Determination of dielectric constant of substrate material using a fractal resonator sensor

Summary form only given. With the rapid evolution in sensor technology and increasing importance in dielectric measurement, low profile, compact size, highly sensitive sensors are in great demand both in industry and medical field. A novel method for measuring the permittivity of dielectric substrate by means of a microstrip fractal resonator is presented in this paper. Miniaturization of loop resonator using the fractal technique is known as Minkowski square loop resonator. The fractal resonator was created by using the initial square pulse (SP) to iterate at each side of the loop. Although the fractal resonators focus on antennas and filters, the geometry is well suited in designing a sensor of compact size. The area of the Minkowski resonator is only 20% of the square loop resonator for the same conductor length. The proposed sensor is designed at 1GHz resonant frequency. The sensor is implemented using planar microstrip technology. The dielectric material is placed above the resonator. As a consequence the near field of the resonator interacts with the material under test (MUT) and the electrical characteristics of the resonator change in relation to the permittivity of the material. The proposed Minkowski resonator was designed using ADS. The prototype is extremely compact and experimentally verified. A vector network analyzer is used to measure the shift in resonant frequency and the corresponding amplitude of the transmission parameter for the fundamental mode was studied. From the relative shift in resonant frequency the dielectric constant of the test material (RT Duroid 6002-dielectric constant 2.94) was calculated by means of the polynomial expression derived for the sensor using curve fitting method.