3D printed terahertz circuits boost for 5G comms and satellite sensors

Car radars, 5G communication systems and satellite-based atmospheric sensors could all be improved as a result of a UK project to develop 3D printed terahertz and microwave circuits.

By Helen Knight
https://www.theengineer.co.uk/3d-terahertz-circuits/

Although 3D printing is widely used in many areas of manufacturing, its use in microwave and terahertz circuits has so far been limited by the level of precision required to build devices at such a small scale.

However, the accuracy of 3D printers has significantly improved in recent years, with some now able to print down to a resolution of five microns or less, according to Michael Lancaster at Birmingham University, who is leading the EPSRC-funded project.

So the research team are aiming to work with 3D printing companies to design and print novel devices at these small scales, he said. By using 3D printing techniques, the researchers hope to rapidly generate novel circuits with complex shapes and multiple functions in a lightweight form, without producing large amounts of waste material.

This should result in reliable, low cost circuits with improved performance, and faster manufacturing lead times.

The project will focus on 3D printed circuits at frequencies above 50GHz, which are typically used for free space communications, security sensing and remote monitoring of the Earth’s atmosphere.

“The immediate applications are 5G communications and car radar, which has frequencies well above 100GHz, and so we’re working with Jaguar Land Rover,” said Lancaster. “In this particular project we’re also working with Rutherford Appleton Laboratory (RAL), who are interested in atmospheric sensing: putting these things on satellites to look down at the atmosphere, to study the weather and other atmospheric conditions,” he said.

The researchers are particularly interested in the filters and other metal components found alongside the antenna and electronics on terahertz and microwave circuits, said Lancaster.

“As the devices go up in frequency these components get more difficult to make,” said Lancaster.

Rather than buying in their own 3D printers, which would no longer be at the cutting edge of the technology by the end of the three-year project, the researchers are buying in printing services from specialist companies.

“We’re looking for the best companies around the world who can print things very accurately,” he said. “At the moment we are talking to a company called 3D MicroPrint in Germany, and Swissto12 in Switzerland.”

Ultrathin and flat graphene metalenses gain morace properties

Lenses made of graphene and precisely pierced gold sheets are able to concentrate terahertz beams to a spot, flip its polarization and modulate its intensity.

https://www.sciencedaily.com/releases/2017/11/171127124731.htm

On the quest for miniaturization, scientists at the Center for Integrated Nanostructure Physics, within the Institute for Basic Science (IBS, South Korea), in collaboration with researchers from the University of Birmingham and the Korea Advanced Institute of Science and Technology (KAIST), develop credit card-thick, flat lenses with tunable features. These optical devices, made of graphene and a punctured gold surface, could become optical components for advanced applications, such as amplitude tunable lenses, lasers (i.e. vortex phase plates), and dynamic holography.

Metasurfaces are new 2D materials that can effectively control the electric and magnetic components of light (and other electromagnetic waves) and bend them to bespoken directions. Controlling the beam's direction can bring out interesting phenomena; the most incredible being the "invisibility cloak effect," where light waves bypass an object recreating the image beyond the object, as flowing water in a river would bypass a stone.

Published in Advanced Optical Materials, the study presents the properties of a metasurface which works as a convex lens. Specifically, it is made of a gold sheet pierced with micrometer-sized U-shaped holes and covered with graphene. As the shape of common convex lenses allows light to be concentrated on a spot (or focus), think about a magnifying glass which can concentrate a light beam and even start a fire, so the particular pattern of the tiny apertures of the metalenses works by focusing the incoming beam.

In addition, these microholes can also change light polarization. While natural light is generally unpolarized before being reflected, the team used circularly polarized waves, that is a light beam where the direction of the electric field is corkscrew spiraling. This metalens can convert the left-circular polarization wave (going counterclockwise if seen straight in front) to right-circular polarization (clockwise). The researchers managed to obtain a conversion rate of 35%. Converting circular polarization could be useful in a number of fields, for example biosensing and telecommunications.

In order to control even more properties, the scientists took advantage of graphene's unique electronic features and used them to tune the output beam's intensity or amplitude. Here graphene plays the role of the exposure of a camera. In the case of the camera, a mechanical control allows a certain shutter's opening time and size to determine the amount of light entering the instrument. These metalenses instead, regulate the exposure via an electric tension applied to the graphene sheet, without the need for bulky components. When voltage is applied to the graphene layer, the output beam becomes weaker. "Using metalenses, you can make microscopes, cameras, and tools used in very sensitive optical measurements, much more compact," clarifies Teun-Teun Kim, the first author of the study.

The metalenses were designed for a type of electromagnetic wave, which falls in-between infrared radiation and microwave radiation, called terahertz radiation. This type of radiation can pass through some materials (like fabrics and plastics), but at a shorter depth than microwave radiation, for this reason it is employed for surveillance and security screening.

"While conventional optical lenses have a thickness of several centimeters to several millimeters, this metalens is just a few tens of micrometers thick. The intensity of the focused light can be effectively controlled and it could find useful applications in ultra-small optical instruments," highlights the scientists.Teun-Teun Kim, the first author of the study.

