Acoustic impedance measurement
AssigneeGeneral Electric Company
InventorAsif A. Syed
Life of this patent
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Abstract
An open-ended acoustic impedance tube is abutted against a material having a known acoustic impedance and a standing wave pattern is established in the tube. A first apparent impedance of the material is derived based on the standing wave pattern. A correction factor is computed based on the known impedance and the first apparent impedance. The open-ended impedance tube is then abutted against a sample material and a second apparent impedance is derived. The actual impedance of the sample is inferred from the second apparent impedance and the correction factor.
Claims6
A method of inferring the actual acoustic impedance of a sample material which is similar in structure and composition to a reference material having a known acoustic impedance, comprising the following steps:
- (a) abutting a waveguide against a first sample material;
- (b) projecting acoustic energy through the waveguide to the first sample material for establishing a standing wave pattern in the waveguide;
- (c) deriving a first apparent acoustic impedance of the first sample material based on the standing wave pattern of (b);
- (d) deriving a correction factor based on the known acoustic impedance and the first apparent impedance of (c);
- (e) repeating the operations of steps (b) and (c), but with respect to a second sample material, for deriving a second apparent sample impedance;
- and
- (f) inferring the actual impedance of the second sample material of (e) as a function of the second apparent sample impedance of (e) and of the correction factor (d).
A method of measuring the acoustic impedance of a laminated material using acoustic energy propagated through an acoustic waveguide, the laminated material containing a surrogate waveguide definable therein which surrogate waveguide extends generally in the same direction as the acoustic waveguide, but is of different cross-sectional size and shape than the acoustic waveguide, the method comprising the following steps:
- (a) measuring an apparent impedance of the material by a procedure which includes abutting the waveguide against the material at a reference location and establishing a standing wave pattern of acoustic energy within the waveguide;
- (b)measuring the actual impedance of the material at the reference location of (a) by a procedure which includes inserting a severed segment of the material into an impedance tube and establishing a standing wave pattern within the impedance tube;
- (c) computing a correction factor as a function of the actual and the apparent impedances;
- (d) measuring an apparent impedance of a sample location on the material by a procedure which includes abutting the waveguide against the sample material and establishing a standing wave pattern of acoustic energy within the waveguide;
- and
- (e) computing an actual impedance of the sample location of (d) as a function of the correction factor and the sample apparent impedance.
A method, which includes the use of an acoustic waveguide, for measuring the acoustic impedance of a sample laminated material having normal and transverse directions definable therein, having a first, acoustically hard, outer face, and a second outer face, and having an internal cellular matrix such that no boundary exists in the matrix which
- (i) comprises walls of the cells
- (ii) extends in the normal direction
- (iii) diminishes acoustic propagation in the transverse directions
- (iv) is similar in size and shape to the cross-sectional shape of the acoustic waveguide,
- the method comprising the following steps:
- (a) measuring the actual acoustic impedance of a reference material which is similar in structure and composition to the sample material;
- (b) measuring the apparent acoustic impedance of the reference material without taking active measures to diminish transverse acoustic propagation;
- (c) deriving a correction factor based on the actual and apparent acoustic impedance values according to a predetermined formula;
- (d) measuring the apparent reflection coefficient of the sample material in a manner similar to the measurement of (b);
- and
- (e) inferring the actual acoustic impedance of the sample material from the apparent reflection coefficient of (d) and the correction factor of (c) according to a predetermined formula.
In the measurement of the acoustic impedance of a material, the improvement for compensating for transverse acoustic propagation which occurs within the material, the improvement comprising:
- (a) measuring the actual acoustic impedance of a reference material, the measurement including the use of means for diminishing transverse acoustic propagation within the material;
- (b) measuring an apparent acoustic impedance of the reference material, the measurement including the non-use of means for diminishing transverse acoustic propagation within the materials;
- (c) deriving a correction factor based on the actual and the apparent reflection coefficients;
- (d) repeating the measurement of (b), but upon a sample material;
- and
- (e) applying the correction factor to the apparent reflection coefficient measured in (e).
Dependencies are inferred from the claim text.