The campaniform sensillum is a displacement sensor found in the external skeleton (cuticle) of insects, lobsters, spiders, etc. It is a hole extending through the cuticle arranged such that its shape changes in response to loads. In specific directions The shape change is rotated through 90° by the suspension of a bell-shaped cap whose deflection is detected by a cell beneath the cuticle. It can be sensitive to displacements of the order of 1 nm.
Engineering mechanics teaches that holes are commonly stress concentrators and crack initiators, not sources of information for sensor engineers. The membrane in a blind hole serves to amplify the strain in the wafer. However the sensitivity of strain sensors could be further enhanced by learning from strain sensors found in biology, for instance the campaniform sensillum of insects. Its unique structure yields strain amplification that enables more sensitive strain detection, even when associated with a stiff material.