In today’s era, sensors are very essential in each and every field like food safety, atmosphere monitoring, disease diagnostics, etc. There are several techniques used for implementing sensors. Few examples of those techniques are surface plasmon resonance, ultrasonic waves, nonmaterial, electrical transducer, etc. But sensors based on these techniques are complex to design, need very sophisticated instruments, and lots of time. In recent years, the metamaterial is widely used in the microwave regime to implement sensors for various applications.

A metamaterial is an artificially designed material that exhibits a negative refractive index (negative permeability and permittivity). Its property depends on its structure and chemical composition. Metamaterials can be designed by making different metallic structures on the substrate like FR4, Roger, etc. These materials are classified into two categories: resonant and non-resonant metamaterial. Split ring resonator (SRR) is a type of resonant metamaterial. In SRR, both permeability and permittivity are negative and have a large varying range. Sensors based on the SRR are very easy to design, cost-effective, very sensitive, and give a quick response. In SRR, the main sensing parameter is its resonant frequency. With the small change in the structure of SRR, a great change in the resonant 58frequency can occur. In this chapter, we will define the metamaterial, SRR, and defected ground structure (DGS). The theory and structure of SRR will also be discussed in detail with the various application of defected ground SRR as sensors.