Abstract:
A radio frequency identification (RFID) system for detecting and identifying lost dentures in a facility, includes readers deployed in fixed locations in the facility. Each of the readers is configured to transmit a first signal and to detect from a distance a second signal, which is generated at an RFID transponder embedded in a denture in response to receiving the first signal by backscattering a part of the first signal. The second signal contains information related to the denture, including an identification of the denture owner. The RFID system also includes a first server located within the facility. The first server is configured to communicate with the readers over a network in the facility and to control operations of the readers. Each of the readers sends the information related to the denture to the first server when it detects the second signal from the RFID transponder.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 13/341,900, filed on Dec. 30, 2011, which claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Application Ser. No. 61/460,305, filed on Jan. 3, 2011, each of which is hereby incorporated by reference herein in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention is related to Ultra High Frequency (UHF) Radio Frequency Identification (RFID) tag antenna that can be embedded in dentures and tuning procedures for matching the embedded antenna&#39;s input impedance to the impedance of an RFID tag microchip under varying dielectric conditions. The present invention is also related to a radio frequency identification (RFID) system for detecting and identifying lost dentures that includes an embedded RFD tag antenna in a facility is provided. 
     A typical RFID system includes readers and RFID tags. The RFID tags are attached to objects of interest and the readers are used to remotely read the information contained in the tags. Most RFID tags include an antenna connected to a microchip. The antenna is used for communication with the reader and the microchip is used for storing and processing information, modulating and demodulating a radio-frequency signal, and other specialized functions. 
     RFID systems can be classified based on the frequency used for communication, the power source for the microchip or the method used for conveying information from the RF tag to the reader. 
     Embedding RFID tags into objects, such as dentures, has several useful applications, such as automated identification, detection, and localization of the objects. For example, detection of dentures can be useful in nursing homes and other long term care facilities for, e.g., the elderly, where frequent loss or misplacement of dentures may be a serious issue. In addition to the cost of replacement, denture loss causes discomfort and deterioration of the health of the denture owners. Not only does a denture owner suffer from poor nutritional intake in the time required to receive a new denture, but he or she may also suffer from the inability to adapt to the new denture. 
     The problem of denture loss in long term care facilities and hospitals has been analyzed in studies/researches using data gathered from a few such facilities around the world, and these studies/researches suggested techniques, such as visual denture marking and enforcement of staff and resident behavior protocols, in order to combat the problem. Use of RFID for denture identification has also been proposed in several studies. These studies proposed the use of miniature transponders embedded in dentures or tooth implants. Similar studies also suggested the idea of placing the transponders into false teeth (mostly molars). The RFID transponders presented in most of these works are very small and have limited read ranges (e.g., 2-4 inches or shorter) and, therefore, these solutions are more suited to denture identification rather than detection of lost dentures. 
     U.S. Pat. No. 6,734,795 discusses an RFID system for detection of lost dentures. However, the system uses a combination of a magnetic strip for detection and a close range RFID transponder for identification, wherein a magnetic detector sounds an alarm whenever a magnetic strip embedded in a denture is brought in its vicinity. The range of detection of the system is small (i.e., around 6 to 8 inches), however, and this small range of detection falls short of making a robust and seamless detection system in practical settings. Moreover, because the magnetic strip does not enable identification, the patent also suggests the use of an alternative method, such as visual marking or close range RFID transponders, in combination with a magnetic strip, such that even if a lost denture is detected someone still has to read the visual marking (e.g., name or other markings) or read the information stored in the close range RFID transponder (e.g., using a RFID scanner) to identify the owner of the denture. 
