An underwater acoustic deception system deceives a sensor installed on a threat existing in or on water by acoustic effect in order to protect ships from the threat. The underwater acoustic deception system is provided with a control device, a laser oscillator and emission optical system. The control device determines a focusing position to focus a laser beam (50) in water in order to generate bubbles (70) at a desired position with a desired scale and emission parameters of the laser beam (50). The laser oscillator generates the laser beam (50) configured to focus in water and generate bubbles. The emission optical system emits the generated laser beam (50) to the focusing position. The underwater acoustic deception system deceives an arbitrary sensor existing in the water by acoustic effect of the bubbles (70) on the surroundings.

Various embodiments include a magnetic compensation device for a drone for triggering mines comprising: a flux-guiding element comprising a soft magnetic material in the shape of an open or closed ring; a receiving chamber for the drone for holding the drone; and an electric coil device coupled magnetically to the flux-guiding element so a predetermined magnetic flux can be coupled into the flux-guiding element using the coil device. The flux-guiding element and the receiving chamber are arranged in relation to one another so that a magnetic flux brought about by the drone can be closed through the ring shape of the flux-guiding element.

An underwater acoustic deception system deceives a sensor installed on a threat existing in or on water by acoustic effect in order to protect ships from the threat. The underwater acoustic deception system is provided with a control device, a laser oscillator and emission optical system. The control device determines a focusing position to focus a laser beam (50) in water in order to generate bubbles (70) at a desired position with a desired scale and emission parameters of the laser beam (50). The laser oscillator generates the laser beam (50) configured to focus in water and generate bubbles. The emission optical system emits the generated laser beam (50) to the focusing position. The underwater acoustic deception system deceives an arbitrary sensor existing in the water by acoustic effect of the bubbles (70) on the surroundings.

Various embodiments include a magnetic compensation device for a drone for triggering mines comprising: a flux-guiding element comprising a soft magnetic material in the shape of an open or closed ring; a receiving chamber for the drone for holding the drone; and an electric coil device coupled magnetically to the flux-guiding element so a predetermined magnetic flux can be coupled into the flux-guiding element using the coil device. The flux-guiding element and the receiving chamber are arranged in relation to one another so that a magnetic flux brought about by the drone can be closed through the ring shape of the flux-guiding element.

A duct arrangement for an internal combustion engine comprises an exhaust duct, an inlet duct and a cooling air duct. The exhaust duct is contained within the cooling air duct for substantially its whole length and the cooling air duct is contained within the inlet duct for substantially its whole length, so that in use the cooling air duct provides a barrier to limit heat transfer between gas flowing in the exhaust duct and gas flowing in the inlet duct. The invention avoids the need for separate inlet and exhaust ducts with their attendant disadvantages. The separation of the inlet and exhaust ducts by the cooling air duct allows the inlet air to be kept as cool as possible, as is necessary for efficient engine operation.