What is the principle of the "electronic absorbent card" in the moistureproof box where photographic equipment is placed?

In fact, the drying principle is to use color-changing silica gel, except that a mesh metal inner box connected with electric heating is added, and an expected outer shell is added outside.

If the color-changing silica gel is simply used, the silica gel will be dried in the microwave oven and then changed back to the original dry blue. The electronic moisture absorption card simplifies the regeneration process of color-changing silica gel, and it will be OK as long as it is plugged in for about an hour, but it will be cut off for more than ten minutes when it is placed in a sealed box. After the temperature drops, it can be put into use. I use Vanderbilt's box and moisture absorption card (if it's bad, it's best to buy a constant humidity drying box with electricity directly). I hope it helps you!