University of Birmingham -Research Fellow on an EPSRC-funded project Terahertz Technology for Future Road Vehicles

http://brightrecruits.com/job/6889/research-fellow-on-an-epsrc-funded-project-terahertz-technology-for-future-road-vehicles

Research Fellow on an EPSRC-funded project Terahertz Technology for Future Road Vehicles

£28,695 to £39,685 per annum | Central England | 03 Dec 2014

Starting salary for this post is between £28,695 and £37,394 per annum with potential progression up to £39,685 a year once in post subject to satisfactory performance.

The post is a Fixed Term Contract - Post is available for up to 36 months.

Applications are invited for a three-year full-time research position in the School of Electronic, Electrical and Computer Engineering at the University of Birmingham, to undertake research in the area of mm-wave and Terahertz antennas and beamformers. The large-scale four year project is funded by EPSRC and addresses the different aspects of antenna technologies, fabrication procedures and systems integration aspects for use in vehicles and unmanned mobile platforms using sub-mm or low THz waves (300 GHz to 1 THz).

The overall aim of this cutting edge project is to lay the fundamental scientific foundations and develop new antenna technologies for automotive radar imaging systems. This will require undertaking theoretical and applied research, involving experimental studies, simulation and modelling. The research aims to determine suitable antenna and beamformer structures for a range of automotive applications of low THz imaging systems, based on cost effective fabrication processes, which will lead to prototype demonstrators and testing in representative systems.

The Research Fellow will work closely with other Research fellows focusing on micromachining fabrication processes and on radiowave propagation and remote sensing. In addition, the post requires close liaison with prestigious industrial partners for integration of the research results and prototypes with existing state of the art sensing technologies.

The project will take place in the Wireless Communications, Remote Sensing and Emerging Device Technologies research groups, where the underlying science, the new technologies and the applications of low THz EM waves are an increasingly important part of the research strategy, which is strongly backed by UK and EU funding. The involvement of major international companies further highlights the importance of the research and the potential impact that can be generated by cooperative work on fundamental research questions.

Person Specification:

The post is available for both UK/EU and international candidates (subject to work permit approval), who should have, or expect soon to obtain, a PhD degree in electronic engineering or physical sciences, ideally with previous experience of conducting research in antenna design, microwave engineering or computational electromagnetics. A mixture of theoretical, experimental and computational skills, as well as mm-wave related expertise will place an applicant in a particularly strong position.

How to apply: 

To download the details of this position and submit an electronic application online please visit hr.bham.ac.uk/jobs, quoting Job Ref in all enquiries. The applicant is required to upload a covering letter, a brief statement of research interests (describing how past experience and future plans fit with the advertised position), CV and the details of two referees as part of his or her online application.

Informal enquiries may be addressed to the project leader Dr. Peter Gardner (p.gardner@bham.ac.uk), or, specifically to the work package investigators Dr. Alex Feresidis (a.feresidis@bham.ac.uk).

Closing date:  5^th January 2015

University of Birmingham-Terahertz waveguide circuits laboratory

http://www.birmingham.ac.uk/research/activity/eese/systems-devices/edt/terahertz-waveguide-circuits-lab.aspx

Terahertz radiation is electromagnetic radiation with a frequency above the RF and microwave region and extending towards the optical. It is an area of the electromagnetic spectrum which is under used at the moment due to the difficulties in producing practical components and systems. However, it is well known that terahertz will be important in the future for many applications. In this laboratory terahertz circuits are designed and tested.

The laboratory is led by Professor Lancaster.

Terahertz radiation has five primary properties for applications: (i) it is able to pass through dielectrics such as paper, plastic, cloth, wood, ceramics and silicon, which are also common packing materials, (ii) metals are highly reflective in the terahertz region; (iii) many chemical and biological agents have unique spectral fingerprints in the terahertz frequency region and (iv) compared with X-rays, terahertz radiations do not present health hazard to people being scanned or to people operating the scanned systems (v) Large bandwidths are available for communications systems. Due to these advantages, there is an increasing interest in terahertz frequencies and many companies and universities are working towards real useful applications.

Waveguide technology is a desirable choice for terahertz wave devices, mainly due to its low loss characteristics. The conventional way of making waveguide components, is precisely controlled CNC metal milling. However, with the increase in the frequency it is more and more challenging to machine out the small features and sometimes it is impossible to achieve complicated internal waveguide structures. Recently various micromachining techniques have been developed to fabricate such devices with higher precision and possibility at a low cost. Among them, thick layer SU8 photoresist technology affords good dimensional accuracy and at the same time only requires standard ultraviolet photolithography, therefore making it a highly desirable choice for high precision and high performance applications. More information on this technology is available elsewhere on the website.

Terahertz filter

This technology has been employed by our research group to demonstrate waveguide filters operating at W-band (75-110 GHz), WR-3 band (220-325 GHz) and WR-1.5 band (500-750 GHz). Here the WR-1.5 filter will be discussed in detail.

