## 1 Introduction  
Carbon fiber reinforced polymer (CFRP) materials are widely used in aerospace, automotive and other industries because of their excellent properties. In application, due to various factors such as overuse and impact, CFRPs can present with various types of defects, which not only greatly affect the performance of products but also may cause fatal safety hazards. Especially in applications such as the automotive and aviation industries, timely and effective nondestructive testing and identification of defects are of great importance [1; 2; 3; 4]. A variety of nondestructive testing (NDT) methods (ultrasonic, radiographic, thermal imaging, eddy current, etc.) have been widely used in these industries to detect the defects of CFRPs to ensure the quality and safe use of the product [5; 6; 7; 8; 9; 10]. In the current applications, there are many existing nondestructive testing methods, but they all have different types of shortcomings. For example, ultrasonic testing requires high surface smoothness of the test piece and requires the use of coupling agents to fill in gaps [11]: Radiographic testing is harmful to the human body and can only be conducted in two directions, making it inconvenient to use [12]; infrared thermal imaging testing is affected by the thermal emissivity of the surface of the test piece and is easily affected by the environment, with low sensitivity for detecting internal defects [13]; and traditional coil-based eddy current testing methods have low mechanical scanning efficiency, limited spatial resolution due to coil size, and vibration noise [14]. Due to the applicable limitations of the above methods, this article aims to explore a new detection method that can make up for the above shortcomings. This nondestructive testing method based on ECMO is a non-contact, one-way testing method that is not harmful and is not affected by surface conditions, has high detection efficiency, and has a high spatial resolution. From the perspective of testing methods, it is an innovation. At present, most NDT methods are developing towards visualization, as in Ref. [15], which can show defects more visually. The research results can also be used in the field of computer vision. EC testing [16] is an electromagnetic detection method that is usually suitable for detecting defects that cause changes in the electromagnetic properties of the tested materials. For CFRPs, cracks (fiber fractures), misalignment, wrinkling and uneven clearance, impact damage and delamination, and other defects can all be detected by the EC method [17]. The German Fraunhofer Institute for Nondestructive Testing (IZFP) uses array EC probes and multi-frequency EC to detect defects in CFRPs and achieves great results [18]. Reference [19] introduces the small signal extraction method by using lock-in amplification, which is used to realize the imaging of CFRPs with medium-frequency EC (150 kHz and 250 kHz) and successfully detect defects such as cracks and impact damage. However, EC coil detection is limited by the size of the coil, the sensitivity of the coil at low frequencies is not high either, the detection depth may be affected by the skin effect at medium and high frequencies, and the impedance characteristics of the coil are usually considered in addition to the electromagnetic characteristics of the test piece. There are several studies about using the superconducting quantum interference detector (SQUID) EC method to detect multiple defects in CFRP materials at lower frequencies [20]. However, SQUID requires refrigeration equipment, which is difficult to miniaturize and expensive. Magneto-optical (MO) detection and imaging can detect alternating magnetic fields in a certain area. Eddy current magneto-optical (ECMO) imaging was first used to detect aircraft skin defects, and the following Refs. [21; 22] further developed and improved the ECMO imaging nondestructive testing system.