KEYWORDS: Ultrasonics, Transducers, Signal detection, Environmental sensing, Ferroelectric materials, Received signal strength, Waveguides, Signal processing, Temperature metrology, Receivers
The paper presents experimental results of applying an ultrasonic monitoring system to a real-world operating hot-water
supply system. The purpose of these experiments is to investigate the feasibility of continuous ultrasonic damage
detection on pipes with permanently mounted piezoelectric transducers under environmental and operational variations.
Ultrasonic guided wave is shown to be an efficient damage detector in laboratory experiments. However, environmental
and operational variations produce dramatic changes in those signals, and therefore a useful signal processing approach
must distinguish change caused by a scatterer from change caused by ongoing variations. We study pressurized pipe
segments (10-in diameter) in a working hot-water supply system that experiences ongoing variations in pressure,
temperature, and flow rate; the system is located in an environment that is mechanically and electrically noisy. We
conduct pitch-catch tests, with a duration of 10 ms, between transducers located roughly 12 diameters apart. We applied
different signal processing techniques to the collected data in order to investigate the ongoing environmental and
operational variations and the stationarity of the signal. We present our analysis of these signals and preliminary
detection results.
Monitoring the structural integrity of vast natural gas pipeline networks requires continuous and economical inspection
technology. Current approaches for inspecting buried pipelines require periodic excavation of sections of pipe to assess
only a couple of hundred meters at a time. These inspection systems for pipelines are temporary and expensive. We
propose to use guided-wave ultrasonics with Time Reversal techniques to develop an active sensing and continuous
monitoring system.
Pipe environments are complex due to the presence of multiple modes and high dispersion. These are treated as adverse
effects by most conventional ultrasonic techniques. However, Time Reversal takes advantage of the multi-modal and
dispersive behaviors to improve the spatial and temporal wave focusing. In this paper, Time Reversal process is
mathematically described and experimentally demonstrated through six laboratory experiments, providing
comprehensive and promising results on guided wave focusing in a pipe with/without welded joint, with/without internal
pressure, and detection of three defects: lateral, longitudinal and corrosion-like. The experimental results show that Time
Reversal can effectively compensate for multiple modes and dispersion in pipes, resulting in an enhanced signal-to-noise
ratio and effective damage detection ability. As a consequence, Time Reversal shows benefits in long-distance and lowpower
pipeline monitoring, as well as potential for applications in other infrastructures.
This paper develops a framework of a cognitive sensor networks system for structure defect monitoring and classification
using guided wave signals. Guided ultrasonic waves that can propagate long distances along civil structures have been
widely studied for inspection and detection of structure damage. Smart ultrasonic sensors arranged as a spatially distributed
cognitive sensor networks system can transmit and receive ultrasonic guided waves to interrogate structure defects such
as cracks and corrosion. A distinguishing characteristic of the cognitive sensor networks system is that it adaptively
probes and learns about the environment, which enables constant optimization in response to its changing understanding
of the defect response. In this paper, we develop a sequential multiple hypothesis testing scheme combined with adaptive
waveform transmission for defect monitoring and classification. The performance is verified using numerical simulations
of guided elastic wave propagation on a pipe model and by Monte Carlo simulations for computing the probability of
correct classification.
Feature-aided target verification is a challenging field of research, with the potential to yield significant increases in the
confidence of re-established target tracks after kinematic confusion events. Using appropriate control algorithms
airborne multi-mode radars can acquire a library of HRR (High Range Resolution) profiles for targets as they are
tracked. When a kinematic confusion event occurs, such as a vehicle dropping below MDV (Minimum Detectable
Velocity) for some period of time, or two target tracks crossing, it is necessary to utilize feature-aided tracking methods
to correctly associate post-confusion tracks with pre-confusion tracks. Many current HRR profile target recognition
methods focus on statistical characteristics of either individual profiles or sets of profiles taken over limited viewing
angles. These methods have not proven to be very effective when the pre- and post- confusion libraries do not overlap in
azimuth angle.
To address this issue we propose a new approach to target recognition from HRR profiles. We present an algorithm that
generates 2-D imagery of targets from the pre- and post-confusion libraries. These images are subsequently used as the
input to a target recognition/classifier process. Since, center-aligned HRR Profiles, while ideal for processing, are not
easily computed in field systems, as they require the airborne platform's center of rotation to line up with the geometric
center of the moving target (this is impossible when multiple targets are being tracked), our algorithm is designed to
work with HRR profiles that are aligned to the leading edge (the first detection above a threshold, commonly referred to
as Edge-Aligned HRR profiles).
Our simulated results demonstrate the effectiveness of this method for classifying target vehicles based on simulations
using both overlapping and non-overlapping HRR profile sets. The algorithm was tested on several test cases using an
input set of .28 m resolution XPATCH generated HRR profiles of 20 test vehicles (civilian and military) at various
elevation angles.
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