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Radar Cross-Section Reduction of the Nozzle of an Airborne Platform Using Lightweight Auxetic Metamaterials

A. Phanendra Kumar, Preeti Kumari, Dineshkumar Harursampath, Vijay Kumar Sutrakar

Abstract

The nozzle of an aircraft is a major source of radar scattering from the rear aspect of the aircraft, which undergoes higher operational temperatures. In order to reduce the radar scattering of these nozzles, high temperature radar absorbing materials (RAM) are essential. The thickness of these RAM typically increases to attain RCS reduction at lower frequencies, which subsequently leads to a higher weight of the structure. Therefore, this research study investigates the weight advantages of a star auxetic (SA) lattice made up of barium titanate to reduce the RCS of aircraft exhaust nozzles in the frequency range of 8-18 GHz. Modelling of SA with a complicated aircraft structure may lead to complexities in terms of Computer Aided Design and electromagnetic modelling and higher computational time for solving the electromagnetic problem using exact solvers. In order to simplify the computational problem, a homogenization and modified transfer matrix method is used to generate the RL performance. The RL from the proposed in-house tools is also compared with the Floquet port analysis. The RL performance obtained from the proposed method is also validated against experimental data. Comparative analyses are performed between SA and solid pure block (PB) barium titanate samples over 32761 SA and PB thickness combinations. Results show that selected SA samples with the same thickness achieve weight saving of approximately 60%, with 20dB lower RL than PB. The median RCS of the nozzle rear aspect also indicates that the SA-based barium titanate has an advantage in terms of weight penalty with similar or better RCS performance. The study demonstrates that auxetic metamaterials will be a multifunctional, lightweight, thermally stable, and radar absorbent structure for high temperature aircraft applications.

Radar Cross-Section Reduction of the Nozzle of an Airborne Platform Using Lightweight Auxetic Metamaterials

Abstract

The nozzle of an aircraft is a major source of radar scattering from the rear aspect of the aircraft, which undergoes higher operational temperatures. In order to reduce the radar scattering of these nozzles, high temperature radar absorbing materials (RAM) are essential. The thickness of these RAM typically increases to attain RCS reduction at lower frequencies, which subsequently leads to a higher weight of the structure. Therefore, this research study investigates the weight advantages of a star auxetic (SA) lattice made up of barium titanate to reduce the RCS of aircraft exhaust nozzles in the frequency range of 8-18 GHz. Modelling of SA with a complicated aircraft structure may lead to complexities in terms of Computer Aided Design and electromagnetic modelling and higher computational time for solving the electromagnetic problem using exact solvers. In order to simplify the computational problem, a homogenization and modified transfer matrix method is used to generate the RL performance. The RL from the proposed in-house tools is also compared with the Floquet port analysis. The RL performance obtained from the proposed method is also validated against experimental data. Comparative analyses are performed between SA and solid pure block (PB) barium titanate samples over 32761 SA and PB thickness combinations. Results show that selected SA samples with the same thickness achieve weight saving of approximately 60%, with 20dB lower RL than PB. The median RCS of the nozzle rear aspect also indicates that the SA-based barium titanate has an advantage in terms of weight penalty with similar or better RCS performance. The study demonstrates that auxetic metamaterials will be a multifunctional, lightweight, thermally stable, and radar absorbent structure for high temperature aircraft applications.

Paper Structure

This paper contains 16 sections, 8 equations, 12 figures, 4 tables.

Table of Contents

  1. Introduction
  2. Materials details and methodology
  3. Materials details
  4. Electromagnetic properties homogenisation
  5. Reflection loss evaluation using MTM
  6. Floquet port analysis
  7. RCS analysis
  8. Results and Discussion
  9. Validation of in-house Homogenisation-MTM computational tools with experimental and Floquet port analysis
  10. Validation of the MTM tool
  11. Validation of the combined tool (Homogenisation and MTM)
  12. Comparison of Reflection loss spectra of BTO-based samples
  13. Reflection loss spectra of flat PB and SA samples with the same thickness
  14. Reflection loss spectra of flat PB and SA samples with enhanced RL and bandwidth
  15. Radar cross-section of aircraft embedded with PB and SA with enhanced RL and bandwidth in the nozzle region
  16. ...and 1 more sections

Figures (12)

  • Figure 1: Schematic representing the flowchart of the methodology being implemented for evaluating the RCS of an aircraft when a star auxetic structure is attached to the engine nozzle.
  • Figure 2: Real and imaginary parts of the relative electric permittivity of annealed BTO in the X and Ku frequency band saini2016dual.
  • Figure 3: Schematic depicting the 2D representation of the periodic star-based auxetic unit cell in x and y directions.
  • Figure 4: Schematic represents the homogenised star auxetic layer of thickness d, with the free space medium on both sides of the homogeneous layer. The electromagnetic continuity conditions ($\bm{\Psi}$) at the interfaces of the layers are also represented appropriately. The absorber with metal backing, considered in the analysis for evaluating the RL spectrum, is also represented.
  • Figure 5: Open source CAD model of a fighter aircraft: (a) Isometric view, and (b) Side view. Nozzle is highlighted in Green colour.
  • ...and 7 more figures