signal to open the tag activator decoder before activation signals are sent out. Key signal enters the tag activator decoder in which it is compared with its duplicate in the tag activator decoder memory. If the key signal corresponds with the duplicate, the tag activator decoder will be opened for activation signals processing otherwise the receiver is locked.  
         [0080]      FIG. 16  shows signals in the RFID system with electronic key signals in the form of a pulse train  41 . If the receiver of the tag is opened by the key signal, a specific signal  42  is created to open the tag activator decoder during the time interval t k  sufficient to receive and process activation signals  34  to  37 .  
         [0081]      FIG. 17  shows a block diagram of the tag activator decoder with electronic key stages built-in. A pulse train  41  enters the input of a pulse comparator  45  to compare with its duplicate. In case of complete correspondence of the key signal with its duplicate, the comparator produces an output signal to activate circuit  46  that creates the signal  42 . This signal  42  will open an electronic switch  47  to pass the activation signals  34  to  37  and to activate the tag transmitter as a result.  
         [0082]     The overall operational algorithm of the RFID system of the present invention is shown in  FIG. 18 . The system assumes the technical parameters such as range R m , range definition          X,          Y, location of antennae, and the speed of electromagnetic or ultrasound wave propagation, are all known for establishing a rule of scanning of total interrogation zone. The present algorithm foresees a survey of the total interrogation zone according to the rule: from left to right, from up to down as shown in  FIG. 7 . The first step  77  of the algorithm operation is to turn RFID system on. The next step  79  is entering the data of read range Rm, antenna aperture d, wave propagation speed C, steps of scanning Δx, Δy from a reader keyboard by the operator for calculating the time interval of signal propagation to a maximum remote point of interrogation zone T R  according to formula (3) and the parameter t o . Next step  80  is to set the total interrogation zone boundaries, thereafter step  81  calculates the start point of area scanning (−R m , R m ). Step  85  calculates the ranges D 1 , D 2 , and D 3  from reader antennae to local the center of the interrogation zone according to formulas (1). The time delay t 21  between signals  14  and  15  as shown in  FIG. 5  is determined by step  83 . Depending on the proportion between D 1  and D 2  estimated by step  84 , a time delay t 1  as shown in  FIG. 5  between the signals transmitted by antennas  11  and  12  is chosen and estimated by steps  85  and  86 . Similar delay t 2  between signals  14  and  33  of  FIG. 5  is estimated and calculated by steps  88 ,  89 ,  90  and  91 . The next step  93  is the creation of a pulse train to operate transmitter signals of tag activator coder in accordance with the calculated delays. The values of time delays are also used in the reader intake for the creation of adaptive antenna consisting of three separate antennae. In accordance with these values, it is introduced a time shift between signals received by antennas  11 ,  12 , and  13  to compensate the delays of the signals caused by different time of propagation of these signals from the tag to each antenna and, finally, to provide in-phase or coherent receiving of tag signals to the reader. For example, a signal received by antenna  2  shifts relative to the signal received by antenna  1  by time t 21 , a signal received by antenna  3  shifts relative to the signal received by antenna  1  by time t 31  which creates a reader coherent receiver. The steps  94 ,  95 , and  96  evaluate the time t D  passed after the beginning of transmitting the activating signal up to the current time and are implemented as a timer for comparing time t D  with a time t R  relative to the time of propagation of signals to maximum remote point of the total interrogation zone. If after transmitting of the activating signals by tag activator coder an answer signal from tag is not received by the reader during the time interval t R , it means that there is no tags in the survey local interrogation zone and the next step in scanning of total interrogation zone would be performed. The situation, in which tag signals received by reader but the time of survey of interrogation zone is not expired, is implemented by steps  94 ,  95 , and  96 . Then the scanning of zone continues in the above order to receive a signal of other probable tag or tags located in the same zone. Step  97  saves the tag coordinates and its electronic codes for the creation of database, monitoring of data and the item images of the display. Step  99  creates the next step of scanning the search area by increasing the current meaning of coordinate X to the value ΔX, after that a control of program is transferred to the block  82  for organizing of next cycle of scanning of the search area. If a new meaning of current coordinate exceeded the bound of total interrogation zone resulting from the analysis in step  100 , step  98  will shift the coordinate X to left in a distance with X=−Rm and the coordinate Y will shift for one step down with a distance of Y=Rm−ΔY. Step  101  analyzes the current value of the Y coordinate. If this value when shifted by a step ΔY became negative then the survey of the search area is considered completed, and step  102  makes a creation and ordering of database, data monitoring and printing. Step  103  stops the RFID device after the total interrogation zone is completely scanned. The above described steps  77 - 101  are implemented by an arithmetic and logic program microprocessor in the control loop.  
