Patent Application
20060283266
The present invention relates generally to structural health monitoring. More specifically, the present invention relates to a single-wire sensor network for structural health monitoring.
The diagnostics and monitoring of structures, such as that carried out in the structural health monitoring field, are often accomplished by employing arrays of sensing elements and/or actuators. However, such arrays often suffer from certain drawbacks. For example, each sensor or actuator is often connected to multiple wires or electrical leads. Large arrays thus often employ an excessive number of wires, resulting in difficulty in installing and maintaining these arrays.
It is therefore desirable to develop sensor/actuator arrays that minimize the number of wires or electrical transmission lines employed. In this manner, sensor/actuator arrays can be made easier to install and use.
The invention can be implemented in numerous ways, including as a method, system, device, apparatus, or computer readable medium. Several embodiments of the invention are discussed below.
As a structural health monitoring system, one embodiment of the invention comprises a plurality of sensors configured to be spatially distributed along a structure and to transmit electrical signals upon detecting stress waves within the structure. Each sensor of the plurality of sensors is placed in electrical communication with each other sensor of the plurality of sensors.
As a further structural health monitoring system, another embodiment of the invention comprises a plurality of sensors electrically interconnected along a single electrical transmission line. The plurality of sensors is configured to be spatially distributed along a structure, and to transmit electrical signals along the electrical transmission line upon detecting stress waves within the structure.
Other aspects and advantages of the invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.
The invention, together with further objects and advantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying drawings in which:
Like reference numerals refer to corresponding parts throughout the drawings. Also, it is understood that the depictions in the figures are diagrammatic and not necessarily to scale.
In one embodiment of the invention, a sensor/actuator network is configured with a number of electrically-interconnected elements. More specifically, the sensors/actuators are each placed in electrical communication with the same transmission line. Various embodiments of such networks employ sensors/actuators connected in electrical series and in electrical parallel. Networks having these configurations, when placed upon a structure, are capable of detecting and/or transmitting stress waves within the structure so as to detect the presence of an impact, or actively query the structure. Advantageously, as these networks employ a single transmission line, they utilize fewer wires than current sensor/actuator networks, thus making them easier to install and maintain. They can also be configured as flexible layers, allowing for further ease of installation and maintenance.
Initially, it should be noted that the networks described herein can be configured both as networks of sensors and networks of actuators. Accordingly, for convenience, the sensor/actuator elements described herein are often simply referred to as sensors. However, the invention encompasses configurations in which actuators are employed instead of sensors. The invention also encompasses configurations employing transducers capable of acting as both sensors and actuators. One of skill will realize that various configurations of the invention can utilize any and all of these elements, and not just sensors.
The diagnostic layer 100 and its operation are further described in U.S. Pat. No. 6,370,964 to Chang et al., which is hereby incorporated by reference in its entirety and for all purposes. Various construction methods for forming the diagnostic layer 100 are explained in U.S. patent application Ser. No. 10/873,548, filed on Jun. 21, 2004, which is also incorporated by reference in its entirety and for all purposes. The sensors 102 can be sensors capable of receiving signals used in structural health monitoring such as stress waves. In certain embodiments, the flexible layer 100 is first coupled to a structure in a manner that allows the sensing elements 102 to detect quantities related to the health of the structure. For instance, the sensors 102 can be strain sensors configured to detect stress waves propagated within the structure, and emit electrical signals accordingly. In some embodiments, the sensors 102 can be known piezoelectric transducers capable of both reacting to a propagating stress wave by generating a voltage signal, and generating diagnostic stress waves upon application of a voltage to the transmission line 104. The invention encompasses other types of sensors 102 besides piezoelectric transducers, for example known fiber optic transducers. One of skill will realize that such alternate embodiments may also differ from the present discussion in other respects, while remaining within the scope of the invention. For example, the use of fiber optic transducers may employ an optical transmission line 104 instead of an electrical one. Analysis of these signals (electrical, optical, or otherwise) highlights properties of the stress wave, such as its magnitude, propagation speed, frequency components, and the like. Such properties are known to be useful in structural health monitoring.
