The sensor comprises a reference bolometer and a plurality of sensing bolometers. Each sensing bolometer is arranged adjacent to the reference bolometer. Each bolometer comprises (i) a substrate, (ii) a cap structure connected to the substrate, the cap structure configured to define a cavity between an inner surface of the cap structure and a first surface of the substrate, (iii) an absorber connected the substrate and arranged within the cavity, the absorber configured to absorb infrared radiation within the cavity, and (iv) a readout circuit connected to the absorber and configured to provide a signal that indicates an amount of infrared radiation absorbed by the absorber. The cap structure of the reference bolometer blocks infrared radiation from entering the cavity from outside the cap structure. The cap structure of each sensing bolometers allows infrared radiation to enter the cavity from outside the cap structure.