Detection Of Acoustic Waves Research Articles

Acoustic detection of UHE neutrinos in the Mediterranean sea: status and perspective

In recent years the astro-particle community is involved in the realization of experimental apparatuses for the detection of high energy neutrinos originated in cosmic sources or produced in the interaction of Cosmic Rays with the Cosmic Microwave Background. For neutrino energies in the TeV-PeV range, optical Cherenkov detectors, that have been so far positively exploited by Baikal[1], IceCube[2] and ANTARES[3], are considered optimal. For higher energies, three different experimental techniques are under study: the detection of radio pulses produced by showers induced by a neutrino interaction, the detection of air showers initiated by neutrinos interacting with rocks or deep Earth’s atmosphere and the detection of acoustic waves produced by deposition of energy following the interaction of neutrinos in an acoustically transparent medium. The potential of the acoustic detection technique, first proposed by Askaryan[4], to build very large neutrino detectors is appealing, thanks to the optimal properties of media such as water or ice as sound propagator. Though the studies on this technique are still in an early stage, acoustic positioning systems used to locate the optical modules in underwater Cherenkov neutrino detectors, give the possibility to study the ambient noise and provide important information for the future analysis of acoustic data.

Theory for optical detection of picosecond shear acoustic gratings

A theoretical formalism describing the heterodyne detection of plane inhomogeneous shear acoustic waves by probe laser-induced gratings is developed. An inhomogeneous plane shear acoustic wave is a purely shear wave with a plane phase front and mechanical displacement vector, which is sinusoidally spatially modulated in magnitude. It could be generated by laser-induced gratings and could be useful for the acoustic testing of sub-micrometer thick membranes and coatings in the gigahertz frequency range. The theory reveals the potential advantages and disadvantages of this wave application in non-destructive testing of materials and fundamental research from the point of view of the feasibility of their experimental detection.

All-optical detection of acoustic pressure waves with applications in photoacoustic spectroscopy.

An all-optical detection method for the detection of acoustic pressure waves is demonstrated. The detection system is based on a stripped (bare) single-mode fiber. The fiber vibrates as a standard cantilever and the optical output from the fiber is imaged to a displacement-sensitive optical detector. The absence of a conventional microphone makes the demonstrated system less susceptible to the effects that a hazardous environment might have on the sensor. The sensor is also useful for measurements in high-temperature (above 200°C) environments where conventional microphones will not operate. The proof-of-concept of the all-optical detection method is demonstrated by detecting sound waves generated by the photoacoustic effect of NO2 excited by a 455nm LED, where a detection sensitivity of approximately 50ppm was achieved.

Partial Discharge Monitoring in Power Transformers Using Low-Cost Piezoelectric Sensors.

Power transformers are crucial in an electric power system. Failures in transformers can affect the quality and cause interruptions in the power supply. Partial discharges are a phenomenon that can cause failures in the transformers if not properly monitored. Typically, the monitoring requires high-cost corrective maintenance or even interruptions of the power system. Therefore, the development of online non-invasive monitoring systems to detect partial discharges in power transformers has great relevance since it can reduce significant maintenance costs. Although commercial acoustic emission sensors have been used to monitor partial discharges in power transformers, they still represent a significant cost. In order to overcome this drawback, this paper presents a study of the feasibility of low-cost piezoelectric sensors to identify partial discharges in mineral insulating oil of power transformers. The analysis of the feasibility of the proposed low-cost sensor is performed by its comparison with a commercial acoustic emission sensor commonly used to detect partial discharges. The comparison between the responses in the time and frequency domain of both sensors was carried out and the experimental results indicate that the proposed piezoelectric sensors have great potential in the detection of acoustic waves generated by partial discharges in insulation oil, contributing for the popularization of this noninvasive technique.

Determination of VOCs in the Indoor Air of a New and a Renovated Apartment

Abstract This study deals with the occurrence of volatile organic compounds (VOCs) in the indoor environment of a new and a renovated apartment. Qualitative determination of VOCs was carried out with a gas chromatograph with surface acoustic wave detector (GC/SAW). Concentrations of total volatile organic compounds (TVOC) were determined by a photoionization detector with UV lamp. Simultaneously, temperature and relative humidity were monitored with a data logger. The aim of this study was to determine of TVOC concentrations, to use of GC/SAW for determination of individual VOCs in indoor air as well as to predict possible sources of VOCs in these apartments. Measurements were performed after each construction work for better resolution of the contributions of individual materials to the levels of VOC. Mean concentrations of TVOC were 624 μg/m3 in the renovated apartment and 1,686 μg/m3 in the new apartment after completion of all works. The results from the renovated apartment showed that the use of new materials can lead to lower levels of organic compounds in indoor air compared to old materials that were less environmentally friendly. Many types of VOCs were found in both apartments. After reviewing the possible sources, it seems that the main sources of these substances were applied coatings and flooring materials.

