A Solid Lens Collimator for High Frequency Near-Field Measurements

摘要

The report describes a solid lens operating as the acoustic equivalent of an optical collimator to produce planar waves. The acoustic collimator uses a single transducer element placed at the focal point of an acoustic lens. Amplitude shading which is required to control the diffraction rings at the edge of the field can be accomplished by proper selection of the attenuation coefficient of the lens material. Also, the directivity of the single transducer element can be designed to achieve appropriate shading of the lens aperture. The report describes collimator lens design considerations and experimental results obtained with a 50 cm diameter polystyrene lens used as a collimator in calibrating a 20 cm square hydrophone in the frequency range 200 to 600 kHz and a 10-cm piston in the frequency range 600 to 1200 kHz. Far-field results and those obtained with the collimator lens in the near-field are compared. (Modified author abstract)