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Structural Dynamics and Monitoring Lab
Sensor Technology Laboratory
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Accurate and economical monitoring of structural characteristics relies heavily on a wide range of both proven and emerging sensor technologies.  The goals of the sensor technology laboratory are to provide careful calibration for existing sensors, and to investigate several promising sensor technologies suitable for structural monitoring.

Electromagnetic Measurement of Stress and Strain

A current emphasis of the sensor laboratory is the measurement of stress in tensioning cables and wires using a magnetoelastic method developed during a mutual collaboration with the Department of Radio Physics in Slovakia.   The method is a non-destructive test method which directly measures force in a sample.  Given a particular ferromagnetic steel, an initial set of tests are required to characterize the relationship between magnetic permeability, stress and temperature. The figures below show equipment which has been designed and successfully used for testing small cables (up to 0.6") and wires.  The equipment includes the load frame, hydraulic jack and grips, a temperature chamber for temperatures both above and below ambient, and a calibration load cell.  The sensor itself is a set of coils and a temperature sensor installed onto the cable.

Figure 3.1 Figure 3.2
Figure 3.1 Figure 3.2

The magnetic field is induced in the steel sample via the discharge of a high voltage capacitor, contained in the DYNAMAG unit at the right (Fig. 3.3).  The applied magnetic field and the flux within the sample are measured via a Walker Scientific Gaussmeter and Fluxmeter.

Figure 3.3
Figure 3.3

A large variety of tensioning steels are currently being investigated.  Several examples are shown in the figures below.

Figure 3.4 Figure 3.5
Figure 3.4 Figure 3.5

Finite element simulation of the sensors, which is desirable for the most precise calibration, can be performed using a Quickfield workstation (figure 3.6).

Figure 3.6
Figure 3.6

PVDF Characterization

A very promising active sensor suitable for a broad range of structural monitoring is based upon the piezoelectric properties of polyvinylindine fluoride (PVDF) films.  The sensor laboratory includes equipment for measuring the response of PVDF materials under both static and dynamic deformations.  Static tests are conducted by mounting the sample in a motion displacement stage or a cantilever test stand, as shown in the photographs.

Figure 3.7 Figure 3.8
Figure 3.7 Figure 3.8

Sensor Durability Laboratory

A practical concern of sensor engineering is developing a complete sensor package which can withstand environmental stresses.  In order to study issues related to this aspect of sensor engineering, the sensor technology laboratory maintains equipment for accelerated testing under adverse conditions of moisture and ultraviolet radiation.  

Figure 3.9

Figure 3.9