Biblio

This report provides a calculation example of hydrodynamic and acoustic characteristics of the ship propulsor using numerical modelling with the help of RANS-models and eddy-resolving approaches in the hydrodynamics task, acoustic analogy in the acoustics tasks and harmonic analysis of the propulsor under hydrodynamic loads.

This paper proposes a method to synthesis acoustic wave (AW) filters with Chebyshev response automatically. Meanwhile, each AW resonator used to design the filter can be easily fabricated on the same piezoelectric substrate. The method is based on an optimization algorithm with constraints for constant electromechanical coupling coefficient ( kt2) to minimize the defined cost function. Finally, the experimental result for a surface acoustic wave (SAW) filter of global positioning system (GPS) frequency band based on the 42° lithium tantalate (LiTaO3) substrate validates the simulation results. The designed filter shows insertion loss (IL) and return loss (RL) better than 2.5dB and 18dB respectively in the pass-band, and out-band reflection larger than 30dB.

There is some uncertainty as to the applicability or accuracy of current theories for wave propagation in sediments. Numerical modelling of acoustic data has long been recognized to be a powerful method of understanding of complicated wave propagation and interaction. In this paper, we used the coupled two-dimensional PSM-BEM program to simulate the process of acoustic wave propagation in the seafloor with distributed multi-scale random media. The effects of fluid flow between the pores and the grains with multi-scale distribution were considered. The results show that the coupled PSM-BEM program can be directly applied to both high and low frequency seafloor acoustics. A given porous frame with the pore space saturated with fluid can greatly increase the magnitude of acoustic anisotropy. acoustic wave velocity dispersion and attenuation are significant over a frequency range which spans at least two orders of magnitude.

In-Band Full-Duplex (IBFD) Underwater Acoustic (UWA) communication technology plays a major role in enhancing the performance of Underwater acoustic sensor networks (UWSN). Self-Interference (SI) is one of the main inherent challenges affecting the performance of IBFD UWA communication. To reconstruct the SI signal and counteract the SI effect, this is important to estimate the short range channel through which the SI signal passes. Inaccurate estimation will result in the performance degradation of IBFD UWA communication. From the perspective of engineering implementation, we consider that the UWA communication modem shell has a significant influence on the short-range SI channel, which will limit the efficiency of self-interference cancellation in the analog domain to some degree. Therefore we utilize a simplified model to simulate the influence of the structure of the IBFD UWA communication modem on the receiving end. This paper studies the effect of acoustic-shell coupling on near-end self-interference signal of IBFD UWA communication modem. Some suggestions on the design of shell structure of IBFD UWA communication modem are given.

Underwater communication is vital for a variety of defence and scientific purposes. Current optical and sonar based carriers can deliver high capacity data rates, but their range and reliability is hampered by heavy propagation loss. A vertical Molecular Communication via Buoyancy (MCvB) channel is experimentally investigated here, where the dominant propagation force is buoyancy. Sequential puffs representing modulated symbols are injected and after the initial loss of momentum, the signal is driven by buoyancy forces which apply to both upwards and downwards channels. Coupled with the complex interaction of turbulent and viscous diffusion, we experimentally demonstrate that sequential symbols exhibit a Gaussian velocity spatial distribution. Our experimental results use Particle Image Velocimetry (PIV) to trace molecular clusters and infer statistical characteristics of their velocity profile. We believe our experimental paper's results can be the basis for long range underwater vertical communication between a deep sea vehicle and a surface buoy, establishing a covert and reliable delay-tolerant data link. The statistical distribution found in this paper is akin to the antenna pattern and the knowledge can be used to improve physical security.

Object identification in the room environment is a key technique in many advanced engineering applications such as the unidentified object recognition in security surveillance, human identification and barrier recognition for AI robots. The identification technique based on the sound field perturbation analysis is capable of giving immersive identification which avoids the occlusion problem in the traditional vision-based method. In this paper, a new insight into the relation between the object and the variation of the sound field is presented. The sound field difference before and after the object locates in the environment is analyzed using the spectral subtraction based on the room impulse response. The spectral subtraction shows that the energy loss caused by the sound absorption is the essential factor which perturbs the sound field. By using the energy loss with high uniqueness as the extracted feature, an object identification technique is constructed under the classical supervised pattern recognition framework. The experiment in a real room validates that the system has high identification accuracy. In addition, based on the feature property of position insensitivity, this technique can achieve high identifying accuracy with a quite small training data set, which demonstrates that the technique has potential to be used in real engineering applications.

