Patent Publication Number: US-2021177537-A1

Title: Rf tag with gravitationally aligned orientation

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of and priority to U.S. Provisional Patent Application Ser. No. 62/948,385 filed Dec. 16, 2019, the entire disclosure of which is incorporated by reference herein. 
    
    
     TECHNICAL FIELD 
     This disclosure relates generally to radio-frequency (RF) tags, and more particularly, to RF tags for use with surgical objects and devices used in body cavities during surgery, which RF tags have a gravitationally aligned orientation. 
     BACKGROUND 
     It is often useful or important to determine whether objects associated with a surgery are present in a patient&#39;s body before completion of the surgery. Such objects may take a variety of forms. For example, the objects may take the form of instruments, for instance scalpels, scissors, forceps, hemostats, and/or clamps. Also for example, the objects may take the form of related accessories and/or disposable objects, for instance surgical sponges, gauzes, and/or pads. Failure to locate an object before closing the patient may require additional surgery, and in some instances may have serious adverse medical consequences. 
     Some hospitals have instituted procedures which include checklists or requiring multiple counts to be performed to track the use and return of objects during surgery. Such a manual approach is inefficient, requiring the time of highly trained personnel, and is prone to error. 
     Another approach employs transponders and a wireless interrogation and detection system. Such an approach employs wireless transponders (e.g., RF tags) which are attached to various objects used during surgery. The interrogation and detection system includes a transmitter that emits pulsed wideband wireless signals (e.g., radio or microwave frequency) and a detector for detecting wireless signals returned by the transponders in response to the emitted pulsed wideband signals. Such an automated system may advantageously increase accuracy while reducing the amount of time required of highly trained and highly compensated personnel. Examples of such an approach are discussed in U.S. Pat. No. 6,026,818, issued Feb. 22, 2000, and U.S. Patent Publication No. US 2004/0250819, published Dec. 16, 2004. 
     Commercial implementation of such an automated system requires that the overall system be cost competitive and highly accurate. In particular, false negatives must be avoided to ensure that objects are not mistakenly left in the patient. Some facilities may wish to install a single interrogation and detection system in each surgery theater, while other facilities may move an interrogation and detection system between multiple surgical theaters. In either case, the overall system will require a large number of transponders, since at least one transponder is carried, attached or otherwise coupled to each object which may or will be used in surgery. Consequently, the transponders must be inexpensive. However, inexpensive transponders typically have a relatively large variation in the frequency of signals they emit, making it difficult to accurately detect the signals returned by the transponders. This may be particularly difficult in some environments which are noisy with respect to the particular resonant frequencies of the transponders. Consequently, a new approach to detection of the presence and absence of transponder that facilitates the use of inexpensive transponders is highly desirable. 
     When trying to locate an RF tagged item it is important for the detection antennas and or the electromagnetic fields to be aligned with the axis of sensitivity of the RF tags. In most cases the orientation of the RF tag (and tagged item) in three dimensional space is unknown and uncontrolled requiring scanning motion or complex antenna geometry to provide adequate detection coverage. 
     Accordingly, it is desired to have an RF tag that aligns its axis of sensitivity with gravity. 
     SUMMARY 
     This disclosure relates to RF tags for use with surgical objects and devices used in body cavities during surgery, which RF tags have a gravitationally aligned orientation. 
     According to an aspect of the disclosure, a transponder for use in a surgical environment and for detection by a detection system is provided. The transponder includes an encapsulant defining a cavity. A suspension medium and a core are contained within the cavity of the encapsulant. The core includes a ferrite rod having a first end and a second end, and defining a longitudinal axis between the first end and the second end. The longitudinal axis of the rod defines an axis of sensitivity of the transponder. A head is supported on the second end of the rod, and the rod and the head are configured to define a center of gravity proximate the second end or in the head, wherein the center of gravity is disposed along the longitudinal axis of the rod. A conductive coil is wrapped around the rod, and a capacitor is coupled to the conductive coil. The core is self-orienting such that the axis of sensitivity of the transponder is parallel with a plumb to gravity axis. 
     The ferrite rod, the conductive coil and the capacitor may form a series inductor/capacitor circuit. 
     According to another aspect of the present disclosure a transponder for use in a surgical environment and for detection by a detection system is provided. The transponder includes an encapsulant defining a cavity. A suspension medium and a core are contained within the cavity of the encapsulant. The core includes a rod having a first end and a second end, and defining a longitudinal axis between the first end and the second end, wherein the longitudinal axis of the rod defines an axis of sensitivity of the transponder. The core defines a center of gravity closer to the second end of the rod as compared to the first end of the rod, and the center of gravity is disposed along the longitudinal axis of the rod. The core further includes a conductive coil wrapped around the rod, and a capacitor coupled to the conductive coil. The core is self-orienting such that the axis of sensitivity of the transponder is parallel with a plumb to gravity axis. 
