Model Of Transducer Research Articles

Deep and Domain Transfer Learning Aided Photoacoustic Microscopy: Acoustic Resolution to Optical Resolution.

Acoustic resolution photoacoustic micros- copy (AR-PAM) can achieve deeper imaging depth in biological tissue, with the sacrifice of imaging resolution compared with optical resolution photoacoustic microscopy (OR-PAM). Here we aim to enhance the AR-PAM image quality towards OR-PAM image, which specifically includes the enhancement of imaging resolution, restoration of micro-vasculatures, and reduction of artifacts. To address this issue, a network (MultiResU-Net) is first trained as generative model with simulated AR-OR image pairs, which are synthesized with physical transducer model. Moderate enhancement results can already be obtained when applying this model to in vivo AR imaging data. Nevertheless, the perceptual quality is unsatisfactory due to domain shift. Further, domain transfer learning technique under generative adversarial network (GAN) framework is proposed to drive the enhanced image's manifold towards that of real OR image. In this way, perceptually convincing AR to OR enhancement result is obtained, which can also be supported by quantitative analysis. Peak Signal to Noise Ratio (PSNR) and Structural Similarity Index (SSIM) values are significantly increased from 14.74 dB to 19.01 dB and from 0.1974 to 0.2937, respectively, validating the improvement of reconstruction correctness and overall perceptual quality. The proposed algorithm has also been validated across different imaging depths with experiments conducted in both shallow and deep tissue. The above AR to OR domain transfer learning with GAN (AODTL-GAN) framework has enabled the enhancement target with limited amount of matched in vivo AR-OR imaging data.

Acoustic and Thermal Characterization of Therapeutic Ultrasonic Langevin Transducers under Continuous- and Pulsed Wave Excitations.

We previously conducted an empirical study on Langevin type transducers in medical use by examining the heat effect on porcine tissue. For maximum acoustic output, the transducer was activated by a continuous sinusoidal wave. In this work, pulsed waves with various duty factors were applied to our transducer model in order to examine their effect on functionality. Acoustic power, electro-acoustic conversion efficiency, acoustic pressure, thermal effect on porcine tissue and bovine muscle, and heat generation in the transducer were investigated under various input conditions. For example, the results of applying a continuous wave of 200 VPP and a pulse wave of 70% duty factor with the same amplitude to the transducer were compared. It was found that continuous waves generated 9.79 W of acoustic power, 6.40% energy efficiency, and 24.84 kPa acoustic pressure. In pulsed excitation, the corresponding values were 9.04 W, 8.44%, and 24.7 kPa, respectively. The maximum temperature increases in bovine muscle are reported to be 83.0 °C and 89.5 °C for each waveform, whereas these values were 102.5 °C and 84.5 °C in fatty porcine tissue. Moreover, the heat generation around the transducer was monitored under continuous and pulsed modes and was found to be 51.3 °C and 50.4 °C. This shows that pulsed excitation gives rise to less thermal influence on the transducer. As a result, it is demonstrated that a transducer triggered by pulsed waves improves the energy efficiency and provides sufficient thermal impact on biological tissues by selecting proper electrical excitation types.

Frequency matching optimization model of ultrasonic scalpel transducer based on neural network and reinforcement learning

Aiming at the problem that the excitation frequency and resonant frequency of the transducer cannot keep synchronous, the output amplitude decreases and the vibration is unstable. In this study, the working principle of piezoelectric transducers is firstly analyzed by the equivalent circuit method and the instantaneous characteristic variables (installing preload, assembly preload, load, and other factors) that affect the frequency matching obtained to establish the equivalent relationship with the resonant frequency. Secondly, in order to make the synchronization between excitation frequency and resonance frequency, the key instantaneous characteristic variables are extracted based on Pearson correlation coefficient. Thirdly, the mathematical model of the mapping relationships between instantaneous characteristic variables and resonance frequency is established with the radial basis function neural network (RBFNN). Fourthly, for the purpose of the adaptation to the characteristics of dynamic load and real-time frequency modulation in the operation of ultrasonic scalpels, the reinforcement learning (Q-learning algorithm) and the weight vector of RBFNN are used to define the eligibility trace, which is used to dynamically adjust the RBFNN frequency matching optimization model in real time and maintain the “constant” amplitude output and stable harmonic response process. Finally, the experimental results show that, compared with the traditional methods, the frequency matching optimization model of ultrasonic scalpel transducer based on RBF neural network and Q-Learning reinforcement learning is effective, and the vibration amplitude of the transducer is increased by 15.25μm. The amplitude fluctuation is stable at 0.92μm. It can provide decision-making guidance for relevant engineering fields.

