3D Printing of Functional Metal and Dielectric Composite Meta‐Atoms

Abstract

VP has very good resolution but a much smaller palette of materials with higher on-average dielectric loss. A similar option to FDM is direct ink writing (DIW), where instead of a filament, functional inks are used. [2] DIW is heavily dependent on the material's viscosity, as the ink flow greatly affects the precision and resolution of the structure, and also determines if a supplementary curing system needs to be used. Inkiet (IJ) printing is a method that uses drops of liquid inks to form conductive patterns on surfaces. [3] Related to IJ is aerosol jet (AJ) printing, using ink droplets for structure fabrication and achieving a higher resolution. [4] Both of these techniques have produced great results for layer or multilayer structures, but truly 3D structures are beyond their scope.In general, FDM works well with many common thermoplastics including acetonitrile butandiene styrene (ABS), poly-lactic acid (PLA), high impact polystyrene (HIPS), and Nylon. Whilst these are all useful structural materials they are not electrically conductive and hence do not immediately lend themselves to the fabrication of antennas and waveguides for instance. Furthermore, not all these materials are good choices for high frequency electronics as they have rather more dielectric loss than is generally preferred. For example, there are reports of solely dielectric resonator antennas produced using FDM, [5,6] however the permittivity of these thermoplastics is generally too low to be of much value for such applications, unless loaded with fillers that can raise their dielectric constant. [7] In order to construct useful radio frequency (RF) devices, such as filters [8] and antennas, [9] conductors are essential to couple feeds, create antennas and form resonant structures. Many examples of conductive filaments have been demonstrated using thermoplastics loaded with particles, including carbon fiber, copper, and silver. [7,10] There are a number of issues faced when using these loaded filaments, from inherent drawbacks, such as relatively low conductivity and sensitivity to moisture, to technical shortcomings, including particles damaging or clogging extrusion nozzles. Whilst lower conductivity is not a barrier to their use, it does generally limit the performance of RF devices which require low loss. An extra complication arises when printing successive layers of conductive materials, resulting in a lower conductivity along the vertical direction (due to the reduced vertical contact between the extruded cylindrical filaments). [11,12] This anisotropic conductivity makes true 3D fabrication quite difficult and limited in scope.In this report, a novel fabrication method, based on casting Field's metal inside dielectric molds made via fused deposition modeling, is presented. Fused deposition modeling (FDM) has become one of the most common rapid prototyping methods. Whilst it generally produces good quality mechanical structures in thermoplastics, few reliable methods have been demonstrated that produce good quality 3D electrically c...

Interface of gallium-based liquid metals: oxide skin, wetting, and applications

“…This method has been widely used to fabricate liquid metal microchannels, antennas, [34][35][36][37][38][39] sensors, [40][41][42][43][44][45][46][47][48][49][50][51] electronics, 49,[52][53][54][55][56][57] conductors, 51,58,59 and 3D structures. [60][61][62] However, this method has some limitations, such as the need for extremely high pressure (B10 MPa) to fill a narrow channel (150 nm in width) or the possibility of trapping air, which can prevent the channel from being filled with the metal. The channel should also have an outlet to allow air to escape during liquid metal injection into the inlet.…”

3D Printing Materials and Techniques for Antennas and Metamaterials: A survey of the latest advances

“…There are also lower-loss thermoplastics available with similar r f properties, such as high-impact polystyrene (HIPS), with an r f of ~2.49 and a tan d of ~8.53 × 10 −4 ; polypropylene (PP), with an r f of ~2.03 and a tan d of ~1.45 × 10 −4 ; and cyclo olefin copolymer (COC), with an r f of ~2.24 and a tan d of ~2.17 × 10 −4 , which makes these materials attractive for RF applications. The dielectric properties of a range of different 3D-printable materials as a function of processing temperature and the r f versus the tan d can be found in [3]. As a general rule with 3D-printed dielectrics, it is important to measure the dielectric properties of test printed samples before fabricating a more complex design, as changes to the printer and its settings can affect the r f and tan d [4].…”

“…An innovative method to create embedded 3D conducting structures was to introduce air channels with an inlet and an exit hole [3] in the 3D-printed structure. These channels were then filled afterward with Field's metal, which has a melting temperature of 65 °C.…”

“…By using a fine 0.2-mm nozzle, repeatable printing of 0.4-mm channels could be achieved that did not leak. 3D resonant metamaterials were designed in this way [3].…”

Topological Flexible 3D Microwave Perfect Absorber

“…[32] Therefore, this study uses the 3D printing method of DIW to form the meta-structures by taking advantage of mathematical precision, high efficiency, and low cost in molding cyclical structures. [33][34][35][36] In this work, we integrate traditional wave-absorbing materials with metamaterials by matching flexible absorbing basement BM with woodpile-shaped 3D photonic crystals. DIW is employed to fabricate the 3D photonic crystals composed of polydimethylsiloxane (PDMS) matrix with either single concentration or coupled concentrations of absorbent.…”