Patent Publication Number: US-2022231526-A1

Title: Base units, transmitter units, wearable devices, and methods of continuous analyte monitoring

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This claims the benefit of U.S. Provisional Patent Application No. 63/140,083, filed Jan. 21, 2021, the disclosure of which is hereby incorporated by reference herein in its entirety for all purposes. 
    
    
     FIELD 
     Embodiments of the present disclosure relate to continuous analyte monitoring apparatus and methods thereof. 
     BACKGROUND 
     Continuous analyte monitoring, such as continuous glucose monitoring (CGM), has become a routine monitoring operation, particularly in diabetes care. CGM provides real-time analyte (e.g., glucose) concentrations to users and/or medical professionals. By monitoring real-time glucose concentrations, therapeutic actions may be applied in a more timely fashion and glycemic conditions may be better controlled. 
     During a CGM operation, a wearable device is attached to a user and a biosensor of the wearable device is inserted subcutaneously. The biosensor is continuously operated in an environment surrounded by tissue and interstitial fluid and generates a signal that is indicative of the user&#39;s blood glucose concentration. This signal or the indication of the blood glucose concentration is transmitted to an external device, such as a reader, smart phone, or computer. 
     The wearable device receives power from an internal power source, such as a battery, which limits the lifespan of the wearable device. Thus, improved wearable devices are sought. 
     SUMMARY 
     In some embodiments, a base unit of a wearable device of a continuous analyte monitoring system is provided. The base unit includes a cup configured to receive a power source; a first power source contact at least partially located in the cup and configured to electrically contact a first terminal of the power source in response to the power source being received in the cup; and at least one base contact electrically coupled to the first power source contact, the at least one base contact configured to electrically contact at least one transmitter contact of a transmitter unit in response to the transmitter unit and the base unit being coupled together. 
     In some embodiments, a transmitter unit of a wearable device of a continuous analyte monitoring system is provided. The transmitter unit includes a recess configured to at least partially receive a battery in response to the transmitter unit and a base unit being coupled together, the battery supplying all power to the transmitter unit. 
     In some embodiments, a wearable device of a continuous analyte monitoring system is provided. The wearable device includes a base unit including: a cup; a power source received in the cup; a power source contact at least partially located in the cup and electrically contacting a terminal of the power source; and one or more one base contacts electrically coupled to the first power source contact. The wearable device also includes a transmitter unit including one or more transmitter contacts electrically contacting the one or more base contacts. 
     In some embodiments, a method of manufacturing a base unit of a wearable device of a continuous analyte monitoring system is provided. The method includes forming a cup configured to receive a power source; locating a power source contact at least partially in the cup, the power source contact configured to electrically contact a terminal of the power source in response to the power source being received in the cup; and electrically coupling at least one base contact with the power source contact, the at least one base contact configured to electrically contact at least one transmitter contact of a transmitter unit in response to the transmitter unit and the base unit being coupled together. 
     Other features, aspects, and advantages of embodiments in accordance with the present disclosure will become more fully apparent from the following detailed description, the claims, and the accompanying drawings by illustrating a number of example embodiments. Various embodiments in accordance with the present disclosure may also be capable of other and different applications, and its several details may be modified in various respects, all without departing from the scope of the claims and their equivalents. Accordingly, the drawings and descriptions are to be regarded as illustrative in nature, and not as restrictive. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings described below are for illustrative purposes and are not necessarily drawn to scale. The drawings are not intended to limit the scope of the disclosure in any way. Accordingly, the drawings are to be regarded as illustrative in nature, and not as restrictive. 
         FIG. 1  illustrates a continuous analyte monitoring system including a side elevation view of a wearable device and a front view of an external device in accordance with one or more embodiments. 
         FIG. 2A  illustrates a bottom isometric view of a transmitter unit of a wearable device of a continuous analyte monitoring system in accordance with one or more embodiments. 
         FIG. 2B  illustrates a top isometric view of a base unit of a wearable device of a continuous analyte monitoring system in accordance with one or more embodiments. 
         FIG. 2C  illustrates a top isometric view of a wearable device of a continuous analyte monitoring system with a transmitter unit and a base unit coupled together in accordance with one or more embodiments. 
         FIG. 2D  illustrates a top isometric view of a battery used in a wearable device of a continuous analyte monitoring system in accordance with one or more embodiments. 
         FIGS. 3A-3F  illustrate top isometric views of various stages of a method of manufacturing of a base unit of a wearable device of a continuous analyte monitoring system in accordance with one or more embodiments. 
         FIG. 4A  illustrates a schematic diagram showing power circuitry between a battery, a transmitter unit, and a base unit of a wearable device of a continuous analyte monitoring system according to one or more embodiments. 
         FIG. 4B  illustrates a schematic diagram showing another embodiment of power circuitry between a battery, a transmitter unit, and a base unit of a wearable device of a continuous analyte monitoring system according to one or more embodiments. 
         FIG. 5A  illustrates a bottom isometric view of a transmitter unit of a wearable device of a continuous analyte monitoring system including a contact configured to electrically contact a terminal of a battery according to one or more embodiments. 
         FIG. 5B  illustrates a top isometric view of a base unit of a wearable device of a continuous analyte monitoring system including a battery configured to electrically contact a contact in the transmitter unit of  FIG. 5A  according to one or more embodiments. 
