A Miniaturized Planar Sensor Using Minkowski Fractal Technique for Material Characterization

This paper presents on a miniaturized planar sensor for characterizing relative permittivity of materials. The proposed planar sensor design is based on a near-field transmission-line measurement technique implemented by a modified complementary square ring resonator (CSRR). The proposed sensor is a simple microstrip transmission-line which is theoretically matched to 50 fl input impedance. On the ground plane, the CSRR is created to generate resonant frequency with the behavior of band reject characteristic. The 1st and 2nd iterations of Minkowski fractal pattern are applied to minimize the size of the CSRR, while still achieving an operating frequency at 2 GHz. By loading a material under test (MUT) on top of the CSRR, the relative permittivity of material can be extracted based on transmitted electromagnetic-wave energy interacting, which is changed depending on the dielectric properties of the material, between the MUT and the CSRR. Five microwave laminates, e.g., RT/duroid 4003, 6002, 6006, DiClad 880, and FR-4, were measured and performed to generate the relative permittivity extraction model. The extracted relative permittivity results from the developed numerical model show an agreement of higher than 94% as compared with the value of microwave laminates, which is identified on datasheet. The size reduction of the modified CSRR by using the 1st and 2nd iterations of Minkowski fractal technique when compared with a square ring resonator (0th iteration) are 45% and 65%, respectively, resulting in reducing the sample size of dielectric measurement. The proposed planar sensor also offers other advantages, such as the ease of design, low-cost, and miniaturization.