BACKGROUND Three-dimensional (3D) printing, known more formally as additive manufacturing, has become the focus of media and public attention in recent years as the decades-old technology has at last approached the performance necessary for direct production of end-use devices. The most popular forms of standard 3D printing include vat photopolymerization, powder bed fusion, material extrusion, sheet lamination, directed energy deposition, material jetting, and binder jetting, each creating parts layer by layer and offering different options in terms of cost, feature detail, and materials. Whereas traditional manufacturing technologies, such as casting, forging, machining, and injection molding, are well suited for mass production of identical commodity items, 3D printing allows for the creation of complex geometric shapes that can be mass-customized, because no die or mold is required and design concepts are translated into products through direct digital manufacturing. Furthermore, the additively layered approach enables the merging of multiple components into a single piece, which removes the requirement for subsequent assembly operations. Recently, the patents for the original 3D printing processes have begun to expire, which is resulting in a burgeoning number of low-cost desktop systems that provide increased accessibility to society at large. Industry has recognized the manufacturing advantages of these technologies and is investing in production systems to make complex components for jet engines, customized bodies for cars, and even pharmaceuticals. Although standard 3D printing technologies have advanced so that it is now possible to print in a wide range of materials including metals, ceramics, and polymers, the resulting structures are generally limited to a single material, or, at best, a limited number of compatible materials. ADVANCES For the technology to become more widely adopted in mainstream manufacturing, 3D printing must provide end-use products by fabricating more than just simple structures with sufficient mechanical strength to retain shape. Recently, research has resulted in the capability to use new materials with commercial 3D printers, and customized printers have been enhanced with complementary traditional manufacturing processes, an approach known as multiprocess or hybrid 3D printing. Collectively, these advancements are leading to fabrications that are not only geometrically complex, but functionally complex as well. By introducing the robotic placement of components, micromachining for intricate detail, embedding of wires, and dispensing of functional inks, complex structures can be constructed with additional electronic, electromagnetic, optical, thermodynamic, chemical, and electromechanical content. OUTLOOK Multiprocess 3D printing is a nascent area of research in which basic 3D printing is augmented to fabricate structures with multifunctionality. Progress will lead to local manufacturing with customized 3D spatial control of material, geometry, and placement of subcomponents. This next generation of printers will allow for the fabrication of arbitrarily shaped end-use devices, leading to direct and distributed manufacturing of products ranging from human organs to satellites. The ramifications are substantial, given that 3D printing will enable the fabrication of customer-specific products locally and on demand, improving personalization and reducing shipping costs and delays. Examples could include replacement components for grain-milling equipment in a remote village in the developing world, biomedical devices created specifically for a patient in a hospital before surgery, and satellite components printed in orbit, thus avoiding the delays and costs associated with launch operations. The automotive, aerospace, defense, pharmaceutical, biomedical, and consumer industries, among others, will benefit from the new design and manufacturing freedom made possible by multiprocess 3D printing.

http://science.sciencemag.org/content/sci/353/6307/aaf2093.full.pdf

Multiprocess 3D printing for increasing component functionality.

3D printed microfluidics and microelectronics

This paper reports on the design, fabrication and characterization of a 3-D printed RF front end for a 2.45 GHz phased array unit cell. The printed unit cell, which includes a circularly-polarized dipole antenna, a miniaturized capacitive-loaded open-loop resonator filter and a 4-bit phase shifter, is fabricated using a direct digital manufacturing (DDM) approach that integrates fused deposition of thermoplastic substrates with micro-dispensing for deposition of conductive traces. The individual components are combined in a passive phased array antenna unit cell comprised of seven stacked substrate layers with seven conductor layers. The measured return loss of the unit cell is ${>}12$ dB across the 2.45 GHz ISM band and the measured gain is ${-}11$ dBi including all components. Experimental and simulation-based characterization is performed to investigate electrical properties of as-printed materials, in particular the inhomogeneity of printed thick-film conductors and substrate surface roughness. The results demonstrate the strong potential for fully-printed RF front ends for light weight, low cost, conformal and readily customized applications.

A 2.45 GHz Phased Array Antenna Unit Cell Fabricated Using 3-D Multi-Layer Direct Digital Manufacturing

The performance of additive manufactured (AM) RF circuits and antennas is continuously improving, and in some cases these AM components are comparable to state-of-the-art circuits made with traditional manufacturing techniques. Medium to high-power waveguides made with AM methods such as copper-plated plastics, selective laser melting (SLM), and copper additive manufacturing (3-D CAM) have shown good performance up to terahertz frequencies. In this paper, binder jetting (BJ) metal printing is characterized using electron beam microscopy [scanning electron microscopy (SEM)] and energy dispersive spectroscopy. The RF performance of the 3-D-printed circuits is benchmarked with Ka-band cavity resonators, waveguide sections, and a filter. An unloaded resonator $Q$ of 616 is achieved, and the average attenuation of the WR-28 waveguide section is 4.3 dB/m. The BJ technology is tested with a meshed parabolic reflector antenna, where the illuminating horn, waveguide feed, and a filter are printed in a single piece. The antenna shows a peak gain of 24.56 dBi at 35 GHz.

Ka-Band Characterization of Binder Jetting for 3-D Printing of Metallic Rectangular Waveguide Circuits and Antennas

This paper presents the design and fabrication of low loss, weight, and cost prototypes in groove gap waveguide technology at Ka-band, manufactured with a metallized 3-D printing technique. A wide analysis of loss mechanisms and printing imperfections has been conducted, as well as the effect of temperature on structural deformations. Metallized 3-D printed and CNC machined prototypes have been compared and characterized with simulations and measurements at a band from 28 to 30 GHz. The average measured losses for metallized plastic prototypes are 1.4 dB/m.

Groove Gap Waveguide in 3-D Printed Technology for Low Loss, Weight, and Cost Distribution Networks

Digital additive manufacturing (AM) is emerging as a promising technology for next-generation RF systems. AM processes that combine multiple materials in a single build and can produce volumetric designs are especially interesting for 3D structural electronics. This paper reports on 3D AM fabricated components for a 2.45 GHz RF front end, specifically a circularly-polarized dipole antenna, a miniaturized capacitive-loaded open-loop resonator filter and a switched-line phase shifter. The printing process integrates fused deposition of thermoplastic substrates with micro-dispensing for deposition of conductive traces. These initial results demonstrate the strong potential for fully-printed RF front ends for light weight, low cost, conformal and readily customized applications.

3D multi-layer additive manufacturing of a 2.45 GHz RF front end

This paper describes a study of dielectric and metallic 3D printing (additive manufacturing) processes that are candidates for digital manufacturing of integrated mobile phone client antennas. The integration of antennas into the packaging of commercial electronics is one of the important applications of emerging digital manufacturing techniques. A novel test fixture for in-situ characterization of digitally manufactured integrated antennas and handset covers is presented along with experimental results for prototypes that were manufactured using different printing processes.

Nicholas Arnal

Papers

A 2.45 GHz Phased Array Antenna Unit Cell Fabricated Using 3-D Multi-Layer Direct Digital Manufacturing

3D multi-layer additive manufacturing of a 2.45 GHz RF front end

3D digital manufacturing and characterization of antennas integrated in mobile handset covers