Patent Publication Number: US-2010123561-A1

Title: Radio frequency identification apparatus with a plurality of radio frequency identification schemes

Description:
PRIORITY STATEMENT 
     This U.S. non-provisional patent application claims priority under 35 U.S.C. §119 to Korean Patent Application No. 10-2008-0115200 filed on Nov. 19, 2008, in the Korean Intellectual Property Office (KIPO), the entire contents of which is hereby incorporated by reference. 
     BACKGROUND 
     1. Field 
     Example embodiments relate to a Radio Frequency Identification (RFID) system. More particularly, example embodiments relate to an RFID apparatus with a plurality of RFID schemes. 
     2. Description of the Related Art 
     In general, an RFID system is a system which recognizes information recorded in a tag via a wireless communication. The recorded information belongs to RFID fields for example a barcode label, a magnetic stripe, etc. An RFID reader receives information stored in the tag via an antenna. The RFID reader recognizes and analyzes the received information, and obtains inherent and circumstance information for a product where the tag is applied or, incorporated. 
     The RFID system includes for example a reader, an antenna, a tag, etc. The antenna performs an intermediation function between the tag and the reader. A power and a signal are sent to the tag via the antenna via a wireless communication, so that the tag is activated. Further, a response from the tag is received via the antenna. 
     The RFID system uses a Near Field Communication (NFC) scheme and a mobile RFID (mRFID) scheme. 
     The RFID system of the NFC scheme, for example, uses a frequency (e.g., 13.56 MHz) of a high frequency band to transmit data at a distance between 10 cm and 60 cm. Since the NFC scheme provides high security, the NFC scheme has been used in applications for example a traffic card, mobile payment, etc. 
     The RFID system of the mRFID scheme, for example, uses a frequency (e.g., 900 MHz) of a ultra high frequency band to transmit data at a distance within 10 m. The mRFID scheme has such advantages that an identification distance is far and the performance is excellent. For these reasons, the mRFID scheme has been used in applications for example harbor container, remote inspection, tire pressure monitoring system (TPMS), distribution logistics, etc. 
     The NFC scheme and the mRFID scheme include used frequencies and applied fields that are different from each other. Hardware configurations of the NFC and mRFID schemes are similar to each other. Integration of the above-described RFID schemes in one RFID apparatus (including a reader and an antenna), that is, a mobile terminal such as cellular phone, personal digital assistant, portable multimedia player, etc., in order to improve the efficiency of a hardware application. 
     SUMMARY 
     Example embodiments provide an RFID apparatus capable of communicating data via a plurality of RFID schemes. 
     The example embodiments provide a radio frequency identification (RFID) apparatus including a first RFID chip configured to control data communication using a first RFID scheme, a second RFID chip configured to control data communication using a second RFID scheme and a loop antenna having first antenna connection terminals for a first length and second antenna connection terminals for a second length. The RFID apparatus further includes a switch circuit connected with the first and second antenna connection terminals of the loop antenna, the first RFID chip and the second RFID chip and a controller configured to control the switch circuit so as to selectively switch the loop antenna into one of the first RFID chip and the second RFID chip based on whether data communication is one of the first and second RFID schemes. 
     The example embodiments provide a radio frequency identification (RFID) apparatus including two or more RFID chips configured to control data communication using two or more RFID schemes, an antenna having two or more antenna connection terminals and having two or more loop lengths, a switch configured to switch the two or more RFID chips between the two or more antenna connection terminals and a controller configured to determine a selected RFID scheme, and to control the switch based on the selected RFID scheme. 
