The Experts below are selected from a list of 3270 Experts worldwide ranked by ideXlab platform
Jeffrey Segal - One of the best experts on this subject based on the ideXlab platform.
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Percutaneous catheterization of the jugular bulb with a Doppler probe: technical note.
Neurosurgery, 1993Co-Authors: Jeffrey SegalAbstract:: On-line measurement of jugular venous bulb oxygen saturation may be of clinical value in patients with head injuries. Cannulation of the jugular bulb may be technically difficult in this group of patients. Trendelenberg positioning and head rotation may be associated with increased morbidity or mortality. A technique is described whereby catheterization can be performed with the head of the bed elevated and the neck in a neutral position. A needle with a Doppler probe is used to distinguish between the carotid artery and the internal jugular vein. The needle and the probe are then directed to the Audible Signal representative of the jugular vein. Once the vein is penetrated, placement of a fiberoptic oxygen saturation catheter is performed in the usual fashion. This technique allows auditory feedback to guide the course of the needle and decreases the morbidity that may be associated with the "blind" technique.
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Percutaneous Catheterization of the Jugular Bulb with a Doppler Probe
Neurosurgery, 1993Co-Authors: Jeffrey SegalAbstract:On-line measurement of jugular venous bulb oxygen saturation may be of clinical value in patients with head injuries. Cannulation of the jugular bulb may be technically difficult in this group of patients. Trendelenberg positioning and head rotation may be associated with increased morbidity or mortality. A technique is described whereby catheterization can be performed with the head of the bed elevated and the neck in a neutral position. A needle with a Doppler probe is used to distinguish between the carotid artery and the internal jugular vein. The needle and the probe are then directed to the Audible Signal representative of the jugular vein. Once the vein is penetrated, placement of a fiberoptic oxygen saturation catheter is performed in the usual fashion. This technique allows auditory feedback to guide the course of the needle and decreases the morbidity that may be associated with the "blind" technique.
Woon-seng Gan - One of the best experts on this subject based on the ideXlab platform.
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Identification of a parametric loudspeaker system using an adaptive Volterra filter
Applied Acoustics, 2012Co-Authors: Woon-seng GanAbstract:Abstract Due to the parametric acoustic array effect in air, the input Audible Signal of a parametric loudspeaker system can be reproduced with high directivity at the target region. However, the reproduced Audible Signal suffers from harmonic distortion, which is the by-product of nonlinear interaction between the primary waves. In order to investigate this inherent nonlinear phenomenon, a nonlinear system identification model is developed based on an adaptive Volterra filter. Unlike the conventional loudspeaker, the nonlinear characteristic of a parametric loudspeaker system is dependent on several primary parameters in nonlinear acoustics, which include the initial pressure of the primary waves, the observing distance and angle, as well as ambient temperature and relative humidity. By using a truncated Volterra series up to the 2nd-order kernel, numerical simulations are conducted to develop a system model with one group of parameters and examine the quadratic nonlinear intensity for different parameters’ settings. Experimental measurements, which take into account of emitter’s response, are carried out to verify the modeling result and evaluate the model performance. Based on the Volterra system model, the sound pressure level and the harmonic distortion can be accurately predicted.
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a comparative analysis of preprocessing methods for the parametric loudspeaker based on the khokhlov zabolotskaya kuznetsov equation for speech reproduction
IEEE Transactions on Audio Speech and Language Processing, 2011Co-Authors: Eeleng Tan, Woon-seng Gan, Jun YangAbstract:Based on the Berktay's farfield solution, various preprocessing methods were proposed to reduce the distortion of the highly directional Audible Signal in the parametric loudspeaker. However, the Berktay's farfield solution is an approximated model of nonlinear acoustic propagation. To determine the effectiveness of these methods, we analyze various preprocessing methods theoretically for directional speech reproduction using the Khokhlov-Zabolotskaya-Kuznetsov (KZK) equation, which provides a more accurate model of nonlinear acoustic propagation. In order to reduce the distortion effectively in the parametric loudspeaker with these preprocessing methods, the initial sound pressure level of the carrier frequency is found to be less than 132 dB according to the KZK equation. Unlike the Berktay' farfield solution that results in a +12 dB/octave gain slope, different gain slopes are derived using the KZK equation and appropriate equalizers are proposed to improve the frequency response of the parametric loudspeaker. The optimal preprocessing method for directional speech reproduction is established based on the KZK equation, which has a relatively flat frequency response of the desired speech Signal and the best total harmonic distortion performance.
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On Grating Lobe Elimination Of Difference Frequency In Parametric Loudspeaker
2010Co-Authors: Chuang Shi, Woon-seng GanAbstract:The parametric loudspeaker differs from other audio systems in its ability to create highly focused sound beam in air. This focused sound beam can be steered by adjusting a set of delays and weights of the ultrasonic transducer array (UTA), which is a component of parametric loudspeakers. In this paper, we use two ultrasonic primary Signals to generate an Audible Signal at difference frequency. Grating lobes of primary Signals occur when the spacing between ultrasonic transducers is larger than half the wavelength of primary Signals, but grating lobes of the difference frequency are rarely observed. Therefore, in this paper, we examine this phenomenon and provide an analytical explanation.
