Abstract:
A capsule endoscopic system with wireless docking device is disclosed, where the system comprises a capsule device and a docking device for receiving the data from the capsule device. The docking device supplies power to the capsule device and retrieves data from the capsule device wirelessly. The capsule device comprises an archival memory to store data captured inside a body lumen by the capsule device, a wireless transmitter to transmit the stored data, a secondary coil. The docking device comprises a primary coil to generate an alternating magnetic field, wherein the magnetic field is coupled to the secondary coil to supply power to the capsule device wirelessly when the capsule device is docked in the docking device and a wireless receiver to receive the data from the capsule device. The wireless link can be a radio frequency (RF) link or an optical link.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present invention claims priority to U.S. Provisional Patent Application No. 61/649,238, filed on May 19, 2012, entitled “Optical Wireless Docking System for Capsule Camera”. The U.S. Provisional Patent Application is hereby incorporated by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to diagnostic imaging inside the human body. In particular, the present invention relates to optical wireless docking system for supplying power to and retrieving data from a capsule camera. 
       BACKGROUND 
       [0003]    Devices for imaging body cavities or passages in vivo are known in the art and include endoscopes and autonomous encapsulated cameras. Endoscopes are flexible or rigid tubes that pass into the body through an orifice or surgical opening, typically into the esophagus via the mouth or into the colon via the rectum. An image is formed at the distal end using a lens and transmitted to the proximal end, outside the body, either by a lens-relay system or by a coherent fiber-optic bundle. Alternatively, the endoscope might record an image electronically at the distal end, for example using a CCD or CMOS array, and transfer the image data as an electrical signal to the proximal end through a cable. Because of the difficulty traversing a convoluted passage, endoscopes cannot easily reach the majority of the small intestine and special techniques and precautions, that add cost, are required to reach its entirety. The cecum and ascending colon also require significant effort and skill to reach with an endoscope. An alternative in vivo image sensor that addresses many of these problems is a capsule endoscope. A camera is housed in a swallowable capsule, along with a radio transmitter for transmitting data, primarily comprising images recorded by the digital camera, to a base-station receiver or transceiver and data recorder outside the body. Another autonomous capsule camera system with on-board data storage was disclosed in the U.S. patent application Ser. No. 11/533,304, filed on Sep. 19, 2006. 
         [0004]    For the above in vivo devices, a large amount of image data is collected traversing through a lumen in the human body such as the gastrointestinal (GI) tract. The images captured, along with other information, are stored in the on-board archival memory inside the capsule camera. The archival memory may come in various forms of non-volatile memories. After the capsule camera exits from the anus, it is retrieved to recover the data stored on-board. In a conventional approach, it would require a fairly expensive data access system that includes opening the capsule and docking to it. Because of the requirement to open the capsule and align contact pins to pads in the capsule, some degree of mechanical complexity is inevitable. Therefore, such tasks usually are performed by specially trained persons. It is desirable to develop a new system that allows data retrieval from the capsule camera without opening the sealed enclosure. Furthermore, it is desired that the new system can operated be easily and quickly so that data retrieval from the capsule camera can be performed in any typical medical service environment. 
       BRIEF SUMMARY OF THE INVENTION 
       [0005]    A capsule endoscopic system is disclosed, where the system comprises a capsule device and a docking device for receiving the first data from the capsule device. The capsule device comprises an archival memory to store first data captured inside a body lumen by the capsule device, a wireless transmitter to transmit the stored data, a secondary coil, and a capsule housing, wherein the archival memory, the wireless transmitter and the secondary coil are sealed in the capsule housing. The docking device comprises a primary coil to generate an alternating magnetic field, wherein the magnetic field is coupled to the secondary coil to supply power to the capsule device wirelessly when the capsule device is docked in the docking device and a wireless receiver to receive the first data from the capsule device. The wireless link can be a radio frequency (RF) link or an optical link. 
         [0006]    In one embodiment, the docking device further comprises a receptacle to hold the capsule device, and at least a portion of the receptacle holding one longitudinal end of the capsule device is transparent to allow light emitted from the capsule device to pass. The receptacle comprises a tapered inner surface, and the tapered inner surface mates with a curved surface of said one longitudinal end of the capsule device to align a longitudinal axis of the capsule device with an optical receiver in the docking device. 