         FIG. 5C  illustrates the base unit of  FIG. 5B  with the battery removed according to one or more embodiments. 
         FIG. 5D  illustrates a side elevation view of an embodiment of the transmitter unit of  FIG. 5A  according to one or more embodiments. 
         FIG. 6  illustrates a schematic diagram of an embodiment of circuitry of a transmitter unit and a base unit of a wearable device of a continuous analyte monitoring system according to one or more embodiments. 
         FIG. 7  illustrates a base unit of a wearable device of a continuous analyte monitoring system including a battery overmolded or otherwise encapsulated in a mold according to one or more embodiments. 
         FIG. 8A  illustrates top isometric view of a base unit of a wearable device of a continuous analyte monitoring system including a spring conductor configured to electrically contact a terminal of a battery and to retain the battery in the base unit according to one or more embodiments. 
         FIG. 8B  illustrates an enlarged top isometric view of an embodiment of the spring conductor of  FIG. 8A  according to one or more embodiments. 
         FIG. 9  illustrates top isometric view of a base unit of a wearable device of a continuous analyte monitoring system including a plurality of spring conductors configured to electrically contact a terminal of a battery and to retain the battery in the base unit according to one or more embodiments. 
         FIG. 10  is a flowchart showing of a method of manufacturing a base unit of a wearable device of a continuous analyte monitoring system according to one or more embodiments. 
         FIG. 11  is a flowchart showing of a method of using a wearable device a continuous analyte monitoring system according to one or more embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     In order to more closely monitor analyte concentrations (e.g., glucose concentration) in people and detect changes in such analyte concentrations, methods and apparatus for continuous analyte monitoring (e.g., continuous glucose monitoring (CGM)) have been developed. 
     Some CGM systems have a wearable portion (a “wearable device”) that is worn on the body and that can communicate (e.g., wirelessly) with an external device, such as a hand-held receiver (reader) or another portable device, such as a smart phone with a suitable application software program. The wearable device may be worn for several days or even several weeks before being removed and replaced. The wearable device includes a biosensor that measures analytes, such as glucose in subcutaneous fluid. In some embodiments, the biosensor may be inserted with the assistance of a trocar or other device (also referred to as an insertion portion) that is inserted along with the biosensor subcutaneously, and then removed leaving the biosensor implanted. The wearable device may include circuitry coupled to the biosensor and configured to electrically bias the biosensor and measure current signals generated by the implanted biosensor. The wearable device may also include processing circuitry that determines analyte (e.g., glucose) concentrations based on the measured current signals, as well as electronic transmitter circuitry for communicating analyte (e.g., glucose) concentrations to the external device. 
     The wearable device of a CGM system is generally worn for up to several weeks and then is removed and replaced with a new wearable device. Having to replace the wearable device of a CGM system every few weeks can significantly increase the cost of performing continuous analyte monitoring. In general, the biosensor may need to be replaced, but other wearable device components can be reused many times, or even indefinitely. However, one of the factors limiting the use of the other components is the lifespan of a power supply that powers the components. 
     The wearable devices disclosed herein include reusable transmitter units that may use replaceable base units. For example, one or more power sources may be located within a replaceable base unit that interfaces and supplies power to a reusable transmitter unit. Thus, the wearable devices are provided with a fresh power supply every time the base unit is replaced. The wearable devices, methods, and systems disclosed herein provide users with a truly reusable transmitter unit without requiring recharging of power sources. In addition, the wearable devices disclosed herein avoid any fire hazards that may be associated with rechargeable batteries. Using a fresh power source(s) every time a new base unit is coupled to a transmitter unit prevents long term interruptions with the wearable devices. For example, use of the wearable device is not interrupted during recharging periods. In addition to the above-described advantages, the wearable devices disclosed herein enable more flexible, space-optimized transmitter units that can have different advantages. For example, the space where a power source would otherwise be located can be utilized for additional components such as sensors, accelerometers, etc., and/or the overall size of the transmitter units can be made much smaller. 
     Both the base unit and transmitter unit of a wearable device may be powered by the one or more power sources located in the base unit. In some embodiments, the transmitter unit provides an entire top portion of the wearable device and the coupling of the transmitter unit and the base unit together may retain the power source in a predetermined fixed location. In some embodiments, one or more of the power sources is located within a pocket in the base unit wherein a conductor configured as a spring mechanism retains the power source within the pocket. In some embodiments, one or more conductors on the transmitter unit may directly connect to one or more terminals of one or more power sources when the transmitter unit and the base unit are coupled together. These and other embodiments and methods are disclosed herein with reference to  FIGS. 1-11 . 
     The description below is described primarily with regard to continuous glucose monitoring, however, the apparatus and methods described below may be readily adapted to monitoring other analytes, such as cholesterol, lactate, uric acid, alcohol, and other analytes, in other continuous analyte monitoring systems. 
     Reference is now made to  FIG. 1 , which illustrates a continuous analyte monitoring system  100  including a side elevation view of a wearable device  102  and a front view of an external device  104 . The wearable device  102  and the external device  104  may be in communication with each other, such as through wireless communication. The wearable device  102  includes a transmitter unit  106  and a base unit  108  that are physically and electrically coupled together. The transmitter unit  106  includes electronic components that enable communications, such as wireless communications, with the external device  104 . The transmitter unit  106  may include other electronic components as described herein. The base unit  108  includes a biosensor  110  that measures one or more analytes. In the embodiment of  FIG. 1 , the biosensor  110  is shown implanted in or below skin  111  of a user. The biosensor  110  may be implanted using a trocar or other insertion tool (not shown, also referred to as an insertion portion). In the embodiments described herein, the analyte is glucose, but the devices, apparatus, and methods may be configured to measure other analytes as described herein. As described in greater detail herein, the base unit  108  also includes a power source (not shown in  FIG. 1 ) that provides power to the base unit  108  and the transmitter unit  106 . 
