Abstract:
A card retention assembly includes a shield and a retraction mechanism. The shield is essentially non-transmissive of radio frequency signals and encloses a card receptacle which retains an RFID card when the retraction mechanism is in a retracted position. The retraction mechanism includes a spool and a retention line connectable to the RFID card and connected to the spool. Manually withdrawing the RFID card from the card receptacle causes the retention line to unwind from the spool and transitions the retraction mechanism from the retracted position to an extended position. The retraction mechanism is biased to the retracted position causing the retention line to wind back onto the spool and automatically returning the RFID card back to the card receptacle when the RFID card is manually released. Radio frequency communication between the RFID card and a proximal card reader is prevented when the RFID card is within the card receptacle and is permitted when the RFID card is outside the card receptacle.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates generally to RFID cards and, more particularly, to a card retention assembly having a shield for protecting the privacy of information contained in an RFID card. 
       BACKGROUND OF THE INVENTION 
       [0002]    Radio frequency identification (RFID) systems generally include at least one reader and a plurality of transponders which are typically termed RFID credentials. One common type of RFID credential comprises a passive radio frequency communication device embedded in a portable substrate, which is in the form of a plastic identification card and is termed an RFID card. The RFID card is carried by a person to be identified or otherwise characterized by a reader of an RFID system. The passive RFID card is dependent on the reader for its power. The reader “excites” or powers up the RFID card by transmitting excitation signals of a given frequency into the space surrounding the reader, which are received by the RFID card and provide the operating power for the circuitry of the recipient RFID card. 
         [0003]    Communication between the reader and the RFID card is enabled by cooperative resonant circuits which are provided in each reader and RFID card. Each resonant circuit includes an inductor, typically in the form of an antenna, which magnetically couples to the inductor of the other resonant circuit through mutual inductance. 
         [0004]    Communication is initiated when an RFID card is proximally positioned relative to the reader. The reader has a power supply which conveys a current to the reader resonant circuit causing the reader antenna to produce an excitation signal in the form of an electromagnetic field. The excitation signal couples to the antenna of the proximally-positioned RFID card through mutual inductance and the excitation signal powers and clocks the card circuitry initiating operation of the RFID card. 
         [0005]    Card operation comprises generation of a response signal at a specified frequency and transmission of the response signal back to the reader. In particular, the card resonant circuit receives a current in response to the excitation signal which causes the card antenna to produce a response signal in the form of an electromagnetic field. The response signal couples to the reader antenna through mutual inductance in substantially the same manner as described above with respect to coupling of the excitation signal to the card antenna. The RFID card typically employs frequency or amplitude modulation of the response signal to encode data stored in the memory of the card circuitry into the response signal. When the response signal couples to the reader antenna, a corresponding current is induced in the reader antenna at the specified frequency. The reader processes the induced current to read the data encoded in the response signal from the RFID card. 
         [0006]    RFID cards are commonly used for personal identification or security access applications during normal workday activities. For example, an individual may require his or her own personal RFID card to gain access into a secured area such as an office building, an elevator floor, an office suite, or a parking complex. To gain access to the secured area, the individual simply places the personal RFID card near a reader positioned at the entrance to the secured area so that the reader, which may be networked to a remote host computer, can identify the individual and authorize access to the secured area if appropriate. 
         [0007]    It is apparent that in many cases it is necessary for an individual to make frequent use of a personal RFID card during the normal course of a work day. Accordingly, it is desirable for an individual to carry a personal RFID card on his or her person at all times during the work day. Although the RFID card is sized to easily fit within a purse, wallet, clothing pocket, briefcase, or other similar conventional mobile storage location, it is often inconvenient and cumbersome for the card holder to recall the specific mobile storage location where the RFID card is being stored at any given moment and to retrieve the RFID card from that location each time the card holder is required to present the RFID card. A more convenient and accessible means for a card holder to carry an RFID card on his or her person is desirable. 
         [0008]    One specialized device a card holder can use to carry a personal RFID card on his or her person, which is both convenient and accessible, is termed a badge reel. Conventional badge reels are widely available, for example, at Sogedex, Parc D&#39;activitès de Pissaloup4, rue Edouard Branly, Bat. Hermès 1, 78190 Trappes, FRANCE (website: www.sogedex.fr) or Baudville, Inc., 5380 52nd Street SE, Grand Rapids, Mich. 49512, USA (website: shop.baudville.com). 
