Ultra-broadband active noise cancellation at the ears via optical microphones

High frequency noise has generally been difficult to be cancelled actively at a person's ears, particularly for active headrest systems aiming to free the listener from noise cancellation headphones. One of the main challenges is to measure the noise precisely at the ears. Here we demonstrate a new error sensing methodology with an optical microphone arrangement for active noise cancellation (ANC). It can measure the noise accurately for ANC without any obstructions at the listener's ears. The demonstrated system, or virtual ANC headphone as we call it, is shown to provide more than 10 dB attenuation for ultra-broadband noise - up to 6000 Hz - inside the ears in a complex sound field. The bandwidth of the controllable noise significantly exceeds the results from the state-of-the-art system, which is below 1000 Hz. The proposed method leads to the next generation of personal hearing protection system and can open up a whole new area of sound control research

An alternative technique for investigating fluid flow around the hand during front crawl

This paper presents the novel application of a technique for measuring flow around the hand during a simulated swim stroke with a view to enable a better understanding of propulsion generation in swimming. The technique relies on the instantaneous, non-intrusive, volumetric measurement of 3D velocity fields using a commercially available optical measurement system. A hand and forearm model was towed through a water tank to replicate the pull phase with fluid flow data being captured at regular intervals in a fixed volume through which the model moved. The measurement system included a single body, three-sensor probe for capturing pairs of images which were then processed to determine particle velocities and to characterise the flow. The results were used to investigate changes in mean velocity for six experimental cases based on three different angles of attack and two towing speeds. The results showed that the V3V system could be used to capture velocity data around the hand and for a 45° increase in angle of attack, the velocity magnitude of the flow reduced by half, indicating the presence of lift forces. © 2013 The Authors

Ultra-broadband local active noise control with remote acoustic sensing.

One enduring challenge for controlling high frequency sound in local active noise control (ANC) systems is to obtain the acoustic signal at the specific location to be controlled. In some applications such as in ANC headrest systems, it is not practical to install error microphones in a person's ears to provide the user a quiet or optimally acoustically controlled environment. Many virtual error sensing approaches have been proposed to estimate the acoustic signal remotely with the current state-of-the-art method using an array of four microphones and a head tracking system to yield sound reduction up to 1 kHz for a single sound source. In the work reported in this paper, a novel approach of incorporating remote acoustic sensing using a laser Doppler vibrometer into an ANC headrest system is investigated. In this "virtual ANC headphone" system, a lightweight retro-reflective membrane pick-up is mounted in each synthetic ear of a head and torso simulator to determine the sound in the ear in real-time with minimal invasiveness. The membrane design and the effects of its location on the system performance are explored, the noise spectra in the ears without and with ANC for a variety of relevant primary sound fields are reported, and the performance of the system during head movements is demonstrated. The test results show that at least 10 dB sound attenuation can be realised in the ears over an extended frequency range (from 500 Hz to 6 kHz) under a complex sound field and for several common types of synthesised environmental noise, even in the presence of head motion

A systematic approach to the characterisation of human impact injury scenarios in sport

Background: In contact sports (e.g. American football or rugby), injuries resulting from impacts are widespread. There have been several attempts to identify and collate, within a conceptual framework, factors influencing the likelihood of an injury. To effectively define an injury event it is necessary to systematically consider all potential causal factors but none of the previous approaches are complete in this respect. Aims: Firstly, to develop a superior deterministic contextual sequential (DCS) model to promote a complete and logical description of interrelated injury event factors. Secondly, to demonstrate systematic use of the model to construct enhanced perspectives for impact-injury research. Method: Previous models were examined and elements of best practice synthesised into a new DCS framework description categorising the types of causal factors influencing injury. The approach’s internal robustness is demonstrated by consideration of its completeness, lack of redundancy, and logical consistency. Results: The model’s external validity and worth are demonstrated through its use to generate superior descriptive injury models, experimental protocols and intervention opportunities. Comprehensive research perspectives have been developed using a common rugby impact-injury scenario as an example; this includes: a detailed description of the injury event, an experimental protocol for a human-on-surrogate reconstruction, and a series of practical interventions in the sport of rugby aimed at mitigating the risk of injury. Conclusions: Our improved characterisation tool presents a structured approach to identify pertinent factors relating to an injury

The Development of a Methodology to Determine the Relationship in Grip Size and Pressure to Racket Head Speed in a Tennis Forehand Stroke

