Towards a 3D printed terahertz circuit technology.

Three-dimensional (3D) printing, also known as additive manufacturing, is now common place in many industries and is used widely. Some types of 3D printers are available for home use at modest cost. However, detailed work, together with demonstrator devices, is still in the very early stages in relation to the manufacture of microwave and terahertz circuits. These requires a level of precision and materials very different from the consumer products.

This proposal is to evaluate and improve the performance of 3D printing for microwave and terahertz passive and diode circuits through measurement, design and demonstration. These high frequencies, from 10 GHz to 1000 GHz, are used for free space communications, security sensing and remote monitoring of the Earth's atmosphere. The focus will be on evaluation of 3D printed circuits at frequencies above about 50 GHz, the small feature sizes required for these frequencies allows only the best printing process to compete; enabling the project to evaluate the most advanced 3D printing approaches. This exciting project will be the most comprehensive academic study worldwide to date.

A strong, experienced, national team, at the University of Birmingham and the STFC Rutherford Appleton Laboratory (RAL) will conduct the research in collaboration with several UK and international industry partners. The Communications and Sensing research group at Birmingham University have already demonstrated significant research in this area, with 3D printed devices published covering the frequency range 0.5 GHz to 100 GHz. The importance of this work has been recognised externally through prizes, invited international presentations and refereed academic publications. Birmingham's partners, the Millimetre Wave Technology Group in the RAL Space department, bring extensive expertise in precision manufacturing of conventional devices for these high frequencies, and knowledge of the demanding space and other requirements that the new 3D circuits must fulfil. RAL staff will conduct post processing of the 3D printed circuits and perform accelerated lifetime measurements under conditions of elevated temperature and humidity.

3D printed microwave and terahertz circuits will have an important beneficial economic impact on UK industry, not only because complex circuits become possible at low cost, but because new design approaches emerge because of the unique manufacturing. The applicants will both work on their own ideas, and closely with industrial partners, during the project. There are a number of hurdles to overcome before the technology becomes mainstream: this proposal tackles these challenges.

The advantages of 3D printing include the availability to rapidly generate novel circuits with complex shapes and multiple functions using low material volumes in a lightweight form. This enables reliable, low cost, superior performance circuits with less waste and reductions in lead time. Considerations to be addressed include the metal coating of polymer circuits which adds an extra step in the production, as well as potentially lower thermal stability and power handling of such circuits. If the polymer is used as a microwave dielectric, power loss may be a problem. For metal 3D printed circuits, power handling and thermal stability is good, but surface roughness may reduce device performance. These problems and others are addressed in the proposal with a methodical investigation based on the measurement of resonant waveguide cavities, the microwave equivalent of a tuning fork. Changes to the frequency and decay time indicate the quality of manufacture.

The project will inform industry and academia through a widely distributed technology development roadmap and external collaborative projects, as well as the provision of advice and guidance. Our finding will also be communicated to national and international colleagues through academic publications, and presentations at relevant conferences.

This project will have a strong impact on a range of industrial sectors. Microwave devices are ubiquitous in all industries and whatever sector is chosen examples of the importance of them can be given. Birmingham have extensive capabilities in terahertz communications (via joint EPSRC work with RAL) and automotive radar for autonomous vehicles and RAL have world class expertise in the space industry.

This project is about moving 3D printed technology, as applied to microwave passive components, efficiently into industrial use. To do this the basic manufacturing is evaluated and improved and device design principles developed. Demonstrators are produced with specific industrial collaborators. The project will have TRL levels 1-4, with collaboration with industry moving to TRL 5 with specific successful designs.

The demonstrators with specific industrial collaborators are an important part of the project; here industry will provide specifications. The demonstrators include:

1. Complex beam forming networks for airborne and satellite environment with integrated feedhorns, polarisers and filters
2. A 220 GHz frequency tripler.
3. A satellite communications orthomode transducer
4. 5G communications from end demonstrator
5. D band multiplexer with polarisation control.
6. Integration of horns, polarisers, OMT and filters with twits and bends in waveguide
7. 300 GHz screen printed filters

With a range of new, novel designs produced in the course of the work, the expectation is that some will be patentable and more will be capable of commercial exploitation.

As well as collaboration with industry on each of the above demonstrators, there is also the Birmingham industrial steering group which will oversees the project. This has members from TeraTech Components, Elite Antennas, BAE Systems, Jaguar Land Rover, Thales and DSTL. In this way, there is a very large industrial oversight to this project.

In addition to the direct industrial oversight/collaboration mentioned above, there is also indirect dissemination to industry through web pages, conferences, seminars, publications and importantly a road map for 3D printed microwave circuits written within the project and disseminated widely.

It can be seen that the potential for new, novel circuits is considerable, such circuits will improve system performance in a number of industries. This programme of research aims to develop the technology and principles of 3D printing and importantly inform industry of the advantages and practical ways forward in using the new manufacturing technique. By disseminating the principles as well as example demonstrators we aim to provide a unique route to impact with rapid take up of 3D printing where it is appropriate. It should be noted although we have given examples above of industrial interest, the manufacturing will be of considerable interest in a variety of microwave areas we are unable to comprehend at this time.