Abstract:
A storage system for storing samples, such as frozen biological samples in RFID-tagged vials. The storage system has a plurality of lowest-level containers, such as sample boxes; a plurality of mid-level containers, such as shelves and racks; and a highest-level container, such as a mechanical freezer. Each lowest-level container receives a plurality of samples in a corresponding plurality of storage locations, each mid-level container receives two or more lowest-level containers, and the highest-level container receives the two or more mid-level containers. Each mid-level container and each lowest-level container has a corresponding indicator device. A controller sub-system tracks the locations of samples stored in the storage system. When a desired sample is to be retrieved from the storage system, the controller sub-system activates (a) the indicator device corresponding to the mid-level container containing the desired sample and (b) the indicator device corresponding to the lowest-level container containing the desired sample.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of co-pending U.S. application Ser. No. 13/026,359, filed on Feb. 14, 2011 as attorney docket no. 1136.006, which application claims the benefit of the filing dates of U.S. provisional application No. 61/304,392, filed on Feb. 12, 2010 as attorney docket no. 1136.005PROV, and U.S. provisional application No. 61/304,481, filed on Feb. 14, 2010 as attorney docket no. 1136.006PROV, the teachings of both of which are incorporated herein by reference in their entirety. 
         [0002]    The subject matter of this application is related to the subject matter of U.S. patent application Ser. No. 12/064,748 (“the &#39;748 application”), filed on Feb. 25, 2008, and U.S. patent application Ser. No. 12/787,729 (“the &#39;729 application”), filed on May 26, 2010, the teachings of both of which are incorporated herein by reference. 
     
    
     BACKGROUND 
       [0003]    1. Field of the Invention 
         [0004]    The present invention relates to RFID tags and, more specifically but not exclusively, to using RFID tags to identify and track samples, such as biological samples stored in freezers. 
         [0005]    2. Description of the Related Art 
         [0006]    This section introduces aspects that may help facilitate a better understanding of the invention. Accordingly, the statements of this section are to be read in this light and are not to be understood as admissions about what is prior art or what is not prior art. 
         [0007]    Biological samples are often stored in vials that are marked with and/or have labels containing bar codes and/or printed or handwritten text and/or numbers that identify the particular biological sample contained within the vial. In order to preserve the biological material, such vials are often stored in freezers containing many hundreds or even thousands of different vials. Over time, labels tend to fade and peal off from the vials, making identification of the stored samples difficult or even impossible. Even when the labels remain intact and legible, when the vials are removed from the freezer, reading the labels is often hampered by ice and frost. 
         [0008]    Technology is being developed to use RFID (radio frequency identification) tags to identify and track biological samples stored in freezers, where each vial has its own RFID tag having a unique RFID number associated with it. Here we define RFID tag to include the RFID chip, the antenna, and a substrate used to hold everything in place. The &#39;748 and &#39;729 applications describe some of this technology. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    Other aspects, features, and advantages of the present invention will become more fully apparent from the following detailed description, the appended claims, and the accompanying drawings in which like reference numerals identify similar or identical elements. 
           [0010]      FIG. 1  illustrates, in an exploded, 3D perspective view, one technique for permanently affixing an RFID tag to a previously untagged vial; 
           [0011]    FIG.  2 (A 1 ) shows a cross-sectional side view of the bottom of a tagged vial according to another technique for permanently affixing an RFID tag to a previously untagged vial, while FIG.  2 (A 2 ) shows a plan view of the RFID tag of FIG.  2 (A 1 ); 
           [0012]    FIGS.  2 (B 1 ) and  2 (B 2 ) through  2 (F 1 ) and  2 (F 2 ) show similar views of tagged vials and RFID tags, respectively, according to five other techniques for permanently affixing RFID tags to previously untagged vials; 
           [0013]    FIG.  3 (A 1 ) shows a cross-sectional side view of a tagged vial having an unvented cavity, and FIG.  3 (A 2 ) shows a magnified, cross-sectional side view of the bottom of the tagged vial of FIG.  3 (A 1 ); 
           [0014]    FIG.  3 (B 1 ) shows a cross-sectional side view of tagged vial having a vented cavity, and FIG.  3 (B 2 ) shows a magnified, cross-sectional side view of the bottom of the tagged vial of FIG.  3 (B 1 ); 
           [0015]      FIG. 4  shows a cross-sectional side view of a liquid nitrogen dewar; 
           [0016]      FIG. 5  shows cross-sectional side view of a transport dewar used for sample transport and its various components; 
           [0017]      FIG. 6  shows a 3D perspective view of a mechanical freezer used to store tagged vials containing, e.g., biological samples; 
           [0018]      FIG. 7(A)  shows a front view of a tissue block repository; 
           [0019]      FIG. 7(B)  shows a top view of one of the drawers of  FIG. 7(A) ; 
           [0020]      FIG. 7(C)  shows a schematic block diagram of one of the tissue blocks of  FIG. 7(B) ; 
           [0021]      FIG. 8  shows an RFID tag formed using an annular bobbin; 
           [0022]      FIG. 9(A)  shows a 3D perspective, partial cut-away view of a conduit that can be used to transfer electrical power and/or data signals between the outside world and the interior of a freezer; 
           [0023]      FIG. 9(B)  shows a cross-sectional view of the interface between the door and the body of a freezer; and 
           [0024]      FIG. 9(C)  shows a cross-sectional view of the interface of  FIG. 9(B)  with conduit  900  installed between the freezer body and the gasket. 