     A practically viable RFID system for prevention of denture loss requires a much longer range of detection distances. For instance, because lost dentures in many situations may be immersed in or surrounded by high dielectric constant materials, such as water, such RFID system should be able to provide sufficiently long reading range under such varying conditions. Existing RFID tags with long reading range requires relatively bulky antenna or separate power source and thus may not be suitable for being embedded in dentures due to their dimensions, shape and/or substrate. Moreover, these tags are often designed for external attachment to objects and hence their uses are limited for operations in free space. Therefore, even if such tags could be somehow embedded in the dentures, the impedance properties would change due to dielectric effects of the denture material and hence the tag antenna would no longer be tuned to the RFID chip to which the antenna is connected. As a result, the existing commercial off-the-shelf RFID tags may not be suitable for a viable solution to this problem, absent a proper tuning. 
     SUMMARY 
     The present invention describes a loop-dipole antenna and tuning procedure. The antenna is connected to an RFID tag microchip that can operate in the UHF frequency range and the combined structure of the antenna and the microchip is embedded into a denture, forming a denture-embedded RFID tag. The information contained in the microchip can be read by a UHF RFID reader at long rages in various environments. 
     In one embodiment, a radio frequency identification (RFID) transponder for use in dentures is provided. The RFID transponder includes a passive RFID microchip configured for storing information related to a denture and a loop dipole antenna configured for sending the information in response to receiving a signal from an RFID reader. The loop dipole antenna in turn includes a wire forming a loop structure and a set of dipole arms going out from the loop structure. Each end of the set of dipole arms is folded at least once to form at least one meander and the dipole arms follow a shape of the denture. The RFID transponder also includes at least one tuning patch configured for tuning input impedance of the loop dipole antenna. The RFID transponder is embedded in the denture and the passive RFID microchip is electrically coupled to the loop structure. 
     In another embodiment, a radio frequency identification (RFID) system for detecting and identifying lost dentures in a facility is provided. The RFID system includes at least one reader deployed, in fixed locations in a facility and configured for transmitting a first signal and detecting from a distance of at least one feet a second signal transmitted from an RFID transponder embedded in a denture in response to receiving the first signal. The RFID system also includes a first server located within the facility and configured for communicating with the at least one reader over a network in the facility and for controlling operations of the at least one reader. The at least one reader sends an alert to the first server when it detects the second signal from the RFID transponder. 
     In yet another embodiment, a radio frequency identification (RFID) system for detecting and identifying lost dentures in a facility is provided. The RFID system includes one or more readers deployed in fixed locations in a facility. Each of the one or more readers is configured to transmit a first interrogation, or query, signal and to detect from a distance of at least one foot (1 ft.) a second signal, which is generated at an RFID transponder embedded in a denture in response to receiving the first signal by reflecting, or backscattering, at least a part of the first signal. The RFID system also includes a first server, or a controller machine, located within the facility and configured to communicate with the readers over a network (e.g., wired Ethernet, Wi-Fi) in the facility and to control operations of the readers. The second signal contains information related to the denture, including an identification of the denture owner, and each of the readers sends an alert including the information related to the denture to the first server when it detects the second signal from the RFID transponder. 
     In yet another embodiment, a radio frequency identification (RFID) system for detecting and identifying lost dentures in a facility is provided. The RFID system includes one or more readers deployed in fixed locations in a facility. Each of the readers is configured to transmit a first signal and to detect from a distance of at least one foot (1 ft.) a second signal, which is generated at an RFID transponder embedded in a denture in response to receiving the first signal by reflecting, or backscattering, at least a part of the second signal. The RFID transponder includes a microchip adapted to store information related to the denture, including an identification of the denture owner. The RFID transponder also includes an antenna connected to the microchip to generate and transmit the second signal in response to receiving the first signal, wherein the second signal contains the information related to the denture. 
     In another embodiment, a method of detecting and identifying lost denture in a facility is provided. The method includes transmitting a first signal at a reader deployed in a fixed location in a facility, detecting from a distance of at least one feet a second signal transmitted from an RFID transponder embedded in a denture in response to the first signal, and sending over a network in the facility an alert to a first server located within the facility in response to detecting the second signal from the RFID transponder. 