         [0009]    A badge reel is essentially a tether for a badge (e.g., card) such as an RFID card. The badge reel consists of a line having one end attached to a spool, which has a mechanical biasing force applied to it to maintain the line wound on the spool. The free end of the line is attached to the RFID card. The badge reel is also provided with a clip for attachment to the outer clothing of a card holder. When the card holder desires to use the RFID card, the card holder simply grasps the RFID card, which is positioned proximal to the body, and pulls the RFID card away from the body to play out the line from the spool. When the line is unwound from the spool, the card holder is able to position the RFID card away from the body where the RFID card can easily be presented to a card reader without requiring the card holder to stand in a specific position. Once the card reader has read the RFID card, the card holder releases the RFID card from grasp. The mechanical biasing force of the spool reels the line back in and the RFID card returns to an unobtrusive position proximal to the body of the card holder. 
         [0010]    Because RFID cards typically contain private and/or confidential information, there is a concern that the information can be inadvertently and undesirably accessed by any card reader which happens to be within the path of the card holder when the card holder is moving about during normal workday activities while carrying his or her personal RFID card. To overcome this concern, a means is needed for rendering the RFID card inoperable when the card holder has no intent or need to use the RFID card, yet which does not diminish the ready accessability of the RFID card when needed by the card holder. 
         [0011]    Accordingly, it is generally an object of the present invention to provide an RFID card retention assembly which prevents information contained in an RFID card from being inadvertently read by a proximal card reader when the card holder does not intend to use the RFID card. It is generally another object of the present invention to provide such an RFID card retention assembly which maintains the RFID card readily accessible to the card holder at all times should the card holder desire to use the RFID card. It is still another object of the present invention to provide such an RFID card retention assembly which shields the RFID card from view when not in use. These objects and others are accomplished in accordance with the invention described hereafter. 
       SUMMARY OF THE INVENTION 
       [0012]    The present invention is a card retention assembly comprising a shield and a retraction mechanism. The shield has a card receptacle and an opening into the card receptacle. Both are cooperatively sized to receive an RFID card into the card receptacle through the opening. The shield is sufficiently non-transmissive of radio frequency signals to enable the shield to essentially prevent radio frequency communication between an RFID card positioned in the card receptacle and a card reader positioned proximal to the shield. 
         [0013]    The retraction mechanism includes a spool and a retention line connected to and windable around the spool. The retention line extends into the card receptacle and is connectable to an RFID card receivable in the card receptacle. The retraction mechanism has a retracted position and an extended position. The retention line unwinds from the spool when the retraction mechanism transitions from the retracted position to the extended position and the retention line winds onto the spool when the retraction mechanism transitions from the extended position to the retracted position. In accordance with one embodiment, the card retention assembly further comprises a biasing spring coupled to the spool. As such, the spool is biased in a rotational direction which biases the retraction mechanism in the retracted position. 
         [0014]    The retraction mechanism preferably further includes a housing enclosing a housing chamber. The spool is disposed within the housing chamber and the housing is coupled to the shield. A housing aperture is preferably formed through the housing and a shield aperture is preferably formed through the shield to provide a retention line pathway between the housing chamber and the card receptacle. 
         [0015]    The shield preferably includes opposing front and rear planar sections bounding the front and rear of the card receptacle, first and second side sections formed between the front and rear planar sections along side edges of the front and rear planar sections and bounding corresponding sides of the card receptacle, and a top section formed between the front and rear planar sections along top edges of the front and rear planar sections and bounding a corresponding top of the card receptacle. Each of the above-recited sections is preferably optically opaque. 
         [0016]    The opening into the card receptacle is positioned between the front and rear planar sections along bottom edges of the front and rear planar sections. The shield may also include an indent sufficiently sized to expose an RFID card positioned in the card receptacle and enable a card holder to grasp the RFID card and manually withdraw the RFID card from the card receptacle. 
         [0017]    In accordance with one embodiment, the shield consists essentially of a shell which is essentially non-transmissive of radio frequency signals. The shell is preferably constructed from a metallized plastic or a metal. 
         [0018]    In accordance with another embodiment, the shield comprises a shell which is relatively non-transmissive of radio frequency signals and an insulative layer which is relatively transmissive of radio frequency signals. The insulative layer disposed on a surface of the shell and is preferably constructed from a polymeric foam. 
