Fig. 1. Block diagram of AP flow

Fig. 2. Flow chart of PSO-ASVR method

Fig. 3. Block diagram of sensor structure

Fig. 4. Physical picture of sensor and standard samples

Fig. 5. Diagram of calibration data

Fig. 6. Diagram of test data

Fig. 7. Fitting error δ obtained by least square method

Fig. 8. Fitting error δ obtained by partial least square method

Fig. 9. Fitting error δ obtained by PSO-ASVR