A Nonlinear Organic Low‐Frequency Sound Sensor Based on Electrochemical Coupling in a Solidified Gel Membrane

Measuring low‐frequency or infrasound acoustic signals plays a crucial role in the monitoring of natural disasters, structural health, and predictive maintenance of critical energy structures. Smart sound sensing systems often consist of linear sound sensors coupled to a separate processing unit, nonlinearly transforming the signal to solve the given task. However, nonlinear sensors have seen increased scientific interest in fields like reservoir computing, with the goal of minimizing power consumption by implementing the signal processing in the sensor itself. Here, the use of an organic electrochemical transistor based on conductive polymeric fibers embedded inside a free‐standing solidified gel membrane as a robust, highly sensitive, and nonlinear low‐frequency sound sensor is demonstrated. The slow dynamics of the device allow sensing in the low‐frequency and infrasound regime with a cutoff‐frequency at around with power consumptions below . Our work further demonstrates that the introduction of a gating mechanism increases sensitivity, nonlinearity, and stability compared to a previously introduced linear two‐terminal sensors. As a demonstration, we show that a three‐terminal device contains sufficient information to classify spoken digits from ten classes, using in‐software reservoir computing.