         [0019]    In accordance with yet another embodiment, the shield comprises a shell which is relatively transmissive of radio frequency signals and an insert which is relatively non-transmissive of radio frequency signals. The insert is disposed within the shell which is preferably constructed from a plastic. The insert is preferably constructed from a metallized plastic or a metal. 
         [0020]    In accordance with still another embodiment, the shield comprises a planar section, a view window, a card receptacle, and an opening into the card receptacle. The view window is positioned in the planar section and the card receptacle is bounded in part by the planar section. The card receptacle and opening are sized to receive an RFID card into the card receptacle through the opening. The planar section and view window are sufficiently non-transmissive of radio frequency signals to enable the shield to essentially prevent radio frequency communication between an RFID card positioned in the card receptacle and a card reader positioned proximal to the shield. The view window is sufficiently optically transparent of light to enable a viewer to view a portion of an RFID card positioned in the card receptacle through the view window. 
         [0021]    The planar section is preferably constructed from a continuous solid sheet of a metallized plastic or a metal and is preferably essentially optically opaque. The view window is likewise preferably constructed from a metallized plastic or a metal, but is configured as a mesh sheet or a perforated sheet to enable optical transparency. The view window is alternately constructed from a sheet of transparent, relatively transmissive material in association with the mesh sheet or perforated sheet of the metallized plastic or metal to form a laminate. 
         [0022]    In another characterization, the present invention is a method for transitioning an RFID card between a retracted position and an extended position. The method connects a first end of a retention line to a spool and an opposite second end of the retention line to an RFID card. The spool is rotated in a retraction rotation direction to wind the retention line around the spool, thereby positioning the RFID card in a retracted position within a card receptacle. The card receptacle is enclosed by a shield sufficiently non-transmissive of radio frequency signals to enable the shield to essentially prevent radio frequency communication between the RFID card positioned in the card receptacle and a card reader when the RFID card is positioned in a read range of the card reader. 
         [0023]    The RFID card is positioned in an extended position by withdrawing the RFID card from the card receptacle, preferably manually, to enable radio frequency communication between the RFID card and the card reader when the RFID card is positioned in the read range of the card reader. The spool rotates in an extension rotation direction opposite the retraction rotation direction to unwind the retention line from around the spool when the RFID card is withdrawn from the card receptacle. 
         [0024]    In accordance with one embodiment, the method further comprises biasing the spool in the retraction rotation direction to bias the RFID card to the retracted position. 
         [0025]    In accordance with another embodiment, the method further comprises positioning the spool external to the card receptacle and providing a shield aperture through the shield to provide a retention line pathway between the spool and the card receptacle. 
         [0026]    In accordance with still another embodiment, the method further comprises extending the retention line through the shield aperture and out the card receptacle when the RFID card is withdrawn from the card receptacle. 
         [0027]    The present invention will be further understood from the drawings and the following detailed description. Although this description sets forth specific details, it is understood that certain embodiments of the invention may be practiced without these specific details. It is also understood that in some instances, well-known techniques or structures have not been shown in detail in order to avoid obscuring the understanding of the invention. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0028]      FIG. 1  is a perspective view of a card retention assembly of the present invention and an associated RFID card. 
           [0029]      FIG. 2  is a cross-sectional rear plan view of the card retention assembly of  FIG. 1 . 
           [0030]      FIG. 3  is an enlarged partial cross-sectional side elevational view of the card retention assembly of  FIG. 1 . 
           [0031]      FIG. 4  is a cross-sectional view of an embodiment of a privacy shield included in the card retention assembly of  FIG. 1  taken along line A-A. 
           [0032]      FIG. 5  is a cross-sectional view of an embodiment of a privacy shield included in the card retention assembly of  FIG. 1  taken along line A-A, wherein the privacy shield has an insulating layer disposed on an inner surface of the privacy shield. 
           [0033]      FIG. 6  is a cross-sectional view of an embodiment of a privacy shield included in the card retention assembly of  FIG. 1  taken along line A-A, wherein the privacy shield has an insulating layer disposed on an inner surface and an outer surface of the privacy shield. 
           [0034]      FIG. 7  is a cross-sectional view of an embodiment of a privacy shield included in the card retention assembly of  FIG. 1  taken along line A-A, wherein the privacy shield has an RF non-transmissive insert disposed within an RF transmissive shell. 