       
    
    
     DETAILED DESCRIPTION 
     Affixing RFID Tags to Vials 
       [0025]    FIGS. 10-13 of the &#39;748 application illustrate different techniques for affixing RFID tags to vials. Each of these techniques involved inserting an existing vial into a tagged tube having an RFID tag hermetically sealed within a bottom compartment of the tagged tube. One problem with these techniques is that the diameter and height of the resulting vial/tube assembly are larger than those of the vial alone. As a result, the vial/tube assembly might not fit within standard storage boxes, centrifuges, and other lab equipment and might force the use of lower-density boxes (i.e., boxes capable of storing fewer vials per unit area). 
         [0026]    Techniques have now been developed for affixing RFID tags to vials without increasing the diameter and/or height of the resulting tagged vials as compared to the original, untagged vials. Some of these techniques can be applied to conventional vials, including conventional vials that already contain biological samples. As such, these techniques can be used to retrofit existing vials with RFID tags. Other techniques involve specially designed vials, which might not yet exist. Although such vials might not yet exist, once they are manufactured, the RFID tags can be affixed to the vials either before or after biological samples are stored in the vials. 
         [0027]      FIG. 1  illustrates, in an exploded, 3D perspective view, one technique for permanently affixing an RFID tag  102  to a previously untagged vial  101 . In particular, RFID tag  102  is inserted into a recess  107  located at the bottom of vial  101 . A retainer  103  (a.k.a. plug or cap) is then inserted into the recess to retain the RFID tag in place, resulting in a tagged vial. As shown in  FIG. 1 , retainer  103  has (e.g., three) rigid (e.g., metal), angled tabs  104  that engage (e.g., gouge into) the relatively soft (e.g., plastic) material of the vial after the retainer is inserted into recess  107 , thereby preventing retainer  103  and RFID tag  102  from being easily removed from the vial. In addition, retainer  103  has (e.g., three) protrusions  105  that fit within (e.g., three) corresponding grooves  108  at the bottom of vial  101  to ensure that tabs  104  (and therefore RFID tag  102 ) are properly aligned within recess  107 . Insert  103  also has (e.g., three) openings  106  (a.k.a. vents) that allow liquid nitrogen (used to keep the biological samples cold) to drain from the tagged vial in order to prevent violent decompression that might otherwise occur as the liquid nitrogen warms up. 
         [0028]    Grooves  108  are used to grab the bottom of the vial during robotic handling and one-handed removal of the cap where the vial is inserted into a socket that meshes with these grooves. Even though the bottom of the vial has been filled with a tag and a retainer, the geometry of the grooves is preserved due to openings  106 . 
         [0029]    Note that, when RFID tag  102  is affixed to vial  101  after a biological sample has already been stored within the vial, the sterility of the stored biological sample remains intact. This technique allows untagged vials to be sterilized using gamma radiation and/or e-beam radiation, which can destroy RFID tags. After biological samples have been placed and hermetically sealed within the sterilized vials, the RFID tags can then be affixed using the technique of  FIG. 1  without jeopardizing the sterility of the stored samples. Note that the sterility of the exterior of the vial is often not an issue so long as the biological sample is appropriately sealed within the sterile interior of the vial. 
         [0030]    When other sterilization techniques are employed (e.g., exposure to ethylene oxide gas or autoclaving, using lower doses of radiation, orienting the radiation away from the RFID tag, or otherwise shielding the RFID tag from the radiation), it may be possible to sterilize the RFID tag as well before affixing it to the vial. 
         [0031]    FIG.  2 (A 1 ) shows a cross-sectional side view of the bottom of a tagged vial  210  according to another, similarly suitable technique for permanently affixing an RFID tag  212  to a previously untagged vial, while FIG.  2 (A 2 ) shows a plan view of RFID tag  212 . FIGS.  2 (B 1 ) and  2 (B 2 ) through FIGS.  2 (F 1 ) and  2 (F 2 ) show similar views of tagged vials and RFID tags, respectively, according to five other, similarly suitable techniques for permanently affixing RFID tags to previously untagged vials. 
         [0032]    Vials  210  and  220  of FIGS.  2 (A 1 ) and  2 (B 1 ), respectively, are conventional vials that are not necessarily manufactured in any special way to accommodate RFID tags  212  and  222 . On the other hand, vials  230 - 260  of FIGS.  2 (C 1 )- 2 (F 1 ), respectively, do have structure specifically designed to accommodate the corresponding RFID tags  232 - 262 . 
         [0033]    Referring to FIGS.  2 (A 1 ) and  2 (A 2 ), a spring  211  is attached to RFID tag  212 , and the resulting tag/spring assembly is press-fit into the recess at the bottom of vial  210 . The tag is oriented properly within the recess as a result of the abutting of the flat, top surface of the tag with the flat, bottom surface of the vial. Spring  211  has pointed, rigid (e.g., metal), angled tabs  213  that keep the tag in place by engaging the relatively soft vial material. If spring  211  is made of a conducting metal, then a gap  214  in the spring will prevent loss of RFID signal due to current that could otherwise be induced in the closed loop formed by a spring without such a gap. 
