High Levels Of Acoustic Noise Research Articles

Acoustic Noise Levels in High-field Magnetic Resonance Imaging Scanners.

7-Tesla (T) magnetic resonance imaging may allow for higher resolution images but may produce greater acoustic noise than 1.5- and 3-T scanners. We sought to characterize the intensity of acoustic noise from 7- versus 3-T scanners. A-weighted sound pressure levels from 5 types of pulse sequences used for brain and inner ear imaging in 3- and 7-T scanners were measured. Time-averaged sound level and maximum sound levels generated for each sequence were compared. Time-averaged sound levels exceeded 95 dB and reached maximums above 105 dB on the majority of 3- and 7-T scans. The mean time-averaged sound level and maximum sound level across pulse sequences were greater in 7- than 3-T (105.6 vs 91.4, P = .01; 114.0 vs. 96.5 dB, P < .01). 7- and 3-T magnetic resonance imaging scanners produce high levels of acoustic noise that exceed acceptable safety limits, emphasizing the need for active and passive noise protection.

Speech enhancement using ultrasonic doppler sonar

The quality of speech reproduced using conventional single-channel speech enhancement schemes is seriously affected by acoustic noise level. Nonacoustic sensors have the ability to reveal certain speech attributes that are lost in noisy acoustic signals. This study validated the use of ultrasonic doppler frequency shifts caused by facial movements for enhancing audio speech contaminated by high levels of acoustic noise. A 40 kHz ultrasonic beam is incident to a speaker’s face. The received signals were first demodulated and converted to a spectral feature parameter. The spectral feature derived from the ultrasonic Doppler signal (UDS) was concatenated with spectral features from noisy speech, which were then used to estimate the magnitude of the spectrum of clean speech. A nonlinear regression approach was employed in this estimation where the relationship between audio-UDS features and the corresponding clean speech is represented by deep neural networks (DNN). The feasibility of the proposed enhancement method was tested on a 1 h audio-UDS corpus and four different types of noise data. The results showed that, both objectively and subjectively, the best performance was obtained when the audio and UDS were used cooperatively. A correlation analysis was also carried out to investigate the usefulness of multi-directional ultrasonic sensing. The results showed that the performance was affected by the number of the adopted UDS channels, particularly in cases of low levels of SNRs.

Silent navigator-triggered silent MRI of the abdomen.

To develop and demonstrate the feasibility of a silent respiratory navigator technique for prospective triggering, which was incorporated into a three-dimensional radial zero-echo-time sequence for respiratory navigated silent abdominal imaging. A nonselective hard excitation radiofrequency pulse was used for the navigator sequence with a derated readout gradient, to avoid generation of high levels of acoustic noise. The acquired navigator signals were processed in real time and used for prospective triggering of the zero-echo-time sequence. Ten healthy volunteers were scanned using the proposed and conventional techniques at 1.5 T. An acoustic noise measurement with A-weighted continuous equivalent sound pressure level was also performed. The sound pressure-level values of the background noise, zero-echo-time imaging, conventional, and silent navigators were 68.3, 68.4, 102.5, and 69.4 dBA, respectively. Excellent correlation with correlation coefficients greater than 0.9 was observed between the bellows signals and displacement values calculated from the navigators. Sharpness of the portal vein of both conventional and silent navigator-triggered images was significantly higher than those of nontriggered images. The silent navigator-triggered zero-echo-time technique is feasible and might improve image quality and workflow of abdominal MRI of patients who are prone to acoustic noise. Magn Reson Med 79:2170-2175, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Making the case for applications of switched reluctance motor technology in automotive products

Switched reluctance machines (SRM) offer attractive attributes for automotive applications. These include robustness to harsh operational conditions, rugged structure, fault resilient performance, and a wide range of speed. The main debate over the adequacy of switched reluctance drives in automotive applications has often focused on efficiency and position sensorless control over the entire speed range, adaptation of control algorithms in the presence of parameter variations, and high levels of acoustic noise and vibration. The present paper demonstrates three key technologies developed over the past few years that have resulted in tangible improvements in the performance of SRM/generators (SRM/G) as related to the above areas of interest. This paper intends to illustrate the new possibilities and remaining challenges in applications of SRM in automotive industry. The proposed technologies have been validated by simulation and experimental results

