Patent Publication Number: US-2021174036-A1

Title: Object identification

Description:
BACKGROUND 
     It can be useful to collect information about items displayed for sale at a customer interaction point, sometimes referred to as a “smart shelf” The collected information can be used to log consumer interactions with the product, update product inventory, and/or other purposes. 
     BRIEF SUMMARY 
     Some embodiments are directed to a system that includes a structure configured to hold items, at least one capacitive sensor, and an item scanner configured to move the capacitive sensor relative to the structure and to identification elements disposed on the items held by the structure. Each identification element represents a multi-digit code. The capacitive sensor is configured to generate a sensor signal comprising sequences of waveforms in response to movement of the capacitive sensor relative to the identification elements. Each sequence of waveforms includes the multi-digit code that identifies one of the items. 
     Some embodiments involve an identification element comprising a pattern of multiple regions. The pattern of multiple regions includes at least a first region having a first dielectric constant and a second region having a second dielectric constant that is different from the first dielectric constant. The identification element can be disposed on an item and the pattern of multiple regions represents a multi-digit code that identifies the item. 
     According to some embodiments, a system comprises a structure configured to hold items. The system further includes a touch implement configured to cause a swiping touch across multiple touch sensors of each item as the item is removed from the structure or placed in the structure. A reader generates an excitation signal and receives a response signal from the item. The response signal includes a sequence of electronic waveforms generated in response to the excitation signal and the swiping touch. The sequence of electronic waveforms includes a multi-digit code. A processor configured to extract the code from the response signal and to identify the removed or replaced item based on the code. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram of a system capable of identifying items on a structure in accordance with some embodiments; 
         FIG. 2  is a diagram illustrating an item identification element in accordance with some embodiments; 
         FIG. 3  shows an identification element having first, second, and third regions having different dielectric constants in accordance with some embodiments; 
         FIG. 4  is a schematic diagram of a version of reader circuitry that may be used in the system of  FIG. 1 ; 
         FIG. 5A  shows an identification element comprising first regions and second dielectric regions in accordance with some embodiments; 
         FIG. 5B  shows the response signal including a sequence of waveforms generated as a capacitive sensor sweeps across the dielectric regions of the identification element of  FIG. 5A ; 
         FIG. 6A  shows an identification element comprising first, second, and third dielectric regions in accordance with some embodiments; 
         FIG. 6B  shows the response signal that includes a sequence of waveforms generated as a capacitive sensor sweeps across the dielectric regions of the identification element of  FIG. 6A ; 
         FIG. 7A  shows an identification element comprising dielectric regions of varying widths in accordance with some embodiments; 
         FIG. 7B  shows the response signal that includes a sequence of waveforms generated as a capacitive sensor sweeps across the dielectric regions of the identification element of  FIG. 7A ; 
         FIG. 8  is a flow diagram representing a process of identifying objects on a structure in accordance with some embodiments; 
         FIGS. 9A and 9B  are block diagrams showing side and front perspectives of a system for identifying items held by a structure in accordance with some embodiments; 
         FIGS. 10A and 10B  illustrate one example of a keyed protrusion on an item and complementary channel in the structure that sets the orientation of the item in the structure in accordance with some embodiments; 
         FIGS. 10C and 10D  depict a structure that includes a biasing element that pushes items toward the front of the structure in accordance with some embodiments; 
         FIG. 11  shows capacitive touch sensors of an identification device that can be disposed on an item to identify the item as it is removed from or placed in a structure in accordance with some embodiments; 
         FIG. 12  provides an electrical schematic diagram of an example version of a transponder coupled to the touch sensors illustrated in  FIG. 11 ; 
         FIG. 13  shows the response signal of the identification device output as each capacitive sensor is activated in turn by a touch implement of a structure in accordance with some embodiments; 
         FIG. 14  is a flow diagram of a process of identifying items in accordance with some embodiments; 
         FIG. 15  is a diagram of two double wrapped planar coils that form a capacitive sensor in accordance with some embodiments; and 
         FIG. 16  is a diagram of interdigitated electrodes that form a capacitive sensor in accordance with some embodiments; 
     
    
    
