Downhole communication

A system for use in downhole communication or detection, the system comprising:

• a downhole arrangement defining a throughbore;
• a primary element;
• and
• a secondary element,
• wherein one of the primary and secondary elements is provided on the downhole arrangement and the other of the primary and secondary elements is provided in the throughbore, and the primary and secondary elements are configurable for coupling of an electromagnetic field therebetween;
• wherein the downhole arrangement is configurable between a first configuration in which coupling of the electromagnetic field between the primary and secondary elements is prevented and a second configuration in which coupling of the electromagnetic field between the primary and secondary elements is permitted;
• wherein the downhole arrangement comprises a cover member, each secondary element is arranged radially outwardly of the cover member relative to a longitudinal axis of the throughbore of the downhole arrangement, and each secondary element and the cover member are moveable relative to one another;
• and
• wherein the cover member extends at least partially between the secondary element and the throughbore of the downhole arrangement in the first configuration and the cover member is at least partially withdrawn from between the secondary element and the throughbore of the downhole arrangement in the second configuration.

A system for use in downhole communication or detection comprising:

• a downhole arrangement defining a throughbore;
• a primary element;
• and
• a plurality of secondary elements,
• wherein one of the primary element and the plurality of secondary elements is provided on the downhole arrangement and the other of the primary element and the plurality of secondary elements is provided in the throughbore, and the primary element and each of the secondary elements are configurable for coupling of an electromagnetic field therebetween,
• wherein each secondary element is unconnected electrically to the other secondary elements,
• wherein each secondary element is configured so as to provide the electromagnetic field coupled between the primary and each secondary element with one or more characteristic features, and
• wherein each secondary element extends around a different axis, each axis arranged along a different radial direction relative to a longitudinal axis of the downhole arrangement.