A Novel Piezoelectric Energy Harvester for Earcanal Dynamic Motion Exploitation Using a Bistable Resonator Cycled by Coupled Hydraulic Valves Made of Collapsed Flexible Tubes.

Scavenging energy from the earcanal's dynamic motion during jaw movements may be a practical way to enhance the battery autonomy of hearing aids. The main challenge is optimizing the amount of energy extracted while working with soft human tissues and the earcanal's restricted volume. This paper proposes a new energy harvester concept: a liquid-filled earplug which transfers energy outside the earcanal to a generator. The latter is composed of a hydraulic amplifier, two hydraulic cylinders that actuate a bistable resonator to raise the source frequency while driving an amplified piezoelectric transducer to generate electricity. The cycling of the resonator is achieved using two innovative flexible hydraulic valves based on the buckling of flexible tubes. A multiphysics-coupled model is established to determine the system operation requirements and to evaluate its theoretical performances. This model exhibits a theoretical energy conversion efficiency of 85%. The electromechanical performance of the resonator coupled to the piezoelectric transducer and the hydraulic behavior of the valves are experimentally investigated. The global model was updated using the experimental data to improve its predictability toward further optimization of the design. Moreover, the energy losses are identified to enhance the entire proposed design and improve the experimental energy conversion efficiency to 26%.

Morphological analysis of the human earcanal deformations during face-related activities.

Ear-related technologies are spreading in our daily life and have become essential in several applications. The comfort, retention and battery life of in-ear devices can be substantially improved by considering the dynamic behavior of the earcanal. A better understanding of the earcanal dynamic motion would not only result in the improved fit and performance of earpieces but could also pave the way to harvest energy from these movements to power future ear-related technologies. The contours of the left and right ears of 18 healthy subjects during closed mouth and 4 activities (mouth opening, turning head left, raising eyebrows and smiling) were discretized. Eight parameters were analyzed to investigate the possible relation between each of these face-related activities and the radial and axial deformations of the earcanal. The largest significant deformations in reference to the closed-mouth geometry were observed during mouth-opening and smiling at the earcanal entrance and between the two bends.

Assessing focus through ear-EEG: a comparative study between conventional cap EEG and mobile in- and around-the-ear EEG systems.

Introduction: As our attention is becoming a commodity that an ever-increasing number of applications are competing for, investing in modern day tools and devices that can detect our mental states and protect them from outside interruptions holds great value. Mental fatigue and distractions are impacting our ability to focus and can cause workplace injuries. Electroencephalography (EEG) may reflect concentration, and if EEG equipment became wearable and inconspicuous, innovative brain-computer interfaces (BCI) could be developed to monitor mental load in daily life situations. The purpose of this study is to investigate the potential of EEG recorded inside and around the human ear to determine levels of attention and focus. Methods: In this study, mobile and wireless ear-EEG were concurrently recorded with conventional EEG (cap) systems to collect data during tasks related to focus: an N-back task to assess working memory and a mental arithmetic task to assess cognitive workload. The power spectral density (PSD) of the EEG signal was analyzed to isolate consistent differences between mental load conditions and classify epochs using step-wise linear discriminant analysis (swLDA). Results and discussion: Results revealed that spectral features differed statistically between levels of cognitive load for both tasks. Classification algorithms were tested on spectral features from twelve and two selected channels, for the cap and the ear-EEG. A two-channel ear-EEG model evaluated the performance of two dry in-ear electrodes specifically. Single-trial classification for both tasks revealed above chance-level accuracies for all subjects, with mean accuracies of: 96% (cap-EEG) and 95% (ear-EEG) for the twelve-channel models, 76% (cap-EEG) and 74% (in-ear-EEG) for the two-channel model for the N-back task; and 82% (cap-EEG) and 85% (ear-EEG) for the twelve-channel, 70% (cap-EEG) and 69% (in-ear-EEG) for the two-channel model for the arithmetic task. These results suggest that neural oscillations recorded with ear-EEG can be used to reliably differentiate between levels of cognitive workload and working memory, in particular when multi-channel recordings are available, and could, in the near future, be integrated into wearable devices.

