Patent Publication Number: US-2011074342-A1

Title: Wireless electricity for electronic devices

Description:
BACKGROUND 
     The present disclosure relates generally to generation of wireless electricity and, more particularly, to the powering of electronic devices by the wireless electricity. 
     This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art. 
     In the field of medicine, doctors often desire to monitor certain physiological characteristics of their patients. Accordingly, a wide variety of devices have been developed for monitoring many such physiological characteristics. Such devices provide doctors and other healthcare personnel with the information they need to provide the best possible healthcare for their patients. As a result, such monitoring devices have become an indispensable part of modern medicine. 
     One technique for monitoring certain physiological characteristics of a patient is commonly referred to as pulse oximetry, and the devices built based upon pulse oximetry techniques are commonly referred to as pulse oximeters. Pulse oximetry may be used to measure various blood flow characteristics, such as the blood-oxygen saturation of hemoglobin in arterial blood, the volume of individual blood pulsations supplying the tissue, and/or the rate of blood pulsations corresponding to each heartbeat of a patient. In fact, the “pulse” in pulse oximetry refers to the time varying amount of arterial blood in the tissue during each cardiac cycle. 
     Pulse oximeters typically utilize a non-invasive sensor that transmits light through a patient&#39;s tissue and that photoelectrically detects the absorption and/or scattering of the transmitted light in such tissue. One or more of the above physiological characteristics may then be calculated based upon the amount of light absorbed or scattered. More specifically, the light passed through the tissue is typically selected to be of one or more wavelengths that may be absorbed or scattered by the blood in an amount correlative to the amount of the blood constituent present in the blood. The amount of light absorbed and/or scattered may then be used to estimate the amount of blood constituent in the tissue using various algorithms. 
     Because of the particular physiological parameters that pulse oximeters are capable of determining, the use of pulse oximeters has become important in places besides hospitals. Traditional pulse oximeters obtain power by plugging into a wall socket. However, wireless sensors have been developed for use in measuring physiological parameters of a patient. Powering of these devices may present a challenge as there are no wires connected to the sensor to provide power to the sensors. Accordingly, alternate powering methods may be necessitated. 
     Furthermore, pulse oximeters may be used to monitor and treat patients outside of a hospital setting, such as in developing nations where constant and regular sources of electricity may be difficult to obtain. This lack of a constant and regular source of electricity renders traditional plug-in pulse oximeters at a disadvantage. While pulse oximeters powered by replaceable batteries can overcome this problem, there still exists a problem that the batteries in such pulse oximeters need to be replaced frequently. When this occurs in situations where replacement batteries are not readily available, these pulse oximeters become similarly disadvantaged as the traditional plug-in pulse oximeters. 
     Additionally, other devices, such as medical implants, portable electronic devices (such as portable computers, media players, cellular phones, personal data organizers, and the like), and/or mobile gaming systems may also fail when power sources, such as batteries, die. As such, alternative powering methods would be advantageous. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Advantages of the disclosed techniques may become apparent upon reading the following detailed description and upon reference to the drawings in which: 
         FIG. 1  illustrates a perspective view of a wireless power system including an electronic device, such as a pulse oximeter, in accordance with an embodiment; 
         FIG. 2  illustrates a simplified block diagram of the pulse oximeter in  FIG. 1 , according to an embodiment; and 
         FIG. 3  illustrates a block diagram of the wireless power system of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS 
     One or more specific embodiments of the present techniques will be described below. In an effort to provide a concise description of these embodiments, not all features of an actual implementation are described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. 
     Present embodiments relate to a system and method for wirelessly powering electronic devices. The system may include a charging station, which may generate electromagnetic charging signals, and a device that may receive the generated electromagnetic charging signals and may utilize the electromagnetic charging signals to generate power to charge a power source, such as a rechargeable battery, in the device. Additionally, the device may include control circuitry that may transmit various signals to the charging station that activate and deactivate the charging station based on the charging requirements of the device. The devices may include, but are not limited to, pulse oximetry sensors, pulse oximetry monitors, portable pulse oximeters, medical implants, portable computers, portable phones, and/or portable gaming devices. Each of these devices may include circuitry for communication with the charging station as well as circuitry for reception and utilization of wireless energy. 
