Solution-concentration sensor using ultrasonic light diffraction effect

Describes the workings of an innovative solution-concentration sensor using an acousto-optic effect. We concentrate here on the sensitivity characteristics for NaCl and sucrose solutions over a range of ultrasonic frequencies (f_a) (9-30 MHz) on which Raman-Nath diffraction occurs. The concentration of NaCl solutions (0-20.0%) has been measured with a sensitivity of 35.20 mV/% at f_a=29.998 MHz, and the sensitivity for sucrose solutions (0-20.0%) have reached 13.48 mV/% at f_a=29.298 MHz. Moreover, temperature sensitivity for water due to strong temperature dependence of sound velocity in liquids have reached 4.75 mV/°C at f_a=9.898 MHz over the range of 25°C±5°C. From experimental results, it was clearly confirmed that the sensitivity increases in proportion to f_a which drives an acousto-optic: (AO) cell. A proportional coefficient S_cf for NaCl solutions is 1.14 mV/%.MHz and that of sucrose is 0.341 mV/%. MHz. From that experimental results and a deviation factor derived from an empirical equation of sound velocity obtained by phase-locked loop (PLL), the sensitivity for a PLL-type AO improves 2.35 times that for an ordinary AO at ultrasonic frequency of 22.898 MHz.