     In yet another embodiment, a method of detecting and identifying lost denture in a facility is provided. The method includes transmitting a first signal at a reader deployed, in a fixed location in a facility, and detecting from a distance of at least one foot a second signal, which is transmitted from an RFID transponder embedded in a denture in response to the first signal. The method also includes sending over a network in the facility an alert to a first server located within the facility in response to detecting the second signal from the RFID transponder. The second signal contains information related to the denture, including an identification of the denture owner. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a structure of a loop-dipole antenna in accordance with one embodiment of the present invention. 
         FIG. 2  illustrates a combined structure of a loop-dipole antenna and a set of metallic tuning patches in accordance with one embodiment of the present invention. 
         FIG. 3  is a flow diagram showing a loop-dipole antenna tuning procedure in accordance with one embodiment of the present invention. 
         FIG. 4  is a flow diagram showing a process for embedding a loop-dipole antenna in a denture in accordance with one embodiment of the present invention. 
         FIG. 5A  shows a loop-dipole antenna embedded in an upper portion of a denture in accordance with one embodiment of the present invention. 
         FIG. 5B  shows a loop-dipole antenna embedded in a lower portion of a denture in accordance with one embodiment of the present invention. 
         FIG. 6A  shows a set of dimensions for a structure of a loop-dipole antenna including a shortest distance between a set of labeled points in accordance with one embodiment of the present invention. 
         FIG. 6B  shows a set of dimensions for a structure of a loop-dipole antenna including a set of wire lengths between a set of labeled points in accordance with one embodiment of the present invention. 
         FIG. 7A  illustrates a real part of an input impedance of a loop-dipole antenna with and without tuning patches in accordance with one embodiment of the present invention. 
         FIG. 7B  illustrates an imaginary part of an input impedance of a loop-dipole antenna with and without tuning patches in accordance with one embodiment of the present invention. 
         FIG. 8  is a diagram illustrating an RFID system that can be used in nursing homes and hospitals in accordance with one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Loop-dipole antenna and tuning procedures are provided. The loop-dipole antenna is connected to an RFID tag microchip that can operate in the UHF frequency range and the combined structure of the antenna and the microchip can be embedded in a denture, forming a denture-embedded RFID tag. 
     In one embodiment, a passive RFID tag microchip is used. Passive RFID tag microchips can operate by harvesting the RF energy transmitted by an RFID reader and as a result, most passive RFID tag microchips exhibit conductive input impedance. In order to achieve desirable impedance matching, the input impedance of the loop-dipole tag antenna should be inductive. 
     The antenna dimensions and form factor should be small enough to allow for efficient embedding into dentures. If an antenna is too small, however, it may be difficult to achieve the desired reading distances. Moreover, the antenna should be tuned to a tag microchip when embedded in a denture and this tuning should remain when the denture is either in free space or in the presence of dielectrics, such as water. 
     The present invention addresses these design goals by providing an antenna with dimensions that are small enough to enable embedding into dentures, but also large enough to obtain a high value of input resistance and hence increased efficiency (e.g., increased reading distance). In one embodiment, a horseshoe shape dipole structure is chosen for the antenna because this follows the shape of the denture, and at the same time provides a length of the embedded antenna for desired input resistance. In one embodiment, the dipole arms of the horseshoe shape antenna are folded in at least one position in order to achieve improved efficiency. Further increasing of the number of folds (also referred to as meanders) will increase the length and hence efficiency of the antenna. However, increased number of meanders accompanies increased difficulty of manufacturing and embedding of the antenna and therefore, a design tradeoff may be involved in selecting the number of meanders for a particular denture antenna. 
     An inductive character of the input impedance of an antenna (e.g., a loop-dipole antenna) can be obtained by an inductive loop. The dimensions of the antenna loop may have substantial influence on the characteristics of the antenna, such as inductivity. 
     Dentures can be of various sizes and shapes depending upon the face and mouth structure of the owners of the dentures. In addition, different dentures can be made of materials (e.g., acrylics) of different permittivity. For example, two antennas of the same dimensions embedded into dentures of different sizes and/or made of different permittivity acrylics may exhibit different input impedances. 
