Investigating commercially available force sensors for bone conduction hearing device evaluation

Bone conduction devices (BCDs) stimulate the auditory system by transmitting audio-frequency vibrations into the head. BCDs have long been used to diagnose and treat hearing loss, but increased interest in BCDs for consumer and communications applications has led to a proliferation of transducer designs. BCD calibration has historically been performed using an artificial mastoid, an expensive device that does not readily accommodate all BCD styles or account for impacts of anatomical variability on BCD coupling. Recent developments in force sensing technology could offer an inexpensive alternative to artificial mastoids for use with human subjects. Here, three commercial off-the-shelf (COTS) sensors were identified that met size, flexibility, and dynamic range requirements necessary for evaluating human BCD performance. Sensor accuracy and repeatability of both static and dynamic force measurements were compared against artificial mastoid measurements. A capacitance-based sensor successfully measured static force coupling but was incapable of capturing dynamic force output due to sensor bandwidth limitations. A piezoresistive sensor had a suitable bandwidth, but required significant signal conditioning to amplify signals and improve accuracy and precision. An alternative piezoresistive sensor utilized integrated circuitry to amplify signals, increasing sensor durability and accuracy. Future research will evaluate additional low-cost solutions for BCD evaluation.