     The external device  104  may receive and/or transmit data and/or instructions to and/or from the wearable device  102 . In some embodiments, the external device  104  may be a cellular telephone or other portable device. In other embodiments, the external device  104  may be a computer or a server. In some embodiments, the external device  104  may be located in a medical professional office or the like. The external device  104  may include a display  112  that displays information to a user, such as analyte concentrations (e.g., glucose concentrations). In addition, the external device  104  may include input devices  114 , such as buttons, that enable a user to input information into the external device  104 . In some embodiments, the external device  104  may process data generated by the wearable device  102  to calculate and/or display glucose concentrations. 
     Additional reference is now made to  FIGS. 2A-2C .  FIG. 2A  illustrates a bottom isometric view of an embodiment of the transmitter unit  106  of the wearable device  102  ( FIG. 2C ).  FIG. 2B  illustrates a top isometric view of an embodiment of the base unit  108  of the wearable device  102  ( FIG. 2C ).  FIG. 2C  illustrates a top isometric view of an embodiment of the wearable device  102  with the transmitter unit  106  and the base unit  108  coupled together and an inserter assembly  209  configured to engage the wearable device  102 . 
     The base unit  108  may include a baseplate  220  onto which components of the base unit  108  may be attached. In the embodiment of  FIGS. 2A-2C , the baseplate  220 , the base unit  108 , the transmitter unit  106 , and the wearable device  102  are round in plan view. The baseplate  220 , the base unit  108 , the transmitter unit  106 , and the wearable device  102  may have other shapes, such as rectangular or oval. An adhesive layer  222  may be attached to the underside of the wearable device  102  and serves to adhere or otherwise attach the wearable device  102  to a user. For example, the adhesive layer  222  may attach the wearable device  102  to skin of a user when the biosensor  110  is implanted subcutaneously. 
     The baseplate  220  may include a base retainer ring  224 A that is configured to mechanically couple to a transmitter retainer ring  224 B attached to the transmitter unit  106  so as to mechanically couple the base unit  108  and the transmitter unit  106  together. In the embodiment of  FIG. 2B , the base retainer ring  224 A may be circular and may be located proximate a perimeter of the baseplate  220 . The transmitter retainer ring  224 B may also be circular and may also be located proximate a perimeter of the transmitter unit  106 . Other devices and configurations of the base retainer ring  224 A and the transmitter retainer ring  224 B may be employed to mechanically couple the transmitter unit  106  and the base unit  108  together. The configuration of the base retainer ring  224 A and the transmitter retainer ring  224 B may also provide for decoupling of the transmitter unit  106  and the base unit  108  from each other. For example, the base unit  108  may be separated from the transmitter unit  106  and a new base unit may be coupled to the existing transmitter unit as described herein. 
     The base retainer ring  224 A may include a plurality of openings  226 A configured to receive a plurality of tabs  226 B located on the transmitter retainer ring  224 B. In some embodiments, the tabs  226 B may be located on the base retainer ring  224 A and the openings  226 A may be located on the transmitter retainer ring  224 B. In some embodiments, the baseplate  220 , the transmitter unit  106 , the base retainer ring  224 A, and/or the transmitter retainer ring  224 B may be flexible (e.g., deformable) to enable the tabs  226 B to be received in and withdrawn from the openings  226 A. For example, the tabs  226 B may be received in the openings  226 A by forcing the transmitter unit  106  and the base unit  108  together. In some embodiments, the tabs  226 B may be withdrawn from the openings  126 B by bending one or both of the transmitter unit  106  or the base unit  108 . 
     The base unit  108  may include a tube  228  extending from the baseplate  220 . The tube  228  may have an opening  228 A that passes through the baseplate  220  as described herein. The opening  228 A may be configured to receive and enable operation of an inserter (e.g., inserter assembly  209 — FIG. 2C ) that implants the biosensor  110  ( FIG. 1 ) subcutaneously. A portion of the biosensor  110  may pass through the side of the tube  228  so as to extend from the bottom of the baseplate  220 . The tube  228  may be configured to be received within an opening  230  in the transmitter unit  106  when the transmitter unit  106  and the base unit  108  are mechanically coupled together so as to form a single passageway through the wearable device  102 . Thus, the inserter may be operated from the top of the wearable device  102  via the opening  230  and the opening  228 A. The tube  228  may include a rim  228 B that may secure the base unit  108  to the transmitter unit  106  as described herein. 
     The transmitter unit  106  may include one or more transmitter contacts  244 A (a few labelled) configured to electrically contact base contacts  244 B (a few labelled) in the base unit  108 . The base contacts  244 B may at least partially encircle the tube  228 . The transmitter contacts  244 A may be mechanically biased toward the base unit  108  so that the transmitter contacts  244 A contact the base contacts  244 B in response to the base unit  108  and the transmitter unit  106  being coupled together. In some embodiments, the transmitter contacts  244 A may be spring-loaded so as to mechanically bias the transmitter contacts  244 A toward the base unit  108 . 
