I. Introduction
Device-associated clot formation and bacteria adhesion are ongoing problems with medical implants and pose a significant burden on the healthcare system. Lubricant-infused surfaces (LIS) have recently gained attention as a promising surface coating to prevent non-specific adhesion on bio-interfaces and medical implants [1]. LIS can repel biological liquids through the presence of a thin lubricant layer integrated within a solid substrate, creating a mobile super-repellent liquid interface. The stability of the lubricant layer under different conditions (e.g., open-air conditions) and when using different solid substrates (e.g., non-porous and porous substrates) is an important factor that affects the function of the coating and needs to be considered [2]. Several approaches have been used to measure the evaporation rate of the lubricant layer, including measuring the volume of the lubricant before and after predetermined time points [3], measuring the contact angle of a water droplet on the surface over time [4], [5], and microscopic techniques [6]. However, these approaches suffer from limitations such as requiring bulky and expensive systems and lacking real-time monitoring features. Therefore, designing a real-time, compact sensor-based technology that measures the evaporation rate of the lubricant layer on surfaces could be highly beneficial. Microwave sensors offer a solid, robust solution for wireless and noncontact sensing applications. A planar split-ring resonator (SRR)-based structures are among the most interesting structures for sensing applications due to their compact structure, simple mass production of the design, and easy integration with Lab-on-a-chip technologies [7]. SRR sensors have shown great enabling potential in various applications, such as biomedicine and biochemistry [8]. More importantly, their noncontact and real-time detection capability makes them a suitable candidate for blood-contacting medical applications.