Dielectric elastomer actuators as artificial muscles for wearable robots

Current powered prosthetic and orthotic devices are mostly based on rigid actuators, which exhibit some intrinsic limitations, such as the reduced number of degrees of freedom, high weight, and limited flexibility. As progress is made in the soft robotics field, artificial muscles arise as potential candidates to replace current rigid actuator technologies. Dielectric elastomer actuators (DEAs) are a very promising class of soft actuator and are attracting attention due to their high energy density, fast response, and high actuation strains, similar or even superior to natural muscles. Such remarkable properties can lead the DEAs to be the next generation of actuators for wearable robots, and overcome the limitations imposed by the rigid actuators currently used. This paper reviews the state of art of the applications of DEAs to prostheses, orthoses, and rehabilitation devices. We analyzed the main configurations that are suitable as artificial muscles for the above-mentioned applications and presented the basic model of a dielectric elastomer transducer. When compared to the properties of natural skeletal muscle, some of these configurations stand out. However, there are still some drawbacks that prevent the large-scale application of DEAs, for instance the high operating voltages, durability issues, and nonlinearities that make them difficult to control. We investigated recent advances in materials, control strategies and fabrication methods that tackle these drawbacks, and they indicate that dielectric elastomers are great candidates to be the next generation of actuators for bionic devices.

Large-Signal Equivalent-Circuit Model of Asymmetric Electrostatic Transducers

This article presents a circuit model that is able to capture the full nonlinear behavior of an asymmetric electrostatic transducer whose dynamics are governed by a single degree of freedom. Effects such as stress-stiffening and pull-in are accounted for. The simulation of a displacement-dependent capacitor and a nonlinear spring is accomplished with arbitrary behavioral sources, which are a standard component of circuit simulators. As an application example, the parameters of the model were fitted to emulate the behavior of an electrostatic MEMS loudspeaker whose finite-element (FEM) simulations and acoustic characterisation where already reported in the literature. The obtained waveforms show good agreement with the amplitude and distortion that was reported both in the transient FEM simulations and in the experimental measurements. This model is also used to predict the performance of this device as a microphone, coupling it to a two-stage charge amplifier. Additional complex behaviors can be introduced to this network model if it is required.

Simulation Study of FEUDT Structure Optimization and Sensitive Film Loading of SAW Devices.

In order to further improve the degree of frequency response of the surface acoustic wave (SAW) sensor for gas detection, the structure of the forked-finger transducer was analyzed, and its optimal structural parameters were simulated and designed. The simulation model of the unidirectional fork-finger transducer is established by using COMSOL finite element software. The thickness of the piezoelectric substrate, the electrode structure and material, and the thickness of the coating film are optimized and simulated. The results show that: the optimal thickness of the piezoelectric substrate is 3λ. The optimal thickness ratio and the lay-up ratio of the forked-finger electrode are 0.02 and 0.5, respectively. The Al electrode is more suitable as the a forked-finger electrode material compared to Cu, Au and Pt materials. Under the same conditions, the metal oxide-sensitive film (ZnO and TiO2) has a higher frequency response than the polymer-sensitive film (polyisobutylene and polystyrene), and the best sensitive film thickness range is 0.5~1 μm.