© 2016 The Authors. Published by Elsevier Ltd. This study developed a methodology to examine the effects of grip size and grip firmness on the kinematic contribution of angular velocity (KCAV) to the generation of racket head speed during a topspin tennis forehand. The KCAV is subdivided into kinematic contribution of joint angular velocity and kinematic contribution of the body segments in the upper trunk translational and angular velocities. Two Babolat Pure Storm GT rackets, with grip sizes 2 and 4 respectively, were used with Tekscan 9811E pressure sensors applied to the handles to examine pressure distribution during the stroke. Upper body kinematic data taken from the racket arm and trunk were obtained by means of a Vicon motion capture system. One elite male tennis player was recruited. Fifty topspin forehand strokes per grip at two nominal grip pressures were performed in a laboratory environment with balls being tossed towards the player and struck on the bounce towards a target on a net in as consistent a way as practically achievable. Processing of the results showed that the firm grip condition led to a significant (p<0.001) increase in average racket head speed compared to a normal grip condition. The normal gripping condition resulted in a significant (p<0.001) increase in average racket head speed for grip size 2 compared to grip size 4. A trend in negative linear relationships was found between upper trunk and shoulder joint in KCAV across conditions. Using the smaller grip also led to a trend in negative linear relationship between shoulder joint and wrist joint in KCAV across grip conditions. Grip pressure for grip size 2 showed the same pattern across gripping conditions. From 50-75% of completion in forward swing, the pressure difference due to grip firmness decreased. This feasibility study managed to quantify the KCAV while performing a topspin forehand, with respect to changing of grip size and grip pressure in an elite male tennis player for the first time

A novel phase-aligned analysis on motion patterns of table tennis strokes

© 2016, Routledge. All rights reserved. A wide range of human motion represent repetitive patterns particularly in racket sports. Quantitative analysis of the continuous variables during the different phases of the motion cycle helps to investigate more deeply the specific movement of the racket or player. Table tennis biomechanics research to date lacks the necessary detail of phase decomposition and phase-based quantitative analysis. Therefore, this study proposes a novel velocity-based piecewise alignment method to identify the different phases of a table tennis forehand stroke. A controlled experiment was conducted on a number of players of two differing ability levels (experts vs. novices) to implement this novel methodology. Detailed results are shown for the quantitative analysis on multiple strokes of the two groups of participants. Significant differences were found in both the displacement and velocity of the racket movement in the backswing, forward swing and follow-through phases. For example, it is clear that experts’ strokes show higher racket resultant velocity than novices during both the forward swing and follow-through phases by up to a factor of two. Furthermore, the phase-based approach to analysing racket motions leads to interrogation over a greater duration than the traditional time-based method which is generally only concerned with impact ±0.25s

Development of a test methodology for the assessment of human impacts in sport

The study described in this paper aims to develop a suitable method for the measurement of contact forces, pressures and velocities of simulated human-on-human impacts typical of those experienced within American Football. A thin-film pressure sensor system was chosen to enable the impacts to be quantified, however, initial testing suggested that the measured impact forces were underestimated by circa 30% with the system calibrated in the standard, static pressure manner. A two-stage, dynamic calibration was therefore developed, in which the sensors were subsequently dynamically loaded in a manner more representative of the impacts, allowing an appropriate dynamic calibration factor to be derived. To determine the typical impact force levels experienced in a shoulder-on-thigh impact event, eight subjects were required to perform three "good" tackles at two different velocities. The processed results identified a peak, transmitted force of 1.1 (0.4) and 1.7 (0.5) kN for "low" and "medium" velocities respectively, with corresponding effective areas of application of 70 (22) cm2 and 85 (25) cm2 and contact times of 0.257 (0.098) s and 0.245 (0.112) s respectively. © 2012 Published by Elsevier Ltd

Research and development of an air-puff excitation system for lightweight structures

© 2019 International Group of Operational Modal Analysis. Lightweight, thin-walled structures appear in numerous engineering and natural structures. Due to their sensitivity, vibration excitation by, now traditional, contacting techniques, such as modally-tuned impact hammers or electrodynamic shakers, to investigate their dynamics is challenging since it typically adds substantial mass and/or stiffness at the excitation location. The research presented in this article, therefore, is intended to yield a system for the non-contact excitation of thin-walled structures through small, controlled blasts of air. An air-puff system, consisting of two fast-acting solenoid-controlled valves, a small air outlet nozzle and bespoke control software with a programmable valve control sequence, is researched and developed. The excitation impulse characteristics are investigated experimentally and described in detail for varying input control parameters. Ultimately, suitability of the system for the excitation of thin-walled structures is explored, for both a 3D-printed micro-satellite panel and a natural bee honeycomb, with promising results when compared to that of an impact hammer

Shoulder joint angle errors caused by marker offset

Crown Copyright © 2015 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license. The International Society of Biomechanics (ISB) has recommended a standardization of the definition of the joint coordinate system (JCS) and use of a sequential rotation to describe human shoulder joint rotation. Markers attached to the surface of the body may move during the process of motion data capture, resulting in an offset from their initial location. This leads to a change of the JCS and therefore affects the calculated shoulder joint angles. In this research study, we presented a simple marker offset model to quantify the shoulder joint errors for both static poses and dynamic activities. Specific conditions of different offsets and elbow flexion angles were studied. Results showed that the errors should not be neglected when the shoulder elevation angle was near -90° and 90°, or elbow flexion was very small. Attention should be paid to these errors for such activities especially walking and throwing