An acoustic touch apparatus, comprising: a substrate , having top and bottom surfaces (53, 103, 253, 353; 55, 105, 255, 355), that is adapted in a first region to propagate surface acoustic waves along substrate surfaces and in a second region to transfer propagating surface acoustic waves from the one of the surfaces to the other surface through the substrate via top-bottom oscillation; at least one acoustic wave transducer on the bottom surface in the second region that is adapted to transmit surface acoustic waves; and at least one acoustic wave transducer on the bottom surface in the second region that is adapted to receive surface acoustic waves from the transmitting transducer, said substrate having, between the transmitting transducer and the receiving transducer, at least one first region disposed between two second regions, characterized in that , the bottom surface is configured with a surface indent that is formed adjacent to the second region around the entire bottom surface so that there is a distinct difference between the thickness (t) of the substrate at the indent and in the second region and the thickness (T) of the substrate in the non-indented first region, wherein the thickness (t) of the substrate at the indent and in the second region is such to permit surface wave energy to be transferred between the front and bottom surfaces and make surface acoustic waves propagating on one surface to appear on the other surface, the thickness (T) of the substrate in the non-indented, first region is such to maintain surface acoustic waves propagating on a respective surface, and the length of the indent and the indented second region is such to accommodate a top-bottom and bottom-top energy transfer. a substrate , having top and bottom surfaces (53, 103, 253, 353; 55, 105, 255, 355), that is adapted in a first region to propagate surface acoustic waves along substrate surfaces and in a second region to transfer propagating surface acoustic waves from the one of the surfaces to the other surface through the substrate via top-bottom oscillation; at least one acoustic wave transducer on the bottom surface in the second region that is adapted to transmit surface acoustic waves; and at least one acoustic wave transducer on the bottom surface in the second region that is adapted to receive surface acoustic waves from the transmitting transducer, said substrate having, between the transmitting transducer and the receiving transducer, at least one first region disposed between two second regions, characterized in that , the bottom surface is configured with a surface indent that is formed adjacent to the second region around the entire bottom surface so that there is a distinct difference between the thickness (t) of the substrate at the indent and in the second region and the thickness (T) of the substrate in the non-indented first region, wherein the thickness (t) of the substrate at the indent and in the second region is such to permit surface wave energy to be transferred between the front and bottom surfaces and make surface acoustic waves propagating on one surface to appear on the other surface, the thickness (T) of the substrate in the non-indented, first region is such to maintain surface acoustic waves propagating on a respective surface, and the length of the indent and the indented second region is such to accommodate a top-bottom and bottom-top energy transfer. <EOS>