Patent Application
20110009773
The present invention generally relates to electromechanical devices, such as micro-electromechanical systems (MEMS) and nano-electromechanical systems (NEMS). More particularly, this invention relates to implantable sensing modules capable of being implanted for the purpose of monitoring physical parameters of a living body and/or monitoring environmental parameters to which the body may be subjected, a particular but nonlimiting example of which is impacts sustained by the body.
Wireless sensor systems are known that have the capability for high reliability, efficiency, and performance. Such systems can be employed in a wide range of applications including supply-chain and logistics, industrial and structural monitoring, healthcare, homeland security, and defense. Generally, it is desired to minimize the power dissipation, size, and cost of these systems by making them low-power and/or operate without a battery. Furthermore, in many applications a batteryless operation is needed due to lack of battery replacement feasibility, or to meet stringent cost, form factor, and lifetime requirements. One approach to address this need is scavenging energy from environmental sources such as ambient heat, radio and magnetic waves, vibrations, and light. However, in many situations, these environmental energy sources are not adequately available to power a sensor. Another approach is to remotely power wireless sensor systems by inductive or electromagnetic coupling, storing energy on a suitable energy storage device, such as one or more integrated capacitors or miniature batteries, and performing sensor operations over short periods of time prior to minimize that discharge rate of the energy storage device.
Because of the size and complexity of many implantable sensing systems and the need for battery replacement to power the systems, individuals and the medical community have been reluctant to implant sensing systems into the human body. In addition, a living body will reject and encapsulate an implanted system in a matter of days, often interfering with their operation and, in the case of chemical sensors, rendering them impractical. However, there are many types of sensors that can monitor the body that do not require direct access to bodily fluids. For example, micro-electromechanical system (MEMS) and nano-electromechanical system (NEMS) sensors have been developed for incorporation into the body for continuous monitoring. These sensors include, but are not limited to temperature, acceleration (including impact or shock), vibration, impact, motion, and blood/capsule pressure sensing.
There are many health problems that could benefit from real-time temperature monitoring, including determining overheating/heat stroke and/or hypothermia in athletes and other individuals. The simplest form of temperature monitor is placed directly on the skin, though a drawback of this method is that the sensor will not provide an accurate indication of body temperature because skin temperature is influenced by environmental conditions such as weather conditions. To accurately indicate core body temperature, a temperature sensing device may be swallowed. However, such a device must be disposable for acceptance and therefore its cost must be very low. Furthermore, the sensed temperature can fluctuate depending on where the sensing device is in the digestive tract, and the sensor package must endure very harsh conditions of the digestive tract (highly acidic and highly basic). Finally, there is the possibility of injury to the individual in the event the sensor package should break.
Acceleration (including impact or shock) is another important parameter of interest in the healthcare industry. For example, impact monitoring can be used to indicate if an individual has suffered from head trauma, a child has been shaken, or an elderly person has fallen. However, existing impact sensing systems are not typically implanted because they were large, require major surgery, and can incur significant health risk to the individual. Existing systems also require batteries that must be changed on a fairly regular basis. In most situations, patients will not want to submit themselves to the risks of surgery if the system is only capable of operating for a few days. Consequently, currently available systems are typically limited to monitoring acceleration or impact on equipment worn by an individual, such as a helmet of the type used in hockey or American football. These systems are typically heavy, consume a significant amount of power, and are very expensive. Furthermore, the transfer function from motion of the helmet to motion of the head is different for every individual, and can depend on the fit of the helmet, tightness of the chin strap, how the helmet is worn, and many other factors varying from individual to individual.
The present invention provides implantable sensing modules and methods for monitoring various physical parameters, including physical parameters of a living body and environmental parameters to which the living body may be subjected, for example, impacts.
