A sensor arrangement for a foreign object detection device for a wireless power transfer system , which includes: a) a current input and a current output , b) a multitude of detection cells (44.1 - 44.2; 144.1 - 144.9), each comprising a sense coil and a capacitive element, forming a resonant tank (45.1 - 45.4), wherein the sensor arrangement has a multitude of input leads (48a, 48b, 148a - 148c) and a multitude of output leads (50a, 50b, 150a - 150c), the total number of input and output leads (48a, 48b, 50a, 50b, 148a - 148c, 150a - 150c) being equal or smaller than the number of detection cells (44.1 - 44.2; 144.1 - 144.9), each detection cell (44.1 - 44.2; 144.1 - 144.9) being connected between one of the input leads (48a, 48b, 148a - 148c) and one of the output leads 50a, 50b, 150a - 150c), in a way that each of the detection cells (44.1 - 44.2; 144.1 - 144.9) is connected to a different pair of input and output leads (48a, 48b, 50a, 50b, 148a - 148c, 150a - 150c), c) the sensor arrangement further including an input selection circuit allowing to selectively establish an electrical connection between the current input and one or more of the input leads (48a, 48b, 148a - 148c), and an output selection circuit allowing to selectively establish an electrical connection between one or more of the output leads (50a, 50b, 150a - 150c) and the current output , d) wherein at least one detection cell (44.1 - 44.2; 144.1 - 144.9) includes a decoupling element (D1 - D4, D11 - D19) connected in series to its resonant tank, wherein e) the sense coils are arranged in more than one layer and wherein the sense coils of the different layers have different sizes. a) a current input and a current output , b) a multitude of detection cells (44.1 - 44.2; 144.1 - 144.9), each comprising a sense coil and a capacitive element, forming a resonant tank (45.1 - 45.4), wherein the sensor arrangement has a multitude of input leads (48a, 48b, 148a - 148c) and a multitude of output leads (50a, 50b, 150a - 150c), the total number of input and output leads (48a, 48b, 50a, 50b, 148a - 148c, 150a - 150c) being equal or smaller than the number of detection cells (44.1 - 44.2; 144.1 - 144.9), each detection cell (44.1 - 44.2; 144.1 - 144.9) being connected between one of the input leads (48a, 48b, 148a - 148c) and one of the output leads 50a, 50b, 150a - 150c), in a way that each of the detection cells (44.1 - 44.2; 144.1 - 144.9) is connected to a different pair of input and output leads (48a, 48b, 50a, 50b, 148a - 148c, 150a - 150c), c) the sensor arrangement further including an input selection circuit allowing to selectively establish an electrical connection between the current input and one or more of the input leads (48a, 48b, 148a - 148c), and an output selection circuit allowing to selectively establish an electrical connection between one or more of the output leads (50a, 50b, 150a - 150c) and the current output , d) wherein at least one detection cell (44.1 - 44.2; 144.1 - 144.9) includes a decoupling element (D1 - D4, D11 - D19) connected in series to its resonant tank, wherein e) the sense coils are arranged in more than one layer and wherein the sense coils of the different layers have different sizes. <EOS>