Abstract: This invention relates to volcanic ash sensing techniques for aircraft, and to related sensing apparatus and methods. We thus describe a volcanic ash sensor for an aircraft, the sensor comprising: an electrically conducting ash charge collection device; an electrically insulating support for mounting said collection device in an air duct; and a charge measurement system having an input electrically coupled to said ash charge collection device; wherein said electrically conducting ash charge collection device is configured such that an air flow over said ash charge collection device is a turbulent flow; and wherein said charge measurement system is configured to determine a level of charge in said ash charge collection device to determine the presence of volcanic ash in said air flow.

Abstract: An opto-mechanical device is constituted by an optically responsive actuating member in which a mechanical strain occurs in response to changes in its illumination. The actuating member is preferably at least partly formed from a semiconducting glassy matrix such as a chalcogenide glass. Preferably the opto-mechanical device illuminates the actuating member with light which is preferably plane polarized. Preferably it also varies the polarization angle of the plane polarized light to cause a change in the strain generated in the actuating member.