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High-speed tomographic imaging of hostile engineering processes using absorptionbased measurements presents a number of difficulties. In some cases, these challenges include severe limitations on the number of available measurement paths through the subject, and the process of designing the geometrical arrangement of those paths for best imaging performance. This paper considers the case of a chemical species tomography system based on near-IR spectroscopic absorption measurements, intended for application to one cylinder of a multicylinder production engine. Some of the results, however, are applicable also to other hardfield tomographic modalities in applications where similar constraints may be encountered. A hitherto unreported design criterion is presented for optimal beam geometry for imaging performance, resulting in an irregular array with only 27 measurement paths through the subject for the engine application. Image reconstruction for this severely limited geometry is considered at length, using both simulated and experimental phantom data. Novel methods are presented for the practical generation of gaseous phantoms for calibration and testing of the system. The propane absorption coefficient at 1700nm is measured. Quantitative imaging of propane plumes in air is demonstrated, showing good localisation of circular plumes with diameter as small as 1/5 of the subject diameter and excellent imaging of multiple plumes.

This article describes experiments on the combined determination of the distribution of liquid metal and argon in the submerged entry nozzle (SEN) and of the flow in the mold of a small-scale physical model of a continuous slab caster. For visualizing the metal distribution in the SEN, mutual inductance tomography (MIT) is applied, while the flow in the mold is determined by contactless inductive flow tomography (CIFT). The results of the latter are validated in part by ultrasonic Doppler velocimetry (UDV). Accompanying measurements provide information about the levels in the tundish and in the mold, as well as on the pressure in the SEN. Depending on the gas flow rate, various flow regimes are identified, among them pressure and mold level oscillations, transitions between double and single vortex flows, and transient single port ejections.

This paper reports the application of optical tomography and Chemical Species Tomography (CST) to the characterisation of the in-cylinder

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Monitoring of the steel flow through the submerged entry nozzle (SEN) during continuous casting presents a challenge for the instrumentation system because of the high temperature environment and the limited access to the nozzle in between the tundish and the mould. Electromagnetic inductance tomography (EMT) presents an attractive tool to visualize the steel flow profile within the SEN. In this paper, we investigate various flow regimes over a range of stopper positions and gas volume flow rates on a model of a submerged entry nozzle. A scaled (approximately 10:1) experimental rig consisting of a tundish, stopper rod, nozzle and mould was used. Argon gas was injected through the centre of the stopper rod and the behaviour of the two-phase GaInSn/argon flow was studied. The experiments were performed with GaInSn as an analogue for liquid steel, because it has similar conductive properties as molten steel and allows measurements at room temperature. The electromagnetic system used in our experiments to monitor the behaviour of the two-phase GaInSn/argon flow consisted of an array of eight equally spaced induction coils arranged around the object, a data acquisition system and a host computer. The present system operates with a sinusoidal excitation waveform with a frequency of 40 kHz and the system has a capture rate of 40 frames per second. The results show the ability of the system to distinguish the different flow regimes and to detect the individual bubbles. Sample tomographic images given in the paper clearly illustrate the different flow regimes.

An Electrical Impedance Tomography (EIT) system has been developed for dynamic three-dimensional imaging of changes in conductivity distribution in the human head, using scalp-mounted electrodes. We attribute these images to changes in cerebral perfusion. At 100 frames per second (fps), voltage measurement is achieved with full-scale signal-to-noise ratio of 105 dB and common-mode rejection ratio > 90 dB. A novel nonlinear method is presented for 3-D imaging of the difference in conductivity distribution in the head, relative to a reference time. The method achieves much reduced modelling error. It successfully localizes conductivity inclusions in experimental and simulation tests, where previous methods fail. For > 50 human volunteers, the rheoencephalography (REG) waveform is observed in EIT voltage measurements for every volunteer, with peak-to-peak amplitudes up to approx. 50 µVrms. Images are presented of the change in conductivity distribution during the REG/cardiac cycle, at 50 fps, showing maximum local conductivity change of approx. 1% in grey/white matter. A total of 17 tests were performed during short (typically 5s) carotid artery occlusions on 5 volunteers, monitored by Transcranial Doppler ultrasound. From EIT measurements averaged over complete REG/cardiac cycles, 13 occlusion tests showed consistently decreased conductivity of cerebral regions on the occluded side, and increased conductivity on the opposite side. The maximum local conductivity change during occlusion was approx. 20%. The simplicity of the carotid artery intervention provides a striking validation of the scalpmounted measurement system in imaging cerebral hemodynamics, and the REG images indicate its unique combination of sensitivity and temporal resolution.

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