In Situ Otoacoustic Emission Monitoring to Assess the Effects of Noise Exposure on Hearing Health.

Noise-induced hearing loss (NIHL) is the largest cause of action for indemnity in North American industries despite the widespread implementation of hearing conservation programs. Possible causes behind the onset of NIHL are the intervals between hearing tests which are generally too long and the tests are insufficiently sensitive to detect temporary hearing changes to act and prevent permanent hearing damage. Moreover, current noise regulations might be too lenient as to the permissible maximum noise levels. Short-interval hearing assessment could help to observe temporary changes in hearing health and prevent permanent damage. This study investigates the short-term effects of noise exposure characteristics using repeated measurements of otoacoustic emission (OAE) growth functions and presents the most significant predictors of hearing health changes as observed in sixteen individuals equipped with OAE earpieces. The experimental results of this study show that the impulsiveness and frequency spectrum of the noise level could be a possible cause of the decline in OAE levels. As a consequence, hearing conservation programs should consider taking these noise metrics into account for proper NIHL risk assessment. Such noise exposure and hearing health monitoring could greatly improve hearing conservation practices in the workplace by acting faster and eventually mitigate occupational hearing loss.

Man Down Situation Detection Using an in-Ear Inertial Platform.

Man down situations (MDS) are a health or life threatening situations occurring largely in high-risk industrial workplaces. MDS automatic detection is crucial for workers safety especially in isolated working conditions where workers could be unable to call for help on their own, either due to loss of consciousness or an incapacitating injury. These solution must be reliable, robust, easy to use, but also have a low false-alarm rate, short response time and good ergonomics. This project aims to improve this technology by providing a global MDS definition according to a combination of three observable critical states based on characterization of body movement and orientation data from inertial measurements (accelerometer and gyroscope): the worker falls (F), worker immobility (I), the worker is down on the ground (D). The MDS detection strategy was established based on the detection of at least two distinct states, such as F-I, F-D or I-D, over a certain period of time. This strategy was tested using a large public database, revealing a significant reduction of the false alarms rate to 1.1%, reaching up to 99% accuracy. The proposed detection strategy was also incorporated into a digital earpiece, designed to address hearing protection issues, and validated according to an in vivo test procedure based on simulations of industrial workers normal activities and critical states.

Custom-Fitted In- and Around-the-Ear Sensors for Unobtrusive and On-the-Go EEG Acquisitions: Development and Validation.

OBJECTIVES: This paper aims to validate the performance and physical design of a wearable, unobtrusive ear-centered electroencephalography (EEG) device, dubbed "EARtrodes", using early and late auditory evoked responses. Results would also offer a proof-of-concept for the device to be used as a concealed brain-computer interface (BCI). DESIGN: The device is composed of a custom-fitted earpiece and an ergonomic behind-the-ear piece with embedded electrodes made of a soft and flexible combination of silicone rubber and carbon fibers. The location of the conductive silicone electrodes inside the ear canal and the optimal geometry of the behind-the-ear piece were obtained through morphological and geometrical analysis of the human ear canal and the region around-the-ear. An entirely conductive generic earpiece was also developed to assess the potential of a universal, more affordable solution. RESULTS: Early latency results illustrate the conductive silicone electrodes' capability to record quality EEG signals, comparable to those obtained with traditional gold-plated electrodes. Additionally, late latency results demonstrate EARtrodes' capacity to reliably detect decision-making processes from the ear. CONCLUSIONS: EEG results validate the performance of EARtrodes as a circum-aural and intra-aural EEG recording system adapted for a wide range of applications in audiology, neuroscience, clinical research, and as an unobtrusive BCI.

Method for protected noise exposure level assessment under an in-ear hearing protection device: a pilot study.

