Abstract:
A method of providing RF energy to a wireless transponder device includes outputting primary RF energy in a form wherein the primary RF energy comprises a plurality of RF bursts, with each consecutive pair of the RF bursts being separated by an associated time interval, and outputting secondary continuous wave RF energy in between each of the RF bursts of the primary RF energy during at least a portion of each of the associated time intervals. Also, a reader device implementing this method.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority under 35 U.S.C. § 1 19(e) from U.S. provisional patent application Ser. No. 61/823,598, entitled “Powering And Reading Implanted Devices” and filed on May 15, 2013, the contents of which are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention pertains to medical implant devices, such as, without limitation, orthopedic implants, cardiac implants, dental implants, general surgical implants, neurological implants, gastrointestinal implants, urological implants, gynecological implants, or some other implantable medical device, and, in particular, to a method and apparatus for powering such a medical implant device that includes a wireless transponder and/or for reading such a medical implant device having an associated sensor. 
         [0004]    2. Description of the Related Art 
         [0005]    U.S. Pat. Nos. 7,333,013 and 7,932,825 describe a system wherein a medical implant device, such as, without limitation, an orthopedic (e.g., an artificial knee or hip) or cardiac implant (e.g., a pacemaker), has a radio frequency identification (RFID) tag mounted thereto. The RFID tag stores information relating to the implant and/or the patient, such as, without limitation, the implant type/model/serial number, the implant manufacturer, the procedure date, the hospital and/or the implanting surgeon. That information may later he obtained from outside of the patient&#39;s body when needed by reading the RFID tag using a properly equipped RFID reader device. For example, that information can be read by the surgeon or another healthcare professional during a post operative or later visit in order to obtain information needed by that individual during the visit in order to properly examine and treat the patient. As another example, that information can also be read and transmitted to a secure patient database for use in medical outcomes research performed by, for example, a healthcare organization or implant manufacturer. 
         [0006]    In one particular implementation, described in U.S. Pat. Nos. 7,333,013 and 7.932,825, the RFID tag mounted to the implant is a passive RFID tag that includes an antenna, and may be read using a conventional RFID reader that is structured to read the implanted passive RFID tag over an air interface. In another particular implementation, an alternative RFID reader may be used, wherein the RFID reader is structured and configured to read the implanted RFID tag by making a direct (i.e., non-air interface) electrical connection to the RFID tag through the patient&#39;s living tissue using a probe provided as part of the RFID reader device (e.g., using transcutaneous contact and transcutaneous near field communication (TNFC) or transcutaneous for field communication (TFFC)). This latter implementation is described in U.S. Pat. Nos. 6,487,844, 7,228,183 and 7,825,807. In both of these implementations, the implanted RFID tag is powered by harvesting energy from the RF energy provided by the RFID reader. 
         [0007]    Certain passive RFID tags provide a voltage output connection for powering other devices when such power is available from the energy harvested from an RFID reader. One use of this voltage is to power implanted sensors, which may be very simple in design because the RFID system provides a convenient method to communicate with the associated electronics. 
         [0008]    As is known in the art, and as shown in  FIG. 1 , prior art RFID readers power and communicate with a passive RFID tags through relatively short bursts  2  of radio frequency (RF) energy (also known as RF pulses having a square wave format). The duration of these bursts  2  is limited by the FCC. 
         [0009]    One type of sensor often used in association with passive RFID tags changes its conductivity when connected in an electrical circuit in order to report variations in the parameter to be measured. In one such embodiment, the sensor device is a voltage divider and is typically categorized as a resistor, i.e., a variable resistor. While an ideal variable resistor will essentially have an instantaneous response to an RF burst, such as burst  2 , from an RFID reader, actual sensor implementations have dynamics associated with them where it takes a nonzero time for the sensor to reach a steady state output value. This behavior is similar to that of a restive/capacitive (RC) circuit, exhibiting what is termed an RC time constant (shown in  FIG. 2 ), or, alternatively, a restive/inductive (RL) circuit, exhibiting what is termed an RL time constant (shown in  FIG. 3 ), or some combination of both RC and RL dynamics. 
