Condensation Detection Using a Wirelessly Powered RF-Temperature Sensor

Abstract

The formation of condensation on windshields can be counteracted and even prevented through the concerted use of an automobile heating, ventilation, and air-conditioning (HVAC) system. By anticipating the formation of dew, through the temperature of the windshield and dew point in the cabin, a condensation-free windshield can be ensured. A new approach toward a system for condensation detection is reported. It uses an actively powered humidity sensor, as well as a remotely and wirelessly powered temperature sensor system. The wirelessly powered temperature detector, which may be embedded in the windshield of an automobile, obtains its energy via an inductively coupled magnetic field and simultaneously transmits data through a load-modulation technique. Such a system approach offers advantages in terms of cost, system life, and maintenance, in comparison with existing wired systems and other wireless solutions. The system is implemented using off-the-shelf components and is discretely designed around application-specific resonant tanks. The resonant tanks were mathematically characterized and compared with measured values. The read range of the wirelessly powered condensation detector at a frequency of 13.56 MHz is more than 4 cm while consuming a maximum power of approximately 2 mW. The application of this technology as part of a climate-control system is discussed in this paper. System concept, design considerations, and prototype characterization are also included.