     The figures are not necessarily to scale. Like numbers used in the figures refer to like components. However, it will be understood that the use of a number to refer to a component in a given figure is not intended to limit the component in another figure labeled with the same number. 
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     Acquiring information from interaction points where consumers interact with products can be useful for maintaining good inventory records and/or or for logging consumer shopping behavior. Approaches describe herein include a “smart shelf” system implemented using capacitive sensing. 
       FIG. 1  is a block diagram of a system  100  capable of identifying items on a structure. The system  100  includes a structure  120  configured to hold items  101 ,  102 ,  103 . For example the structure  120  may comprise one or more racks, shelves, or other features  121  that hold the items  101 ,  102 ,  103  in the structure  120  as shown in  FIG. 1 . The system  100  includes at least one capacitive sensor  130  arranged to capacitively detect sense identification elements  111 ,  112 ,  113  disposed on the items  101 ,  102 ,  103 . Each identification element  111 ,  112 ,  113  includes material regions  111 - 1 - 111 - 5 ,  112 - 1 - 112 - 5 ,  113 - 1 - 113 - 5  having varying dielectric constants. A multi-digit code that identifies the item  101 ,  102 ,  103  is encoded in the variation of dielectric constants of the material regions  111 - 1 - 111 - 5 ,  112 - 1 - 112 - 5 ,  113 - 1 - 113 - 5 . 
     An item scanner  141  is configured to scan the sense identification elements  111 ,  112 ,  113  disposed on the items  101 ,  102 ,  103 . The scanner  141  is configured to move one or more capacitive sensors  130  relative to the structure  120  and to the sense identification elements  111 ,  112 ,  113 . The scanner  141  may comprise a stepper motor and belt or any other mechanism suitable to move the capacitive sensor  130  relative to the identification elements  111 ,  112 ,  113 . 
     The item scanner  141  may be configured to scan the items according to a predetermined time schedule, e.g., once per second or once per minute, etc. In some embodiments, the structure includes a sensor  140  that detects when an item has been removed from the structure or placed in the structure. For example, the sensor  140  may comprise a load cell that detects a change in the weight supported by the structure. In other embodiments, the sensor may comprise an optical sensor that optically detects removal of an item from the structure or placement of an item in the structure; the sensor may include a magnetic sensor that magnetically detects removal of the item. In embodiments that include a sensor  140 , the output of the sensor  140  may trigger the scanner  141  to scan the items  101 ,  102 ,  103  in the structure  120 . 
     In response to movement of the capacitive sensor  130  relative to the sense identification elements  111 ,  112 ,  113 , the capacitive sensor  130  generates a sensor signal comprising sequences of waveforms. Each sequence of waveforms represents a multi-digit code that identifies one of the items  101 ,  102 ,  103 . For example, as the sensor  130  moves past regions  111 - 1 ,  111 - 2 ,  111 - 3 ,  111 - 4 ,  111 - 5  of identification element  111 , a sensor signal comprising a sequence of waveforms that includes the multi-digit code for item  101  is generated at an output of the sensor  130 . 
     Optionally, in some embodiments, the capacitive sensor  130  is coupled to a reader  142  that receives the sensor signals  142 . The reader  142  may be communicatively coupled to the sensor  130  by a wireless connection, for example. The reader  142  can be configured to generate an electromagnetic interrogation signal that is transmitted wirelessly to the sensor  130  to interrogate the sensor  130 . In response to the interrogation signal from the reader  142 , the sensor  130  transmits an electromagnetic response signal to the reader  142 . The response signal comprises some representation of the multi-digit code. In some embodiments, the electromagnetic interrogation signal generated by the reader may provide power to the sensor  130 . Optionally, the system  100  may further include a processor  150  configured to extract the multi-digit codes from the response or sensor signal and provide information about items on the structure  120  based on the extracted multi-digit codes. The processor  150  may be coupled to the reader circuitry  142  or directly to the sensor  130  by a wireless or wired connection. 
