The physics textbooks presents the fundamental concepts of wave beating from an interference process of two plane waves at the time domain. In this work, we propose a teaching practice, based on computational simulation, at undergraduate level, combining the beating caused by waves transmitted from two plane circular pistons vibrating on thickness mode with the resulting acoustic field. The proposal leads to the perception of the beating at the spatial domain. The results show that the pressure amplitude generated from the beating has periodic variations along the central axis from a boundary location. This boundary is determined by the number of extreme values and the ratio between source radius and wavelength.

Abstract The optimization of three-dimensional device has widely been explored and designated as computational challenge in photonic device design. In this context, this work presents a novel multi-symmetric level (MSL) optimization procedure based on Genetic Algorithm (GA) to decrease the computational requirements in a three-dimensional photonic coupler device optimization. The proposed procedure divides the device optimization into many local regions by dimensional symmetric aspects, being based on divide- to-conquer strategies. As the optimization converges to acceptance values, the number of symmetric areas are decreasing until a unique local area that modeled the total 3D photonic device. This procedure was validated by the minimization of a photonic coupler modeled to interconnect optical waveguides with different height, width and refractive indices.

Abstract 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.

A potência de sinal é um importante parâmetro a ser considerado em um projeto de implantação de rede de sensores sem fio no meio agrícola. Este trabalho tem como objetivo coletar dados de qualidade de sinal transmitido entre uma estação base e um nó sensor situado no interior de uma casa de vegetação, localizada no campo experimental da Faculdade de Engenharia Agrícola - UNICAMP, com o auxílio de ferramentas computacionais. Após a implantação do nó sensor foram realizados experimentos com vista a se verificar alcance e qualidade do sinal de acordo com sua potência. Através desses ensaios foi possível concluir que uma potência de sinal com valor de -12,2 dBm é suficiente para manter a transmissão entre a estação base e nó sensor. Testes também foram realizados com uma potência de sinal de -9,2 dBm e mostraram que a rede possuía qualidade classificada "muito alta" porém, através do teste de duração da bateria, nota-se que existe economia de energia ao se utilizar a potência de sinal de -12,2 dBm. Foi avaliada a influência que o valor da potência de sinal tem sobre a qualidade do sinal de transmissão e recepção, o gasto de bateria e o alcance do sinal.

The signal strength is an important parameter to be considered in a project to establish network of wireless sensors in an agricultural environment. This work aims to collect quality data signals transmitted between a base station and a sensor node located inside a greenhouse, which is an experimental field located in the College of Agricultural Engineering - UNICAMP, with the help of computational tools. After sensor node deployment, experiments were performed in order to check range and signal quality. Through these experiments, it was concluded that a radiofrequency power value of -12.2 dBm is sufficient to maintain transmissions between base station and the sensor. Tests were also performed to a radiofrequency power of -9.2 dBm, and showed that the network had quality rated as "very high". However, by testing the battery life, it is noted that there is an energy saving when the radiofrequency power of -12.2 dBm is used. It was shown that the value of the signal strength has an influence on the quality of signal transmission and reception, battery depletion and signal range.

Neste trabalho é apresentado um método de análise de transdutores piezelétricos baseado numa simplificação do circuito elétrico equivalente de Mason. Empregou-se uma adaptação do teorema de Thévenin para analisar o comportamento de transdutores piezelétricos usados como transmissores (conversão de energia elétrica em mecânica), levando em conta uma configuração tipicamente empregada em aplicações de alta potência. Os transdutores foram modelados uni-dimensionalmente considerando-se apenas modos de vibração longitudinais. Um circuito elétrico equivalente foi obtido e simulado computacionalmente. Os resultados experimentais e os calculados pelo modelo elétrico apresentaram bom ajuste. Aspectos referentes à simplificação do modelo empregado e sua viabilidade para ensino são discutidos.

In this work, a method of analysis of piezoelectric transducers is shown. This method is based on the simplification of Mason’s equivalent electric circuit. An adaptation of Thévenin theorem has been employed to study the behavior of piezoelectric transducers used as transmitters (electric into mechanic energy conversion). This study was restricted to transducers with a typical configuration employed in high power applications. The transducers were one-dimensionally modeled, considering only longitudinal vibration modes. An equivalent electric circuit was obtained and computationally simulated. The experimental and calculated results show a good fitting. Features related to the simplification of the model employed and their feasibility for teaching are discussed.

Quando um transdutor eletro-acústico é excitado eletricamente, ele produz no meio de propagação onde está inserido um campo acústico. Através do conhecimento dos campos acústicos pode-se colher importantes subsídios para projetos de transdutores e estudos da interação com os meios de propagação. Neste trabalho é apresentada uma proposta de atividade interdisciplinar envolvendo conteúdos de Física, Matemática e Computação ministrados nas disciplinas introdutórias dos cursos superiores de ciências exatas e tecnológicas. O trabalho propõe a discussão dos fenômenos de interferência ondulatória, o cálculo do campo acústico usando coordenadas cilíndricas e a programação do método matemático através de instruções básicas de uma linguagem de programação. As simulações de alguns campos acústicos são apresentadas na forma de gráficos bi e tridimensionais e os resultados são discutidos.

When an electro-acoustical transducer is electrically supplied, it yields an acoustic field in the propagation medium. The acoustic field knowledge allows us to obtain significant help to transducers design and propagation medium interaction studies. In this paper, it is shown a proposal of classroom work involving the studied contents of physics, mathematic and computing in the introductory lessons of degree course of exact science. It is proposed the discussion about wave interference phenomena, the determination of acoustic field using cylindrical coordinates and the software of the mathematical method applying basic instructions of a computational language. The simulations of some acoustic fields are shown in bi and tri-dimensional graphics and the results are discussed.