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Many applications of the above-described sensor networks exist. For example, signals from networks of sensors 102 can be analyzed not only to determine the occurrence of an impact, but also to analyze and determine various characteristics of that impact. Such an analysis can often yield useful information, such as the dominant frequencies of the stress waves generated by the impact. This in turn can be useful in determining helpful information such as the type of body that impacted upon the structure.
In operation, the sensor network 202 is affixed to a structure, whereupon it generates electrical (or other) signals upon detecting an impact upon that structure. Attenuation circuitry 204 attenuates the amplitudes of these electrical signals, so as to prevent excessively high-amplitude signals (such as those generated by severe impacts) from damaging other components of the system 200. The attenuated signals are then filtered by the filtering elements 206-212 so as to isolate the signals in different frequency ranges. The amplitudes of the signals from different filters with different frequency ranges are compared by the analyzer 214, and the dominant frequency range is then identified. For instance, if a user of the system 200 is interested in detecting impacts from softer, more flexible bodies with dominant frequencies in the range of approximately 70-100 Hz, the filtering elements 206-212 can be band-pass filters configured to pass electrical signals in frequency ranges from approximately 10-40 Hz, 40-70 Hz, 70-100 Hz, 100-130 Hz, 130-160 Hz, and 160-190 Hz, respectively. By comparing the amplitudes of signals in these different frequency ranges, the analyzer 214 can identify whether the dominant frequency lies within the frequency range of interest, i.e., lies within the 70-100 Hz range. One of skill will realize that the filtering elements 206-212 need not be limited to this approach to characterizing impacts, but rather can utilize any high-pass, low-pass, band-pass, or other types of filters capable of isolating and analyzing frequencies of interest to the users of system 200.
Once the signals from the sensors 102 are appropriately attenuated and filtered (if necessary), the analyzer 214 analyzes the amplitudes of the signals to identify the remaining dominant frequencies. The presence of such frequencies can indicate an impact of interest, whereas the absence of such frequencies can indicate an impact that is of lesser concern. In this manner, “false alarm” impacts can be screened out, allowing users to be notified only of those impacts that are of concern.
The object protection system 306 is not limited by the invention, and can be any system configured to take actions in response to a “single-wire” type sensor network. By way of example, one such system 306 can be a pedestrian protection system. Elements of such systems are known, and include mechanisms such as actuators configured to open the hoods of automobiles so that pedestrians who are hit by a car are sent over its roof instead of suffering a potentially more damaging collision with its windshield.
As described above, the invention is not limited to the use of purely passive sensors. Instead, the invention discloses multiple sensors and/or actuators that are interconnected along the same circuit. In this manner, stress wave detected by any of the sensors 102 of a network will generate a voltage along the transmission line 104. This allows a single, relatively simple sensing system to detect impacts along many different areas of a structure. Conversely, the sensors 102 can instead be actuators. In this manner, a single electrical signal can be applied to the transmission line 104 so as to induce every actuator along the line 104 to generate stress waves. This allows a system to utilize a single signal to generate a distributed stress wave from multiple actuators.
As an extension of this concept, it should be noted that the invention includes the use of multiple such passive and active systems to both actively query a structure, and detect/process the resulting diagnostic stress waves. Returning to
The foregoing description, for purposes of explanation, used specific nomenclature to provide a thorough understanding of the invention. However, it will be apparent to one skilled in the art that the specific details are not required in order to practice the invention. Thus, the foregoing descriptions of specific embodiments of the present invention are presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations are possible in view of the above teachings. For example, the sensors 102 can be interconnected along the transmission line 104 in electrical series or in electrical parallel. Also, the invention is not limited to the interconnection of sensors 102, but rather includes the interconnection of passive sensors, active actuators, and/or multifunction transducers along the transmission line 104. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated.