     For example, the processor  150  may provide information that items  101 ,  102 ,  103  have been removed from or placed on the structure  120  based on the extracted multi-digit codes. As another example, the processor  150  may optionally compare the codes extracted from the response signal to a stored inventory list of item codes and determine one or more items that have been removed from or placed on the structure  120  based on the comparison. Optionally, the processor  150  may maintain logs of consumer interactions with the items  101 ,  102 ,  103  based on the removal of the items  101 ,  102 ,  103  from the structure  120  and/or placement or replacement of items  111 ,  112 ,  113  on the structure. For example, the processor  150  may log the number of times the item was removed from the shelf and then replaced and/or the number of times the item was removed from the shelf and not replaced. The processor  150  may also be configured to identify misplaced items on the structure, e.g., items that do not belong on the structure. 
     In some embodiments the system  100  can include an output device, such as the display  151  shown in  FIG. 1 . The output device  151  may be configured to display information such as a list of items presently on the structure and/or reports of consumer interactions with the items. In some embodiments, the processor  150  may identify the item that has been removed by comparing a previous scan at which the item was present in the structure to a more recent scan of the items in which the item was not present in the structure. If the processor  150  determines that an item has been removed, e.g., by a consumer or other user, the processor  150  may wirelessly send product information about the item to an application running on the consumer&#39;s or user&#39;s hand held device  160 . 
       FIG. 2  is a diagram illustrating an item identification element  200  in accordance with some embodiments. The identification element  200  includes a pattern of multiple regions  201 - 207 . The pattern includes one or more first regions  201 - 207  having a first dielectric constant, ε 1 , and one or more second regions  202 - 206  having a second dielectric constant, ε 2 , wherein ε 1 ≠ε 2 . The pattern of multiple regions  201 - 207  having varying dielectric constants represent a multi-digit code that identifies the item. 
       FIG. 2  shows a path  299  of a capacitive sensor  230  across the regions  201 - 207 . As the capacitive sensor  230  moves along the x axis past regions  201 - 207 , the sensor  230  encounters regions  201 - 207  having dielectric constant that varies between ε 1  and ε 2 . Responsive to the variation in the dielectric constant, the response signal at the output of the reader (not shown), includes a sequence of waveforms having a variation that corresponds to the variation in dielectric constant. Thus a multi-digit code is encoded in the pattern of varying dielectric constants of the regions  201 - 207  of the identification element  200 . 
     In some embodiments, an identification element may include regions having three, four, or more different dielectric constants.  FIG. 3  shows an identification element  300  having one or more first regions  301 - 307  having a first dielectric constant, ε 1 , one or more second regions  302 ,  304  having a second dielectric constant, ε 2 , and one or more third regions  306  having a third dielectric constant, ε 3 , wherein ε 1 ≠ε 2 ≠ε 3 . Materials suitable for the regions of the identification devices  200 ,  300  include glass, plastic, hydrogel, polyvinylidene difluoride (PDVF), and/or other suitable materials. 
       FIG. 4  is a schematic diagram of a version of a capacitive sensor  400  that may be used in the system  100  of  FIG. 1 . Many schematic configurations for the disclosed capacitive sensor  400  are possible and  FIG. 4  provides one implementation discussed here for purposes of illustration and not limitation. 
     In the illustrated embodiment, a sensor excitation voltage, e.g., an AC voltage, is provided to the circuitry  400  at terminal EXC. As indicated in  FIG. 4 , VREF is a reference voltage for the sensor excitation voltage. The output of the reader circuitry at EXT 1  is characterized by the equation: 
     
