Eddy current sensor for non-destructive testing of a substrate, comprising a control unit; and a plurality of eddy current sensor elements (2, 2a, 2b, 2c, 2d), with each eddy current sensor elements (2, 2a, 2b, 2c, 2d) comprising an assembly of at least a first and a second flat coil, wherein the first flat coil and the second flat coil each have a triangular shape with a first to third coil edge (4a, 4b, 4c, 14a, 14b, 14c), wherein one of the edges (4b; 4c) of the first flat coil and one of the edges of the second flat coil are arranged adjacent and parallel to each other, and wherein the assembly has a square shape, wherein the eddy current sensor elements (2, 2a, 2b, 2c, 2d) are arranged in a quadrangular order, adjacent and parallel to each other, such that any two adjacent eddy current sensor elements (2, 2a, 2b, 2c, 2d) have two parallel edges, characterized in that the control unit is configured to simultaneously and jointly apply a first signal to the coils of a first sub-group, wherein the first sub group comprises at least two adjacent elements of the plurality of eddy current sensor elements (2, 2a, 2b, 2c, 2d), wherein the control unit is further configured to shift the sub-group in at least two directions (15, 16) by applying a second signal to a second sub-group of the coils, wherein the second sub-group comprises at least two adjacent elements of the plurality of eddy current sensor elements (2, 2a, 2b, 2c, 2d) with at least one of the eddy current sensor elements (2a, 2c) of the second sub-group (2a,2b; 2c, 2d) also forming part of the first sub-group (2, 2a; 2, 2c); the first and the second signals being such that adjacent inner edges of the flat coils of each sub-group are provided with currents in anti-parallel directions and such that the collective outer edge of the flat coils of each sub group is provided with a current in a collective circumferential direction, the control unit being further configured to sense the response of the substrate by detecting a change in impedance of the coils to which the signal has been applied. a control unit; and a plurality of eddy current sensor elements (2, 2a, 2b, 2c, 2d), with each eddy current sensor elements (2, 2a, 2b, 2c, 2d) comprising an assembly of at least a first and a second flat coil, wherein the first flat coil and the second flat coil each have a triangular shape with a first to third coil edge (4a, 4b, 4c, 14a, 14b, 14c), wherein one of the edges (4b; 4c) of the first flat coil and one of the edges of the second flat coil are arranged adjacent and parallel to each other, and wherein the assembly has a square shape, wherein the eddy current sensor elements (2, 2a, 2b, 2c, 2d) are arranged in a quadrangular order, adjacent and parallel to each other, such that any two adjacent eddy current sensor elements (2, 2a, 2b, 2c, 2d) have two parallel edges, characterized in that the control unit is configured to simultaneously and jointly apply a first signal to the coils of a first sub-group, wherein the first sub group comprises at least two adjacent elements of the plurality of eddy current sensor elements (2, 2a, 2b, 2c, 2d), wherein the control unit is further configured to shift the sub-group in at least two directions (15, 16) by applying a second signal to a second sub-group of the coils, wherein the second sub-group comprises at least two adjacent elements of the plurality of eddy current sensor elements (2, 2a, 2b, 2c, 2d) with at least one of the eddy current sensor elements (2a, 2c) of the second sub-group (2a,2b; 2c, 2d) also forming part of the first sub-group (2, 2a; 2, 2c); the first and the second signals being such that adjacent inner edges of the flat coils of each sub-group are provided with currents in anti-parallel directions and such that the collective outer edge of the flat coils of each sub group is provided with a current in a collective circumferential direction, the control unit being further configured to sense the response of the substrate by detecting a change in impedance of the coils to which the signal has been applied.