         [0010]    If the RC and/or RL dynamics of the sensor are sufficiently fast, the reading can be accomplished within the time duration) of the energy burst of the RFID reader (e.g., within the duration, T, of burst  2  shown in  FIG. 1 ). However, if the RC and/or RL dynamics of the sensor are such that the sensor is not able to reach an accurate steady state value within the duration of the energy burst of the RFID reader (e.g., within the duration, T, of burst  2  shown in  FIG. 1 ), then problems will arise. In such a case, in order to get an accurate reading, the time during which RF energy used for powering is provided must be extended. However, FCC regulations limit the duration of RF bursts that may be output by an RFID reader or similar device over an air medium (i.e., the regulations set a maximum length for such duration). Thus, due to the FCC regulations, manufacturers of commercial off the shelf (COTS) RFID reader devices will not be willing to alter their devices to allow them to exceed this regulated limit because COTS RFID reader devices are specifically designed to transmit over an air medium. Furthermore, while the application of the reader in the transcutaneous method described above is not an over the air regulated situation, asking the COTS reader manufacturers to alter their reader would defeat the COTS availability of such readers for a much wider market. 
       SUMMARY OF THE INVENTION 
       [0011]    In one embodiment, an RFID reader device is provided that includes a primary RF source structured to output primary RF energy in a form wherein the primary RF energy comprises a plurality of RF bursts, with each consecutive pair of the RF bursts being separated by an associated time interval, and a supplemental RF source structured to output secondary continuous wave RF energy in between each of the RF bursts of the primary RF energy during at least a portion of each of the associated time intervals. 
         [0012]    In another embodiment, a method of providing RF energy to a wireless transponder device is provided. The method includes outputting primary RF energy in a form wherein the primary RF energy comprises a plurality of RF bursts, with each consecutive pair of the RF bursts being separated by an associated time interval, and outputting secondary continuous wave RF energy in between each of the RF bursts of the primary RF energy during at least a portion of each of the associated time intervals. 
         [0013]    In still a further embodiment, a wireless transponder device is provided that includes electronic circuitry structured to receive an output of a sensor device associated with the wireless transponder device, the output having a transient response portion followed by a steady state portion, and determine a reading for the sensor device based on the transient response portion and not the steady state portion of the output. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a schematic representation of the RF output of a prior art RFID reader device; 
           [0015]      FIGS. 2 and 3  are schematic representations of the output of prior art sensors showing RC and RL dynamics, respectively; 
           [0016]      FIG. 4  is a schematic diagram of an RFID system according to an exemplary embodiment of the present invention wherein information may be read from and written to a medical implant that has been surgically implanted in a patient; 
           [0017]      FIG. 5  is an isometric, view of an exemplary medical implant that may he used in the system of  FIG. 4 ; 
           [0018]      FIG. 6  is a schematic representation of one particular, non-limiting embodiment of a passive RFID transponder device that may be employed in the system of  FIG. 4 ; 
           [0019]      FIG. 7  is a schematic diagram of a touch probe RFID reader device according to one non-limiting exemplary embodiment that may be employed in the system of  FIG. 4 ; 
           [0020]      FIG. 8  is a schematic representation of the output of the touch probe RFID reader device of  FIG. 7 ; and 
           [0021]      FIGS. 9 and 10  are schematic representations showing how the transient outputs of is sensor device can be correlated to sensor reading in one particular exemplary embodiment. 
       
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0022]    As used herein, the singular form of “a”, “an”, and “the” include plural references unless the context clearly dictates otherwise. As used herein, the statement that two or more parts or components are “coupled” shall mean that the parts are joined or operate together either directly or indirectly, i.e., through one or more intermediate parts or components, so long as a link occurs. As used herein, “directly coupled” means that two elements are directly in contact with each other. As used herein, “fixedly coupled” or “fixed” means that two components are coupled so as to move as one while maintaining a constant orientation relative to each other. 
         [0023]    As used herein, the word “unitary” means a component is created as a single piece or unit. That is, a component that includes pieces that are created separately and then coupled together as a unit is not a “unitary” component or body. As employed herein, the statement that two or more parts or components “engage” one another shall mean that the parts exert a force against one another either directly or through one or more intermediate parts or components. As employed herein, the term “number” shall mean one or an integer greater than one (i.e., a plurality). 
         [0024]    Directional phrases used herein, such as, for example and without limitation, top, bottom, left, right, upper, lower, front, back, and derivatives thereof, relate to the orientation of the elements shown in the drawings and are not limiting upon the claims unless expressly recited therein. 
