Pressure sensitive inductive detector for use in user interfaces

A pressure-sensitive detector of user input on a user interface comprising:

• a first generally laminar inductive component;
• a second generally laminar inductive component;
• and
• a resilient panel,
• wherein the first inductive component and the second inductive component are arranged in facing relation and are mutually spaced;
• wherein the resilient panel deforms under the pressure of a user and is arranged for flexural movement relative to the second inductive component and the first inductive component is arranged for movement with the resilient panel,
• whereby, in use, pressure applied to the resilient panel causes movement of the first inductive component relative to the second inductive component, and a consequent change in the inductive coupling between the first and second inductive components;
• said detector further comprising at least one electronic detection circuit for detecting said change in the inductive coupling;
• said change being indicative of the pressure applied by the user on said user interface,
• wherein the resilient panel has a stiffness of at least 500 N/m and the ratio of the mutually overlapping area of the first and second inductive components to the square of the spacing of the first and second inductive components is greater than 150 to 1,
• wherein one of the first and second inductive components comprises a plurality of spiral windings wound around respective points;
• said spiral windings being in the plane of said laminar inductive component and wound around respective axes orthogonal to the plane of said laminar inductive component;
• and
• said detector further comprises a spacer sheet for spacing said first inductive component from said second inductive component;
• said spacer sheet comprising a plurality of apertures which define a plurality of sensitive regions of the detector;
• said apertures each comprising only one of said at least one spiral winding wound around a point;
• the spacer sheet supporting said resilient layer outside of said aperture to isolate mechanically said sensitive regions of the detector,
• wherein said other one of said first and second inductive components is a passive continuous component which deforms into said apertures solely when a user applies pressure onto said user interface and returns resiliently to its original state after pressure has been applied, and
• wherein said detector comprises a reference inductor, whereby a measured inductance value of a spiral winding is compared to an inductance value of said reference inductor in order to measure a change in inductance ratio.