         [0034]    The technique illustrated in FIGS.  2 (B 1 ) and  2 (B 2 ) is very similar to that of FIGS.  2 (A 1 ) and  2 (A 2 ). In this technique, however, RFID tag  222  is oriented properly within the recess as a result of the abutting of the curved, top surface  221  of the tag with the curved, bottom surface of vial  220 . 
         [0035]    Referring to FIGS.  2 (C 1 ) and  2 (C 2 ), the bottom of vial  230  has a number (e.g., at least three) of flexible (e.g., plastic), outer clips  231  (or a single, flexible, ring-shaped clip) that allow a disk-shaped (or washer-shaped) RFID tag  232  to be inserted into and then permanently retained within the recess at the bottom of the vial. Here, too, abutting of the flat (alternatively, curved), top surface of the tag with the flat (alternatively, curved), bottom surface of the vial ensures proper orientation of the tag within the vial recess. 
         [0036]    Referring to FIGS.  2 (D 1 ) and  2 (D 2 ), the bottom of vial  240  has a number (e.g., at least three) of flexible (e.g., plastic), inner clips  241  (or a single, flexible, ring-shaped, inner clip) and a number of outer stops  243  (or a single, ring-shaped, outer stop) that allow a washer-shaped RFID tag  242  to be inserted into and then permanently retained within the recess at the bottom of the vial. Here, too, abutting of the flat, top surface of the tag with the flat, bottom surfaces of the stops ensures proper orientation of the tag within the vial recess. 
         [0037]    Referring to FIGS.  2 (E 1 ) and  2 (E 2 ), the cylindrical recess side wall at the bottom of vial  250  has (e.g., four) holes  253  that receive (e.g., four) corresponding tabs  251  that protrude from the outer, cylindrical edge of disk-shaped (or washer-shaped) RFID tag  252 . Beveled edges  254  on the flexible recess side wall assist during the insertion of the tag into the vial recess. Here, the positioning of tabs  251  into holes  253  ensures proper orientation of the tag within the vial recess. 
         [0038]    The technique illustrated in FIGS.  2 (F 1 ) and  2 (F 2 ) is very similar to that of FIGS.  2 (D 1 ) and  2 (D 2 ). In this technique, however, vial  260  has outer clips  261 , similar to outer clips  231  of FIG.  2 (C 1 ), instead of inner clips, and inner guides  263 , instead of outer stops. Here, abutting of the flat, top surface of the tag with the flat, top surfaces of the guides ensures proper orientation of the tag within the vial recess. 
         [0039]    Note that all of the techniques illustrated in  FIGS. 1 and 2  enable permanent attachment of RFID tags to sterile vials, where, in typical applications, the term “permanent” implies that the RFID tags will stay in place during the g forces encountered during centrifugation. In addition, all of these techniques result in tagged vials having the same diameter and the same height as the corresponding untagged vials. 
         [0040]    Although not necessarily illustrated in these figures, it is contemplated that the vials associated with some or all of these different techniques enable conventional methods for removing and replacing the caps at the tops of the vials. These methods usually involve teeth or slots at the bottom of the vials that engage complementary slots or teeth in a desktop receptacle that allows the user to twist the cap off or onto a received vial with one hand. The vials may also have other vial characteristics such as seals, indentations for single-hand and/or robotic manipulation, etc., that conform with and enable conventional laboratory practices. 
         [0041]    Although the embodiments of  FIG. 2  were described in the context of labels  212 - 262  identifying RFID tags, it should be understood that those figures would also apply to techniques in which the elements labeled  212 - 262  are retainers analogous to retainer  103  of  FIG. 1  that hold in place RFID tags analogous to RFID tag  102  of  FIG. 1 . Note that the RFID tag and/or the retainer might need to be modified from the configurations shown in  FIG. 2  depending on the characteristics of the embodiment. For example, in  FIGS. 2(D) and 2(F) , both the RFID tag and the retainer would need to be washer shaped. In  FIG. 2(B) , the top surface of the RFID tag, and perhaps not the top surface of the retainer, would have the curved shape to abut the curved, bottom surface of the vial. 
         [0042]    Although  FIGS. 1 and 2  illustrate seven different techniques for affixing RFID tags to vials, those skilled in the art will appreciate that the same result can be achieved using different designs and configurations of vials and tags. Note that some of these other techniques might not retain the same diameter and/or the same height as the untagged vial. In addition, some of these techniques may allow selective removal of an RFID tag from a previously tagged vial. 
         [0043]    Note that, when an untagged vial has no recess, an RFID tag can be affixed to (e.g., the bottom of) the vial (i) using a suitable adhesive, such as a hot-melt adhesive, or (ii) by partially melting the (e.g., plastic) vial material to accommodate the tag. 