Laser generation and electromagnetic detection of normal acoustic waves in ferromagnetic metals

Noncontact generation and detection of normal acoustic waves in a ferromagnetic metal sheet made of the 32NKD alloy are experimentally studied. The main relationships of the parameters of such processes are determined.

On the Detectability of Acoustic Waves Induced Following Irradiation by a Radiotherapy Linear Accelerator.

Irradiating an object with a megavoltage photon beam generated by a clinical radiotherapy linear accelerator (linac) induces acoustic waves through the photoacoustic effect. The detection and characterization of such acoustic waves has potential applications in radiation therapy dosimetry. The purpose of this work was to gain insight into the properties of such acoustic waves by simulating and experimentally detecting them in a well-defined system consisting of a metal block suspended in a water tank. A novel simulation workflow was developed by combining radiotherapy Monte Carlo and acoustic wave transport simulation techniques. Different set-up parameters such as photon beam energy, metal block depth, metal block width, and metal block material were varied, and the simulated and experimental acoustic waveforms showed the same relative amplitude trends and frequency variations for such setup changes. The simulation platform developed in this work can easily be extended to other irradiation situations, and will be an invaluable tool for developing a radiotherapy dosimetry system based on the detection of the acoustic waves induced following linear accelerator irradiation.

Precise rainbow trapping for low-frequency acoustic waves with micro Mie resonance-based structures

We have realized the acoustic rainbow trapping in the low frequency region (200–500 Hz) through micro Mie resonance-based structures. The structure has eight channels with a high refractive index obtained by coiling space, that can excite strong interactions with incident waves and support various orders of multipoles due to the Mie resonances of the microstructure. By utilizing the structure, the precise spatial modulation of the acoustic wave is demonstrated both theoretically and experimentally. The effect of trapping broadband acoustic waves and spatially separating different frequency components are ascribed to the monopolar Mie resonances of the structures. The trapping frequency is derived and the trapping positions can be tuned arbitrarily. With enhanced wave-structure interactions and tailored frequency responses, such micro structures show precise spectral-spatial control of acoustic waves and open a diverse venue for high performance acoustic wave detection, sensing, filtering, and a nondestructive test.

Thermal Conductivity, Heat Capacity, and Elastic Constants of Water-Soluble Polymers and Polymer Blends

We use time-domain thermoreflectance (TDTR), and the generation and detection of longitudinal and surface acoustic waves, to study the thermal conductivity, heat capacity, and elastic properties of thin films of poly(vinyl alcohol) (PVA), poly(acrylic acid) (PAA), polyacrylamide (PAM), poly(vinylpyrrolidone) (PVP), methyl cellulose (MC), poly(4-styrenesulfonic acid) (PSS), poly(N-acryloylpiperidine) (PAP), poly(methyl methacrylate) (PMMA), and a polymer blend of PVA/PAA. The thermal conductivity of six water-soluble polymers in the dry state varies by a factor of ≈2, from 0.21 to 0.38 W m–1 K–1, where the largest values appear among polymers with a high concentration of hydrogen bonding (PAA, PAM, PSS). The longitudinal elastic constants range from 7.4 to 24.5 GPa and scale linearly with the shear elastic constants, suggesting a narrow distribution of Possion’s ratio 0.35 < ν < 0.40. The thermal conductivity increases with the average sound velocity, as expected based on the model of the minimum thermal c...

Design and assessment of an acoustic ground cloak with layered structure

In this paper, a two-dimensional acoustic ground cloak with alternating layered structure composed of mercury and water is designed on the basis of transformation acoustics and effective medium theory. The cloak exhibits excellent cloaking performance to hide an object from the detection of acoustic waves. Cosine similarity is proposed to precisely quantize and evaluate the cloaking performance, which turns out to be succinct and effective. Numerical simulations confirm that the cloak could work well in a broad frequency band in which the cloaking performance displays an oscillatory decrease with increasing frequency. In addition, the omnidirectional property, larger incident angle of the acoustic beam has the better cloaking performance, is analyzed. This multilayered structure of cloak may offer an access to fabrication simplicity and experimental demonstration. The concept of cosine similarity may be an enrichment of the assessment system for acoustic cloaks.