Exploiting Nonacoustic Sensors for Speech Encoding

The intelligibility of speech transmitted through low-rate coders is severely degraded when high levels of acoustic noise are present in the acoustic environment. Recent advances in nonacoustic sensors, including microwave radar, skin vibration, and bone conduction sensors, provide the exciting possibility of both glottal excitation and, more generally, vocal tract measurements that are relatively immune to acoustic disturbances and can supplement the acoustic speech waveform. We are currently investigating methods of combining the output of these sensors for use in low-rate encoding according to their capability in representing specific speech characteristics in different frequency bands. Nonacoustic sensors have the ability to reveal certain speech attributes lost in the noisy acoustic signal; for example, low-energy consonant voice bars, nasality, and glottalized excitation. By fusing nonacoustic low-frequency and pitch content with acoustic-microphone content, we have achieved significant intelligibility performance gains using the DRT across a variety of environments over the government standard 2400-bps MELPe coder. By fusing quantized high-band 4-to-8-kHz speech, requiring only an additional 116 bps, we obtain further DRT performance gains by exploiting the ear's insensitivity to fine spectral detail in this frequency region.

Is Magnetic Resonance Image Guidance the Key to Opening Chronic Total Occlusions?

Through progressive plaque growth or fibrotic organization of occlusive thrombus, atherosclerosis may result in chronic total occlusion (CTO) of a major arterial conduit. If CTO develops slowly, collateral pathways may supply sufficient perfusion to retain tissue viability despite occlusion of the major inflow conduit. However, such collateral-mediated perfusion rarely matches that provided by an open main conduit, particularly during the peak demand of regional muscular activity. Although strategies to limit regional oxygen demand (eg, β-blockers for the treatment of angina pectoris) or to enhance collateral function (eg, a walking program for superficial femoral occlusion, experimental angiogenesis) may be of some benefit, these approaches generally offer less complete return of normal physiology and relief of ischemic symptoms than does direct revascularization of the occluded vessel. With surgical bypass, the nature of the occlusion (its length, duration, tortuosity, calcification) is less important than the presence of a suitable distal anastomotic target. On the other hand, with catheter-based techniques, success depends heavily on these lesion characteristics. In fact, crossing such occluded segments with a guidewire remains the dominant barrier to catheter-based treatments of occluded arterial segments. Once the guidewire has been passed successfully into the distal true lumen, the process of dilating and stenting the segment is usually straightforward and durable, at least with the use of drug-eluting stents in coronary CTOs.1,2 Article p 1101 Devices designed to cross CTOs should have 3 key features: an ability to distinguish a true luminal path from one created within (dissection) or through (perforation) the vessel wall of the occluded segment, an ability to change direction (steer) to correct deviations from the desired path through the occlusion, and an ability to penetrate the frequently fibrotic and focally calcific substance of the occlusion through the use of either mechanical stiffness or an alternative energy modality (laser, …

Analogue modeling of instabilities in crater lake hydrothermal systems

We carried out analogue experiments on two‐phase boiling systems, using a porous vertical cylinder, saturated with water. The base of the cylinder was heated, and the top was cooled, as in a natural hydrothermal system. Previous work had shown that once the two‐phase zone reached a certain level, thermal instabilities would develop. We made measurements of the acoustic energy related to boiling, and we found that high levels of acoustic noise were associated with the part of the cycle in which there was upward water movement. We repeated our experiments with a cooling water tank at the top of the system, representing a crater lake. This showed that periodic thermal instabilities still developed in this situation. We then compared our analogue measurements to two natural systems known to exhibit periodic behavior. There is good agreement between the thermal and acoustic cycling seen in our model and the observations made at Inferno Crater Lake in the Waimangu Geothermal area, New Zealand, whose level cycles by nearly 10 m, with a typical period of 38 days. Particularly notable is how in both systems high levels of acoustic noise are associated with rising water level. The much larger Ruapehu Crater Lake, also in New Zealand, cycled with a period of several months to a year for over a decade prior to the 1995 eruption. Strong acoustic and seismic energy usually occurred just before the lake temperature started to rise. This suggests a slightly different model, in which the increasing two‐phase flow zone triggers more general convection once it reaches the base of the lake.

