Mode-selective ultrasonic wave sensor and its characteristics

A magnetostrictive sensor is proposed that can selectively measure the specified mode among two kinds of elastic waves transmitted through a ferromagnetic shaft, and its various characteristics are examined by experiments. The magnetic circuit of the proposed sensor is configured by using permanent magnets and its mode selection is accomplished by only reversing the poles of the permanent magnets. By means of finite element analysis, the validity of the proposed sensor is verified. Prototype sensors are made and their sensitivity and linearity are investigated as basic characteristics. The results show the proposed sensors are able to measure the target mode waves with good sensitivity and linearity. By exciting undesirable modes of waves intentionally, it is verified that the sensor can measure the target modes and reject the undesirable wave modes considerably.