     The rod may be fabricated from a ferrous material. The rod, the conductive coil and the capacitor may form a series inductor/capacitor circuit. 
     According to yet another aspect of the present disclosure, a surgical article for placement in a cavity of a patient during surgery is provided. The surgical article includes a deformable object capable of absorbing body fluid, and a transponder connected to the deformable object. 
     The transponder includes an encapsulant defining a cavity. A suspension medium and a core are contained within the cavity of the encapsulant. The core includes a ferrite rod having a first end and a second end, and defining a longitudinal axis between the first end and the second end. The longitudinal axis of the rod defines an axis of sensitivity of the transponder, and the core defines a center of gravity closer to the second end of the rod as compared to the first end of the rod. The center of gravity is disposed along the longitudinal axis of the rod. The core further includes a conductive coil wrapped around the rod, and a capacitor coupled to the conductive coil. The core is self-orienting such that the axis of sensitivity of the transponder is parallel with a plumb to gravity axis. 
     The core may include a head supported on the second end of the rod. 
     The capacitor may be located proximate the second end of the rod. 
     The encapsulant may be fabricated from a bio-inert plastic. The encapsulant may have a spherical outer profile. 
     The suspension medium may include a pure silicone fluid, a silicone gel and/or a water cellulose mixture. 
     The head of the core may have a hemi-spherical outer profile. 
     The cavity of the encapsulant may have a spherical inner profile. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings, identical reference numbers identify similar elements or acts. The sizes and relative positions of elements in the drawings are not necessarily drawn to scale. For example, the shapes of various elements and angles are not drawn to scale, and some of these elements are arbitrarily enlarged and positioned to improve drawing legibility. Further, the particular shapes of the elements as drawn, are not intended to convey any information regarding the actual shape of the particular elements, and have been solely selected for ease of recognition in the drawings. 
       Various embodiments of the presently disclosed RF tags, transponders, and articles containing them are described herein below with reference to the drawings, wherein: 
         FIG. 1  is a schematic diagram showing a surgical environment illustrating a medical provider using an interrogation and detection system to detect an object in a patient that is tagged with a transponder according to one illustrated embodiment; and 
         FIG. 2  is a schematic illustration of a transponder, according to one illustrated embodiment. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     In the following description, certain specific details are set forth in order to provide a thorough understanding of disclosed embodiments. However, one skilled in the relevant art will recognize that embodiments may be practiced without one or more of these specific details, or with other methods, components, materials, etc. In other instances, well-known structures associated with transmitters, receivers, or transceivers have not been shown or described in detail to avoid unnecessarily obscuring descriptions of the embodiments. 
     Unless the context requires otherwise, throughout the specification and claims which follow, the word “comprise” and variations thereof, such as, “comprises” and “comprising” are to be construed in an open, inclusive sense, that is as “including, but not limited to.” 
     Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. 
     As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the content clearly dictates otherwise. It should also be noted that the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise. 
     As used herein, the terms parallel and perpendicular are understood to include relative configurations that are substantially parallel and substantially perpendicular up to about + or −10 degrees from true parallel and true perpendicular. 
     The headings and Abstract of the Disclosure provided herein are for convenience only and do not interpret the scope or meaning of the embodiments. 
       FIG. 1  depicts a surgical environment  10  in which a medical provider  12  operates an interrogation and detection system  14  to ascertain the presence or absence of objects  16  in, or on, a patient  18 . The interrogation and detection system  14  may include a controller  20 , and an antenna  22  coupled to the controller  20  by one or more communication paths, for example coaxial cable  24 . The antenna  22  may take the form of a hand-held wand  22   a.    
     The object  16  may take a variety of forms, for example instruments, accessories and/or disposable objects useful in performing surgical procedures. For instance, the object  16  may take the form of scalpels, scissors, forceps, hemostats, and/or clamps. Also for example, the objects  16  may take the form of surgical sponges, gauze and/or padding. The object  16  is tagged, carrying, attached or otherwise coupled to a transponder or RF tag  26 . Embodiments of the interrogation and detection system  14  disclosed herein are particularly suited to operate with transponders  26  which are not accurately tuned to a chosen or selected resonant frequency. Consequently, the transponders  26  do not require high manufacturing tolerances or expensive materials, and thus may be inexpensive to manufacture. 
     In use, the medical provider  12  may position the wand  22  approximate the patient  18  in order to detect the presence or absence of the transponder  26  and hence an object  16 . The medical provider  12  may in some embodiments move the wand  22   a  along and/or across the body of the patient  18 . In some embodiments, the wand  22   a  may be sized to fit at least partially in a body cavity  28  of the patient  18 . 
