Francisco José Arnold

Commercial ultrasonic baths employ piezoelectric ceramic to generate cavitation. These ceramics vibrate with large amplitudes and their physical characteristics may be changed decreasing of the performance due to the heating. We develop an experimental study to evaluate the changes in the Butterworth-Van Dyke equivalent electric circuit of a piezoelectric disk caused by the temperature at range from 30 °C to 90 °C, typical of the commercial ultrasonic baths. The results show that motional resistance is significantly modified increasing the mechanical loss. The evaluation of the temperature effects suggests that is not need to use electronic circuits in these systems as resonance tracking.

Although pre-stressing is a requirement for the operation of a high-power piezo transducers, its impact on the model, the performance and the design of such devices is still not yet fully covered in the literature. This work attempts to bridge this gap by analyzing how the components of the Butterworth-Van Dyke model, the resonances, electrical impedances, electromechanical coupling factor, mechanical losses, and the tuning inductance are determined as a function of mechanical pre-stress. We have employed the Butterworth Van-Dyke model to study piezoelectric transducers tightened with a range of pre-stressing levels (12.2–60.1 MPa). As expected, the experimental results indicate that the components of the Butterworth-Van Dyke model are dependent upon the mechanical pre-stressing. The conclusions point out that, under mechanical pre-stressing levels between a threshold value and 60.1 MPa, the transducers used in this work tend to stabilize and enhance their performances. Also, upon stabilization, the transducers can be tuned with a constant inductance, which may also aid the design of ultrasonic systems. Overall, this work contributes to the definition of pre-stressing levels and its relationship with the length of the transducer, the mechanical losses, and the tuning.

In this work, we have studied the electrical response of a sandwiched piezoelectric transducer as a function of the height of a water column used as an acoustical load. This study covers investigations about the behavior of resonance, anti-resonance, electromechanical coupling factor, motional resistance, and mechanical loss. The results show that the performance of the transducer is dependent on the acoustic load. The heights where the conversion is maximum coincides with the minimum value for the mechanical loss. These results can be used for the design of the hardware in ultrasonic systems that include dynamical resonance tracking and control of power supply.

This work shows the construction, calibration and validation of a system to determine sound speed in liquids. We used the pulse method for the measurements. Piezoelectric transducers are used to transmit and receive acoustic wave pulses. The pulse travel time is determined by a counter implemented in a logic programmable device (FPGA). Initially the system is calibrated using pure water. We performed measurements in NaCl and CuSO4 solutions at different concentrations. The system detected speed variations of approximately 1.0 m/s in relation to the concentrations. Therefore, from didactical point of view, it is possible to perform experiments where small changes in the impurities concentration can be detected and measured. Further, the construction or even the enhancement of the system may be stimulant to students devoted to electronic instrumentation.

Modern electronic instrumentation techniques are being introduced in the programs of the Physics and Physical Engineering courses and, in this context, the programmable logic devices play an important role. We present the fundamental steps for the design, development, and validation of systems based on programmable logic devices. Two digital filters have been implemented for illustrating the guide procedures. The results show that the function–response complies with the common requirements of generic filter performance. This work is targeted at students and lectures and aims stimulate and challenge them to develop electronic instrumentation using programmable logic devices in teaching activities.

Young’s modulus is addressed in the introductory courses of physics as a constant. In metals, for a large amplitude of stresses, this property has a constant behaviour. Unlike metals, elastomers do not present a constant Young’s modulus, but depend on the strain of the material. This work presents an experimental teaching practice of Young’s modulus determination of elastomers under small mechanical stresses by means of capacitance measurements. The capacitances were measured in capacitors constructed with dielectrics made with elastomers. An electronic circuit capable of producing electrical voltages from variations of the order of pF in the capacitors was used. The results show that for low levels of stress, Young’s modulus has nonlinear increases with the applied mechanical stress. The methodology employed in this work can be adapted for other experiments with didactical aims.

O estudo sobre a conservação do momento linear e as forças impulsivas nos cursos introdutórios de física tem abordagem baseada na colisão de objetos que se comportam como partículas. Neste trabalho busca-se por um aprofundamento no tema, introduzindo-se atividades experimentais direcionadas para laboratórios de ensino de física em que se considera a colisão entre uma bola de borracha e uma superfície rígida e plana. Estes experimentos permitem investigar características da colisão, tais como o tempo de impacto, a força impulsiva, a área de contato e o coeficiente de restituição. A modelagem, baseada na teoria de Hertz, inclui as propriedades elásticas da bola. Os resultados experimentais são comparados com valores teóricos provenientes do tratamento convencional (desconsiderando a deformação dos corpos) e da teoria de Hertz. Também são fornecidas indicações sobre a elaboração de experimentos visando aprimoramentos por parte de professores e alunos.