Single Transducer Research Articles

Knock Recognition System in a PCCI Engine Powered by Diesel

The measurement of engine vibrations components is used to identify combustion phases in a single-cylinder PCCI diesel engine in this work. A single channel Knock transducer was used to measure engine vibration caused by combustion pressure forces and knocking tendency. The transducer is used to obtain the engine's frequency spectrum in the temporal domain. Categorization discrete wavelet analysis is used to isolate the observed vibration data. Spectral analysis and filtration of fragmented sections of the source signal are used in this approach. Fast Fourier transforms (FFT) and short-time Fourier transform (STFT) are used to investigating the discrete parts of the observed signals (STFT). In order to study engine events, time is given in milliseconds in the time-frequency domain. The engine knocking is determined from the observed signal using time-frequency analysis. The outcomes reveal that the engine events derived from vibration signals are closely connected to the premixing fuel ratio, as expected.

Detection of Hand Poses with a Single-Channel Optical Fiber Force Myography Sensor: A Proof-of-Concept Study

Force myography (FMG) detects hand gestures based on muscular contractions, featuring as an alternative to surface electromyography. However, typical FMG systems rely on spatially-distributed arrays of force-sensing resistors to resolve ambiguities. The aim of this proof-of-concept study is to develop a method for identifying hand poses from the static and dynamic components of FMG waveforms based on a compact, single-channel optical fiber sensor. As the user performs a gesture, a micro-bending transducer positioned on the belly of the forearm muscles registers the dynamic optical signals resulting from the exerted forces. A Raspberry Pi 3 minicomputer performs data acquisition and processing. Then, convolutional neural networks correlate the FMG waveforms with the target postures, yielding a classification accuracy of (93.98 ± 1.54)% for eight postures, based on the interrogation of a single fiber transducer.

The use of circumferential guided waves to monitor axial cracks in pipes

Guided wave testing is in routine use to detect corrosion, particularly in the oil and gas sector, but the detection of axial cracking is difficult using the axially propagating waves commonly used for corrosion detection. This paper presents a novel guided wave monitoring technique for the detection of axial cracking in piping. Circumferential SH0 waves, travelling around the circumference were used in a monitoring configuration to detect axial defects in a 6 inch schedule 80 steel pipe. Finite Element (FE) analysis showed that both the defect reflection and the decline in the transmitted SH0 wave can be used for defect detection. Baseline subtraction was utilised to produce residual signals that can be better analysed for small defect reflections. The Root-Mean-Square (RMS) of the residual signal after baseline subtraction was found to be the most satisfactory means of monitoring defect progression. An amplification effect was identified where the residual signal is compounded by continued interaction with the defect on each revolution of the incident wave. The FE predictions were validated by an experiment in which an Electrical Discharge Machining (EDM) notch was grown in four stages. Temperature compensation using Location Specific Temperature Compensation (LSTC) was applied to the experimental data, allowing residuals to be compared for a ∼10 °C temperature swing over a monitoring period of over 2 months. It was determined that a 10 mm long (∼23% of wavelength), 5 mm deep (∼45% of the wall thickness) defect at an axial offset from the line of the transducers of 1.5 wavelengths (65 mm) would be readily detectable with a very high Probability of Detection (POD) and virtually no chance of a false call. Therefore, this novel guided wave monitoring system for axial crack detection is likely to be attractive for applications in a range of industries for its sensitivity to axial cracking combined with large coverage from a single transducer location.

A metasurface radar for steering ultrasonic guided waves

This article presents a new metasurface made of shape memory alloy (SMA) unit cells for steering ultrasonic guided waves in desired emitting directions. The philosophy behind the controllable wave steering performance of the metamaterial system resides in the tunability of its stopband. Such a tunable feature originates from the reversible dramatic variation of the elastic modulus of the shape memory element under the thermal loads. The research starts with the investigation of the adjustable bandgap behavior of the metastructure at different statuses from the scrutiny of the wave dispersive characteristics. Additionally, a systematic parametric study is carried out to unfold the bandgap evolution principle by changing the SMA stub height. Subsequently, numerical modeling of the wave steering behavior is performed by shifting the stopband of one sector within the unit-cell-ring away from the excitation frequency. The wavefield images associated with the wave directionality plots demonstrate that the thermally-activated metasurface area can open up a transmission path for the ultrasonic waves, while the rest portion will not allow guided waves to penetrate. By rotating the designated sector, the metamaterial structure could work like a wave emission radar, realizing the steerable unidirectional wave radiation from a single piezoelectric transducer. In the end, the targeting phenomena are validated by the Scanning Laser Doppler Vibrometry (SLDV) experimental tests. The proposed active metasurface system with the controllable ultrasonic wave interrogating capability may find its application for directional guided wavefield generation in future Structural Health Monitoring (SHM) and Nondestructive Evaluation (NDE) systems.