Simulation and Optimization of Ultrasonic Transducer

The ultrasonic transducers have numerous applications in industries, including medical probes for performing ultrasound scans. One of the significant drawbacks of the ultrasonic transducer is the wastage of a large portion of energy, due to high acoustic impedance, while transmitting ultrasonic waves to the target object. The present study is aimed to investigate the material design of the piezo-composite transducer and improve its performance. Different piezo-composite transducers were simulated in the COMSOL environment by varying input parameters, and three key performance indicators (KPI) were calculated. Many constraint-based multivariable optimization algorithms have been used to maximize the KPIs. A set of parameters, such as Sensitivity and Fractional Bandwidth, have been found to increase the performance of piezo-composite transducer model and its overall efficiency. This study is intended to impinge unidirectional property to the transducer which is found to be beneficial in more accurate medical as well as structural reports and cost savings.

Design and Development of a Solar Electric Delivery Pod

The ultrasonic transducers have numerous applications in industries, including medical probes for performing ultrasound scans. One of the significant drawbacks of the ultrasonic transducer is the wastage of a large portion of energy, due to high acoustic impedance, while transmitting ultrasonic waves to the target object. The present study is aimed to investigate the material design of the piezo-composite transducer and improve its performance. Different piezo-composite transducers were simulated in the COMSOL environment by varying input parameters, and three key performance indicators (KPI) were calculated. Many constraint-based multivariable optimization algorithms have been used to maximize the KPIs. A set of parameters, such as Sensitivity and Fractional Bandwidth, have been found to increase the performance of piezo-composite transducer model and its overall efficiency. This study is intended to impinge unidirectional property to the transducer which is found to be beneficial in more accurate medical as well as structural reports and cost savings.

A lumped parameter model of the longitudinal NiMnGa transducer based on piezomagnetic equations.

The NiMnGa alloy is a typical magnetic shape memory alloy with up to 6% immense strain, high energy density, and low effective elastic modulus. These comprehensive characteristics make it possible to realize a low-frequency underwater acoustic transducer. To describe the field-induced dynamic strain, an equivalent circuit model (ECM) of a longitudinal NiMnGa transducer is presented as a lumped parameter model, which couples magnetics, mechanics, and acoustics. In this paper, we focus on the piezomagnetic equations as the constitutive relationship of the NiMnGa element with a dynamic magnetic field. Furthermore, combined with the dynamic kinetic equation, the equivalent circuit is derived, and it has the advantage of containing acoustical terminals. The proposed model can predict the resonance frequency, effective stiffness, and input impedance of the NiMnGa transducer. Finally, a finite element model (FEM) is developed to verify the lumped parameter model. The results indicate that the spring's stiffness increases the resonance frequency, while the mass load is on the contrary, and they both agree well with the results of ECM. In addition, the FEM and ECM can also predict the dynamic responses, which provide a guideline for the design of longitudinal NiMnGa transducers.

Numerical modelling of ultrasonic guided waves for detection and characterization of debonds in FRP strengthened beams

Debonding failure in fibre reinforced polymer (FRP) strengthened structures is one of the most critical modes of failure. Timely detection of the debonds are vital for the safety of the structure. This study compares the three numerical models of ultrasonic guided wave generation in FRP strengthened concrete beam in an effort to detect and characterize debonds at the concrete-FRP interface. Numerical models of a carbon reinforced polymer (CFRP) strengthened beam with debonds of different sizes are prepared using commercially available finite element (FE) software ABAQUS®. The ultrasonic guided waves are introduced in the beam by the application of narrowband transient vertical and in-plane surface excitations representing contact type and surface bonded piezoelectric (PZT) transducers, respectively. A new model of angle beam transducer is also proposed, aiming to generate a particular guided wave mode in the CFRP strengthened beam. The wedge angle of the transducer is chosen in accordance with Snell’s law so that the desired mode is propagated in the beam. To prevent the reflections within the transducer, infinite elements are used for modelling the transducer boundary. Moreover, to minimise the computational cost, infinite elements are also used in the beam side faces. The models are validated by comparing the group velocity with the velocity obtained by the dispersion curve. Later, extensive parametric studies are conducted with the aim to relate the wave propagation characteristics to the debond sizes. It is found out that the amplitude of hilbert transform of the scattered wave increases with the increase in debond. size.

