Apparatus and method for measuring a composition of a fluid

A method for measuring a composition of a fluid, comprising:

• providing a fluid in a fluid flow path defined by a wall of a fluid conduit;
• electromagnetically coupling a transmitting antenna and a receiving antenna with an electrically conductive waveguide member;
• guiding an electromagnetic field from the transmitting antenna to the receiving antenna along a waveguide path defined by the waveguide member,
• wherein the waveguide member is separated from the fluid flow path by an electrically insulating inner region of the wall and the waveguide member defines an opening which is disposed towards the fluid flow path to permit a portion of the electromagnetic field to extend through the opening and the inner region of the wall into the fluid flow path,
• wherein the waveguide member defines a helical groove disposed towards the fluid flow path and the helical groove defines the opening.

A method for manufacturing an apparatus for measuring a composition of a fluid, the method comprising:

• providing a fluid conduit having a wall which defines a fluid flow path;
• providing a transmitting antenna;
• providing a receiving antenna;
• and
• providing an electrically conductive waveguide member which is configured for electromagnetic coupling with the transmitting antenna and the receiving antenna and for guiding an electromagnetic field from the transmitting antenna to the receiving antenna along a waveguide path,
• wherein the waveguide member is separated from the fluid flow path by an electrically insulating inner region of the wall and the waveguide member defines an opening which is disposed towards the fluid flow path to permit a portion of the electromagnetic field to extend through the opening and the inner region of the wall into the fluid flow path,
• wherein the waveguide member defines a helical groove disposed towards the fluid flow path and the helical groove defines the opening.