       Venting Tagged Vials 
       [0044]    FIG.  3 (A 1 ) shows a cross-sectional side view of tagged vial  331 , and FIG.  3 (A 2 ) shows a magnified, cross-sectional side view of the bottom of tagged vial  331 . The bottom of the tagged vial has an enclosed cavity  332  that can be used to hold an RFID tag and/or a label containing a 2D bar code, text, and/or numbers, collectively labeled  333 . Such a tagged vial can trap liquid nitrogen within the enclosed cavity as a result of cracks or pinhole defects in the (plastic) vial material that are formed during manufacture or during repeated freeze/thaw cycles. When such vials are removed from cold storage and brought to room temperature, the trapped liquid nitrogen evaporates into gas. If the gas cannot escape quickly enough from the enclosed cavity, high pressures can build up, possibly resulting in violent decompression of the trapped gas and any remaining liquid, resulting in sample loss and possible injury. 
         [0045]    As described previously, retainer  103  of  FIG. 1  has one or more holes  106  that allow venting of liquid nitrogen trapped within the recess of tagged vial  101 . An analogous technique can be employed in the case of a vial having an enclosed cavity, such as that shown in  FIG. 3 . 
         [0046]    FIG.  3 (B 1 ) shows a cross-sectional side view of tagged vial  351 , and FIG.  3 (B 2 ) shows a magnified, cross-sectional side view of the bottom of tagged vial  351 . Tagged vial  351  is identical to tagged vial  331  of  FIG. 3(A) , except that there are one or more vent holes  341  at the bottom (and/or at the side) of cavity  352  that allow liquid nitrogen to drain from the cavity as the vial is removed from the freezer. The holes also vent nitrogen gas as the liquid evaporates, thereby preventing pressure build-up and the concomitant violent decompression. 
         [0047]    Note that venting holes can also be incorporated into the design of the tagged tubes shown in FIGS. 10-13 of the &#39;748 application. 
       Wireless Power/Data Transfer in a Liquid Nitrogen Dewar 
       [0048]    RFID-tagged vials containing biological samples can be stored in ultra-low-temperature biological repositories, such as liquid nitrogen dewars and mechanical freezers. For example, in a dewar, multiple tagged vials are stored in each of multiple boxes, multiple such boxes are stored in each of multiple racks that are housed within the dewar. In a mechanical freezer, multiple such boxes can be stored in each of multiple shelves within the freezer. In designing such cold storage systems, one challenge is getting electrical power and downlink data to the RFID tags and reading uplink data from the RFID tags. 
         [0049]      FIG. 4  shows a cross-sectional side view of a liquid nitrogen dewar  400  that uses wireless coupling to transfer electrical power and/or downlink data to and uplink data from different sets of electronics that are themselves responsible for interacting with the RFID tags of tagged vials stored within the dewar. 
         [0050]      FIG. 4  shows two different power coils  402  and  412  (e.g., annular antennas) configured within dewar  400 . Depending on the particular implementation, dewar  400  may have only one of these two power coils or both. Although not explicitly shown in  FIG. 4 , each coil is powered via cabling that is, for example, threaded through a hole in dewar lid  413  or through the interface between the lid and the dewar body  401 . The following description assumes that dewar  400  has power coil  402 , but not power coil  412 , although analogous teachings would apply to the other two possible implementations of dewar  400 . 
         [0051]    As illustrated in  FIG. 4 , dewar  400  stores two different types of racks: type A and type B. In rack type A, rack  404  has rack circuit  403 , and each box  406  stored in the rack has a box circuit  407 . Associated with rack circuit  403  is rack electronics  405 , and associated with each box circuit  407  is a different set of box electronics  408 . Although not explicitly shown in  FIG. 4 , each circuit is hard-wired to its corresponding set of electronics. 
         [0052]    In operation, AC electrical power from outside dewar  400  is provided to power coil  402  via the previously described (but not illustrated) cabling through or adjacent to plug  413 . The frequency of the AC electrical power is selected such that electromagnetic radiation generated by power coil  402  is wirelessly received by rack circuit  403  and box circuits  407 . The electrical power induced in these circuits is then transferred via hard-wiring to provide operating power to the corresponding sets of electronics. 
         [0053]    In rack type B, rack  414  has rack circuit  409 , which is connected via hard-wiring to rack electronics  410  and to rack coils  416  on the rack side. Inductively coupled to each rack coil  416  is a corresponding box coil  415  in each box, which is, in turn, connected via hard-wiring (not shown) to a corresponding set of box electronics  411 . In this case, the electromagnetic radiation generated by power coil  402  is wirelessly received by rack circuit  409 , and the electrical power induced in that circuit is then distributed to all of the different sets of electronics. 
         [0054]    Other types of racks are also possible having different configurations of wireless and wired power and data transfer. 
         [0055]    Independent of the rack type, the power transfer and data signaling between each set of box electronics and the corresponding individual RFID tags in the stored vials are achieved by inductive coupling of closely positioned coils as described in the &#39;748 and &#39;729 applications. 
         [0056]    In a similar manner that electrical power can be transferred from outside of dewar  400  to the different sets of electronics via power coil  402  and the various circuits so too can downlink data be transfer along that same path using standard AM and/or FM or any other communication technique. In addition, in a reciprocal manner, uplink data can be transferred from the various sets of electronics to outside of dewar  400  via the various circuits and power coil  402  using similar communication techniques. 
