Fabrication of flat Luneburg lens using functional additive manufacturing

Summary form only given. The Luneburg Lens offers an exciting and elegant solution to beam scanning and multiple beam forming that can be used to implement low resolution radar systems and high directivity wireless communications. Traditionally, these lenses have been created by aligning discrete layers of materials with varying effective permittivity to emulate the Luneburg dielectric distribution given by: e_r = e_s(2 - (r/R)²). To realize this graded permittivity distribution experimentally can be quite challenging. Traditional methods include subtractive manufacturing, which utilizes a computer numerically controlled (CNC) drill or milling machine to produce an array of voids within a homogenous dielectric material (Sato K. and Hiroshi U., Electronics and Communications in Japan, 85, 1-12). Spatially varying the local volume fraction of the voids results in an effective permittivity distribution. While subtractive methods achieve reasonably good electromagnetic performance, the resulting part is often too fragile for many practical applications. Other designs have employed metamaterials and transformational electromagnetics to reproduce the properties of the Luneburg lens. This approach, while quite interesting, often results in a narrow frequency band of operation. In this presentation we will describe an alternative fabrication methodology based on functional additive manufacturing. Commercial additive manufacturing systems or 3D printers create three dimensional (3D) structures by patterning consecutive layers of base material. Unfortunately, these current additive manufacturing techniques are limited in their base materials and not well suited for creating electromagnetically functionalized structures with graded EM properties. Recently our group has built a custom printer for realizing rigid substrates with embedded three dimensionally varying graded dielectrics (Roper D. et. al, Smart Materials and Structures, accepted for p- blication). Our system employs an ultrasonic powder deposition system (S. Yang and J. Evans, Powder Technology, 129, 55-60, 2004) designed to pattern high dielectric powders onto a low loss dielectric substrate. The powder dispenser acts like an ink jet printer head for dry powders. The powders - which could be high dielectric powders, magnetic powders, conductive powders or polymer powders - are injected under computer control onto a structurally reinforced substrate. To produce a 3D distribution of dielectric properties, multiple layers are patterned, aligned, stacked and post-processed (i.e. cured in an autoclave). The final sample is a solid structure with integrated 3D graded dielectric properties. With this system, we designed, fabricated and experimentally characterized a Luneburg Lens within a structurally rigid composite. In this presentation we will provide the design and characterization of our graded dielectric printer as well as the construction and analysis of the Luneburg Lens.