The objective of this paper is to present an improved design of a wireless inductive sensor with novel compressive parts and its integration with a suitable mechanical device. The proposed system can be used as a seat occupancy detector with adjustable weight threshold. It consists of a sensor (inductor, steel springs, and ferrite plate), an antenna, and a mechanical device for transferring the scaled weight to the sensor. The sensor is designed in such a way that the weight applied to its surface causes the built-in springs to compression, and as a result, the reduction of the distance between the inductor and the ferrite plate, which in turn changes in the sensor's inductance, and consequently the antenna-sensor resonant frequency, which is used as the electric output. The mechanical device, which serves as a weight converter, has also been developed. The prototype of the system is fabricated and experimentally tested in order to confirm its functionality and performance. A three-segment linear characteristic is obtained with the following sensitivities: 0.9 MHz/kg for the weights of 0-20 kg, 1.86 MHz/kg for the weights of 20-40 kg, and 0.19 MHz/kg for the weights of 40-50 kg. These results show that the developed system can detect the presence of weight and, therefore, can be used for seat occupancy detection in a vehicle safety restraint and airbag systems. It can also be used as the indicator in the airbag safety restraint systems when the occupant's weight exceeds the defined weight threshold for the airbag activation.
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