Abstract:
According to typical inventive practice, each inventive sensor node performs computer processing that is tri-chotomized in a progressive, power-regulating scheme of three processors, namely, a low-performance processor, a middle-performance processor (which remains in sleep mode until activated upon demand for a middle-computation function), and a high-performance processor (which remains in sleep mode until activated upon demand for a high-computation function). The low-performance processor performs low computation functions such as routine sensing functions. The middle-performance processor performs middle-computation functions such as validative sensing functions. The high-performance processor performs high computation functions such as remedial communicative functions. Each sensor node has one or more transceivers for wirelessly transmitting and receiving radio signals (e.g. remedial communication) to and from transceivers of other sensor nodes. Some transceivers may be specifically dedicated to wirelessly communicating “wake-up” signals among nodes. Inventive practice is notably efficacious in furtherance of situational awareness of damage events onboard naval ships.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. provisional application No. 61/388,480, filing date 30 Sep. 2010, hereby incorporated herein by reference, invention title “Power-Managing Energy-Harvesting Sensor Node for Situationally Aware Wireless Networking,” joint inventors Albert Ortiz, Donald D. Dalessandro, Qing Dong, and John K. Overby. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to wireless communications, more particularly to power management of sensor nodes of a wireless sensor network. 
     The United States Navy uses sensors (detectors) to maintain situational awareness in association with shipboard electromechanical systems such as machinery automation and control systems. Sensors useful for such purposes include position sensors, temperature sensors, chemical compound sensors, infrared (IR) sensors, image spectrum analyzers, etc. Networking of sensors has traditionally involved wiring—i.e., wired powering of sensors, and wired communication between sensors. Wireless networking of sensors is being considered and developed by the Navy because of beneficial prospects of distribution, decentralization, survivability, and reconfigurability as pertain to machinery automation and control for ship operations. 
     Power can be supplied to a sensor via conventional approaches such as wiring (e.g., shipboard wiring) from a power source (direct current or alternating current), or close association of a direct current power supply with (e.g., embedment of one or more batteries in) the sensor. Cumbersome, proliferative wiring is often undesirable or impractical. Direct current power sources such as batteries run out of power and require replacement or continual recharging. 
     It is known generally that energy can be harvested from ambient sources such as light (electromagnetism), sound, vibration, heat, etc. A solar cell, for instance, is a common type of energy harvester. Recent literature has disclosed management of power consumption in wireless systems, such as through energy (power) harvesting, and/or power reduction (e.g., “sleep mode”) under prescribed circumstances. Some energy harvesting technologies require communication devices to periodically sleep in duty cycles so that energy can be harvested and stored. Due to the variability of environmental energy sources for harvesting, energy harvesting technology may provide a very low duty cycle with an event-triggered interrupt function. See, e.g., the following United States patents: Townsend et al. U.S. Pat. No. 7,764,958 B2, Arms et al. U.S. Pat. No. 7,719,416 B2, Hamel et al. U.S. Pat. No. 7,429,805 B2, Cohen U.S. Pat. No. 7,400,253 B2, Arms et al. U.S. Pat. No. 7,256,505 B2, Hamel et al. U.S. Pat. No. 7,081,693 B2, incorporated herein by reference. See also, Ortiz et al., “Energy Harvester Power Management for Wireless Sensor Networks,” ASNE Proceedings, Automation and Controls Symposium, 10-11 Dec. 2007, Biloxi, Miss., incorporated herein by reference. 
     While energy harvesting appears to represent a piece of the puzzle, there is plenty of room for improvement for implementing energy harvesting in the context of a wireless sensor network so as to supply power to each sensor node in an economical, sustainable, and feasible manner. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, it is an object of the present invention to provide an improved methodology for managing power supplied to each sensor device in a wireless network of sensor. 
     The present invention, as typically embodied, provides a sensor unit that is autonomous in terms of functions including sensing, processing, and communicating (e.g., with other sensors), and in terms of powering of such functions. Inventive embodiments include sensing-communicating devices, systems of sensing-communicating devices, methods for sensing and communicating, computer programs products for performing such methods, and computer systems having such computer program products resident in memory. 