     Turning to  FIG. 1 , a perspective view of a medical device is illustrated in accordance with an embodiment. The medical device may be a pulse oximeter  100 . The pulse oximeter  100  may include a monitor  102 , such as those available from Nellcor Puritan Bennett LLC. The monitor  102  may be configured to display calculated parameters on a display  104 . As illustrated in  FIG. 1 , the display  104  may be integrated into the monitor  102 . However, the monitor  102  may be configured to provide data via a port to a display (not shown) that is not integrated with the monitor  102 . The display  104  may be configured to display computed physiological data including, for example, an oxygen saturation percentage, a pulse rate, and/or a plethysmographic waveform  106 . As is known in the art, the oxygen saturation percentage may be a functional arterial hemoglobin oxygen saturation measurement in units of percentage SpO 2 , while the pulse rate may indicate a patient&#39;s pulse rate in beats per minute. The monitor  102  may also display information related to alarms, monitor settings, and/or signal quality via indicator lights  108 . 
     To facilitate user input, the monitor  102  may include a plurality of control inputs  110 . The control inputs  110  may include fixed function keys, programmable function keys, and soft keys. Specifically, the control inputs  110  may correspond to soft key icons in the display  104 . Pressing control inputs  110  associated with, or adjacent to, an icon in the display may select a corresponding option. The monitor  102  may also include a casing  111 . The casing  111  may aid in the protection of the internal elements of the monitor  102  from damage. 
     The monitor  102  may further include a transceiver  112 . The transceiver  112  may allow for wireless operation signals to be transmitted to and received from an external sensor  114 . In this manner, the monitor  102  and the sensor  114  may communicate wirelessly. The sensor  114  may be of a disposable or a non-disposable type. Furthermore, the sensor  114  may obtain readings from a patient that can be used by the monitor  102  to calculate certain physiological characteristics such as the blood-oxygen saturation of hemoglobin in arterial blood, the volume of individual blood pulsations supplying the tissue, and/or the rate of blood pulsations corresponding to each heartbeat of a patient. As will be discussed in greater detail below, the monitor  102  and the sensor  114  may each include a charging device  113  and  115 , respectively, for reception of wireless energy and charging of a power source in each of the monitor  102  and the sensor  114 . 
     For example, the pulse oximeter  100  may receive electromagnetic charging signals  103 A (to monitor  102 ) and  103 B (to sensor  114 ) from a charging station  105 , as well as communicate wirelessly  107 A and  107 B (from monitor  102  and sensor  114 , respectively) with the charging station  105 . The charging station  105  may be, for example, a power adapter inclusive of one or more inductors, tuned coils, or a radio frequency transmitter. The wireless communication  107 A-B that may take place between the pulse oximeter  100  and the charging station  105  may include a handshake recognition function whereby the charging control circuits ( 158  and  162  of  FIG. 2 ) of the monitor  102  and sensor  114  may each transmit an identification signal to the charging station  105 . This identification signal may, for example, be a radio-frequency identification (RFID) that identifies each element of the pulse oximeter  100  as a device for use with the charging station  105 . Until this identification signal is received, the charging station  105  may remain in an “off” state, i.e., not transmitting wireless electromagnetic charging signals  103 A-B. The charging station  105  may remain “off”, for example, to reduce overall power consumption until a compatible device is within the range of transmission. Thus, the handshake recognition function between either of the elements of the pulse oximeter  100  (i.e., the monitor  102  or the sensor  114 ) and the charging station  105  may operate to activate and deactivate the charging station  105 . 
