A Wireless Monitoring System Using a Tunneling Sensor Array in a Smart Oral Appliance for Sleep Apnea Treatment

Abstract

Sleep apnea is a serious sleep disorder, and the most common type is obstructive sleep apnea (OSA). Untreated OSA will cause lots of potential health problems. Oral appliance therapy is an effective and popular approach for OSA treatment, but making a perfect fit for each patient is time-consuming and decreases its efficiency considerably. This paper proposes a System-on-a-Chip (SoC) enabled sleep monitoring system in a smart oral appliance, which is capable of intelligently collecting the physiological data about tongue movement through the whole therapy. A tunneling sensor array with an ultra-high sensitivity is incorporated to accurately detect the subtle pressure from the tongue. When the device is placed on the wireless platform, the temporary stored data will be retrieved and wirelessly transmitted to personal computers and cloud storages. The battery will be recharged by harvesting external RF power from the platform. A compact prototype module, whose size is 4.5 × 2.5 × 0.9 cm³, is implemented and embedded inside the oral appliance to demonstrate the tongue movement detection in continuous time frames. The functions of this design are verified by the presented measurement results. This design aims to increase efficiency and make it a total solution for OSA treatment.

Keywords: OSA; SoC; prototype module; sleep apnea; sleep monitoring; smart oral appliance; tunneling sensor; wireless.

Figure 1

Application scenario of the proposed system.

Figure 2

(a) Cross-sectional view and operational principle of the tunneling sensor; (b) SEM image of the contact surface of interlocked microdomes.

Figure 3

The preparation of conductive prepolymer used in the proposed sensor array.

Figure 4

Block diagram of the proposed SoC enabled monitoring system.

Figure 5

Experimental setup for testing the sensor array.

Figure 6

Sensor fabrication results: (a) Polyimide substrate layer with interdigitated electrodes; (b) Topped conductive polymer layer with interlocked microdome structures; (c) Flexibility of the assembled array.

Figure 7

(a) Measured piezoresistive response of the tunneling sensor; (b) Normalized measured response under 8 kPa.

Figure 8

(a) Repeatability test for 7200 cycles at 2 Hz force pressing; (b) 20-cycles subset of (a) (200~210 s).

Figure 9

(a) Schematic of the proposed sensing array for the crosstalk study; (b) Measured resistance variation of the proposed sensing array.

Figure 10

Prototype module for the demonstration of tongue position detecting.

Figure 11

Measurement results of the prototype module in pressure detection: (a) Measured step transient response; (b) Measured characteristic of digital output code versus pressure.

Figure 12

Tongue position detecting demonstration by the prototype module: (a) Fingertip pressing on the array; (b) corresponding force images recorded in continuous time frames using an interval of 4 s.

Figure 13

(a) Pressing test with a button battery and its corresponding force image; (b) Pressing test with a USB drive and its corresponding force image.

Figure 14

Measurement results of the power management unit: (a) Measured output waveform of the RF-DC converter; (b) Measured waveform of charging progress by the on-chip charger.

Figure 15

Measurement results of the MICS band transmitter: (a) Measured output waveforms of MCU and transmitter; (b) Measured transmitter output spectrum.

Figure 16

(a) The micrograph of the proposed SoC; (b) Measured performance summary.