     The example embodiments provide a method for operating a radio frequency identification (RFID) device with two or more RFID chips, the method including determining if a select signal has been detected, determining if the select signal selects a first RFID scheme if the select signal has been detected, switching an antenna, having first antenna connection terminals for a first length and second antenna connection terminals for a second length, such that the first antenna connection terminals and a first RFID chip are selected if the first RFID scheme is selected, the first RFID chip configured to perform the first RFID scheme and switching the antenna such that the second antenna connection terminals and a second RFID chip of the RFID chips are selected to receive the data communications if the first chip is not selected, the second RFID chip configured to perform a second RFID scheme. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       Example embodiments will be more clearly understood from the following brief description taken in conjunction with the accompanying drawings.  FIGS. 1-9  represent non-limiting, example embodiments as described herein. 
         FIG. 1  is a diagram showing an antenna structure of an RFID apparatus adopting an NFC manner according to the example embodiment. 
         FIG. 2  is a diagram showing an antenna structure of an RFID apparatus adopting an mRFID manner according to the example embodiment. 
         FIG. 3  is a block diagram showing an RFID apparatus according to the example embodiment. 
         FIG. 4  is a circuit diagram showing a resonance circuit according to adoption of an NFC manner. 
         FIG. 5  is a diagram showing an antenna structure according to the example embodiment. 
         FIG. 6  is a diagram showing a switch structure according to the example embodiment. 
         FIG. 7  is a diagram showing a switch structure according to another example embodiment. 
         FIG. 8  is a diagram showing a switch structure according to still other example embodiment. 
         FIG. 9  is a flowchart for describing an operation of an RFID apparatus according to the example embodiment. 
     
    
    
     It should be noted that these Figures are intended to illustrate the general characteristics of methods, structure and/or materials utilized in certain example embodiments and to supplement the written description provided below. These drawings are not, however, to scale and may not precisely reflect the precise structural or performance characteristics of any given embodiment, and should not be interpreted as defining or limiting the range of values or properties encompassed by example embodiments. For example, the relative thicknesses and positioning of molecules, layers, regions and/or structural elements may be reduced or exaggerated for clarity. The use of similar or identical reference numbers in the various drawings is intended to indicate the presence of a similar or identical element or feature. 
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Example embodiments will now be described more fully with reference to the accompanying drawings, in which example embodiments are shown. Example embodiments may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of example embodiments to those of ordinary skill in the art. In the drawings, the thicknesses of layers and regions are exaggerated for clarity. Like reference numerals in the drawings denote like elements, and thus their description will be omitted. 
     It will be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present. Like numbers indicate like elements throughout. As used herein the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     It will be understood that, although the terms “first”, “second”, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of example embodiments. 
     Spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the exemplary term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     Example embodiments are described herein with reference to cross-sectional illustrations that are schematic illustrations of idealized embodiments (and intermediate structures) of example embodiments. As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, example embodiments should not be construed as limited to the particular shapes of regions illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. For example, an implanted region illustrated as a rectangle may have rounded or curved features and/or a gradient of implant concentration at its edges rather than a binary change from implanted to non-implanted region. Likewise, a buried region formed by implantation may result in some implantation in the region between the buried region and the surface through which the implantation takes place. Thus, the regions illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the actual shape of a region of a device and are not intended to limit the scope of example embodiments. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which example embodiments belong. It will be further understood that terms, such as those defined in commonly-used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
     An RFID system may include an RFID apparatus which uses a plurality of RFID schemes. In particular, the RFID apparatus is configured to use an NFC manner and an mRFID schemes. 
     The example embodiment will be described using an example where the NFC scheme using a high frequency band and the mRFID scheme using an ultra high frequency band are applied. Example embodiments may be applied to RFID schemes using at least two bands of a low frequency band, a high frequency band, an ultra high frequency band, and a microwave band. 
     The low frequency band may be between 30 kHz and 300 kHz (a frequency of Industrial Scientific Medical (ISM) band, below 135 kHz), the high frequency band may be between 3 MHz and 30 MHz (ISM frequency, 6.78 MHz, 13.56 MHz, 27.125 MHz, and 40.68 MHz), the ultra high frequency band may be between 300 MHz and 3 GHz (ISM frequency, 433.92 MHz, 869 MHz, and 915 MHz), and the microwave band may be over 3 GHz (ISM frequency, 2.45 GHz, 5.8 GHz, and 24.125 GHz). 