OBJECTIVE: To properly measure the effective noise exposure level of workers with hearing protection devices (HPD), the use of in-ear noise dosimeters (IEND) is increasing. Commercial IENDs typically feature one in-ear microphone that captures all noises inside the ear and do not discriminate the residual noise in the earcanal from wearer-induced disturbances (WID) to calculate the in-ear sound pressure levels (SPL). A method to alleviate this particular issue with IENDs and calculate the hearing protection level on-site is therefore proposed. DESIGN: The sound captured by an outer-ear microphone is filtered with the modelled HPD transfer function to estimate the in-ear SPL, this way part of the WIDs mostly captured by the in-ear microphone can be rejected from the SPL. The level of protection provided by the earplugs can then be estimated from the difference between in-ear and outer-ear SPLs. The proposed method is validated by comparing the outcome of the proposed WID rejection method to a reference method. STUDY SAMPLE: The detailed methods are assessed on audio recordings from 16 industrial workers monitored for up to 4 days. RESULTS: The merits of the proposed WID rejection approach are discussed in terms of residual SPL and hearing protection level estimation accuracy. CONCLUSIONS: Based on the findings, a method to integrate the proposed WID rejection algorithm in future IENDs is suggested.

Mobile In-Ear Power Sensor for Jaw Joint Activity.

In only a short time, in-ear wearables have gone from hearing aids to a host of electronic devices such as wireless earbuds and digital earplugs. To operate, these devices rely exclusively on batteries, which are not only cumbersome but known for several drawbacks. In this paper, the earcanal dynamic movements generated by jaw activity are evaluated as an alternative source of energy that could replace batteries. A mobile in-ear power sensor device capable of measuring jaw activity metrics is prototyped and tested on three test subjects. The test results are subsequently analyzed using a detection algorithm to detect the jaw activity based on the captured audio signals and to classify them into four main categories, namely chewing, swallowing, coughing and talking. The mean power associated with each category of activity is then calculated by using the pressure signals as measured by a water-inflated earplug subjected to earcanal dynamic movement. The results show that 3.8 mW of power, achieved mainly by the chewing movement, is readily available on average from within the earcanal.

An in-ear speech database in varying conditions of the audio-phonation loop.

With the rise of hearables and the advantages of using in-ear microphones with intra-aural devices, accessibility to an in-ear speech database in adverse conditions is essential. Speech captured inside the occluded ear is limited in its frequency bandwidth and has an amplified low frequency content. In addition, occluding the ear canal affects speech production, especially in noisy environments. These changes to speech production have a detrimental effect on speech-based algorithms. Yet, to the authors' knowledge, there are no speech databases that account for these changes. This paper presents a speech-in-ear database, of speech captured inside an occluded ear in noise and in quiet. The database is bilingual (in French and in English) and is intended to aid researchers in developing algorithms for intra-aural devices utilizing in-ear microphones.

Validation and Benchmarking of a Wearable EEG Acquisition Platform for Real-World Applications.

This paper presents the experimental validation of a readout circuit for the acquisition, amplification, and transmission of extremely weak biopotentials with a focus on electroencephalography (EEG) signals. The device, dubbed CochlEEG, benefits from a low-power design for long-term power autonomy and provides configurable gain and sampling rates to suit the needs of various EEG applications. CochlEEG features high sampling rates, up to 4 kHz, low-noise signal acquisitions, support for active electrodes, and a potential for Wi-Fi data transmission. Moreover, it is lightweight, pocket size, and affordable, which makes CochlEEG suitable for wearable and real-world applications. The efficiency of CochlEEG in EEG data acquisition is also investigated in this paper. Auditory steady-state responses acquisition results validate CochlEEG's capability in recording EEG with a signal quality comparable to commercial mobile or research EEG acquisition devices. Moreover, the results of an oddball paradigm experiment prove the capability of CochlEEG in recording event-related potentials and demonstrate its potential for brain-computer interface applications and electrophysiological research applications requiring higher temporal resolution.

Effects of ear canal occlusion on hearing sensitivity: A loudness experiment.

