From Retro-Reflection to Optical Camouflage

GEK1521/PC1326

Physics in the Life Sciences

From

Retro-reflection to

Optical Camouflage

Tr

Truong Son Ca

U081786A

Introduction

Invisibility has been long ago a quixotic desire of human beings and can only be seen in magical movies. However, the recent advances in optical and computing technology have pulled science nearer to magic. Initiated by a Japanese scientist, Professor Susumu Tachi in 2004, cloaking of invisibility has become a spotlight of many research projects at several top universities such as Tokyo University or University of California Berkeley. There are two types of approaches applied in invisibility technology including optical camouflage and meta-materials. This article only focuses on analyzing the former approach.

Optical camouflage takes advantage of retro-reflective material which bends the light rays back to their original sources with minimal light scattering. The first section of the article seeks to study retro-reflection, the critical physical principle behind optical camouflage technique. The second section demonstrates how optical camouflage enables the creation of invisible cloak while the third one points out some limitations of this technology. Last but not least, various real-world invisibility applications are described in details in the fourth section.

Reflection, Refraction and Retro-reflection

When light strikes a surface, or the interface between two different mediums, part of it returns to the original light source; the rest travels through the surface. The former event is called reflection, while the latter is refraction. More precisely, reflection happens when light is bended at a reflective surface and returns to where it comes from. Refraction refers to the change in wave direction when it travels from one to another medium due to the change in speed.

The mechanism of reflection and refraction relates to the characteristics of light. Light is considered as the wave of electromagnetic field....