In this work, a mechanical vibrational analysis of an ultrasonic atomizer is carried out to control its atomization mass transfer rate. An ultrasonic atomizer is a device constructed with a piezoelectric ring coupled to a metallic circular thin plate with micro-apertures. The mechanism of mass transfer by atomization is a complex phenomenon to model because of the coupling effect between the fluid transfer and dynamic mechanics controlled by a piezoelectric vibrating ring element. Here, the effect of the micro-apertures shape of the meshed thin plate coupled to a piezoelectric ring during vibration, as well as the resonance frequency modes, are numerically studied using a finite element analysis and compared with theoretical and experimental results. Good correlations between the predicted and experimental results of the resonant frequencies and atomization rates were found.

Multiwire cables are widely used in important engineering structures. Since they are exposed to several dynamic and static loads as well as detrimental environmental conditions, their structural health can be compromised. Due to the critical role played by multiwire cables, it is necessary to develop a non-destructive health monitoring method to maintain their structure and proper performance. Ultrasonic inspection using guided waves is a promising non-destructive damage monitoring technique for rods, single and multiwire cables. However, the propagated guided waves are composed of an infinite number of dispersive vibrational modes making their analysis difficult. In this work, an entropy-based method to identify small changes in non-stationary signals is proposed. An experimental system to capture and post-process acoustic signals is implemented. The discrete wavelet transform is computed in order to obtain the reconstructed wavelet coefficients of the signals and to analyze the energy at different scales. The use of the concept of entropy evolution of non-stationary signals to detect damage in multiwire cables is evaluated. The results show that there is a correlation between the entropy value and level of damage of the cable including breaking of single wires and change in the mechanical contact conditions among the wires. It is found that the studied method has low sensitivity to signal noise and can reduce the computational complexity encountered in a typical time–frequency analysis.

Defect detection and characterization are critical tasks for structural health monitoring of pipe-like engineering structures. Propagation and detection of ultrasonic helical Lamb waves using macro fiber composite (MFC) sensors is studied. Experiments for defect detection and characterization on an aluminum hollow cylinder (114mm in outer-diameter and 6mm of wall thickness) were carried out. An experimental setup using MFC sensors coupled to the cylinder's surface in a pitch-catch configuration is presented. Time-frequency representation (TFR) using wavelets is employed to accurately perform mode identification of the ultrasonic captured signals. The initial results indicate that the use of helical waves could allow the monitoring of damage in difficult to access critical areas by locating the sensors only on a small region of the periphery of the cylindrical structure under inspection

This work presents the proprietary design and implementation of a lead zirconate titanate (PZT) sensor for simple digital transmission and reception of guided waves using a high-temperature and corrosion-resistant multiple-wire 1K22 MP-35N cable as a communication channel. These cables are commonly used in the hostile oil and gas borehole environments of the petroleum industry. The sensor design involves electrical/mechanical coupling, instrumentation and casing. The PZT guided wave transmitter instrumentation includes a microcontroller-based pulse position modulator, a signal booster, a PZT-5H crystal and a 9 V battery. The receiver sensor consists of a PZT-5H crystal, an amplifier and a real-time digital signal processing (RT DSP) and data acquisition module connected to a personal computer. Dispersion curves were obtained using Disperse software and a simplified model of the cable. Dynamic linear 3D finite element modelling of the sensor was performed to support the correct frequency selection. To evaluate the sensor design, the transmitter generated 60 kHz guided wave pulse position modulation (PPM) energy packages. Experimental tests were conducted in the laboratory using 1 m and 10 m cables. The results showed that, although there was significant dispersion and there were multiple mode excitations of the transmitted pulses, the system correctly identified 10-bit frames of guided wave PPM-encoded information.