Loudspeaker virtualization–Part II: The inverse transducer model and the Direct-Inverse-Direct Chain

This manuscript, the second of a two-part series, shows how a discrete-time circuital model of loudspeakers, which is extensively analyzed in the first part, can be exploited to develop a method for loudspeaker virtualization. This method can be used to alter the behavior of a physical loudspeaker in such a way to match that of a target loudspeaker. Examples of applications include loudspeaker equalization or linearization. The method is characterized by a structure called Direct-Inverse-Direct Chain, which is composed of three blocks: a digital model of the target loudspeaker; a digital model of the inverse loudspeaker; and the physical loudspeaker. The inverse loudspeaker model is derived from the equivalent circuit of the direct system using a two-port element known in circuit theory as “nullor”. We show how this inverse model can be efficiently implemented in the discrete-time domain with no iterative solvers by exploiting Wave Digital Filter principles. The proposed virtualization algorithm is extensively tested both through simulations and applications to real loudspeakers. In particular, we show how the algorithm can reduce the distortion of the transducer output pressure signal, and how it can make a loudspeaker sound like a target loudspeaker with a desired nonlinear behavior.

Air-Borne Ultrasonic Transducers Based on Cross-Linked Polypropylene Ferro/Piezoelectrets

Air-borne ultrasonic transducers based on irradiated cross-linked polypropylene (IXPP) ferro/piezoelectret films, which exhibit a high longitudinal piezoelectric activity and a low acoustic impedance, were analyzed, fabricated, and measured in this work. Equivalent circuits and finite element models for IXPP film transducers were built to predict and confirm the transducer performances. Circular IXPP transducers which are 20 mm in diameter show a maximum radiated pressure of 3.2 Pa (104 dB) driven by 100 Vrms and a receiving sensitivity of 8 mV/Pa when resonance occurs at around 45 kHz, both at a distance of 60 cm, as confirmed by analytical and numerical models. Pulse-echo response of the transducers was obtained from theoretical calculation and simulation as well, indicating a −6 dB bandwidth of around 25% is achieved. Besides, the directivity patterns of IXPP film transducers at various frequencies were measured and analyzed. This work may introduce a novel material for flexible ultrasonic transducers with a demand of high sensitivity.

Ultrasonic guided wave estimation of minimum remaining wall thickness using Gaussian process regression

Ultrasonic Guided Waves (UGW) offer the possibility of inspecting a strip across a structure rather than just the point under a traditional bulk wave transducer. This can increase the rate of inspection and enable inspection under obstructions. This paper investigates the instantaneous phase characteristics of the shear horizontal guided waves for various defect depths and widths. The Gaussian process regression is then evaluated for estimating the minimum remaining wall thickness between a pair of transducers. A Gaussian process regression model is built using the fusion of large-scale simulated and low-scale real experimental data. For this purpose, a more precise model of an electromagnetic acoustic transducer is initially built by integrating both electromagnetic and elastic wave fields. Then the simulated data set is built after having been calibrated using a genetic algorithm. The examination of an unseen simulated evaluation data set shows that 96 % of data has an error during thickness gauging of less than 10 per cent of wall thickness. Finally, an experimental testing data set containing three different defects with depths of 3.7, 5.7 and 9.2 mm was examined, resulting in a good depth prediction of large defects with less than 1 mm error for defects wider than one wavelength.