         [0007]    One aspect of the present invention addresses the configuration of the primary coil and the secondary coil. In one embodiment, the docking device comprises a primary core outside the capsule device when the capsule device is docked in the docking device and the primary core contains at least a portion of magnetic flux associated with the primary coil, wherein the primary core contains ferromagnetic or ferrimagnetic material. The primary core can be configured as a shell and the primary coil is enclosed by the shell. The capsule device can be positioned into the shell through an opening of the shell when the capsule device is docked in the docking device. The capsule device may penetrate into an inner surface of the shell or partially into the inner surface of the shell. When the capsule device partially penetrates the inner surface of the shell, the batteries inside the capsule device are not enclosed by the inner surface of the shell when the capsule device is docked in the docking device. 
         [0008]    Another aspect of the invention addresses arrangement of an optical link between the capsule device and the docking device. A light passage between the capsule device and the docking device is provided for a system using a shell. In one embodiment, the capsule device comprises a modulated light source which emits modulated light passing through an opening in the shell to an optical receiver in the docking device. The docking device may include a lens of positive refractive power to reduce divergence of the modulated light from the modulated light source. The docking device may also include a light pipe, such as an optical fiber, passing into the opening in the shell and the modulated light from the modulated light source passes through the light pipe to the optical receiver. 
         [0009]    Yet another aspect of the present invention addresses means for a hinged lid or removable cover to keep the capsule device from being picked up when the hinged lid or removable cover is opened. A spring-loaded plunger or an elastic membrane can be used to apply push force on the capsule device when the hinged lid or removable cover is opened. 
         [0010]    A docking device without the need of need of hinged lid or removable cover is also disclosed. Instead of using a power switch along with an external magnetic force to reset the electrical system of the capsule device, the alternative configuration uses a software or firmware based control that polls the polls a control signal from the docking device and manages transmission of the first data in response to the control signal. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  illustrates an example of system architecture of an optical wireless docking system according to the present invention. 
           [0012]      FIGS. 2A-B  illustrate an exemplary optical wireless docking system according to the present invention, where the system is configured with longitudinal-field geometry. 
           [0013]      FIG. 3  illustrates an exemplary optical wireless docking system according to the present invention, where the system is configured with alternative longitudinal-field geometry. 
           [0014]      FIG. 4  illustrates an exemplary optical wireless docking system according to the present invention, where the system is configured with lateral-field geometry. 
           [0015]      FIG. 5  illustrates an exemplary optical wireless docking system according to the present invention, where the system is configured with lateral-field geometry using two sets of primary ferrites with poles positioned orthogonally. 
           [0016]      FIG. 6  illustrates a cross-section view of an exemplary optical wireless docking system according to the present invention, where the system is configured with longitudinal-field geometry. 
           [0017]      FIG. 7  illustrates a cross-section view of an exemplary optical wireless docking system according to the present invention, where the system is configured with longitudinal-field geometry and an uplink is provided using optic fibers as transmission media. 
           [0018]      FIG. 8  illustrates a cross-section view of another exemplary optical wireless docking system according to the present invention, where the system is configured with longitudinal-field geometry and an uplink is provided using space as transmission media. 
           [0019]      FIG. 9  illustrates an exemplary optical wireless docking system according to the present invention. 
           [0020]      FIG. 10  illustrates an exploded view of the hinged lid of the optical wireless docking system in  FIG. 9 . 
           [0021]      FIG. 11  illustrates a cross-section view of the exemplary optical wireless docking system in  FIG. 9 . 
           [0022]      FIG. 12  illustrates a cross-section view of an optical wireless docking system, where foam is added between the lid and the retention cap. 
           [0023]      FIG. 13  illustrates a cross-section view of an optical wireless docking system, where a push force is applied to the capsule device by a spring when the lid is opened. 
           [0024]      FIG. 14  illustrates a cross-section view of an optical wireless docking system, where an elastic membrane is used to provide water tight feature and push force on the capsule device when the lid is opened. 
           [0025]      FIG. 15  illustrates a cross-section view of an alternative optical wireless docking system with an elastic membrane to provide water tight feature and push force on the capsule device when the lid is opened. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0026]    It will be readily understood that the components of the present invention, as generally described and illustrated in the figures herein, may be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of the embodiments of the systems and methods of the present invention, as represented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. Reference throughout this specification to “one embodiment,” “an embodiment,” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the present invention. Thus, 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. 
         [0027]    Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. One skilled in the relevant art will recognize, however, that the invention can be practiced without one or more of the specific details, or with other methods, components, etc. In other instances, well-known structures, or operations are not shown or described in detail to avoid obscuring aspects of the invention. The illustrated embodiments of the invention will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout. The following description is intended only by way of example, and simply illustrates certain selected embodiments of apparatus and methods that are consistent with the invention as claimed herein. 