Maximum Likelihood Identification of Cavitation Instabilities in Axial Inducers

Abstract The article illustrates the results of an exploratory study on the effectiveness of maximum likelihood Bayesian estimation in the identification of cavitation instabilities in axial inducers using the blade-to-blade pressure measured by a single transducer flush-mounted on the impeller casing. The typical azimuthal distribution of the pressure in the blade channels is parameterized and modulated in space and time for theoretically reproducing the expected pressure generated by known forms of cavitation instabilities (cavitation surge auto-oscillations, n-lobed synchronous/asynchronous rotating cavitation, and higher-order surge/rotating cavitation modes). The power spectra of the theoretical pressure so obtained in the rotating frame are transformed in the stationary frame, corrected for frequency broadening effects, and parametrically fitted by maximum likelihood estimation to the measurements of the pressure on the inducer casing just downstream of the blade leading edges. In addition to its fundamental frequency, each form of instability generates a characteristic spectral distribution of sidebands. The identification uses this information for successfully discriminating flow oscillation modes occurring simultaneously with intensities differing by up to one order of magnitude. The method returns the estimates of the model parameters and their standard errors, allowing one to assess the accuracy and statistical significance of the identification. The results first demonstrate that elementary maximum likelihood Bayesian identification is indeed capable to effectively detect and characterize the occurrence of flow instabilities in cavitating inducers at a fraction of the experimental and postprocessing costs and complexities of traditional cross-correlation methods.

Ultrasonic inspection of near surface defects with additive manufactured metasurface lens

Acoustic metasurfaces have been increasingly explored in the past 10 years because of their compact structure and wave manipulation capabilities. In this work, we explore the feasibility of using an acoustic metasurface lens (MSL) for the characterization of near surface defects in NDT. First, we delimited the design space for a MSL operating at 100 kHz, in terms of spatial footprint and materials, and then realized a library of labyrinthine cells optimized for transmission. Then, we assembled the unit cells into lens and simulated its performance in a hole inspection process. The time-domain simulations predicted an increase in scattering and interface effects but, thanks to the focusing behavior, they also showed a much lower drop in the peak amplitude (20%, compared to 70% without MSL). Finally, we validated the simulations using a UTR9000-based MSL on an acrylic sample. Experiments with the MSL showed a converging energy profile, reduced to half of its width without the lens, and the presence of additional transmission peaks allowed to determine the defect diameter with excellent precision, thus circumventing near surface interference. Our study may be the first step towards flexible beam control systems based on a single transducer.

Comparison of Phase-Screen and Geometry-Based Phase Aberration Correction Techniques for Real-Time Transcranial Ultrasound Imaging

While transcranial ultrasound imaging is a promising diagnostic modality, it is still hindered due to phase aberration and multiple scattering caused by the skull. In this paper, we compare near-field phase-screen modeling (PS) to a geometry-based phase aberration correction technique (GB) when an ultrafast imaging sequence (five plane waves tilted from −15 to +15 degrees in the cutaneous tissue layer) is used for data acquisition. With simulation data, the aberration profile (AP) of two aberrator models (flat and realistic temporal bone) was estimated in five isoplanatic patches, while the wave-speed of the brain tissue surrounding the point targets was either modeled homogeneously (ideal) or slightly heterogeneously to generate speckle (for mimicking a more realistic brain tissue). For the experiment, a phased array P4-1 transducer was used to image a wire phantom; a 4.2-mm-thick bone-mimicking plate was placed in front of the probe. The AP of the plate was estimated in three isoplanatic patches. The numerical results indicate that, while all the scatterers are detectable in the image reconstructed by the GB method, many scatterers are not detected with the PS method when the dataset used for AP estimation is generated with a realistic bone model and heterogeneous brain tissue. The experimental results show that the GB method increases the signal-to-clutter ratio (SCR) by 7.5 dB and 6.5 dB compared to the PS and conventional reconstruction methods, respectively. The GB method reduces the axial/lateral localization error by 1.97/0.66 mm and 2.08/0.7 mm compared to the PS method and conventional reconstruction, respectively. The lateral spatial resolution (full-width-half-maximum) is also improved by 0.1 mm and 1.06 mm compared to the PS method and conventional reconstruction, respectively. Our comparison study suggests that GB aberration correction outperforms the PS method when an ultrafast multi-angle plane wave sequence is used for transcranial imaging with a single transducer.