Impulsively Excited Surface Phononic Crystals: A Route Toward Novel Sensing Schemes

The application of all-optical time resolved techniques to nanostructured surface phononic crystals (SPCs) enables the generation and detection of hypersonic frequency surface acoustic waves up to 50 GHz, with great potential for innovations in nanometrology and sensing applications. In this paper, we review the advances in this field in both experiments and theory, focusing on the progress in nondestructive nanometrology of ultrathin films, on the potential for a dramatic increase in the sensitivity of mass sensors due to enhanced acoustic wave surface confinement, and on the evolution of this approach to include polymer-coated SPCs for soft material and gas sensing applications. A survey of the enabling innovative optical technologies involved is presented.

Flexible suspended gate organic thin-film transistors for ultra-sensitive pressure detection.

The utilization of organic devices as pressure-sensing elements in artificial intelligence and healthcare applications represents a fascinating opportunity for the next-generation electronic products. To satisfy the critical requirements of these promising applications, the low-cost construction of large-area ultra-sensitive organic pressure devices with outstanding flexibility is highly desired. Here we present flexible suspended gate organic thin-film transistors (SGOTFTs) as a model platform that enables ultra-sensitive pressure detection. More importantly, the unique device geometry of SGOTFTs allows the fine-tuning of their sensitivity by the suspended gate. An unprecedented sensitivity of 192 kPa−1, a low limit-of-detection pressure of <0.5 Pa and a short response time of 10 ms were successfully realized, allowing the real-time detection of acoustic waves. These excellent sensing properties of SGOTFTs, together with their advantages of facile large-area fabrication and versatility in detecting various pressure signals, make SGOTFTs a powerful strategy for spatial pressure mapping in practical applications.

Fabrication of Cheap Optical Transducers (CHOTs) on film carriers for in-situ application and generation of surface acoustic waves

Cheap optical transducers (CHOTs) are patterns on the surface of a component activated by lasers to generate and detect ultrasound. Excited optically, with minimal surface impact, and fully customizable, CHOTs provide a simple alternative to conventional piezoelectric transducers, offering wireless, remote operation. Of particular interest is application of CHOTs for in-situ ultrasonic inspection of hard-to reach and complex-geometry components such as those of aero-engines. A suitable fabrication method has been developed to allow in-situ application of CHOTs onto large size and curved components, as well as those already in service, challenging for current laboratory-based micro-patterning methods. This work describes the fabrication of a transferable g-CHOT for generation of ultrasound. The g- CHOT has been made on an SU8 carrier film using a sacrificial polystyrene layer, allowing the transducer to be transferred from the substrate and subsequently delivered and applied to the surface of the sample in-situ. The functionality of the fabricated transducer is demonstrated by detection of the Surface Acoustic Waves (SAW) generated by the g-CHOT transferred onto glass and aluminium samples.

Pushing the limits of acoustics at the nanoscale using femtosecond transient interferometry

Picosecond acoustics is the perfect technique for measuring elastic properties at nanoscale. But there still are some limitations to reach in-plane properties of ultra-thin films related to optical detection of ultra-high frequency surface acoustic waves. Here, we demonstrate that it is possible to push the limits of the technique using an interferometric detection instead of a usual reflectometry scheme. The experimental observations are supported by a simple model which explains from where comes the previous limitations and why it is possible to overcome it using the interferometric setup. Thanks to those results, it is possible to excite and detect very high frequency surface acoustic waves confined in ultra-thin layer using conventional femtosecond laser and optical setup.

Noncontact photoacoustic imaging based on all-fiber heterodyne interferometer.

We report on a noncontact photoacoustic imaging system utilizing an all-fiber-optic heterodyne interferometer as an acoustic wave detector. The acoustic wave generated by a short laser pulse via the photoacoustic effect and arriving at the sample surface could be detected with the fiber-optic heterodyne interferometer without physical contact or using an impedance matching medium. A phantom experiment was conducted to evaluate the proposed system, and the initial acoustic pressure distribution was calculated using a Fourier-based reconstruction algorithm. It is expected that the all-fiber-optic configuration of the proposed system can be applied as a minimally invasive diagnostic tool.

