# Development of a Metalens for Radio Wave Ground- Penetrating Radars
## 3 Experimental Study
Figure 10: Field distribution at a distance of 10 cm (**a**), 30 cm (**b**), 50 cm (**c**), 70 cm (**d**), 90 cm (**e**), and 110 cm (**f**). Further experimental research was based on the detection of objects in a stand with sand. The depth of the box was 50 cm. The wooden sample (Figure 12a) was placed in a box with sand to a depth of 20 cm. The experiment was carried out in several stages. For a comparison with the proposed system using the metamaterial, a probing system was chosen from a UWB antenna with a parabolic mirror. To create a narrow radiation pattern, the antenna was shifted from the focus of the parabolic reflector. For the convenience of the experiment, the antenna and the parabolic mirror were placed in a styrofoam cube (Figure 13a). The measurements were carried out with a Planar CABAN R140 vector reflectometer in the frequency band of 0.5-3 GHz. To obtain a picture, scanning was carried out by moving the antennas along the stand with a step of 1 cm. In the first stage, scanning was carried out using an antenna with a parabolic mirror (Figure 13). The layout of the installation is also shown in Figure 13c, where 1 is a bench with sand, 2 is a caban R140 reflectometer, 3 is a wooden sample under study, 4 is an antenna element developed by this group of authors, and 5 is a parabolic mirror. Based on the received data of the reflected signal, an oscillogram was constructed. The restored oscillogram shows that the wooden sample was found (highlighted by an oval in Figure 13b). However, the quality of the received radio image is extremely weak against the background of signals reflected both from the upper boundary of the sand (1 in Figure 13b) and from  
Figure 11: Field distribution at a distance of 70 cm (**a**) and 90 cm (**b**) without the metamaterial. Figure 12: Stand with sand for the experiment, top view with a wooden plate (**a**) and without a wooden plate (**b**). the lower boundary of the box (2 in Figure 13b). Figure 13d also shows a one-dimensional cut in the area where the wooden sample was located. The second stage of the experimental study was scanning using the fabricated system with the metamaterial. The antenna and metamaterial were placed in a 10 cm-thick foam sheet. The metamaterial was fixed at a distance of 5 cm from the antenna (Figure 14a). Scanning was carried out in a similar way and in the same frequency band. Figure 14b shows the reconstructed georadiogram. The object is clearly visible in it (highlighted by an oval), and the upper boundary of the air-sand interface (1 in Figure 14b) and the lower boundary of the stand (2 in Figure 14b) are also clearly visible. Since this image was obtained without additional mathematical processing, the boundaries of the focusing system made of the metamaterial are clearly visible (3 in Figure 14b). Figure 14c also shows the scheme of the installation, which includes the 1 stand with sand, 2 caban r140 reflectometer, 3 wooden sample under study, 4 antenna element developed by this group of authors, and 5 four-layer metamaterial. The antenna and the metamaterial were placed inside the foam to maintain a distance of 5 cm between them. A comparison of the images obtained in two experiments shows the advantage of the system using the metamaterial. The desired object is seen much more clearly. In the third stage of the experimental study, two metal plates were placed above the object on top of the sand at a distance of 20 cm from each other; they imitated railway sleepers (Figure 15a). Scanning was carried out in a similar way with a step of 1 cm and in the same frequency band of 0.5-3 GHz. Figure 15b shows the reconstructed radiogram. In it, objects such as the metal plates (highlighted by blue circles) and the wooden object (highlighted by a red oval) were observed. Thus, the system created for geosounding shows its viability. Figure 13: Experimental study using a UWB antenna with a parabolic mirror photo stand (**a**), reconstructed image (**b**), scheme of the experimental setup (**c**), and one-dimensional section of the georadiogram (**d**).