Thin and lightweight radar absorbing structure with periodic pattern surface using PEDOT:PSS based conductive paste

Abstract

The need for the development of radar absorbing technology is emphasized as the expansion into various fields even in economical and industrial perspectives, as well as military purposes. The objective of this paper is to develop a thin and lightweight radar absorbing structure for various applications where radar absorbing characteristics are required but the system performance and efficiency is closely related to the weight increase of the structure. Radar absorber with periodic structure using resistive materials can make lightweight absorber, and a thin absorber is also realizable through the various impedance control of periodic structure. Therefore, study on the radar absorbing structure with periodic pattern surface using conductive paste was conducted. The electromagnetic wave theory, radar absorber principle, and design methodology were investigated to study radar absorber. Also, the methods to evaluate the electromagnetic characteristics of radar absorber were organized. First, the reflection and transmission characteristics of normal incidence and oblique incidence at the planar boundary were understood. Next, the radar absorber was converted to the transmission line model and an equivalent input impedance to define the zero-reflection condition of impedance matching for radar absorber design. Lastly, the experimental methods to evaluate the electromagnetic characteristics of composite materials and radar absorbers were organized. A study to develop resistive lossy material using conducting polymer for radar absorber with periodic structure was conducted. First, the conductive paste was developed using a PEDOT:PSS polymer with high con-ductivity and polyurethane binder with excellent mechanical property. Next, the experiments using various addi-tives were conducted to improve mechanical and electrical properties of the synthesized paste. Also, the function and effect of each solvent were verified and an optimum fabrication process was derived. Finally, the chemical and morphological analyses were conducted to identify the conductivity enhancement in the PEDOT:PSS film by DMSO solvent and the mechanism of conductivity increase were explained and suggested. A Salisbury screen absorber was designed, fabricated and its radar absorbing characteristics was meas-ured in order to evaluate the applicability of the developed PEDOT:PSS based conductive paste. The fabricated radar absorber had outstanding radar absorbing performance and the applicability of the conductive paste was sufficiently verified. Next, environment tests of temperature and UV radiation were conducted in order to assess the environmental stability of the paste. According to the results, the surface resistance had no significant changes and remained almost constant up to the maximum surface temperature of $130^\circ C$. However, the surface resistance continued to increase with the increase in time duration of the exposure to UV-A. A study to design a thin and lightweight radar absorbing structure using periodic pattern surface was conducted. First, the principle and design method of radar absorber with periodic structure was organized and design parameters were defined to satisfy the zero-reflection condition of impedance matching. Next, radar ab-sorbing performance difference between various pattern shapes was analyzed and oblique angle stability between various pattern shapes was investigated using the optimization function of the CST-MWS program. Lastly, a thin and lightweight radar absorbing structure using square PPS was designed, which had a substrate thickness of 1.6 mm, a resonance frequency of 10.0 GHz, and - 10 dB bandwidth of 2.5 GHz between 9.0 and 11.5 GHz. The concept of radar absorbing wind turbine blade that can solve the problem of radar signal interference was proposed. First, radar absorbing structure with PPS was designed and fabricated, and the reflection loss was measured to assess the performance. The fabricated RAS had a resonance frequency of 10.1 GHz, a reflection loss of - 34.6 dB, and - 10 dB bandwidth of 4.2 GHz within the X-band. Next, radar absorbing wind turbine blade with PPS using conductive paste was manufactured and radar cross section was measured. The RCS of fabricated stealth wind blade was reduced over 90 % for the whole azimuth angle range. Moreover, the RCS reduction of the suction part at $78^\circ$ and the pressure part at $280^\circ$ was more than 94 % and 83 % in the whole X-band, respectively. Therefore, the wind turbine blade with periodic pattern surface minimizing radar signal interference was developed.