         [0057]    To locate a particular tagged vial stored within dewar  400 , its physical address can be reported to the outside world. In this case, one or all of the tagged vials can be queried either simultaneously or sequentially in groups of one or more vials by the different sets of rack and box electronics until the desired vial is located. The location of that vial within its box would then be reported to the corresponding set of box electronics, which would then report that intra-box information along with the identity of the box to the corresponding rack electronics, which would then report the intra-box information, the box identity, and the identity of the rack to the outside world. With this information, a user could remove the identified rack from dewar  400 , remove the identified box from that rack, and then remove the tagged vial from the identified location within that box. 
         [0058]    Depending on the particular implementation, the different sets of electronics can be powered and activated either simultaneously or sequentially by assigning different sets of electronics to different non-overlapping time slots, where the particular time slot for a given set of electronics can be assigned as a function of the physical location of the electronics. For example, the time slot for the box at the top of rack  404  would be based on the rack position of the box, not the particular box per se. As such, if that box were swapped with another box in another position, then their time slots would also be swapped. Analogous allocation and swapping of time slots may also be applied to different racks located at different positions within dewar  400 . 
         [0059]    Other methods of collision mitigation can be used as well. 
         [0060]    For freezers, power coils analogous to power coils  402  and/or  412  can be installed inside a freezer and powered via cabling to the outside world with analogous circuits configured to the shelves and boxes within the freezer to achieve wireless power and/or data transfer between those power coils and circuits that provide operating power and data to and from different sets of shelf and box electronics. 
         [0061]    The frequency of the transmitted electromagnetic radiation used to transfer power would typically be in the range of about 1 MHz to about 10 MHz, which has a wavelength of about 30 m to about 300 m, which is much bigger than typical dewars and freezers. This enables dewars and freezers to be designed to have few if any “dead spots” (i.e., locations with intolerably small field strengths resulting from destructive interference) within their interiors. Since dewars and freezers are essentially very cold Faraday cages, any wireless signals escaping to the outside world would be relatively small, thereby making FCC compliance relatively easy. 
         [0062]      FIG. 5(A)  shows a cross-sectional side view of a transport dewar—another (smaller) type of liquid nitrogen dewar  500 —that may be used, for example, to transport samples of animal sperm to and from farms. As in the case of larger liquid nitrogen dewars, like dewar  400  of  FIG. 4 , and mechanical freezers, here, too, it is important to know the identity and location of samples within dewar  500 . 
         [0063]    As shown in  FIG. 5(A) , dewar  500  holds multiple canisters  507 , each of which holds multiple canes  509  (see  FIG. 5(B) ) having clips  513  that can hold two different types of tagged containers: tagged straws  510  (see  FIG. 5(C) ) and tagged vials  511  (see FIG.  5 (D)), each instance of both of which has a unique RFID tag  512 .  FIG. 5(E)  shows a cane  509  holding a single goblet  514  containing multiple tagged straws  510 , while  FIG. 5(F)  shows a cane  509  holding three tagged vials  511  (one per clip  513 ). Dewar  500  may also hold other suitable types of tagged containers (i.e., other than vials and straws). 
         [0064]    Each canister  507  is connected by a suspending bar  506  to a corresponding handle  504  that extends outside of dewar  500  adjacent to a loose-fitting plug  503 . Handle  504  enables the corresponding canister, along with its associated goblets, straws, and vials, to be removed from and then replaced back into dewar  500 . 
         [0065]    As shown in  FIG. 5(A) , each canister  507  has one or more RFID antennae  508  that can communicate with the RFID tags attached to the tagged containers stored in that canister. These antennae are controlled by a circuit  505  (e.g., located within plug  503 ) that can inventory the contents of the dewar as needed. Circuit  505  can be powered either from the outside world via external wiring (not shown) or by a battery  516  (e.g., also located within plug  503 ) that is connected to circuit  505  via internal wiring (not shown). Depending on the implementation, circuit  505  can communicate with an external computer, for example, via Ethernet or USB or wirelessly. The external computer can also be a handheld device, a smart phone, or any other suitable mobile computing device for use in the field. This device can, in turn, communicate with a central database and/or provide a graphical user interface to show the contents of the dewar and/or to illuminate an LED  515  located on dewar plug  503  and/or an LED  517  located on handle  504  to show the user which dewar and which canister holds a desired sample. 
         [0066]    The power for reading the RFID tags can be adjusted so that antennae  508  in a particular canister  507  read only the RFID tags  512  in that canister. In any case, adjacent canisters will be well shielded from each other due to the canister&#39;s conductive metallic composition. 
         [0067]    In one implementation, circuit  505  can connect to antennae  508  via connectors (not shown) attached to suspending bars  506 , where the connectors automatically plug in when the corresponding handle is in place. In an alternative implementation, antennae  508  can be coupled inductively through an air core transformer in which a coil  518  in plug  503  is hard wired ( 520 ) to circuit  505  and wirelessly transmits and receives RFID signals to and from a coil  519  hardwired to each canister  507 . 
         [0068]    It should be noted that high power-transfer efficiency can be achieved when the transmitting and receiving circuit are in resonance. The resonance condition can greatly extend the distance at which power and data can be exchanged. Thus, all of the components in the system might be designed so that the transmitting/receiving pair would be operating under resonance conditions. In addition, different transmitter/receiver pairs can operate at different frequencies, for example, data and power circuits can use different frequencies. 