           [0035]      FIG. 8  is a cross-sectional view of an embodiment of a privacy shield included in the card retention assembly of  FIG. 1  taken along line A-A, wherein the privacy shield has a plurality of RF non-transmissive inserts disposed within an RF transmissive shell. 
           [0036]      FIG. 9  is a front plan view of an alternate embodiment of the card retention assembly of the present invention and an associated RFID card. 
       
    
    
       [0037]    Embodiments of the invention are illustrated by way of example and not by way of limitation in the above-recited figures of the drawings in which like reference characters indicate the same or similar elements. It should be noted that common references to “an embodiment”, “one embodiment”, “an alternate embodiment”, “a preferred embodiment”, or the like herein are not necessarily references to the same embodiment. 
       DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0038]    A card retention assembly generally designated  10  is shown and described with initial reference to  FIGS. 1 and 2 . The card retention assembly  10  comprises a privacy shield  12  and a retraction mechanism  14  coupled to the privacy shield  12 . The retraction mechanism  14  includes a retention line  16  and a connection strap  18  which is attached to an end of the retention line  16 . The retraction mechanism  14  has a retracted position and a range of extended positions culminating in a fully extended position. The retraction mechanism  14  is shown in a partially extended position in  FIG. 1  and in the retracted position in  FIG. 2 . The positions of the retraction mechanism  14  are described in greater detail below. 
         [0039]    The card retention assembly  10  is configured for cooperative use with a radio frequency identification (RFID) card  20 . An RFID card, as the term is used herein, refers to: 1) passive transponders configured as cards which communicate with a card reader in a contactless manner at a nominal carrier frequency of about 125 kHz frequency (commonly termed proximity cards), 2) passive transponders configured as cards which communicate with a card reader in a contactless manner at a nominal carrier frequency of about 13.56 MHz (commonly termed smart cards), or 3) passive transponders configured as cards which communicate with a card reader in a contactless manner at substantially any other radio frequency. The privacy shield  12  encloses a card receptacle  22  which is an open-ended chamber for receiving and retaining an RFID card  20  when the retraction mechanism  14  is in the retracted position. The connection strap  18  is configured for attachment to the RFID card  20 , thereby effecting secure connection of the retention line  16  to the RFID card  20  at all times. 
         [0040]    The RFID card  20  is a plastic card having physical characteristics similar to a conventional credit card or photo identification card. Passive transponder components are embedded in the RFID card  20  which include an integrated circuit  24  and an antenna  26 . The integrated circuit  24  embodies the processing and memory capabilities of the RFID card  20 . The antenna  26  is coupled to the integrated circuit  24  and is a “dual-function antenna” which performs both the receiving and transmitting functions of the RFID card  20 . Alternatively, two separate receiving and transmitting antennas can be substituted for the single “dual function antenna” in the RFID card. 
         [0041]    The RFID card  20  is typically carried by an authorized person termed the card holder. Information contained in the RFID card  20  enables a compatible card reader to identify or otherwise characterize the card holder when the RFID card  20  is presented to the card reader. In particular, information in digital form is stored in the integrated circuit  24  of the RFID card  20 , which is electronically read in a conventional contactless manner as described above when a card holder positions the RFID card  20  near the compatible card reader. The RFID card  20  optionally includes one or more supplemental components not shown in  FIG. 1 , which enable alternate identification technologies in addition to the present non-contact RFID technology, such as magnetic stripe, Wiegand, contact smart chip, barcode, biometric, photo identification, or graphic (including holographic and text) technology. 
         [0042]    The RFID card  20  is shown, by way of example, to include other functionalities in addition to the RFID functionality, i.e., components  24 ,  26 . In particular, the RFID card  20  has a magnetic stripe  27  containing magnetically stored information which enables magnetic stripe technology. In many cases the RFID card  20  includes an optical medium (not shown) in addition to the magnetic strip  27 , which enables one or more additional technologies. In such cases, the magnetic strip  27  and the optical medium are oftentimes positioned on opposite faces of the RFID card  20 . For example, the magnetic strip  27  is positioned on a rear face  28  of the RFID card  20  and the optical medium is displayed on a front face  29  of the RFID card  20 . 