     The present invention may be embodied, for example, as an independent sensor for a survivable machinery automation and control system such as may be found onboard naval ships. A typical inventive embodiment is powered by an array of energy power harvesters and/or power storage devices, and effects a novel power management strategy to minimize power consumption during sensing, computation, and wireless communication. The inventive sensor is an integral device that harvests power, stores power, and judicially manages power consumption. An inventive sensor device can be embodied to synthesize an array of varied energy power harvesting sources so as to supply optimal low-power levels of required electrical power. 
     Energy can be harvested locally from vibration, light, acoustic, thermal, and/or other sources. All of the harvested energy can be combined utilizing an energy storage device for low duty-cycle sensor operation. A typical embodiment of the present invention&#39;s independent sensor can be used for machinery automation and control to perform the functions of sensing, computation, power management, and wireless communication as a self-powered unit, without reliance on external power supplied via cable/wires. The present invention provides (for instance, for machinery automation and control) a sensor that is “wireless” in the truest sense of the word. Inventive practice integrates low power hardware, energy harvesting and storage, and a power management scheme into a single independent sensing unit. That is, the present invention&#39;s power management methodology integrates elements including the following into a single independent sensing unit: low power sensing; low power radio frequency (RF) wireless transceiving; energy harvesting; energy storage; and, a power consumption management strategy, such as involving scheduling and event-driven activity. 
     Typically according to the inventive power management methodology, the computer processing is “tri-chotomized,” in a “stepped” regime, into computer processing components including the following: (i) a low-performance processor, for processing of routine sensing; if the low-performance processor&#39;s routine sensing detects an extraordinary circumstance), (ii) a middle-performance processor, for processing of “validative” sensing; and, if the middle-performance processor validates the extraordinary circumstance), (iii) a high-performance processor, for processing of high-computational functions such as wireless routing and information. 
     Among possible applications of the present invention are those affording capabilities of continuous sensing and situational awareness before, during and after a damage event, such as may take place onboard a naval ship. Of interest in this regard, and incorporated herein by reference, is U.S. provisional patent application Ser. No. 61/386,077, filing date 24 Sep. 2010, listed inventors Qing Dong, Albert Ortiz, Donald D. Dalessandro, and David J. Kocsik, invention title “Active-Avoidance-Based Routing in a Wireless Ad Hoc Network.” Dong et al. &#39;077 disclose a novel wireless routing algorithm that successfully routes communication when a destructive event takes place and is rapidly expanding in area, which are circumstances under which a conventional wireless routing algorithm will likely fail. 
     According to frequent practice of the present invention, prior to a damage event, the present invention&#39;s independent sensor unit provides routine sensory information to the undamaged ship machinery automation and control network. During and after the damage event, the present invention&#39;s independent sensor unit continues to provide sensing data (provided that the present invention&#39;s independent sensor unit is undamaged) in the main damage area, notwithstanding disruption or termination of power and communication. Using local harvested power, the present invention&#39;s independent sensor unit retains the ability, in the context of an ad hoc wireless network, to communicate to a different (e.g., the closest) operational node on the control network, thereby providing the important/necessary sensor information. 
     Of some interest herein is co-pending U.S. patent application Ser. No. 13/161,652, filing date 16 Jun. 2011, incorporated herein by reference, invention title “Wireless Electric Power Transmission Through Wall,” joint inventors Albert Ortiz, Donald D. Dalessandro, John M. Roach, Donald R. Longo, and Qing Dong. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order that the present invention may be clearly understood, it will now be described, by way of example, with reference to the accompanying drawings, wherein: 
         FIG. 1  is a schematic diagram of an embodiment of an independent, energy-harvesting, power-managing wireless sensor unit in accordance with the present invention. 
         FIG. 2  is a flow diagram of an embodiment of stepped tri-processing computer logic in accordance with the present invention. 
         FIG. 3  is a diagram illustrative of structural and functional aspects, such as shown in  FIG. 1  and  FIG. 2 , of typical practice of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the figures, the present invention&#39;s autonomous sensing unit  90  includes low-level computer  10  (which includes microprocessor  11  and memory  12 ), mid-level computer  20  (which includes microprocessor  21  and memory  22 ), high-level computer  30  (which includes microprocessor  31  and memory  32 ), one or more sensors  40 , a radio frequency (RF) transceiver  50  (which includes an RF receiver  51  and an RF transmitter  52 ), an energy/power storage device (such as a supercapacitor)  60 , “primary” energy/power harvester apparatus (such as an array of power harvesters)  70 , and “auxiliary” energy/power harvester apparatus  80 . 