     The transmitter unit  106  may include transmitter circuitry (e.g., transmitter circuitry  456 ,  FIG. 4A ) encased or otherwise located in a structure  258 , such as a molded structure or other structure. In some embodiments, the structure  258  may be an overmold of the transmitter circuitry  456 . Example transmitter circuitry  456  may include an analog front end configured to electrically bias conductors and the like electrically coupled to the biosensor  110  ( FIG. 1 ) and to sense current passing through the biosensor  110 . The transmitter circuitry  456  may include operational amplifiers, current sources, current sensing circuitry, comparators, etc. Other transmitter circuitry  456  may include processing circuitry such as analog-to-digital converters for digitizing current signals, and memory for storing digitized current signals. The transmitter circuitry  456  may also include a controller such as a microprocessor, a microcontroller, or the like configured to compute analyte concentration levels based on measured current signals, and circuitry for transmitting analyte concentration levels to the external device  104  ( FIG. 1 ). 
     The transmitter unit  106  may also include a recess  260  configured to partially receive the battery  234 . The recess  260  may be formed in a portion of the structure  258 , for example. In other embodiments, the recess  260  may be formed from another structure (not shown). The recess  260  may hold the battery  234  in a predetermined location when the transmitter unit  106  and the base unit  108  are coupled together. The recess  260  may include a rim  260 A that at least partially surrounds the recess  260 . The rim  260 A contacts a side portion of the battery  234  when the transmitter unit  106  and the base unit  108  are coupled together to maintain the battery  234  in the fixed location. 
     The base unit  108  may include the battery  234  or other power source or may be configured to receive the battery  234  or other power source. The battery  234  or other power source may supply power to both the base unit  108  and the transmitter unit  106  when the base unit  108  and the transmitter unit  106  are coupled together. The base unit  108  is described herein as having the battery  234  received therein, however, the base unit  108  may have other power sources received therein. In some embodiments, the battery  234  is the sole source of power for the wearable device  102 . 
     Additional reference is made to  FIG. 2D , which is a top isometric view of an embodiment of the battery  234 . The battery  234  may include a conductive case, which may be the cathode terminal  234 C. A center portion of the top of the battery  234  includes the anode terminal  234 A. The cathode terminal  234 C and the anode terminal  234 A are separated by an insulator  2341 . The battery  234  shown in  FIG. 2B  is oriented with the anode terminal  234 A facing the baseplate  220  and is out of view. In other embodiments, the anode terminal  234 A may face away from the baseplate  120  and may contact a component on the transmitter unit  106  as described herein. Examples of the battery  234  include flexible lithium polymer batteries, coin cell batteries such as lithium manganese, silver oxide, and alkaline coin batteries (e.g., CR 2032, SR516, and LR60 type coin batteries), or the like. Other power sources and/or battery types may be used. 
     As described herein, the base unit  108  may be sterilized with the battery  234  located therein, so the battery  234  may be configured to withstand (e.g., remain operational) when the base unit  108  is sterilized. In some embodiments, the base unit  108  is sterilized using electron beam sterilization (e.g., E-beam radiation or sterilization), so the battery  234  may be configured to remain functional after exposure to the E-beam radiation. In some embodiments, the electron beam sterilization level is up to 25 KGy. Other radiation levels may be used and the battery  234  may be configured to withstand these other radiation levels. As also described herein, the base unit  108  may have components applied (e.g., molded) thereto, so the battery  234  may be configured to withstand a molding environment. In some embodiments, the molding may expose the battery  234  to a temperature of up to 90° C. for one minute. Accordingly, the battery  134  may be configured to withstand a temperature of 90° C. for one minute. The molding may subject the battery  234  to other temperatures for other time periods. Accordingly, the battery  234  may be configured to withstand the other temperatures and time periods. 
     In the embodiment of  FIG. 2B , the base unit  108  may include a cup  238  that retains the battery  234  in the base unit  108 . The cup  238  may be affixed to the baseplate  220 . In some embodiments, the cup  238  may be formed by an overmold process performed after formation of the baseplate  220 , for example. In other embodiments, the cup  238  may be a component that is attached to the baseplate  220  as described herein. The cup  238  may include a rim  238 A that may secure the battery  234  and/or maintain the battery  234  in a fixed location. In some embodiments, the rim  238 A may encircle the cup  238 . In other embodiments, the rim  238 A may partially encircle the cup  238 . 
     The wearable device  102  illustrated in  FIG. 2C  shows an inserter assembly  209  configured to engage the wearable device. For example, the inserter assembly  209  may include a trocar  209 A that is configured to be received in the opening  230  to locate the biosensor  110  ( FIG. 1 ) subcutaneously. 
     Additional reference is made to  FIGS. 3A-3F , which illustrate various stages of the base unit  108  ( FIG. 2B ) during a process of manufacturing an embodiment of the base unit  108 . The process commences with forming the baseplate  220  as shown in  FIG. 3A , which is an isometric view of the baseplate  220 . The baseplate  220  may have a hole  330  extending there through. The hole  330  may be aligned with the opening  228 A ( FIG. 3B ) in the tube  228  when the base unit  108  ( FIG. 2B ) and the transmitter unit  106  ( FIG. 2A ) are coupled together. Accordingly, the hole  330  may be sized to receive an insertion tool (not shown) that inserts the biosensor  110  ( FIG. 1 ) subcutaneously. In some embodiments, the baseplate  220  may be disc-shaped. In some embodiments, the baseplate  220  may be formed from a plastic, such as, but not limited to, acrylonitrile butadiene styrene (ABS), polycarbonate, nylon, acetal, polyphthalamide (PPA), polysulfone, polyethersulfone, polyetheretherketone (PEEK), polypropylene, high-density polyethylene (HDPE), and low-density polyethelene (LDPE). Other suitable materials may be used in the baseplate  220 . 
