In recent years, due to the unique ability of metamaterial absorbers to control electromagnetic waves in the terahertz frequency range, they have attracted much attention [[1], [2], [3]]. These absorbers consist of sub-wavelength structures that can be used to absorb or transmit terahertz radiation by designing different structures [[4], [5], [6]]. Terahertz band (THz) is a new frequency band between microwave and infrared bands; which has attracted the attention of many researchers. A large number of electromagnetic metamaterial devices have been designed and verified in the THz band [7,8]. Metamaterials are not naturally found in natural materials, and due to their unique characteristics, they give us the ability to change the permeability and permittivity coefficient by applying changes in the shape and configuration of the metal and dielectric layers of the structure. The development of metamaterial-based absorbers in the terahertz region has provided new avenues for various applications, including antenna [9,10], filters [11,12], biosensors [13,14], perfect absorbers [15,16], and antireflection coatings [17]. Terahertz sensors based on metamaterials have a high ability to detect very small amounts of chemical and biochemical substances. Placing the test substance on top of the absorber structure, causes a change in the amount or shift of the absorption peak, which can be used to identify and measure a specific biomolecule. The performance of these sensors can be improved by increasing the quality factor and sensitivity of the sensor [[18], [19], [20]]. By using phase change materials (PCM), researchers have been able to overcome the limitations of biosensors that are limited by the resonance frequency and bandwidth. By applying external conditions such as temperature, or pressure, phase change materials can change their state and properties. Therefore, by integrating metamaterial absorbers with phase change materials, dynamic, tunable, and reconfigurable photonic devices can be created [21]. This method provides a solution to adjust the resonance frequency in absorbers and increase the performance of biosensors. For this reason, scientists’ attention has been directed toward the design and fabrication of terahertz metamaterial absorbers with sensing and switching capabilities using phase change materials, which enables the construction of multifunctional devices [22,23].

GST (germanium-antimony-tellurium) material is one of the most widely used phase change materials and has attracted the attention of many researchers. The popularity of this material is due to its distinct optical and electrical properties, which it shows in two amorphous and crystalline states. In addition, it is compatible with CMOS technology and has a high reversible phase change speed. Metamaterial structures based on this phase change material have shown promising results in diverse fields such as memory devices, optical modulators, and energy harvesting. The nature of GST is temperature dependent, and with increasing temperature, its state changes from amorphous to crystalline and exhibits different optical properties [24,25].

In this paper, a polarization-insensitive and tunable terahertz metamaterial using GST phase change material has been designed and simulated with the application of switching and sensing. The effect of changing the geometric parameters and applying the error percentage during the construction of the proposed structure has been investigated. In addition, the equivalent circuit of the proposed structure has been presented and the simulation results and ECM results have been checked and compared.