     A frequency of 13.56 MHz may be used at the NFC scheme and a frequency of 900 MHz may be used at the mRFID scheme. 
     The RFID apparatus of the example embodiment may be configured to include a reader and an antenna among constituent elements of the RFID system. 
     In the RFID apparatus, integrating antennas for performing an intermediation role between a tag and a reader may be required in order to integrate the NFC scheme and the mRFID scheme. A loop antenna is used as an antenna for supporting the NFC and mRFID schemes. 
       FIG. 1  is a diagram showing an antenna structure of an RFID apparatus adopting an NFC scheme according to the example embodiment. 
     Referring to  FIG. 1 , a loop antenna may be used for data communication in the NFC scheme. In the NFC scheme, the loop antenna has an inductance value L antenna  and determines a frequency for data communication via resonance (e.g., LC resonance) with a capacitance value C chip  of a chip. An operating frequency of the NFC scheme may be expressed as the following equation 1. 
         f   r =½π√{square root over ( L   antenna   C   chip )} 
     In equation 1, the symbol f r  is a frequency of the NFC band, the symbol C chip  is a capacitance value, and L antenna  is an inductance value. The inductance value L antenna  may be determined according to a length of an antenna, and the capacitance value C chip  may be determined by an inductance value L antenna  which may be dependent on an antenna having a given length. 
     If an antenna has a length of about 10 cm, In this case, the loop antenna may have an inductance value of 3 uH. Since a frequency of the NFC band is 13.56 MHz, the capacitance value C chip  is determined to be 50 pF. 
     If the RFID apparatus adopting the NFC scheme, since a capacitance value of a chip may be determined according to a length of a loop antenna, using loop antennas with various lengths may be possible. Further, adopting the NFC scheme by inserting a loop antenna in a small-sized RFID apparatus such as a mobile terminal may be possible. 
       FIG. 2  is a diagram showing an antenna structure of an RFID apparatus adopting an mRFID scheme according to the example embodiment. 
     Referring to  FIG. 2 , a loop antenna may be able to be used for data communication in the mRFID scheme. A length and/or a structure of the loop antenna may be determined according to a frequency used in the mRFID scheme. The length of the antenna may be expressed as the following equation 2. 
         I=λ/ 4 
     In the equation 2, a symbol ‘I’ indicates a length of a loop antenna, and a symbol ‘λ’ indicates an antenna length constant (for example, 30 cm at 1 GHz) determined according to each frequency band. A loop antenna used in the mRFID manner of 900 MHz has a length of about 7 cm. 
     The above description may show that the NFC scheme and the mRFID scheme may be integrated by controlling a length of a loop antenna applied to the RFID apparatus. Therefore, a length of the loop antenna may be determined to support both the NFC scheme and the mRFID scheme at the resonance frequency. 
       FIG. 3  is a block diagram showing an RFID apparatus according to the example embodiment. 
     Referring to  FIG. 3 , an RFID apparatus  60  includes an NFC chip  10 , an mRFIC chip  20 , a switch circuit  30 , a controller  50 , and an antenna  40 . 
     The NFC chip  10  is a chip which may be configured to conduct data communication in the NFC scheme. The NFC chip  10  may be configured to include at least a capacitor having a given/adjustable capacitance value which may be used for the LC resonance with an inductance value made by the antenna  40 . 
     The antenna  40  may be, for example, a loop antenna, having a length suitable for supporting two RFID schemes, for example, the NFC scheme and the mRFID scheme. In other words, the loop antenna may have a length suitable for supporting a frequency band of the NFC scheme and a frequency band of the mRFID scheme at a resonance frequency. A structure of a usable loop antenna will be more fully described with reference to  FIG. 5 . 
