Motion energy harvesting with wireless sensors

A system and method for generating power when one or more motion sensitive structures are moved. The system may include one or more sensing components which, acting alone or in combination, are capable of generating data related to one or more physiological parameters. The system may also include wireless communication circuitry capable of wirelessly transmitting the data related to the one or more physiological parameters. Furthermore, at least one of the one or more sensing components or the wireless communication circuitry may be at least partially powered, directly or indirectly, by the one or more motion sensitive structures.

BACKGROUND

The present disclosure relates generally to medical devices and, more particularly, to sensors used for sensing physiological parameters of a patient.

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'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.

Wireless sensors have been developed for use in measuring physiological parameters of a patient. Powering of these devices may present a challenge as there may be no wires connected to the sensor available to provide power to the sensors. While internal power sources such as batteries may be utilized, problems may exist in which the internal power source is drained, yielding an undesirable operational lifetime. Accordingly, alternate powering methods may be useful.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

Present embodiments relate to a system and method for converting movement into power for powering electronic devices. The system may include one or more motion sensitive structures that, when moved, may generate electromagnetic charging signals. The system may further include one or more elements that may receive the generated electromagnetic charging signals and may utilize the electromagnetic charging signals to charge a power source, such as a rechargeable battery, of a device. Additionally and/or alternatively, the electromagnetic charging signals may be utilized to power the device directly. The device may include, but is not limited to, pulse oximetry sensors, pulse oximetry monitors, portable pulse oximeters, and/or medical implants. That is, the system may include a device with one or more sensing components which, acting alone or in combination, are capable of generating data related to one or more physiological parameters. The system may also include wireless communication circuitry capable of wirelessly transmitting the data related to the one or more physiological parameters. In one embodiment, at least one of the one or more sensing components or the wireless communication circuitry of the device may be at least partially powered, directly or indirectly, by energy harvested through movement by one or more of the motion sensitive structures.

Turning toFIG. 1, a perspective view of a medical device is illustrated in accordance with an embodiment. The medical device may be a pulse oximeter100. The pulse oximeter100may include a monitor102, such as those available from Nellcor Puritan Bennett LLC. The monitor102may be configured to display calculated parameters on a display104. As illustrated inFIG. 1, the display104may be integrated into the monitor102. However, the monitor102may be configured to provide data via a port to a display (not shown) that is not integrated with the monitor102. The display104may be configured to display computed physiological data including, for example, an oxygen saturation percentage, a pulse rate, and/or a plethysmographic waveform106. As is known in the art, the oxygen saturation percentage may be a functional arterial hemoglobin oxygen saturation measurement in units of percentage SpO2, while the pulse rate may indicate a patient's pulse rate in beats per minute. The monitor102may also display information related to alarms, monitor settings, and/or signal quality via indicator lights108.

To facilitate user input, the monitor102may include a plurality of control inputs110. The control inputs110may include fixed function keys, programmable function keys, and soft keys. Specifically, the control inputs110may correspond to soft key icons in the display104. Pressing control inputs110associated with, or adjacent to, an icon in the display may select a corresponding option. The monitor102may also include a casing111. The casing111may aid in the protection of the internal elements of the monitor102from damage.

The monitor102may further include a transceiver112. The transceiver112may allow for wireless operation signals to be transmitted to and received from an external sensor114. In this manner, the monitor102and the sensor114may communicate wirelessly. The sensor114may be of a disposable or a non-disposable type. Furthermore, the sensor114may obtain readings from a patient that can be used by the monitor102to 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 sensor114may include a charging device115, respectively, for harnessing of energy for use by the sensor114.