       
         
           
             
               
                 V 
                 
                   EXT 
                    
                   
                       
                   
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                   1 
                 
               
               = 
               
                 
                   V 
                   REF 
                 
                  
                 
                   
                     C 
                     REF 
                   
                   
                     
                       C 
                       REF 
                     
                     + 
                     
                       C 
                       SENS 
                     
                   
                 
               
             
             , 
           
         
       
     
     where C REF  is a fixed reference capacitance of reference capacitor  402  and C SENS  is the capacitance of sense capacitor  401 . The sense and reference capacitors  401 ,  402  may comprise any type of capacitors suitable for the application. Several possible embodiments for the sense capacitor  401  are discussed below with reference to  FIGS. 14 and 15 . 
     The capacitance C SENS  of the sense capacitor  401  is altered as the sense capacitor  401  moves proximate to first and second materials having different dielectric constants. As the sense capacitor  401  is swept past the identification element, the regions having different dielectric constants cause a variation in C SENS . The variation in C SENS  alters the current being carried in the sense capacitor output and causes a variation in the electronic waveform generated at EXT 1 . 
       FIGS. 5A through 6B  illustrate various identification elements  500 ,  600  and the waveforms  590 ,  690  generated at EXT 1  when the capacitive sensor discussed in connection with  FIG. 4  scans across the regions of the identification elements. 
       FIG. 5A  shows an identification element  500  comprising first regions  501 ,  503 ,  505 ,  507  having a first dielectric constant and second regions  502 ,  504 ,  506  having a second dielectric constant different from the first dielectric constant. 
       FIG. 5B  shows the response signal  590  including a sequence of waveforms generated as a capacitive sensor sweeps across the dielectric regions  501 - 507  along the x-axis at constant velocity. The sequence of waveforms includes waveform  592  (a positive going peak) that is generated when the capacitive sensor sweeps over region  502 ; waveform  594  (a positive going peak) that is generated when the capacitive sensor sweeps over region  504 , and waveform  596  (a positive going peak) that is generated when the capacitive sensor sweeps over region  506 . The response signal returns to the zero or nominal level at  591 ,  593 ,  595 ,  597  when the capacitive sensor sweeps across regions  501 ,  503 ,  505 , and  507 . 
     The amplitudes of the positive going peaks in  FIG. 5B  in waveforms  502 ,  504 , and  506  have about the same amplitude and the amplitudes of the negative going peaks in waveforms  502 ,  504 , and  506  have about the same amplitude. This result occurs because the regions  502 ,  504 , and  506  have the same dielectric constant. The response signal amplitude returns to the same zero or nominal level at  591 ,  593 ,  595 , and  597  because regions  501 ,  503 ,  505 , and  507  have the same dielectric constant that is different from the dielectric constant of regions  502 ,  504 , and  506 . 
     In some embodiments, the identification element includes regions having more than two different dielectric constants as shown in  FIG. 6A .  FIG. 6A  shows an identification element  600  comprising first regions  601 ,  603 ,  605 ,  607  having a first dielectric constant, El, a second region  602  having a second dielectric constant, ε 2 , a third region  603  having a third dielectric constant, ε 3 , and a fourth region  604  having a fourth dielectric constant, ε 4 , where ε 1 ≠ε 2 ≠ε 3 ≠ε 4 . 
       FIG. 6B  shows the response signal  690  that includes a sequence of waveforms generated as a capacitive sensor sweeps across the dielectric regions  601 - 607  along the x-axis at constant velocity. The sequence of waveforms includes waveform  692  (a positive going peak) that is generated when the capacitive sensor sweeps over region  602 ; waveform  694  (a positive going peak) that is generated when the capacitive sensor sweeps over region  604 , and waveform  696  (a positive going peak) that is generated when the capacitive sensor sweeps over region  606 . The response signal returns to the zero or nominal level when the capacitive sensor sweeps across regions  601 ,  603 ,  605 , and  607 . 
     The amplitudes of the positive going peaks in  FIG. 6B  in waveforms  602 ,  604 , and  606  each have different amplitudes from one another. This result occurs because the regions  602 ,  604 ,  606  each have different dielectric constants, ε 2 , ε 3 , ε 4 , respectively. The response signal amplitude returns to the same zero or nominal level at portions  691 ,  693 ,  695 , and  697  of the response signal  690  because regions  601 ,  603 ,  605 , and  607  have the same dielectric constant, ε 1 , that is different from the dielectric constant of regions  602 ,  604 , and  606 . 
     As discussed above, the multi-digit code can be encoded in the pattern of regions in the identification element having different dielectric constants. The different dielectric constant materials cause the response signal to include waveforms of different amplitudes. Additionally or alternatively, the regions of the identification element may include other variations that encode the multi-digit code. For example, as illustrated by  FIGS. 7A and 7B , the multi-digit code can be encoded in the spacings between the regions of different dielectric constant.  FIG. 7A  shows an identification element  700  comprising regions  701 ,  703 ,  705 ,  707 ,  709  having a first dielectric constant, ε 1 , and second regions  702 ,  704 ,  706 ,  708  having a second dielectric constant, ε 2 , where ε 1 ≠ε 2 . In addition to variation in dielectric constant, regions  701 - 709  also vary in width. Regions  702 ,  704 , and  706  have width w 1 ; region  708  has width w 2 ; regions  701 ,  703 ,  705  and  709  have width w 3 ; and region  707  has width w 4 . 
