Wearable Wireless Magnetic-Reluctance-Based Pressure Sensing Module for Intraoral Pressure Monitoring

In this article, we report a wearable magnetic-reluctance-based wireless pressure sensing module to measure intraoral pressure for clinical orthodontic treatment. The sensing module consists of two parts: first part is a transmitting/receiving electromagnet (EM $_{\mathrm {T}}$ ) which is connected to a reference electromagnet (EM $_{\mathrm {R}}$ ); second part is a high-permeable sensing diaphragm embedded into a bi-layered wearable orthodontic aligner. These electromagnets are placed outside of the mouth, while the aligner (consisting of the sensing diaphragm) is placed inside of the mouth. An ac current is applied to the transmitting electromagnet to produce ac magnetic flux, consequently by the electromagnetic induction, an ac voltage is induced in the receiving electromagnet. When people use cheek muscle (i.e., stress the cheek muscle), pressure in the oral cavity is changed. Consequently, a pressure difference is formed to deflect the sensing diaphragm toward or backward the EMT. Due to this, the magnetic reluctance between the sensing diaphragm and the EMT is changed. Through the electromagnetic induction, voltage output is induced in the receiving electromagnet. By analyzing the voltage output, we can know the change of the pressure. Based on above principle, we fabricated above parts and conducted pressure sensing test. According to the test results, the sensing module successfully senses the pressure ranging from 0 to 30 kPa with a sensitivity of 3.52 to $0.82 \mu \text{V}$ /kPa, when the EMT is placed 7–13 mm away from the sensing module respectively. This achieves the wearable wireless intraoral pressure sensing and consequently provides useful monitoring information for clinical orthodontic treatment.