Rapid multichannel electrochemical impedance spectroscopy via sparse-frequency acquisition and embedded spectrum reconstruction

Electrochemical impedance spectroscopy (EIS) provides information-rich frequency-dependent measurements but can become a throughput bottleneck when spectra are acquired sequentially across multiple channels. We developed a portable eight-channel EIS platform that combines grouped multichannel acquisition, sparse-frequency measurement, and embedded spectrum reconstruction. Eighteen frequencies (CS18) are physically acquired from a predefined 68-frequency reference grid (FULL68), reducing measured frequency points by 73.53%. RouteC, a lightweight log-frequency PCHIP plus Ridge residual-correction method, reconstructs the corresponding reference-grid complex-impedance spectrum on an STM32H7 microcontroller. The deployed Ridge coefficients were derived from public battery-EIS development data and transferred without aqueous-domain refitting; a controlled 116-pair aqueous-electrochemical dataset was used separately for grouped architecture-level validation. Ridge residual correction reduced complex NRMSE relative to PCHIP-only by 26.3% on the public held-out benchmark and 24.6% in the aqueous grouped analysis. External comparison with a CS3104 workstation showed 1.13% and 0.48% cross-instrument differences for nominal 330 Ω and 1.2 kΩ loads, while the validated 50 Hz-5 kHz RC comparison yielded 3.32% magnitude MAPE, 1.53° phase MAE, and 3.86% complex NRMSE. In four real-water matrices, RouteC-versus-FULL68 complex NRMSE ranged from 0.823% to 2.746%; conductivity-derived TDS-equivalent estimates showed a mean sample-level MAPE of 3.63% relative to a handheld reference. Spectrum-generation time decreased from 75 to 22 s for one channel and from 160 to 48 s for eight channels. These results support rapid multichannel EIS with embedded reference-grid reconstruction under the investigated conditions.