Silent BOLD imaging.

Pulsed magnetic field gradients in magnetic resonance imaging produce high levels of acoustic noise. In functional magnetic resonance imaging, acoustic scanner noise causes unwanted masking effects. Recently, we proposed a method to perform magnetic resonance imaging experiments undisturbed by acoustic scanner noise by utilizing the property of standard gradient coils to poorly submit acoustic noise in the low frequency range. The silent gradient scheme is now incorporated into a standard T(2)*-weighted sequence. Additionally, simultaneous multi-slice excitation (SIMEX) pulses were implemented to improve the intrinsic low volume coverage of the silent sequence. The proposed silent SIMEX technique was tested and compared with a standard noisy technique using auditory and visual stimulation paradigms. The scanner noise during the silent experiments could be reduced below the range of the ambient noise of the magnet room. This feasibility study shows a trend of decreased activated areas in the noisy experiment for both, the visual and auditory paradigm.

The use of active noise control (ANC) to reduce acoustic noise generated during MRI scanning: Some initial results

MRI scanning generates high levels of acoustic noise that cannot only pose a safety hazard, but also impair communication between staff and patient. In this article we present active noise control (ANC) techniques that introduce antiphase noise to destructively interfere with the MRI noise and with the aim of producing a zone of quiet around the patient's ears. Using noise recorded from a 1.0 Tesla midfield MR scanner the acoustic noise generated by three standard MR imaging sequences was replayed to a real time two channel ANC system. The results obtained show a useful attenuation of low-frequency periodic acoustic noise components. Therefore, in combination with standard passive ear protection, this suggests that MR generated acoustic noise can be effectively attenuated at both low and high frequencies leading to improved patient comfort.

A versatile scanning tunnelling microscope for use in air

A scanning tunnelling microscope for use in air is described. Despite the apparent simplicity of the stage it is capable of high performance and this is largely due to its inherent stability resulting from miniaturisation and the use of stressed cantilever beams. It also employs a novel three-axis piezo scanner assembly which provides a fast response. Because of its stability, the microscope can be used in areas suffering from high levels of acoustic noise and vibration without additional isolation.

Robust 8000 bit/s sub-band speech coder

A speech coding technique has been developed to provide a method of digitising speech at bit rates in the region of 8000 bit/s which is insensitive to the effects of acoustic background noise and bit errors on the digital link. The main aim of the work has been to develop a coding scheme which provides speech quality and robustness against noise and errors that is similar to a 16 000 bit/s CVSD coder, but which operates at half its data rate. The result is a sub-band coder (SBC), with seven bands covering the frequency range 330 to 3200 Hz. The design is unusual in that it does not employ quadrature mirror filters (QMFs) but instead uses parallel finite-impulse-response (FIR) filters which are implemented efficiently with discrete Fourier transforms (DFTs) and prefiltering or windowing which is common to a group of filters. These DFT-based filters naturally provide output samples which are complex baseband vectors, and the quantisers are designed to handle these vectors in an optimum way that would not be possible with the purely real signals from a conventional QMF. The phase and amplitude components of the vectors are coded in ways that attempt to minimise the subjective effects of quantisation distortion and of bit errors between the encoder and decoder. Informal subjective tests indicate that the speech is of good ‘communications’ quality, and the coder can tolerate high levels of acoustic noise and a random bit error rate up to 10%.

Farfield Acoustic Effects of the Launch of the Saturn Space-Flight Vehicle

The launch of large space-flight vehicles has resulted in the production of very high levels of acoustic noise. The largest of these to reach flight status, the SATURN C-1 vehicle, generates an estimated 40 MW. Sound-pressure-level measurements were recorded along three widely separated azimuths from the launch pad. Data are presented showing the variation of the sound-energy distribution as a function of both time and range. Spectral information is presented, along with the measured attenuation coefficients. The measured launch data are compared to similar data taken during static test.