Research

Here we will extend the basic ideas of spatial transformations specifically towards practical applications. This acts as a cornerstone for the entire programme.

The concept of spatial transformations (STs) provides new intuition and offers novel methods for solving EM problems. We will develop a systematic strategy for the design of QUEST devices, and identify new types of transformations with the potential to generate practical applications. Initially, we will consider conventional materials, and implement transformations, for example, based on discrete layering of dielectric or magnetic blocks. We will subsequently consider materials with effectively negative values of permittivity and permeability, and will exploit active materials in order to mitigate the inherent losses encountered. In addition, we will investigate the fundamental physics suitable for offering user-specified refractive index values over broad bandwidths in the MHz and GHz domains, and extend these concepts to the THz. The myriad of possible directions for ST development will be constrained to those that can be integrated to the modelling/design approaches of SP2 and the reduction to practice in SP3 and SP4. As such, this SP will be responsive to the emerging opportunities, constraints and possibilities from elsewhere in the programme.

We will establish a suite of computational capabilities to allow the design of devices and test structures generated by new concepts from SP1, and the numerical modelling of the performance of test structures in practical environments, which will then be experimentally verified in SP4.

The constituent parameters of a medium in which coordinates have been transformed can be simulated by anisotropic materials, with user-specified, spatially and frequency varying permittivity and permeability functions. This requires the development of computationally efficient EM analysis models and practical software tools that both determine idealised material property variations for devices, as well as having the ability to implement experimentally-derived material properties. Newly developed transformation techniques from SP1 will be combined with closed-form models to yield a desired material response. These findings will be used to guide the fabrication and characterisation investigations (SP3), and the proof of concept experiments (SP4).

This task will focus on developing new materials with a broad range of EM parameters required for ST and demonstrator devices.

Isotropic “positive” index materials provide the necessary palette for a subset of STs, such as Maxwell’s fish eye lens. However, the use of “conventional” materials alone does not provide a suitably broad “palette” required for more sophisticated transformations. Non-isotropic, multi-lithic materials, in which the EM properties vary in at least one dimension in a controlled and pre-designed way, will be manufactured in Oxford. Focused ion beam etching and rapid prototyping facilities at Exeter will also be utilised. EM characterisation of the new materials will be performed to inform materials palette development. Limitations in the experimental performance of materials will be fed back into SP2 and, if severe restrictions are apparent, alternative transformation methods will be considered in SP1 that demand less challenging material characteristics. There will be a very close feedback cycle between this SP and the proof of concept experiments on devices in SP4.

We will undertake proof-of-principle tests, firstly on materials needed for STs and subsequently on ST demonstrator device implementations.

The outputs of SP2 and SP3 will combine to yield a series of device designs that will be optimised to utilise realisable geometries and experimentally proven material parameters. In SP4, we will provide an on-going programme to carry out pioneering proof-of-concept experiments on prototype devices that will be relevant to academia and potential industrial end users, and which will be disseminated appropriately. These begin with passive microwave devices, initially taking an all-dielectric approach, such as flat parabolic mirrors, and enhanced transmission through apertures. During the first half of the programme, we will also consider how STs can be used to guide the control of the propagation of EM waves on the surface of materials, and how this concept can aid the development of surface wave absorbing materials. We will also develop pioneering designs of thin structures for the absorption of free-space radiation, compact and directional antennas for communication and wireless energy transfer, and cloaking and imaging technologies. We will progress on to more challenging aspects of STs and electromagnetic devices later in the programme; this will include tuneability and an extension to THz, visible and acoustic domains. The outcomes of these proof-of-principle studies will feed directly into the industrial engagement programme for commercial exploitation.