       Guided Retrieval System 
       [0069]      FIG. 6  shows a 3D perspective view of a mechanical freezer  600  used to store tagged vials containing, e.g., biological samples. Mechanical freezer  600  may be only one of a number of different mechanical freezers and possibly other types of cold storage devices, such as liquid nitrogen dewars, or even room-temperature storage devices, such as formalin fixed paraffin embedded tissue block cabinets, that are located in a single facility. 
         [0070]    As represented in  FIG. 6 , mechanical freezer  600  has (e.g., five) shelves, one behind each different vapor door  603 , where each shelf has (e.g., five) racks  605 . Each rack  605  contains a number of boxes  607 , each of which stores a number of tagged vials (not shown). At the top  601  of freezer  600  is an (e.g., LED) freezer indicator light  602 . In addition, each vapor door  603  has a corresponding (e.g., LED) shelf indicator light  604 , each rack  605  has a corresponding (e.g., LED) rack indicator light  606 , and each box  607  has a corresponding (e.g., LED) box indicator light  608 . 
         [0071]    Although not depicted in  FIG. 6 , freezer  600  has a hierarchical internal electronic configuration and is connected to an external computer in a manner analogous to that shown in FIGS. 1 and 5-9 of the &#39;748 application. This external computer keeps track of the current locations of all of the samples stored in mechanical freezer  600  and in any other storage devices in the facility. When one or more samples are to be retrieved, the computer selectively illuminates appropriate indicator lights to guide a user to the tagged vials containing those samples. 
         [0072]    For example, if only a single sample is to be retrieved from freezer  600 , then the computer will illuminate freezer indicator light  602 , the corresponding shelf indicator light  604 , the corresponding rack indicator light  606 , and the corresponding box indicator light  608  to guide the user to that particular box in which the tagged vial containing the desired sample is currently stored. 
         [0073]    Depending on the particular implementation, the computer might not illuminate the corresponding shelf indicator light  604  until after the user opens the freezer&#39;s door. Similarly, the computer might not illuminate the corresponding rack indicator light  606  until after the user opens the corresponding vapor door  603 , and the computer might not illuminate the corresponding box indicator light  608  until after the user partially removes the corresponding rack  605 . 
         [0074]    If more than one sample is to be retrieved from freezer  600 , depending on the particular implementation, the computer may either illuminate all appropriate indicator lights simultaneously or sequentially as different samples are retrieved. 
         [0075]    Assume, for example, that three different samples are to be retrieved from freezer  600 : two samples located in the partially removed (i.e., first) box  607  in the partially removed (i.e., fourth) rack  605  behind the open (i.e., second) vapor door  603  depicted in  FIG. 7  and the third sample located behind the bottom-most (i.e., fifth) vapor door  603  in freezer  600 . Indicator patterns will also cue the user when the incorrect sample is removed. For example, all of the indicator lights might blink to indicate to the user that he removed a sample that was not supposed to be removed. 
         [0076]    For an implementation involving simultaneous illumination of indicator lights, the computer would initially illuminate freezer indicator light  602 . When the user opens the freezer&#39;s door, the computer would then illuminate the shelf indicator lights  604  for the second and fifth vapor doors  603 . When the user opens the second vapor door  603 , the computer would then illuminate the rack indicator light  606  for the fourth rack  605 . When the user partially removes the fourth rack  605 , the computer would then illuminate the box indicator light  608  for the first box  607 . After the user removes the two desired samples from that first box  607  and replaces the box into the fourth rack  605 , the computer would then turn off the indicator lights for the first box, the fourth rack, and the second vapor door, since no more samples need to be retrieved from the second shelf. 
         [0077]    After returning the fourth rack into the second shelf and closing the second vapor door, the user would then proceed to open the fifth vapor door in order to remove the third desired sample from the fifth shelf with the computer first illuminating and then turning off the appropriate indicator lights in a similar manner as just described. 
         [0078]    Note that the computer can determine that a sample has been retrieved from freezer  600  either by automatically detecting that the tagged vial has been removed from its box or by the user manually scanning the retrieved vial using an appropriate RFID scanning device configured to communicate with the computer. 
         [0079]    For an implementation involving sequential illumination, the computer would illuminate the various indicator lights for only one sample at a time, but the computer would preferably organize the desired samples into an efficient sequence grouping nearby samples together, such that all samples in a given box would be retrieved before proceeding to another box, all samples in a given rack would be retrieved before proceeding to another rack, all samples in a given shelf would be retrieved before proceeding to another shelf, and lastly all samples in a given storage device would be retrieved before proceeding to another storage device. Thus, in the previous example, after guiding the user to retrieve the first desired sample from the first box in the fourth rack in the second shelf of freezer  600 , the computer would illuminate appropriate indicator lights to guide the user to remove the second desired sample from that same box before proceeding to illuminate a different set of indicator lights to guide the user to retrieve the third desired sample from the fifth shelf. 
         [0080]    Although freezer  600  has indicator lights at the freezer level, the shelf level, the rack level, and the box level, in alternative embodiments, a freezer might not have indicator lights at one or more of the lower levels. 