     The loop antenna  40  may have the first antenna connection terminals for the first length and the second antenna connection terminals for the second length. The first length is identical to or different from the second length. If the first length is identical to the second length, each of the first and second lengths may be suitable for supporting the two RFID schemes. 
     If the first length is different from the second length, since the NFC scheme needs a loop antenna having a longer length than that of the mRFID scheme, one of the first and second lengths has a longer length than the other. The first antenna connection terminals are connected to the NFC chip  10 , and the first length has a longer length than the second length. 
     The controller  50  may be configured to determine the use of one of the NFC scheme and the mRFID scheme. For example, the controller  50  may receive a selection signal from a user via an input part (not shown) to control the switch circuit  30  in response to the received selection signal. 
     The controller  50  may be configured to control the switch circuit  30 , having switches sw 1  and sw 2 , and the chips  10  and  20  which may be individual modules. The controller  50  may be included in any one of the chips  10  and  20  or in each of the chips  10  and  20 . 
     The switch circuit  30  may connect terminals of the antenna  40  to the NFC chip  10  or the mRFID chip  20  in response to a control of the controller  50 . The switch circuit  30  may conduct a switching operation according to a control signal generated from the controller  50 . The switch circuit  30  may connect the terminals of the antenna  40  to the NFC chip  10  when data communication is conducted in the NFC scheme and to the mRFID chip  20  when data communication is conducted in the mRFID scheme. 
     If the select signal is not received (detected), the data communication may be in a default manner under the control of the controller  50 . In other words, at an initial stage of the data communication, the terminals of the antenna  40  may be connected to any one of the NFC and mRFID chips  10  and  20 . This means that the data communication may be at an initial/default connection state between the antenna  40  and an NFC/mRFID chip when no select signal is received. 
     If the NFC chip  10  and the mRFID chip  20  are individual modules, the switch circuit  30  may be an individual module. The switch circuit  30  may be implemented by a single chip  60  together with the NFC chip  10  and the mRFID chip  20 . In this case, the single chip  60  may include the controller  50 . 
       FIG. 4  shows a resonance circuit when the NFC scheme is adopted. 
     Referring to  FIG. 4 , the resonance circuit may include a capacitor  100  and an inductor  200 . The inductor  200  may have an inductance value L antenna  determined by a loop antenna which may have a given length. The capacitor  100  may have a capacitance value C chip  enabling an LC resonance according to the inductance value. 
     The illustrated resonance circuit may include the inductor  200  having an inductance value L antenna  of an antenna and the capacitor  100  having a capacitance value C chip  of the NFC chip  10 . Since the capacitance value of the NFC chip  10  may be variable, a length of a loop antenna so as to have an appropriate length may be determined. 
       FIGS. 5A and 5B  are diagrams showing an antenna structure according to the example embodiment. In  FIGS. 5A and 5B , there are illustrated loop antennas which may be formed by winding a wire in a rectangle shape.  FIG. 5A  illustrates a single turn loop antenna with a single layer structure, and  FIG. 5B  illustrates a multi turn loop antenna with a multiple layer structure. The multi turn loop antenna makes the winding number be increased. 
     As illustrated in  FIGS. 5A and 5B , the loop antenna may be formed to have a single layer structure or a multiple layer structure. A shape where a wire is wound may be changed variously. For example, the loop antenna may be formed by winding a wire in various shapes such as a regular square shape, a rectangle shape, a triangle shape, a circle shape, etc. 
       FIG. 6  is a diagram showing a switch structure according to the example embodiment. 
     Referring to  FIG. 6 , illustrated is an antenna  40 , for example, a loop antenna may have two terminals  41  and  42 . A switch circuit  30  may be configured to switch two terminals  41  and  42  connected with the antenna  40  into four terminals  11 ,  12 ,  21 , and  22  connected with NFC and mRFID chips. 