     Once a proper identification signal is received, the charging station  105  may be placed into the “on” state. In the “on” state, the charging station  105  may generate and broadcast electromagnetic charging signals  103 A-B based on power received via prongs  109  from a power outlet. These prongs  109  may be affixed to the body of the charging station  105  or, alternatively, the prongs  109  may be connected to the charging station  105  via a power cord. Regardless, the prongs  109  may act to receive power from a power outlet for eventual generation of electromagnetic charging signals  103 A-B by the charging station  105  when requested by the any element of the pulse oximeter  100 , as described below with respect to  FIGS. 2 and 3 . 
     Turning to  FIG. 2 , a simplified block diagram of a pulse oximeter  100  is illustrated in accordance with an embodiment. Specifically, certain components of the sensor  114  and the monitor  102  are illustrated in  FIG. 2 . As previously noted, the sensor  114  may include a charging device  115 . The sensor  114  may also include an emitter  116 , a detector  118 , and an encoder  120 . It should be noted that the emitter  116  may be capable of emitting at least two wavelengths of light, e.g., RED and infrared (IR) light, into the tissue of a patient  117  to calculate the patient&#39;s  117  physiological characteristics, where the RED wavelength may be between about 600 nanometers (nm) and about 700 nm, and the IR wavelength may be between about 800 nm and about 1000 nm. 
     Alternative light sources may be used in other embodiments. For example, a single wide-spectrum light source may be used, and the detector  118  may be capable of detecting certain wavelengths of light. In another example, the detector  118  may detect a wide spectrum of wavelengths of light, and the monitor  102  may process only those wavelengths which are of interest for use in measuring, for example, water fractions, hematocrit, or other physiologic parameters of the patient  117 . It should be understood that, as used herein, the term “light” may refer to one or more of ultrasound, radio, microwave, millimeter wave, infrared, visible, ultraviolet, gamma ray or X-ray electromagnetic radiation, and may also include any wavelength within the radio, microwave, infrared, visible, ultraviolet, or X-ray spectra, and that any suitable wavelength of light may be appropriate for use with the present disclosure. 
     Additionally the sensor  114  may include an encoder  120 , which may contain information about the sensor  114 , such as what type of sensor it is (e.g., whether the sensor is intended for placement on a forehead or digit) and the wavelengths of light emitted by the emitter  116 . This information may allow the monitor  102  to select appropriate algorithms and/or calibration coefficients for calculating the patient&#39;s  117  physiological characteristics. Additionally, the encoder  120  may include information relating to the proper charging of the sensor  112 . The encoder  120  may, for instance, be a memory on which one or more of the following information may be stored for communication to the monitor  102 ; the type of the sensor  114 ; the wavelengths of light emitted by the emitter  116 ; and the proper calibration coefficients and/or algorithms to be used for calculating the patient&#39;s  117  physiological characteristics. The sensor  114  may be any suitable physiological sensor, such as those available from Nellcor Puritan Bennett LLC. 
     Signals from the detector  118  and the encoder  120  (if utilized) may be transmitted to the monitor  102  via a transmitter  122  that may be located in a transceiver  124 . The transceiver  124  may also include a receiver  126  that may be used to receive signals form the monitor  102 . As may be seen, the receiver  126  may transmit received signals to the emitter  116  for transmission to a patient  117 . The transmitter  122  may receive signals from both the detector  118  and the encoder  120  for transmission to the monitor  120 . As previously described, the signals used in conjunction with the emitter  116  and the detector  118  may be utilized for the monitoring of physiologic parameters of the patient  117  while the signals from the encoder may contain information about the sensor  114  to allow the monitor  102  to select appropriate algorithms and/or calibration coefficients for calculating the patient&#39;s  117  physiological characteristics. 