     The varying widths of the regions  701 - 709  affects the timing of the waveforms in the response signal  790  as illustrated by  FIG. 7B .  FIG. 7B  shows the response signal  790  that includes a sequence of waveforms generated as a capacitive sensor sweeps across the dielectric regions  701 - 709  along the x-axis at constant velocity. The sequence of waveforms includes waveform  792  (a positive going peak) that is generated when the capacitive sensor sweeps over region  702 ; waveform  794  (a positive going peak followed by a negative going peak) that is generated when the capacitive sensor sweeps over region  704 , waveform  796  (a positive going peak) that is generated as the capacitive sensor sweeps over region  706 , and waveform  798  (a positive going peak) that is generated as the capacitive sensor sweeps over region  709 . The response signal  790  returns to the zero or nominal level as the capacitive sensor sweeps across regions  701 ,  703 ,  705 ,  707 , and  709 . The multi-digit code is encoded in the waveforms  792 ,  794 ,  796  and  798  generated by regions  701 - 709  having a pattern of differing dielectric constant and also in the time periods p 11 , p 12 , p 13 , p 2  of the waveforms  792 ,  794 ,  796 ,  798  and the time periods p 31 , p 32 , p 4  between the waveforms  792 ,  794 ,  796 ,  798 . 
     The time periods p 11 , p 12 , p 13  of waveforms  792 ,  794 ,  796  are equal to one another because they correspond to regions  702 ,  704 ,  706  that have equal width, w 1 . The time period p 2  of waveform  798  is greater than p 11 , p 12 , and p 13  because time period p 2  corresponds to region  708  having width w 2 &gt;w 1 . Time period p 31  between waveforms  792  and  794  and time period p 32  between waveforms  794  and  796  are equal because they correspond to regions  703 ,  705  that have the same width, w 3 . Time period p 4  between waveforms  796  and  798  is greater than time periods p 31  and p 32  because time period p 4  corresponds to region  707  which has width w 4 &gt;w 3 . The processor can discriminate between different identification elements based on the multi-digit code which is encoded in the number of waveforms, the amplitudes of the waveforms, the time periods of the waveforms, and/or the time periods between the waveforms. 
       FIG. 8  is a flow diagram representing a process of identifying objects on a structure. The method involves moving  810  a capacitive sensor relative to identification elements disposed on items held by a structure. A sensor signal is generated  820  in response to moving the capacitive sensor relative to the identification elements. The sensor signal comprises sequences of waveforms, wherein each sequence of waveforms represents a multi-digit code identifying at least one of the items. The multi-digit codes can be extracted  830  from the sensor signal and used as a basis for further action. For example, information about the items can be provided based on the extracted multi-digit codes. The extracted multi-digit codes can optionally be compared  840  to a previous inventory list of codes to determine a current inventory and/or to update the inventory based on items that are present in the structure. Other appropriate actions can be taken in response to extracting the multi-digit codes. 
     According to some embodiments, capacitive sensors may be disposed on the items themselves rather than on the structure. Each item may include an identification device comprising an arrangement of touch sensitive elements, e.g., capacitive touch sensors that correspond to a multi-digit code. The structure includes a touch implement that activates the capacitive sensors as the items are removed from or placed in the structure. The touch implement comprises a dielectric material which has a much higher dielectric constant than nearby structures. The touch implement can include high dielectric material such as PVDF, hydrogel, rubber and/or other materials that have a dielectric close to the dielectric of a human finger. As used herein a “touch” occurs when the touch implement physically contacts a sensor or is brought sufficiently close to the sensor to activate the capacitive sensor. 
       FIGS. 9A and 9B  are block diagrams showing side and front perspectives of a system  900  for identifying items  901  held by a structure  921  in accordance with some embodiments. The items  901  held by the structure  921  each include at least one identification device  910  that includes multiple touch sensors  911 - 1 - 911 - 4  and a transponder  905 . The identification device  910  communicates with a reader  942  over a wireless communication link. 
     The identification device  910  can be wirelessly powered by excitation signals generated by a reader  942 . The transponder  905  receives excitation signals generated by the reader  942  through an antenna  912 . The transponder  905  harvests energy from the excitation signal to power the identification device  910 . 
     The identification device  910  comprises multiple touch sensors  911 - 1 - 911 - 4  that can be activated by a touch implement  930  which is a component of the structure  921 . The touch implement  930  emulates a finger touch, for example. The sensors  911 - 1 - 911 - 4  are electrically coupled to the transponder  905  and are configured to produce electronic waveforms in response to contact with or proximity to the implement  930 . The sensors  911 - 1 - 911 - 4  can be arranged to generate a sequence of electronic waveforms representing a sequential multi-digit code that identifies the item in response to a swiping contact or proximity of the touch implement  930  across the touch sensors  911 - 1 - 911 - 4 . The structure  921  can be configured such that the swiping contact or proximity of the implement  930  occurs as the item  901  is removed from the structure  921  or is placed in the structure  921 . The touch implement  930  may be biased toward the touch sensors  911 - 1 - 911 - 4 , e.g., by a spring, an elastomeric article, or other biasing element, to facilitate contact or close proximity to the sensors  911 - 1 - 911 - 4  as the item  901  is drawn from the structure  120  or placed in the structure  120 . 
