A quantitative study for body perspiration with conductivity-based humidity sensing system

The whole measuring system in this study was composed of temperature sensor (a T type of nickel-copper alloy), humidity sensor, flow meter, conductimeter and personal computer. The mini-chip humidity sensor with temperature compensation was fabricated by a conductive poly-(2-acrylamido-2-methyl-propane sulfonate) layer coated on an interdigitated style electrode surface, and was used to detect the slight variation of relative humidity (RH) in a 0.5 ml of closed space. The detection range for RH was 30 to 90 %RH with respect to the conductance response from 1 μS to 85 mS, and the resolution was obtained to be 6 %RH mS^-1. This sensor unit was placed on a specific skin surface for sweating monitor and recorded the electrical signal output. Three indexes were characterized for sweating quantification in our experiments. (1) The maximum sweating rate (MSR, %RHmin^-1), being used to calculate the first derivative from the sweating data in the first two minute, is acceleration ability for sweat gland to sweating. (2) The partial area of sweating (SPA, %RH min), being used to evaluate the kinetic function of sweating by the SPA obtained from the time with RH value integral in the first two minute. (3) The whole area of sweating (SWA, %RH min), being got from the total area calculation for a complete interval, described the actual amount of sweating in monitor phase. These (MSR, SPA, SWA) values were statistically tried to estimate the sweating difference for any body areas. Based on our results, the average of R and L palms (87.3 ± 4.71, 60.46 ± 2.28, 123.12 ± 10.9, n=12) and the average of R and L soles (78.167 ± 6.128, 42.33 ± 6.6, 133.67 ± 14.61, n=11) were more significant for sweating than chest (44.5 ± 1.87, 23.0 ± 0.89, 99 ± 3.6, n=6) and back (43.7 ± 2.5, 25.16 ± 1.47, 103.5 ± 1.87, n=6). This result was found to be well matching to the actual distribution of sweat gland in body. Therefore, the device with conductivity-based humidity sensing system is practicable in clinical sweat monitoring.