Tsuneharu Nitta

Ceramic Humidity Sensors

A novel humidity sensor using a MgCr 2 0 4 -TiO2 porous ceramic has been developed for an automatic microwave oven. Physical properties of the MgCr 2 0 4 -TiO2 ceramic, construction and humidity characteristics of the sensors, and outlines of the control of the automatic microwave oven by humidity sensing are described. The MgCr 2 0 4 -TiO2 ceramic exhibits a typical porous structure and semiconduction. The porous ceramic easily absorbs water vapor throughout the pores. The ceramic grain surfaces behave like electrolytes. The ceramic humidity sensor utilizing its humidity sensitive effects and rejuvenating response to heat treatment exhibits high humidity and long term stability. The novel humidity sensor has been applied in many processes such as microwave ovens, air conditioners, dryers, etc.

Multifunctional ceramic sensors: Humidity-gas sensor and temperature-humidity sensor

Two types of multifunctional ceramic sensors have been developed in response to strong demands for automatic control systems in cooking ovens, air conditioners, etc. The first sensing device can detect both humidity and particular reducing agents, such as alcohols and smokes, with a high sensitivity and selectivity. This novel ceramic sensor utilizes gas chemisorption at 400°-500°C as well as water physisorption at <150°C on the grain surface of MgCr2O4-TiO2ceramic with a porous structure and p-type semiconduction. The other sensor is composed of a porous dielectric Ba0.5MSr0.5TiO3ceramic characterized by a high temperature dependence of the dielectric constant. The sensing device can independently detect simultaneously and rapidly both temperature and humidity. These sensors exhibit long-term stability, in combination with heat treatment.