     The transponder  905  is electrically connected to the touch sensors  911 - 1 - 911 - 4  so as to receive the sequence of electronic waveforms generated by the touch sensors  911 - 1 - 911 - 4  in response to the proximate touch implement  930 . The transponder  905  transmits a transponder response signal that includes the sequence of electronic waveforms through the antenna  912  to the antenna  941  of the reader  942 . 
     A processor  950  coupled to the reader  942  extracts the multi-digit code that identifies the item  901  removed or replaced in the structure  921  from the response signal. The processor  950  can use the identification of items removed or replaced in the structure to maintain inventory, to log consumer interactions with various items, to detect misplaced items, and/or for other useful purposes. In some embodiments, the processor  950  may include an output device  951  that displays information associated with the identified item. In some embodiments, the processor  950  may wirelessly transmit information about the item to an external device  960 , e.g., a handheld device. 
       FIG. 9B  shows an end view of the item  901  on the structure  921  as the item  901  is being removed from the structure  921  along the x axis. As the item  901  moves along the x axis, the touch sensors  911 - 1 - 911 - 4  sequentially move past the touch implement  930  starting with touch sensor  911 - 4  which is shown in  FIG. 9B  and ending with touch sensor  911 - 1  shown in  FIG. 9A . As the sensors move past the touch implement, a sequence of waveforms are generated that represent a multi-digit code. These waveforms are included in the response signal transmitted from the transponder  905  to the reader  942 . 
     In some embodiments, the item  901  may include a second set of sensors including touch sensor  911 - 4 ′ disposed on a side of the item  902  opposite the first set of touch sensors  911 - 1 - 911 - 4 . The second set of touch sensors move past a second touch implement  930 ′ located on the opposite side of the structure  921  to the first touch implement  930 . As the second set of touch sensors including sensor  911 - 4 ′ move past the second touch implement  930 ′a second set of sequential waveforms are generated that represent a second multi-digit code. These second waveforms can be included in a second response signal from the transponder  905  to the reader  942 . 
     The use of two sets of touch sensors and two touch implements as illustrated in  FIG. 9B  can be useful to confirm the identity of the item and/or to detect the direction that the object is moving, e.g., whether the item is being removed from the structure or placed in the structure. 
     It can be useful to ensure that the item is oriented on the structure in a predetermined way. To this purpose, in some embodiments the item may include a feature that is compatible with a feature of the structure that sets the orientation of the item. For example, the item&#39;s feature may comprise a keyed protrusion that can be inserted into a compatible channel in the structure to set the orientation of the item in the structure.  FIGS. 10A and 10B  illustrate one example of a keyed protrusion  1099  on an item  1001  and complementary channel  1098  in the structure  1021  that sets the orientation of the item  1001  in the structure  1021 . Due to the channel  1098  and protrusion  1099 , when the item  1001  is placed in the structure  1021  along the x axis, the item  1001  is constrained to enter the structure  1021  from back  1001 - 2  to front  1001 - 1 . Likewise, when the item  1001  is removed from the structure  1021  along the x axis, the item  1001  is constrained to leave the structure  1021  from front  1001 - 1  to back  1001 - 2 . These constraints ensure that the regions or sensors of the identification element  1011  are encountered in the correct order and the processor can detect whether the item  1001  is being removed or replaced based on the sequence of waveforms included in the response signal. 
     As depicted in  FIGS. 10C and 10D , in some embodiments, a structure  1022  can include a spring  1023  or other type of biasing element arranged to push items (numbered  1 - 9  in  FIGS. 10C and 10D ) towards the front  1022 a of the structure  1022 . When a customer pulls the front item out (labeled as item  1 ), items  2 - 9  behind the front item  1  will move forward in the structure  1022 . 
       FIG. 11  shows capacitive touch sensors  1113   a  through  1113   f  of an identification device that can be disposed on an item to identify the item as it is removed from or placed in the structure.  FIG. 12  provides an electrical schematic diagram of an example version of a transponder  1205  coupled to the touch sensors  1113   a  through  1113   f . The reader will appreciate that many schematic configurations for the disclosed device are possible and this is but one implementation discussed for purposes of illustration. In this particular configuration, the touch sensors  1113   a - f  are all connected to the same output signal line  1290 , for example. 
     Each capacitive touch sensor  1113   a - f  includes first and second electrical conductors, e.g., electrically conductive traces, which form the plates of the capacitor separated by an electrically non-conductive gap. The capacitance of touch sensor  1113   a  is Ca; the capacitance of touch sensor  1113   b  is Cb, the capacitance of touch sensitive element sensor  1113   c  is Cc, the capacitance of touch sensitive element  1113   d  is Cd; the capacitance of touch sensitive element  1113   e  is Ce; and the capacitance of touch sensitive element  1113   f  is Cf. 
     In this particular example, the transponder  1205  has no internal source of power and harvests energy from the excitation signal transmitted by the reader (not shown in  FIG. 12 ) to the input device  210 . In the illustrated embodiment, the transponder  1205  uses the harvested energy to provide a sensor excitation voltage, e.g., an AC voltage (shown as EXC in  FIG. 12 ) to the touch sensors  1113   a - f . As indicated in  FIG. 12 , VREF is a reference voltage for the sensor excitation voltage. The output of the touch sensor  1213  is connected to the transponder  1205  at EXT 1 . The total equivalent capacitance (C SENS ) of the sensor capacitors ( 213   a ,  213   c , and  213   f ) is Ca+Cc+Cf, and the total capacitance (C REF ) of the reference capacitance is Cb+Cd+Ce. The output of the touch sensor at EXT 1  is characterized by the equation: 
     
