Provided is an unmanned aerial vehicle for measuring the wall thickness of a structure. The unmanned aerial vehicle may be an intrinsically safe unmanned aerial vehicle and may include an arm having an electromagnetic acoustic transducer (EMAT) coupled to one end of the arm and a power and control assembly may be coupled to the other end of the arm as a counterweight. The power and control assembly may include an activation device for the EMAT, such as a proximity sensor. The EMAT may be coupled to a spring that compresses in response to a force normal to the wall being measured to prevent excessive force from being applied to the structure and the EMAT. Methods of measuring wall thickness using an unmanned aerial vehicle and a retrofit kit for an unmanned aerial vehicle are also provided.
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