Compact and high frequency detection resolution microwave microstrip sensor based on a flower-shaped resonator for permittivity measurement of liquids

In this study, a microstrip microwave sensor employing a flower-shaped resonator has been designed and introduced for the characterization of the real component of the relative permittivity of different liquid samples. The operating principle of the sensor relies on variations in its resonant frequency; specifically, when a sample is positioned within the sensing area, a difference arises between the resonance frequency in the unloaded state and that in the loaded condition. To assess the performance of the device, ethanol, methanol, an aqueous glucose solution, and deionized water were utilized as test specimens. The sensor was fabricated on an RO4003 substrate with overall dimensions of 30 × 12 mm 2 and a thickness of 0.508 mm. In the absence of any sample (unloaded state), it resonates at 3.5 GHz and exhibits a quality factor of 310. Upon introducing liquid samples into the sensing region, the resonant frequency shifts from its initial value of 3.5 GHz toward lower frequencies. The proposed sensor offers compact size, portability, low cost, and ease of integration with other system components. A comparison with 151 sensors reported in reputable journals during 2025–2026 demonstrates that the proposed sensor represents a promising candidate for industrial, medical, and diagnostic applications.