Figure 1 Diagrams of the WR-1.5 band filter formed of three SU8 layers with a same thickness. (a) Illustration of the filter. The standard UG-387 waveguide flange dowel pins holes and screws holes are shown. (b) Front view of one SU8 layer. (c) Diagram of the filter structure, which is thefunctional bluepart also shown in (a). (d) A schematic front-view diagram of the filter structure. The first and third resonators are represented using red rectangles, whereas the blue rectanglerepresents thesecond resonator; the offset determines the filter properties.

As shown in Figure 1, the filter is composed of three silver-coated SU8 layers, each of the same nominal thickness of 191 µm. Rather than placing the resonators in alignment and controlling the couplings through irises, this WR-1.5 filter shifts the relative positions of resonators to achieve the desired specified external and internal coupling coefficients and therefore the desired frequency response. This is shown in Figure 1 (c)-(d). This novel structure is ideally suitable for the layered SU8 micromachining process as it avoids irises features within a layer, and is thereby more robust for fabrication. It also has a very accurate flange for connecting to the measurement equipment. Figure 2 shows a photograph of several silver-coated SU8 layers before they are put together into the final filter.

Figure 2 Photograph of a few silver-coated SU8 layers.

These SU8 layers are delicate due to their small thickness, and carefully mounted onto a separate metal straight though waveguide section and then inserted between the two ports of a network analyser to perform the measurement as shown in Figure 3 (a).

Measurements of the filter were performed using an Agilent N5247A Network Analyzer with a pair of VDI (Virginia Diodes Inc.) extension modules. During the measurement the SU8 filter and the waveguide section were placed in the middle of two standard WR-1.5 waveguide flanges (i.e. UG-387), as shown in Figure 3 (b). The four alignment pins of the waveguide flanges addressed both the accuracy to which the three SU8 layers were aligned and the accuracy to which the micromachined filter was aligned to flanges of network analyzer.

Figure 3 (a) SU8 shims mounted to a 1-in long straight through waveguide section. This prevents the SU8 shims from bending or wrapping. (b) Test setup for the micromachined SU8 waveguide filter.

Figure 4 Measurement results of the WR1.5 SU8 filter.

The measurement results of the SU8 filter together are shown in Figure 4, which exhibits a 3 dB bandwidth of 53.7 GHz at a centre frequency of 671 GHz. The median passband insertion loss is measured to be 0.65 dB, which is close to the theoretical value of 0.28 dB obtained from a simulation using the conductivity of silver The measured return loss is better than 11 dB across the whole passband. These are excellent results and this filter is one of a very few demonstrated at this frequency in the world.

Terahertz antenna

In addition to filters terahertz antennas are an important area for the EDT group. Rectangular waveguide slot antennas have been chosen and are widely used in the field of millimetre-wave applications and radar systems due to having high gain, inherent low transmission losses, and simplicity in fabrication. They also offer significant advantages in terms of weight, volume, and radiation characteristics. These antennas are very attractive due to their planar, compact, and rugged construction and a made by slots in a waveguide. The dimensions of the slots in the waveguide walls can be controlled to realise the desired pattern shape.

A Micromachined 300-GHz slotted waveguide antenna is demonstrated here using a simple fabrication technique based on metal-coated SU-8 thick resist. The configuration of the design is shown in Figure 5. The top layer contains 8 slots which are positioned at the centre of the narrow-wall of the waveguide. The next three layers form the rectangular waveguide, and the whole design is enclosed by the last layer (layer 5).

Figure 5. Illustration of the design of 8-slots in the narrow-wall of the waveguide with the H-bend input port. The dark blue shows the extent of the air filled waveguide and slot sections.

An embedded five layer H-plane bend is designed in order to connect the device with the waveguide flange easily and accurately, as shown in Figure 5. The effect of the bend on the performance of the device is negligible. Figure 6 shows the assembled antenna.

Figure 6: Diagrams of the assembled antenna seen from (left) the radiation side and (right) the feed side. The holes are for (A) precision alignment pins, (B) flange dowel pins, (C) flange screws, and (D) pressure screws.

Figure 7: Connection of the 300-GHz slotted waveguide antenna with the test port flange for measurement.

The radiation patterns of the antenna were measured at the Rutherford Appleton Laboratory, in an anechoic chamber with a WR-2.8 corrugated feed horn. The mm-wave source module and the detector were connected to a network analyser as shown in Figure 7. At least 40 dB dynamic range was maintained during the measurement. Figure 8 shows the measured normalized H pane radiation pattern which agrees very well with the simulation. This indicates good dimensional accuracy for the radiation slots, rendered by the lithography-based fabrication process.

Figure 8. Measured H-plane radiation patterns in comparison to simulations. For “measurement-1,” no absorbing material is applied to the antenna. For “measurement- 2,” a sheet absorber is attached to the brass plate on the radiation side. Again, the simulation model includes the brass plates and some metal cylinders representing the effects of the screws.