## 2 Background  
For the effective utilization of underground utility management technology, a technology that can grasp location information inexpensively and conveniently is essential. Existing technologies include electromagnetic locators, ground penetrating radar (GPR), and RFID [5]. All three technologies use electromagnetic waves to locate underground utilities. However, they differ in their utilization methods. The electromagnetic locator method is a search method for electromagnetic fields generated or intentionally induced in underground utilities, and it can utilize various frequencies depending on the purpose [6]. As it detects metallic pipes, tracking lines should be attached to underground utilities with low conductivity. It is difficult to use if the connection is poor or the tracking line is damaged. If the distance between the underground utilities is significantly short, interference between electromagnetic fields occurs, making it difficult to detect the exact location [7]. The underground detection method using GPR was developed in Germany around 1911 and has been actively developed and utilized since the 1970s [8]. It uses the transmission/reception time difference of electromagnetic waves reflected from the interface of different media to locate underground utilities [9]. GPR is utilized in various types of methods such as time domain, FMCW (Frequency Modulated Continuous Waveform), and SFCW (Stepped Frequency Modulated Waveform) [10]. There are previous studies on recognizing underground facilities by applying GPR [11]. The electromagnetic locator has disadvantages when the tracking cable is damaged. In addition, when the underground area is crowded or cables are installed very close to each other, interference occurs between electromagnetic fields, making it difficult to measure the location. In the case of the ground penetrating radar method, the accuracy is low, and there is deviation between the analyst's experience and personal interpretation. It is not suitable for use in multistory structures, i.e., road structures with multiple interfaces. Since both methods can only find the shape of buried objects in the ground, but cannot provide information (data), it is difficult to help systematic history management. To overcome these disadvantages, it is possible to use the location search equipment to which RFID technology is applied. This is advantageous for history management by increasing the accuracy of location exploration and reliably maintaining utility information. The Virginia Department of Transportation suggested the possibility of using a commercial product in the underground facility reinstallation work conducted around 2010. In a pilot project, a method of acquiring location information with GPS (Global Positioning System) and linking it to a spatial information system was tested [12]. UHF RFID operates with a mechanism similar to location exploration but can transmit data through electromagnetic wave modulation. A tag is attached to the target to be identified, and the reader recognizes the object. Compared to the two methods described above, it is possible to quickly determine the exact location of the underground utility and the presence or absence of pipes regardless of the mastery status of the operator and to systematically manage the history by providing identification data. Depending on the operating frequency band, RFID exploration methods are classified as low frequency, high frequency, ultra-high frequency (UHF), and microwave. Depending on the tag power source, they are classified as passive, active, and semi-active. The 900 MHz UHF method is best suited for this study due to its small antenna size, fast signal transmission speed, and relatively long recognizable distance. Furthermore, the passive RFID method is the most suitable, considering the field use. The passive RFID system generates DC power by passing a signal (a kind of s sinusoid wave) received from the reader through the Greinacher half-wave rectifier.