         [0028]    In order to overcome the shortcoming in a conventional docking system, an optical wireless docking system according to the present invention is disclosed herein. A wireless docking system is attractive because the capsule need not be opened or precisely aligned. After the capsule camera exits from the anus, the batteries inside are likely depleted or nearly depleted. Therefore, power must be supplied from outside the capsule, by magnetic induction for example. Also, data has to be transmitted wirelessly, such as by an optical or radio means. 
         [0029]    In one embodiment according to the present invention, the docking system utilizes inductive powering and optical transmission. Nevertheless, radio transmission may also be used to practice the present invention. Any optical source requiring very little space to fit into the capsule may be considered. The optical source should be able to support fast data transmission. The amount of data stored in a capsule camera may be as much as 500 Mbytes and the data size will continue to grow along with the trend of high-resolution demand. If 1 Mbps (million bits per second) transmission speed is supported, it may take around 100 minutes to read out 500 Mbytes data if overhead in data transmission protocol is taken into account. Therefore, it is preferably to select an optical source that can support higher data rate. As one example, the optical source can be a directly modulated LED or Vertical-Cavity Surface-Emitting Laser diode (VCSEL) with a target bit rate of 10 Mbps. 
         [0030]    Exemplary system architecture is shown in  FIG. 1 , where LED  116  is used as a light source and a Photo Diode (PD) is used as the receiver. Control circuit  115  is shown inside capsule camera  110 . Control circuit  115  will read data stored in the archival memory (not shown) and process the retrieved data so that the data can be properly transmitted by light source  116 . Light emitted from light source  116  will travel through the transparent window (not explicitly shown) of the capsule camera. The light from light source  116  will be received by a light receiving device such as photo diode  125  at docking system  120 . The received signal will be properly amplified by amplifier  126 . The amplified signal is then processed by receiver circuit  127  where data and clock will be recovered. The data recovered can be stored on a media such as a flash drive or computer hard disk drive. Alternatively, the data recovered may be provided to a workstation or a display station for further processing or viewing. 
         [0031]    The output buffer from control circuit  115  will provide needed power for light source  116 . For example, 2 mA current may be provided, which should be adequate to drive either an LED or VCSEL. The LED wavelength may be in the near Infrared (NIR), for example at 830 nm. Other LED wavelengths may also be used to practice the present invention. With a 3V drive voltage, the correct drive current is produced with series resistance  117 . A bit rate of 10 Mbps or more can be achieved. 
         [0032]    The receiver consists of photodiode  125 , trans-impedance amplifier  126 , and data/clock recovery module  127 . This module could be implemented using a limiting amplifier and a PLL. However, this functionality could be performed digitally by sampling the waveform and using DSP to recover data and clock. The use of a UART might obviate the need for clock recovery. The interface protocol may be used for the intended operation around 10 Mbps frequency range. Other standard digital data interfaces may also be used. In  FIG. 1 , optical link is shown as a wireless link between the capsule device and the docking device, a radio frequency (RF) link may also be used as the wireless link. 
         [0033]    Inductive coupling relies on the mutual inductance of a primary coil outside the capsule and a secondary coil inside the capsule. The primary is driven by a sinusoidal voltage, and the secondary signal is rectified to produce a DC voltage. Exemplary system architecture is shown in  FIG. 1 . The system comprises capsule camera  110  and docking system  120 . The inductive power is supplied from docking system  120  to capsule camera  110  through coupling coils  122  and  111 . Coil  122  at the docking system side is referred to as primary side and coil  111  on the capsule camera side is referred to the secondary side. At the primary side, signal source  121  provides the driving signal to primary coil  122 . While a sinusoidal driving signal is shown, other alternating signals such as square wave or triangular wave may also be used. The driving signal from signal source  121  may be amplified by amplifier  123 . Various other known means of producing an alternating current may be utilized to drive the primary. The voltage across primary coil  122  is named primary voltage V1 and the voltage across secondary coil  111  is named secondary voltage V2. It is well known in the art that the induced alternating voltage at the secondary side can be converted into a DC voltage to be used by the circuits inside the capsule camera. Rectifiers are often used for converting AC power to DC power. Two rectifiers  112   a  and  112   b  are shown in  FIG. 1  to provide different DC outputs as required by the capsule camera. Furthermore, the circuits in the capsule device can be configured to charge rechargeable batteries inside the capsule device when the capsule device is docked in the docking device. For example, battery  118  may be a rechargeable battery and can be charged by the voltage output from rectifier  112   a . Depending on the capsule camera design, it may require more or fewer voltage outputs. The rectifiers may also be integrated into a package or a module. The rectifier may be followed by a simple regulator, such as a Zenor-diode circuit or other voltage control circuits, to allow larger variability and stability in secondary voltage. Additionally, the rectifier may include voltage multiplication with a Greinacher or Cockcroft-Walton circuit. The components are selected to minimize the volume in order to fit into the limited space available inside the capsule camera. A voltage multiplier allows a smaller and lighter secondary coil to be used but requires additional diodes and capacitors. 