Finite Element Modeling and Experimental Characterization of Piezoceramic Frequency Steerable Acoustic Transducers

This paper presents a novel implementation of Frequency Steerable Acoustic Transducers (FSATs) for guided waves (GWs) inspections. Unlike the conventional phased array systems, which demand a large number of transducers and complex wiring, FSATs benefit from inherent directional properties for generation and sensing ultrasonic guided waves, resulting in significant hardware simplification and cost reductions for GWs-based systems. The FSATs exploit the frequency-dependent spatial filtering effect, leading to a direct relationship between the direction of propagation and the frequency content of the transmitted signal. The proposed Piezoceramic FSAT is fabricated through patterning the spiral electrodes on a Piezoelectric (PZT) plate bonded on a supporting aluminum plate. In light of the need to investigate the influence of the generated stiffness caused by the PZT plate on the coupling behavior between the FSAT and the aluminum plate, Finite Element (FE) simulations were carried out. Furthermore, experimental validations were conducted using a Scanning Laser Doppler Vibrometer (SLDV) to highlight the directional capabilities of such devices. The results show that the generation of directional GWs in a host structure is substantially improved thanks to the high actuation strength of Piezoceramic materials employed in the proposed transducer.

Theory and shape optimization of acoustic driven triboelectric nanogenerators

As a clean, sustainable, and wildly distributing energy source, acoustic waves are rarely available for energy conversion because of their high entropy and low energy density. Although the triboelectric nanogenerator (TENG) has been utilized for efficient acoustic energy harvesting, and most works are focusing on the design and geometry structures of TENG devices towards specific applications, a theoretical framework and models of the complex energy conversion system are still limited. Here, a multi-physical field coupling model of an acoustic driven TENG is presented that establishes the theoretical guidelines and optimal strategies for a typical acoustic energy system. This coupling model is composed of a basic acoustic transducer model, a TENG model, and an external circuit model coupling the acoustic field, mechanical field, and the quasi-electrostatic field. Using the finite element method (FEM), the energy conversion process including acoustic vibrations, wave propagation, and transducer reception are simulated systematically which allow us to reveal the dynamic power output behaviors of the acoustic driven TENG. The built multi-physical model and comprehensive analysis in this work provides a new research frame and platform for the design, optimization, and application of the TENG acoustic energy harvesting system.

OPERATION FEATURES OF AN ULTRASONIC FLOW TRANSDUCER WITH A COMPLEX TRAJECTORY OF THE MEASURING PATH

To measure the flowrate of fuel and energy resources, different methods are used, which determine the range of measuring instruments. Instruments based on ultrasonic measurement methods are widely used in measurement practice due to the provision of high accuracy, a wide range of measured flowrates, the absence of additional pressure losses and the design simplicity. Such instruments are easily integrated into automated readout systems for collecting and transmitting information. The asymmetry of the measured medium flow is a significant problem in the use of single-channel ultrasonic meters. This issue is successfully solved by using multi-channel flow transducers.
 The disadvantages of multi-channel ultrasonic flow transducers include a significant complication of the hydraulic channel design, the need to use more complex mathematical algorithms for processing the obtained output signal. This requires the use of high performance electronic elements, first of all microprocessors.
 The use of a transducer with multiple reflection of one measuring beam from the wall of the measuring path acts as an alternative to multi-channel measurement.
 The aim of the work is to create a mathematical model of an ultrasonic flow transducer with a complex measuring path trajectory. For research, a scheme with sounding along three chords was chosen, which implements the time-pulse measurement method, it provides for determining the flow rate by the difference in the time of passage of the measuring path along the flow and against it. In this case, the projections of the chords on the cross section of the measuring section create an equilateral triangle. An analytical expression for the conversion response is obtained for the case of several beam reflections in different planes.
 The authors reproduced the hydraulic part of the investigated flow transducer using simulation modeling implemented on the basis of the finite element method. Transducer’s operation simulation in the range of measured flow rates in the conditions of an ideally formed profile of the gas flow velocity in the transducer inlet cross-section has been carried out. The results obtained confirmed the absence of influence of the measuring circuit elements (beam reflectors) on the flow profile and the measuring beam trajectory.

