Additive manufacturing can reduce the time and material costs in a design cycle and enable the on-demand printing of customized parts. Recent advances in 3D printing technology now enable antennas and RF electronics to be designed and prototyped significantly faster than conventional manufacturing time scales. New multi-material 3D printers that can print both metal and dielectric materials enable the additive manufacturing of antennas and RF components. New printers and materials on the market now provide affordable access to RF rapid prototyping. Useful RF and antenna structures can be 3D printed which has the potential to revolutionize the design, supply and
sustainment phases of an acquisition program.
There are several reasons to consider using an additive manufacturing system to 3D print RF components. If you consider the range of available applications and the flexibility provided by an additive manufacturing system, RF component designers will have the ability to quickly tune, test, and optimize the design of new components to achieve high-performance applications that are the lightest weight and smallest physical volume possible.
In the defense and aerospace industries, outsourcing the manufacture of RF systems creates potential security concerns and sourcing concerns. Fabrication and assembly houses must be compliant with ITAR regulations, and they must be registered with the federal government in most cases. In addition, these outside manufacturers will charge a premium for quick-turn, low-volume rapid prototyping runs. R&D and NPI for unique RF components require high precision, low-volume manufacturing runs. Thus, working with an outside manufacturer early in the ideation process is cost and volume prohibitive. Relying on an outside, traditional PCB manufacturer, will also incur significant lead times, especially when creating complex electronics structures, ultimately slowing down the R&D process.
These concerns can be easily resolved when your fabrication and assembly capabilities are kept in-house. Companies with these capabilities can print their own RF components in a day rather than weeks, in a single step process without additional machining or assembling. Keeping these systems in-house also alleviates security and compliance problems that arise when working with an external manufacturer.
The flexibility provided by additive manufacturing does more than just alleviate sourcing, manufacturability, and security concerns. 3D-printed devices are not limited by the constraints of traditional manufacturing processes, giving designers the capability to design devices with unique geometries and capabilities. Designers can fine-tune the capabilities of their RF components without being limited by traditional PCB fabrication techniques, opening up huge potential for innovation in many sectors from consumer electronics to defense and space.
Control over Frequency, Sensitivity, and Form factor
Perhaps the most important aspect of designing RF components is tuning the operating frequency to lie in a specific band. With more specialized antennas or receiver designs, designers can tune the antenna to operate in multiple bands. Although dual-band antennas are available on the market, they easily exceed the costs of a 3D-printed circuit board and do not offer tunability to every frequency band.
RF circuit designers must consider the power received/transmitted, as well as the bandwidth of their device when optimizing their design and choosing an appropriate substrate material. The transmission line geometry—i.e., microstrip, stripline, or grounded coplanar waveguide—also influences the expected performance.
3D printing RF components directly onto a 3D-printed PCB offers designers the ability to tune the operating frequency to nearly any band within the limits of available materials. The impedance of the radiating/receiving conductor will depend on the trace geometry and substrate properties. Using an additive manufacturing system allows designers to quickly experiment with many different trace geometries, ground plane designs and other design techniques with the goal of optimizing return/insertion loss and radiated power in the desired frequency band.
With antennas, as the RF carrier frequency increases, the thickness required for a highly sensitive antenna decreases and can eventually reach the resolution limit for the printer. The electromagnetic field can only penetrate a few skin depths into the conductor, thus the effective thickness of a printed conductor should not significantly exceed the skin depth (e.g., 2 μm of silver at 10 GHz).
When selecting an additive manufacturing system for RF components, you’ll need to take the printer’s vertical resolution limits and the conductivity of your printed conductors into account to maximize the sensitivity of your component. Compared to fused deposition molding, where the printing resolution is limited by the nozzle aperture, inkjet 3D printers that use nanoparticle conductive inks provide superior resolution, in the order of a few microns. This makes inkjet printing ideal for printing conductors for high-frequency, high-performance RF components.
Finally, 3D printing allows fabrication of RF components on PCBs with a unique footprint or even non-planar geometry. This allows the shape of a component to be adapted to the shape of its enclosure, rather than being constrained by packaging compromises. Lamination and cutting procedures that are normally used with traditional PCB manufacturing processes are not needed, which decreases product development time and ultimately time to market.
