Low coordinate metal complexes can exhibit superlative physicochemical properties, but this chemistry is challenging for the lanthanides (Ln) due to their tendency to maximize electrostatic contacts in predominantly ionic bonding regimes. Although a handful of Ln 2+ complexes with only two monodentate ligands have been isolated, examples in the most common +3 oxidation state have remained elusive due to the greater electrostatic forces of Ln 3+ ions. Here, we report bent Ln 3+ complexes with two bis(silyl)amide ligands; in the solid state the Yb 3+ analogue exhibits a crystal field similar to its three coordinate precursor rather than that expected for an axial system. This unanticipated finding is in opposition to the predicted electronic structure for two-coordinate systems, indicating that geometries can be more important than the Ln ion identity for dictating the magnetic ground states of low coordinate complexes; this is crucial transferable information for the construction of systems with enhanced magnetic properties.

This paper explores the limitation that is imposed on the spatial resolution of electrical impedance tomographic images by the relatively low numbers of independent projections. In the present work the levels of recoverable image content are improved by attaching electrodes to a rotating central impeller. Incorporating the rotational motion of the electrode array into an optimized measurement strategy provides more independent measurements without compromising the stability of a consistently regularized inverse solution. A new measurement strategy, together with a mesh mapping algorithm, delivers improved results, in terms of the image contrast, from experiments on a small laboratory vessel. Initial findings suggest that the use of non-stationary electrodes has the potential to produce images with four times the amount of independent information over a conventional EIT measurement technique. The challenges in implementing an impeller-mounted electrode array are briefly discussed.

Linear arrays of electrodes in conjunction with electrical impedance tomography have been used to spatially interrogate industrial processes that have only limited access for sensor placement. This paper explores the compromises that are to be expected when using a small number of vertically positioned linear arrays to facilitate 3D imaging using electrical tomography. A configuration with three arrays is found to give reasonable results when compared with a ‘conventional’ arrangement of circumferential electrodes. A single array yields highly localized sensitivity that struggles to image the whole space. Strategies have been tested on a small-scale version of a sludge settling application that is of relevance to the industrial sponsor. A new electrode excitation strategy, referred to here as ‘planar cross drive’, is found to give superior results to an extended version of the adjacent electrodes technique due to the improved uniformity of the sensitivity across the domain. Recommendations are suggested for parameters to inform the scale-up to industrial vessels.

A new electrical tomograph that is designed specifically for low-cost and accessibility is described. It offers a unique environment for three-dimensional (3D) electrical impedance imaging. Using a cross-bar switch, the hardware can support ad hoc measurement strategies and is linked to control software, which integrates the complete process from 3D finite element modelling through to image reconstruction and generation of movie files. Digital signal processing algorithms are used to derive measurements of complex impedance from the measurement of amplitude and phase difference between the driven and received signals. This is achieved by rapid sampling of sinusoidal signals having frequencies between 1.0 Hz and 1.0 MHz. The instrument can deliver about 100 measurements per second, corresponding to a typical 16-electrode tomography frame, and is targeted at processes with modest dynamics or for laboratory development of tomographic applications and algorithms. The latest version (LCT2) is described here and uses a USB2 link to provide data transfer rates up to 20 MBytes per second. Sinusoidal excitation signals are derived using a direct digital synthesis chip. Voltage measurements are digitized to 16-bit accuracy and the standard system can accommodate 64 electrodes. The software embraces the EIDORS-3D soft-field reconstruction algorithms and the resulting impedance imaging capability of the device and characterization of the signals are described.

The information content in electrical impedance tomography (EIT) reconstructions is limited by the number of independent impedance measurements acquired for each image frame. This paper describes the design and construction of an electrode array mounted onto a rotating impeller used for mixing processes. By combining the process compliant rotation of the electrodes with a dynamic measurement protocol, a substantial increase in the number of independent measurements is reported. A pitch-blade impeller is built and fitted with four electrodes. A number of challenges associated with operating a rotating electrode array have been addressed including a wireless communications protocol. The impeller has been accurately modelled and measurement simulations closely correspond to those acquired using the array. The apparatus has been used to successfully visualize a test distribution to a consistent standard compared to a conventional EIT electrode array and strategy. Presently, the limiting factor to this approach is the necessary high measurement acquistion rates which lead to restricted impeller velocities.