         [0043]    An optical medium is characterized herein as displaying information in visual form which requires visual access to read and is readable by an appropriate person and/or machine. Examples of optical media include text, photos, bar codes, holograms, biometric images, and the like. The phrase “information contained in the RFID card” as used herein, unless specifically stated otherwise, refers generally to information which is stored in a storage medium mounted within or on the RFID card as well as to information which is visually displayed on the face of the RFID card. 
         [0044]    The retraction mechanism  14  is provided to automatically return the RFID card  20  to the card receptacle  22  when the RFID card  20  has been withdrawn from the card receptacle  22  for use as described below, but use of the RFID card  20  is no longer required. The retraction mechanism  14  is essentially a reel which, in addition to the retention line  16  and connection strap  18 , further includes a housing  30 , a spool  32  and a biasing spring  34 . The housing  30  is securely attached to a top section  36  of the privacy shield  12  and substantially encloses a housing chamber  38 . The spool  32  and cooperative biasing spring  34  are operatively disposed within the housing chamber  38 . 
         [0045]    Referring additionally to  FIG. 3 , the cylindrically configured spool  32  is rotationally mounted to the inside wall of the housing  30  which enables rotation of the spool  32  about its central axis within the housing chamber  38 . A first end of the retention line  16  is securely attached to the spool  32  and the opposite second end of the retention line  16  is securely attached to the connection strap  18  by any suitable fastening means. The connection strap  18  is in turn securely attached to the RFID card  20  likewise by any suitable fastening means. For example, attachment of the connection strap  18  to the RFID card  20  is effected by threading the connection strap  18  through a connection hole  40  formed through the card  20 , looping the strap  18  back onto itself, and riveting the strap  18  to itself. A preferred material of the connection strap  18  is a thin plastic ribbon. The retention line  16  is a thin, durable, highly-pliable line formed from substantially any suitable material such as a string, thread, ribbon, cord, cable, or the like, and is preferably formed from a high-strength string. An exemplary length of the retention line  16  is approximately 2 to 3 feet, while an exemplary length of the connection strap  18  is approximately 1 inch. 
         [0046]    Although not a limitation of the present invention, materials of the retention line  16  and connection strap  18  are preferably essentially non-stretchable during routine operation of the card retention assembly  10 . Furthermore, although the retraction mechanism  14  of the present embodiment is distinct from and essentially external to the privacy shield  12 , it is within the scope of the present invention to alternately configure the privacy shield  12  and retraction mechanism  14  such that the retraction mechanism  14  is integral with the privacy shield  12  and/or is positioned within the interior of the privacy shield  12 . 
         [0047]    The retraction mechanism  14  has an attachment clip  42 , such as a conventional alligator clip, mounted on a rear exterior surface of the housing  32  as shown or alternatively on a rear exterior surface of the privacy shield  12 . The attachment clip  42  permits releasable attachment of the card retention assembly  10  to clothing or a belt so that the card holder can wear the card retention assembly  10  outside his or her clothing, but in a predictable unobtrusive location proximal to the body. As a result the card holder has ready access to the RFID card  20  when retained by the card retention assembly  10 . It is noted that the attachment clip  42  is only one example of a suitable means permitting the card holder ready access to the RFID card  20 . Alternate means within the scope of the present invention include a neck strap which is attachable to the retraction mechanism  14  or privacy shield  12  and is adaptable for wearing around the neck of the card holder. 
         [0048]    The housing  30  has an aperture  44  aligned with an aperture  46  formed in the top section  36  of the privacy shield  12 . The aligned apertures  44 ,  46  provide an unimpeded pathway for the retention line  16  between the housing chamber  38  and the card receptacle  22 . When the retraction mechanism  14  is in the retracted position, essentially the entirety of the retention line  16  is wound around the circumferential edge of the spool  32  with only a relatively short segment of the retention line  16  extending through the apertures  44 ,  46  for attachment to the connection strap  18  as shown in  FIG. 3 . When the retraction mechanism  14  is in the retracted position, essentially the entirety of the connection strap  18  and RFID card  20  resides in the card receptacle  22  of the privacy shield  12  as shown in  FIGS. 2 and 3 . 
