固体板中SH型板波的二阶和频积累波发生

当各向同性固体板中传播的ＳＨ型板波模式饱含两个频率成分时，板材的非线性将导致二阶和频及差频声波的发生。本文在二阶近似条件下对此问题进行了研究，得到了如下结论：１）二阶差频声波不具有随传播距离积累增长的性质；２）两个ＳＨ型板波模式的阶数和频率满足一定关系时，二阶和频声波可以个具有积累增长的性质；３）二阶和频积累波声场呈对称性质。本文还给出满足边界条件和初始条件的二阶和频各累波解的解析表达式。

Generation of second-order sum frequency cumulative waves of SH plate modes in an isotropic plate

Generation of second order sum frequency and difference frequency acoustic waves due to the bulk nonlinearity of the plate material will occur once SH plate modes propagating in an isotropic plate include two frequencies.An approach based on second order approximation is described for studying the generation of second order acoustic waves,which arise from the cross interaction of the partial bulk waves of two SH plate modes with different frequencies.One can draw the following conclusions:1)second order difference frequency acoustic waves must not have the character of cumulative growth;2)second order sum frequency acoustic waves may have the character of cumulative growth once some conditions between the excitation frequencies and the order numbers of two SH plate modes are satisfied;3)the fields of second order sum frequency cumulative waves retain the symmetry character.The present article also gives out the analytical expressions of second order sum frequency cumulative waves,which satisfy the boundary and initial conditions of excitation.