     As previously discussed, the monitor  102  may include a transceiver  112 . The transceiver  112  may include a receiver  128  and a transmitter  130 . The receiver  128  may receive transmitted signals from the transmitter  122  of the sensor  114  while the transmitter  130  of the monitor  102  may operate to transmit signals to the receiver  126  of the sensor  114 . In this manner, the sensor  114  may wirelessly communicate with the monitor  102  (i.e., the sensor  114  may be a wireless sensor  114 ). The monitor  102  may further include one or more processors  132  coupled to an internal bus  134 . Also connected to the bus may be a RAM memory  136  and the display  104 . A time processing unit (TPU)  138  may provide timing control signals to light drive circuitry  140 , which controls (e.g., via the transmitter  130 ), when the emitter  116  is activated, and if multiple light sources are used, the multiplexed timing for the different light sources. TPU  138  may also control the gating-in of signals from detector  118  through an amplifier  142  and a switching circuit  134 . The amplifier  142  may amplify, for example, the signals from the detector  118  received at the receiver  128 . The TPU  138  may control the gating-in of signals from detector  118  through an amplifier  142  to insure that the signals are sampled at the proper time, which may depend at least in part upon which of multiple light sources is activated, if multiple light sources are used. The received signal from the detector  118  may be passed through an (optional) amplifier  146 , a low pass filter  148 , and an analog-to-digital converter  150  for amplifying, filtering, and digitizing the electrical signals the from the sensor  114 . The digital data may then be stored in a queued serial module (QSM)  152 , for later downloading to RAM  136  as QSM  152  fills up. In an embodiment, there may be multiple parallel paths of separate amplifier, filter, and A/D converters for multiple light wavelengths or spectra received. 
     In an embodiment, based at least in part upon the received signals corresponding to the light received by detector  118 , processor  122  may calculate the oxygen saturation using various algorithms. These algorithms may use coefficients, which may be empirically determined, and may correspond to the wavelengths of light used. The algorithms may be stored in a ROM  154  and accessed and operated according to processor  122  instructions. The monitor  102  may also include a detector/decoder  155  that may receive signals (via the receiver  128 ) from the encoder  120 . The detector/decoder  155  may, for instance, decode the signals from the encoder  120  and may provide the decoded information to the processor  132 . The decoded signals may provide information to the processor such as the type of the sensor  114  and the wavelengths of light emitted by the emitter  116  so that proper calibration coefficients and/or algorithms to be used for calculating the patient&#39;s  117  physiological characteristics may be selected and utilized by the processor  132 . 
     The monitor  102  may also include a power source  156  that may be used to transmit power to the components located in the monitor  102 . In one embodiment, the power source  156  may be one or more batteries, such as a rechargeable battery. The battery may be user-removable or may be secured within the housing of the monitor  102 . Use of a battery may, for example, allow the oximeter  100  to be highly portable, thus allowing a user to carry and use the oximeter  100  in a variety of situations and locations. Additionally, the power source  156  may include AC power, such as provided by an electrical outlet, and the power source  156  may be connected to the AC power via a power adapter through a power cord (not shown). This power adapter may also be used to directly recharge one or more batteries of the power source  156  and/or to power the pulse oximeter  100 . In this manner, the power adapter may operate as a charging device  113 . 
     In another embodiment, the charging device  113  may alternately and/or additionally include a wireless charging apparatus that may include, for example, an inductor that wirelessly receives electromagnetic charging signals  103 A and generates electrical current as a result of the received electromagnetic charging signals  103 B. That is, a current may be electrically induced in the charging device  113  wirelessly. This current may be utilized to directly recharge one or more batteries of the power source  156  and/or to power the monitor  102 . Accordingly, the charging device  113  may allow for the pulse oximeter to be used in situations where a power outlet is unavailable near a patient  117 . 
     As may be seen in  FIG. 2 , the charging device  113  may be positioned lengthwise across the monitor  102 , so as to maximize the length of the charging device  113  to aid in increasing the distance at which the charging device  113  may receive and utilize electromagnetic charging signals  103 A. In one embodiment, the charging device  113  may be approximately 9 to 10 inches in length. Furthermore, the charging device  113  may be integrated into monitor  102 , or, alternatively, the charging device  113  may be affixed externally to the enclosure  111  of the pulse oximeter  100 . 