Shunts vs networks: tuning and comparison of centralized and decentralized piezoelectric vibration absorbers

This work develops a unified modeling framework for piezoelectric structures controlled by passive shunts connected to a single transducer and/or networks interconnecting multiple transducers. A common tuning procedure for these different control approaches, termed decentralized and centralized approaches, respectively, is proposed. The generic model is then used to compare them in terms of vibration mitigation performance. It is shown that decentralization can be detrimental to performance in general. Digital vibration absorbers are then leveraged to realize the shunts and/or networks. In this regard, the proposed tuning procedure solely relies on characteristics that can be identified from the digital units of these absorbers. The theoretical developments are numerically and experimentally validated on piezoelectric beams.

Preclinical robotic device for magnetic resonance imaging guided focussed ultrasound.

A robotic device featuring three motion axes was manufactured for preclinical research on focussed ultrasound (FUS). The device comprises a 2.75MHz single element ultrasonic transducer and is guided by Magnetic Resonance Imaging (MRI). The compatibility of the device with the MRI was evaluated by estimating the influence on the signal-to-noise ratio (SNR). The efficacy of the transducer in generating ablative temperatures was evaluated in phantoms and excised porcine tissue. System's activation in the MRI scanner reduced the SNR to an acceptable level without compromising the image quality. The transducer demonstrated efficient heating ability as proved by MR thermometry. Discrete and overlapping thermal lesions were inflicted in excised tissue. The FUS system was proven effective for FUS thermal applications in the MRI setting. It can thus be used for multiple preclinical applications of the emerging MRI-guided FUS technology. The device can be scaled-up for human use with minor modifications.

Programmable Droplet Microfluidics Based on Machine Learning and Acoustic Manipulation.

Typical microfluidic devices are application-specific and have to be carefully designed to implement the necessary functionalities for the targeted application. Programmable microfluidic chips try to overcome this by offering reconfigurable functionalities, allowing the same chip to be used in multiple different applications. In this work, we demonstrate a programmable microfluidic chip for the two-dimensional manipulation of droplets, based on ultrasonic bulk acoustic waves and a closed-loop machine-learning-based control algorithm. The algorithm has no prior knowledge of the acoustic fields but learns to control the droplets on the fly. The manipulation is based on switching the frequency of a single ultrasonic transducer. Using this method, we demonstrate 2D transportation and merging of water droplets in oil and oil droplets in water, and we performed the chemistry that underlies the basis of a colorimetric glucose assay. We show that we can manipulate drops with volumes ranging from ∼200 pL up to ∼30 nL with our setup. We also demonstrate that our method is robust, by changing the system parameters and showing that the machine learning algorithm can still complete the manipulation tasks. In short, our method uses ultrasonics to flexibly manipulate droplets, enabling programmable droplet microfluidic devices.

Modelling and characterisation ultrasonic phased array transducers for pipe inspections

Nuclear pipes require regular inspection to prevent critical damage and extend their safe working lifetime. Ultrasonic inspection using phased array transducers is a Non-Destructive Testing (NDT) method used to monitor the condition of pipes, providing internal integrity information using multiple small transducer elements. This grants a controllable ultrasonic beam that provides more detail than a conventional single element transducer. This paper presents a hybrid simulation model to characterise phased array ultrasonic transducers for pressure pipe inspections. The paper focuses on identifying defects on pipe surfaces, which have total propagation path lengths in the order of 170 ultrasound wavelengths. Simulating inspections with such large path lengths is challenging due to unreliable results from numerical dispersion errors in large finite element models. The model presented here combines the benefits of finite element modelling with analytical extrapolation to overcome the issue of large propagation distances. A practical experiment demonstrates and verifies that the hybrid simulation model matches real world inspections. Inspection accuracy was quantified using the hybrid simulation model over frequency (5, 7.5 and 10 MHz) and number of elements (8, 16 and 32) to inspect two defect shapes (rectangular and V-shape). The 10 MHz transducer showed the highest resolution for the depth measurement, while the 5 MHz transducer presented the strongest penetration to inspect the defects on the pipe's outer surface. The largest aperture transducer, 32 elements, brought about the most accurate defect size measurement. This work serves to inexpensively guide the selection and later deployment of phased array inspection tools in nuclear pipe defect detection and monitoring.

