It has previously been shown that a three-dimensional mapping of an acoustic field's amplitude and phase may be calculated from a set of TV-holography measurements by use of tomographic techniques. In this paper a thorough mathematical description of this measuring technique is given. An increased number of measured projections improves the tomographic reconstructions significantly. Techniques for obtaining quantitative data for the pressure amplitude of the acoustic field are implemented. The technique is demonstrated by measurements of the near field of a loudspeaker and these measurements are shown to agree well with measurements obtained with a microphone.
We describe a hybrid evanescent-wave sensor component that we fabricated by using an integrated optical interferometer with a specially adapted photodetector array. The design of the interferometer is based on the use of tapered waveguides to obtain two intersecting collimated beams. Phase shifts can be measured with an angular precision of better than 10(-3) rad, which corresponds to a superstrate index change inferior of 10(-6) with our structure. The interest in the device as a chemical sensor is experimentally demonstrated. The same optical component could be used in a variety of other sensor applications, e.g., biological and immunological sensors.
Time-averaged TV holography has been shown to be a useful technique for investigating acoustic fields in transparent media. The theory of time-averaged TV-holography measurements of ultrasonic fields in water is described. Projections of the phase and the amplitude of a 3.25-MHz ultrasonic field from an annular ultrasound probe operated in cw mode are presented. Quantitative measurements with a spatial resolution of better than 100 mum have been obtained. A set of such projections may be processed into a three-dimensional mapping of the phase and the amplitude of the acoustic field by tomographic techniques. This process is described, and an example of a tomographic reconstruction of the same ultrasonic field is presented.
A vibrating sound source causes periodic variations of the refractive index in the surrounding medium. A light wave passing through the sound field will experience a corresponding variation of its path length which can be measured by interferometric techniques like TV holography. One TV-holography recording represents the integrated optical pathlength in one direction. The sound source is rotated to record cross sections of the field as seen from different directions. By tomographic backprojection of these recordings, afterward the amplitude and phase of the sound field in any plane of the volume are reconstructed.
Members of our group have previously demonstrated that TV holography may be used to measure the amplitude and the phase distributions of a sound field in air. This technique is not limited to acoustic fields in air, but may be applied to acoustic fields in any transparent medium. Its applicability to ultrasonic fields in water is demonstrated in this Letter.
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