A radio frequency identification (RFID) tag adapted to wirelessly communicate with a remote transceiver, comprising: a substrate (110; 210; 310; 410; 510; 930); an antenna (135; 220; 320; 420, 425; 520; 635; 635C; 935; 1030; 1130) disposed on the substrate; first and second integrated circuits (ICs) (342, 362; 440, 445; 1120, 1122) disposed on the substrate, each IC being electrically coupled to the antenna; characterised by first and second heating elements (344, 364) for heating respective first and second target areas and being electrically coupled to the respective first and second ICs, each of the first and second target areas having a thermal characteristic, the thermal characteristic of the first target area being known, the thermal characteristic of the second target area being unknown, the first target area being disposed on the substrate and being thermally coupled to the first heating element, the first heating element and target area being thermally isolated from the second heating element and being adapted to be thermally isolated from the second target area; and first and second sensing elements (346, 366; 950) being thermally coupled to the respective first and second heating elements for sensing a temperature of the corresponding heating element, such that when the second heating element is thermally coupled to the second target area, the RFID tag wirelessly receives an input power having an input form from a transceiver (130, 132; 632C), the first and second ICs transform the input power to respective first and second powers having respective first and second forms and deliver the first and second powers to the corresponding heating element, the first and second sensing elements sense a time variation of the corresponding heating element temperature, and the RFID tag wirelessly transmits to the transceiver a thermal characteristic of the second target area based on comparing the time variation of the first and second heating elements temperatures. a substrate (110; 210; 310; 410; 510; 930); an antenna (135; 220; 320; 420, 425; 520; 635; 635C; 935; 1030; 1130) disposed on the substrate; first and second integrated circuits (ICs) (342, 362; 440, 445; 1120, 1122) disposed on the substrate, each IC being electrically coupled to the antenna; characterised by first and second heating elements (344, 364) for heating respective first and second target areas and being electrically coupled to the respective first and second ICs, each of the first and second target areas having a thermal characteristic, the thermal characteristic of the first target area being known, the thermal characteristic of the second target area being unknown, the first target area being disposed on the substrate and being thermally coupled to the first heating element, the first heating element and target area being thermally isolated from the second heating element and being adapted to be thermally isolated from the second target area; and first and second sensing elements (346, 366; 950) being thermally coupled to the respective first and second heating elements for sensing a temperature of the corresponding heating element, such that when the second heating element is thermally coupled to the second target area, the RFID tag wirelessly receives an input power having an input form from a transceiver (130, 132; 632C), the first and second ICs transform the input power to respective first and second powers having respective first and second forms and deliver the first and second powers to the corresponding heating element, the first and second sensing elements sense a time variation of the corresponding heating element temperature, and the RFID tag wirelessly transmits to the transceiver a thermal characteristic of the second target area based on comparing the time variation of the first and second heating elements temperatures.