Herein is described a chemical sensor that can detect the frequency of ultrasound. Exposure of aqueous n-alkyl sulfate or sulfonate surfactant solutions to high-intensity ultrasound results in the formation of secondary carbon-centered radicals. The yield of these radicals reaches a maximum plateau, the magnitude of which is limited by the dynamic ability of the surfactant to accumulate at the rapidly oscillating gas/solution interface of cavitation bubbles. For this reason, the maximum plateau yield observed following sonolysis of sodium butane sulfonate solutions compared to that of sodium dodecyl sulfate solutions (i.e., CHSBso,/CHSDS) Was greater than 1. Interestingly, it was found that the CHSBSo/CHSDS ratio had a linear dependence on ultrasound frequency. Since it is known from earlier studies that the CHSBSs/CHSDS ratio is independent of ultrasound intensity and of the geometry of flat plate exposure systems, a plot of the CHSBSo/CHSDS ratio against ultrasound frequency yields a calibration curve. With this calibration curve, the CHSBSo/CHSDS ratio can be used to detect the frequency of ultrasound in flat plate transducer systems. The effect can best be described in terms of the dynamic surface tension of surfactants in relation to the influence of ultrasound frequency on the lifetime of the gas/solution interface of sonochemically active cavitation bubbles.