         [0025]      FIG. 4  is a schematic diagram of an RFID system  4  according to an exemplary embodiment of the present invention wherein information may be read from and written to a medical implant  6  (such as, without limitation, an artificial knee shown schematically in the illustrated embodiment and in an isometric view in  FIG. 5 ) that has been surgically implanted in a patient  6 . As described in greater detail herein, medical implant  6  has a passive RFID transponder device  10  (e.g., a passive RFID tag) ( FIG. 5 ) coupled thereto that may be read using touch probe RFID reader device  12  (described in greater detail elsewhere herein) that is structured and configured to read the implanted RFID transponder device  10  by making a direct non-air interface) electrical connection to RFID transponder device  10  through the living tissue of patient  8  using a probe provided as part of touch probe RFID reader device  12  (e.g., using transcutaneous contact and transcutaneous near field communication (TNFC) or transcutaneous far field communication (TFFC)). 
         [0026]    As described above, RFID transponder device  10  is a passive device powered by the RF signal sent by touch probe RFID reader device  12 . One passive tag technology, known as backscatter technology, generates signals by backscattering the carder signal sent from the RFID reader. In another technology, described in U.S. Pat. Nos. 6,289,237, 6,615,074, 6,856,291, 7,057,514, and 7,084,605 (and commonly referred to as energy harvesting), RF energy from the RFID reader is harvested and converted to a DC voltage by an antenna/matching circuit/charge pump combination. The DC voltage is then used to power the circuitry that transmits information to the RFID reader at, for example, a different frequency. 
         [0027]      FIG. 6  is a schematic representation of RFID transponder device  10  according to one particular, non-limiting embodiment of the present invention wherein passive technology in the form of energy harvesting as just described is employed to power the electronic components of RFID transponder device  10 . RFID transponder device  10  includes an integrated circuit chip  14  operatively coupled to probe contacts  16 A and  16 B in the form of interfacing conductors, the function of which is described herein. 
         [0028]    In addition, RFID transponder device  10  further includes an implanted sensor device  18  that is operatively coupled to integrated circuit chip  14 . Sensor device  18  is structured to measure one or more parameters relating to the state (e.g., health state) patient  8  and provide that information to integrated circuit chip  14  so that it may then be communicated to touch probe RFID reader device  12  as described herein. In the exemplary embodiment, sensor device  18  exhibits RC and/or dynamics such that it take a certain time period for sensor device  18  to reach an accurate steady state value when it is making a measurement. Thus, in the exemplary embodiment, the output of sensor device  18  will resemble one of  FIGS. 2 and 3  (depending on the particular configuration of sensor device  18 ) 
         [0029]    As seen in  FIG. 6 , integrated circuit chip  14  of the present embodiment also includes energy harvesting circuitry  20  that is operatively coupled to (i) probe contacts  16 A and  16 B at an input end thereof, and (i) on-board electronic circuitry  22  and sensor device  18  at an output end thereof. In the illustrated embodiment, on-board electronic circuitry  22  includes control circuitry  24 , such as a microprocessor, a microcontroller or some other suitable custom control circuitry along with an associated memory, and transmitter circuitry  26 . In operation, energy harvesting circuitry  20  is structured to receive RF energy from RFID reader device  12  (via a touch probe in the manner described herein) and harvest energy therefrom by converting the received RF energy into DC energy, e.g., a DC voltage. The DC voltage is then used to power on-board electronic circuitry  22  and sensor device  18 . Transmitter circuitry  26  is structured to transmit an RF information signal to RFID reader device  12  through probe contacts  16 A and  16 B. 
         [0030]    In the particular embodiment shown in  FIG. 6 , energy harvesting circuitry  20  of integrated circuit chip  14  includes a matching network  28  electrically connected to probe contacts  16 A and  16 B. Matching network  28  is also electrically connected to a voltage boosting and rectifying circuit preferably in the form of a one or more stage charge pump  30 . Charge pumps are well known in the art. Basically, one stage of a charge pump increases the effective amplitude of an AC input voltage with the resulting increased DC voltage appearing on an output capacitor. Successive stages of a charge pump, if present, will essentially increase the voltage from the previous stage resulting in an increased output voltage. In operation, probe contacts  16 A and  16 B receive RF energy that is provided by RFID reader device  12  as described herein. The received RF energy is provided, in the form of an AC signal, to charge pump  30  through the associated matching, network  28 . Charge pump  30  rectifies the received AC signal to produce a DC signal that is amplified as compared to what it would have been had a simple rectifier been used. In the exemplary embodiment, matching network  28  is chosen (i.e., its impedance is chosen) so as to maximize some criterion such as the voltage of the DC signal output by charge pump  30 . 
