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The investigation of quickly-evolving flow patterns in high-pressure and high-temperature flow rigs requires the use of a high-speed and non-intrusive imaging technique. Electrical Impedance Tomography (EIT) allows reconstructing the admittivity distribution characterizing a flow from the knowledge of currents and voltages on its periphery. The need for images at high frame rates leads to the strategy of simultaneous multi-frequency voltage excitations and simultaneous current measurements, which are discriminated using fast Fourier transforms. The present study introduces the theory for a 16-electrode simultaneous EIT system, which is then built based on a field programmable gate array data acquisition system. An analysis of the propagation of uncertainties through the measurement process is investigated, and experimental results with fifteen simultaneous signals are presented. It is shown that the signals are successfully retrieved experimentally at a rate of 1953 frames per second. The associated signal-to-noise ratio varies from 59.6–69.1 dB, depending on the generated frequency. These preliminary results confirm the relevance and the feasibility of simultaneous multi-frequency excitations and measurements in EIT as a means to significantly increase the imaging rate.

This paper presents a concept for soft field tomographic scan of all the projections of electromagnetic waves emanating from an array of electrodes. Instead of the sequential excitation of all pairs of electrodes in the list of all projections, the new method present here consists of a single and continuous excitation. This excitation signal is the linear combination of the excitation signals in the projection set at different AC frequencies. The response to a given projection is discriminated by selecting the corresponding AC frequency component in the signal spectra of the digitally demodulated signals. The main advantage of this method is the suppression of transients after each projection, which is particularly problematic in electrical impedance tomography due to contact impedance phenomena and skin effect. The second benefit over the sequential scan method is the increased number of samples for each measurement for reduced noise sensitivity with digital demodulation. The third benefit is the increased temporal resolution in high-speed applications. The main drawback is the increased number of signal sources required (one per electrode). This paper focuses on electrical impedance tomography, based on earlier work by the authors. An experimental proof-of-concept using a simple 4-electrodes electrical impedance tomographic system is presented using simulations and laboratory data. The method presented here may be extended to other modalities (ultrasonic, microwave, optical, etc.).

The investigation of quickly-evolving flow patterns in high-pressure and high-temperature flow rigs is crucial due to inherent hazards. There is a dire need for a high-speed, non-intrusive imaging technique to identify characteristic flow phenomena to alleviate these hazards. Electrical Impedance Tomography (EIT) enables reconstruction of the admittivity distribution of the flowing medium(s), facilitating the characterisation of its/their flow. The requirement for images at high frame-rates led to simultaneous voltage excitations over electrodes on the periphery of the flow associated to Frequency Division Multiplexing (FDM), doped ONe Excitation for Simultaneous High-speed Operation Tomography (ONE-SHOT) method. In previous studies, we have demonstrated the possibility of the full implementation of simultaneous excitations and measurements strategies for EIT, which maximise the number of measurements for 16 electrodes. This article presents the details of the proposed method and the signal generation/acquisitionfirmware based on a Field Programmable Gate Array (FPGA) data acquisition system focusing on hardware and software integration and the signal processing involved in realising the ONE-SHOT operation of the EIT. It is shown that the simultaneously generated signals are successfully discriminated and used for image reconstruction, at a rate up to 3906 frames per second (fps). The associated signal-to-noise ratio varies in the 55.6 dB-69.1 dB range, depending on the generated frequency in the range of 3.906 kHz-468.7 kHz.