An Electromagnetic Acoustic Transducer for Generating Acoustic Waves in Lithium-Ion Pouch Cells

The need for monitoring Lithium-ion pouch cells is constantly increasing as the number of assembled cells in various applications grows. The State of Charge (SoC) and State of Health (SoH) are two important states to observe. A novel approach to estimating SoC is to monitor the mechanical properties of the battery as they change during the charge/discharge process. Hereby, an acoustic wave is generated inside the cell by a transmitter. After a certain Time of Flight (ToF), the propagating acoustic wave is detected by a receiver. The measured ToF between transmitter and receiver is an indicator for the SoC. For such a ToF measurement, it is preferable to excite only one single wave inside the battery, as this allows a clear detection of the wave and simplifies the ToF evaluation. In this paper an Electromagnetic Acoustic Transducer (EMAT) design is presented for an explicit generation of a defined wave mode inside the battery cell. The sole presence of the the defined generated mode inside the cell is demonstrated by means of acceleration measurements. The corresponding ToF is estimated by evaluating the cross-correlation result of the measured acceleration signal and the excitation signal.