         [0034]    The ratio of the secondary to primary voltage is: 
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         [0000]    where N 2  is the number of secondary coil turns, N 1  is the number of primary coil turns. The coupling coefficient is the ratio of the coil fluxes: 
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         [0035]    The flux through a coil is given by integration of the flux density through a surface defined by the coil perimeter 
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         [0036]    The coupling coefficient β can be increased by making the secondary coil area larger and by designing pole pieces for the primary and/or secondary that concentrate the magnetic flux. For sinusoidal modulation of the primary at frequency f, the flux amplitude in the primary and secondary is given by 
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         [0037]    As mentioned before, the secondary coil is located inside the capsule camera. In order to properly couple the electro-magnetic field from the primary coil to the secondary coil, the two coils have to be correctly positioned and aligned. On the other hand, in order to read out data from the capsule camera optically, light passage has to be provided between the light source and the light detector. Accordingly, one exemplary system configuration to provide light passage as well magnetic field coupling is shown in cross section in  FIGS. 2A and 2B , where  FIG. 2B  represents a bottom view of the capsule camera. The type of arrangement is called longitudinal-field geometry. 
         [0038]    Primary coil  221  wraps around capsule housing  210  of capsule  200 . Secondary coil  214  is on the perimeter of bottom PCB  212  in the capsule. Primary coil  221  and secondary coil  214  should be centered on the same plane. Secondary coil  221  can also be implemented as a printed circuit as a spiral on multiple layers of PCB  212 , although the practical pitch of the traces limits the number of turns. Alternatively, a coil can be produced with thin-gauge insulated wires held in shape with shellac and mounted to the PCB as a through-hole or surface mount component. 
         [0039]    Light source  216  (LED or VCSEL) sits on the center of the board facing down. Batteries  211  are located at the other end of the capsule camera so that the batteries will not block light passage  224  from the light source to the light receiver. Lens  223  may be used to focus the light onto light receiver  225  such as a photodiode. Optional Band Pass Filter (BPF)  222  for the light can be installed in light passage  224  between light source  216  and light receiver  225 . The components including the primary coil  221 , the light BPF  222 , the lens  223 , the light receiver  225  and associated Printed Circuit Board  226  are housed in the docking system  220 . The arrangement is symmetrical so that the rotational orientation of the capsule is not significant to the inductive coupling or the received optical power. A disadvantage is that eddy currents will be induced in the traces and power planes on PCB  212  itself. These currents can cause heating and also produce noise in the circuit. In the worst case, where a circuit trace forms a loop around the PCB, the induced voltage in the trace is V 2 /N 2 . Increasing the number of turns will decrease the noise but increase the volume occupied by the secondary coil. The noise can also be limited by minimizing the loop area of traces. 
         [0040]      FIG. 3  illustrates another primary coil arrangement where ferrite core  320  for the primary coil on the primary side can reduce the magnetic flux reaching the batteries. The ferrite core  320  is also referred to as a primary core in this disclosure. The primary core may have a shell structure to enclose the primary coil. The shell has an opening to allow the capsule device to be docked through the opening. The primary core may be a ferrimagnetic material or may be a ferromagnetic material such as steel. A ferrite has the advantage of low electrical conductivity and, as a result, low eddy current loss. Coin-cell silver oxide or lithium batteries have high energy density and a round package that fits well in a capsule, but these generally have steel cases that could be inductively heated, creating the potential for battery bursting. The core also will reduce the field emitted by the system, which might be an issue for electromagnetic compatibility (EMC) requirement compliance. Photodiode  326 , mounted on PCB  328 , sits above post piece  325 . Primary coil  322  is wrapped around post piece  325 . Signal source  324  provides driving signal to primary coil  322 . This design has no lens, but uses VCSEL  316 , which has an output beam with much lower divergence than an LED. 
         [0041]    The problem of spurious eddy currents can be reduced by orienting the field horizontally to PCB and batteries as shown in  FIG. 4 . The arrangement between the primary coil and secondary coil is named lateral-field geometry. Small coil  414  wrapped around ferrite  416  is placed on PCB  412  aligned to the post pieces  426 . Capsule  400  with housing  410  must be oriented to post pieces  426 . β is reduced relative to the geometry of  FIG. 2A  because of the small area of secondary coil  414 . On the other hand, ferrite core  416  will concentrate the field lines within secondary coil  414  to some degree. This effect is maximized if the gap between the post pieces is minimized and the length of the ferrite  416  is maximized. However, the length is limited by the available space in the capsule. Primary coil  422  is wrapped around primary core  420  and is driven by driving signal  424 . While a C-shaped primary core is used, a toroidal-shaped structure or similar can also be used. 
