There is described a sensing apparatus having a transmit aerial, which is operable to generate a magnetic field, and a receive aerial. The electromagnetic coupling between the transmit aerial and the receive aerial varies in dependence upon the shape of a flexible (19) member, thereby enabling information about the shape of the flexible member to be determined by processing the sense signal induced in the receive aerial by the magnetic field generated by the transmit aerial. In an embodiment, the sensing apparatus forms an airbag deployment sensor, with the shape of the flexible member varying as the airbag (3) inflates.
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