Method and apparatus for measuring the intensity of an acoustic field.

摘要

The meter includes a liquid crystal cell (12) for detecting acoustic energy and a control circuit (14) for applying an electric field to the cell. The cell includes a liquid crystal material having elongated molecules. The preferred liquid crystal is in the form of a layer of the nematic type which is homeotropically aligned. The elongated liquid crystal molecules exhibit positive dielectric anisotropy wherein the dielectric constant parallel to the molecule's axis is greater than the dielectric constant perpendicular to the molecule's axis. In the unexcited condition, the nematic layer is dark. In the ultrasonically excited condition, the nematic layer exhibit birefringence. A restoring electric force can be applied to the liquid crystal material to suppress the acoustically-induced birefringence condition of the cell to the dark appearance associated with the unexcited condition. The strength of the electric field required to suppress the birefringence is proportional to the acoustic intensity of the ultrasonic beam or acoustic field applied to the cell.