     To address such varying nature of the input impedance, a tuning procedure is provided to achieve acceptable matching for an antenna embedded in any dentures. In one embodiment, thin metallic plates are embedded in the denture along with a loop-dipole antenna to be used as tuning patches. The tuning patches may be positioned near the ends of the dipole arms of the antenna. In one embodiment, the size of the tuning patches is varied to obtain acceptable matching input impedances as well as a desired range of tag reading distances even when the denture is immersed in or surrounded by materials of high permittivity (e.g., water). 
     In one embodiment, an RFID system operating in the Ultra High Frequency (UHF) range is provided. The RFID system uses one or more passive RFID microchips that can obtain power for operation from the electromagnetic field transmitted by a reader and communicate back with the reader using the principle of backscatter modulation. The RFID system utilizes a loop-dipole antenna that is coupled to the RFID microchips in order to achieve a long range of reading distances (e.g., 20 ft. in certain conditions). The input impedance of the loop-dipole antenna is also matched to the microchips. The antenna may be designed to facilitate embedding into dentures while not affecting the fit, feel, strength or durability of the denture. 
     In one embodiment, a tuning procedure may be used to allow the performance of the RFID system to be optimized for different denture geometries and various operating environments such as denture in wet clothes or garbage or in a bowl of water or soup. A combination of a long reading range along with one or more tag microchips that can identify the denture owner can make such design well suited for detection of lost dentures in long term care facilities and hospitals. 
     In one embodiment, dentures equipped with an RFID tag structure is used to store important information related to the denture owners, including basic identification information as well as the owners&#39; medical records. For instance, in a hospital environment, an RFID reader portal could be set up at the entrance of an area, allowing for partial medical records of denture-wearing patients to be read automatically. This can be more efficient and seamless than a similar application enabled by close range tags, which would require the denture-wearing patients to remove dentures from their mouth and place them very close to a reader in order for the information in the tag microchips to be read. 
       FIG. 1  shows a structure of a loop-dipole antenna  100  in accordance with one embodiment of the present invention. In one embodiment, loop-dipole antenna  100  is symmetrical with a line of symmetry passing through points A and S. An RFID tag microchip may be positioned at the symmetry line of the antenna. For example, a tag microchip may be positioned at or near point A. The antenna may consist of a wire dipole  101  with the ends of its arms folded to form meanders  103 . The antenna may also have a loop  102  represented by the points (B-C-S-C′-B′). Dipole  101  and loop  102  are connected at points B and B′. In one embodiment, dipole  101  and loop  102  is made of the same material. In other embodiments, dipole  101  and loop  102  may be made of different materials. 
     In one embodiment, the shape of the wire between points B and B′ is quasi-elliptical. The wire between points C and C may be also quasi-elliptical and have a shape that is similar to shape of the wire between points B and B′. In some embodiments, the wire between points B and C and points B′ and C can form a shape other than a straight line. The wire between points B and D may be quasi-elliptical. The wire between points F and F may be parallel or almost parallel to the wire between points B and D. In one embodiment, the wire between points D and F may have a circular or quasi-elliptical shape, but in other embodiments the same wire can also be the shape of a straight line. 
       FIG. 2  shows a combined structure  200  of loop-dipole antenna  100  and a set of metallic tuning patches  201  in accordance with one embodiment of the present invention. In one embodiment, tuning patches  201  are symmetrically positioned. In one embodiment, tuning patches  201  are positioned above the ends of dipole arms. Tuning patches  201  can be of an arbitrary shape, including the shape of an elongated rectangle. In one embodiment, tuning patches  201  are positioned near a surface of the denture and covered with a thin layer of denture material. 
     In practice, each denture is of a different shape and size and is made of different materials having a wide range of different permittivity. In one embodiment, the real part of the permittivity of the denture materials can range from about 2.2 to about 3.5 whereas the imaginary part of the permittivity may range from about 0.02 to about 0.04. 
