Abstract: Methods and apparatus for extracting the first arrival wave packet of an acoustic signal in a structural health monitoring (SHM) system include receiving an acoustic signal transmitted between two transducers thereof. Electromagnetic cross-talk is removed from the signal. Signal amplitude threshold values used for picking out the first arrival wave packet are chosen based on signal characteristics or chosen adaptively as the value that leads to the minimum variance of the group velocity estimates of all the actuation-sensing transducer pairs. The group velocity is estimated as the known actuator-sensor distance divided by the propagation time of the first wave packet of which the envelope exceeds a candidate threshold value. The first arrival wave packet is determined as the signal segment where the signal envelope first exceeds the chosen amplitude threshold and the segment length exceeds a specified threshold of time width.

Abstract: A method of improving damage detection in a structural health monitoring system includes obtaining a baseline set of signals corresponding to a range of values of an environmental effect variable for a plurality of first selected paths between pairs of a plurality of transducers configured in an array attached to a structure. Threshold levels are established for each of the selected paths for determining detection of damage in the structure based on differences in the baseline set of signals for the selected path. A current signal is acquired for each of the selected paths. The plurality of current signals are analyzed based on the threshold levels to detect damage in the structure.

Abstract: A method useful in structural health monitoring (SHM) systems for detecting damages in metal structures includes extracting the zero-order symmetric and anti-symmetric mode signal components from each of a plurality of current sensor signals of an array of transducers mounted on the structure, matching the extracted signal components with corresponding signal components of a plurality of baseline sensor signals previously detected in the structure, computing respective indices IS0 and IA0 for each of the matched extracted current and baseline signal components based on respective signal energies thereof, and determining the presence of a damage in the structure if either of the indices IS0 and IA0 of a plurality of neighboring sensor paths of the structure is greater than a selected threshold value.

Abstract: A method and system of compensating for environmental effect when detecting signals using a structural health monitoring system includes collecting baseline data signals for one or more values of the environmental effect variable from signals transmitted along selected paths between transducers in an array attached to the structure. A threshold is selected based on the baseline data for determining if the signal is detected. Current data signals are collected and matched to the best fit baseline data. The value of the environmental effect variable is determined on the basis of the matching. A signal is detected according to the selected threshold.

Abstract: A method for calculating the probable damage size in a structure includes defining a configuration of an array of transducers mounted on the structure. Any pair of the transducers includes an actuator and a sensor, and each pair defines a propagation path in the structure. All propagation paths that are affected by being touched by a damage of the structure, and all adjacent paths that are untouched and thereby unaffected by the damage, are identified. A range of sizes of the damage is determined, and a probability density of the damage versus damage size is calculated on the basis of the transducer array configuration and the affected and unaffected propagation paths identified. On the basis of the probability density, a most probable damage size is determined, and the probability of the damage being greater or less than the most probable damage size is also determined.

Abstract: Methods and apparatus for reducing crosstalk in a structural health monitoring system. A pair of actuator input signals are sent to an actuator, each resulting in the transmission of stress waves to a corresponding sensor. The sensor then converts these stress waves to a pair of output signals, each having a crosstalk portion due to electromagnetic interference from the input signals to the actuator, and a stress wave portion corresponding to the stress waves. Various methods of varying the actuator input signals, the input to the actuator, and the output of the sensor result in two output signals that can be combined so as to reduce the crosstalk portions and isolate the stress wave portions. This allows actuators and sensors to be placed sufficiently close together that the stress wave portions of sensor output signals can overlap their crosstalk, without corrupting or otherwise compromising the data contained therein.

Abstract: Methods and apparatus for extracting the first arrival wave packet of an acoustic signal in a structural health monitoring (SHM) system include receiving an acoustic signal transmitted between two transducers thereof. Electromagnetic cross-talk is removed from the signal. Signal amplitude threshold values used for picking out the first arrival wave packet are chosen based on signal characteristics or chosen adaptively as the value that leads to the minimum variance of the group velocity estimates of all the actuation-sensing transducer pairs. The group velocity is estimated as the known actuator-sensor distance divided by the propagation time of the first wave packet of which the envelope exceeds a candidate threshold value. The first arrival wave packet is determined as the signal segment where the signal envelope first exceeds the chosen amplitude threshold and the segment length exceeds a specified threshold of time width.

Abstract: A method for both detecting and analyzing a change in the loading condition of a structure. A flexible substrate is employed, in which a distributed network of sensors is built. This substrate is either affixed to the surface of the structure, or built within it, so as to be able to detect propagating stress waves. After load change is detected, the resulting sensor signals are analyzed to determine the location, severity, and/or any characteristic frequencies of the load change. This information is then used to determine an appropriate response.

Abstract: Methods of manufacturing a diagnostic layer containing an array of sensing elements. The sensing elements, associated wires, and any accompanying circuit elements, are incorporated various layers of a thin, flexible substrate. This substrate can then be affixed to a structure so that the array of sensing elements can analyze the structure in accordance with structural health monitoring techniques. The substrate can also be designed to be incorporated into the body of the structure itself, such as in the case of composite structures.

Abstract: Use of a single line for switching multiple monitoring elements on/off, and a single line for sending signals to, or receiving signals from, those elements that are switched on. Monitoring elements each have an associated switching element, and each switching element is connected to a common switching line, or control line. A signal from the control line turns each switch on or off. Each monitoring element is also connected to a single signal line, and only those monitoring elements that are turned on can transmit/receive data signals along this signal line.

Abstract: A sensor/actuator network 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.