KEYWORDS: Sensors, Acoustics, Modulation, Data communications, Structural health monitoring, Sensor networks, Telecommunications, Wave propagation, Digital signal processing, Analog electronics
The recurrent monitoring of an aerial vehicle for structural damage detection and identification by acoustic sensors increases its reliability and remaining useful lifetime. In order to reach full structural health monitoring (SHM) autonomy, there is a need to combine sensing and communication functions into smart multifunctional sensors. Through this fusion, the information gathered by the SHM sensors could be transmitted in real time to a central processing unit without any human intervention. To that end, this research paper proposes reusing the existing network of acoustic SHM sensors mounted or embedded in the structure to enable acoustic multi-sensor wireless communication through the structure itself using elastic waves as the carrier signals. By doing so, the proposed acoustic communication system does not generate additional radio-frequency (RF) interference to other RF communication systems on board such as those used for vehicle control and safety-related services. This paper describes the design of the proposed acoustic wireless sensor network for autonomous SHM of aerial vehicles. First, the network topology and sensors placement are described along with the data routing algorithm. Then, the time-reversal based time division multiple access technique is introduced for multi-sensor communication using elastic waves. The data transmission across the elastic channel using time-reversal pulse position modulation is also presented. Finally, the system is evaluated based on the acoustic channel response of the horizontal stabilizer of an Ercoupe 415-C aircraft.
Autonomous structural health monitoring (SHM) of aerostructures strengthens the reliability, increases the lifetime, and reduces the maintenance cost of aerovehicles such as airplanes and unmanned aerial vehicles (UAV). The continuous monitoring of aerostructures for early damage detection and identification is made possible through a wireless network of sensors deployed on the structure. Usually, the data collected by these sensors is communicated to a central unit for real-time data processing using electromagnetic waves at radio frequencies (RF). However, the emission of RF signals for autonomous SHM creates additional sources of interference to on-board RF communication systems used for aircraft control and safety-related services. To overcome this issue, we propose in this paper an acoustic data communication system for autonomous health monitoring of aerostructures which are modeled as thin plate-like structures. In the proposed system, both damage detection and wireless communication are performed using guided elastic waves. Data communication across an elastic channel is challenging because of the severe frequency-dispersive and multimodal propagation in solid media which distorts, delays, and greatly attenuates the transmitted data signals. To cope with this problem, we introduce a sensor network based on time-reversal pulse position modulation that compensates for channel dispersion and improves the signal-to-noise ratio of the communication link without relying on sophisticated channel estimation algorithms. We demonstrate the viability of the presented system by conducting experiments on an homogeneous and isotropic aluminum plate specimen using Lead Zirconate Titanate (PZT) sensor discs at a resonant frequency of 300 kHz.
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