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. 2020 Jul:2020:1448-1451.
doi: 10.1109/EMBC44109.2020.9175910.

Performance of an Adaptive Current Source for EIT Driving Loads through a Shielded Coaxial Cable

Ahmed Abdelwahab, Omid Rajabi Shishvan, Gary J Saulnier

Performance of an Adaptive Current Source for EIT Driving Loads through a Shielded Coaxial Cable

Ahmed Abdelwahab et al. Annu Int Conf IEEE Eng Med Biol Soc. 2020 Jul.

Abstract

In Electrical Impedance Tomography (EIT) the coaxial cables used to connect the electrodes to the electronics have long been a concern due to their impact on system performance. Driving the shield of the cable is useful, since it mitigates the shunt capacitance. However, this approach introduces complexity and, sometimes, stability issues. Using "active electrodes", i.e. placing the front end of the electronics at the electrode end of the cables, is also helpful but can introduce packaging and hygiene problems. In this paper, a new type of high-precision current source is described and its performance is studied when driving loads through a coaxial cable. This new current source adjusts its current output to compensate for current lost in any shunt impedance to ground, including the shunt losses in the cable. Experimental results for frequencies up to 1 MHz are provided, comparing performance with resistive and complex loads connected without a cable, with 1 m of RG-174 coaxial cable with a driven shield, and 1 m of RG-174 coaxial cable with a grounded shield. The results for all 3 cases are similar, demonstrating that the source can provide satisfactory performance with a grounded-shield cable.

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Figures

Fig. 1:
Fig. 1:
New current source block diagram.
Fig. 2:
Fig. 2:
Conventional passive electrodes EIT system.
Fig. 3:
Fig. 3:
Electrical model of a current driven load
Fig. 4:
Fig. 4:
Shield driver schematic
Fig. 5:
Fig. 5:
System response across 1 MHz band for 1 kΩ load with no cable
Fig. 6:
Fig. 6:
Open circuit capacitance measurements
Fig. 7:
Fig. 7:
Current source with shield grounded/driven response
Fig. 8:
Fig. 8:
Adaptive Cole-Cole load
See this image and copyright information in PMC

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