Material evaluation with new modulation method in photoacoustic technique

The proposed new method partially solves the problem of low signal-to-noise-ratio (SNR) when modulation frequency increases. In this paper, the authors suggest keeping the amplitude of the detected photoacoustic (PA) signal constant by linearly increasing the modulation voltage versus the frequency. This technique decreases the SNR at low frequencies but increases the SNR in the usual noisy band and the PA signal of the sample can be easily estimated by FFT. Furthermore, the technique is demonstrated to effectively detect a subsurface defect in a graphite sample in the 10-100 Hz frequency range.