A vehicle-mounted radar system for quick tunnel defection inspection

• Vehicle-mounted Multi-antenna Synthesized Ultra-wideband Ground-penetrating Radar. • Realization of multi-angle multi-direction rapid synchronous defect inspection. • Enables deep tunnel structural tunnel defect inspection. Ground-penetrating radar (GPR) has been widely used to detect concealed defects behind tunnel linings. However, the limited penetration capability of traditional GPR in complex media such as concrete constrains tunnel-lining inspection. This limitation makes it difficult to obtain clear images of deeper structures. Furthermore, achieving rapid, multi-directional, and multi-angle inspections with traditional methods is challenging, especially in operational tunnels. In this paper, a vehicle-mounted multi-antenna synthesized ultra-wideband (UWB) GPR system is designed for tunnel inspection. First, we introduce a synthesized UWB signal design method that uses a field-programmable gate array (FPGA) to dynamically generate transmit signals from 0.3 to 1.0 GHz. This approach balances inspection depth and resolution. Second, we propose a delayed phase-locked synchronization technique to achieve high-precision time synchronization between the transmitter and receiver. Additionally, we design a semi-elliptical antipodal Vivaldi antenna array that outperforms conventional designs and obtains higher-quality inspection data in real tunnel environments. We systematically verified the feasibility and effectiveness of the proposed system through four experiments, including reflection analysis of multi-material targets, non-contact detection of buried objects in sandy media, dynamic scanning-based imaging in tunnel structures, and identification and imaging of typical defects in complex tunnel environments. The experimental results demonstrate that the system can effectively detect various types of subsurface targets under non-contact conditions. In the future, the system is expected to provide an efficient solution for multi-directional, multi-angle, deep, and rapid tunnel defect detection, particularly in complex engineering scenarios such as operational tunnels.