A Howland current source module with auxiliary buffering and compensation feedback for electrical impedance tomography.

Electrical impedance tomography (EIT) relies on a controlled ac excitation current, while the effective load of a multiplexed instrument varies with electrode switching, contact impedance, excitation frequency, and object conductivity. This work develops a Howland current source module with auxiliary buffering and compensation feedback for EIT instrumentation. The architecture retains the main Howland current setting loop while adding a voltage follower and a dedicated compensation branch that acts on an internal node coupled to the output path rather than directly sensing the external load terminal. The module was characterized against a conventional single op amp Howland circuit in terms of frequency-dependent current accuracy, resistive load sensitivity, output signal-to-noise ratio (SNR), and estimated effective output impedance and was integrated into a 16-electrode EIT instrument for water tank validation. In the frequency sweep, at 100 kHz with a 5 kΩ load, the proposed module delivered 0.4935 mA RMS with an error of -1.30%, compared with 0.3768 mA RMS and -24.64% for the conventional circuit. Over a 1-5 kΩ load sweep at 100 kHz, the current variation decreased from 44.23% to 10.90%. At 100 kHz with a 3 kΩ load, the output SNR increased from 30.0 to 41.2 dB, while the estimated effective output impedance increased from 15.4 to 31.7 kΩ. Water tank experiments with conductive, insulating, and mixed targets further demonstrated end-to-end operation within the complete EIT measurement chain. Overall, the results demonstrate improved excitation performance and practical system level integration for EIT instrumentation.