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An actuation method for atomic force microscope (AFM) cantilevers in fluids is reported. The radiation pressure generated by a focused acoustic transducer at radio frequency (rf) (100–300 MHz) exerts a localized force of controlled amplitude at a desired location on the AFM cantilever. This force can be used to measure the spring constant and other dynamic properties of the cantilever. Furthermore, by amplitude modulating the rf signal input to the acoustic transducer, the cantilever is actuated in the dc–MHz frequency range. This provides a broadband actuation and characterization method for AFM cantilevers with arbitrary geometry. The technique is demonstrated on AFM cantilevers with spring constants in the 0.01–10 N/m range using a micromachined acoustic transducer/Fresnel lens structure operating at 179 MHz in water. © 2001 American Institute of Physics.