Turning toFIG. 2, a simplified block diagram of the pulse oximeter100is illustrated in accordance with an embodiment. Specifically, certain components of the sensor114and the monitor102are illustrated inFIG. 2. As previously noted, the sensor114may include a charging device115. The sensor114may also include an emitter116, a detector118, and an encoder120. It should be noted that the emitter116may be capable of emitting at least two wavelengths of light, e.g., RED and infrared (IR) light, into the tissue of a patient117to calculate the patient's117physiological 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 detector118may be capable of detecting certain wavelengths of light. In another example, the detector118may detect a wide spectrum of wavelengths of light, and the monitor102may process only those wavelengths which are of interest for use in measuring, for example, water fractions, hematocrit, or other physiologic parameters of the patient117. 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 sensor114may include an encoder120, which may contain information about the sensor114, 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 emitter116. This information may allow the monitor102to select appropriate algorithms and/or calibration coefficients for calculating the patient's117physiological characteristics. Additionally, the encoder120may include information relating to the proper charging of the sensor112. The encoder120may, for instance, be a memory on which one or more of the following information may be stored for communication to the monitor102; the type of the sensor114; the wavelengths of light emitted by the emitter116; the proper calibration coefficients and/or algorithms to be used for calculating the patient's117physiological characteristics; and/or information regarding a charging device for the sensor114. The sensor114may be any suitable physiological sensor, such as those available from Nellcor Puritan Bennett LLC.

Signals from the detector118and the encoder120(if utilized) may be transmitted to the monitor102via a transmitter122that may be located in a transceiver124. The transceiver124may also include a receiver126that may be used to receive signals form the monitor102. As may be seen, the receiver126may transmit received signals to the emitter116for transmission to a patient117. The transmitter122may receive signals from both the detector118and the encoder120for transmission to the monitor102. As previously described, the signals used in conjunction with the emitter116and the detector118may be utilized for the monitoring of physiologic parameters of the patient117while the signals from the encoder may contain information about the sensor114to allow the monitor102to select appropriate algorithms and/or calibration coefficients for calculating the patient's117physiological characteristics.

As previously discussed, the monitor102may include a transceiver112. The transceiver112may include a receiver128and a transmitter130. The receiver128may receive transmitted signals from the transmitter122of the sensor114while the transmitter130of the monitor102may operate to transmit signals to the receiver126of the sensor114. In this manner, the sensor114may wirelessly communicate with the monitor102(i.e., the sensor114may be a wireless sensor114). The monitor102may further include one or more processors132coupled to an internal bus134. Also connected to the bus may be a RAM memory136and the display104. A time processing unit (TPU)138may provide timing control signals to light drive circuitry140, which controls (e.g., via the transmitter130), when the emitter116is activated, and if multiple light sources are used, the multiplexed timing for the different light sources. TPU138may also control the gating-in of signals from detector118through an amplifier142and a switching circuit134. The amplifier142may amplify, for example, the signals from the detector118received at the receiver128. The TPU138may control the gating-in of signals from detector118through an amplifier142to 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 detector118may be passed through an (optional) amplifier146, a low pass filter148, and an analog-to-digital converter150for amplifying, filtering, and digitizing the electrical signals the from the sensor114. The digital data may then be stored in a queued serial module (QSM)152, for later downloading to RAM136as QSM152fills 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 detector118, processor122may 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 ROM154and accessed and operated according to processor122instructions. The monitor102may also include a detector/decoder155that may receive signals (via the receiver128) from the encoder120. The detector/decoder155may, for instance, decode the signals from the encoder120and may provide the decoded information to the processor132. The decoded signals may provide information to the processor such as the type of the sensor114and the wavelengths of light emitted by the emitter116so that proper calibration coefficients and/or algorithms to be used for calculating the patient's117physiological characteristics may be selected and utilized by the processor132.

The monitor102may also include a power source156that may be used to transmit power to the components located in the monitor102. In one embodiment, the power source156may 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 monitor102. Use of a battery may, for example, allow the oximeter100to be highly portable, thus allowing a user to carry and use the oximeter100in a variety of situations and locations. Additionally, the power source156may include AC power, such as provided by an electrical outlet, and the power source156may 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 source156and/or to power the pulse oximeter100. In this manner, the power adapter may operate as a charging device158.