         [0081]    Instead of or in addition to indicator lights, a user could be guided by a hand-held device that indicates to the user in some appropriate manner (e.g., visually or audibly) the identities of the storage device, shelf, rack, and box for the next sample to be retrieved. 
         [0082]    The power for illuminating the indicator lights can be derived from the same power source used to power the various other sets of electronics located within the freezer. In the case of wireless power transmission, a rack could remain powered and its indicator lights illuminated even when the rack is partially removed. A box might have sufficient energy storage to light indicators for a period, e.g., 5 minutes, after removal from the system, along with a power indicator to show that the other box indicators are reliable. 
         [0083]      FIG. 7(A)  shows a front view of a tissue block repository  700  having (e.g., seven) cabinets  701 , each containing (e.g., five) drawers  703 .  FIG. 7(B)  shows a top view of one of the drawers  703  of  FIG. 7(A)  containing (e.g.,  50 ) tissue blocks  705 .  FIG. 7(C)  shows a schematic block diagram of one of the tissue blocks  705  of  FIG. 7(B) . 
         [0084]    As represented in  FIGS. 7(A) and 7(B) , respectively, each drawer  703  has a corresponding (e.g., LED) drawer indicator light  704 , and each tissue block  705  has a corresponding (e.g., LED) block indicator light  706 . 
         [0085]    As shown in  FIG. 7(C) , each tissue block  705  has a tissue sample  710  and an RFID circuit  720 . RFID circuit  720  has an RFID chip  721 , an antenna  722  of some appropriate form, a power source  723 , and the corresponding block indicator light  706 . Power source  723  can be a battery, a wirelessly and inductively coupled coil, or any other suitable power source that can illuminate block indicator light  706 . RFID chip  721  has a controllable switch  724  that can be selectively closed or opened to turn on or off block indicator light  706 . RFID chip  721  may be a 2GiL+RFID chip from NXP Semiconductors N.V. of Eindhoven, Netherlands, although other suitable chips could be used in alternative implementations. 
         [0086]    Repository  700  also has one or more (e.g., distributed) RFID readers  730  that can read the RFID tag associated with each sample as well as communicate with (i) drawer-level electronics (not shown) to control each drawer indicator light  704  and (ii) each RFID chip  721  to control the corresponding block indicator light  706 . The one or more RFID readers  730  are configured to communicate with an external computer (not shown), analogous to the external computer described previously in the context of  FIG. 6 . 
         [0087]    Similar to the operations described for freezer  600 , for repository  700 , the computer would selectively illuminate (either simultaneously or sequentially) appropriate drawer and block indicator lights  704  and  706  to guide a user to retrieve one or more desired tissue samples from the repository. When a particular tissue sample  710  is to be retrieved, the computer would instruct an appropriate RFID reader  730  to communicate with the RFID chip  721  in the corresponding RFID circuit  720  via antenna  722  to instruct the RFID chip to close its switch  724  to illuminate the corresponding block indicator light  706 . After the tissue sample has been removed, the computer would instruct the RFID reader to communicate with the RFID chip to instruct the RFID chip to open its switch to turn off the block indicator light. 
         [0088]    Although repository  700  has indicator lights at the cabinet, drawer, and sample level, in alternative embodiments, a repository might not have indicator lights at one or more of the lower levels. 
         [0089]    Although guided retrieval has been described in the context of biological samples, those skilled in the art will appreciate that guided retrieval can be implemented in other contexts as well, such for any collection of similar items that need to be identified individually. 
       Bobbin-Based RFID Tags 
       [0090]      FIG. 8  shows an RFID tag  800  formed using an annular bobbin  801 . In particular, bobbin  801  is made from a non-conducting (e.g., plastic, ceramic) material and has a groove  807  running around its circumference. Mounted (e.g., using a suitable silicon-die-compatible adhesive) onto a relatively flat portion  806  within the groove is an RFID chip  804 . Connected at each end by wire-bonding to a different die contact  803  of the RFID chip is a wire  802  that runs around bobbin  801  within groove  807  to form and function as a loop antenna for the RFID tag. To protect the RFID tag, wire  802  and chip  804  can be encapsulated by filling groove  807  with a suitable encapsulant, such as a filled epoxy, having matching thermal-expansion characteristics. 
         [0091]    Notch  805 , angularly aligned with flat portion  806 , can be included in the bobbin design to help position and orient the flat portion during tag assembly. In alternative embodiments, bobbin  801  may have additional flat portions, notches, grooves, and/or other suitable features to (a) help align the bobbin during tag assembly, (b) protect the wire, chip, and other components, and/or (c) mate the resulting RFID tag  800  to other structures (e.g., insertion of the tag into the recess of an untagged vial as in  FIGS. 1 and 2 ). 
         [0092]      FIG. 8  shows a single turn of wire, which can be used to function as a loop antenna for UHF (ultra high frequency) RFID tags. In alternative embodiments, insulated wire can be used to provide multiple wire turns within groove  807  to function as a loop antenna for lower frequency (e.g., HF) RFID tags. Alternatively, the turns might be positioned in space such that different turns of the wire do not touch each other. Once encapsulated, the same goal of multiple wire turns can be achieved without insulating the wire. 