     Dentures having an embedded loop-dipole antenna can be placed in many different surroundings. If such a denture is placed in a glass of water, for example, the effective permittivity of the denture can change dramatically, causing a change in the antenna input impedance. Therefore, it is desired that the antenna be designed such that sufficient tag detection range in different surroundings. A tuning procedure is provided in order to obtain desired performance for varying dimensions and varying dielectric properties of materials used in fabrication of the dentures. 
       FIG. 3  is a flow diagram showing a loop-dipole antenna tuning procedure  300  in accordance with one embodiment of the present invention. At  301 , a loop-dipole antenna, such as antenna  100 , embedded in a denture is optimized for performance in water before one or more tuning patches are coupled to the antenna. For example, the dimension of the antenna may be chosen so as to enable maximum reading distance when the denture is immersed in a glass of water (maximum reading distance is greater when denture is in water than when it is in free space). In one embodiment, the denture is made of a material having a relative permittivity of about 3.5. 
     At  303 , one or more tuning patches, such as tuning patches  201 , having an initial length are installed in the denture along with the loop-dipole antenna. At  305 , the antenna coupled to the tuning patches is optimized for performance in free space (e.g., in air). For example, the length of the tuning patches may be chosen such that the antenna with tuning patches can achieve a maximum reading distance in free space (maximum reading distance of denture with tuning patches is greater when in free space rather than in water). In one embodiment, the tuning patches are made of a material having a relative permittivity of about 2.2. At  307 , a detection range is measured for the antenna with the tuning patches both in free space and in water. 
     At  309 , the maximum detection distance is measured for the patched antenna in free space and is compared to the maximum detection distance measured in water to determine whether the maximum distances are equal. If the distances are determined to be equal at  309 , the tuning is deemed to be complete (i.e., antenna is tuned) and the tuning process ends at  311 . If however, the detected ranges are determined to be unequal at  309 , the length of the tuning patches are adjusted at  313  and  307  and  309  are repeated until the antenna is tuned. 
       FIG. 4  is a flow diagram showing a process  400  for embedding a loop-dipole antenna in accordance with one embodiment of the present invention. At  401 , an antenna pattern is marked for a loop-dipole antenna on a denture. In one embodiment, the antenna pattern is marked using ink or a paper label. At  403 , a groove is created for the loop-dipole antenna along the marked pattern. In one embodiment, the groove is between 0.5 mm to 1.5 mm in depth. 
     At  405 , the loop-dipole antenna wire is placed into the groove. At  407 , the groove holding the antenna wire is filled with the same material of which the denture is made. In one embodiment, the denture material is an acrylic. At  409 , tuning patches are installed in or near the loop-dipole antenna. In one embodiment, if an RFID microchip has not already been coupled to the antenna, an RFID microchip is coupled to the antenna. 
     At  411 , the antenna is tuned by following a tuning procedure, such as tuning procedure  300  shown in  FIG. 3 . In one embodiment, the dimensions of the tuning patches are adjusted to achieve desired tuning. At  413 , the tuning patches and, if an RFID microchip has been coupled to the antenna along with the tuning patches, the RFID microchip are covered. In one embodiment, a light cure or cold cure acrylic material is used to cover the tuning patches or the tuning patches and the RFID microchip. In one embodiment, the denture including the antenna tag is polished with various finishing touches to fit the antenna tag and to restore the look and feel of the denture. 
     In one embodiment, the antenna can be made of a metal, or a combination of metals, of high conductivity, including copper, silver, platinum, gold or aluminum. In one embodiment, parts of the antenna, such as the loop and dipole arms, are made of thin wire having radius of between 0.1 mm and 1 mm. Increasing wire diameter improves antenna efficiency and decreases losses. On the other hand, however, using thick wire for an antenna limits the antenna&#39;s use. For some dentures, for example, the bulkiness of the antenna made of thick wire may not be suitable. In one embodiment, tuning patches are made of thin metallic plate, such as copper tape, a layer of silver paint and the like, that can enable ready variation in length of the tuning patches. 