     Additional reference is made to  FIG. 3B , which illustrates an isometric view of the baseplate  220  with a substrate  342  and the tube  228  attached thereto. In some embodiments, the substrate  342  may be a printed circuit board and may have electrical traces (not shown) located therein. As shown in  FIG. 3B , the substrate  342  may include a hole  342 A that is configured to receive the tube  228 . In some embodiments, the substrate  342  may not include the hole  342 A, but may have a shape that at least partially receives or accommodates the tube  228 . In some embodiments, the substrate  342  may be flexible so as to flex with the baseplate  220 . The flexibility may prevent the substrate  342  from being damaged as the base unit  108  is flexed to couple to and decouple from the transmitter unit  106 . 
     The substrate  342  may include the one or more base contacts  244 B configured to electrically contact the transmitter contacts  244 A ( FIG. 2A ) located in the transmitter unit  106 . As described in greater detail below, the base contacts  244 B may conduct current between the battery  234  and the transmitter unit  106  ( FIG. 2A ) by way of the electrical contact between the base contacts  244 B and the transmitter contacts  244 A. In the configuration of the substrate  342  shown in  FIGS. 3B-3E , the substrate  342  may include a first battery contact  346 A (e.g., a first power source contact) and a second battery contact  346 B (e.g., a second power source contact) that are configured to electrically contact terminals of the battery  234  ( FIG. 2D ). For example, the first battery contact  346 A may be configured to electrically contact the cathode terminal  234 C ( FIG. 2D ) of the battery  234  and the second battery contact  346 B may be configured to electrically contact the anode terminal  234 A ( FIG. 2D ) of the battery  234 . The heights of the first battery contact  346 A and the second battery contact  346 B may be different to accommodate different heights of the cathode terminal  234 C and the anode terminal  234 A. Other configurations of contacts between the terminals of the battery  234  and contacts within the wearable device  102  ( FIG. 2C ) are described herein. The coupling of the base unit  108  and the transmitter unit  106  may provide a force on the battery  234  that forces the battery  234  to at least one of the first battery contact  346 A or the second battery contact  346 B. 
     Additional reference is made to  FIG. 3C , which illustrates base circuitry  348  coupled to the substrate  342 . The portion of the base unit  108  shown in  FIG. 3C  may contain electrical connectors and the like that electrically couple the portion of the base unit  108  configured to be subcutaneously implanted to the base circuitry  348 . In some embodiments, the base circuitry  348  is electrically coupled to traces (not shown) or the like that electrically couple to the base contacts  244 B. In some embodiments, other components (not shown) may be electrically and mechanically coupled to the base circuitry  348  and electrically coupled to the base contacts  244 B. 
     Additional reference is made to  FIG. 3D , which shows the base unit  108  with the cup  238  attached to the substrate  342 . In some embodiments, the cup  238  may also be at least partially attached to the baseplate  220 . In the embodiment of  FIGS. 3D-3F , the cup  238  is configured to encircle the battery  234  when the battery  234  is received in the cup  238 . In some embodiments, the cup  238  may be formed by a molding process. In other embodiments, the cup  238  may be formed separate from the base unit  108  and attached to the substrate  342  and/or the baseplate  220 . In some embodiments, the cup  238  may be flexible or made of a flexible material and may be slightly smaller than the diameter of the battery  234 , so that the battery  234  fits snuggly within the cup  238 . For example, friction between the battery  234  and the rim  238 A may retain the battery  234  within the cup  238 . In other embodiments, the rim  238 A and/or the cup  238  may partially encircle the battery  234 . 
     Additional reference is made to  FIG. 3E , which shows the base unit  108  with the base retainer ring  224 A attached thereto. In some embodiments, the base retainer ring  224 A may be attached to the baseplate  220 . In some embodiments, the base retainer ring  224 A may be made of the same material as the baseplate  220  and the baseplate  220  may remain flexible even with the attachment of the base retainer ring  224 A. In some embodiments, the base retainer ring  224 A may be molded to the base unit  108 , such as molded to the baseplate  220 . In other embodiments, the base retainer ring  224 A may be fabricated separate from the other components of the base unit  108  and attached using and adhesive, for example. 
     Additional reference is made to  FIG. 3F , which shows an embodiment of the finished base unit  108 . In the embodiment of  FIG. 3F , a portion of the substrate  342  has been covered by a coating  350 . In some embodiments, the coating  350  may be a conformal coating or a mold compound. Other coating materials and processes may be used. The coating  350  may provide a liquid seal over the substrate  342  to protect the substrate  342 , the base circuitry  348 , and other components thereon from exposure to contaminants. In the embodiment of  FIG. 3F , the base contacts  244 B are not covered by the coating  350  so that the base contacts  244 B may electrically contact the transmitter contacts  244 A ( FIG. 2A ) in response to the base unit  108  and the transmitter unit  106  being coupled together. 