Biometric recognition systems based on ultrasound images have been investigated for several decades, and nowadays ultrasonic fingerprint sensors are fully integrated in portable devices. Main advantage of the Ultrasound over other technologies are the possibility to collect 3D images, allowing to gain information on under-skin features, which improve recognition accuracy and resistance to spoofing. Also, ultrasound images are not sensible to several skin contaminations, humidity and not uniform ambient illumination. An ultrasound system, able to acquire 3D images of the human palm has been recently proposed. In this work, a recognition procedure based on 2D palmprint images collected with this system is proposed and evaluated through verification experiments carried out on a home made database composed of 141 samples collected from 24 users. Perspective of the proposed method by upgrading the recognition procedure to provide a 3D template able to accounts for palm lines' depth are finally highlighted and discussed.

This paper designed a longitudinal bending coupled piezoelectric transducer. The transducer is composed of a rear metal block, a longitudinally polarized piezoelectric ceramic piece and a slotted round front cover. The longitudinal vibration of the piezoelectric oscillators drive the front cover to generate bending vibration to widen the operating frequency band while reducing the fluctuation of transmission voltage response. In this paper, the design method of this multimode coupled transducer is given, and the method is verified by numerical simulation. The results show that the analytical theory and numerical simulation results have good consistency. This longitudinal-flexural coupled vibration transducer widens the bandwidth while preserving the emission voltage response.

Modal Energy Analysis (MODENA) is a new method which focuses on structural-acoustic coupling problems in recent years. It can predict the energy response of the system quickly and accurately. An algorithm that integrates Finite Element (FE) and MODENA is proposed to solve the structural-acoustic coupling analyses of complex dynamic systems when modes information cannot be solved by analytical ways. The proposed algorithm is applied to a complex structural-acoustic coupling system. Results show that the FE-MODENA method gives a fine estimation to the structural-acoustic response analyses compared with Dual Modal Formulation results, especially when considering multi-point random excitation.

Surface acoustic wave (SAW) optical sensor based on two-dimensional (2D) sensing layer can always provide extremely high sensitivity. As an attractive option, the application of exfoliated 2D perovskite on acousto-optic coupling optical sensor is investigated. In this work, exfoliated 2D (PEA)2PbI4 sheet was transferred as a sensing layer onto the delay area of a dual-port SAW resonator with resonant frequency 497 MHz. From the response under 532 nm laser with intensity of 0.9 mW/cm2, a largest frequency shift of 13.92 MHz was observed. The ultrahigh sensitivity up to 31.6 ppm/(μW/cm2) was calculated by experiment results. We also carried out theoretical analysis and finite element simulation of 3D model to demonstrate the mechanism and validity for optical sensing. The fabricated optical sensor expressed great potential for a variety of optical applications.

This paper reported the polymer coated film bulk acoustic resonators (FBAR) as a sensitive detector in micro chromatography for the detection of trace chemical warfare agents (CWA) simulants. The FBAR sensor was enclosed in a microfluidic channel and then coupled with microfabricated separation column. The subsequent chromatographic analysis successfully demonstrated the detection of parts per billion (ppb) concentrations of chemical warfare agents (CWAs) simulants in a five components gas mixture. This work represented an important step toward the realization of FBAR based handheld micro chromatography for CWA detection in the field.

To experimentally study the characteristics of ultrasonic sensors, a wideband air-coupled ultrasonic transducer, wideband electromagnetic dynamic acoustic transducer (WEMDAT), is designed and fabricated. Characterisation methods, including electrical impedance analysis, laser Doppler vibrometry and pressure-field microphone measurement, are used to examine the performance of the WEMDAT, which have shown that the transducer has a wide bandwidth ranging approximately from 47 kHz to 145 kHz and a good directivity with a beam angle of around 20˚ with no evident side lobes. A 40 kHz commercial flexural ultrasonic transducer (FUT) is then taken as an example to receive ultrasonic waves in a pitch-catch configuration to evaluate the performance of the WEMDAT as an acoustic source. Experiment results have demonstrated that the WEMDAT can maintain the most of the frequency content of a 5 cycle 40 kHz tone burst electric signal and convert it into an ultrasonic wave for studying the dynamic characteristic and the directivity pattern of the ultrasonic receiver. A comparison of the dynamic characteristics between the transmitting and the receiving processes of the same FUT reveals that the FUT has a wider bandwidth when operating as an ultrasonic receiver than operating as a transmitter, which indicates that it is necessary to quantitatively investigate the receiving process of an ultrasonic transducer, demonstrating a huge potential of the WEMDAT serving as a standard acoustic source for ultrasonic sensors for various air-coupled ultrasonic applications.

