Sensor of a measuring device designed to measure a mass flow or a density of a medium flowing through at least one measuring tube of the sensor, said sensor comprising: the at least one measuring tube with an inlet and an outlet, wherein the tube is designed to conduct the medium between the inlet and the outlet; at least an exciter, which is designed to make the at least one measuring tube vibrate; and at least two sensors, which are designed to measure the deflection of the vibrations of the at least one measuring tube, wherein the exciter and the sensors each have a coil unit and a magnet unit, wherein the magnet units can be moved in relation to the respective coil unit, and wherein the magnet unit and the coil unit of an exciter or a sensor interact with one another by means of magnetic fields, wherein the sensor comprises a support body, wherein said support body is designed to hold the at least one measuring tube, wherein the coil unit comprises a printed circuit board with at least a printed circuit board layer, wherein each printed circuit board layer comprises a first side surface (3.1) and a second side surface (3.2) parallel to the first side surface, wherein the coil unit has at least a coil, wherein the coil is formed at least in sections by means of an electrically conductive conductor path (4.3), wherein the coil is arranged on the first side surface and/or on the second side surface of a printed circuit board layer, wherein the at least one coil has a first coil end (4.1) and a second coil end (4.2), wherein at least a first coil end and at least a second coil end are each connected to a contact, wherein the at least one coil has, in each case, a winding area and a central area without windings, wherein the central area of a coil has a rectangular shape with opposing first sides and with opposing second sides, wherein the first sides have a first side length and the second sides have a second side length, wherein the rectangular shape of the central area has a first side median associated with the first side and a second side median associated with the second side, wherein the electric conductor path has a conductor path width of at least 30 micrometers, wherein the coil is designed to detect a magnetic field that varies over time, produced by a relative movement of a magnet of a magnet unit of the sensor, characterized in that a ratio of the first side length to the second side length is greater than 3.25 and particularly greater than 3.5 and preferably greater than 3.75, wherein a deflection of the vibrations of the measuring tube has a vibration direction parallel to the second side of the rectangular shape of the central area. the at least one measuring tube with an inlet and an outlet, wherein the tube is designed to conduct the medium between the inlet and the outlet; at least an exciter, which is designed to make the at least one measuring tube vibrate; and at least two sensors, which are designed to measure the deflection of the vibrations of the at least one measuring tube, wherein the exciter and the sensors each have a coil unit and a magnet unit, wherein the magnet units can be moved in relation to the respective coil unit, and wherein the magnet unit and the coil unit of an exciter or a sensor interact with one another by means of magnetic fields, wherein the sensor comprises a support body, wherein said support body is designed to hold the at least one measuring tube, wherein the coil unit comprises a printed circuit board with at least a printed circuit board layer, wherein each printed circuit board layer comprises a first side surface (3.1) and a second side surface (3.2) parallel to the first side surface, wherein the coil unit has at least a coil, wherein the coil is formed at least in sections by means of an electrically conductive conductor path (4.3), wherein the coil is arranged on the first side surface and/or on the second side surface of a printed circuit board layer, wherein the at least one coil has a first coil end (4.1) and a second coil end (4.2), wherein at least a first coil end and at least a second coil end are each connected to a contact, wherein the at least one coil has, in each case, a winding area and a central area without windings, wherein the central area of a coil has a rectangular shape with opposing first sides and with opposing second sides, wherein the first sides have a first side length and the second sides have a second side length, wherein the rectangular shape of the central area has a first side median associated with the first side and a second side median associated with the second side, wherein the electric conductor path has a conductor path width of at least 30 micrometers, wherein the coil is designed to detect a magnetic field that varies over time, produced by a relative movement of a magnet of a magnet unit of the sensor, characterized in that a ratio of the first side length to the second side length is greater than 3.25 and particularly greater than 3.5 and preferably greater than 3.75, wherein a deflection of the vibrations of the measuring tube has a vibration direction parallel to the second side of the rectangular shape of the central area.