     The completed base unit  108  may be packaged for market and then sterilized. For example, the base unit  108  may be packaged in a sealed package that ultimately may be sent to a user of the base unit  108 . In some embodiments, the package may be hermetically sealed. Other methods of sealing the package may prevent contaminants, including biological material, from contacting the base unit  108 . Sterilization may include exposing the base unit  108 , while in the package, to radiation, such as e-beam sterilization. As described herein, the battery  234  may be rad-hard, so it is not damaged and remains functional when exposed to the radiation. In some embodiments, gamma ray, E-beam sterilization, or another sterilization method may be employed to sterilize the base unit  108 . In some embodiments, the E-beam sterilization is applied at a level of 25 KGy and the battery  234  is configured to withstand this radiation. 
     Reference is made to  FIGS. 2A-2C  to describe coupling the transmitter unit  106  and the base unit  108  together. In the embodiment of  FIG. 2B , the base unit  108  is complete and includes the battery  234  or other power source that provides power to both the transmitter unit  106  and the base unit  108 . The transmitter unit  106  and the base unit  108  may have orientation features that only enable coupling of the transmitter unit  106  and the base unit  108  when the transmitter unit  106  and the base unit  108  are properly aligned. In some embodiments, the openings  226 A and the tabs  226 B are not evenly spaced, so the tabs  226 B will only engage the openings  226 A when the transmitter unit  106  and the base unit  108  are properly aligned. Other alignment devices may be used. 
     A user may mechanically couple the transmitter unit  106  and the base unit  108  together as described herein. For example, a user may press the transmitter unit  106  and the base unit  108  together, which forces the tabs  226 B of the transmitter retainer ring  224 B into the openings  226 A of the base retainer ring  224 A. In addition to the foregoing coupling, the rim  228 B of the tube  228  may engage with the opening  230 . In some embodiments, the engagement of the opening  230  with the rim  228 B may further secure and/or couple the transmitter unit  106  and the base unit  108  together. In some embodiments, the engagement of the rim  228 B with the opening  230  may enhance the rigidity of the wearable device  102 . For example, the tube  228  may prevent the wearable device  102  from crushing. During the coupling, the battery  234  (or other power source) may be received in the recess  260  and may abut against the rim  260 A to maintain the battery  234  in a fixed location. 
     In response to the mechanical coupling of the transmitter unit  106  and the base unit  108 , the battery  234  may provide power to the transmitter unit  106  and the base unit  108 . Reference is made to  FIG. 4A , which is a schematic diagram showing an embodiment of power circuitry between the battery  234 , the transmitter unit  106 , and the base unit  108 . In the embodiment of  FIG. 4A , the transmitter contacts  244 A have electrically contacted the base contacts  244 B in response to the transmitter unit  106  and the base unit  108  being coupled together. As described above, the transmitter contacts  244 A may be mechanically biased toward the base unit  108  or the base contacts  244 B when the transmitter unit  106  and the base unit  108  are coupled together to improve or make electrical coupling between the transmitter contacts  244 A and the base contacts  244 B. In other embodiments, the base contacts  244 B may be biased toward the transmitter contacts  244 A. 
     As described herein, the battery  234  may conduct power to the transmitter unit  106  and the base unit  108  in response to the coupling of the transmitter unit  106  and the base unit  108 . A first base contact  464 A may be electrically coupled to the cathode terminal  234 C of the battery  234  and may be electrically coupled to a first transmitter contact  466 A. The first transmitter contact  466 A may be electrically coupled to a second transmitter contact  466 B by a conductor within the transmitter unit  106 . The second transmitter contact  466 B may be electrically coupled to the transmitter circuitry  456  and a second base contact  464 B, which may be electrically coupled to the base circuitry  348  in the base unit  108 . 
     The anode of the battery  234  is coupled to the base circuitry  348  and a third base contact  464 C, which contacts a third transmitter contact  466 C. The third transmitter contact  466 C is electrically coupled to the transmitter circuitry  456 . As shown in  FIG. 4A , both the transmitter circuitry  456  and the base circuitry  348  receive power in response to the coupling of the transmitter unit  106  and the base unit  108 . In some embodiments, the transmitter unit  106  and the base unit  108  may include other contacts that conduct data and/or electrical signals between the transmitter unit  106  and the base unit  108 . In addition to the foregoing, the battery  234  is not electrically connected to any components unless the transmitter unit  106  and the base unit  108  are coupled together, which prevents drainage of the battery  234 . 
     Reference is now made to  FIG. 4B , which is a schematic diagram showing another embodiment of power circuitry within the wearable device  102 . In the embodiment of  FIG. 4B , the cathode terminal  234 C of the battery  234  is electrically coupled to the first base contact  464 A and the anode terminal  234 A of the battery  234  is electrically coupled to the second base contact  464 B. The first base contact  464 A contacts the first transmitter contact  466 A and the second base contact  464 B contacts the second transmitter contact  466 B in response to coupling of the transmitter unit  106  and the base unit  108 . As shown in  FIG. 4B , the first transmitter contact  466 A and the second transmitter contact  466 B are electrically coupled to the transmitter circuitry  456  and, thus, provide power from the battery  234  to the transmitter circuitry  456  in response to the coupling of the transmitter unit  106  and the base unit  108 . 