Georgia Tech Researchers demonstrate Capabilities of the Voxel8 Printer
The Voxel8 Developer’s Kit is a low-cost 3D printer capable of 3D printing in two materials: PLA and conductive silver ink, with the PLA stored in the base of the printer and the ink located directly in the printhead itself. Sounds simple, but the Developer’s Kit opens up a huge range of possibilities. With it, the startup has already been able to construct some extremely impressive objects. For instance, at CES, the company will be displaying, alongside their amazing printer, a quadcopter produced almost entirely in one piece from their machine. The PLA and connective circuits of the quadcopter were 3D printed in one go, with the electronics, battery, and motors inserted throughout the printing process. The benefits of such a process are almost endless.
As Voxel8 Business Director, Daniel Oliver, explains, “Effectively, you could build a quadcopter with any geometry you want, stuff it with the components – on the motor- and the board-side – and, basically, have a fully functioning quadcopter without any wiring harnesses.” He continues, “People will also be able to start creating circuits on their desks. So, if you wanted to test out a circuit design, you could print out a circuit board directly on your desk. You’d have to stuff the components in, as you were doing it, but we’ve shown that you can print out what is basically an Arduino board on our printer.”
Georgia Tech Researchers designed three example components using Voxel8 printer to validate the performance of the tools and hardware: an L-band balun, an S-band antenna array and a Ku-band antenna element.
Developments in software are critical to leveraging this capability; good tools allow more effort to go towards creation than implementation. Several existing tools and sites provide the ability to customize mechanical structures; this concept is expanded into the RF domain with software that uses a high-level design parameter to create the circuit, model the performance, and create Computer Assisted Manufacturing
(CAM) files. By intelligently leveraging this process, the design can be readily updated or customized after the initial development.
A Computer Assisted Drafting (CAD) tool may further modify the structure to customize the mechanical interface and a machine toolpathing code (a slicer) is used to translate the CAM files to a format the printer can use. The final software tool needed is a machine toolpathing algorithm (slicer) to translate the mechanical CAM files into the machine control language of the 3D printer.
The plastic used for these prints is polylactic acid (PLA), which is popular for prototyping in part because it has less toxic fumes than other plastics. The initial measurement used a focused beam system to measure the permittivity for four colors of PLA, each approximately 3.1 mm thick. These values were validated with a coaxial airline technique and through the measure-model agreement of the various RF circuits.
Voxel8 Standard Silver ink, a room-temperature-curing silver conductive ink, was used for these prints. The vendor lists the DC conductivity as 3.45 MS/m. A 250-m-thick board with a 1.5-mm-wide, 71-mm-long microstrip line constructed and measured to back out the conductivity of the silver ink showed good agreement using 3.45 MS/m in a simulation that agrees with the measurement. For reference, pure silver has a conductivity of 61 MS/m.
When designing printed circuit boards, it is common to consider the trace and space tolerances; that is, the accuracy to which one can maintain a desired trace width and the gap between traces. Because the 3D printer deposits the ink with a 0.25-mm nozzle, it should be expected that small traces might not print as designed. The vendor recommends 0.5-mm lines for general prints (two passes); however, RF circuits generally require more design flexibility.
CAES and SWISSto12 Launch Strategic Alliance for 3D Printed RF Technology
CAES, the leading provider of RF technologies and related mission critical electronic solutions, and SWISSto12, the leading provider of 3D printed technology for RF applications in the aerospace and defense industry, announced in April 2021 a strategic alliance to enable CAES to bring additive manufacturing and 3D printing technology to US customers.
“We are proud to offer this innovative technology to leading US aerospace and defense primes,” said David Young, Chief Technology Officer, CAES. “This alliance enables fully trusted next-generation RF solutions for our customers that require the highest level of security, including Department of Defense and classified applications. Through the transfer of best-in-class technology to a US market leader, leading aerospace and defense primes will now be able to deploy this technology on key programs requiring RF, microwave and millimeter wave innovation. Our decades-long relationships with our prime customers and our track record of successfully delivering on our programs, combined with SWISSto12 ’s market-leading additive manufacturing intellectual property and flight heritage in space, electronic warfare and other applications will ensure that the US government can fully exploit this emerging technology,” he continued.
Additive Manufacturing (AM), or 3D printing, for RF systems requires high precision formats and complex geometries that allow form factors and performance that cannot be achieved with standard manufacturing solutions. Integrated subsystems that combine multiple components in one single homogeneous part that reduces weight and complexity, a key favor for prime companies where cost and space are at a premium. SWISSto12 pioneered the development of tailored and patented AM technologies aimed at delivering advanced RF performance, size and weight savings as well as product competitiveness through optimized manufacturing tolerances, surface finishes, plating techniques and RF designs. The technology and associated products address the increasingly challenging size, weight, power and cost (SWaP-C) requirements of defense prime contractors.
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