         [0042]    To avoid the requirement of capsule alignment, a second set of pole pieces can be placed orthogonal to the first and driven in quadrature as shown in  FIG. 5 , where a top view is presented. The pole pieces of first primary ferrite  520   a  are configured to be orthogonal to the pole pieces of second primary ferrite  520   b . First primary coil  522   a  is driven by first driving signal  524   a  and second primary coil  522   b  is driven by second driving signal  524   b . Driving signals  524   a  and  524   b  have to be quadrature. For example, the pair of signals I 0  cos (2π ft) and I 0  cos (2π ft+π/2) can be used to drive signal sources  524   a  and  524   b . Capsule  500  is shown at the center of the sets of poles. Secondary coil  514  is wrapped around ferrite core  516 . The orientation of the secondary coil is shown at a slant angle from the orientations of the two sets of poles. The magnetic field will rotate and the flux through the coil will vary approximately sinusoidally independent of capsule orientation. The flux amplitude will have some dependence on orientation if the secondary ferrite is not rotationally symmetrical, however. 
         [0043]    The secondary coil may be an off-the-shelf inductor, as long as it is not shielded. Surface-mount inductors that comprise a ferrite with a fine wire wrapping it would be a convenient and low-cost solution. For example, two chip inductors from CoilCraft that could be used are: 
         [0044]    0805LS-273XJLB 27 μH 15 mg 
         [0045]    0603LS-223XJLB 22 μH 5 mg 
         [0046]    The 0805LS-273 has a coil cross section of A 2 ≈1.5 mm 2 . Assume the primary pole pieces have an area of A 1 ≈32 mm 2 . The magnetic flux density in the secondary will be less than that in the primary due to field fringing, although the ferrite in the secondary will concentrate the field to some extent. As a rough estimate, assume the flux density is reduced by 10×. The coupling is thus 
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         [0047]    A disadvantage of low coupling is worse load regulation. The inductor could be placed at the periphery of capsule close to a pole piece to further increase coupling. However, an alignment of the capsule would be required. 
         [0048]    The capsule can be inserted into an opening in the system housing. At the bottom of the hole is a window, where a band pass filter at the LED wavelength can be placed. A lens may be used to focus the emitted light onto the photodiode.  FIG. 6  illustrates an exemplary optical wireless docking system according to the present invention. The components for the docking device side can be placed inside the docking device housing. The exemplary docking system in  FIG. 6  consists of base part  620  and holder part or cover part  630 . Holder/cover part  630  can be pulled open or separated from the base part to insert or remove capsule  610 . Secondary coil  612  inside the capsule and primary coil  622  are configured longitudinally. Part of the primary coil is wrapped around center post  625  of primary ferrite  624  (or primary core). 
         [0049]    The primary ferrite has a shell-shaped structure to provide passage  627  between light source  618  inside capsule  600  and light receiver  626 . A bore in the center of the post serves as the passage. Light source  618  may be mounted on circuit board  619  within capsule housing  610 , where other circuits for the capsule camera may also be mounted on the board. Light receiver  626  may be mounted on PCB  628  where other circuits for the docking system can be implemented. The bore in the post is aligned with the longitudinal axis of the capsule device to allow light emitted from the light source  618  to pass through the light passage to reach light receiver  626 . The capsule device is shown partially into the inner surface of the shell (i.e., primary core  624 ) so that the batteries remain outside the shell to reduce the influence of the magnetic flux on the batteries. A recessed structure ( 629 ) is formed in the center of the base part ( 620 ) of the docking device and is used as a receptacle for the capsule device. 
         [0050]    The capsule retrieved after it exits from the anus may still have some remaining battery power, which may prevent the capsule circuits from resetting properly. In order to ensure proper data retrieval operation, an internal power off switch under the control of an external magnetic field is applied. Accordingly, magnet  632  is incorporated in holder/cover part  630 . When the hold/cover is at a close position, the internal switch will be under the influence of the magnetic force to cause the batteries disconnected from the capsule circuits. 
         [0051]    An alternative docking system according to the present invention is shown in  FIG. 7 , where optical communication link, named uplink, from the docking system to the capsule is also provided. The uplink allows the system to provide commands, controls, acknowledgements, programming or testing to the capsule. The data speed for the uplink does not have a high speed requirement. In order to provide the uplink, one or more light receiving devices (not shown in  FIG. 7 ), such as photoresistors, phototransistors and photodiodes are used inside the capsule camera. Since the center location has been used by the light source in the capsule, the light receiving device(s) will be arranged off center inside the capsule. 