     The third transmitter contact  466 C contacts the third base contact  464 C and a fourth transmitter contact  466 D contacts a fourth base contact  464 D in response to the coupling of the transmitter unit  106  and the base unit  108  together. These contacts electrically couple the transmitter circuitry  456  with the base circuitry  348 . Thus, electric signals and/or voltages may be transmitted between the transmitter circuitry  456  and the base circuitry  348  in response to coupling of the transmitter unit  106  and the base unit  108  together. In addition, the battery  234  is not electrically coupled to any components unless the transmitter unit  106  and the base unit  108  are coupled together, which prevents drainage of the battery  234 . 
     Reference is now made to  FIGS. 5A-5D , which illustrate embodiments of the transmitter unit  106  and the base unit  108 , wherein one terminal of the battery  234  is configured to directly electrically contact a contact in the transmitter unit  106  in response to the transmitter unit  106  and the base unit  108  being coupled together. Referring to  FIG. 5A , the transmitter unit  106  may include a transmitter contact  544 T that electrically contacts a terminal of the battery  234  ( FIG. 5B ) in response to the transmitter unit  106  and the base unit  108  being coupled together. In the embodiment of  FIG. 5A , the transmitter contact  544 T is located in the recess  260  that is configured to retain the battery  234  in response to the transmitter unit  106  and the base unit  108  being coupled together. In some embodiments, the transmitter contact  544 T is a dome pad or the like extending from a circuit board  544  or the like. In some embodiments, the transmitter contact  544 T is biased toward the base unit  108  by a spring or similar device (not shown) that provides a sturdy electrical connection between the transmitter contact  544 T and the battery  234  in response to the transmitter unit  106  and the base unit  108  being coupled together. 
     The embodiment of the base unit  108  shown in  FIG. 5B  includes the battery  234  received in the cup  238 . In the embodiment of  FIG. 5B , the cathode terminal  234 C of the battery  234  faces the transmitter unit  106  and is configured to contact the transmitter contact  544 T in response to the transmitter unit  106  and the base unit  108  being coupled together. In other embodiments, the wearable device  102  may be configured so that the anode terminal  234 A of the battery  234  contacts the transmitter contact  544 T in response to the transmitter unit  106  and the base unit  108  being coupled together. 
       FIG. 5C  illustrates an embodiment of the base unit  108  with the battery removed. As shown in  FIG. 5C , the cup  238  may include a base contact  544 B that is configured to contact the anode terminal  234 A ( FIG. 2D ) or the cathode terminal  234 C of the battery  234  in response to the battery  234  being received in the cup  238  as shown in  FIG. 5B . In some embodiments, the cup  238  may include only a single base contact  544 B. 
       FIG. 5D  illustrates a side elevation view of the transmitter unit  106  with the transmitter retainer ring  224 B ( FIG. 5A ) removed. The transmitter unit  106  may include a plate  546 , which may be a substrate. The plate  546  has a surface  546 S which may face the base unit  108  when the transmitter unit  106  and the base unit  108  are coupled together. The view of  FIG. 5D  shows the transmitter contact  544 T being at least partially dome-shaped and extending from the surface  546 S of the plate  546 . The dome shape of the transmitter contact  544 T enables the transmitter contact  544 T to contact the battery  234  or other contact in the base unit  108 . As shown, the circuit board  544  is configured to conduct current between the battery  234  and the transmitter circuitry. 
     Additional reference is made to  FIG. 6 , which schematically illustrates an embodiment of circuitry of the wearable device shown in  FIGS. 5A-5D . In the schematic diagram of  FIG. 6 , the base unit  108  and the transmitter unit  106  are coupled together. As shown in  FIG. 6 , the transmitter contact  544 T electrically contacts the cathode terminal  234 C of the battery  234 . The embodiments of  FIGS. 5A-6  illustrate using one of the terminals of the battery  234  as a contact of the base unit  108 , which reduces the number of remaining contacts in the base unit  108 . In addition, the embodiments of  FIGS. 5A-6  do not permit any leakage from the battery  234  until the transmitter unit  106  and the base unit  108  are coupled together, which completes a circuit between the battery  234  and the transmitter unit  106 . 
     Additional reference is now made to  FIG. 7 , which illustrates an embodiment of the base unit  108  with the battery (not shown in  FIG. 7 ) overmolded or otherwise encased in a mold  770  (e.g., an encapsulant). In some embodiments, the mold  770  may be applied to the configuration of the base unit  108  shown in  FIG. 3F  wherein a portion of the battery  234  is exposed. In some embodiments, the entire baseplate  220 , except for the base contacts  244 B, is covered by the mold  770 . In other embodiments, the mold  770  may cover just the battery  234  ( FIG. 3F ) and/or locations proximate the battery  234 . For example, the mold  770  may cover the rim  238 A. In some embodiments, the mold  770  may secure the battery  234  into a specific location, such as the cup  238  ( FIG. 2B ), in the baseplate  220 . 
     In some embodiments, the mold  770  may be formed from a single layer or multiple layers. For example, the mold  770  may be formed from one or more layers of liquid silicone rubber (LSR), a thermoplastic elastomer (TPE), or the like. Other materials may be used such as, but not limited to, ABS, polycarbonate, nylon, acetal, PPA, polysulfone, polyethersulfone, PEEK, polypropylene, HDPE, LDPE, etc. Other materials may be used. In some embodiments, the mold  770  may be formed at a temperature of greater than 100° C. and in some embodiments the mold  770  may be formed at a temperature of greater than 80° C. The battery  234  may be configured to withstand the temperatures of the mold  770 . 