According to a first aspect of the invention, a method is provided for monitoring impacts to which a living body is subjected. The method entails the use of an implantable sensing module that comprises a rigid housing containing at least one energy storage device, at least one electromechanical sensing element that is responsive to impacts, means for generating outputs corresponding to impacts to which the electromechanical sensing element is subjected, and means for recording the outputs. The module is implanted in a living body so that the module is located internally within the living body and is connected to a rigid portion of the living body, in particular, a bone or tooth. Impacts to the living body are then monitored by monitoring levels of impacts to which the electromechanical sensing element is subjected within the living body. Outputs corresponding to the levels of the impacts sensed by the electromechanical sensing element are then produced, and the outputs stored in the recording means within the module. These outputs can then be wirelessly retrieved from the recording means while the module remains implanted in the living body.
In view of the above, it can be seen that an implantable sensing module according to the first aspect of the invention is capable of very accurately monitoring impacts to a body as a result of being directly attached to a rigid surface of the body of head impacts, thereby improving diagnosis and treatment methodologies. In a preferred but optional embodiment, the module is also configured to operate with minimal power so that power is available for system operation over longer periods of time. In a particularly preferred embodiment, the electromechanical sensing elements scavenge power from the body, providing a continuous monitoring capability over extended periods of time. The module is preferably configured to quickly and accurately record data, yet can also be small enough to be implanted using a needle or through a small incision.
According to a second aspect of the invention, a method is provided for monitoring at least one external input to a living body, in particular, a physical parameter of the body or an environmental parameter to which the body is subjected. The method entails the use of an electromechanical system module that comprises at least one integrated energy storage device and a plurality of integrated electromechanical switches. The electromechanical switches define open electrical paths and are operable to define closed electrical paths to produce outputs in response to the external input. Furthermore, the electromechanical switches have different levels of sensitivity to the external input. After implanting the module in a living body, the body may be subjected to the external input that causes two or more of the electromechanical switches to define at least two of the closed electrical paths in response to different input levels of the external input. The closed electrical paths produce at least two outputs corresponding to the different input levels of the external input. Finally, the outputs are obtained from the module.
In view of the above, it can be seen that an implantable sensing module according to the second aspect of the invention is well suited for implantation in a living body as a result of its size being minimized and its operation extended as a result of the electromechanical switches operating only during sensing events. As such, the implantable sensing module is capable of longer periods of operation compared to conventional implantable sensors that require continuous power from a battery, and is capable of a far greater level of functionality as compared to implantable sensors that do not have any internal energy storage capability. As with the module according to the first aspect of the invention, the module can be configured to quickly and accurately record data, yet can also be small enough to be implanted using a needle or through a small incision.
According to another aspect of the invention, an implantable sensing module is provided for monitoring impacts to which a living body is subjected. The module includes a housing and at least one energy storage device and at least one set of electromechanical sensing elements within the housing. The sensing elements are responsive to impacts, each defines an open electrical path when not subjected to an impact, and each is operable to define a closed electrical path that produces an output in response to an impact only while the sensing element is subject to the impact and if the impact exceeds a threshold of the sensing element. Each sensing element again defines the open electrical path thereof so as not to produce an output when no longer subject to the impact that exceeded its threshold. The housing further contains means for generating data corresponding to the outputs of the sensing elements, and means for recording the data. The sensing elements, generating means, and recording means are powered only by the energy storage device when, respectively, producing the output, generating the data, and recording the data in response to an impact that exceeded the threshold of one or more of the sensing elements.
Other objects and advantages of this invention will be better appreciated from the following detailed description.
The present invention provides miniature implantable sensing modules whose small size enables the modules to be placed into a living body, preferably to a bone, tooth or other rigid surface where it can monitor and generate data relating to an external input, such as physiological parameters of the body and/or environmental parameters to which the body may be subjected. The modules make use of an energy storage device and one or more electromechanical sensing elements. The modules also preferably make use of non-volatile memory to store the data and a wireless communication system that enables the data to be retrieved from the modules by an external reader. The components of the modules are preferably selected so that the modules require very little power for their operation, enabling the modules to remain implanted and operable for long periods of time, potentially on the order of years, without need for replacement.
