## 1 Introduction  
Nondestructive testing (NDT), also referred to as nondestructive inspection (NDI) or nondestructive evaluation (NDE), refers to a set of analysis techniques used in various fields and industries to inspect and test the properties of a material, component, or system without causing damage. The nondestructive nature of theses evaluations makes them ideal for ongoing monitoring and quality control during manufacturing or in-service inspections [1]. They offer cost-effectiveness by preventing the unnecessary destruction of utilizable parts while ensuring safety and reliability by detecting potential failures before they occur. On the other hand, destructive testing, which involves subjecting a test sample to failure conditions, provides definitive results about the material's properties under specific conditions; however, this comes at the expense of the sample. Thus, destructive testing is less suitable for finished goods or applications where preserving the item's integrity is critical. Nondestructive and destructive testing are fundamental approaches that are used across various industries, each having distinct applications, advantages, and limitations. NDT is widely used in sectors where component failure could lead to significant hazards or economic losses [2]. For example, inspecting aircraft components and structuresin the aviation sector is essential for ensuring safety without causing any damage or changes to the objective under test [3, 4]. Similarly, in the oil and gas industry, NDT is used for pipeline and infrastructure inspection to prevent leaks and guarantee operational safety without affecting the integrity of the structure under test [5, 6]. In the manufacturing industry, NDT serves the purpose of quality control by verifying the integrity of products without affecting their usability [7]. This technique is also vital in the civil infrastructure domain, where it is applied to bridges [8, 9], buildings [10], and other critical structures to detect potential failures and enhance safety without damaging them [11, 12]. NDT is also employed in the transportation sector, which encompasses rail [13], automotive [14], and maritime areas [15], to conduct thorough inspections of vehicles and infrastructure without interrupting transportation operations. By integrating NDT into regular maintenance and inspection routines, these industries can significantly reduce the risk of unexpected failures, thus improving efficiency across operations [16]. On the contrary to NDT, destructive testing involves evaluating a material's properties by intentionally making it fail. It is primarily used to determine material properties such as tensile strength, ductility, and hardness through various tests. Typically, destructive testing is used for testing prototypes from batches in industries where the loss of one component is not economically critical. However, it is often not cost-effective or feasible to apply destructive testing to large and expensive structures such as bridges, large machinery, and aircraft prototypes, owing to the associated heavy losses yielded by taking such structures to failure. The objective of this paper is to conduct a comprehensive review of NDT techniques and methodologies, with a focus on microwave NDT (MNDT) techniques. This study distinguishes between traditional NDT and MNDT techniques by providing an in-depth analysis of each method. In Section 2, such distinction is achieved by initially exploring the practical applications, benefits, and inherent limitations of standard NDT techniques. Next, in Sections 3 and 4, this review shifts attention towards MNDT, showing recent progress in the field and comparing diverse strategies for defect detection. Finally, traditional algorithms used in MNDT are discussed and compared against emerging algorithms that utilize artificial intelligence (AI) in Section 5.