     Reference is made to  FIG. 8A , which illustrates an embodiment of the base unit  108  with a spring contact  868  configured to force the battery  234  ( FIG. 2D ) against the rim  238 A of the cup  238 .  FIG. 8B  illustrates an enlarged view of an embodiment the spring contact  868  of  FIG. 8A . The spring contact  868  may be made of a conductive material and flexible material, such as steel, that forces the battery  234  to the rim  238 A of the cup  238 . The spring contact  868  may include a base portion  868 A that may be affixed to a structure within the base unit  108  that conducts current from the battery  234 . The spring contact  868  may include one or more spring members that extend from the base portion  868 A and flex relative to the base portion  868 A so as to force the battery  234  to the rim  238 A of the cup  238 . In the embodiment of  FIGS. 8A and 8B , the spring contact  868  has a first spring member  868 B and a second spring member  868 C attached to the base portion  868 A. In use, the battery  234  is positioned into the cup  238 . The anode terminal  234 A electrically contacts with the second battery contact  346 B and the cathode terminal  234 C electrically contacts with the spring contact  868 . The spring contact  868  conducts current similar to the first battery contact  346 A ( FIG. 3B ) and/or the second battery contact  346 B ( FIG. 3B ). The battery  234  and/or other components of the base unit  108  may be overmolded to retain the battery  234  within the cup  238 . 
     Additional reference is made to  FIG. 9 , which illustrates an embodiment of the base unit  108  including a plurality of spring contacts  968  configured to contact at least one of the terminals of the battery  234  ( FIG. 2D ). In some embodiments, one or more of the spring contacts  968  may be identical or substantially similar to the spring contact  868  ( FIG. 8B ). In the embodiment of  FIG. 9 , the base unit  108  includes four spring contacts  968 . In other embodiments, the base unit  108  may include different numbers of spring contacts  968 . The spring contacts  968  may mechanically and electrically contact the cathode terminal  234 C ( FIG. 2D ) of the battery  234 . For example, the spring contacts  968  may contact the perimeter  234 P of the battery  234 , wherein friction between the spring contacts  968  and the perimeter  234 P retains the battery  234  in a fixed location in the base unit  108 . Accordingly, the plurality of spring contacts  968  may form a cup that retains the battery  234 . The fixed location maintains electrical contact between the anode terminal  234 A of the battery  234  and the first battery contact  346 A, which completes a circuit with the battery  234 . The recess  260  ( FIG. 5A ) in the transmitter unit  106  may further retain the battery  234  in the fixed location. 
     Referring to  FIGS. 2A-2C , both the transmitter unit  106  and the base unit  108  may be sealed units (e.g., waterproof), with only electrical contacts of the transmitter unit  106  and the base unit  108  exposed as described herein. Once the transmitter unit  106  and the base unit  108  are physically coupled together, the electrical contacts may also be sealed from the external environment, such as by the use of a sealing member (not shown). 
     Reference is now made to  FIG. 10 , which illustrates a flowchart showing a method  1000  of manufacturing a base unit (e.g., base unit  108 ) of a wearable device (e.g., wearable device  102 ) of a continuous analyte monitoring system (e.g., continuous analyte monitoring system  100 ). The method  1000  includes, in  1002 , forming a cup (e.g., cup  238 ) configured to receive a power source (e.g., battery  234 ). The method  1000  includes, in  1004 , locating a power source contact (e.g., first battery contact  346 A, second battery contact  346 B) at least partially in the cup, the power source contact configured to electrically contact a first terminal (e.g., anode terminal  234 A, cathode terminal  234 C) of the power source in response to the power source being received in the cup. The method  1000  includes, in  1006 , electrically coupling at least one base contact (e.g., base contacts  244 B) with the first power source contact, the at least one base contact configured to electrically contact at least one transmitter contact (e.g., transmitter contacts  244 A) of a transmitter unit (e.g., transmitter unit  106 ) in response to the transmitter unit and the base unit being coupled together. 
     Reference is made to  FIG. 11 , which illustrates a flowchart showing a method  1100  of using a wearing device (e.g., wearable device  102 ) of a continuous analyte monitoring system (e.g., continuous analyte monitoring system  100 ). The method  1100  includes, in  1102 , providing a base unit (e.g., base unit  108 ) comprising: a cup (e.g., cup  238 ); a power source (e.g., battery  234 ) received in the cup; a power source contact (e.g., first battery contact  346 A, second battery contact  346 B) at least partially located in the cup and electrically contacting a terminal (e.g., anode terminal  234 A, cathode terminal  234 C) of the power source; and one or more base contacts (e.g., base contacts  244 B) electrically coupled to the power source contact. The method  1100  includes, in  1104 , providing a transmitter unit (e.g., transmitter unit  106 ) comprising one or more transmitter contacts (e.g., transmitter contacts  244 A) electrically contacting the one or more base contacts. The method  1100  includes, in  1106 , coupling the base unit and the transmitter unit together, wherein the one or more transmitter contacts electrically contact the one or more base contacts in response to the base unit and the transmitter unit being coupled together. 
     The foregoing description discloses only example embodiments. Modifications of the above-disclosed apparatus and methods which fall within the scope of this disclosure will be readily apparent to those of ordinary skill in the art.