| 摘要 |
PURPOSE:To eliminate unnecessary spurious signals due to the reflection, by devising the shape of the remotest end of an outer ridge of a bus bar, taking the length in the surface wave propagation direction and forming ruggedness at a right angle in the direction of propagation. CONSTITUTION:The bus bar 5 is formed for the inner ridge almost along the envelope of weighting, and the outer ridge is formed with a projection 8 with a lambda/4 of step difference in the direction of surface waves. Enlarged view of a part B surrounded with a dotted circle is shown below. The remotest end of the outer ridge of the bus bar is taken as a shape as shown in figure, allowing to eliminate the reflection of the surface waves due to the difference between the acoustic impedance of the region where an electrode exists and not. That is, there is a difference of path by lambda/2 in the reflection waves as shown in arrows 11 and 12, then the phase difference is 180 deg. and they are cancelled with each other. Since the reflecting waves are cancelled with each other at the ruggedness, the unnecessary spurious signals are all eliminated, the lengths (l) and l') of the ruggedness are equal and less than lambda. |
