ObjectiveAccurate velocity measurement of high-speed projectiles, such as those launched by electromagnetic guns or artillery systems, is essential for evaluating weapon performance in terms of range, trajectory stability, and terminal effects. Traditional photoelectric velocimetry technologies, including laser screens, radar, and high-speed photography, face severe limitations in environments with plasma, smoke, and electromagnetic interference. For instance, visible and infrared wavelengths are strongly attenuated by smoke and high-temperature backgrounds, while microwave-based systems exhibit poor plasma penetration and susceptibility to low-frequency noise. Additionally, X-ray methods, though penetrative, suffer from bulky equipment and radiation hazards. To address these challenges, this study proposes a terahertz-based velocimetry system that leverages the unique advantages of terahertz waves (0.1-10 THz), including their ability to penetrate plasma and smoke, immunity to electromagnetic interference, and non-ionizing safety. The research aims to establish a compact, high-precision measurement framework capable of operating in complex battlefield environments.
MethodsThe proposed system integrates a single terahertz source (94 GHz) with a multi-channel AlGaN/GaN high-electron-mobility transistor (HEMT) detector array. The terahertz wave is generated by a Gunn diode and collimated using a conical horn antenna and polytetrafluoroethylene (PTFE) lens, achieving a narrow beam divergence of 0.1 mrad and a gain of 34.5 dBi (
Fig.5). The detector array comprises 50 pixels with a 3 mm pitch and 110 GHz sensitivity, designed with silicon lens-coupled non-symmetric dipole antennas to enhance signal capture efficiency. A hybrid Gaussian quasi-optical-Poisson point positioning (GQ-PPP) algorithm is developed to resolve terahertz diffraction effects and beam divergence. This algorithm processes the "W"-shaped voltage response generated by the detector array, identifying local maxima (Poisson points) within filtered signal intervals through Savitzky-Golay filtering and arithmetic averaging (
Fig.3,
Fig.7(c)). The system’s compact architecture reduces optical components by 50% through a single-source multi-channel illumination strategy, supported by lithium battery power and modular signal processing units to minimize environmental interference. Experimental validation combines numerical simulations—modeling Gaussian beam propagation and diffraction effects (
Fig.2,
Fig.4)—with laboratory tests using a motor-driven aluminum foil target to replicate
3000 m/s projectile motion under controlled conditions.
Results and DiscussionsThe GQ-PPP algorithm effectively suppresses terahertz diffraction, enabling precise time-stamp extraction from the "W"-shaped voltage response (
Fig.3). Geometric correction for beam divergence, derived from Gaussian beam propagation theory (Eq.11), reduces velocity errors from >10% to 0.83% at
3000 m/s (
Tab.1). Laboratory tests demonstrate corrected velocities with a maximum error of 0.288% across a 3.5-4.5 m measurement range (
Tab.1). The system achieves 0.1 mrad beam collimation and a 40% volume reduction compared to conventional laser-based setups (
Fig.5). Key innovations include the integration of terahertz penetration capabilities with high-speed HEMT detectors and the miniaturized architecture, resolving the traditional trade-off between beam collimation and energy density. Error analysis identifies spatial misalignment (e.g., ±0.1 mm detector pitch error contributing 0.167% velocity error) and beam divergence calibration as primary error sources. These errors are mitigated through high-frequency sampling (10 MHz), adaptive signal filtering, and laser-assisted alignment techniques. The system’s robustness is further validated through repeated experiments, showing an average relative error of 0.83% under varying propagation distances and target size. The terahertz wave’s longer wavelength (3.2 mm) inherently reduces sensitivity to small-scale environmental disturbances, while the HEMT detector’s pW-level sensitivity ensures reliable signal detection even in low-power scenarios.
ConclusionsThis study establishes a robust terahertz interception velocimetry framework for high-speed projectile measurement in complex environments. By combining terahertz wave advantages, HEMT detector arrays, and the GQ-PPP algorithm, the system achieves sub-1% velocity errors, outperforming traditional photoelectric methods in terms of penetration, accuracy, and portability. The compact design, enabled by single-source multi-channel architecture and lithium battery power, demonstrates significant potential for field deployment. Future work will focus on high-density detector arrays to improve spatial resolution, FPGA-based real-time processing for dynamic target tracking, and field testing under realistic battlefield conditions to validate practical reliability. These advancements position terahertz velocimetry as a transformative technology for military and industrial applications requiring high-precision measurements in adverse environments.