350
4 Speckle-Optical Methods and Devices for Studying …
composition of time-varying speckle-fields. The described method is protected by
certificate of authorship No 1310624 (the USSR) [71].
4.8 Method for Measurement of Movement Velocity Vector
of Diffuse Objects
The method described in Sect. 5.1 for measurement of muscle tissue velocity, which
uses pinhole aperture, gives the possibility to determine module but not the direction
of the movement velocity. There are methods where an aperture with preferential
direction is applied [120]. They give the possibility to ascertain the direction of
velocity, but here the sign stays indefinite, and the possibility of real-time measurements is lost. Besides registration of the speckle-pattern averaged on the larger area
of the aperture minimizes signal fluctuations significantly. And amplifiers have to
be used with much greater amplification coefficients, which lead to the increased
nonlinear distortions under other equal conditions.
In this sense, speckle-counting method appears to be easier and more flexible. On
its basis, a method for determining the velocity vector of the diffuse object as well as
the device for its realization was developed [121]. Its essence consists in preliminary
known additional movement, which is imparted to speckles, and measurement of
velocity variation module gives the opportunity to determine direction of the movement. The scheme of the device implementing this method is presented in Fig. 4.20a.
If mirrors M 1 and M 2 are stationary, then movement of speckles caused by object
movement is registered with the speckle-counting method (Fig. 4.21).
If the mirrors are made to rotate around the perpendicular axes at an angular
velocity ω, then the speckle-structure will be shifted through the aperture at a velocity
of
υ + δ
υ. The scheme parameters are selected in such a way that |δ
υ| < | υ|. After
imparting additional motion to speckles in two directions, total velocities will have
different modules |
υ 1 | and |
υ 2 | that gives the possibility to calculate the initial velocity
vector. After measurements of modules |
υ 1 | and |
υ 2 | (Fig. 4.21) consequently or
simultaneously, supposing that additions δ
υ 1 and δ
υ 2 are perpendicular and equal in
size, the following formulae can be obtained for calculation
|
υ| =
|
υ 1 |
2 + |
υ 2 |
2
2
− |δ
υ|
2 ;
(4.78)
tgα =
|
υ 2 |
2 − |
υ|
2 − |δ
υ|
2
|
υ 1 |
2 − |
υ|
2 − |δ
υ|
2
.
(4.79)
Accuracy of determining α-angle can be estimated according to the latter formula.
Taking into account that |δ
υ| || υ| after some transformations, the dispersion of
angle change can be found
4 Speckle-Optical Methods and Devices for Studying …
composition of time-varying speckle-fields. The described method is protected by
certificate of authorship No 1310624 (the USSR) [71].
4.8 Method for Measurement of Movement Velocity Vector
of Diffuse Objects
The method described in Sect. 5.1 for measurement of muscle tissue velocity, which
uses pinhole aperture, gives the possibility to determine module but not the direction
of the movement velocity. There are methods where an aperture with preferential
direction is applied [120]. They give the possibility to ascertain the direction of
velocity, but here the sign stays indefinite, and the possibility of real-time measurements is lost. Besides registration of the speckle-pattern averaged on the larger area
of the aperture minimizes signal fluctuations significantly. And amplifiers have to
be used with much greater amplification coefficients, which lead to the increased
nonlinear distortions under other equal conditions.
In this sense, speckle-counting method appears to be easier and more flexible. On
its basis, a method for determining the velocity vector of the diffuse object as well as
the device for its realization was developed [121]. Its essence consists in preliminary
known additional movement, which is imparted to speckles, and measurement of
velocity variation module gives the opportunity to determine direction of the movement. The scheme of the device implementing this method is presented in Fig. 4.20a.
If mirrors M 1 and M 2 are stationary, then movement of speckles caused by object
movement is registered with the speckle-counting method (Fig. 4.21).
If the mirrors are made to rotate around the perpendicular axes at an angular
velocity ω, then the speckle-structure will be shifted through the aperture at a velocity
of
υ + δ
υ. The scheme parameters are selected in such a way that |δ
υ| < | υ|. After
imparting additional motion to speckles in two directions, total velocities will have
different modules |
υ 1 | and |
υ 2 | that gives the possibility to calculate the initial velocity
vector. After measurements of modules |
υ 1 | and |
υ 2 | (Fig. 4.21) consequently or
simultaneously, supposing that additions δ
υ 1 and δ
υ 2 are perpendicular and equal in
size, the following formulae can be obtained for calculation
|
υ| =
|
υ 1 |
2 + |
υ 2 |
2
2
− |δ
υ|
2 ;
(4.78)
tgα =
|
υ 2 |
2 − |
υ|
2 − |δ
υ|
2
|
υ 1 |
2 − |
υ|
2 − |δ
υ|
2
.
(4.79)
Accuracy of determining α-angle can be estimated according to the latter formula.
Taking into account that |δ
υ| || υ| after some transformations, the dispersion of
angle change can be found