Department of Electrical Engineering, Stanford University, Stanford, CA, United States of America. Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA, United States of America. Author to whom any correspondence should be addressed.
J Neural Eng. 2020 Jun 2;17(3):035001. doi: 10.1088/1741-2552/ab89fd.
Avoidance of the adverse electrochemical reactions at the electrode-electrolyte interface defines the voltage safety window and limits the charge injection capacity (CIC) of an electrode material. For an electrode that is not ideally capacitive, the CIC depends on the waveform of the stimulus. We study the modeling of the charge injection dynamics to optimize the waveforms for efficient neural stimulation within the electrochemical safety limits.
The charge injection dynamics at the electrode-electrolyte interface is typically characterized by the electrochemical impedance spectrum, and is often approximated by discrete-element circuit models. We compare the modeling of the complete circuit, including a non-linear driver such as a photodiode, based on the harmonic-balance (HB) analysis with the analysis based on various - (discrete-element) approximations. To validate the modeling results, we performed experiments with iridium-oxide electrodes driven by a current source with diodes in parallel, which mimics a photovoltaic circuit.
Application of HB analysis based on a full impedance spectrum eliminates the complication of finding the discrete-element circuit model in traditional approaches. HB-based results agree with the experimental data better than the discrete-element circuit. HB technique can be applied not only to demonstrate the circuit response to periodic stimulation, but also to describe the initial transient behavior when a burst waveform is applied.
HB-based circuit analysis accurately describes the dynamics of electrode-electrolyte interfaces and driving circuits for all pulsing schemes. This allows optimizing the stimulus waveform to maximize the CIC, based on the impedance spectrum alone.
避免电极-电解质界面的不良电化学反应定义了电压安全窗口，并限制了电极材料的充电注入容量（CIC）。对于不是理想电容性的电极，CIC 取决于刺激的波形。我们研究了充电注入动力学的建模，以优化在电化学安全限制内进行有效神经刺激的波形。
电极-电解质界面的充电注入动力学通常通过电化学阻抗谱来表征，并且通常通过离散元件电路模型来近似。我们比较了完整电路的建模，包括基于谐波平衡（HB）分析的非线性驱动器（例如光电二极管），以及基于各种离散元件近似的分析。为了验证建模结果，我们使用电流源驱动的氧化铱电极进行了实验，其中并联了二极管，这模拟了光伏电路。
基于完整阻抗谱的 HB 分析应用消除了在传统方法中寻找离散元件电路模型的复杂性。基于 HB 的结果比离散元件电路更符合实验数据。HB 技术不仅可以应用于演示电路对周期性刺激的响应，还可以描述应用突发波形时的初始瞬态行为。
基于 HB 的电路分析准确描述了所有脉冲方案的电极-电解质界面和驱动电路的动力学。这允许仅基于阻抗谱优化刺激波形以最大化 CIC。