         [0031]      FIG. 7  is a schematic diagram of touch probe RFD reader device  12  according to one non-limiting exemplary embodiment of the present invention. As noted elsewhere herein and as described in detail below, touch probe RFID reader device  12  is able to read information from and write information to RFID transponder device  10  by making a direct (i.e.,. non-air interface) electrical connection thereto. RFID reader device  12  includes a control system  34 , a primary radio module  36 , logic circuitry  35 , and a supplemental RF source  37 , such as, without limitation, an RF oscillator. 
         [0032]    In the exemplary embodiment shown in  FIG. 7 , control system  34  includes a processor  38 , such as a microcontroller or microprocessor, and a digital signal processor (DSP)  40 , although other configurations are possible. Processor  38  provides control over high level operation of touch probe RFID reader device  12  and may communicate with an external network and/or peripheral devices such as, without limitation, an I/O apparatus  42  (which enables information to be input into and output from touch probe RFID reader device  12 ). I/O apparatus  42  may include a display, a keyboard, a touchscreen, or some combination thereof. DSP  40  provides direct control over all operations of radio module  36  in response to high level commands provided by processor  38 , and processes data signals received from RFID transponder device  10  as described herein. Radio module  36  is adapted to provide for communications to/from RFID transponder device  10  by generating and receiving. RF signals in the manner described herein, and is structured to provide an RF output that resembles the output shown in  FIG. 1  (i.e., a number of RF bursts  2  each having a duration as governed/limited by FCC regulations). 
         [0033]    More particularly, radio module  36  further comprises a transmitter portion  44 , a receiver portion  46 , and a hybrid  48 . Hybrid  48  may further comprise a circulator. Transmitter portion  44  preferably includes a local oscillator that generates an RF carrier frequency. Transmitter portion  44  sends a transmission signal modulated by the RF carrier frequency to hybrid  48 , which in turn passes the signal to a touch probe device  50 . Hybrid  48  connects transmitter portion  44  and receiver portion  46  to touch probe device  50  while isolating them from each other. In particular, hybrid  48  allows a relatively strong signal to be sent from transmitter portion  44  while simultaneously receiving a weaker signal received from RFID transponder device  10 . Touch probe device  50  includes one or more electrical contacts or electrodes that are adapted to be selectively and temporarily mated and brought into electrical contact with probe contacts  16 A and  16 B of RFID transponder device  10 . As such, the signals generated by touch probe RFID reader device  12 , that would in known RFID readers be sent over an air interface, ma instead be directly transmitted (i.e., not over an air interface) to RFID transponder device  10  (e.g., through the living tissue of patient  8 ), and thus integrated circuit chip  14  provided therein. Similarly, the signals generated by integrated circuit chip  14 , that in the prior art would have been sent via antenna over an air interface to an RFID reader, may instead be directly transmitted (i.e., not over an air interface) to RFID reader device  12  through touch probe device  50 , in one particular embodiment, touch probe device  50  is a wand-like device having two conductors fixed at the end thereof with a center to center distance to accommodate the spacing of probe contacts  16 A and  16 B. In this embodiment, the wand-like touch probe device  50  is used to manually bring the conductors into electrical contact with probe contacts  16 A and  16 B through the tissue of patient  8  (i.e., transcutaneous contact) as needed. 
         [0034]    The signals from RFID transponder device  10  (which may, for example, include the readings of sensor device  18 ) transmitted through touch probe device  50  are passed back to hybrid  48 , which forwards the signals to receiver portion  46 . Receiver portion  46  mixes the captured signals with the RF carrier frequency generated by the local oscillator to directly downconvert the captured signals to a baseband information signal, which is provided to DSP  40  for processing thereby. 
         [0035]    In the exemplary embodiment, the RC and/or RL dynamics of sensor device  18  are such that it is not able to reach an accurate steady state value within the duration of the RF energy bursts output by touch probe RFID reader device  12 . Thus, in order to avoid problems in obtaining accurate readings from sensor device  18 , touch probe RFID reader device  12  is, as described, below, structured in a manner to provide RF energy used for powering for an extended period. 
         [0036]    More specifically, as seen in  FIG. 7 , touch probe RFID reader device  12  also includes logic circuitry  35  and supplemental RF source  37  which together are structured to provide RF energy that may be used for powering RFID transponder device  10  during the periods in between the RF energy bursts output by touch probe RFID reader device  12 . In operation, logic circuitry  35  monitors the output of radio module  36  to detect the end (falling edge) of each RF burst output by radio module  36 . In response to detecting the end of an RF burst, logic circuitry  35  sends a trigger signal to supplemental RF source  37  which causes supplemental RF source  37  to output a second RF continuous wave (CW) to touch probe  50  for a certain time period/duration such that RF continuous wave output will end just before radio module  36  produces its next RF burst (the certain time period/duration of the secondary RF CW may be programmed based on the known interval between the RF bursts of radio module  36 ). The secondary RF CW output by does not need to be modulated. 
