Biblio

According to the technical difficulties of the air-coupled piezoelectric ultrasonic transducer, 1-3 type piezoelectric composites and double matching layers structure are adopted in order to solve the acoustic impedance mismatch at the interface between the piezoelectric materials and air. The optimal design of the matching layer thickness for double matching layers structure air-coupled ultrasonic transducer is also completed through experiments. Based on this, 440 kHz flat-plate and focused air-coupled piezoelectric ultrasonic transducer are designed, fabricated and characterized. Finally, surface cracks are detected using the focused air-coupled piezoelectric ultrasonic transducer.

Each year, large ground motions from earthquakes cause infrastructure damage and loss of life worldwide. Here we present a novel concept that redirects and attenuates hazardous seismic waves using an engineered seismic-muffler acting as a cloaking device. The device employs vertically-oriented, sloping-opposing boreholes or trenches to form muffler walls and is designed to: 1) reflect and divert large amplitude surface waves as a barrier, while 2) dissipating body and converted waves traveling from depth upward into the muffler duct. Seismic wave propagation models suggest that a seismic-muffler can effectively reduce broadband ground motion directly above the muffler. 3D simulations are also compared for validation with experimental data obtained from bench-scale blocks containing machined borehole arrays and trenches. Computer models are then scaled to an earth-sized model. Results suggest a devastating seismic energy magnitude 7.0-\$\textbackslashtextbackslashmathrm M\_\textbackslashtextbackslashmathrm E\$ earthquake can be reduced to less damaging magnitudes experienced in the muffler vicinity, 4.5- \$\textbackslashtextbackslashmathrm M\_\textbackslashtextbackslashmathrm E\$ (surface wave) and 5.7- \$\textbackslashtextbackslashmathrm M\_\textbackslashtextbackslashmathrm E\$ (upgoing coupling into the muffler). Our findings imply that seismic-muffler structures significantly reduce the impact of the peak ground velocity of dangerous surface waves, while, seismic transmission upward through the muffler base at depth has marginal effects.