       
         
           
             
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                 EXT 
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                 1 
               
             
             = 
             
               
                 V 
                 REF 
               
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                   C 
                   REF 
                 
                 
                   
                     C 
                     REF 
                   
                   + 
                   
                     C 
                     SENS 
                   
                 
               
             
           
         
       
     
     For any of the touch sensors  1113   a - f , when the touch implement is not present at the touch sensor, any capacitive coupling at the gap stays fairly constant. When the touch implement of the structure touches or nearly touches a touch sensor, the previously existing capacitive coupling is altered. The touch implement shunts a portion of the capacitive field whereby charge across the gap is altered. The variation in the capacitive coupling alters the current being carried in the sensor output and causes a variation in the electronic waveform at EXT 1 . 
       FIG. 13  shows the response signal of the identification device output at EXT 1  as each capacitive sensor  1113   a - 1113   f  is activated in turn by the touch implement on the structure. As the touch implement passes sensor  1113   a  peak  1391  is generated; as the touch implement passes sensor  1113   b  peak  1392  is generated; as the touch implement passes sensor  1113   c  peak  1393  is generated; as the touch implement passes sensor  1113   d  peak  1394  is generated; as the touch implement passes sensor  1113   e  peak  1395  is generated; and as the touch implement passes sensor  1113   f  peak  1396  is generated. The sequence of waveforms  1391 - 1396  represents the multi-digit code that identifies the item associated with the touch sensors  1113   a - f . The multi-digit code may also be encoded by different spacing between the touch sensor and/or different sizes of the touch sensors. The different spacing produces corresponding differing timing between the waveforms in the response signal and the different sizes of the touch sensors produces corresponding differing amplitudes of the waveforms. The processor may be capable of discriminating between removal of an item from the structure and placement of the item in the structure by the order of the waveforms generated by the touch sensors. For example, when the item is removed from the structure, the waveform sequence order may be waveform  1391 , followed by waveform  1392 , followed by waveform  1393 , followed by waveform  1394 , followed by waveform  1395 , followed by waveform  1396  as shown in  FIG. 13 . When the item is replaced in the structure, the reverse waveform order would occur: waveform  1396  followed by waveform  1395  followed by waveform  1394  followed by waveform  1393  followed by waveform  1392  followed by waveform  1391 . The processor may detect the order that the waveforms occur in the response signal to determine whether the item is being removed or replaced. 
     The item may include additional touch sensors that can be swiped by a consumer who interacts with the item as discussed in commonly owned U.S. patent application Ser. No. 16/589676 filed on Oct. 1, 2019 which is incorporated herein by reference. Swiping the additional touch sensors can cause information about the item to be transmitted to the consumer&#39;s handheld device. U.S. patent application Ser. No. 6/589676 also discusses different configurations of capacitive sensors and groups of sensors that can be employed in the approaches above. 
       FIG. 14  is a flow diagram of a process of identifying items in accordance with some embodiments. The method includes generating  1401  electronic waveforms in response to a touch implement swiping on or near capacitive touch sensors disposed on the item as the item is removed from or placed in the structure. The electronic waveforms represent a sequential multi-digit code and are incorporated  1402  in a response input signal that is wirelessly transmitted  1403  to a reader. The electronic waveforms are extracted  1404  from the response signal. The sequential multi-digit code is determined  1405  based on the sequence of electronic waveforms in the response signal. The item that corresponds to the sequential multi-digit code is identified  1406 . The system takes action e.g., displays information, makes a sound, logs consumer interaction, updates inventory etc., based on the item removed or replaced in the structure. 
       FIGS. 15 and 16  illustrate examples of capacitive sensors  1500 ,  1600  suitable for many applications including the applications discussed in  FIGS. 1-14  herein. In a first embodiment, each electrical conductor  1571 ,  1572  of a capacitive sensor  1500  may be a planar coil. The two coils  1571 ,  1572  of the sensor  1500  can be a double wrapped and electrically isolated from one another by a gap  1573  as shown in  FIG. 15 . In some embodiments, the electrical conductors  1571 ,  1572  are implemented as conductive traces printed onto a substrate  1570 . Additional details of double wrapped coils used for capacitive sensing are discussed in commonly owned U.S. Pat. No. 9,874,984 which is incorporated herein by reference. 
