Abstract
Electrical impedance tomography (EIT) is an imaging method that can be applied over stretchable conductive-fabric materials to realize soft and wearable pressure sensors through current injections and voltage measurements at electrodes placed at the boundary of a conductive medium. In common EIT systems, the voltage data are serially measured by means of multiplexers, and are hence collected at slightly different times, which affects the real-time performance of the system. They also tend to have complicated hardware, which increases power consumption. In this paper, we present our design of a 16-electrode high-speed EIT system that simultaneously implements constant current injection and differential potential measurements. This leads to a faster, simpler-to-implement and less-noisy technique, when compared with traditional EIT approaches. Our system consists of a Howland current pump with two multiplexers for a constant DC current supply, and a data acquisition card. It guarantees a data collection rate of 78 frames/s. The results from our conductive stretchable fabric sensor show that the system successfully performs voltage data collection with a mean signal-to-noise ratio (SNR) of 55 dB, and a mean absolute deviation (MAD) of 0.5 mV. The power consumption can be brought down to 3 mW; therefore, it is suitable for battery-powered applications. Finally, pressure contacts over the sensor are properly reconstructed, thereby validating the efficiency of our EIT system for soft and stretchable sensor applications.
Highlights
Electrical impedance tomography (EIT) is a method in which an image of the internal conductivity distribution of an object is reconstructed from potential measurements made at the electrodes placed around its boundary [1,2]
We present our electronic design of a printed circuit board (PCB) for 16-electrode high-speed EIT sensor applications
A high-speed EIT system that concurrently implements constant current injection and differential potential measurements has been developed for EIT-based sensor applications
Summary
Electrical impedance tomography (EIT) is a method in which an image of the internal conductivity distribution of an object is reconstructed from potential measurements made at the electrodes placed around its boundary [1,2]. In [13], a fast EIT system is presented; it injects a switched DC current pulse into the drive electrode pairs and measures the voltage waveform, whereby parallel data acquisition is taken during the half part of the cycle. The problem with such a system is that, in order to achieve a fast response, the measurement time has to be small, limiting the measurement sensitivity. Parallel data acquisition consents for a higher data capture rate; this design allows for an increased temporal resolution It decreases the electrical common-mode noise, as the voltage data are collected in the differential mode.
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