## 4 Evaluation
### Optimal Design of Sensor Heating Layer  
In the theoretical analysis of the heat transfer of the humidity sensor, the article assumes the uniformity of the heating of the sensor. It analyzes the importance of the heater structure. However, in practice, due to the influence of the heating structure, there are differences in the heating temperature of the sensor, and the difference between high and low temperatures significantly impacts the sensor's performance. In addition, the energy for high-altitude meteorological detection is very precious, limiting the electrodes' heating power. To expand the heating area of the sensor when the input voltage is constant, we improve the uniformity of heating, and reduce the system's power consumption simultaneously. We need to optimize the design of the sensor heating layer structure and its heating strategy to improve sensor performance further. To design a sensor heating electrode structure that is more in line with the needs of meteorological detection, we use Comsol finite element analysis software to analyze the heat transfer of several common heater structures. We set the ambient temperature to \(-70\,\mathrm{\SIUnitSymbolCelsius}\), the substrate material to be silicon, the heater to be a nickel-chromium alloy, the electrode material to be silver, and the air convection coefficient to be \(5\,\mathrm{W}\big{/}(\mathrm{m}^{2}\cdot\mathrm{K})\). At the same time, we ensure that the total volume of each heater structure is the same, which is \(0.86975\,\mathrm{mm}^{3}\). We assume that the thermal conductivity variation of the sensor material is negligible to simplify the simulation model. The heating power of the four structures is set to be the same, which is \(0.02\) W. Figure 12 shows the results of the steady-state finite element analysis of heat transfer for each system. The temperature of the four structures is raised to about \(-8\,\mathrm{\SIUnitSymbolCelsius}\), much higher than the ambient temperature, which meets the conditions for eliminating sensor condensation. In addition, we drew the temperature distribution curves of each structure's longitudinal centers to further analyze each system's heat transfer uniformity, as shown in Figure 13.  
The total area where the surface temperature difference is less than \(0.5\,\mathrm{\SIUnitSymbolCelsius}\) when the heating reaches a steady state is selected as the optimal heating area of the sensor. The optimum heat transfer areas of the four structures are \(5.41\), \(5.87\), \(6.42\), and \(6.39\) mm\({}^{2}\), respectively. It can be seen from the figure that compared with the first two structures, the thicker electrode structure has a shorter total circuit length, and the heating area and uniformity are not as good as the thinner heating structure. In addition, the power loss is increased under the same input voltage due to the small resistance value of the thick electrode. The latter two systems increase the complexity of the structural design  
Figure 11: (**a**) Simulation verification of moisture-sensitive layer optimization scheme. (**b**) Simulation verification of electrode layer optimization scheme. to increase the heat transfer area and reduce the useless power loss. However, the third structure destroys the uniformity of the longitudinal resistance arrangement, and the temperature is concave in the central area, and the uniformity is poor. The fourth structure is longitudinally symmetrical, and the heating result is more uniform, but the heat transfer area is slightly lower. Figure 12: Finite element analysis of heat transfer for four traditional heating structures. (**a**) Thick serpentine heating electrode. (**b**) Thin serpentine heating electrodes. (**c**) Complex serpentine heating electrodes. (**d**) Spiral heating electrode. Figure 13: Temperature distribution of four traditional heating structures. (**a**) Thick serpentine heating electrode. (**b**) Thin serpentine heating electrodes. (**c**) Complex serpentine heating electrodes. (**d**) Spiral heating electrode.