     Turning to  FIG. 2 , a transponder  26 , according to one illustrated embodiment, is shown. The transponder  26  includes a core  29  contained in an encapsulant  36 . The core  29  of the transponder  26  includes a miniature ferrite rod  30  having a first or free end  30   a , and second or supported end  30   b  integrally connected to or secured to an enlarged head  31 . The head  31  of the core  29  of the transponder  26  may be fabricated from ferrite or other weighted materials, such as, for example, nickel-iron, cobalt-iron, iron and oxides of iron, ferrite, silicone-steel and/or amorphous metallic alloys. The rod  30  and the head  31  have a substantially mushroom-shaped profile. As so arranged and constructed, the core  29  of the transponder  26  defines a center of gravity (G) located proximate second end  30   b  of the rod  30 , or within the head  31 . It is contemplated that the head  31  may have a hemi-spherical outer profile. 
     The transponder  26  includes a conductive coil  32  wrapped about an exterior surface of the rod  30  to form an inductor (L), and a capacitor (C)  34  coupled to the conductive coil  32  to form a series LC circuit. The conductive coil  32  may, for example, take the form of a spiral wound conductive wire with an electrically insulative sheath or sleeve. The capacitor (C)  34  is disposed closer to second end  30   b  of the rod  30  as compared to first end  30   a , in order to help maintain the center of gravity (G) closer to the head  31 . However, it is contemplated that the capacitor (C)  34  may be disposed at any location along a length of the rod  30 . 
     The rod  30  of the core  29  defines a longitudinal axis “X” which also defines an axis of sensitivity of the transponder  26 . The sizes and configurations of the rod  30  and the head  31  are selected such that the center of gravity (G) of core  29  is disposed along the longitudinal axis “X”. 
     The transponder  26 , as mentioned above, includes an encapsulation  36  that encapsulates the rod  30 , the conductive coil  32 , and the capacitor  34 . The encapsulant  36  may be a bio-inert plastic that protects the rod  30 , the conductive coil  32 , and/or the capacitor  34  from pressure and/or from fluids, for example bodily fluids. The encapsulant  36  may have a spherical profile. Specifically, the encapsulant  36  defines an inner cavity  36   a  having a spherical profile, while an outer profile of the encapsulant  36  can be spherical or any other functionally beneficial shape or configuration sufficiently large to permit core  29  to freely float, rotate or spin therein. 
     The inner cavity  36   a  of the encapsulant  36  is filled, at least partially, with a non-corroding suspension medium or fluid (F)  38  including and not limited to a pure silicone fluid, a silicone gel and/or a water methyl cellulose mixture. 
     As so constructed, the core  29  of the transducer  26  is suspended in the encapsulant  36  such that the center of gravity (G) of the core  29  forces the core  29  to orient itself such that the longitudinal axis “X” of the rod  30  (e.g., the axis of sensitivity of the transponder  26 ) is axially aligned with a plumb to gravity axis “Z′” (e.g., the core  29  is in an upright orientation). 
     In some embodiments, the transponder  26  may include eyelets, hooks, fastening features and the like that may be used to attach the transponder  26  to various types of objects  16 , for example surgical sponges. 
     The transponder  26  may have a length of about 6-10 millimeters, specifically about 8 millimeters and a diameter of about 1.5-3 millimeters, specifically about 2 millimeters. Employing such small dimensions ensures that the transponder  26  does not impede deformation of objects  16  such as sponges. 
     The transponder  26  may include an optional diode (not shown), to protect against over-voltage occurrences caused by other electronic instruments. 
     Alternatively, in an embodiment, and in accordance with this disclosure, it is contemplated that transducer  26  (or core  29 ) may self-orient due to application of a magnetic field thereto, such as, for example, by a magnetic orientation system (not shown). Such a magnetic orientation system is configured to align or orient transducer  26  with a plumb to gravity axis “Z”′ (e.g., the core  29  is in an upright orientation) via application of a magnetic field thereto, or in response to receipt of a magnetic field therefrom. It is contemplated that application of a magnetic field to transducer  26  may effect one end of core  29 , or one end of core  29  may generate a magnetic field for sensing by receiver or the like. 
     While an embodiment of the disclosure have been shown in the drawings, it is not intended that the disclosure be limited thereto, as it is intended that the disclosure be as broad in scope as the art will allow and that the specification be read likewise. Therefore, the above description should not be construed as limiting, but merely as exemplifications of particular embodiments. Those skilled in the art will envision other modifications within the scope and spirit of the claims appended hereto.