Measuring and testing – Liquid analysis or analysis of the suspension of solids in a... – Viscosity
Patent
1992-07-03
1994-04-19
Housel, James C.
Measuring and testing
Liquid analysis or analysis of the suspension of solids in a...
Viscosity
73 5423, 73 5428, 73 5437, 73 5439, G01N 1114
Patent
active
053035780
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a device for investigating the properties of a viscoelastic medium, and more particularly, to a rheometer for measuring the dynamic rheological properties of gels, melts, polymer solutions, and other highly viscous media.
Conventional dynamic rheological techniques involve the forced generation of shear waves of varying magnitude in the medium under investigation and the recording of displacements of a wave-receiving and reflecting surface using a suitable transducing device. Phase and magnitude relationships between corresponding force and displacement waveforms are then analysed to determine the rheological properties of the medium. The major disadvantage of such techniques lies in the fact that accurate determination of the dynamic stresses and strains at measuring geometry boundaries is required to produce meaningful results. Such accurate determination is difficult to achieve at high frequencies.
SUMMARY OF THE INVENTION
The present invention enables a technique to be used relying on the utilisation of phase and magnitude relationships between corresponding displacement waveforms (relative to a common forcing source) generated by transducers connected to two wave receivers/reflectors disposed at different distances from the source, to determine the shear wave velocity and attenuation.
According to a first aspect of the invention, there is provided apparatus for investigating dynamic rheological properties of a viscoelastic medium comprising: in said medium on oscillation of said driven member; surface; generating surface, which may be the same as, or different to, said one wave generating surface, said second shear wave receiving surface being spaced from said second wave generating surface by an amount different to the spacing between said first shear wave receiving surface and said one shear wave generating surface; and sensing variations in physical parameters affecting said wave receiving surfaces induced by oscillation of said driven member, and capable of generating an output signal.
Preferably two shear wave generating surfaces are provided, in which case it is preferable that each of the shear wave receiving surfaces substantially faces a respective opposed shear wave generating surface. It is further preferred that each of the shear wave generating surfaces should be substantially planar and should oscillate in a respective plane, the respective planes being substantially parallel to a corresponding substantially planar receiving surfaces.
Preferably, means for adjusting the separation between at least one of the wave generating surfaces and a respective wave receiving surface is provided. The adjusting means may be a micrometer connected to at least one of the wave generating surfaces.
It is preferred that the oscillatable member should be driven by a suitably arranged set of Helmholtz coils energised by a voltage supplied by a signal generator. It is further preferred that the voltage supplied should be sinusoidal.
The oscillations are preferably of relatively small amplitude, such that linear viscoelastic behaviour is invoked in the medium and the frequency of oscillation preferably lies in the range of 50 Hz to 3 kHz.
The transducers may be of piezo-crystal type or preferably of the non contacting inductive or capacitive type.
Further adjustment means may be provided enabling the driving member to be movable in directions substantially normal to, and substantially parallel to, the planes of the wave receiving surfaces.
It is preferred that the output signal from each transducer should be passed to signal processing means (as shown by reference numeral 17 in FIG. 1) arranged to provided a signal representative of the rheological properties of the test viscoelastic medium, determined according to computed values derived from the measured response from the respective transducers. The resulting signal may be processed by signal conditioning means for output display purposes.
According to a second aspect of the invention, there i
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patent: 3943753 (1976-03-01), Simon
patent: 4148214 (1979-04-01), Madsen
patent: 4488427 (1984-12-01), Matusik et al.
patent: 4535621 (1985-08-01), Gervais et al.
patent: 4566324 (1986-01-01), Vinogradov et al.
patent: 5056358 (1991-10-01), Laskowski et al.
Williams David J. A.
Williams Phylip R.
Carri-Med Limited
Collins Laura E.
Gordon David P.
Housel James C.
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