Low Frequency Ultrasonic Voice Activity Detection using Convolutional Neural Networks

Low frequency ultrasonic mouth state detection uses reflected audio chirps from the face in the region of the mouth to determine lip state, whether open, closed or partially open. The chirps are located in a frequency range just above the threshold of human hearing and are thus both inaudible as well as unaffected by interfering speech, yet can be produced and sensed using inexpensive equipment. To determine mouth open or closed state, and hence form a measure of voice activity detection, this recently invented technique relies upon the difference in the reflected chirp caused by resonances introduced by the open or partially open mouth cavity. Voice activity is then inferred from lip state through patterns of mouth movement, in a similar way to video-based lip-reading technologies. This paper introduces a new metric based on spectrogram features extracted from the reflected chirp, with a convolutional neural network classification back-end, that yields excellent performance without needing the periodic resetting of the template closed-mouth reflection required by the original technique

Numerical Investigation of Second Mode Attenuation over Carbon/Carbon Surfaces on a Sharp Slender Cone

We have carried out axisymmetric numerical simulations of a spatially developing hypersonic boundary layer over a sharp 7$^{\circ{}}$-half-angle cone at $M_\infty=7.5$ inspired by the experimental investigations by Wagner (2015). Simulations are first performed with impermeable (or solid) walls with a one-time broadband pulse excitation applied upstream to determine the most convectively-amplified frequencies resulting in the range 260kHz -- 400kHz, consistent with experimental observations of second-mode instability waves. Subsequently, we introduce harmonic disturbances via continuous periodic suction and blowing at 270kHz and 350kHz. For each of these forcing frequencies complex impedance boundary conditions (IBC), modeling the acoustic response of two different carbon/carbon (C/C) ultrasonically absorptive porous surfaces, are applied at the wall. The IBCs are derived as an output of a pore-scale aeroacoustic analysis -- the inverse Helmholtz Solver (iHS) -- which is able to return the broadband real and imaginary components of the surface-averaged impedance. The introduction of the IBCs in all cases leads to a significant attenuation of the harmonically-forced second-mode wave. In particular, we observe a higher attenuation rate of the introduced waves with frequency of 350kHz in comparison with 270kHz, and, along with the iHS impedance results, we establish that the C/C surfaces absorb acoustic energy more effectively at higher frequencies.Comment: AIAA-SciTech 201

Sensors for biomedical applications

This paper considers the impact during the last decade of modern IC technology, microelectronics, thin- and thick-film technology, fibre optic technology, etc. on the development of sensors for biomedical applications

Wireless recording of the calls of Rousettus aegyptiacus and their reproduction using electrostatic transducers

Bats are capable of imaging their surroundings in great detail using echolocation. To apply similar methods to human engineering systems requires the capability to measure and recreate the signals used, and to understand the processing applied to returning echoes. In this work, the emitted and reflected echolocation signals of Rousettus aegyptiacus are recorded while the bat is in flight, using a wireless sensor mounted on the bat. The sensor is designed to replicate the acoustic gain control which bats are known to use, applying a gain to returning echoes that is dependent on the incurred time delay. Employing this technique allows emitted and reflected echolocation calls, which have a wide dynamic range, to be recorded. The recorded echoes demonstrate the complexity of environment reconstruction using echolocation. The sensor is also used to make accurate recordings of the emitted calls, and these calls are recreated in the laboratory using custom-built wideband electrostatic transducers, allied with a spectral equalization technique. This technique is further demonstrated by recreating multi-harmonic bioinspired FM chirps. The ability to record and accurately synthesize echolocation calls enables the exploitation of biological signals in human engineering systems for sonar, materials characterization and imaging

Mealiness Detection in Agricultural Crops: Destructive and Nondestructive Tests: A Review

Mealiness is known as an important internal quality attribute of fruits/vegetables, which has significant influence on consumer purchasing decisions. Mealiness has been a topic of research interest over the past several decades. A number of destructive and nondestructive techniques are introduced for mealiness detection. Nondestructive methods are more interesting because they are rapid, noninvasive, and suitable for real-time purposes. In this review, the concept of mealiness is presented for potato, apple, and peach, followed by an in-depth discussion about applications of destructive and nondestructive techniques developed for mealiness detection. The results suggest the potential of electromagnetic-based techniques for nondestructive mealiness evaluation. Further investigations are in progress to find more appropriate nondestructive techniques as well as cost and performance

Aerospace Medicine and Biology: A continuing bibliography with indexes, supplement 171

This bibliography lists 186 reports, articles, and other documents introduced into the NASA scientific and technical information system in August 1977

Nucleation threshold and deactivation mechanisms of nanoscopic cavitation nuclei

The acoustic nucleation threshold for bubbles trapped in cavities has theoretically been predicted within the crevice theory by Atchley and Prosperetti [“The crevice model of bubble nucleation,” J. Acoust. Soc. Am. 86, 1065 (1989)]. Here, we determine this threshold experimentally, by applying\ud a single pressure pulse to bubbles trapped in cylindrical nanoscopic pits (“artificial crevices”) with radii down to 50 nm. By decreasing the minimum pressure stepwise, we observe the threshold for which the bubbles start to nucleate. The experimental results are quantitatively in good agreement with the theoretical predictions of Atchley and Prosperetti. In addition, we provide the mechanism which explains the deactivation of cavitation nuclei: gas diffusion together with an aspherical bubble collapse. Finally, we present superhydrophobic nuclei which cannot be deactivated, unless with a high-speed liquid jet directed into the pit

Application of Nondestructive Testing in Inspection of Boiler and Pressure Vessel and Pressure Piping

Non-destructive testing technology has been widely used in all occupations. The testing of equipment is called non-destructive testing technology. During the testing process, there is no need to pre-process the equipment to test, nor add other testing substances, which is especially suitable for the testing of boiler equipment in industrial production. Boiler and pressure vessel equipment is an important part of industrial production. The boiler pressure vessel has been in an operating environment with relatively high temperature for a long time, and it is common for the boiler pressure vessel to rupture. At this time, non-destructive testing technology came into being. It can detect damage to the boiler structure without damaging it, which plays a vital role for boilers, especially pressure pipes. This article analyzes the advantages, disadvantages and principles of pressure pipeline non-destructive testing technology, and discusses its application in boiler flaw detection to provide guidance for future work

Development of microwave NDT inspection techniques for large solid propellant rocket motors Final report

Microwave nondestructive testing techniques for large solid propellant rocket engine