     The monitor  102  may also include a charging control circuit  158 , which may, for example, allow for the adaptive control of wireless energy received from the external charging station  105 . The charging control circuit  158  may, for example, include a processing circuit and a transmitter. In one embodiment, the processing circuit may include the processor  132 . In another embodiment, the processing circuit may be a separate processor from the processor  132 . Regardless, the processing circuit may determine the current level of charge remaining in the power source  156 , and may transmit a request, via the transmitter in the charging control circuit  158 , for a charging station  105  external to the oximeter  100  to transmit the wireless electromagnetic charging signals  103 A used by the charging device  113  to generate an electrical current for recharging of the power source  156 . 
     The charging control circuit  158  may also, for example, determine if the charging device  113  is unable to charge the power source  156 . That is, the charging station  105  fails to generate an electromagnetic charging signal  103 A for charging of the power source  156 , and may generate a corresponding error message for display on the monitor  102 . The error message may indicate to a user that the pulse oximeter  100  is low on power and may also direct the user to plug the pulse oximeter  100  into an outlet via the power adapter. This error message may be generated when the charging control circuit  158  determines that the power source  156  has reached a certain charge level, for example, 20% of the total charge remains in the power source  156 . The charging control circuit  158  may also perform a handshake recognition function with the charging station  105 . 
     The sensor  114  may also include both a power source  160  and a charging control circuit  162 , which may operate in a similar manner to the power source  156  and charging control circuit  158  described above. That is, the power source  160  may be used to transmit power to the components located in the sensor  114 . In one embodiment, the power source  160  may be one or more batteries, such as a rechargeable battery that may be user-removable or may be secured within the housing of the sensor  114 . The charging device  115  may include a wireless charging apparatus, for example, an inductor that wirelessly receives electromagnetic charging signals  103 B and generates electrical current as a result of the received electromagnetic charging signals  103 B. That is, a current may be electrically induced in the charging device  115  wirelessly. This current may be utilized to directly recharge one or more batteries of the power source  160  and/or to power the sensor  114 . 
     The sensor  114  may also include a charging control circuit  162 , which may, for example, allow for the adaptive control of wireless energy received from an external charging station  105 . The charging control circuit  162  may, for example, include a processing circuit and a transmitter for determining the current level of charge remaining in the power source  160 , and for transmitting a request, via the transmitter in the charging control circuit  162 , for a charging station  105  external to the sensor  114  to transmit wireless electromagnetic charging signals  103 B used by the charging device  115  to generate an electrical current for recharging of the power source  160 . 
     The charging control circuit  158  may also, for example, determine if the charging device  115  is unable to charge the power source  160 , for example, if a charging station  105  is failing to generate electromagnetic charging signals  103 B for charging of the power source  160 , the charging control circuit  162  may generate a signal to be transmitted by the transmitter  122  indicating that the sensor is not recharging properly. This signal may cause the processor  132  to generate a corresponding error message for display on the display  104  of the monitor  102 . The error message may indicate to a user that the recharging system of the sensor is potentially malfunctioning, and may direct the user, for example, to use replace the sensor  114 . This error message may be generated when the charging control circuit  162  determines that the power source  160  has fallen to a certain charge level, for example, to 20% of a total charge of the power source  160 . The charging control circuit  162  may also interface with a charging station  105  in a manner similar to the charging control circuit  158 , as will be described below with respect to  FIG. 3 . 
     The block diagram of  FIG. 3  illustrates the components of the charging station  105  and the sensor  114  that may combine to form a wireless inductive power system  164 . As illustrated, the sensor  114  may include a charging device  115 , a power source  160 , and a charging control circuit  162 . The charging station  105  may include an alternating current (AC) power converter  166 , a transmission control unit  168 , and a power transmitter  170 . The AC power converter  166  may represent the power that is received from a wall outlet, for example, via prongs  109 . This power may be ultimately be transmitted to the power transmitter  170  via the transmission control unit  168 . 
     The transmission control unit  168  may include a receiver and a processing unit. The receiver may receive an identification signal from the charging control circuit  162 , and may, as described above, enter an “on” state. Once in the “on” state, the processing unit of the transmission control unit  168 , which may be a processor, may await a power transmission request from the charging control circuit  162  of the sensor  114 . The charging control circuit  162  may, for example, monitor the charge level of the power source  160  and may transmit a power transmission request when the stored charge of the power source  160  reaches a certain threshold, for example, 40% of the total charge of the power source  160 . 