         [0049]    The retraction mechanism  14  transitions from the retracted position to the extended position by drawing the RFID card  20  out of the card receptacle  22  and away from privacy shield  12 , while retaining the retention line  16  in connection with the RFID card  20  via the connection strap  18  as shown in  FIG. 1  and simultaneously retaining the retention line  16  in engagement with the spool  32  (thereby correspondingly drawing the retention line  16  through the apertures  44 ,  46 ). Displacement of the RFID card  20  from the card receptacle  22  rotates the spool  32  in a first rotational direction which unwinds an increasingly longer segment of the retention line  16  from the spool  32 . The distance that the RFID card  20  separates from the privacy shield  12  corresponds essentially to the length of the unwound segment of the retention line  16  less the length of the privacy shield  12 . 
         [0050]    The retraction mechanism  14  preferably reaches the fully extended position when the retention line  16  is fully played out, i.e., essentially the entire length of the retention line  16  is unwound from the spool  32 . The distance that the RFID card  20  is separated from the privacy shield  12  when the retraction mechanism  14  is in the fully extended position, corresponds essentially to the entire length of the retention line  16  less the length of the privacy shield  12  (which is essentially negligible relative to the entire length of the retention line  16 ). Thus, in an exemplary case where the length of the retention line  16  is two feet, the fully extended position of the retraction mechanism  14  provides the RFID card  20  with approximately 2 feet of clearance from the body of the card holder. 
         [0051]    The biasing spring  34 , which may be a conventional coil or leaf spring, is coupled to the spool  32  in a manner which biases rotation of the spool  32  in a second rotational direction opposite the first rotational direction that winds the retention line  16  onto the spool  32 . Unwinding the retention line  16  from the spool  32  requires application of an opposing external force to the retraction mechanism  14  which is greater than the biasing force of the spring  34  to rotate the spool  32  in the first rotational direction. Accordingly, the biasing spring  34  returns the retraction mechanism  14  to the retracted position whenever the retraction mechanism  14  is in the fully extended position or a partially extended position in the absence of a sufficient opposing external force being applied to the retraction mechanism  14 . 
         [0052]    The privacy shield  12  functions as a shroud for the RFID card  20  when the card  20  is not in use for its intended application. Intended RFID card applications include identification, security access, logical access, and cash transactions to name a few. The dimensions and configuration of the privacy shield  12  and correspondingly the card receptacle  22  are a function of the dimensions and configuration of the RFID card  20 . In a preferred embodiment, the privacy shield  12  and correspondingly the card receptacle  22  each have a rectangular configuration such that the card receptacle  22  accommodates a single conventionally sized RFID card. 
         [0053]    The privacy shield  12  is defined by a rear planar section  48 , a front planar section  50 , first and second side sections  52 ,  54  and the top section  36 . The rear and front planar sections  48 ,  50  of the privacy shield  12  are essentially identically constructed and are disposed in spaced-apart relationship to one another forming the card receptacle  22  therebetween. The first and second side sections  52 ,  54  of the privacy shield  12  are essentially identically constructed and engage the side edges of the rear and front planar sections  48 ,  50  and enclose the sides of the card receptacle  22 . The top section  36  similarly engages the top edges of the rear and front planar sections  48 ,  50  and encloses the top of the card receptacle  22 . The bottom of the card receptacle  22  is a slotted opening  56  which maintains the card receptacle  22  open to the outside and freely permits removal or insertion of the RFID card  22  from or into the card receptacle  22 . 
         [0054]    The bottom opening  56  is preferably sized to receive a narrow leading edge of the RFID card  22 . The rear and front planar sections  48 ,  50  of the privacy shield  12  preferably have correspondingly aligned indents  58   a ,  58   b  formed along their exposed bottom edges to expose a small portion of the tail end of the RFID card  20  when the retraction mechanism  14  is in the retracted position and the RFID card  20  is retained in the card receptacle  22 . The indents  58   a ,  58   b  enable the card holder to grasp the RFID card  20  with the fingers when the card holder desires to withdraw the RFID card  20  from the card receptacle  22  to transition the retraction mechanism  14  from the retracted position to the extended position. 
         [0055]    The privacy shield  12  is preferably constructed as a single integral structure or is alternatively constructed in separate sections, which are joined or otherwise assembled together. Various specific embodiments of privacy shield constructions are shown and described below with reference to  FIGS. 4 through 8 , which all have alternate utility in the card retention assembly  10  shown in  FIGS. 1-3 . 