Over the last century, hearing research has repeatedly reported differences in loudness perception when different types of transducers are being used. One of the effects of using different transducers is that listening may be performed via an open ear (loudspeaker), a cushioned ear (headphones), or an occluded ear (hearing aid receivers, insert earphones). The question of whether varying the acoustic load applied to the ear canal might impact hearing sensitivity has therefore become essential given the need to establish realistic noise damage risk criteria in an attempt to prevent noise-induced hearing loss for any given listening condition. Although such loudness discrepancies in the cushioned ear have been recently proven to be caused by loudness measurement artifacts, currently available data do not exclude a possible impact of ear canal occlusion on loudness perception. This paper presents the results of a loudness balance test carried out on 18 normal-hearing listeners. Using an earplug to occlude the canal, in-ear sound pressure levels were compared between the occluded ear and the cushioned ear at equal loudness. The results show agreement within 1 dB between the two listening conditions, and support the conclusion that loudness does not depend on the type of acoustic load applied to the ear canal.

In-Ear Audio Wearable: Measurement of Heart and Breathing Rates for Health and Safety Monitoring.

OBJECTIVE: This paper examines the integration of a noninvasive vital sign monitoring feature into the workers' hearing protection devices (HPDs) by using a microphone positioned within the earcanal under the HPD. METHODS: 25 test-subjects were asked to breathe at various rhythms and intensities and these realistic sound events were recorded in the earcanal. Digital signal processing algorithms were then developed to assess heart and breathing rates. Finally, to test the robustness of theses algorithms in noisy work environments, industrial noise was added to the in-ear recorded signals and an adaptive denoising filter was used. RESULTS: The developed algorithms show an absolute mean error of 4.3 beats per minute (BPM) and 2.7 cycles per minute (CPM). The mean difference estimate is -0.44 BPM with a limit of agreement (LoA) interval of -14.3 to 13.4 BPM and 2.40 CPM with a LoA interval of -2.62 to 7.48 CPM. Excellent denoising is achieved with the adaptive filter, able to cope with ambient sound pressure levels of up to 110 dB SPL, resulting in a small error for heart rate detection, but a much larger error for breathing rate detection. CONCLUSION: Extraction of the heart and breathing rates from an acoustical measurement in the occluded earcanal under an HPD is possible and can even be conducted in the presence of a high level of ambient noise. SIGNIFICANCE: This proof of concept enables the development of a wide range of noninvasive health and safety monitoring audio wearables for industrial workplaces and life-critical applications where HPDs are used.

Modeling Speech Level as a Function of Background Noise Level and Talker-to-Listener Distance for Talkers Wearing Hearing Protection Devices.

Purpose: Studying the variations in speech levels with changing background noise level and talker-to-listener distance for talkers wearing hearing protection devices (HPDs) can aid in understanding communication in background noise. Method: Speech was recorded using an intra-aural HPD from 12 different talkers at 5 different distances in 3 different noise conditions and 2 quiet conditions. Results: This article proposes models that can predict the difference in speech level as a function of background noise level and talker-to-listener distance for occluded talkers. The proposed model complements the existing model presented by Pelegrín-García, Smits, Brunskog, and Jeong (2011) and expands on it by taking into account the effects of occlusion and background noise level on changes in speech sound level. Conclusions: Three models of the relationship between vocal effort, background noise level, and talker-to-listener distance for talkers wearing HPDs are presented. The model with the best prediction intervals is a talker-dependent model that requires the users' unoccluded speech level at 10 m as a reference. A model describing the relationship between speech level, talker-to-listener distance, and background noise level for occluded talkers could eventually be incorporated with radio protocols to transmit verbal communication only to an intended set of listeners within a given spatial range-this range being dependent on the changes in speech level and background noise level.

Field Monitoring of Otoacoustic Emissions During Noise Exposure: Pilot Study in Controlled Environment.

