## 1 Introduction  
### Motivation  
This paper compares the two most promising NDT methods for evaluating the basic parameters of reinforced concrete (RC) structures. Such evaluation is needed for acceptance tests or to determine the physical properties of old objects whose basic parameters are unknown.  
RC has been used as a primary construction material for over a century. Hundreds of millions of reinforced concrete (RC) structures of various types and sizes have been built globally during this time. Identifying fundamental parameters in these structures is crucial for investors and construction inspectors. The acceptance tests ensure that the structural parameters and materials meet design specifications. Usually, investigations of this kind include the evaluation of parameters like concrete cover thickness (\(h\)), rebar diameter (\(D\)), and the class of steel (ductility and hardness of the alloy [1]). Nowadays, acceptance testsare mainly conducted using destructive testing methods. The concrete cover is removed during the investigation, and the materials are evaluated visually [2; 3; 4; 5].  
Additionally, the parameters can be evaluated on existing structures before renovation or modernization works (if documents are lost and the structure specification needs to be discovered). Knowledge about the materials used is essential, for example, to calculate the structure's load-bearing capacity and determine whether proposed changes are feasible and safe [2; 3].  
Due to the worldwide scale effect (the number of RC structures), such tests have enormous practical importance. Substituting destructive techniques with nondestructive testing (NDT) methods would greatly expedite the testing process and enable reductions in the associated costs. These advancements could increase the prevalence of such tests, ultimately improving overall safety by ensuring the use of materials in accordance with the project. Therefore, developing innovative nondestructive testing (NDT) methods tailored explicitly for inspecting reinforced concrete (RC) structures is a critical concern.  
The direct nondestructive evaluation of reinforcing bars is mainly achievable through electromagnetic and specific mechanical techniques. However, only electromagnetic methods are specifically designed for assessing metal components (such as rebars), while mechanical methods offer greater versatility. Electromagnetic techniques facilitate direct interaction with rebar, reducing interference and attenuation from the surrounding concrete cover. Among these methods, the eddy current (EC) technique is the preferred option for assessing reinforced concrete (RC) structures. However, the magnetic method presents a solid alternative to EC. Recent advancements in magnetic sensor technology have significantly increased the popularity of such systems in various nondestructive testing (NDT) applications. Magnetic flux leakage (MFL) is the most promising among the different magnetic methods [6].  
This paper offers a comparative analysis of the eddy current (EC) method and the magnetic flux leakage (MFL) approach. Both techniques have been adapted for evaluating RC structures and compared regarding system complexity, spatial resolution, effective range, and simplicity of basic RC structure parameter identification.