Semiconductor superlattices: A tool for terahertz acoustics

The properties of optical to acoustic transduction of semiconductor superlattices have been explored for several years in the sub terahertz frequency range. Using femtosecond laser pulses focused on these structures, acoustic modes are excited with a frequency related to the periodicity of the structure stacking. We have shown that these acoustic waves can be extracted and can propagate in the underlying substrate. We study superlattices ability to be quasi monochromatic generators. On the other hand, superlattices have been found to be very sensitive and selective detectors. We present a set of experimental results concerning the generation, propagation over large distances and detection of acoustic waves at high frequencies, up to the challenging 1THz by picosecond ultrasonics experiments in transmission geometry.

Fundamentals of picosecond laser ultrasonics

The aim of this article is to provide an introduction to picosecond laser ultrasonics, a means by which gigahertz–terahertz ultrasonic waves can be generated and detected by ultrashort light pulses. This method can be used to characterize materials with nanometer spatial resolution. With reference to key experiments, we first review the theoretical background for normal-incidence optical detection of longitudinal acoustic waves in opaque single-layer isotropic thin films. The theory is extended to handle isotropic multilayer samples, and is again compared to experiment. We then review applications to anisotropic samples, including oblique-incidence optical probing, and treat the generation and detection of shear waves. Solids including metals and semiconductors are mainly discussed, although liquids are briefly mentioned.

The SKED: speckle knife edge detector

The knife edge detector—also known as optical beam deflection—is a simple and robust method of detecting ultrasonic waves using a laser. It is particularly suitable for detection of high frequency surface acoustic waves as the response is proportional to variation of the local tilt of the surface. In the case of a specular reflection of the incident laser beam from a smooth surface, any lateral movement of the reflected beam caused by the ultrasonic waves is easily detected by a pair of photodiodes. The major disadvantage of the knife edge detector is that it does not cope well with optically rough surfaces, those that give a speckled reflection. The optical speckles from a rough surface adversely affect the efficiency of the knife edge detector, because 'dark' speckles move synchronously with 'bright' speckles, and their contributions to the ultrasonic signal cancel each other out. We have developed a new self-adapting sensor which can cope with the optical speckles reflected from a rough surface. It is inelegantly called the SKED—speckle knife edge detector—and like its smooth surface namesake it is simple, cheap, compact, and robust. We describe the theory of its operation, and present preliminary experimental results validating the overall concept and the operation of the prototype device.

Sub-terahertz sound excitation and detection by a long Josephson junction

The paper reports on experimental observations of sub-terahertz sound wave generation and detection by a long Josephson junction. This effect was discovered in spectral measurements of sub-terahertz electromagnetic emission from a flux-flow oscillator (FFO) deposited on an optically polished Si substrate. The ‘back action’ of the acoustic waves generated by the FFO and reflected by the bottom surface of the Si substrate results in the appearance of resonant steps in the FFO IVCs with spacings as small as 29 nV for a 0.3 mm substrate thickness; these steps manifest themselves in a pronounced resonant structure in the emission spectra, with spacings of about 14 MHz, precisely according to the Josephson relation. The mechanism of acoustic wave generation and detection by the FFO is discussed; a possibility for employing the discovered effect for FFO frequency stabilization has been demonstrated. A simple and reliable way to suppress the superfine resonant structure has been developed and proved; this invention allows continuous frequency tuning and FFO phase locking at any desired frequency, all of which are vitally important for most applications.

Ultrasonic subwavelength focusing above periodic membrane arrays in immersion

Subwavelength focusing and imaging has been a long sought after goal and one that metamaterials can possibly achieve. In 2011, Lemoult et al. used time reversal techniques to focus sound to as small as λ/25 in air by using the evanescent wave field above a gird of soda cans acting as Helmholtz resonators [Lemoult et al. Phys. Rev. Lett. 107, 064301, (2011)]. This paper will demonstrate subwavelength focusing in immersion in the 11–0 MHz frequency range with capacitive micromachined ultrasonic transducer (CMUT) arrays. CMUTs are microscale (10–100 μm wide) membrane arrays, which support evanescent surface waves that derive their dispersive properties not only from the periodic structure of the array, but also from the membrane resonance. Furthermore, CMUTs have embedded electrodes for electrostatic excitation and detection of acoustic waves which allow implementation of time reversal techniques to focus the dispersive evanescent surface waves using only the CMUTs on the same substrate as sources and receivers. Using a finite boundary element method simulation, we demonstrate subwavelength focusing at points in the near-field above a 2D CMUT array in immersion.