         [0056]    Referring initially to  FIG. 4 , an embodiment of a privacy shield generally designated  12   a  is shown and described. The privacy shield  12   a  is a durable hard shell  60  preferably constructed essentially in its entirety from a single material. The shell  60  is characterized as being essentially non-transmissive of RF energy. A structure generally characterized as being essentially non-transmissive of RF energy herein can be more particularly characterized as being either sufficiently reflective or absorptive of RF energy or both to substantially prevent all or a substantial portion of the RF energy contacting the structure to pass through the structure. Exemplary materials which can be used to construct the non-transmissive shell  60  include those which are deemed metallic in character such as metal or metallized plastic. Metallized plastic structures are typically constructed by molding the molten metallized plastic into the desired configuration of the shell  60 . Metal structures are typically constructed by forming one or more sheets of the metal into the desired configuration. In any case, the non-transmissive shell  60  renders an RFID card essentially inoperable when positioned between the RFID card and a compatible card reader. 
         [0057]    Referring to  FIG. 5 , an alternate embodiment of a privacy shield generally designated  12   b  is shown and described. The privacy shield  12   b  includes a shell  60  having essentially the same construction and properties as the shell  60  of the privacy shield  12   a , but further includes an inner insulative layer  62  disposed as a liner on an inner surface of the shell  60 . As such, the inner insulative layer  62  partially or entirely lines the walls of the card receptacle  22 . The inner insulative layer  62  is relatively more pliant and more RF transmissive than the shell  60 . As such, the inner insulative layer  62  insulates the RFID card  20  from contact with the shell  60  and correspondingly protects the RFID card  20  from possible damage due to abrasion from the shell  60 . A preferred material of the insulative layer  62  is a polymeric foam. 
         [0058]    Referring to  FIG. 6 , an alternate embodiment of a privacy shield generally designated  12   c  is shown and described. The privacy shield  12   c  includes a shell  60  and an inner insulative layer  62  having essentially the same construction and properties as the shell  60  and inner insulative layer  62  of the privacy shield  12   b , and further includes an outer insulative layer  64  disposed as a coating on an outer surface of the shell  60 . The outer insulative layer  64  is preferably formed from the same or a substantially similar material as the inner insulative layer  62 . 
         [0059]    Referring to  FIG. 7 , an alternate embodiment of a privacy shield generally designated  12   d  is shown and described. The privacy shield  12   d  includes a relatively RF transmissive shell  66  and a relatively RF non-transmissive insert  68 . The shell  66  is formed from a material which is relatively less hard than the material of the insert  68 . An exemplary material of the shell  66  is an RF transmissive plastic or a resin and an exemplary material of the insert  68  is an RF non-transmissive metal or a metallized plastic. The privacy shield  12   d  is preferably constructed by injection molding the shell  66  around essentially the entirety of the insert  68 , which is preferably a four- or five-sided essentially continuous unitary structure. The non-transmissive insert  68  renders an RFID card essentially inoperable when positioned between the RFID card and a compatible card reader. 
         [0060]    Referring to  FIG. 8 , an alternate embodiment of a privacy shield generally designated  12   e  is shown and described. The privacy shield  12   e  includes a relatively RF transmissive shell  66  and a plurality of relatively RF non-transmissive inserts  70   a ,  70   b . The shell  66  has essentially the same construction and properties as the shell  66  of the privacy shield  12   d . The inserts  70   a ,  70   b  likewise have essentially the same properties as the shell  66  of the privacy shield  12   d . However, rather than having a single continuous insert construction, the privacy shield  12   e  disposes the insert  70   a  in the front of the shell  66  and the separate and distinct insert  70   b  in the back of the shell  66  with the inserts  70   a ,  70   b  being discontinuous on the sides of the shell  66 . The non-transmissive inserts  70   a ,  70   b  render an RFID card essentially inoperable when either is positioned between the RFID card and a compatible card reader. 
         [0061]    In sum, it is apparent that all of the above-recited embodiments of the privacy shield  12   a ,  12   b ,  12   c ,  12   d ,  12   e  render the RFID card  20  inoperable for its RFID functionality when the RFID card  20  is enclosed within the card receptacle  22  by the privacy shield  12 , i.e., when the retraction mechanism  14  is in the retracted position. Specifically, the RF non-transmissive character of the privacy shield  12  essentially blocks the transmission of electromagnetic energy, namely, RF signals, in either direction past the privacy shield  12 . When it is desired to return the RFID card  20  to RFID operability, the card holder simply withdraws the RFID card  20  from the card receptacle  22  and transitions the retraction mechanism  14  to an extended position. 
