An inspection system comprising: a microwave transmitter; one or more processors operably coupled to the microwave transmitter and configured to control the microwave transmitter to emit microwaves into multiple different portions of an object during a first sweep of the object and during a subsequent, second sweep of the object; and an infrared camera operably coupled to the one or more processors and configured to generate thermal image data of each of the portions of the object after the portions are heated by the microwaves during the first sweep and to generate select thermal image data after the portions are heated by the microwaves during the second sweep, wherein, during the first sweep, the one or more processors are configured to control the microwave transmitter to sequentially emit microwaves having multiple different frequencies within a designated frequency range into each of the multiple portions such that microwaves having a first frequency within the designated frequency range are emitted into a first portion of the portions during a first time period and microwaves having a second frequency within the designated frequency range are emitted into the first portion during a second time period subsequent to the first time period, wherein the one or more processors are configured to analyze the thermal image data generated by the IR camera during the first sweep to determine, for each of the portions of the object, a respective selected frequency within the designated frequency range which provides greater heating of the corresponding portion of the object than the other frequencies of microwaves emitted into the corresponding portion, and wherein, during the second sweep, the one or more processors are configured to control the microwave transmitter to emit microwaves having only the respective selected frequency into each corresponding portion of the object, and wherein the one or more processors are configured to analyze the select thermal image data generated by the IR camera during the second sweep to detect a thermal signature representative of an element in the object. a microwave transmitter; one or more processors operably coupled to the microwave transmitter and configured to control the microwave transmitter to emit microwaves into multiple different portions of an object during a first sweep of the object and during a subsequent, second sweep of the object; and an infrared camera operably coupled to the one or more processors and configured to generate thermal image data of each of the portions of the object after the portions are heated by the microwaves during the first sweep and to generate select thermal image data after the portions are heated by the microwaves during the second sweep, wherein, during the first sweep, the one or more processors are configured to control the microwave transmitter to sequentially emit microwaves having multiple different frequencies within a designated frequency range into each of the multiple portions such that microwaves having a first frequency within the designated frequency range are emitted into a first portion of the portions during a first time period and microwaves having a second frequency within the designated frequency range are emitted into the first portion during a second time period subsequent to the first time period, wherein the one or more processors are configured to analyze the thermal image data generated by the IR camera during the first sweep to determine, for each of the portions of the object, a respective selected frequency within the designated frequency range which provides greater heating of the corresponding portion of the object than the other frequencies of microwaves emitted into the corresponding portion, and wherein, during the second sweep, the one or more processors are configured to control the microwave transmitter to emit microwaves having only the respective selected frequency into each corresponding portion of the object, and wherein the one or more processors are configured to analyze the select thermal image data generated by the IR camera during the second sweep to detect a thermal signature representative of an element in the object.