Research identifies and develops new capabilities. It ranges from the conception of completely novel ideas, through feasibilities studies, proof-of-concept demonstrators, to prototypes and incremental improvements to mission proven systems.

The maturity of any research is benchmarked by its step on the Technology Readiness Level (TRL) scale. These steps have strict definitions; the scale ranges from TRL1 for novel conception to TRL8 for mission proven systems. Lower TRL research is conducted usually by universities and research centres. Higher TRL research is carried out by commercial companies, sometimes outsourced to other institutes.

Public sources of funding can be available for funding research between TRL1 and TRL4. Companies normally fund TRL of six and above, when low-risk routes to market are identified. Total costs involved in transiting a step on the TRL scale increase by an order of magnitude for each step. 

Projects below build on peer reviewed work to date and on-going dynamic research activities, driving forward technology and techniques on a number of fronts simultaneously. Projects may run from short 3-month contracts, through PhD studentships, to long-term research and development programmes.

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Stand-Off Security Screening

Investigate the feasibility of full polarimetric radar to screen individuals at distances of tens of metres for concealed threats. This active technique (whereby a coherent electromagnetic wave is transmitted to the subject and the reflection measured) enables a greater information content to be extracted than with a polarimetric passive system or an intensity polarimetric radar. This is critical in a regime where the spatial information content (limited by diffraction) is low and where the passive signature from threats is very much smaller than the background emission.

The target is polarimetrically probed by coherent millimetre waves at a number of different frequencies to capture the rich information content about the threat. Calibrations of the phase and amplitude of returned signals enables co- and cross-polar signatures of the target to be analysed and matched to classes of threats. This will revolutionise the way stand-off security screening is performed at checkpoints and in public places for protection of the general public.

Data from forward simulation or experimental kit can be generated, then inversion techniques and decomposition algorithms from synthetic aperture radar (SAR) remote sensing can be used to identify characteristic features of weapons. Huynen Target Parameters or the H-alpha decomposition components can be analysed in radiation frequency space by neural networks to identify targets. These techniques are non-invasive, violate no privacy laws and enable remote recognition of guns and knives carried on a person under their clothing.


Portal Security Screening

Investigate aperture synthesis image generation algorithms for three dimensional imaging of subjects in walk-through, high-performance airport security screening portals. Algorithms are already available to generate cross-correlations from three-dimensional subjects carrying threats and the Gerchberg-Saxton technique can be used to invert these to generate a 3-D image of the original subject. The field-of-view and depth-of-field of this technique is unlimited, so all threats are in focus, ideally suited to walk-through security screening. Radiometric aperture synthesis (a technique from radio astronomy) has the capability to deliver artefact free, machine interpretable imagery of threats concealed in areas of the body that are normally difficult to screen using conventional coherently illuminating millimetre wave systems.

Being able to identify non-metallic threats concealed anywhere on the human body, rapidly and efficiently, is ideal for airport security and will lead to spin out products for other deployment scenarios (e.g. entrances to public transport systems, buildings, arenas etc.). The measured signature, being a combination of known reflectance and thermal emission from the human body, means this screening technique is virtually impossible to defeat. The system hardware for aperture synthesis imagers will he heavily dependent on millimetre wave receivers linked to FPGA based digital cross-correlators running at GHz sample rates. Aperture synthesis image creation algorithms can be investigated using existing validated forward simulation software, whilst hardware for portals is developed in parallel.


Scene Simulation

Investigate full polarimetric ray tracing algorithms and processing in Graphical Processor Units (GPUs) to enable high-speed scene simulations, including the effects of scattering and semitransparency of materials for active and passive imaging. The software can be used to investigation the full spectrum of applications for markets such as:

* Portal and stand-off security screening of persons
* All-weather imaging in fog/cloud:
- Landing aircraft close to obstacles (incl. brownout)
- Sea vessel littoral manoeuvre in coastal fog
- Warnings of approaching small (RIBs) sea craft
* Vehicle screening at ports for stowaways
* Satellite based earth observation.

Scene simulations are an excellent way of illustrating how phenomenology changes through the different atmospheric transmission windows (eg. 35, 94, 140 & 220 GHz) and absorption bands (at 60 & 183 GHz). The analysis of much experimental imagery has validated the simulation techniques. Simulation provides a means of assessing imager system performance for a wide range of (air, sea, land and spaced sensor based) scenarios without having to conduct lengthy and expensive trials and experiments. 

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Medical Sensing

Investigate the signatures of human skin and tissue in healthy and unhealthy states and determine how these may be measured with precision for medical applications. Signatures already measured show healthy tissue to have a range of emissivities dependent on the area of the body and the cardiovascular state on an individual. Unhealthy or diseased skin has signatures outside these ranges.  

A diversity of imaging and sensing techniques are possible, such as electronic beam-forming, quasi-optical imaging and near-field scanning microscope probes. Lateral and depth spatial resolutions, dependent on wavelength and electrical properties of tissue, are down to ~0.1 mm in the millimetre wave band. These resolutions will extend down to a depth of ~ 1 mm into the skin, with greater penetration possible at frequencies below the millimetre wave band (< 30 GHz).

Measured signatures contain information about skin water and electrolyte content, granularity, layer structure and internal temperature profile. Measurements over specific areas of the body, or over the whole of the human body, will be a completely novel diagnostic technique, revealing new information about the state of patients' health. It will lead to new sensing modalities in medicine, either as a stand-alone system, or in conjunction with other medical sensing techniques.


Quantum Entanglement

Investigate if quantum entanglement may be demonstrated in the Rayleigh-Jeans (RJ) regime, a domain where the thermal energy kT is greater than the photon energy hf. Since the 1980's entanglement has been researched in the in the quantum regime, that being where the photon energy is greater than the thermal energy (hf>kT), a restriction to the visible band, or at lower frequencies using cryogenic cooling.

The challenge here is to build an ambient temperature mm-wave homodyne Bell Test interferometer and demonstrate the existence of entangled photons in the millimetre wave band, thus showing that entangled state signatures well below the level of the natural thermal noise can be detected. In this system the Bell Test statistic 'S' would be measured to determine if the Bell inequality is violated, ie local reality has been broken.

Sensors based on R-J entanglement may lead the way to novel sensors in the millimetre wave band that can deliver quantum capabilities below the level of thermal noise. The technique will have applications in novel imaging, covert radar and secure communications.

A source of entangled mm-wave photons for the Bell Test concept is currently being sought. Candidates for this are materials with non-linear susceptibilities (eg. ferroelectrics, ferrimagnets, electro-optic crystals), or non-linear devices (eg junction devices, semiconductors, acousto-optic crystals) or metamaterials built from a combination of these. In the case of spontaneous parametric down-conversion (SPDC) for entangled pair production, the probability of this process scales with the fourth power of frequency. This indicates only extremely non-linear materials or devices will make suitable entangled photon sources. 


High-speed digital (FPGA Interface/Processing)

Investigate how Field Programmable Gate Arrays (FPGAs) can interface to millimetre wave receivers, to sample and process data at GHz rates for next-generation aperture synthesis imaging, radar sensing and quantum applications. Short word, or single bit, digitisation at ~ 1 giga sample per second using comparators and FPGAs means electric fields of millimetre wave radiation can be processed to enable cross-correlators and phased array receivers to operate in real-time for sensing applications.

Opting for short words enables large bandwidths to be realised at much reduced cost, resulting in greater sensitivities and information gathering capacities. These developments will revolutionise millimetre wave sensing capabilities, so they can be widely deployed in market driven applications of security screening and all-weather imaging and research into medical and quantum applications.