This work shows the utilization of a coaxial cable for the fabrication of a long period Bragg grating. The grating is fabricated removing the dielectric in short pieces of the cable so that the discontinuities account for the variation in the medium refractive index. Simulated and experimental results of the grating resonances are shown as a function of the scattering parameters S, demonstrating the feasibility of the technique. By using the sensor in the MHz frequency range cheaper electronics can be employed, which reduce the overall cost of the sensing system.

Este trabalho propõe a utilização de um sensor para caracterizar o comportamento de amostras de óleo vegetal submetidas a ciclos de aquecimento e resfriamento e busca correlacionar esse comportamento com a constante dielétrica das amostras. Os valores da constante dielétrica das amostras de óleo de soja foram medidos durante quatro ciclos de aquecimento e resfriamento num intervalo de 20 a 120 ºC. No ciclo de aquecimento, a constante dielétrica das amostras aumentou até três vezes o seu valor inicial e, no resfriamento, a curva de diminuição da constante dielétrica foi diferente daquela obtida no aquecimento. Após cada ciclo completo de aquecimento e resfriamento, o valor da constante dielétrica sofreu aumento, indicando uma alteração permanente nas propriedades físico-químicas das amostras. Estes resultados sugerem que a medição da constante dielétrica pode ser um método rápido e barato para caracterizar óleos vegetais submetidos a variações de temperatura. A aplicação deste teste simples poderá ser útil na avaliação da qualidade do óleo de soja utilizado em sucessivos processos de fritura de alimentos.

This paper suggests the use of a sensor to characterize the behavior of vegetable oils submitted to heating/cooling cycles, as an attempt to correlate this behavior with the dielectric constant of oil. Dielectric constant values were measured in soybean oil samples subjected to four heating/cooling cycles from 20 to 120 ºC. In the heating cycle, the dielectric constant of the samples had increased up to three times its initial value and the decay curve of dielectric constant obtained during cooling was different from that of the heating cycle. After each heating/cooling cycle, the value of dielectric constant was increased, signaling a permanent change in the physicochemical properties of the samples. These results suggest that measuring the dielectric constant can be a fast and inexpensive method to characterize vegetable oils subjected to temperature variations. The application of this simple test may be useful in the quality assessment of the soybean oil used in successive operations of food frying.