     Once both the identification signal and the power transmission request, i.e., the wireless communications  107 B, have been received by the transmission control unit  168 , the transmission control unit  168  may allow power to flow to the power transmitter  170 . The transmission control unit  168  may continue to allow power to flow to the power transmitter  170  until a halt power transmission signal is received from the charging control circuit  162 . The halt power transmission signal may be generated and transmitted by the charging control circuit  162  when, for example a threshold of charge level is met in the power source  160 . For example, this threshold may be approximately 95% of a full charge of the power source  160 . Once a halt signal is received, the charging control circuit  162  may operate to prevent the flow of power to the power transmitter  170 , thus ending the wireless power transmission to the sensor  114  until a power transmission request is received again. In this manner, the sensor  114  may control the charging of the power source  160  wirelessly. Various wireless powering techniques will be described below. 
     The power transmitter  170  and the charging device  115  may together form a transformer, that is, an energy transfer mechanism whereby electrical energy is transmitted from the power transmitter  170  to the charging device  115  through inductively coupled conductors. In one embodiment, the inductively coupled conductors may be solenoids, i.e., a metal coil, in each of the power transmitter  170  and the charging device  115 . Specifically, a change in current in the inductively coupled conductor of the power transmitter  170  induces a voltage in the conductor of the charging device  115  via generated electromagnetic charging signals  103 B. However, because charging signals  103 B may radiate in all directions, their intensity may drop off rapidly. Accordingly, the sensor  114  may only be able to be charged when it is at a distance approximately equal to the length of the charging device  115 , i.e. within a distance approximately equal to the length of the inductively coupled conductor of the charging device  115 . To increase this distance, resonant inductive coupling techniques may be utilized. 
     Resonant inductive coupling may aid in increasing the transmission distance of the electromagnetic charging signals  103 B through the use of at least one capacitor in conjunction with the inductively coupled conductor of the power transmitter  170  and/or the charging device  115 . For example, a capacitor and the inductively coupled conductor of the power transmitter  170  may form an LC circuit that may be “tuned” to transmit electromagnetic charging signals  103 B at a frequency that resonates with the natural resonance frequency of the inductively coupled conductor of the charging device  115 . That is, as electricity travels through the inductively coupled conductor of the charging device  115 , the conductor resonates as a product of the inductance of the conductor and the capacitance of the one or more capacitors. 
     In this manner, energy may be generated at a specified “tuned” frequency that allows for focused energy generation at a specific frequency. By generating energy at this specific frequency, instead of at a plurality of frequencies, the generated electromagnetic charging signal  103 B will be stronger, thus allowing for increased range of transmission. For example, by utilizing resonant inductive coupling techniques, the transmission range of the electromagnetic charging signals  103 B may increase to approximately 3 to 4 times the length of the inductively coupled conductor of the charging device  115 . This distance may allow for a single charging station  105  to be placed, for example, in a wall between two rooms in a hospital or clinic, such that a single charging station  105  might provide wireless power to monitors  102  and wireless sensors  114  in each room. This increase in range may also allow for greater ease in placement of an oximeter  100  near a patient  117  regardless of whether there is a power outlet near the patient  117 . 
     Other techniques for wireless electricity generation and utilization may, be applied in conjunction with the systems described above. For example, magnetic resonance techniques may be applied by the charging station  105  when in communication with, for example, a sensor  114 . Magnetic resonant electricity generation may include utilization of near field inductive coupling through magnetic fields, (i.e., magnetic field resonance), to generate wireless electricity. This may be accomplished through the use of two coils, whereby one is located in the power transmitter  170  and the other is located in the charging device  115 . Furthermore, one of the coils may be powered, for example, the coil in the power transmitter  170 , to generate magnetic resonance. Furthermore, the coils may be tuned, such that magnetic resonance in the powered coil results in a magnetic resonance being generated in the receiving coil (i.e., the coil in the charging device). This may lead to magnetically coupled resonance between the coils whereby the coils resonate at the same frequency to exchange energy efficiently. This exchange of energy may occur to wirelessly power, for example, the sensor  114 . 
