Aspects of the disclosure provide a sensing apparatus including a sensing device, a memory, and processing circuitry. The sensing device includes resonators having respective resonant frequencies. The resonators include an array of inductive coils positioned on a surface of the apparatus. The sensing device can output a signal indicating changes of the resonant frequencies caused by presence of an object proximate to the surface. The memory stores reference signals corresponding to reference objects. Each reference signal indicates changes of the resonant frequencies caused by the respective reference object proximate to the surface. The processing circuitry can receive, from the sensing device, a particular signal indicating changes of the resonant frequencies caused by presence of a particular object proximate to the surface. The processing circuitry compares the particular signal with the stored reference signals of the reference objects to determine an identity of the particular object.