As will be evident from the following description, a particular object of this invention is to extend the life of an implantable sensing module that employs an energy storage device, for example, a capacitor, battery or other suitable energy storage device. As will be discussed in more detail below, one such approach is to configure the electromechanical sensing elements to operate in response to the external input without drawing power from the energy storage device. Preferred electromechanical sensing elements are micro-electromechanical system (MEMS) and nano-electromechanical system (NEMS) sensing elements. As used herein, the terms MEMS and NEMS denote miniature devices generally on a scale of less than a millimeter and less than a micrometer, respectively, that incorporate both electronic and mechanical functionalities, and are produced by micromachining techniques, such as bulk etching and surface thin-film etching.
Wireless communication between the module 10 and the reader unit may be through a passive RFID communications protocol, though other wireless protocols are also foreseeable. RFID standard (ISO-15693) supports simultaneous data collection by a single reader unit from up to fifteen modules 10 having unique electronic ID codes. When a communications (e.g., interrogation) signal generated by a reader unit is received by the wireless communications block 20, the data stored in the memory 16 is accessed. The wireless communications block 20 can also be used to scavenge energy from the communications signal received from the reader unit and store the energy into the energy storage device (e.g., capacitor, battery, etc.) within the energy storage unit 18. The module 10 may also be electronically configurable through its wireless link to initialize the sensing elements 13 and their sensing ranges, designate the parameters that are to be recorded in the memory 16, and reset the sensing elements 13 and memory 16 as may be desired, for example, after data have been uploaded to the reader unit.
The overall the combination of small-size, light-weight, wireless data and command link, and electronic configurability enable the modules 10 and 30 to be useful for implantation into a living body, as well as embedding in various personnel and protective gear, sections of vehicles/equipment, etc. As noted above, in preferred embodiments of the modules 10 and 30, the memory 16 is able to store the data generated by the sensing elements 12/32 even if there is no external power supplied to the module 10 for extended periods of time. In this manner, the modules 10 and 30 are particularly well suited for implantation in the human body. In particular, the implantable wireless sensing modules of the type described in reference to
Various potential locations are possible for the implantation of the modules 10 and 30. For accurately monitoring head trauma, placement of the modules 10 and 30 is preferably by direct attachment to the skull to improve the correlation between the impact sensed by the sensing elements 13 and 33 and the actual impact to which the brain is subjected. By placing the modules 10 and 30 containing highly sensitive sensing elements 13 and 33 directly to the skull to monitor its movement, a more accurate picture of potential brain injury can be determined. The invention also encompasses the attachment of the modules 10 and 30 to other bones to more accurately monitor impacts to which they are subjected, as well as monitor activity to determine or assess a wide range of maladies. The modules 10 and 30 can be fabricated to be sufficiently small to permit implantation with a needle or a small incision.
Implantation or placement of the modules 10 and 30 on a tooth is also within the scope of the invention. Because teeth are rigidly attached to the skull, attachment of the modules 10 and 30 to a tooth can provide excellent correlation between movement, acceleration and impact sensed by the sensing elements 13 and 33 and impacts to which the brain is subjected to assess the risk of brain injury.
In each case, because the modules 10 and 30 are implanted beneath the skin, there is excellent compliance for monitoring patients, as well as excellent correlation to external inputs often of interest, for example, internal temperature, pressure, and bone movement.
The functionality and life of the modules 10 and 30 can be considerably enhanced by configuring the sensing elements 13 and 33 to be scalable. According to preferred aspects of the invention, scalability, functionality and power efficiency of the sensing elements 13 and 33 can be greatly enhanced by configuring the sensing elements as switches with direct digital outputs covering a wide dynamic range. By configuring the sensing elements 13 and 33 to directly respond to external inputs without the requirement for power to be supplied to the elements 13 and 33, an ultra-low power electromechanical sensing system is provided that is entirely event-driven. As such, preferred sensing elements 13 and 33 extract energy from the external input they are intended to sense (e.g., pressure pulses, acceleration (impact, shock, vibration, movement, etc.), temperature, chemical species, blood alcohol level, etc.) to provide a direct digital output. When used to sense movement and acceleration (including impact or shock), switches are also capable of providing the advantage of minimum latency and capturing the rising edge of a shock/impact impulse.
