Wireless connectivity is becoming increasingly important in modern society with a forecast of several hundreds of millions of connected devices in the UK alone by 2022, carrying out more than a billion daily data transactions. A large part of these connections will be machine-to-machine (M2M) communications through the rapidly increasing Internet of Things (IoT) that will connect a large number of sensing devices for a wide range of applications. Depending on the application, these wireless connections will span a large area of the radio frequency (RF) and microwave spectrum, from low UHF to mm-wave bands. Compact wireless devices and sensors for IoT with enhanced capabilities and multiple functionalities are required in order to meet the demands of the envisaged systems. The development of new communication and sensing systems for aircrafts (including unmanned air vehicles - UAVs) and automotive vehicles is also becoming crucial for the successful deployment of the next generations of these platforms, such as autonomous air vehicles and driverless cars. Military and civilian aircrafts as well as automotive vehicles are required to cope with an increasing demand for radio frequency communication and sensing capability. With the current trend of increasing wireless connectivity functionalities both in air/automotive vehicles and in compact IoT devices, the size and number of antennas may end up defining the overall size, cost and/or power requirements (e.g. battery life in the case of IoT sensors) of the system. A promising solution to the challenges outlined above is the developing science of RF/microwave metamaterials. Metamaterials and metasurfaces are artificial structures capable of achieving electromagnetic properties and behaviours that are not available from natural materials. This proposal aims to develop new paradigms of multi-functional and tunable metamaterials that will enable the development of novel multi-functional antennas for the two major applications sectors mentioned above, namely IoT wireless devices and autonomous air/automotive vehicles. The outcomes of this work would place the UK at the centre of developments in this transformative area. Importantly, this proposal brings together a leading academic research group with key industrial partners who will help to shape the programme and shorten the lag between fundamental research and product development thus further increasing impact generation.

EPSRC have a delivery plan to align their portfolio to areas of UK strengths and national importance and have designated a number of 'Grow' areas. This application addresses two of these areas: 'RF and microwave communications' and 'RF and microwave devices', specifically matching the terahertz technology aspect of the latter. Why has EPSRC highlighted these areas? The answer is that society is evolving with a continuously increasing demand for the exchange of digital information. There is an expectation that everyone will be permanently connected to the Internet, no matter where they are. People are expecting that more information of a higher quality is delivered immediately: therefore newer services are requiring higher and higher data volumes and transfer rates. On demand video is an excellent example, with in-home delivery with standard definition now common place and demonstrations of new 4k on demand video now taking place. The data rates expected for these services are vast and the infrastructure needs adapt to cope. One way to achieve this is to move to higher frequencies for wireless links. We propose to demonstrate new building block components for such a communications system, designing and building these on an entirely new basis. A frequency of 300 GHz is chosen as it is at the cusp of technology; systems are now being deployed at frequencies below about 100 GHz where as systems approaching 1000 GHz are some years away because of the lack of active circuits. The components will also be applicable in radar and sensing scenarios. Once the individual components have been demonstrated, a full communications system will be designed, built and tested. There are very few demonstrations of communication systems at 300 GHz and the unique design methodology will provide a world-class demonstration. Three groups are collaborating in this project: the Fraunhofer Institute in Freiburg, Germany (IAF), and it the UK the Rutherford Appleton Laboratory (RAL) and Birmingham University. All partners have substantial design and measurement capabilities at these very high frequencies. IAF are world leaders in the production of submillimetre wave integrated circuits and will be supplying transistors for the amplifiers. RAL will deliver world class Schottky barrier and the University of Birmingham has advanced micromachining capabilities. At Birmingham a new interconnect principle has been developed to link the Schottky diodes and transistors. Instead of using wires and their analogues, hollow waveguide tube based resonant cavities will be used. Currently 300 GHz components are mounting in conventionally milled gold pated blocks. The required waveguide dimensions are about 0.8 mm by 0.4 mm. Although conventional milling machines can machine this, once internal structures for resonators are required, milling becomes difficult or impossible. A technology that can be used for the waveguide cavities, and for smaller resonators at higher frequencies, is micromachining. Birmingham University have demonstrated micromachined waveguides, filters, diplexers and antennas at and above 300 GHz. This technology is now ready for the next step, which is the inclusion of active and non-linear devices. The micromachining work at Birmingham has been done by a number of techniques, the primarily technique is by etching an ultraviolet sensitive photoresist called SU8. This allows a pattern to be defined photolithographically by a mask and then etching sections produces the waveguide. The final structure is made by bonding a number of SU8 etched layers together and then metal coating them. The performance of the SU8 waveguides has been shown to be as good as metal. Other techniques for micromachining circuits will be investigated in order to find the optimum solution.

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.

The last 20 years have witnessed a remarkable growth in the field of THz frequency science and engineering, which has matured into a vibrant international research area. The modern THz field arguably began with the development of a pulsed (single-cycle) THz emitter - the semiconductor photoconductive switch - and the subsequent development of THz time-domain spectroscopy (TDS). Since then, considerable success has been achieved in the further development of this and other THz sources, including the uni-travelling carrier (UTC) photodiode and the quantum cascade laser (QCL). However, notwithstanding this, it is only the THz-TDS technology that has been developed sufficiently for commercialization as a complete system, leaving other THz devices, components and techniques still restricted to the academic laboratory. This is unfortunate, since despite the success of THz-TDS, the technique has a number of shortcomings including its high fs-laser dominated cost, low power, and limited frequency and spatial resolution, which could be addressed by QCL and UTC technologies if they were to be engineered into appropriate instruments. In fact, a cursory comparison with the neighbouring microwave and optical regions of the spectrum reveals that THz frequency science and technology is still in its infancy, and not just in the context of commercial uptake. For example, the THz region significantly lags in the availability of precision spectroscopy instrumentation required to address sharp spectral features inherent to gases, for example, in atmospheric analysis, or in materials with long excited state lifetimes. THz technology also significantly lags in the fields of non-linear spectroscopy and coherent control, where powerful and controlled pulses of electromagnetic radiation interact with matter and manipulate its properties. In the optical and microwave regions, fascinating phenomena including electron-spin resonance and nuclear magnetic resonance were major breakthroughs, revealing a wealth of new science and engineering applications. These techniques, now standard across many disciplines, support much contemporary research and technology activity. A further example of how THz technology compares unfavourably with other spectral ranges is in the context of THz microscopy and analysis below the diffraction limit, which intrinsically restricts such measurements to ensemble sampling of physical properties averaged over the size, structure, orientation and density of, for example, nanoparticles, nanocrystals or nanodomains. Although near-field imaging approaches have been adapted from the visible/infrared regions enabling THz measurements on the micro/nano-scale, no THz instrument currently provides the required spatial resolution and sensitivity, nor can address the enormous range of length-scales (spanning five orders of magnitude from electron confinement lengths (<10 nm) to the THz wavelength (~300 um)), nor can operate at cryogenic temperatures. In fact, on this point, the THz field is deficient even in the provision of basic technologies such as waveguides and coupling optics required to deliver THz signals with low loss into cryostats or industrial apparatus. In this programme we will create the first comprehensive instrumentation for precise THz frequency spectroscopy, microscopy, and coherent control. This will be based upon our unique and proprietary capabilities to generate, and manipulate photonically, THz signals of unprecedentedly narrow (Hz) linewidth and with sub-wavelength spatial resolution. The instrumentation will then be exploited to create new challenge-led applications in non-destructive testing and spectroscopic analysis for electronics and atmospheric sensing, inter alia, as well as discovery-led opportunities within physics, quantum technologies, materials science, atmospheric chemistry and astronomy.