The sensor114may also include a charging control circuit162, which may, for example, allow for the adaptive control of wireless energy harvested from the charging device115for use in the power source160of the sensor114. In one embodiment, the power source160may be one or more batteries, such as a rechargeable battery that may be user-removable or may be secured within the housing of the sensor114. Alternatively, the power source160may be one or more capacitors for storage of charge. The charging control circuit162may, for example, include a processing circuit that may determine the current level of charge remaining in the power source160, as well as the current amount of power being harvested by the charging device. For example, the charging control circuit162may determine if the charging device115is generating too little power to charge the power source160. In response to determining that the charging device115is generating too little power to charge the power source160and that the power source160is low on power, the charging control circuit162may generate an error signal that may be transmitted to the monitor102for generation of a corresponding error message for display on the display104of the monitor102by, for example, the processor132. The error message may indicate to a user that the sensor102is low on power and may also direct the user to take action, such as changing the power source160(i.e., installing new batteries), charging the power source160(i.e. by plugging the sensor102into a charging unit or into an electrical outlet via a power adapter). Alternatively, 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 replace the sensor114. In one embodiment, the error message may be generated when the charging control circuit162determines that the power source160has reached a certain charge level, for example 20% of the total charge remains in the power source160. Additionally, as described below in greater detail, the charging control circuit162may also include conversion translation circuitry, such as a rectifier circuit, for conversion of alternating current generated via the charging device115into direct current.

Furthermore, the charging device115may be one of a multitude of energy harvesting components that utilize, for example, inductive energy generation techniques and/or piezoelectric energy generation techniques. Through use of these techniques, power may be harvested, for example, through motion of a patient117, and utilized to directly recharge one or more batteries (or capacitors) of the power source160and/or to power the sensor114.FIG. 3illustrates a first embodiment of a charging device115.

The charging device115may include an energy harvester164that includes a case166, a magnet168, one or more buffers170, a coil172, and one or more leads174. It should be noted that one or more energy harvesters164may be utilized in conjunction with one another and that the energy harvester164may be sized to be imbedded in the sensor114or attached thereto. For example, the energy harvester164, as well as the components that make up the energy harvester164, may be, for example, microelectromechanical systems (MEMS) and/or nano electromechanical systems (NEMS) made up of components sized between 1 to 100 micrometers. However, the energy harvester164, as well as the components that make up the energy harvester164, may also be larger than MEMS and NEMS, as long as they may be integrated into or attached to a given sensor114.

Returning to the components of the energy harvester164, the case166may be composed of plastic or any other non-conducting material. The case166may enclose the magnet168and the buffers170. The case166may also be sized to allow lateral movement of magnet168. In one embodiment, the case166is cylindrical in shape. The magnet168may be sized to fit within the case166and move laterally within the case166. The magnet168may be a permanent magnet. The magnet168may be capable of sliding from one end of the case166to the other in response to an input of kinetic energy. In one embodiment, the kinetic energy may include patient117movement that causes the magnet168to move through the case166of the energy harvester164. The movement of the magnet168through the case166causes the magnet to pass through the coil172. The coil172may be made up of a conductive substance and may be wrapped around the case166. In one embodiment, the coil172may be made from coiled aluminum. In another embodiment, the coil172may be made from coiled copper wire. The copper wire may be covered by thin insulation.

As the magnet168passes through the coil172, electricity is generated via electromagnetic induction. This electricity may then be transmitted via the leads174to the charging control circuit162or directly to the power source160. In one embodiment, the generated electricity may be passed through a rectifier circuit, which may be located in, for example, the charging control circuit162, and may translate the alternating current generated via electromechanical induction into direct current. The rectifier circuit may, for example, be a full wave rectifier made up of, for example, diodes. The rectification of the electricity by the rectifier circuit may also include smoothing the output of the rectifier circuit. A filter, such as a reservoir capacitor, may be used to smooth the output of the rectifier circuit prior to its transmission to the power storage device160. Additionally, it should be noted that the leads174may include a single wire, two wires, or three wires (or other conductors) for allowing the leads174to conduct one, two, or three phase power.