U.S. Pat. Nos. 7,495,368 and 7,619,346 and U.S. patent application Ser. No. 11/671,130 disclose electromechanical switches particularly suitable for sensing a wide variety of parameters, including pressure, acceleration, and temperature, that can be formed as scalable arrays. As disclosed by these prior patent documents, whose contents are incorporated herein by reference, arrays of electromechanical switches are operable to close a contact if an input parameter exceeds a designed threshold to produce a digital output signal that results from current flowing through the closed contacts from an energy storage device. This mode of operation provides an ultra-low power scheme that is capable of using as little as about 10−12 joules (pJ's) of energy from an energy storage device to produce a digital output signal for each event that results in the operation of a switch. The overall energy dissipation for an array of several thousand sensing elements (switches) is on the order of about 10−6 joules (μJ's), which is one hundred to one thousand times lower than state-of-the-art analog pressure or acceleration sensors coupled to analog-to-digital (ADC) circuits. Consequently, the power requirements of the modules 10 and 30 can be drastically reduced with the use of electromechanical switches, which in some cases can allow for the elimination of the need for a battery as the energy storage device, and allow for the use of capacitors and other relatively simple devices capable of storing energy. The use of electromechanical switches as the sensing elements 13 and 33 also enables the modules 10 and 30 to be operated to be fully event-triggered with standby current draws of less than 0.1 μA, and with fast wake-up and event capture response times on the order of a few micro-seconds.
In view of the above, a preferred aspect of the invention is that the arrays 12 and 32 of sensing elements 13 and 33 operate by extracting mechanical or thermal energy from the body in which the module 10 or 30 is implanted to close a contact, thereby closing a previously open electrical path, and produce a digital output signal through the resulting closed electrical path. This mode of sensing is capable of achieving considerable energy efficiency compared to conventional analog pressure, acceleration and temperature sensors. Another preferred aspect of the invention is that individual sensing elements 13 and 33 have different levels of sensitivity to the external input. For examples, the sensing elements 13 and 33 can be fabricated as switches that close at different threshold levels, such that different individual switches produce digital output signals in response to different input levels of the external input, with the result that the data stored in the memory 16 can be readily correlated to the overall level (amplitude) of the external input. The very small size to which the switches can be fabricated permits the integration of thousands of sensing elements 13 and 33 on a single chip measuring a few millimeters on a side using current NEMS and MEMS manufacturing processes, such that a wide range of amplitudes can be sensed.
The preferred operation for electromechanical switches for use as the sensing elements 13 and 33 in the present invention is to allow each individual switch to freely return to original open position after the level of the external input has dropped below the threshold level for the switch. In this manner, the duration that each switch is closed also provides a direct indication of the duration that the external input was above the threshold. As such, the controller 14 is able to process the outputs of all of the switches (elements 13 or 33) to not only generate data corresponding to the amplitude of an external input (for example, an impact), but also data corresponding to the duration of the external input. The controller 14 may also be operable to combine or integrate the amplitude and duration data according to a mathematical model, thereby reducing the amount of data that must be stored in the memory 16 and transmitted to a reader unit outside the module 10 or 30.
Exemplary but nonlimiting examples of MEMS and NEMS electromechanical switches capable of use with the present invention are represented in
In the embodiments of
The movable mechanical structures of
As a result of its multilayer bimorphic construction, the cantilevered beam 56 freely deflects with temperature change due to the CTE mismatch of the films 58 and 60.
