US 4,339,954 A · Measurement of small movements

Abstract

Measurement of small oscillatory movements of an irregular surface involves the production of a speckle pattern therefrom by coherent light illumination, and the arrangement of a photodetector for direct response to such pattern, variations in photodetector output component at the frequency of the surface movement representing that movement. Another, stationary, illuminated irregular surface can be involved to produce a speckle interference pattern for response of the photodectector thereto and, in the case where the two surfaces are closely adjacent, a single beam can be used to illuminate the first and other surfaces predominantly and by stray light, respectively. This common beam illumination can be used in prior speckle interferometry. The first surface can be an eardrum oscillated by a sound wave, suitably of swept frequency or impulse form, with detection of the photodetector variations respectively being in synchronous manner or by Fourier analysis, respectively.

Claims14

Dependent claims

A method of measuring the out of plane movement of an oscillating irregular surface, comprising the steps of:

illuminating the surface with coherent light, the reflexions and scattering of the coherent light from the surface forming a speckle pattern,
detecting with a spatially integrating photodetector, variations caused by the out-of-plane movement in the speckle pattern and generating a photodetector signal indicative thereof and
continuously detecting, from the photodetector signal, amplitude variations thereof at the frequency of the out-of-plane movement to represent such movement.

Dependencies are inferred from the claim text.

Measurement of small movements

Life of this patent

Measurement of small movements

Life of this patent

Abstract

Claims14