         [0052]    The docking system consists of base part  720  and holder part or cover part  730 . Holder/cover part  730  can be pulled open or separated from the base part to insert or remove capsule  700 . The capsule camera illustrated is substantially the same as capsule camera  600  in  FIG. 6 . The parts that are the same are assigned the same numerical references. Primary coil  722  is wrapped around center post  725  of primary ferrite  724 . The primary ferrite structure provides a passage to allow two optic fibers running between light source  618  and a light receiver (not shown) inside capsule housing  610  and light receiver/light transmitter  728  respectively. While light receiver/light transmitter  728  is shown as a standalone box, receiver/light transmitter  728  may also be mounted on a circuit board, where the same board also includes other circuits for the docking unit. An additional ferrite ( 734 ) is shown in holder/cover part  730  in  FIG. 7 , where the additional ferrite can be configured to direct more magnetic fluxes to go through the secondary coil. Primary core  724  in the base part of the docking device and the additional ferrite ( 734 ) in the holder/cover form a shell to provide needed shielding of the magnetic flux. 
         [0053]    The two-way communication can be operated in half duplex or full duplex. The communication may adopt spatial or wavelength division multiplexing to avoid cross talk. A transparent window between capsule  600  and tips of light pipes  726  and  727  to allow optical signals passed between capsule  700  and light receiver/light transmitter  728 . Again, the bore in the center of the post serves as the passage. The bore in the post is aligned with the longitudinal axis of the capsule device as shown in  FIG. 7 . The light pipes can be optical fibers. Accordingly, transparent piece  740  is placed on the concaved top side of base part  720 . The capsule may not be fully cleaned and dried when it is inserted into the docking station. To prevent any liquid to leak into the base part, it is desirable to seal between the edges of transparent piece  740  and base part  720  as indicated by arrows  750 . Ferrule  760  may be used to strengthen optical fibers  726  and  727  and keep them in position. 
         [0054]    Yet another alternative docking system according to the present invention is shown in  FIG. 8 , where an uplink is also provided. Unlike the docking system in  FIG. 7  where optic fibers are used as a transmission media, the docking system in  FIG. 8  uses space as transmission media. For the uplink, LED transmitter  829  is used as a light source and one or more photoresistors inside the capsule housing (not shown in  FIG. 8 ) are used as light receivers. Since the center location has been used by the light source in the capsule, the light receiving device(s) will be arranged off center inside the capsule. The docking system consists of base part  820  and holder part or cover part  630 , which are substantially the same as these in  FIG. 6 . Also, capsule camera  800  illustrated is similar to the capsule camera  600  of  FIG. 6 . However, an optical receiver is incorporated in the capsule device to receive the uplink signal emitted from the optical transmitter in the docking device. The parts that are the same are assigned the same numerical references. The base part  820  includes ferrite primary core  824  and center post  825 . The space between primary coil  822  and center post  825  is used to accommodate LED transmitter  829 . 
         [0055]    Capsule  800  may include one or more photoresistors inside the capsule housing to be used as optical receiver for receiving light from LED  829 . The two-way communication can be operated in half duplex or full duplex. The communication may adopt spatial or wavelength division multiplexing to avoid cross talk.  FIG. 8  also illustrates a different design for the receptacle ( 823 ), where the receptacle comprises a tapered inner surface to mate with the curved surface of one longitudinal end of the capsule device to align a longitudinal axis of the capsule device with the optical receiver in the docking device. At least a portion of the receptacle is transparent to allow light to pass through the capsule device. A bore in the center of the post serves as the passage. The bore in the post is aligned with the longitudinal axis of the capsule device to allow light emitted from the light source  618  to pass through the light passage to reach light receiver  626 . 
         [0056]      FIG. 9  illustrates a docking system embodying the present invention. The docking system comprises lid/cover part  930  and base part  920 . Capsule  900  is situated in the capsule bay of the base part. The cover includes sub-assembly  932  and subassembly  934 .  FIG. 10  illustrates more detailed structure of lid/cover part  930 , where the lid/cover part is shown upside down. An exploded view of subassembly  932  and subassembly  934  is shown. Subassembly  932  comprises magnet  1010 , VHB (adhesive)  1012 , flange  1014 , compression spring  1016 , and plunger  1018 . The subassembly  934  comprises magnet  1030  and bumper  1032 . When lid/cover  930  is lowered to a closed position, magnet  1010  will be a short distance from capsule  900 . The magnetic force of magnet  1010  will cause capsule  900  to disconnect at least some of its circuits from the batteries. Plunger  1018  is spring-loaded. When the lid/cover part is opened, the plunger will push capsule  900  away from magnet so that it is pushed to the bottom of the “bay” (receptacle) and does not lift. Bumper  1032  can absorb some impact force when the lid is closed down and magnet  1030  can interact with a second magnet, a ferromagnetic component, or a ferrimagnetic component in the base part to provide a holding force between the lid and the base part. 