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Method to enhance the low‐frequency perception from a parametric array loudspeaker
The Journal of the Acoustical Society of America, 2001Co-Authors: Furi Andi Karnapi, Yew Hin Liew, Kelvin Lee, Woon-seng GanAbstract:Human auditory system does not perceive the sound Signal of all frequencies with equal loudness. Based on equal loudness curves, it is known that a low‐frequency Signal needs to be produced with a higher‐power level to have the same loudness as the middle frequency part. There are two ways to overcome this problem; either boosting the power of the low‐frequency part or utilizing the psychoacoustics effect called the missing fundamental. There are many works which have been done utilizing psychoacoustics to enhance the low‐frequency perception of audio Signal. These works are implemented to normal audio systems. Normal audio systems are comprised of a loudspeaker as the audio reproduction end. It is proposed to implement the low‐frequency enhancement to a parametric array loudspeaker. The use of a parametric array loudspeaker to generate highly directional Audible Signal has been reported in several literatures. However, this Audible Signal lacks low‐frequency content. One of the reasons is the relatively low‐power level produced by the existing parametric array. By utilizing the nonlinearity property of the air itself, it is proposed to psychoacoustically enhance the perception of the low‐frequency part.
Jun Yang - One of the best experts on this subject based on the ideXlab platform.
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a comparative analysis of preprocessing methods for the parametric loudspeaker based on the khokhlov zabolotskaya kuznetsov equation for speech reproduction
IEEE Transactions on Audio Speech and Language Processing, 2011Co-Authors: Eeleng Tan, Woon-seng Gan, Jun YangAbstract:Based on the Berktay's farfield solution, various preprocessing methods were proposed to reduce the distortion of the highly directional Audible Signal in the parametric loudspeaker. However, the Berktay's farfield solution is an approximated model of nonlinear acoustic propagation. To determine the effectiveness of these methods, we analyze various preprocessing methods theoretically for directional speech reproduction using the Khokhlov-Zabolotskaya-Kuznetsov (KZK) equation, which provides a more accurate model of nonlinear acoustic propagation. In order to reduce the distortion effectively in the parametric loudspeaker with these preprocessing methods, the initial sound pressure level of the carrier frequency is found to be less than 132 dB according to the KZK equation. Unlike the Berktay' farfield solution that results in a +12 dB/octave gain slope, different gain slopes are derived using the KZK equation and appropriate equalizers are proposed to improve the frequency response of the parametric loudspeaker. The optimal preprocessing method for directional speech reproduction is established based on the KZK equation, which has a relatively flat frequency response of the desired speech Signal and the best total harmonic distortion performance.
Dinei Florencio - One of the best experts on this subject based on the ideXlab platform.
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ICASSP - 3D numerical modeling of parametric speaker using finite-difference time-domain
2015 IEEE International Conference on Acoustics Speech and Signal Processing (ICASSP), 2015Co-Authors: Lijun Zhu, Dinei FlorencioAbstract:Parametric speakers produce sound by emitting ultrasound, and using the small nonlinearity in air to demodulate it back to Audible sound. The use of ultrasound allows for producing very narrow audio beams, which finds application in a number of military and consumer scenarios. However, designing better parametric speakers has been hard: closed-form solution of the nonlinear wave equation for generic geometries is nearly impossible, and the only existing solution was derived for the simple case of a cylindrical beam. FDTD methods were considered not practical since the desired (Audible) Signal is orders of magnitude weaker than the ultrasound Signal, and thus the noise floor (from the numerical approximation) will dwarf the Audible Signal. In this paper, we introduce a novel FDTD scheme that models nonlinear sound propagation for parametric speakers. By taking the difference between linear and nonlinear FDTD simulations, we successfully suppress the numerical noise floor and extract the Audible Signal. Both spectrum and radiation pattern of simulation match the measurements well. This offers a simulation tool for further research in creating advanced parametric speakers.
John C. Drummond - One of the best experts on this subject based on the ideXlab platform.
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precordial doppler probe placement for optimal detection of venous air embolism during craniotomy
Anesthesia & Analgesia, 2006Co-Authors: Armin Schubert, Anupa Deogaonkar, John C. DrummondAbstract:Verification of appropriate precordial Doppler probe position over the anterior chest wall is crucial for early detection of venous air embolism. We studied responses to normal saline (NS) and carbon dioxide (CO 2 ) test injections at various probe locations during elective craniotomy. All patients received four IV injections (10 mL of NS and 1 mL of CO 2 via central and peripheral venous catheters). Doppler sounds were simultaneously recorded with two separate probes. In Group A, probes were placed in left and right parasternal positions. In Group B, the left probe was intentionally malpositioned as far laterally over the left precordium as was compatible with an Audible Signal. In Group A (n = 23), a left parasternal Doppler Signal was easily obtainable in 23 of 23 patients, versus 18 of 23 patients for the right parasternal probe (P < 0.05). In Group B (n = 17), central CO 2 injection yielded a positive right parasternal response rate of 88% compared with 29% over the far left precordium (P < 0.015), where central NS injections yielded a 76% response rate (P < 0.015 versus central CO 2 injection). Left parasternal placement is at least as sensitive to clinical venous air embolism events as right parasternal placement. Peripheral saline injection represents a viable alternative (83% response rate). Vigorous central injection of 10 mL of NS however, risks false positive verification of left lateral precordial probe placement.