       FIG. 5A  is an image showing a loop-dipole antenna  503  embedded in an upper denture (a.k.a., maxillary denture)  501  in accordance with one embodiment and  FIG. 5B  is an image showing a loop-dipole antenna  507  embedded in a lower denture (a.k.a., mandibular denture)  505  in accordance with one embodiment of the present invention. The images show antennas before the tuning patches are added. 
       FIG. 6A  shows a set of dimensions for a structure of a loop-dipole antenna  600 A including a shortest distance between a set of labeled points in accordance with one embodiment of the present invention.  FIG. 6B  shows a set of dimensions for a structure of a loop-dipole antenna  600 B including a set of wire lengths between a set of labeled points in accordance with one embodiment of the present invention. 
       FIG. 7A  illustrates a real part of an input impedance of a loop-dipole antenna with tuning patches of two different sizes as well as without tuning patches in accordance with one embodiment of the present invention.  FIG. 7B  illustrates an imaginary part of an input impedance of a loop-dipole antenna with tuning patches of two different sizes as well as without tuning patches in accordance with one embodiment of the present invention. As illustrated in the figures, increasing the size (e.g., length) of tuning patches causes the characteristic of the antenna to move toward lower frequencies. This property is useful because it allows setting an optimal working point of the antenna by varying the size of the patches. The tuning patches can have arbitrary size and shape. In one embodiment, an elongated rectangle shape of tuning patches is used. 
     Dentures embedded with a long range, passive RFID tag can enable various useful applications. One such application is prevention of denture loss in nursing home, hospitals and other senior care settings. A system for preventing denture loss may include a loop-dipole antenna with RED microchip, which is embedded in dentures, and a detection infrastructure including readers deployed throughout such facilities. In one embodiment, most common loss scenarios are identified to be used in designing a strategic detection system. Some of the loss scenarios that have been identified include dentures left on food trays after meals, dentures left in soiled linen or garbage carts, and dentures left in rooms and other common areas. 
     In one embodiment, a deployment infrastructure is designed based on such denture loss scenarios. The deployment infrastructure may include fixed RFID readers with multiple antennas mounted, e.g., in the hallways leading to the laundry and garbage disposal areas as well as in the food tray breakdown area (also referred to as “choke points”). In one embodiment, a handheld RFID reader may be also used in addition to the fixed RFID readers in these choke points for scanning lost dentures in residential living spaces. 
     The RFID tag with a loop-dipole antenna that is embedded in a denture can both detect and identify the denture if it is lost. In one embodiment, the identification information corresponding to the owner of a denture is programmed into a tag RFID microchip after the denture is retrofitted with the RFID tag with a loop-dipole antenna. In one embodiment, a denture loss prevention system includes a registration reader. A registration reader is an RFID reader that can be used for programming identification information into the tagged dentures. 
       FIG. 8  is a diagram illustrating an RFID system  800  that can be used in nursing homes and hospitals in accordance with one embodiment of the present invention. RFID system  800  includes fixed readers  801  deployed at strategic choke points, handheld readers  803  for scanning other areas of the facility and a registration reader  805  for programming identification information into a tagged denture. All the readers (fixed readers  801 , handheld reader  805 , and registration reader  805 ) can communicate over a network in the facility with a client machine  807  that is deployed internally within the facility network. Client machine  807  runs all the programs to control the operation of the readers within the facility and also interacts with an external remote server  809 . Remote server  809  hosts a web application and a database that allows users to access and control the system deployed within the facility simply by using a web browser on their computers or mobile devices. 
     In one embodiment, each choke point is equipped with an audible and visual alarm. Whenever the fixed reader at the choke point detects a tagged denture passing thru it, these alarms can be set off. In addition to these localized alarms, the information about the detection is conveyed to client machine  807  and in turn to remote server  809 . Remote server  809  runs an alerting mechanism whereby emails, text messages, pager messages or voice messages can be sent instantly to designated personnel, thereby the system provides both local alerts as well as alerts for personnel who may or may not be off site.