The EarLens system: New sound transduction methods

Abstract

The hypothesis is tested that an open-canal hearing device, with a microphone in the ear canal, can be designed to provide amplification over a wide bandwidth and without acoustic feedback. In the design under consideration, a transducer consisting of a thin silicone platform with an embedded magnet is placed directly on the tympanic membrane. Sound picked up by a microphone in the ear canal, including sound-localization cues thought to be useful for speech perception in noisy environments, is processed and amplified, and then used to drive a coil near the tympanic-membrane transducer. The perception of sound results from the vibration of the transducer in response the electromagnetic field produced by the coil. Sixteen subjects (ranging from normal-hearing to moderately hearing-impaired) wore this transducer for up to a ten-month period, and were monitored for any adverse reactions. Three key functional characteristics were measured: 1) the maximum equivalent pressure output (MEPO) of the transducer; 2) the feedback gain margin (GM), which describes the maximum allowable gain before feedback occurs; and 3) the tympanic-membrane damping effect (D TM ), which describes the change in hearing level due to placement of the transducer on the eardrum. Results indicate that the tympanic-membrane transducer remains in place and is well tolerated. The system can produce sufficient output to reach threshold for those with as much as 60 dBHL of hearing impairment for up to 8 kHz in 86% of the study population, and up to 11.2 kHz in 50% of the population. The feedback gain margin is on average 30 dB except at the ear canal resonance frequencies of 3 and 9 kHz, where the average was reduced to 12 dB and 23 dB respectively. The average value of D TM is close to 0 dB everywhere except in the 2-4 kHz range, where it peaks at 8 dB. A new alternative system that uses photonic energy to transmit both the signal and power to a photodiode and micro-actuator on an EarLens platform is also described.

Preliminary Evaluation of a Light-Based Contact Hearing Device for the Hearing Impaired

“…The calibration curves were used along with known system specifications to calculate the maximum output and effective bandwidth of the system (12), which is represented in terms of the maximum equivalent pressure output (MEPO) on the ear. Because of the way MEPO values are calculated, they are representative of the system’s behavior independent of the hearing level of the ear.…”

“…This measurement was then used to calculate (see 12) the maximum gain that could be applied to an input signal before generating positive acoustic feedback, which is a function of the individual’s anatomy but does not depend on their hearing level.…”

A micro-drive hearing aid: a novel non-invasive hearing prosthesis actuator

“…But, since it recreates sound by mechanically moving the tympanic membrane and the ossicular chain, sound quality limitations, such as feedback and the occlusion effect, can be reduced. In addition to our work, other groups have also explored direct actuation of the tympanic membrane and ossicular chain, for example, by using an electromagnet to drive a small magnet attached to the tympanic membrane (Perkins et al 2010). …”

Finite element analysis of the coupling between ossicular chain and mass loading for evaluation of implantable hearing device

“…The magnet may be mounted outside the coil (extra-coil electromagnet (ECE)) or within the coils (intra-coil electromagnet (ICE)). Several authors have proposed simpler ECE device, such as contactless electromagnetic transducer (CLT) consisting of a coil and a permanent magnet (Goode et al, 1995;Hamanishi et al, 2004;Hough et al, 2000;Huber et al, 2006;Maniglia et al, 1996;Perkins et al, 2010;Stieger et al, 2004). The magnet was attached to the ossicular chain in various locations, or was placed on the tympanic membrane.…”

“…However, its performance depends on not only the frequency characteristic of the actuator, but also the mass, attachment location and mounting parameters (Abel et al, 2004;Needham et al, 2005;Perkins et al, 2010). In the existing literature, performance of transducers has been evaluated in several aspects: (a) mass loading effect on residual hearing (Gan et al, 2001;Needham et al, 2005;Nishihara et al, 1993;Perkins et al, 2010;Rosowski et al, 2007); (b) equivalent sound pressure output (Bornitz et al, 2010;Perkins et al, 2010;Rosowski et al, 2007); (c) feedback gain (Bornitz et al, 2010;Perkins et al, 2010) and (d) non linear distortion or sound fidelity (Hong et al, 2009;Rosowski et al, 2007). It is difficult to determine the impact of systematic variations of one or more mounting parameters by temporal bone experiments.…”