         [0057]    A portion of a cross section drawing of a capsule docking station incorporating an embodiment of the present invention is shown in  FIG. 11 . Capsule  1100  sits in receptacle  1120 . A ring-shaped magnet ( 1112 ) with a tapered bore is held in hinged lid  1110  and comes into close proximity of the capsule when the lid is lowered. A compression spring ( 1116 ) along with plunger  1114  and magnet  1112  are housed in retention cap  1118 . When the lid is in a closed position, the plunger pushes the capsule down toward the bottom of the receptacle. The lower portion of  FIG. 11  corresponds to the cross section of the base part of the docking device. The receptacle in the base part is used to receive the capsule. The bottom of the receptacle corresponds to a transparent window ( 1130 ) to allow light to pass between the capsule and light receiver  1134  through passage  1132 , which may contain an optical fiber or light pipe. The taper in the sides of receptacle  1120  near the bottom centers the capsule with the passage  1132 . The light receiver can be mounted on PCB  1136 . Also shown in  FIG. 11  are ferrite  1140 , ferrite post  1142  and primary coil  1122 . The secondary coil inside the capsule is not shown in  FIG. 11 . The magnet must come to within about 0.2 mm of touching the capsule to reliably disconnect the batteries from electrical circuits in the capsule. 
         [0058]    When the capsule is attracted to the magnet, the optical coupling will be reduced if it lifts up off the bottom of the receptacle to meet the magnet. The capsule must rest on the taper of the receptacle to be properly aligned to the optical fiber. Also, when the lid is lifted, it will take the capsule with it. In order to overcome these problems, the system includes a spring-loaded plunger that passes through the bore of the magnet. The plunger pushes the capsule down into the receptacle during download and also as the lid is lifted, until the plunger is fully extended. Without a holding force, the lid would be pushed up by the plunger spring. It must be held down somehow during download. Accordingly, the lid has two lid magnets that are attracted to magnets in the base and these magnets hold the lid down. These lid magnets should not be so strong that the entire system is lifted up off the table when the lid is lifted. 
         [0059]    One embodiment according to the present invention is to introduce compliance into the plunger magnet position with the addition of a spring connecting the magnet to the lid. The compliance compensates for mechanical tolerances so that the magnet will reliably touch the capsule or sit sufficiently close to the capsule (e.g. less than 0.2 mm) to cause the capsule to disconnect internal circuits from the batteries while the lid is closed and the capsule is pushed to the bottom of the receptacle. Adhesive-backed foam  1210  is inserted between the retention cap ( 1218 ) and the lid as shown in  FIG. 12 . The foam is a form of spring that provides some compliance to the magnet position. 
         [0060]    One embodiment according to the present invention is shown in  FIG. 13 . Instead of gluing the magnet to the retention cap, a spring ( 1320 ) loaded with a short range of vertical travel is used to provide compliance to the magnet. The flange on plunger  1314  is reduced in diameter to fit inside an inner cylinder. The spring pushing magnet  1312  sits between the inner cylinder and retention cap  1318 . The spring force needs only be strong enough to keep the plunger pushed against the capsule and prevent rattling when lid  1310  is moved. 
         [0061]    There is a potential problem with the designs shown above. The liquids remaining on the capsule can flow into the retention cap through the gap between the plunger and the plunger magnet. If the magnet is movable, then another gap exists around the outside of the magnet. The capsule will touch the plunger and the magnet. If the capsule is still wet, this moisture could wick into the opening, become trapped, and lead to microbial growth. Also, users may want to wipe down and disinfect the system. Cleaning liquids could also flow through the opening and become trapped. A design that seals this region may be desirable. 
