Non-contact experimental modal analysis using air excitation and a microphone array

Experimental modal analysis (EMA) is the empirical study of the dynamic properties of structures under vibrational excitation. Non-contact EMA is advantageous when the target is susceptible to damage or contamination. In this study, we investigated non-contact EMA as we excite a cantilever beam using a collimated air impulse controlled by a solenoid valve. The reflected airwave from the beam surface was measured by a microphone array. The air actuation is calibrated by utilizing a separate pressure sensor that simultaneously measures the air impulse. The effect of changing the pressure and the opening time interval of the solenoid valve are investigated and found to be adequate for the frequency range of interest. The force transferred from the air impulse to the target depends on the upstream pressure, as well as the gap between the target and the nozzle. The effect of changing both the pressure and the gap distance between the target and the nozzle on the magnitude of force is investigated with a series of tests. Pre-processing is performed on the reflected signals to minimize the noise level, and the optimal gap distance between the sensor array and the target is found. The experimental tests demonstrate the effectiveness of the proposed methodology to both accurately and cost-effectively measure structural dynamics in translational and rotational degrees using a non-contact excitation and sensor mechanism.