The application of the principle of orthogonality of the vibration mode shapes of a structure to the design of shaped modal sensors, which detect the vibrational response of the structure for the mode for which they are designed, is presented. The principle was applied in the design of shaped polyvinylidene fluoride (PVDF) modal sensors for detecting the first and second modes of the bending vibration of a simply-supported beam. These sensors, which are designed as the mode 1 and the mode 2 sensors, respectively, were bonded to the same surface of a simply-supported steel beam. The beam was subjected to random vibration by an electromagnetic exciter connected to the opposite surface of the beam. The vibrational responses of the beam measured by the distributed mode 1 and mode 2 PVDF shaped sensors are compared with the vibrational responses measured using an accelerometer. It is shown that the distributed sensors produce maximum voltage output for modes 1 and 2, respectively, for which they were designed. Furthermore, is shown that by dividing the mode 1 and mode 2 sensors into two separate halves and adding or subtracting the output signals of these halves, the mode 1 sensor can be used to detect the second mode of vibration of the beam while the mode 2 sensor can be used to detect the first mode of vibration of the beam.