A floating wide-band current source for electrical impedance tomography

An alternative excitation method for electrical impedance tomography

Electrical impedance tomography (EIT) can be utilized to image the conductivity distribution of material under test. The EIT measurements depend on the quality in the current injection and voltage measuring circuits. The current source plays a vital role in the EIT instruments. In most of the research studies, the push-pull current sources were employed for the source and sink signal generation. It usually requires frequent calibration to achieve proper functioning, especially for the sweeping frequency measurements. In this paper, an alternative excitation method has been proposed for simplifying the design of the current source in EIT instruments, which aims to achieve the performance of the push-pull current source by using a single-ended current source. It could offer the following advantages: (1) hardware simplification and (2) reduced requirements on current source calibration. The corrected measurements could be consistent with that using push-pull excitation, as confirmed by the numerical simulations. In addition, the reconstructed images have also been investigated to illustrate the effectiveness of the proposed method.

A FPGA-based adaptive differential current source for electrical impedance tomography

A high output impedance current source with a wide bandwidth is needed in electrical impedance tomography systems. Limitations appear mainly at higher frequencies and non-simple loads. In order to adjust the output current, the amplitude and phase are made to achieve the expected value automatically. A current source based on the field programmable gate array is designed. In this paper, we proposed a double DAC differential current source structure. By measuring the voltage of the sampling resistor in series with the load and using the proposed dynamic reference point demodulation algorithm, the actual current amplitude and phase on the load can be quickly obtained. Through the adaptive compensation module, the output current is adjusted to the expected value. The experimental results show that the output resistance of the current source can reach 10 MΩ and the output capacitance can be less than 0.8 pF in the frequency range of 10 kHz-1.28 MHz. At the same time, the current amplitude attenuation is less than 0.016%, and the phase error is less than 0.0025° after compensation. Therefore, the proposed current source achieves widebands, biocompatibility, and high precision.

DSP-based current source for electrical impedance tomography

OBJECTIVE

EIT systems, particularly those that use a parallel, multiple source architecture, require current sources with very high output impedance. To meet this requirement, sources often use complex analog circuits and require manual or electronically-controlled adjustments. The goal is to implement a current source with simple, adjustment-free analog electronics with high effective output impedance even with significant stray impedance at its output.

APPROACH

The excitation provided to the voltage-to-current converter is adjusted to accommodate the current lost in the finite output and stray impedances. The adaptive algorithm uses the measured voltage and the previously-measured output and stray impedance to determine the needed current adjustment.

MAIN RESULTS

The structure of the source is presented along with an implementation, and experimental results that show the effectiveness of the approach for frequencies up to 1 MHz. The measured output impedance with and without the adaptive compensation are presented as well as measurements of resistive and complex loads.

SIGNIFICANCE

The new current source has low analog complexity, operates over a wide range of frequencies, and can compensate for a significant stray shunt impedance. It can be used to implement improved parallel or serial EIT systems.