     The switch circuit  30  may include the first switch SW 1  and the second switch SW 2 . The antenna  40  may have the first antenna terminal  41  and the second antenna terminal  42 , the NFC chip may have the first NFC chip terminal  11  and the second NFC chip terminal  12 , and the mRFID chip may have the first mRFID chip terminal  21  and the second mRFID chip terminal  22 . 
     The first switch SW 1  may connect the first antenna terminal  41  to the first NFC chip terminal  11  or the first mRFID chip terminal  21  according to an adopted/selected RFID scheme, that is, the NFC scheme or the mRFID scheme. The second switch SW 2  connects the second antenna terminal  42  to the second NFC chip terminal  12  or the second mRFID chip terminal  22  according to an adopted/selected RFID scheme, that is, the NFC scheme or the mRFID scheme. 
       FIG. 7  is a diagram showing a switch structure according to an example embodiment. 
     Referring to  FIG. 7 , illustrated is an antenna  40 - 1 , that is, a loop antenna may have four terminals  41 ,  42 ,  43 , and  44 . A switch circuit  30 - 1  may be configured to switch the four terminals  41  to  44  connected with the antenna  40 - 1  into four terminals  11 ,  12 ,  21 , and  22  connected with NFC and mRFID chips. 
     The switch circuit  30 - 1  may include the first switch SW 1 , the second switch SW 2 , the third switch SW 3 , and the fourth switch SW 4 . The antenna  40 - 1  may include the first and second antenna terminals  41  and  42  for the first length and the third and fourth antenna terminals  43  and  44  for the second length. The NFC chip has the first NFC chip terminal  11  and the second NFC chip terminal  12 , and the mRFID chip has the first mRFID chip terminal  21  and the second mRFID chip terminal  22 . 
     The second and third switches SW 2  and SW 3  may connect the first and second antenna terminals  41  and  42  to the first and second NFC chip terminals  11  and  12 , respectively, according to an applied/selected RFID scheme, that is, the NFC or mRFID scheme. The first and fourth switches SW 1  and SW 4  may connect the third and fourth antenna terminals  43  and  44  to the first and second mRFID chip terminals  21  and  22 , respectively, according to an applied/selected RFID scheme, that is, the NFC or mRFID scheme. That is, the second and third switches SW 2  and SW 3  may form a switch pair, and the first and fourth switches SW 1  and SW 4  may form a switch pair. Thus, the antenna  40 - 1  may be connected to the NFC or mRFID chip via one of the switch pairs according to the applied/selected RFID scheme. 
       FIG. 8  is a diagram showing a switch structure according to an example embodiment. 
     Referring to  FIG. 8 , illustrated is an antenna  40 - 2 , that is, a loop antenna may have three terminals  41 ,  42 , and  45 . A switch circuit  30 - 2  may be configured to switch the three terminals  41 ,  42 , and  45  connected with the antenna  40 - 2  into four terminals  11 ,  12 ,  21 , and  22  connected with NFC and mRFID chips. 
     A switch  30 - 2  may include the first to third switches SW 1 , SW 2 , and SW 3 . The antenna  40 - 2  may have the first to third antenna terminals  41 ,  42 , and  45 . The first and second antenna terminals  41  and  42  may be used to form the first length, and the first and third antenna terminals  41  and  45  are used to form the second length. The NFC chip may have the first NFC chip terminal  11  and the second NFC chip terminal  12 , and the mRFID chip may have the first mRFID chip terminal  21  and the second mRFID chip terminal  22 . 
     The first and second switches SW 1  and SW 2  may connect the first and second antenna terminals  41  and  42  to the first and second NFC chip terminals  11  and  12 , respectively, according to an applied/selected RFID scheme, that is, the NFC or mRFID scheme. The second and third switches SW 2  and SW 3  may connect the second and third antenna terminals  42  and  45  to the first and second mRFID chip terminals  21  and  22 , respectively, according to an applied/selected RFID scheme, that is, the NFC or mRFID scheme. That is, the second switch SW 2  may be used to form a switch pair together with the first switch SW 1  or with the third switch SW 3 . Thus, the antenna  40 - 1  may be connected to the NFC or mRFID chip via a switch pair, which may be SW 1  and SW 2  or SW 2  and SW 3 , according to the applied/selected RFID schemer. 
