A method comprising: applying a specimen to an active surface that includes a plurality of microposts extending outwards from a substrate, wherein each micropost includes a proximal end attached to the substrate, a distal end opposite the proximal end, and a metallic, ferromagnetic or ferroelectric material on at least a portion of some of the microposts; generating an actuation force in proximity to the micropost array that compels at least some of the microposts to exhibit motion, wherein the actuation force is applied in accordance with a) a varying actuation force amplitude or b) a varying actuation force frequency; detecting light that is emitted by an illumination source and interacts with the active surface while the at least some microposts exhibit motion in response to the actuation force; measuring an amplitude or wavelength of the detected light interacting with the active surface; and determining at least one physical property of the specimen based on the measured amplitude or wavelength and feedback data pertaining to either a) the varying actuation force amplitude when the actuation force is applied with a variable amplitude, a fixed frequency and a fixed duty cycle or b) the varying actuation force frequency when the actuation force is applied with a fixed amplitude, a variable frequency and a variable duty cycle; wherein the feedback data is used to adjust the amplitude or frequency of the actuation force. applying a specimen to an active surface that includes a plurality of microposts extending outwards from a substrate, wherein each micropost includes a proximal end attached to the substrate, a distal end opposite the proximal end, and a metallic, ferromagnetic or ferroelectric material on at least a portion of some of the microposts; generating an actuation force in proximity to the micropost array that compels at least some of the microposts to exhibit motion, wherein the actuation force is applied in accordance with a) a varying actuation force amplitude or b) a varying actuation force frequency; a) a varying actuation force amplitude or b) a varying actuation force frequency; detecting light that is emitted by an illumination source and interacts with the active surface while the at least some microposts exhibit motion in response to the actuation force; measuring an amplitude or wavelength of the detected light interacting with the active surface; and determining at least one physical property of the specimen based on the measured amplitude or wavelength and feedback data pertaining to either a) the varying actuation force amplitude when the actuation force is applied with a variable amplitude, a fixed frequency and a fixed duty cycle or b) the varying actuation force frequency when the actuation force is applied with a fixed amplitude, a variable frequency and a variable duty cycle; a) the varying actuation force amplitude when the actuation force is applied with a variable amplitude, a fixed frequency and a fixed duty cycle or b) the varying actuation force frequency when the actuation force is applied with a fixed amplitude, a variable frequency and a variable duty cycle; wherein the feedback data is used to adjust the amplitude or frequency of the actuation force. <EOS>