An apparatus for determining physical, chemical and/or biological properties of a medium, comprising - an acoustic waveguide, which has a conduction element with an inner side that faces the medium and an outer side that lies opposite this inner side, - at least one transmitter (S/E1, S/E2), by means of which at least one first surface wave is excitable at the conduction element, said at least one first surface wave propagating along the conduction element and, moreover, at least partly coupling into the medium as an acoustic wave, wherein the waveguide is embodied and configured such that the acoustic wave at least partly couples into the conduction element again as a second surface wave, - at least one receiver (S/E2, S/E1), by means of which both first and second surface waves (OW1, OW2) are receivable, and - one electronic evaluation device that is coupled at least to the receiver (S/E2, S/E1), by means of which evaluation device physical, chemical and/or biological properties of the medium are determinable on the basis of received first and second surface waves (OW1, OW2), wherein - the inner side facing the medium is curved in concave fashion and the outer side is curved in convex fashion and the waveguide with the conduction element curved in that way is configured such that a second surface wave coupling-in at the concave inner side propagates along a propagation direction to the receiver (S/E2, S/E1), and - provision is made of at least one damping element (10, 12, 22a, 22b) that lies downstream of the receiver (S/E1, S/E2) in the propagation direction of the second surface wave, said damping element prevents surface waves propagating counter to the propagation direction of the at least one second surface wave from reaching the receiver (S/E1, S/E2), characterized in that the conduction element is adjoined by a portion of the waveguide as a damping element (10, 12), which is curved and/or bent counter to the conduction element. - an acoustic waveguide, which has a conduction element with an inner side that faces the medium and an outer side that lies opposite this inner side, - at least one transmitter (S/E1, S/E2), by means of which at least one first surface wave is excitable at the conduction element, said at least one first surface wave propagating along the conduction element and, moreover, at least partly coupling into the medium as an acoustic wave, wherein the waveguide is embodied and configured such that the acoustic wave at least partly couples into the conduction element again as a second surface wave, - at least one receiver (S/E2, S/E1), by means of which both first and second surface waves (OW1, OW2) are receivable, and - one electronic evaluation device that is coupled at least to the receiver (S/E2, S/E1), by means of which evaluation device physical, chemical and/or biological properties of the medium are determinable on the basis of received first and second surface waves (OW1, OW2), wherein - the inner side facing the medium is curved in concave fashion and the outer side is curved in convex fashion and the waveguide with the conduction element curved in that way is configured such that a second surface wave coupling-in at the concave inner side propagates along a propagation direction to the receiver (S/E2, S/E1), and - provision is made of at least one damping element (10, 12, 22a, 22b) that lies downstream of the receiver (S/E1, S/E2) in the propagation direction of the second surface wave, said damping element prevents surface waves propagating counter to the propagation direction of the at least one second surface wave from reaching the receiver (S/E1, S/E2), characterized in that the conduction element is adjoined by a portion of the waveguide as a damping element (10, 12), which is curved and/or bent counter to the conduction element. characterized in that the conduction element is adjoined by a portion of the waveguide as a damping element (10, 12), which is curved and/or bent counter to the conduction element.