Also similar to the temperature switch 36 of
As previously noted, the beams 56 and diaphragm 74 can be configured to deflect while subjected to the external input, thereby producing a digital output that is detected and processed by the controller 14 and stored in the memory 16, and then return to their non-deflected positions once the external input is absent. Alternatively, the beams 56 and diaphragm 74 or their respective contacts 62, 64, and 76 may be connected to the energy management unit 18 so as to be maintained at different electrical voltages. As a result, once contact is made, the voltage difference can result in a sufficiently large electrostatic force that keeps the beam 56 or 74 in a closed position with its contacts. As represented with the beam 56 in
By appropriately selecting the suspension beam, proof mass, and gap between the contacts, desired switching thresholds can be obtained for the switches 36 represented in
In view of the foregoing, it should be appreciated that the modules 10 and 30 can be produced using post-CMOS mass production MEMS technologies. To further reduce package size and external parasitic impedance, the micro- or nano-electromechanical (MEMS or NEMS) sensing elements 13 and 33 can be integrated directly on the integrated circuit chip on which the circuitry for the controller 14 is fabricated. The sensing elements 13 and 33 can be fabricated subsequent to forming the CMOS integrated circuits, and then integrated onto the surface of the CMOS chip, or fabricated and attached to the CMOS chip using techniques such as flip-chip bonding, wire-bonding or other methodologies known to those skilled in the art. Encapsulation of the circuits and sensing elements 13 and 33 may be achieved using any of a variety of techniques, but is not limited to solder bonding, gold eutectic bonding, fusion bonding, polymer bonding, or any other technique known to those skilled in the art. Wafer-level packaging of the modules 10 and 30 can be employed to reduce costs and seal the components of the modules 10 and 30 from the damaging effects of the body. By hermetically sealing the packaging, the modules 10 and 30 can be implanted for many years.
Power efficient digital signal processing enabled by the digital outputs of an array of switches can be employed to provide flexibility and programmability, in conjunction with extended features such as on-chip calculations capable of correlating the injury to the recorded parameters. While many sensing systems and research utilize peak impact to determine levels of head trauma, it has been determined that both amplitude of impact and duration are important for determining the level of head trauma. Models such as Head Injury Criterion (HIC), which is currently used to evaluate the efficacy of helmets, provide output based upon mathematical models that factor in both levels of impact and duration criteria. As previously discussed, the implantable modules 10 and 30 of this invention can have the capability of recording both amplitudes and durations of impacts, and the controller 14 can be used to combine and integrate amplitude and duration data based on the mathematical model employed to calculate HIC. As such, the data retrieved from the modules 10 and 30 can be directly employed to predict the likelihood or risk of injury resulting from one or more impacts suffered by an individual.
The modules 10 and 30 are also well suited for use in head trauma monitoring systems. Such a capability is of particular interest in view of investigations concerning the long term effects of multiple mild traumatic brain injuries (TBIs). Postmortem studies of the brains of American football players that have suffered from multiple concussions have shown that there is widespread damage throughout the brain. The brain tissue damage in autopsied brains appeared similar to tissue from patients suffering from Alzheimer's disease, even though many of the subjects were otherwise young and healthy. In these subjects, none of this damage appeared on MRI or CT scans, yet damage due to concussions can affect parts of the brain that effect emotion, rage, etc. and it has been found that the even mild TBI can kill brain cells and neural connections. Occurrence of mental disorders including major depression and attention deficit in people that have suffered from multiple concussions has been shown to be common. It is anticipated that early detection and treatment of head impacts would provide improved recovery from these injuries. For example, recent studies have shown that certain Alzheimer's disease medications can be helpful in reducing the damage caused by TBI if treated in a timely manner. Certain embodiments of the modules 10 and 30 of this invention are capable of monitoring head trauma to quickly and accurately determine level of trauma, which enables medical personnel to more accurately assessment of injury, improving treatment methodologies through early intervention.
From the foregoing, it will be appreciated that modules 10 and 30 with the low power dissipation capabilities described above can be adapted for use in a wide variety of applications that can be implemented with wired and wireless sensor modules, or used in conjunction with passive and active RFID tags for RFID-based sensors. Therefore, while the invention has been described in terms of particular embodiments, it is apparent that other forms could be adopted by one skilled in the art. For example, the physical configurations and uses of the modules 10, switches 36, etc., could differ from that shown and described, and materials and processes other than those noted could be use. Therefore, the scope of the invention is to be limited only by the following claims.
This application claims the benefit of U.S. Provisional Application No. 61/272,066, filed Aug. 13, 2009, and is a continuation-in-part patent application of co-pending U.S. patent application Ser. No. 11/671,130, filed Feb. 5, 2007, which claimed the benefit of U.S. Provisional Application No. 60/765,244, filed Feb. 4, 2006. The contents of these prior applications are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61272066 | Aug 2009 | US | |
| 60765244 | Feb 2006 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11671130 | Feb 2007 | US |
| Child | 12856011 | US |