         [0083]     Referring to  FIGS. 19 and 20 , a block diagram of RFID system is illustrated. It consists of a RFID reader  105  and RFID transponder  109  and a channel called tag activator for activating the transponder. A tag activator coder  106  is implemented in the reader  105  and a tag activator decoder  104  is implemented in a tag to control the transponder  109 . The reader for receiving the tag information signal consists of an antenna  29 , a controller  112  operating for transmission and reception of signals, creation of control and information signals, data accumulation and monitoring, signal processor  111 , the reader receiver  110 , the database  113  and monitor  114  for storage and the display of digital, text and graphic information about the transponders and the code, location etc., of these components.  
         [0084]     The tag activator coder  104  consists of a tag activator controller  116 , an activation signal former  117  and a transmitter  115 . The tag activator controller  116  calculates the signal activation parameters for creating signals in accordance with a rule of total interrogation zone scanning to operate the transmitter  115  and the transmit activation signals by the antennae in the direction of activating tag.  
         [0085]     Tag activator decoder  104  consists of an antenna  29 , a preamplifier  30 , a demodulator  31  for obtaining a signal envelope, a tag location decoder  107  for tag activation signals processing and to create input signal if a tag is supposed to be activated. A transponder control circuit  108  is provided for operating the transmitter of the transponder  109  which is activated when the transponder is connected to a battery with the operation of an electronic switch. The output of the transponder  109  is connected to an antenna for transmitting an information signal containing the tag electronic code. Each transponder is provided with active power supply such as a built-in buttery or a passive power supply  48 . If the transponder is within the range of the reader, a power supply will be induced in the transponder antenna by the electromagnetic or ultrasound field strength.  
         [0086]     The transmitter  115  of tag activator coder, the activation signal former  117 , controller  116 , the antenna  29 , preamplifier  30 , demodulator  31 , tag location decoder  107 , transponder control circuit  108 , other elements of reader  105  and transponder  109  can be implemented in analog hardware, digital hardware and software or in their combination.  
         [0087]      FIGS. 21-22  show a block diagram of RFID system which use amplitude modulated signals, namely, single pulses as activating ones named ASK—Amplitude Shift Keying System consisting of a RFID couple of reader  105  and transponder  109 , and a channel comprises of two devices to activate the transponder, the tag activator coder  106  and the tag activator decoder  104 . The operation of this system is similar to that described above for FIGS.  19  to  20 . But, in addition to that described above, in this system the reader output stages such as that from the omnidirectional antennae  29  and dual directional couplers  118  are used to transmit activation signals from the tag activator coder  106  outward to receive tag signals, as well as to provide power to the tag transmitter. The dual directional couplers  118  uncouples the transmitter and receiver, compensating delay lines  119  for creating a coherent receiver of transponder signals by control of signal delays, controller  112  for controlling transmitting, receiving and creation of activation and information data signals, and accumulation and monitoring of data. The receiver  110  receives RF signal and sends it to the signal processor and controller  112 . A controller creates, operates and monitors data consisting of digital, text and graphic information from transponders in the database storage  113  and monitor  114 . The tag activator coder  106  consists of an activation signal former  117  and transmitter  115 . The controller  112  calculates and creates signals to operate signal former  117 . Radio frequency signals from former  117  enter transmitter  115  to radiate activating pulses outward in accordance with rules of interrogation zone scanning. The tag activator decoder  104  consists of antenna  29 , preamplifier  30  of RF activating signals, demodulator of signals  31 , delay lines  24  and control logic  25 . The control logic  25  compares activating signals as described above for that shown in  FIG. 6 . The control logic  25  sends a signal to the transponder control circuit  108  which controls the transmitter of transponder  109  by operating, for example, an electronic switch connecting the battery to transponder to radiate information signal from the transponder outward to the reader. Each transponder is provided with active or passive power supply  48 .  