The coupled thermohydroelastic processes of acoustic wave and heat propagation in weak viscous fluid and elastic bodies form the basis of dissipative acoustics. The problems of dissipative acoustics have many applications in engineering practice, in particular in the development of appropriate medical equipment. This paper presents mathematical models for time and frequency domain problems in terms of unknown displacements and temperatures in both the fluid and the elastic body. Formulated corresponding variational problems and constructed numerical schemes for their solution based on the Galerkin approximations. The method of proving the well-posedness of the considered variational problems is proposed.

This work investigates the electromechanical coupling coefficient (kt2) attained by two available piezoelectric acoustic resonator technologies relying on Aluminum Scandium Nitride (ScyAl1-yN) films to operate. In particular, by using a theoretical approach, we extracted the maximum kt2-value attainable, for different scandium-doping concentrations (from 0% to 40%), by Film-Bulk-Acoustic-Resonators (FBARs) and Cross-Sectional-Lamé-Mode Resonators (CLMRs). For the first time, we show how the use of higher scandium doping concentrations can render the kt2 of CLMRs higher (35%) than the one attained by FBARs (28%). Such a unique feature renders CLMRs as ideal candidates to form lithographically defined resonators and filters for next-generation wideband radiofrequency (RF) front-ends.

Emerging next generation wireless communication devices call for high-performance filters that operate at 3-10 GHz frequency range and offer low loss, small form factor, wide bandwidth and steep skirts. Bulk and surface acoustic wave devices have been long used in the RF front-end for filtering applications, however their operation frequencies are mostly below 2.6 GHz band. To scale up the frequency of the filters, the thickness of the piezoelectric material needs to be reduced to sub-micron ranges. One of the challenges of such scaling is maintaining high electromechanical coupling as the film thickness decreases, which in turn, determines the filter bandwidth.Aluminum Nitride (AlN) - popular in today's film bulk acoustic resonators (FBARs) and mostly deposited using sputtering techniques-shows degraded crystal quality and poor electromechanical coupling when the thickness of AlN film is smaller than 1 μm.In this work, we propose using high-quality single-crystalline AlN and Scandium (Sc)-doped AlN epi-layers grown on Si substrates, wherein high crystal quality is maintained for ultra-thin films of only 400 nm thickness. Experimental results verify improved kt2 for 3-10 GHz resonators, with quality factors of the order of 250 and kt2 values of up to 5%based on bulk acoustic wave resonators. The experimental results suggest that single-crystal Sc-AlN is a great material candidate for 5G resonators and filters.

According to the technical difficulties of the air-coupled piezoelectric ultrasonic transducer, 1-3 type piezoelectric composites and double matching layers structure are adopted in order to solve the acoustic impedance mismatch at the interface between the piezoelectric materials and air. The optimal design of the matching layer thickness for double matching layers structure air-coupled ultrasonic transducer is also completed through experiments. Based on this, 440 kHz flat-plate and focused air-coupled piezoelectric ultrasonic transducer are designed, fabricated and characterized. Finally, surface cracks are detected using the focused air-coupled piezoelectric ultrasonic transducer.

Mechanism to-Rube Goldberg invention accord is normal habituated to for apartment phones and Internet of Things. Agree and central knowledge are open to meet an unfailing turning between twosome gadgets. In ignoble fracas, factual methodologies many a time eon wait on a prefabricated solitarily pronunciation database and bear the ill effects of serene age rate. We verifiable GeneWave, a brusque gadget inspection and root assention convention for item cell phones. GeneWave mischievous accomplishes bidirectional ingenious inspection office on the physical reaction meantime between two gadgets. To evade the resolution of interim in compliance, we overshadow overseas time fragility on ware gadgets skim through steep flag location and excess time crossing out. At zigzag goal, we success out the elementary acoustic channel reaction for gadget verification. We combination an extraordinary coding pointing for virtual key assention while guaranteeing security. Consequently, two gadgets heart signal couple choice and safely concur on a symmetric key.

This paper presents netsim, a combined software/hardware system for performing realtime realistic operation of autonomous underwater vehicles (AUVs) with acoustic modem telemetry in a virtual ocean environment. The design of the system is flexible to the choice of physical link hardware, allowing for the system to be tested against existing and new modems. Additionally, the virtual ocean channel simulator is designed to perform in real time by coupling less frequent asynchronous queries to high-fidelity models of the ocean environment and acoustic propagation with frequent pertubation-based updates for the exact position of the simulated AUVs. The results demonstrate the performance of this system using the WHOI Micro-Modem 2 hardware in the virtual ocean environment of the Arctic Beaufort Sea around 73 degrees latitude. The acoustic environment in this area has changed dramatically in recent years due to the changing climate.