         [0093]    Wire  802  can be copper, aluminum, gold, or any suitable alloy used in wire bonding of integrated circuit chips. Furthermore, ball bonding or wedge bonding can be used if appropriate. For a strapped die, the wire would be attached by pressure or using a conductive adhesive. 
       Minimally Invasive Wiring Technique 
       [0094]      FIG. 9(A)  shows a 3D perspective, partial cut-away view of a conduit  900  that can be used to transfer electrical power and/or data signals between the outside world and the interior of a freezer, such as freezer  600  of  FIG. 6 . Conduit  900  comprises (e.g., metal) conductors  904  and  905  electrically isolated from one another and sandwiched between an insulating (e.g., rubber or plastic) substrate  903  and an insulating (e.g., rubber or plastic) cover  901 . Depending on the application, conduit  900  can have one or more relatively wide conductors  904  (e.g., for power transfer) and one or more relatively thin conductors  905  (e.g., for data transfer). Conduit  900  preferably has tapered edges  902 . 
         [0095]      FIG. 9(B)  shows a cross-sectional view of the interface between the door  906  and the body  908  of a freezer, like freezer  600 , having an intervening, flexible (e.g., rubber) gasket  907  permanently attached to the freezer door and forming a seal between the freezer door and the freezer body when the door is closed. 
         [0096]      FIG. 9(C)  shows a cross-sectional view of the interface of  FIG. 9(B)  with conduit  900  installed between the freezer body  908  and gasket  907 . In one implementation, conduit  900  is permanently mounted to the freezer body with the conduit&#39;s substrate  903  facing towards the freezer body and the conduit&#39;s cover  901  facing towards gasket  907 . Substrate  903  may have an adhesive backing for mounting the conduit to the freezer body. 
         [0097]    Note that conduit  900  can be used for any suitable application in which electrical signals need to be transferred between a first space having one environment (e.g., ambient room conditions) and a second space having a different environment (e.g., the interior of a freezer, a refrigerator, an oven, a clean room, or other similar apparatus or location). 
         [0098]    When heat transfer through conduit  900  needs to be minimized, the thermal conductivity of conduit  900  can be reduced by designing conductors  904  and  905  to have an appropriate geometry. For example, conductors having a zig-zag shape provide a longer thermal conduction path and thereby reduce heat transfer as compared to straight conductors. 
         [0099]    Using a metal having low thermal conductivity, such as stainless steel instead of copper, for the conductors can also reduce heat transfer. Copper-coated stainless steel can provide the desired characteristics for conduit  900  of low thermal conductivity and high electrical conductivity, especially at high frequencies where the skin effect is significant. Furthermore, optical fibers having low thermal conductivity can be used in place of metal conductors in conduit  900  for data transfer. 
         [0100]    Cover  901  can have a metal layer to provide electromagnetic shielding for signals as well as mechanical protection that prevents chafing by the gasket. 
         [0101]    Conduit  900  can also be used in situations in which there is no gasket. For example, in a liquid nitrogen dewar, such as dewar  400  of  FIG. 4 , a curved version of conduit  900  could be positioned within the interface between the loose-fitting lid  413  and the dewar body  401 . Conduit  900  can also be used in situations in which there are two gaskets (e.g., one attached to the freezer door and the other attached to the freezer body), where the conduit is positioned between the two gaskets, e.g., permanently mounted to one of the two gaskets. 
         [0102]    It should be appreciated by those of ordinary skill in the art that any block diagrams herein represent conceptual views of illustrative circuitry embodying the principles of the invention. Similarly, it will be appreciated that any flow charts, flow diagrams, state transition diagrams, pseudo code, and the like represent various processes which may be substantially represented in computer readable medium and so executed by a computer or processor, whether or not such computer or processor is explicitly shown. 
         [0103]    Unless explicitly stated otherwise, each numerical value and range should be interpreted as being approximate as if the word “about” or “approximately” preceded the value of the value or range. 
         [0104]    It will be further understood that various changes in the details, materials, and arrangements of the parts which have been described and illustrated in order to explain the nature of this invention may be made by those skilled in the art without departing from the scope of the invention as expressed in the following claims. 
         [0105]    The use of figure numbers and/or figure reference labels in the claims is intended to identify one or more possible embodiments of the claimed subject matter in order to facilitate the interpretation of the claims. Such use is not to be construed as necessarily limiting the scope of those claims to the embodiments shown in the corresponding figures. 
         [0106]    It should be understood that the steps of the exemplary methods set forth herein are not necessarily required to be performed in the order described, and the order of the steps of such methods should be understood to be merely exemplary. Likewise, additional steps may be included in such methods, and certain steps may be omitted or combined, in methods consistent with various embodiments of the present invention. 
         [0107]    Although the elements in the following method claims, if any, are recited in a particular sequence with corresponding labeling, unless the claim recitations otherwise imply a particular sequence for implementing some or all of those elements, those elements are not necessarily intended to be limited to being implemented in that particular sequence. 
         [0108]    Reference herein to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments necessarily mutually exclusive of other embodiments. The same applies to the term “implementation.” 
         [0109]    The embodiments covered by the claims in this application are limited to embodiments that (1) are enabled by this specification and (2) correspond to statutory subject matter. Non-enabled embodiments and embodiments that correspond to non-statutory subject matter are explicitly disclaimed even if they fall within the scope of the claims.