A Variable-Reluctance Based Wireless Sensing Module for Intraoral Pressure Measurement

We report a variable-reluctance based wireless sensing module to measure intraoral pressure for clinical orthodontic treatment. The wireless sensing module consists of two parts; first is a set of coils, i.e., a transmitting and a receiving coil and second is a variable- reluctance based pressure sensor. The coils are placed in a concentric arrangement at a certain distance from the sensor. An AC voltage is applied to the transmitting coil to produce AC magnetic flux and by electromagnetic-induction, an AC voltage is induced in the receiving coil. When the pressure inside the pressure chamber changes, the diaphragm of the sensor deflects towards or away from the coils, resulting in change of air-gap between the same. This causes the magnetic reluctance between the diaphragm and the receiving coil to change. Consequently, the output voltage of receiving coil is changed. Based on above principle, we fabricated above parts and conducted pressure sensing test. According to our results, the pressure can be successfully sensed. The pressure sensitivities of 3.62 µV/mbar and 2.66 µV/mbar is measured when the gap between the coils and the sensor is 10 mm and 20 mm respectively. Furthermore, to validate the viability that the pressure can be sensed in different regions inside the mouth, the sensor is placed on an inclined tooth and pressure sensing test is performed. For this case, the pressure sensitivities of 1.23 µV/mbar and 1.48 µV/mbar is measured when the gap between the coils and the sensor is 10 mm and 20 mm respectively.