Fully 3D-Printed Microwave Sensor for Permittivity Measurement

This article presents the design and performance evaluation of a novel 3D-printed microwave sensor for dielectric characterization. The sensor utilizes a modified complementary split-ring resonator (CSRR) structure integrated within the ground plane. The sensor’s ability to measure both solids and liquids is demonstrated, with solid samples placed in proximity to the resonator and fluids injected into the embedded channel, thereby avoiding additional materials for fluidic channels. The sensor’s performance is evaluated based on changes in resonant frequency due to variations in dielectric constants. For solids, the resonant frequency shifts from 4.24 to 2.66 GHz with increasing permittivity. For liquids, the frequency ranges from 4.24 to 3.27 GHz for permittivity values between 1 and 80. An equivalent circuit model is developed to validate the sensor’s performance. The sensor is fabricated using the fused deposition modeling (FDM) method with conductive layers applied via copper aerosol spray. The sensor’s versatility is demonstrated through testing with a range of solid substrates, such as Rogers 5880, FR4, Rogers 3006, and Rogers 6010, as well as four liquid samples—methanol, ethanol, propanol, and distilled water. The sensor effectively measures dielectric constants by monitoring shifts in resonant frequency, which vary with the permittivity of the tested samples. With an overall compact design of $30\times 40\times 1.6$ mm, the sensor requires minimal liquid volume and achieves comparable sensitivity, with 4.05% for solids and 0.3% for liquids. The sensor’s resolution, accuracy, and low fabrication cost make it a promising tool for precise dielectric constant measurement.