         [0062]    Referring to  FIG. 9 , a specific embodiment of a card retention assembly generally designated  10   f  is shown and described along with an associated RFID card  20   f . The card retention assembly  10   f  is essentially the same as the card retention assembly  10  of  FIGS. 1-3  except that the privacy shield  12   f  of the card retention assembly  10   f  is shown to include a view window  72  positioned in the front planar section  50  of the privacy shield  12   f . The view window  72  is preferably a discrete planar member closely fitted into a window opening formed in the front planar section  50  and integrally joined with the edges  73  of the window opening which are sized identically to the outer perimeter of the view window  72 . The view window  72 , like the remainder of the privacy shield  12   f , is characterized as RF non-transmissive, but is also further characterized as having specific optical properties. In particular, the view window  72  is characterized as being sufficiently optically transparent to light to enable the viewer to view the portion of the RFID card  20   f  positioned behind the view window  72  when the retraction mechanism  14  is in the retracted position with the RFID card  20   f  retained within the card receptacle  22  of the privacy shield  12   f.    
         [0063]    The view window  72  is preferably located in the front planar section  50  of the privacy shield  12   f  so that the view window  72  faces outward when the card retention assembly  10   f  is being worn by a card holder. The view window  72  is specifically positioned relative to the front planar section  50  so that the view window  72  aligns with an optical medium  74  visually displayed on the front face  29  of the RFID card  20   f , such as an ID photo of a card holder, when the RFID card  20   f  is retained within the card receptacle  22 . Thus, the view window  72  enables a viewer to view the optical medium  74  though the view window  72  of the privacy shield  12   f  without requiring the card holder or viewer to withdraw the RFID card  20   f  from the card receptacle  22  even if the remainder of the privacy shield  12   f  other than the view window  72  is opaque. 
         [0064]    The view window  72  can be constructed from substantially any material which provides the view window  72  with the desired characteristics of RF non-transmissiveness and optical transparency. In accordance with one embodiment, the view window  72  is constructed at least in part from the same RF non-transmissive material as the remainder of the privacy shield  12  such as a metal or metallized plastic. Most metal or metallized plastic is essentially optically opaque when configured as a continuous sheet, which is a preferred configuration of the privacy shield  12  of  FIGS. 1-3 . However, the metal or metallized plastic can be reconfigured to a diaphanous form such as a mesh or perforated sheet for construction of the view window  72 . Thus, the view window  72  is preferably a mesh or perforated sheet which has sufficiently small openings formed therein to substantially prevent all or a substantial portion of the RF energy contacting the view window  72  from passing through the view window  72 , but which has a sufficient number of such openings formed therein to substantially enable a viewer looking at the view window  72  to see through the view window  72 . 
         [0065]    The view window  72  can alternatively be a laminate comprising the mesh or perforated sheet of metallic material bonded to or sandwiched between one or more sheets of transparent glass or plastic which is both RF and optically transmissive. This type of construction is common to view windows which are employed in doors of conventional microwave ovens. 
         [0066]    It is apparent that each embodiment of a privacy shield described above with reference to  FIGS. 4-8  can be readily adapted by the skilled artisan applying the teaching herein to include a view window as described above within the respective embodiment of the privacy shield. 
         [0067]    The card retention assembly  10  and its specific embodiment  10   f  as described above have a number of practical advantages. Such a card retention assembly is relatively inexpensive to manufacture and convenient to use. The card retention assembly effectively prevents unintended reading of information contained in an RFID card and/or effectively prevents undesired detection of an RFID card by a proximal card reader. The card retention assembly also effectively prevents a card holder from losing or misplacing an RFID card. It is further noted that the outer surface of the privacy shield  12  is highly visible when the card retention assembly is worn by a card holder. Accordingly, the privacy shield  12  provides an effective placement for advertisements, company logos, or other types of graphic designs or alpha-numeric messages. 
         [0068]    While the forgoing preferred embodiments of the invention have been described and shown, it is understood that alternatives and modifications, such as those suggested and others, may be made thereto and fall within the scope of the invention.