     Another technique for the transmission of wireless energy in a wireless inductive power system  164  may include radio frequency (RF) energy transmission. The power transmitter  170  may include a transmitter. This transmitter may broadcast an RF signal at a chosen frequency. This transmission, for example, may travel across several feet of empty space (e.g., through the room of a patient  117 ) and may be received by a receiver, which may be included in the charging device  115 . This receiver in the sensor  114  may be an RF rectenna, that is, a RF rectifying antenna. An RF rectenna may be an antenna used to directly convert RF energy into DC electricity for charging of the power source. Elements of the RF rectenna may include a rectifier disposed between the dipoles of the antenna portion of the rectenna such that the rectifier rectifies the current induced in the antenna by the RF signals. In this manner, RF signals may be harvested and converted to electricity for charging the power source  160  of the sensor  114 . 
     In another embodiment, the monitor  102  may be physically and electrically coupled to the charging station  105  via, for example, a power cable. Accordingly, the transmission control unit  168  and the power transmitter  170  may be located in the monitor  102 , e.g., coupled to the charging device  113 . In this manner, the monitor  102  may be plugged into the wall to receive AC power and may transmit electricity wirelessly to the charging device  115  in the sensor  114 . Accordingly, because the monitor  102  may be in close proximity to the patient  117  (and subsequent sensors  114 ), the transmission distance and power requirements may be minimized. 
     It should be noted that while the wireless inductive power system  164  of  FIG. 3  was described in conjunction with a sensor  114 , other devices may be substituted for the sensor  114  in the wireless inductive power system  164 . For example, the charging station  105  may communicate with any number of electronic devices to negotiate the transmission of wireless electricity to the devices. These devices may include, but are not limited to, portable electronic devices, such as a laptop or notebook computers, portable gaming devices, viewable media players, cellular phones, personal data organizers, or the like. Similarly, the electronic devices that may communicate with the charging station  105  to receive wireless electricity may include medical implants, such as pacemakers, or portable pulse oximeters  100  that utilize wireless and/or cord connected sensors  114 . 
     In one embodiment, the charging station  105  may be portable, such that the charging station  105  may be moved closer to a device that will be charged. In the case of the portable charging station  105 , a power source, such as a rechargeable battery, may provide the power to transmit the wireless electricity via induction, magnetic resonance, or RF signals. For example, utilization of a portable charging station  105  may be advantageous for use with a patient  117  with a pacemaker implant. The charging station  105  may be placed on the chest of a patient  117  to insure that a pacemaker in the patient  117  is receiving wireless energy to recharge a power source in the pacemaker, in a manner consistent with that set forth above with respect to  FIGS. 1-3 . Alternatively, the charging station may be placed at a distance from the patient  117 , for example, anchored in a wall near the patient  117  such that the wireless energy may still reach the patient  117  and may adequately charge the power source in the medical implant. The use of wirelessly charging a device may be beneficial with respect to medical implants, as replacement of a power source, such as a battery, in the implanted medical device might otherwise require surgery on a patient  117  to replace a depleted power source. 
     While the disclosure may be susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and have been described in detail herein. However, it should be understood that the embodiments provided herein are not intended to be limited to the particular forms disclosed. Indeed, the disclosed embodiments may not only be applied to measurements of blood oxygen saturation, but these techniques may also be utilized for the measurement and/or analysis of other blood constituents. For example, using the same, different, or additional wavelengths, the present techniques may be utilized for the measurement and/or analysis of carboxyhemoglobin, met-hemoglobin, total hemoglobin, fractional hemoglobin, intravascular dyes, and/or water content. Rather, the various embodiments may cover all modifications, equivalents, and alternatives falling within the spirit and scope of the disclosure as defined by the following appended claims.