Fig. 1. Schematic diagram of MSDM demodulation system

Fig. 2. Structure of EFPI sensor head and simulation of Eq.（2）and Eq.（6）

Fig. 3. Error bound and condition number of SDM and MSDM

Fig. 4. The demodulation error of the two methods varies with cavity length，signal frequency，amplitude and error of $\mathrm{c}\mathrm{o}\mathrm{s}\delta$

Fig. 5. The result difference after demodulation by SDM and MSDM for simulation signal

Fig. 6. Figure and spectrum of EFPI sensor head

Fig. 7. The difference after demodulation by SDM and MSDM for same signal

Fig. 8. Waveforms of $R_{\mathrm{1}}$，$R_{\mathrm{2}}$，$\alpha$，$\beta$ in other experiment groups

Fig. 9. The theoretical value of $\mathrm{c}\mathrm{o}\mathrm{s}\delta$ when the cavity length is about 200 μm，the linearity between sound pressure and the amplitude of MSDM demodulation results and MSDM demodulation result spectra of other frequencies