ASR - VLSP 2021: Automatic Speech Recognition with Blank Label Re-weighting

End-to-end models have significant potential in most languages and recently proved the robustness in ASR tasks. Many robust architectures are proposed, and among many techniques, Recurrent Neural Network - Transducer (RNN-T) shows remarkable success. However, with background noise or reverb in spontaneous speech, this architecture generally suffers from high deletion error problems. For this reason, we propose the blank label re-weighting technique to improve the state-of-the-art Conformer transducer model. Our proposed system adopts the Stochastic Weight Averaging approach, stabilizing the training process. Our work achieved the first rank with a 4.17% of word error rate in Task 2 of the VLSP 2021 Competition.

Synthesis of Computable Regular Functions of Infinite Words

Regular functions from infinite words to infinite words can be equivalently specified by MSO-transducers, streaming $\omega$-string transducers as well as deterministic two-way transducers with look-ahead. In their one-way restriction, the latter transducers define the class of rational functions. Even though regular functions are robustly characterised by several finite-state devices, even the subclass of rational functions may contain functions which are not computable (by a Turing machine with infinite input). This paper proposes a decision procedure for the following synthesis problem: given a regular function $f$ (equivalently specified by one of the aforementioned transducer model), is $f$ computable and if it is, synthesize a Turing machine computing it. For regular functions, we show that computability is equivalent to continuity, and therefore the problem boils down to deciding continuity. We establish a generic characterisation of continuity for functions preserving regular languages under inverse image (such as regular functions). We exploit this characterisation to show the decidability of continuity (and hence computability) of rational and regular functions. For rational functions, we show that this can be done in $\mathsf{NLogSpace}$ (it was already known to be in $\mathsf{PTime}$ by Prieur). In a similar fashion, we also effectively characterise uniform continuity of regular functions, and relate it to the notion of uniform computability, which offers stronger efficiency guarantees.

Lightweight Piezoelectric Bending Beam-Based Energy Harvester for Capturing Energy From Human Knee Motion

Harvesting energy from the human body has attracted substantial attention from industries and academics as it is a promising solution to address the battery life issue. In this article, we developed a bimorph piezoelectric bending beam-based energy harvester to scavenge energy from the human knee motion for powering body-worn electronics such as smartwatches and health monitors. During walking, the human knee will flex and extend to periodically deform piezoelectric macro fiber composites (MFC) bounded to the bending beam, thus generating electricity. The mathematical models of the whole system including the model of the large deflection of the bending beam, movement analysis of the end of the bending beam (slider-crank mechanism), the model of piezoelectric transducers, and measurement of the human knee angle are developed to comprehensively study the harvester. To validate the presented mathematical models, experimental testing on a human body when the subject walks on a treadmill at three different walking speeds is conducted here. The experimental results show good agreement with the simulation results, which indicates that the developed models can characterize the harvester. In addition, the performance of the harvester walking in different contexts is also evaluated. The average power can reach 12.79 mW for level-ground walking, 9.91 mW for stair descending, and 7.70 mW for stair ascending, when walking at a self-selected speed.

Transducer Design for Clamp-on Guided Wave Flow Measurement in Thin-Walled Pipes

Clamp-on ultrasonic transit time difference flow meters provide opportunities for metering where it is impractical or undesirable to cut into an existing pipeline to install an alternative flow meter. Up until now, it has been difficult to perform this type of measurement on thin-walled metal pipes, due to the difficulty of interpreting the guided wave modes in the combined pipe wall and internal fluid system, but a new method has been reported recently that utilises these guided wave modes for flow measurement. Through computational modelling, and construction and testing of different transducers, the design considerations for clamp-on transducers are highlighted and their impact on guided wave flow rate measurement is evaluated. The design features considered include a curved contact face to provide focusing of the ultrasound within the pipe and a scattering surface to reduce internal reflections. It is found that additional unwanted ultrasonic modes can be minimised by ultrasonic transducer wedge design features such as profiling the curvature of the transducer to conform to the pipe wall or creating a scattering edge to minimise internal wedge reflections. It is also observed that minimising these unwanted modes does not offer any advantage for the transit time difference measurement used in calculating flow.