         [0088]      FIGS. 23-24  show a block diagrams of RFID system of the present invention which use amplitude modulated signals, namely, single pulses as activating ones with different carrier frequencies, called AFSK—Amplitude and Frequency Shift Keying System consisting of a RFID couple including reader  105  and transponder  109  and a channel of transponder activation having tag activator coder  106  and tag activator decoder  104 . Reader output stages such as omnidirectional antennae  29 , dual directional couplers  118  are used for transmitting activation signals from the tag activator coder  106  outward, to receive transponder signals, as well as to provide transponder transmitter with power. The reader consists of compensating delay lines  119  that create a coherent receiver of transponder signals by control of signal delays, controller  112 , signal processor  111 , receiver  110 , database  113  and monitor  114 . Dual directional couplers  118  uncouple the transmitter and receiver. In operation, the receiver  110  receives the RF signal and forwards it to signal processor and controller  112 . The controller  112  creates, operates and monitors data including digital, text and graphic information from transponders in the database storage  113  and monitor  114 .  
         [0089]     Tag activator coder  106  consists of activation signal former  117  and transmitter  115 . Controller  112  calculates and creates signals to operate the signal former  117 . The former  117  generates three pulses with different carrier frequencies and variable time of transmitting in accordance with a total interrogation zone location. Transmitter  115  sends the activating pulses to proper antennae  29  to radiate them to a search zone. The tag activator decoder  104  consists of antenna  29 , preamplifier of RF for activating signals  30 , mixer  120 , local oscillator  121 , band pass filters  67 ,  68 , and  69 , adder  122 , envelope detector  70 , control logic  32 , and transponder control circuit  108 . Radio frequency signals from the antenna  29  enter the preamplifier  30  input. Mixer  120  converts the carrier frequencies of the activating signals down by mixing them with the signal from a local oscillator  121 . Band pass filters  67 ,  68 , and  69  select and pass low frequency signals in accordance with initial position of each activating signal from the tag activator coder. Envelope detectors  70  create envelopes of activating signals which are fed to the inputs of control logic  32  after summing it in the adder  122 . The control logic  32  compares the activating signals and create an output signal to control the transmitter of the transponder  109  which is actuated by operating an electronic switch for connecting a battery to the transponder so as to radiate the information signal from the transponder outwards to the reader. Each transponder is provided with active or passive power supply  48 .  
         [0090]      FIGS. 25-26  show block diagrams of the RFID system of the present invention, which uses amplitude modulated ultrasound pulses as activating signals named This ultrasound embodiment consists of a RFID couple including the reader  105  and transponder  109  and a channel of transponder activation having tag activator coder  106  and tag activator decoder  104 . The reader consists of at least one radio frequency antenna  29 , dual directional coupler  118 , controller  112 , signal processor  111 , receiver  110 , transmitter  115 , database  113  and monitor  114 . The tag activator coder consists of activation signal former  117 , transmitter  125 , pulse distributor  126  and an ultrasound transducers  127 . In operation, the activation signal former  125  creates activating pulses  14 ,  15 , and  34  as shown in  FIG. 5  in accordance with commands from the controller  112  and sends them to the transmitter  125 . The pulse distributor  126  distributes activating signals to appropriate ultrasound transducers  127  for transmitting them to tag interrogation zone. The tag activator decoder consists of an ultrasound microphone  123 , preamplifier and band pass filter  124 , envelope detector  71 , delay lines  24 , control logic  32 , and transponder control circuit  108 . The ultrasound microphone  123  receives ultrasound pulses and converts them into electrical signals. Band pass filters and amplifier  124  amplify and select activating signals, and the envelope detector  70  creates activating pulse envelopes which are fed to the inputs of control logic  32  after being delayed by the delay lines  24 . The control logic  32  compares activating signals and creates an output signal for controlling the transmitter of transponder  109  after actuating electronic switch for connecting a battery to the transponder to radiate information signal from the transponder outward to the reader. Each transponder is provided with active or passive power supply  48 . Another way to provide transponder of ultrasound RFID system with power supply is to obtain supply voltage  49  from the ultrasound microphone output  123 . The reader may include optionally a RF transmitter  115  to provide a tag with power supply by induced electromagnetic radiation.  
