A Development of Sensorized Ear Model for New Behind-the-ear (BTE) Hearing Aid

Behind-the-ear (BTE) hearing aids have become indispensable devices for individuals with hearing impairments. However, one common issue faced by users is external ear discomfort or pressure points caused by improper fitting or dimensions of the device. Comfort remains a critical factor in user satisfaction and long-term usage. Currently, there is no available ear model device that measures and quantifies the pressure points or pain points on the external ear. Comfort level assessment is qualitative and conducted through user survey. This paper aims to quantify the pressure points through development of sensorized ear model. Quantifying the pressure points can aid in optimization of the hearing aid tubing length and bend and correlate them to comfort level during hearing aid fitting. Five (5) MEMS-based force sensors that each has a resolution of 10 mN are assembled on polyimide flexible printed circuit board (FPCB) substrates that is 3.0 mm in width, 150 mm in length, and 0.15 mm in thickness. Each force sensor was tested from 0-500 mN on a micromanipulator stage with a force gauge set-up. To read the analog output of each sensor, a separate reader circuit board is fabricated. AD623 single-supply instrumentation amplifier, passive components, FPC connector, and input/output wires are assembled on the circuit board. The force sensors are characterized on PCB and further tested on FPCB before integration with silicone ear model. The measured average output voltage at zero force load (0 mN) is 537 mV on PCB and 589 mV on FPCB. The sensors can read and differentiate 10 mN (1.0 g-f) iterations; this coincides with the resolution of the force sensor at 0.01 N (10 mN). The measured sensitivity is 2.2 mV/mN. The force sensors also exhibited high linear relationship between the input force load and the output voltage. Five different BTE hearing aids are utilized as force loads which were subsequently quantified, on both left and right silicone ear models.