The magnet168also may contact buffers170as it passes through the case166. The buffers170may be made of elastic material such as rubber. In another embodiment, the buffers170may be springs. The buffers170at to help conserve the kinetic energy being focused into the sliding magnet168by redirecting the magnet168back through the case166when the buffer170is contacted by the magnet168. In this manner, the buffers170aid in the conversion of kinetic energy into usable electricity.

Another embodiment for the charging device115is illustrated inFIG. 4. The charging device115may include an energy harvester176that includes a mass178that may be utilized to generate rotational torque. One or more energy harvesters176may be utilized in conjunction with one another and the energy harvester176may be sized to be imbedded in the sensor114or attached thereto as MEMS, NEMS, or as other systems.

In operation, the mass178in energy harvester176may be free to rotate circumferentially180in response to movements by the patient117. The mass178may be attached to a gear train182. As the mass178rotates circumferentially180, the gear train182may operate to transfer the rotational torque from the mass178to a permanent magnet184, causing circumferential180rotation of the magnet184. In one embodiment, the gear train182is set to create increased rotations of the magnet184relative to rotations of the mass178. The magnet184may be positioned adjacent to a coil186. The rotational motion of the magnet184induces an electrical current in the coil186which may be transmitted via conductive leads188to the charging control circuit162or directly to the power source160. As noted above, the current generated may pass through a rectifier circuit, a transformer, or a phase converter as, for example, part of the charging control circuit162. Accordingly, the energy harvester176may convert inputted kinetic energy, for example, movement by a patient117causing rotational movement of a mass178, into electricity useable by the pulse oximeter100.

An additional embodiment for the charging device115is illustrated inFIG. 5. The charging device115may include an energy harvester190that may convert vibratory motion along an axis192into electrical energy. One or more energy harvesters190may be utilized in conjunction with one another and the energy harvester190may be sized to be imbedded in the sensor114or attached thereto as MEMS, NEMS, or as other systems. The energy harvester190may be enclosed by, for example, four partitions194,196,198, and200. As may be seen, partitions194and196may be opposite paired partitions while partitions198and200may also be opposite paired partitions. The energy harvester190may further include one or more attachment devices, such as springs202, which may be utilized to suspend enclosure204from partitions198and200. The springs202may allow for reciprocating movement of the enclosure204relative to partitions194and196only along the axis192. This movement of the enclosure204may be in response to movement by the patient117.

Additionally, the enclosure204of the energy harvester190may include one or more magnets206attached thereto. Accordingly, the enclosure204, may allow for reciprocating movement of the magnets206relative to the partitions194and196. Indeed, one or more coils208may be attached to the partitions194and196such that the reciprocating movement of the magnets206inductively generates a current in the coils208. This induces current in coils208may be transmitted via conductive leads210to the charging control circuit162or directly to the power source160. As noted above, the current generated may pass through a rectifier circuit, a transformer, or a phase converter as, for example, part of the charging control circuit162. Accordingly, the energy harvester190may convert inputted kinetic energy, for example, movement by a patient117causing reciprocating movement of an enclosure204(and thus the magnets206attached thereto), into electricity useable by the pulse oximeter100.

FIGS. 6A and 6Billustrate an embodiment of the charging device115that makes use of a piezoelectric energy harvester212in a first and a second position, respectively. One or more piezoelectric energy harvesters212may be utilized in conjunction with one another and the piezoelectric energy harvester212may be sized to be imbedded in the sensor114or attached thereto as MEMS, NEMS, or as other systems.

