Abstract: An anti-fouling system for producing vibrations in an underwater structure to inhibit the attachment of aquatic life forms to the structure. The system includes a controller which drives one or more transducer. The transducer comprises a housing, one end of which is closed by a resilient diaphragm. An electromagnet with soft magnetic core is contained in the housing spaced from an unsupported portion of the diaphragm. The unsupported portion of the diaphragm is mounted over an underwater structure. In operation, the electromagnet is excited with a current pulse, which deforms the diaphragm so that the housing moves towards the structure. As the current drops off, the diaphragm is restored to its original shape and the housing moves away from the structure imparting a vibrational force to the structure. The transducer includes an elastic membrane to compensate for changes in temperature and pressure commonly found when working under water.

Abstract: Supermarket point of purchase advertising typically consists of advertisements, brochures, coupons and the like disposed on shelving units. To attract prospective purchasers to such advertising and to constitute point of purchase advertising itself, there is disclosed a shelf-edge mounted device which senses an approaching shopper and then delivers an audio message. The device has an optical sensor which is pointed underneath a shelf and towards the interior of the shelving unit, and detects the shadow of the approaching shopper cast on the back of the shelving unit. A background plate in the field of view of the sensor improves its sensitivity.