Wireless sensors market is growing very fast these last years tanks to the availability of cheap, small and efficient micro-sensors, batteries, analog and RF circuits, and to the presence of standardized communication protocols. Even if these active sensors are very attractive for a lot of applications, they suffer from weak energy autonomy and they are not compatible with harsh environment. In order to overcome these problems, we have developed a new kind of wireless sensors using electromagnetic transducers and radar interrogation. These passive sensors (battery-less and without electronic components) have been studied for pressure, temperature, gas and stress applications.