Acoustic Reflection

Acoustic reflection is a technique developed for and best suited to the measurement of the thickness of materials such as concrete and steel.  It is used on concrete floor slabs to non-destructively measure the slab thickness with millimetre accuracy, thereby saving numerous core holes or drill holes.  It can also be used to measure column or wall construction thicknesses, such as retaining walls.

The method requires an operator to place a vibration sensor firmly against the measuring surface.  A small hammer is then used to strike the surface, causing acoustic energy to propagate into the material being measured.  The underside of the material then reflects a proportion of the acoustic energy back to the geophone, creating a spike in the time/energy graph.  Tabulated data or a site specific test could be used to determine velocity, allowing the travel time to be converted to thickness.