PURPOSE: In spite of all the efforts to implement workplace hearing conservation programs, noise-induced hearing loss remains the leading cause of disability for North American workers. Nonetheless, an individual's susceptibility to noise-induced hearing loss can be estimated by monitoring changes in hearing status in relation to the level of ambient noise exposure. The purpose of this study was to validate an approach that could improve workplace hearing conservation practices. The approach was developed using a portable and robust system designed for noisy environments and consisted of taking continuous measurements with high temporal resolution of the health status of the inner ear using otoacoustic emissions (OAEs). METHOD: A pilot study was conducted in a laboratory, exposing human subjects to industrial noise recordings at realistic levels. In parallel, OAEs were measured periodically using the designed OAE system as well as with a commercially available OAE system, used as a reference. RESULTS: Variations in OAE levels were analyzed and discussed along with the limitations of the reference and designed systems. CONCLUSIONS: This study demonstrates that the monitoring of an individual's OAEs could be useful in monitoring temporary changes in hearing status induced by exposure to ambient noise and could be considered as a new tool for effective hearing conservation programs in the workplace.

In-ear microphone speech quality enhancement via adaptive filtering and artificial bandwidth extension.

Bone and tissue conducted speech has been used in noisy environments to provide a relatively high signal-to-noise ratio signal. However, the limited bandwidth of bone and tissue conducted speech degrades the quality of the speech signal. Moreover in very noisy conditions, bandwidth extension of the bone and tissue conducted speech becomes problematic. In this paper, speech generated from bone and tissue conduction captured using an in-ear microphone is enhanced using adaptive filtering and a non-linear bandwidth extension method. Objective and subjective tests are used to evaluate the performance of the proposed techniques. Both evaluations show a statistically significant quality enhancement of the noisy in-ear microphone speech with ρ<0.0001 after denoising and ρ<0.01 after bandwidth extension.

Variations in voice level and fundamental frequency with changing background noise level and talker-to-listener distance while wearing hearing protectors: A pilot study.

OBJECTIVE: Speech production in noise with varying talker-to-listener distance has been well studied for the open ear condition. However, occluding the ear canal can affect the auditory feedback and cause deviations from the models presented for the open-ear condition. Communication is a main concern for people wearing hearing protection devices (HPD). Although practical, radio communication is cumbersome, as it does not distinguish designated receivers. A smarter radio communication protocol must be developed to alleviate this problem. Thus, it is necessary to model speech production in noise while wearing HPDs. Such a model opens the door to radio communication systems that distinguish receivers and offer more efficient communication between persons wearing HPDs. DESIGN: This paper presents the results of a pilot study aimed to investigate the effects of occluding the ear on changes in voice level and fundamental frequency in noise and with varying talker-to-listener distance. STUDY SAMPLE: Twelve participants with a mean age of 28 participated in this study. RESULTS: Compared to existing data, results show a trend similar to the open ear condition with the exception of the occluded quiet condition. CONCLUSIONS: This implies that a model can be developed to better understand speech production for the occluded ear.

Systematic Evaluation of the Relationship between Physical and Psychoacoustical Measurements of Hearing Protectors' Attenuation.

The most commonly used methods to measure hearing protectors attenuation can be divided into two categories: psychoacoustical (subjective) and physical (objective) methods. In order to better understand the relationship between these methods, this article presents various factors relating attenuation values obtained with these methods through a series of tests. Experiments on human subjects were carried out where the subjects were instrumented on both ears with miniature microphones outside and underneath the protector. The subjects were then asked to go through a series of hearing threshold measurements (psychoacoustical method) followed by microphone sound recordings using high-level diffuse field broadband noises (physical method). The proposed test protocol allowed obtaining various factors relating the test methods as well as attenuation values and ratings for different protection conditions (open ear, earmuffs, earplugs, and dual protection). Results are presented for three models of passive earmuffs, three models of earplugs and all their combinations as dual hearing protectors. The validity and the relative importance of various terms used to correct the physical attenuation values when comparing with psychoacoustical attenuation values are examined.