We investigate directional differences when coupling Lamb waves in a structure to guided modes in an optical fiber sensor for detection of the ultrasonic wave propagation through the structure.

A new class of multi-band acoustic-wave-Iumped-ele-ment-resonator (AWLR)-based bandstop filters (BSFs) is reported. It is based on\$N\$multi-resonant A WLRs-shaped by\$K\$AWLRs and 2K inverters-that are connected to an all-pass network and result in\$\textbackslashtextbackslashpmbK\textbackslashtextbackslash Nˆth\$order rejection bands. The proposed concept allows the realization of multiple rejection bands with the following characteristics: i) fractional bandwidths (FBWs) larger than the electromechanical coupling coefficient\$\textbackslashtextbackslashpmbk\_tˆ\textbackslashtextbackslash 2\$of its constituent acoustic-wave resonators, ii) continuously variable and inde-pendently-controlled FBWs, iii) intrinsically-switched stopbands, and iv) an all pass state. For proof-of-concept validation purposes a dual-band prototype was designed, built, and tested. It exhibits two stopbands centered at 418 and 433 MHz that can be continu-ously-tuned in FBW (up to 7.7:1 tuning range) and in number.

Analysis of acoustic wave scattering by a finite flat impedance strip grating is presented. The associated two-dimensional (2-D) boundary-value problem is considered in the full-wave manner and cast to a set of coupled integral equations. Based on them, we build several mathematical models. The focus of research is on the acoustic plane wave scattering by a grating of narrow impedance strips that has explicit asymptotic solution.

The engine is a significant and dynamic component of the aircraft. Because of the complicated structure and severe operating environment, the fault detection of the engine has always been the key and difficult issue in the field of reliability. Based on an engine and the acoustic emission technology, we propose a method of identifying fault types and determining different components in the engine by constructing the attenuation coefficient. There are several common faults of engines, and three different types of fault sources are generated experimentally in this work. Then the fault signal of the above fault sources propagating in different engine components are obtained. Finally, the acoustic emission characteristics of the fault signal are extracted and judged by the attenuation coefficient. The work effectively identifies different types of faults and studies the effects of different structural components on the propagation of fault acoustic emission signals, which provides a method for the use of acoustic emission technology to identify the faults types of the engine and to study the propagation characteristics of AE signals on the engine.*

We report time-domain measurements of acoustic-wave-induced magnetization dynamics in magnetic tunnel junctions. The acoustic pulses are generated by femtosecond laser excitation and interact with the magnetization through magnetoelastic coupling. The induced magnetization precession is not only dependent on the externally applied magnetic field, but also on the laser excitation position. The presented method even allows us to coherently control the precession using two laser pulses at various magnetic fields and excitation positions.

The aim of the project SIMOPERA is to simulate and optimize the acoustics in large and complex rooms, with special focus on the Deutsche Oper Berlin as an example of application. Firstly, characteristic subspaces of the opera are considered such as the orchestra pit, the stage and the auditorium. Special attention is paid to the orchestra pit, where high sound pressure levels can occur, leading to noise related risks for the musicians. However, lowering the sound pressure level in the orchestra pit should not violate other objectives as the propagation of sound into the auditorium, the balance between the stage performers and the orchestra across the hall, and the mutual audibility between performers and orchestra members. For that reason, a hybrid simulation method consisting of the wave-based Finite Element Method (FEM) and the Boundary Element Method (BEM) for low frequencies and geometrical methods like the mirror source method and ray tracing for higher frequencies is developed in order to determine the relevant room acoustic quantities such as impulse response functions, reverberation time, clarity, center time etc. Measurements in the opera will continuously accompany the numerical calculations. Finally, selected constructive means for reducing the sound level in the orchestra pit will be analyzed.

Wireless transmission of power has been in research for over a century. Our project aims at transmitting electric power over a distance of room. Various methods using microwaves, lasers, inductive coupling, capacitive coupling and acoustic medium have been used. In our project, we are majorly focusing on acoustic method of transferring power. Previous attempts of transferring power using acoustic methods have employed the usage of ultrasonic sound. In our project, we are using infrasonic sound as a medium to transfer electrical power. For this purpose, we are using suitable transducers and converters to transmit electric power from the 220V AC power supply to a load over a considerable distance. This technology can be used to wirelessly charge various devices more effectively.