     In accordance with the switch structures in  FIGS. 7 and 8 , one loop antenna may have two lengths. If an antenna length described in  FIGS. 1 and 2  is used, for example, data communication may be in the NFC scheme (about 10 cm) using a loop antenna with a relatively longer length as compared with the mRFID manner (about 7 cm). 
     As described above, if one loop antenna is set to have two lengths, hardware using an antenna length suitable for each RFID scheme may be more easily configured. 
     In  FIGS. 6 to 8 , the example embodiments are described using an example where a single turn loop antenna is applied. A multi turn loop antenna may also be applied to the example embodiment. 
     An antenna length according to an RFID scheme may be adjusted by further providing at least one connection terminal to a loop antenna which has two connection terminals. 
       FIG. 9  is a flowchart for describing an operation of an RFID apparatus according to the example embodiment. 
     Referring to  FIG. 9 , in step S 100 , the RFID apparatus, for example, a controller  50  may determine whether a select signal is received. The select signal may be provided by a user to select either one of a plurality of RFID schemes, for example, the NFC scheme and the mRFID scheme. If the select signal is not received, the procedure moves to step S 110 . In step S 110 , data communication may be communicated via a default scheme, for example, the NFC scheme or the mRFID scheme, under the control of the controller  50 . After data communication is completed via the default scheme, the procedure ends. 
     If, in step S 100 , the select signal is detected, in step S 120 , the controller  50  may determine whether the received select signal indicates that data communication is made in the NFC scheme. If so, the procedure goes to step S 130 , where a switch circuit  30  connects a loop antenna  40  to an NFC chip  10  under the control of the controller  50 . The procedure moves to step S 150 . 
     If, in step S 120 , the received select signal does not indicate that data communication is communicated in the NFC scheme, the procedure moves to step S 140 . In step S 140 , the switch circuit  30  connects the loop antenna  40  to an mRFID chip  20  under the control of the controller  50 . The procedure moves to step S 150 . In step S 150 , the data communication may be communicator via a chip, for example, the NFC chip  10  or the mRFID chip  20  in the RFID apparatus, connected with the loop antenna. When data communication is completed via the selected scheme by the select signal, the procedure ends. 
     In accordance with the RFID apparatus, when a plurality of RFID schemes are used in the RFID apparatus, preventing additional antennas from being used may be possible via sharing of one loop antenna. Further, the RFID apparatus may be configured to control a length of the loop antenna. If the RFID apparatus is applied to small-sized mobile terminals, reducing an antenna-occupied area may be possible via controlling of the antenna length. 
     Although example embodiments have been described to include the RFID schemes described above, the examples are only used for illustrative purposes. One of ordinary skill in the art will understand that variations including additional RFID schemes and apparatus including more than the described RFID schemes described above is within the scope of this disclosure. 
     The RFID apparatus may include mobile terminals such as cellular phone, PDA, PMP, and the like and support a plurality of RFID manners by switching one loop antenna into a chip corresponding to each RFID manner. 
     The above-disclosed subject matter is to be considered illustrative, and not restrictive, and the appended claims are intended to cover all such modifications, enhancements, and other embodiments, which fall within the true spirit and scope. Thus, to the maximum extent allowed by law, the scope is to be determined by the broadest permissible interpretation of the following claims and their equivalents, and shall not be restricted or limited by the foregoing detailed description. 
     While example embodiments have been particularly shown and described, it will be understood by one of ordinary skill in the art that variations in form and detail may be made therein without departing from the spirit and scope of the claims.