     The gap  1573  between the double wrapped coils  1571 ,  1572  can be about 3 μm to about 1 mm, e.g., about 90 μm, for example. The double wrapped coils  1571 ,  1572  can be approximately circular in shape, can be or rectangular in shape as illustrated in  FIG. 15 , or can have any other suitable shape. For circular-shaped coils, the diameter of each coil can range from about 50 μm to about 20 mm depending on the application. For rectangular shaped planar coils, the length, L, and width, W, of the rectangle can range between about 50 μm to about 20 mm depending on the application. The overall length of the coil conductors depends on the design of the gap, shape, and size of the coil. In some embodiments, the total diameter (or the length and width) of the double-wrapped coils may be about 3.4 mm and the total length of the gap may be about 426 mm (2 times the length of a coil). 
     As shown in  FIG. 16 , in some embodiments, the electrical conductors  1671 ,  1672  of a capacitive sensor  1600  may be co-planar interdigitated electrodes. The two interdigitated electrodes  1671 ,  1672  of the sensor are electrically isolated from one another by a gap  1673  as shown in  FIG. 16 . In some embodiments, the electrical conductors  1671 ,  1672  are implemented as conductive traces printed onto a substrate  1670 . 
     The gap  1673  between the interdigitated electrodes  1671 ,  1672  can be about 3 μm to about 1 mm, e.g., about 90 μm, for example. The interdigitated electrodes  1671 ,  1672  can be approximately rectangular in shape as illustrated in  FIG. 16 , or can have any other suitable shape. The length, L, and width, W, of the rectangle formed by the interdigitated electrodes can range between about 50 μm to about 20 mm depending on the application. The overall length of each conductor depends on the design of the gap, shape, and size of the coil. In some embodiments, the total length of the gap between the interdigitated electrodes  1671 ,  1672  is about the number of the electrodes times the width, W. 
     The double-wrapped coils or interdigitated electrodes as illustrated in  FIGS. 15 and 16  form a co-planar capacitor with a long gap between two neighboring conductors. The geometry provides a large capacitance change when an the sensor touches or comes close to the identification elements on items (see, e.g.,  FIGS. 1-8  and associated discussion in the disclosure) and/or when a touch implement of the structure touches or comes close to sensors of an identification device (see, e.g.,  FIGS. 9-13  and associated discussion in the disclosure). The large capacitance change yields efficient sensing and enhances signal/noise (S/N) ratio. 
     In various embodiments, a capacitive sensor comprising double wrapped coils or interdigitated electrodes can be patterned on a printable substrate. Techniques for patterning the conductive traces include, for example, inkjet printing, gravure printing, screen-printing, aerosol printing, and/or photolithography, among other patterning technologies. The printable substrate may be flexible or rigid. The printable substrate can include a polymeric material, such a polyethylene naphthalate (PEN), polyethylene terephthalate (PET), polymide, etc. In some embodiments the substrate may comprise paper, or woven or non-woven fabrics, for example. The material of the traces that form the coils or electrodes may be a flexible electrically conductive material. The flexible conductive material of the coils or electrodes may include silver, gold, copper, or conductive carbon, among others. 
     In some embodiments, a first conductor of a capacitive sensor, e.g., coil or electrode is deposited, e.g., printed, on a substrate and a second conductor of the capacitive touch sensitive element is deposited, e.g. printed, on the same substrate but without touching the first coil. In alternative embodiments, the first conductor of the capacitive sensor is deposited, e.g., by printing, on a first substrate and a second conductor of the capacitive touch sensitive element is deposited on a different second substrate. In further alternative embodiments, the first conductor of the capacitive sensor and second conductor of the capacitive sensor are deposited sequentially; simultaneously; parts of the two conductors are printed and then the rest of the conductor parts are printed; or by any other useful printing order. 
     Various modifications and alterations of the embodiments discussed above will be apparent to those skilled in the art, and it should be understood that this disclosure is not limited to the illustrative embodiments set forth herein. The reader should assume that features of one disclosed embodiment can also be applied to all other disclosed embodiments unless otherwise indicated. It should also be understood that all U.S. patents, patent applications, patent application publications, and other patent and non-patent documents referred to herein are incorporated by reference, to the extent they do not contradict the foregoing disclosure.