Determining Smartphone’s Placement Through Material Detection, Using Multiple Features Produced in Sound Echoes

This paper proposes a system to determine the placement of a smartphone by using the acoustic properties of the surface materials nearby. Detecting the surrounding materials allows the smartphone to change its notification method automatically, based on situational factors. Researchers have studied how to recognize the position in which smartphones are worn while walking, using accelerometer data; however, it is difficult to identify a smartphone's position while stationary, because the accelerometer value does not change significantly when the smartphone is put down. In this paper, we developed a method to recognize surface materials close to a smartphone, using echoes; this method is based on the assumption that echoes of a selected frequency will differ in their properties, depending on the smartphone's placement and the surface materials nearby. Through our experiment, we found that our proposed method can classify 12 kinds of placement with 82.1% accuracy.