3D printed non-resonant metamaterial components and circuits

3D printed non-resonant metamaterial components and circuit

Fused filament fabrication additive manufacturing and characterisation at Loughborough University for RF applications

This paper discusses the research related to 3D printed radiofrequency (RF) devices, using fused filament fabrication, carried out at Loughborough University. Different multidisciplinary aspects include the ability to 3D print unique shapes, the ability to tailor the infill to make functionally graded and heterogeneous substrates, characterizing the dielectric properties and how these materials can be used for antennas and other RF designs. </p

Experimental results for carbon nanotube-sheet based microstrip patch antenna

The paper presents the potential of carbon nanotube-sheet (CNS) for microstrip antennas. A 20 μm CNS was measured for conductivity using a single post dielectric resonator (SiPDR), and then a microstrip patch was fabricated on a Rogers RT5880 substrate. The measured results of the patch antenna showed good agreement with the simulated version using the CNS measured conductivity. Results were also compared to the simulated PEC version for comparison. </p

Optimization and experimental validation of a bi-focal lens in the microwave domain

The design of photonic devices is usually done through analytical modeling or variation in geometry and material parameters to obtain the required functionalities. Here, we report the use of topology optimization to obtain a bi-focal lens that concentrates the electromagnetic field at different spatial positions depending on the wavelength. Numerical inverse design is carried out to obtain the permittivity layout, satisfying this objective. The resulting device is then 3D printed using two low-loss dielectrics, and experimental field mapping at microwaves demonstrates the ability to enhance the field locally at distinct locations for two separate frequencies

Demonstration and control of “spoof-plasmon” scattering from 3D spherical metaparticles

Geometries that replicate the behavior of metal nanostructures at much lower frequencies via texturing surfaces so they will support a surface wave have been a central pillar of metamaterials research. However, previous work has focused largely on geometries that can be reduced to symmetries in one or two dimensions, such as strips, flat planes, and cylinders. Shapes with isotropic responses in three dimensions are important for applications, such as radar scattering and the replication of certain nanoscale behaviors. This work presents a detailed exploration of the scattering behavior of 3D spherical “spoof plasmonic” metaparticles, based on the platonic solids. Their behavior is compared to an effective medium model through simulation and experiment, and the vast range of behaviors that can be produced from a metal sphere of a given radius via tuning its internal structure is explored in detail.</p

3D printing materials and techniques for antennas and metamaterials: a survey of the latest advances

This is a review article of the latest advances in 3D printing for enabling new materials and new geometries for radio-frequency (RF) devices, antennas, and metamaterials. The article discusses the achievable material properties and various optimized applications that are achievable by creating new shapes in either dielectric or metal. This article demonstrates what is currently possible with additive manufacturing and the current limitations. Various additively manufactured RF devices are reviewed.</p

Multi-material additive manufacture and microwave-assisted sintering of a metal/ceramic metamaterial antenna structure

Multi-material metal/ceramic 3D structures comprising of metallic silver and ultra-low sintering temperature silver molybdenum oxide ceramics, have been additively manufactured and hybrid densified using microwave-assisted sintering for the first time. Optimum densification conditions at 440°C / 1 hour, resulted in relative permittivity, εr = 10.99 ± 0.04, dielectric losses, tanδ = 0.005 ± 0.001 and microwave quality factor, Q × f = 2597 ± 540 GHz. Applying 2 kW microwave energy at 2.45 GHz for 60 minutes, was proven sufficient, to densify the metallic Ag infilling electrodes, without causing any macroscopic defects. A fully functional multi-layered antenna structure with a metamaterial artificial magnetic conductor was designed, dual-printed and densified, to showcase the potential of combining multi-material additive manufacturing with microwave-assisted sintering.</p

Fabrication of artificial dielectrics via stereolithography based 3D-printing

In this research, stereolithography (SLA) based additive manufacturing (AM) has been investigated as a fabrication method for producing artificial dielectrics. Initially, the effect of the curing time on the microwave electromagnetic properties (X-band) on the photoinitiated resin used was measured and found to be negligible after 15 minutes of UV curing. Artificial dielectric isotropic and anisotropic lattice structures were then designed and fabricated, allowing for varying permittivity between 1.23 and 2.80 through the control of the structure’s density. As a demonstration of the ability to grade permittivity through a high-resolution printing process, lattice structures were embedded into solid substrates. The ability to do this allowed for the printing of a graded permittivity substrate which is showcased in a design for a circularly polarized patch antenna

Wide-range soft anisotropic thermistor with a direct wireless radio frequency interface

Temperature sensors are one of the most fundamental sensors and are found in industrial, environmental, and biomedical applications. The traditional approach of reading the resistive response of Positive Temperature Coefficient thermistors at DC hindered their adoption as wide-range temperature sensors. Here, we present a large-area thermistor, based on a flexible and stretchable short carbon fibre incorporated Polydimethylsiloxane composite, enabled by a radio frequency sensing interface. The radio frequency readout overcomes the decades-old sensing range limit of thermistors. The composite exhibits a resistance sensitivity over 1000 °C−1, while maintaining stability against bending (20,000 cycles) and stretching (1000 cycles). Leveraging its large-area processing, the anisotropic composite is used as a substrate for sub-6 GHz radio frequency components, where the thermistor-based microwave resonators achieve a wide temperature sensing range (30 to 205 °C) compared to reported flexible temperature sensors, and high sensitivity (3.2 MHz/°C) compared to radio frequency temperature sensors. Wireless sensing is demonstrated using a microstrip patch antenna based on a thermistor substrate, and a battery-less radio frequency identification tag. This radio frequency-based sensor readout technique could enable functional materials to be directly integrated in wireless sensing applications.</p

Synthesis and dielectric characterisation of a low loss BaSrTiO₃/ABS ceramic/polymer composite for fused filament fabrication additive manufacturing

Composite polymer/ceramic filaments for material extrusion-based fused filament fabrication additive manufacturing, using barium strontium titanium oxide (BST) ceramics and acrylonitrile butadiene styrene (ABS) thermoplastics were produced; their dielectric and physical properties have been characterised for the first time. The dielectric properties, relative permittivity (εr), quality factor (Q×f) and dielectric loss (tanδ) were measured as a function of ceramic solid loading (%) at 5 GHz for 3D printed samples. A relative permittivity εr = 6.05, Q×f = 10,433 GHz and dielectric loss tanδ = 0.007 were obtained for a BST/ABS ceramic polymer composite, with 50 wt% (15 vol%) solid loading. The composite materials exhibit reduced dielectric losses compared to standard laminates currently used in the radiofrequency (RF) and telecommunications industry. Based on polymer/ceramic composite filament, a prototype microstrip patch 5 G antenna and a hemispherical dielectric lens were designed and manufactured. Through testing, it shows good antenna performance with a centre frequency of f0 = 3.78 GHz and a (−10 dB) bandwidth of 90.6 MHz. The dielectric lens increased the antenna gain by 3.86 dBi.</p