         [0091]      FIGS. 27-28  in combination shows a block diagram of a Light Activated system (LA RFID) according to the present invention, which uses amplitude modulated light pulses as activating signals. The system consists of RFID couple having a reader  105  and transponder  109  and a channel of transponder activation including tag activator coder  106  and tag activator decoder  104 . A reader consists of at least one radio frequency antenna  29 , dual directional coupler  118 , controller  112 , signal processor  111 , receiver  110 , transmitter  115 , data base  113  and monitor  114 . The tag activator coder consists of activation signal former  117 , pulse distributor  131 , and light generators  132 . Activation signal former  117  for creating activating pulses  14 ,  15 ,  34  in accordance with commands from controller  112  as shown in  FIG. 5  and forwards them to the pulse distributor  131 . The pulse distributor  131  distributes activating signals to initialize light emission of appropriate light generator  132  for transmitting them to the tag interrogation zone.  
         [0092]     The tag activator decoder consists of receiver includes photo sensor  128 , amplifier  129 , signal former  130 , delay lines  24 , control logic  32 , and transponder control circuit  108 . A photo sensor  128  receives light pulses and converting them into electrical signals. An amplifier  129  amplifies the activating signals and forwards them to the signal former  130 . Former  130  operates as a low pass filter, for example, for creating activating pulse envelopes, which are fed to the inputs of the control logic  32  after having been delayed at delay lines  24 . The control logic  32  compares the activating signals to create an output signal for controlling the transmitter of the transponder  109  by operating an electronic switch for connecting the power supply battery to the transponder. Each transponder is provided with an active or passive power supply  48 . Another way to provide transponder of Light Activated RFID system with power supply is to obtain supply voltage  49  from photo sensor  128  which converts light into electrical power. The reader may optionally include a RF transmitter  115  to provide the tag with power supply by induced electromagnetic radiation. This is a simple way to activate a selected tag by merely sending a narrow beam of light at the tag location. Some optional elements such as the pulse distributor  131 , delay lines  24 , control logic  107  can be omitted from the Light Activated RFID System block diagram. Another logical device consisting of a controller for comparing envelopes of signals for turning on selected RFID tags by reference level must be provided in tag activator decoder.  
         [0093]      FIG. 29  shows a block-diagram of the tag activator decoder for the above described RFID Reader as shown in  FIG. 22 , in which the method of selective tag activation is provided by receiving signals from reader antennas by a tag and comparing of time intervals between signals and by specific interval. The tag activator decoder  104  consists of an antenna  29 , dual dual directional couple  118  and receiver  133 , including preamplifier of RF activating signals and their demodulator, pulse generator  51 , electronic switch  52 , controller  112 , transponder control circuit  108 , and transponder  109 . The pulse generator  51  produces the clock pulses  50  as shown in  FIG. 29 . The controller operates the electronic switch  52  to create pulse trains N 1  and N 2  by opening and closing depending on signals from the receiver  133 . The controller  112  compares the numbers of clock pulses N 1  and N 2  between itself and by interval t o  as well and depending on whether the numbers N 1  and N 2  correspond to each other and with number N o  (specific number calculated by dividing t o  by the interval between clock pulses), the controller  112  sends a signal to the transponder control circuit  108 . Circuit  108  controls the transmitter of the transponder  109  such as by the operation of an electronic switch for connecting a battery to the transponder to radiate information signal from the transponder outward to the reader. Each transponder is provided with active or passive power supply  48 .  
         [0094]     It is to be understood that variations and modifications of the present invention can be made without departing from the scope of the invention. It is also to be understood that the scope of the invention is not to be interpreted as limited to the specific embodiments disclosed herein, but only in accordance with the appended claims when read in light of the forgoing disclosure.