214 超音波によるアクリル棒中定在波の可視化

抄録

At the nodes of standing wave particles in the medium alternatively receive contractive and expansive forces, and this causes the build up of the heat. 24KHz of ultrasound is continuously introduced into the one end of the acrylic bar, which is laid horizontally and 1.5 cm wide and 0.5 cm thick. The other end works just as the free end. The standing wave is well established when the length of the bar is 13.5, 18.5, 23.0 and 27.5 cm in every 4.5-5.0 cm. The thermographic pictures of these bars showed distinctive hot and cold images. Hot parts are nodes where the stress is high and the distance between each node is 4.7 cm which is nearly as same as a half-wavelength theoretically estimated. Then fine sand particles (about 10μm) distributed uniformly on the acrylic bar also draw a patterned image. The bands of sand gathèred locate almost same spots of the hot parts, which are the nodes. This phenomenon is very interesting and further discussion is necessary to describe why the sandy particles tend to gather at the nodes.