Apparatus for high frequency scanning a product being manufactured in a continuous linear process, the apparatus comprising: two high frequency generators (3,4) providing output of identical frequency but of opposing phase, a magnetic foil with a mirrored face mounted for oscillation about a torsion axis, the foil being magnetised to provide regions of opposite polarity thereon respectively to each side of said torsion axis, a pair of induction coils (5,6) operatively associated with each of said generators (3,4), each coil (5,6) generating a magnetic force of alternating positive and negative polarity under the influence of said opposed phase output frequencies of the generators, the magnetic force interacting respectively with said regions to provide a main magnetic driving force acting on one of said regions to oscillate the foil about the torsion axis and an opposing control magnetic force acting on the other one of said regions to stabilise said oscillation and control the angular extent thereof, wherein the amplitude of the main magnetic driving force is greater than the amplitude of the control magnetic force, a light source for projecting a ray of light onto the mirrored face of the foil as it oscillates to direct successive curtains of parallel rays across the product in its linear path of travel to scan the product at the frequency of the generators (3,4), and detector means for receiving the resulting format of the parallel rays of light on the other side of the product after the passage of the product, there through, and analysis means for analysing the format of the resulting light rays after passage across the product and adapted to provide dimensional measurements and surface integrity of the product. two high frequency generators (3,4) providing output of identical frequency but of opposing phase, a magnetic foil with a mirrored face mounted for oscillation about a torsion axis, the foil being magnetised to provide regions of opposite polarity thereon respectively to each side of said torsion axis, a pair of induction coils (5,6) operatively associated with each of said generators (3,4), each coil (5,6) generating a magnetic force of alternating positive and negative polarity under the influence of said opposed phase output frequencies of the generators, the magnetic force interacting respectively with said regions to provide a main magnetic driving force acting on one of said regions to oscillate the foil about the torsion axis and an opposing control magnetic force acting on the other one of said regions to stabilise said oscillation and control the angular extent thereof, wherein the amplitude of the main magnetic driving force is greater than the amplitude of the control magnetic force, a light source for projecting a ray of light onto the mirrored face of the foil as it oscillates to direct successive curtains of parallel rays across the product in its linear path of travel to scan the product at the frequency of the generators (3,4), and detector means for receiving the resulting format of the parallel rays of light on the other side of the product after the passage of the product, there through, and analysis means for analysing the format of the resulting light rays after passage across the product and adapted to provide dimensional measurements and surface integrity of the product.