本论文考虑Helmholtz系统下分片常数性质的磁导率和介电常数的重构.首先,我们将卡尔德隆等式推广到Helmholtz系统下,然后通过对一次测量数据限制适当的条件,可以证明重构具有唯一性.这在现有文献中是全新的.“,”We consider the recovery of piecewise constants permeability and permittivity distributions in the Helmholtz system.First,the so called Calderón\'s identity is extended to suit for Helmholtz system.Then we show that the uniquenessof recovery by using only one measurement under some mild condition on the measurement,which is new to the literature.