Transducer having metal housing and employing mode conversion

The process of measuring the flow velocity of a fluid in a conduit by injecting an ultrasonic wave into the interior of a metal conduit which carries a fluid in order to measure the flow of said fluid;

• said conduit having a characteristic shear mode velocity for sonic energy which propagates axially along said conduit;
• said process comprising producing longitudinal mode sonic energy wave in a metallic transducer housing;
• converting said longitudinal mode sonic energy wave into shear mode energy wave, by internal reflection of said longitudinal mode sonic energy wave from a surface of said metallic transducer housing;
• and applying said shear mode sonic energy from said transducer housing to the outer surface of said metal conduit;
• the angle of travel of said shear mode sonic energy wave relative to the axis of said conduit being such that the phase velocity of said shear mode sonic energy wave in said housing as it reaches the surface of said conduit equals the said shear mode velocity in said conduit.

A transducer comprising, in combination, a transducer element and a metal housing having the shape of a trapezohedron;

• said trapezohedron having a first planar edge surface defining an output energy surface and a second planar edge surface defining a mode conversion surface by internal reflection of a longitudinal mode wave;
• said first and second planar surfaces intersecting one another with an internal angle .phi.;
• said transducer element being a flat, thin element disposed within an opening in said metal housing and disposed in a plane which has a normal which forms an internal angle .beta. with respect to a normal to said second planar surface;
• longitudinal sonic energy from said transducer element being reflected from the interior of said second surface and being converted into shear mode sonic energy which is directed away from said second surface in a direction which forms an internal angle .gamma. with respect to a normal to said second planar surface and on the side of said normal away from the side thereof defining said angle .beta.;
• wherein .phi.=.alpha.+.gamma.;
• .alpha. is the internal angle between the direction of propagation of said shear mode wave and a normal to said first planar surface;
• and sin .gamma.=(v.sub.cs /v.sub.cl) sin .beta. wherein v.sub.cs is the shear mode velocity of said metal and v.sub.c is the longitudinal mode velocity of said metal;
• said second surface being coupled to a hollow elongated metal conduit;
• said metal conduit having a characteristic shear mode velocity v.sub.ps and wherein sin .alpha.=(v.sub.cs /v.sub.ps).

A flow monitoring system for measuring the flow in a metal conduit comprising first and second transducers clamped to the exterior of said conduit and axially displaced from one another;

• each of said transducers comprising, in combination:
• a transducer element and a metal housing having the shape of a trapezohedron;
• said trapezohedron having a first planar edge surface defining an output energy surface and a second planar edge surface defining a mode conversion surface by internal reflection of a longitudinal mode wave;
• said first and second planar surfaces intersecting one another with an internal angle .phi.;
• said transducer element being a flat, thin element fixed to said metal housing and disposed in a plane which has a normal which forms an internal angle .beta. with respect to a normal to said second planar surface;
• longitudinal sonic energy from said transducer element being reflected from the interior of said second surface and being converted into shear mode sonic energy which is directed away from said second surface in a direction which forms an internal angle .gamma. with respect to a normal to said second planar surface and on the side of said normal away from the side thereof defining said angle .beta., wherein .phi.=.alpha.+.gamma.;
• .alpha. is the internal angle between the direction of propagation of said shear mode wave and a normal to said first surface;
• and sin .gamma.=(v.sub.cs /v.sub.cl) sin .beta., wherein v.sub.cs is the shear mode velocity of said metal housing and v.sub.cl is the longitudinal mode velocity of said metal housing;
• and electronic means connected to said first and second transducers for measuring the difference in transit time of sonic energy through the fluid in said conduit in the upstream and downstream directions.

A flow monitoring system for measuring the flow of a fluid in a metal conduit comprising first and second transducers clamped to the exterior of said conduit and axially displaced from one another;

• each of said transducers comprising a transducer element and a metal transducer housing;
• said transducer element generating a longitudinal mode sonic energy beam in said housing which has a greater velocity than the shear mode velocity v.sub.ps of said conduit;
• each of said transducer elements including mode conversion surface means intercepting said longitudinal mode sonic energy beam and converting it to a shear mode sonic beam of velocity v.sub.cs which is less than said shear mode velocity of said conduit;
• said shear mode sonic energy beam in said housing forming an angle .alpha. to a normal to the axis of said conduit such that sin .alpha.=(v.sub.cs v.sub.ps);
• and electronic means connected to said first and second transducers for measuring the difference in transit time of sonic energy through the fluid in said conduit in the upstream and downstream directions.