         [0037]    Thus, the combined output to touch probe  50  will appear as shown in  FIG. 8 , wherein waveform  52  (solid line) represents the output of radio module  36  and waveform  54  (dotted line) represents the output of supplemental RF source  37 . As will be appreciated, the addition of the secondary RF CW from supplemental RF source  37  will provide extended powering time for sensor device  18  to reach a steady state value. As seen in  FIG. 8 , there can be short intervals with no RF energy supply during the period that radio module  36  is shutting off its burst, and supplemental RF source  37  is turning on, and during the period when supplemental RF source  37  is shutting down and radio module  36  is turning on. This is not a problem in that if sensor device  18  has dynamics requiring additional time for charging, those same dynamics win allow for short intervals of no RF energy. 
         [0038]    Furthermore, while RFID transponder device  10  shown in  FIG. 6  is one exemplary embodiment of a passive RFID transponder that may be used in connection with the concepts of the present invention, it will be understood that that is not meant to be limiting and that alternative passive RFID transponder implementations may also be used. For example, and without limitation, alternative passive RF LD transponder implementations may be as shown and described in U.S. patent application Ser. No. 13/552,225, the disclosure of which is incorporated herein by reference, including the implementations that employ an RFID strap. 
         [0039]    In addition, in the exemplary embodiment, touch probe RFID reader device  12  employs a touch probe  50  having two electrical contacts. It will be understood, however, that the concept of the present invention may also be employed in a touch probe RFID reader device having a single electrical contact (a mono-probe) in conjunction with appropriately configured passive RFID transponder implementations as described in U.S. patent application Ser. No. 13/552225. 
         [0040]    Moreover, in one embodiment, the reading of sensor device  18  is based on the steady state output value of sensor device  18 . In some implementations, however, the steady state output values of sensor device  18  may vary by only small amounts, thus making it difficult to discern different sensor readings. Thus, according to an alternative embodiment, the reading of sensor device  18  is based not on the steady state signal of sensor device  18 , but instead on the transient portion of the signal that is output by sensor device  18 . 
         [0041]    More specifically, as noted elsewhere herein, sensor device  18  exhibits RC and/or RL dynamics such that its output for any particular reading will have a transient response portion followed by a steady state portion. The transient response portion will resemble an RC or RL curve as shown in, for example,  FIGS. 2 and 3 , and may be characterized as a first order linear time invariant (LTI) system. As is known in the art, each such transient response portion will be characterized by and have associated with it a time constant which indicates how fast the transient output reaches a steady state value, and more particularly is the time that it takes the transient output to reach a certain % (about 63.2%) of either its initial value or its steady state value. In the present alternative embodiment, each one of a family of possible transient outputs of sensor device  18  is correlated to a particular sensor reading/value so that the sensor reading/value of sensor device  18  is able to be based on some characteristic, such as the time constant, of the transient response portion of the output of sensor device  18  (rather than the steady state portion). This is illustrated in one embodiment in  FIG. 9 , wherein a plurality of different possible transient outputs (labeled  60 A,  60 B,  60 C) of sensor device  18  (each having an RC curve form) are shown, with each one having an associated time constant (τ) that is correlated to a particular sensor reading/value, and in another embodiment in  FIG. 10 , wherein another plurality of different possible transient outputs (labeled  62 A,  62 B,  62 C) of sensor device  18  (each having an RL curve form) are shown, with each one having an associated time constant (τ) that is correlated to a particular sensor reading/value. 
         [0042]    In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word “comprising” or “including” does not exclude the presence of elements or steps other than those listed in a claim. In a device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The word “a” or “an” preceding an element does not exclude the presence of a plurality of such elements. In any device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere filet that certain elements are recited in mutually different dependent claims does not indicate that these elements cannot be used in combination. 
         [0043]    Although the invention has been described in detail for the purpose of illustration based on what is currently considered to be the most practical and preferred embodiments, it is to be understood that such detail is solely for that purpose and that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover modifications and equivalent arrangements that are within the spirit and scope of the appended claims. For example, it is to be understood that the present invention contemplates that, to the extent possible, one or more features of any embodiment can be combined with one or more features of any other embodiment.