     Depending on the inventive application, sensing devices  40  can measure any of a variety of physical parameters such as position, motion, temperature, chemical, infrared, image spectrum, etc. Parts/components/circuits of sensors  40  should be selected (such as CMOS ICs) to promote reduction of energy consumption. Radio frequency (RF) transceiver  50  for many inventive embodiments is preferably a low-power, short-transmit-range transceiver using a system-on-chip design. According to frequent inventive practice, RF transceiver  50  supports a software protocol that enables a wireless mesh network with ad hoc routing capability. Wireless ad hoc mesh networks support network reconfiguration in static, dynamic, or hybrid communication modes. 
     The machinery automation and control environment is replete with wasted/unused energy such as from thermal, vibration, and/or light sources. Primary energy harvester  70  and auxiliary energy harvester  80  can implement current energy harvesting technologies in order to power various elements of inventive sensor device  90 . It is a fundamental challenge for wireless sensor networks to supply each wireless sensor node with sufficient power without connecting to a wired power supply, and without introducing excessive battery or other maintenance requirements. According to typical inventive practice, an energy storage unit  60  (e.g., a capacitor, such as a supercapacitor) is needed. For some inventive embodiments, an advanced technology battery may be used as a power option in addition to or in lieu of energy harvesting and storage. 
     Inventive sensor node unit  90  is equipped with three processor/controller systems ordered in terms of increasing computational intelligence, viz., low-level computer  10 , mid-level computer  20 , and high-level computer  30 . Generally speaking, a higher performance processor consumes more power than a lower performance processor. 
     Low-level computer  10  performs routine sensing functions (referred to herein as “initial” sensing functions). Mid-level computer  20  performs sensing functions (referred to herein as “validative” sensing functions) that are somewhat more sophisticated than the initial sensing functions performed by low-level computer  10 . High-level computer  30  performs functions (referred to herein as “high computation” or “remedial action”), including communicative functions, that are significantly more sophisticated than the validative sensing functions performed by mid-level computer  20 . The present invention thus establishes a hierarchy of three computers, according to which the processing takes place in three stages. 
     The first stage involves routine sensory monitoring, presided over by low-level computer  10 . During the first-stage processing, the first-stage computer (viz., low-level computer  10 ) is in “active mode” (synonymously referred to herein as “active state”); meanwhile, the second-stage computer (viz., mid-level computer  20 ) and the third-stage computer (viz., high-level computer  30 ) each remain in “sleep mode” (synonymously referred to herein as “sleep state”). The first-stage computer (viz., low-level computer  10 ) processes signals received from sensor(s)  40  to determine whether any value has been measured that constitutes a threshold value triggering the second stage. Otherwise expressed, low-level computer  10  establishes values, or ranges of values, of “normal” versus “abnormal” data sent by sensor(s)  40 . 
     An abnormal sensory reading indicates a damage event or other exigent situation, such as a fire). For example, let us assume that a sensor  40  measures heat (temperature). Low-level computer  10  may have resident, in the non-volatile section of its memory  12 , a relatively simple algorithmic software that sets a threshold of at least 110° F. for commencing the second stage, that is, for activating mid-level computer  20 . Hence, if low-level computer  10  determines that a 110° F. or greater temperature has been measured by sensor  40 , low-level computer  10  awakens mid-level computer  20 , thus commencing the second stage. 
     The second stage involves validative sensory monitoring, presided over by mid-level computer  20 . During the second-stage processing, the third-stage computer (viz., high-level computer  30 ) remains in “sleep mode.” According to some inventive embodiments, low-level computer  10  remains in active mode during the second stage; however, according to other inventive embodiments, low-level computer  10  transforms from active mode to sleep mode at the beginning of the second stage, thereby joining high-level computer  30  in sleep mode. The return of low-level computer  10  to sleep mode may be prompted by either mid-level computer  20  or by low-level computer  10  itself. Mid-level computer  20  processes signals received from sensor(s)  40  to determine whether the determination by low-level computer  10  of an abnormal condition is valid. Validation by mid-level computer  20  can be performed in various ways, depending on the inventive embodiment. For instance, mid-level computer may repeat measurements taken by sensor(s)  40  over a period of time, in order to ensure that the measurement noted by low-level computer  10  is not an anomalous one. 