         [0062]    Accordingly, one embodiment of the present invention to achieve a liquid barrier is shown in  FIG. 14 . The ring magnet is replaced by a rod magnet ( 1412 ). The rod magnet has the advantage of relaxing the lateral alignment requirement between the capsule receptacle and the magnet on the lid ( 1410 ). The magnet has a short travel distance which takes up all of the vertical tolerance stack-up. The magnet is pushed downward by a soft spring ( 1416 ), whose main function is to prevent the magnet rattling around in its bore. A flexible membrane ( 1420 ) covers the magnet assembly ( 1418 ) and provides a seal. In  FIG. 14 , membrane  1420  is elastic and acts like a trampoline to provide the force F_Plunger pushing the capsule down. The membrane needs to be a material that retains its mechanical properties after exposure to the environment, including modest levels of UV light and alcohol and other mild cleaning agents. Also, the membrane should be tough enough to resist puncture and abrasion under reasonable use. Polyester polyurethane can meet these requirements. The membrane can be made taught by gluing it to an outer ring ( 1422 ) and then pressing it over a step ( 1424 ) as shown in  FIG. 14 . 
         [0063]    Another embodiment of the present invention to achieve a liquid barrier is shown in  FIG. 15 , where the membrane ( 1510 ) is inelastic and is bonded to a ring ( 1516 ). The force F_Plunger pushing on the capsule is provided by a second spring ( 1518 ) pushing on ring  1516 . An accordion ( 1512 ) or similar structure allows the membrane and ring to move without breaking the seal. Cap structure  1514  is attached to the lid to provide travel space for ring  1516  and also allow the accordion structure to be affixed to cap structure  1514 . While exemplary arrangements to achieve a liquid barrier are shown in  FIG. 14  and  FIG. 15 , a person skill in the art may use other similar arrangement to achieve a liquid barrier. 
         [0064]    Instead of a plunger or elastic membrane providing a force F_Plunger pushing the capsule away from the magnet, a frictional force may be employed to hold the capsule in the receptacle when the lid is lifted. The frictional force must exceed the force of the magnet. The frictional force may be supplied by compliant member that presses against the side of the capsule. The receptacle might be flexible, in which case the user must push the capsule into the receptacle and some force is required to overcome the frictional holding force and pull it out. Alternatively, the rubber ring mating the receptacle to the housing in  FIG. 11  may have a reduced inner diameter so that it interferes with the capsule, bends when the capsule is inserted, and applies a holding force. A clamp may also be used to hold the capsule in the receptacle while the lid is lifted. The clamp may engage automatically or be actuated by the user. 
         [0065]    Instead of preventing the capsule from being pulled out of the receptacle when the lid is lifted, the system may have the feature that the capsule is removed from the receptacle when the lid is lifted, held by the magnet. The user may then remove the capsule from the magnet. The system should be designed to either repeatably lift the capsule with the lid or repeatably leave the capsule in the receptacle when the lid is lifted so that the behavior is predictable to the user. 
         [0066]    In another embodiment, the capsule may have a magnetically actuated switch located in another location internal to the capsule besides the capsule tip. Also, the switch may be sufficiently sensitive to a magnetic field such that a magnet may be positioned close to, but not touching the capsule. The magnet may be positioned in the base of the docking system on one or more sides of the capsule receptacle, rather than on the lid. For example, a longitudinal magnetic field could be produced in the capsule by one or more rod magnets with vertical polarity located on one or more sides of the capsule (when it is in the receptacle in the docking system) or a ring magnet could be positioned around the capsule. The switch might be actuated by a transverse field, in which case a magnet with lateral polarity could be positioned to the side of the capsule, and, in this case, the capsule rotational orientation might need to be aligned relative to the direction of the magnetic field. The magnetic field could be produced by a permanent magnet or an electromagnet. 
         [0067]    The docking devices as shown in  FIGS. 6-15  incorporate a lid and a magnet. The magnet will cause the capsule to disconnect the batteries from electrical circuits inside the capsule when the lid is closed. In another embodiment of the present invention, the need for the magnet and lid is obviated. The capsule firmware periodically polls for a docking system signal so that the capsule does not require power-on reset prior to download. Therefore, there is no need to use a magnet to cause the capsule to disconnect the batteries from the electrical circuits inside the capsule. 
         [0068]    Without the magnet and the lid, the docking system will have no moving parts. As such, it will be easier to ensure usability, reliability, and durability of the product. The lid hinge area is the most likely section to break if the system is dropped or otherwise abused. The assembly process will be simplified. Also, the cost associated with the docking device can be reduced. 
         [0069]    The above description is presented to enable a person of ordinary skill in the art to practice the present invention as provided in the context of a particular application and its requirements. Various modifications to the described embodiments will be apparent to those with skill in the art, and the general principles defined herein may be applied to other embodiments. Therefore, the present invention is not intended to be limited to the particular embodiments shown and described, but is to be accorded the widest scope consistent with the principles and novel features herein disclosed. In the above detailed description, various specific details are illustrated in order to provide a thorough understanding of the present invention. Nevertheless, it will be understood by those skilled in the art that the present invention may be practiced. 
         [0070]    The invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described examples are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.