FIGS. 6A and 6Billustrate a sensor114that may be utilized in conjunction with a finger214of a patient117. As may be seen, the emitter116and the detector118, as well as the transceiver124are illustrated as elements of the sensor114. As depicted, the emitter116and detector118may be arranged in a reflectance-type configuration in which the emitter116and detector118are typically placed on the same side of the sensor site. Reflectance type sensors may operate by emitting light into the tissue (e.g., finger214) and detecting the reflected light that is transmitted and scattered by the tissue. That is, reflectance type sensors detect light photons that are scattered back to the detector118. The sensor114may alternatively be configured as a transmittance type sensor whereby the emitter116and detector118are typically placed on differing sides of the sensor site. In this manner, the detector118may detect light that has passed through one side of a tissue site to an opposite side of the tissue site.

As illustrated in bothFIGS. 6A and 6B, the sensor114may also include a piezoelectric energy harvester212. The piezoelectric energy harvester212may, for example, include a piezoelectric wire216contacted at two ends by conductive materials, such as metal, and mounted on a flexible substrate. This piezoelectric wire216may be comprised of, for example, Zinc Oxide (ZnO), Arium titanate (BaTiO3), Lead titanate (PbTiO3), Lead zirconate titanate (commonly known as PZT), and/or potassium niobate (KNbO3). The piezoelectric wire216(as well as any piezoelectric material) has the ability to generate an electric potential in response to applied mechanical stress. Accordingly, piezoelectric wire216in the piezoelectric energy harvester212may operate to drive a current back and forth across the piezoelectric energy harvester212as the piezoelectric wire216is stretched, as may be seen inFIG. 6A, and compressed, as may be seen inFIG. 6B. This current may be transmitted to the charging control circuit162or directly to the power source160of the sensor114. As noted above, the current generated may pass through a rectifier circuit, a transformer, or a phase converter as, for example, part of the charging control circuit162. Accordingly, the piezoelectric energy harvester212may convert inputted kinetic energy, for example, movement by a patient117such as bending of a finger214, into electricity useable by the pulse oximeter100via the piezoelectric wire216.

FIG. 7illustrates an embodiment whereby the charging device115may be located externally from the sensor114. As illustrated, the charging device115may be attached to the sensor114via a lead218. The lead218may be an electrical conductor, such as a power cable, that transmits harvested power to the sensor114. The lead218may terminate with the charging device115which may be integrated into (or be attached to) a bracelet220. The bracelet220may be, for example, a medical bracelet. Furthermore, the lead218may be connected to and separated from the charging device115. That is, the lead218may be separable (i.e., releasable) from the charging device115, the bracelet220, and/or the sensor114. Alternatively, the lead218may be permanently affixed to the charging device115and/or the bracelet220. Regardless, by separating the charging device115from the sensor114, more available area in the bracelet220may be available for harvesting of energy via patient117movement. That is, with greater area available for the charging device115, a greater number of energy harvesters164,176,190, and/or212may be utilized, thus increasing the overall amount of energy that may be harvested.

FIG. 8illustrates a second embodiment whereby the charging device115may be located externally from the sensor114. As illustrated, the charging device115may be attached to the sensor114via a lead218. The lead218may be an electrical conductor, such as a power cable, that transmits power to the sensor114and may terminate with the charging device115which may be integrated into (or be attached to) a garment222. Again, the lead218may be separable (i.e., releasable) from the charging device115, the garment222, and/or the sensor114. The garment222may be, for example, a shirt or a sleeve of a shirt. The use of the a garment222to house the charging device115may allow for the charging device115to be expanded in size, or for more than one charging devices115to be utilized in conjunction, while still allowing for the garment222to be comfortably worn. Thus a greater number of energy harvesters164,176,190, and/or212may be utilized, which may increase the overall amount of energy that may be harvested. Additionally, by utilizing a large area, such as the garment222, movements of a patient117across a plurality of regions of the patient117may be utilized to harvest energy from. That is, movements in the chest, arms, etc. of the patient117may be translated into power for use by the sensor114. In this manner, a greater number of movements of a patient117may be harvested into power for use with the sensor114relative to energy harvesters164,176,190, and/or212located in the sensor114.

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.