     Revisiting the example in which a sensor  40  measures thermal temperature, mid-level computer  20  may have resident, in the non-volatile section of its memory  22 , an algorithmic software (slightly more complicated than the algorithmic software resident in low-level computer  10 &#39;s memory  12 ) that prescribes a repetition of temperature measurements over a period of time, e.g., five seconds. If the abnormal temperature reading is sustained over that period of time, this suggests that the initial temperature abnormality determination, via the first stage, is valid. If the abnormal temperature reading returns to normal over that period of time, this suggests that the initial temperature abnormality determination, via the first stage, is invalid (anomalous), e.g., attributable to a transient/fleeting (and presumably harmless) temperature increase. If second-stage processing validates the abnormal condition, then the third stage is commenced, that is, high-level computer  30  is activated. 
     Thus, to begin the third stage, mid-level computer  20  awakens high-level computer  30 . Since the abnormal condition has been validated, high-computation functionality is demanded. The third stage is presided over by high-level computer  30 , and typically involves communication related to (e.g., responsive to) the previously validated abnormal condition. In the context of a wireless sensor network, high-level computer may determine what information to transmit, to whom to transmit the information, and how to route the wireless transmission of the information. For instance, continuing the example of an abnormally high temperature, high-level computer  30  may cause transceiver  50  to transmit communication as source node to another wireless sensor as destination node, such communication directing activation of a water sprinkler (e.g., via opening of a water sprinkler valve). 
     During the third-stage processing, various approaches may be taken in inventive practice as to whether either or both of low-level computer  10  and mid-level computer  20  remain in an active state. Depending on the inventive embodiment, at the beginning of the third stage, neither or either or both of low-level computer  10  and mid-level computer  20  may transform from active mode to sleep mode. For instance, high-level computer  30  may prompt the change from active state to sleep state in either or both of low-level computer  10  and mid-level computer  20 . Or, for instance, mid-level computer  20  may prompt its own change from active state to sleep state. 
     Inventive practice may provide for wireless communication (e.g., transmitting and receiving) of “wake-up” radio signals between different sensor nodes  90 , such as via transceivers  50  shown in  FIG. 1 . According to some inventive embodiments, a second RF transceiver is included in sensor node  90 , such as “over-the-air-interrupt transceiver”  55  shown in  FIG. 1 . The over-the-air-interrupt transceivers  55  are used for the specific purpose of wirelessly communicating “wake-up” signals between different sensor nodes  90 . Each over-the-air-interrupt transceiver  55  includes an RF receiver  56  and an RF transmitter  57 , preferably requires minimal power, and can either wirelessly transmit or wirelessly receive signals that awaken a device or device component from sleep mode. 
     The present invention&#39;s three-stage, three-processor strategy for sensing and communicating is particularly effective when availing itself of energy harvesting, thereby making complete the autonomous quality of an inventive wireless sensor  90 . Some inventive embodiments utilize exclusively a single energy harvester and storage of energy therefrom. Thus, as shown in  FIG. 1 , primary energy harvester  70  feeds power to power storage device  60 , which in turn provides power for each of inventive sensor node  90 &#39;s main elements, viz., low-level computer  10 , mid-level computer  20 , high-level computer  30 , sensors(s)  40 , and transceiver  50 . 
     As shown in  FIG. 1  by way of alternative, according to some inventive embodiments primary energy harvester  70  is supplemented by an auxiliary energy harvester  80 , under predetermined circumstances. For instance, in the afore-discussed example of an abnormally high temperature, the extreme heat that is generated by a fire may, paradoxically, be taken advantage of for providing a quick burst of energy by auxiliary energy harvester  80 , which harvests energy from the ambient heat generated by the fire. Auxiliary energy harvester  80  can feed energy storage device  60  so as to quickly and incrementally increase its energy supply, and which in turn can power third-stage functions including processing by high-level computer  30  and radio frequency communication by transceiver  50  (e.g., wireless transmission by transmitter  52 ). 
     The present invention, which is disclosed herein, is not to be limited by the embodiments described or illustrated herein, which are given by way of example and not of limitation. Other embodiments of the present invention will be apparent to those skilled in the art from consideration of the instant disclosure or from practice of the present invention. Various omissions, modifications, and changes to the principles disclosed herein may be made by one skilled in the art without departing from the true scope and spirit of the present invention, which is indicated by the following claims.