압전 단결정을 이용한 고감도 광대역 링 트랜스듀서의 수중 음향특성 분석

In this study, the design and underwater acoustic characteristics of a ring transducer composed of a piezoelectric single crystal as the active material was reported. The PIN-PMN-PT piezoelectric single crystals with improved thermal durability have superior piezoelectric performance compared to PZT-4, widely used in underwater acoustic sensors. A 33-mode ring transducer was designed and its acoustic characteristics were estimated through electro-mechanical-acoustic coupled analysis. Furthermore, the acoustic characteristics of the ring transducers, composed of piezoelectric single crystals or PZT-4, were compared. The piezoelectric single crystals ring transducer is expected to have a higher transmitting voltage response (TVR) and receiving voltage sensitivity (RVS) compared to the PZT-4 ring transducer due to a high electro-mechanical coupling coefficient. It is also expected to have wideband performance due to a low mechanical quality factor. The acoustic characteristics of the fabricated piezoelectric single crystals ring transducer were measured and analyzed with the results of the electro-mechanical-acoustic coupled analysis. Upon applying piezoelectric single crystals as active materials, the ring transducer provided high sensitivity and broadband performance.

Robotic device for transcranial focussed ultrasound applications in small animal models.

Focussed Ultrasound (FUS) combined with microbubbles (MBs) was proven a promising modality for non-invasive blood brain barrier disruption (BBBD). Herein, two devices for FUS-mediated BBBD in rodents are presented. A two-axes robotic device was manufactured for navigating a single element FUS transducer of 1MHz relative to the brain of rodents. A second more compact device featuring a single motorized vertical axis was also developed. Their performance was assessed in terms of motion accuracy, MRI compatibility and trans-skull BBBD in wild type mice using MBs in synergy with pulsed FUS. Successful BBBD was evidenced by the Evans Blue dye method, as well as by Fibronectin and Fibrinogen immunostaining. BBB permeability was enhanced when the applied acoustic intensity was increased. The proposed devices constitute a cost-effective and ergonomic solution for FUS-mediated BBBD in small animal models. Further experimentation is needed to examine the repeatability of results and optimise the therapeutic protocol.

Nb and Mn Co-Modified Na0.5Bi4.5Ti4O15 Bismuth-Layered Ceramics for High-Frequency Transducer Applications.

Lead-free environmentally friendly piezoelectrical materials with enhanced piezoelectric properties are of great significance for high-resolution ultrasound imaging applications. In this paper, Na0.5Bi4.5Ti3.86Mn0.06Nb0.08O15+y (NBT-Nb-Mn) bismuth-layer-structured ceramics were prepared by solid-phase synthesis. The crystallographic structure, micromorphology, and piezoelectrical and electromechanical properties of NBT-Nb-Mn ceramics were examined, showing their enhanced piezoelectricity (d33 = 33 pC/N) and relatively high electromechanical coupling coefficient (kt = 0.4). The purpose of this article is to describe the development of single element ultrasonic transducers based on these piezoelectric ceramics. The as-prepared high-frequency tightly focused transducer (ƒ-number = 1.13) had an electromechanical coupling coefficient of 0.48. The center frequency was determined to be 37.4 MHz and the −6 dB bandwidth to be 47.2%. According to the B-mode imaging experiment of 25 μm tungsten wires, lateral resolution of the transducer was calculated as 56 μm. Additionally, the experimental results were highly correlated to the results simulated by COMSOL software. By scanning a coin, the imaging effect of the transducer was further evaluated, demonstrating the application advantages of the prepared transducer in the field of high-sensitivity ultrasound imaging.

Performance enhancement of ultrasonic transducer made of textured PNN-PZT ceramic

In this paper, 0.36Pb(Ni[Formula: see text]Nb[Formula: see text])O3–0.24PbZrO3–0.40PbTiO3(PNN-PZT) ceramic was prepared, and texture engineering was performed on this PNN-PZT ceramic to improve its electromechanical properties and temperature stability. Single element ultrasonic transducers were prepared using PNN-PZT, PNN-PZT textured ceramics, and their performance were evaluated and compared using a PZT-5H ceramic based transducer as the benchmark. It is shown that the sensitivity and bandwidth of the PNN-PZT textured ceramic-based transducer are much superior to regular PNN-PZT ceramic and PZT-5H ceramic based transducers.

QS2. High Frequency Spectral Ultrasound Imaging Detects Early Post Traumatic Muscle Fibrosis in Rodents

Purpose: Muscle fibrosis is a devastating condition that can occur following traumatic injury leading to loss of function and poor outcomes. Limited noninvasive modalities exist to diagnose and characterize the extent of muscle damage. Here we investigate spectral ultrasound imaging (SUSI), a quantitative imaging technique which detects tissue parameters based on intrinsic structure and composition, to identify early muscle fibrosis based on fibrotic changes established in a rat model. We hypothesize that SUSI will detect early traumatic muscle fibrosis in a clinically translational rat muscle injury model. Methods: Adult male Sprague Dawley rats were sedated, prepped, and underwent a soft tissue crush injury that generated 20lbs/in2 of pressure using a digital force gauge. A superficial 1.5 cm incisional wound was then made over the quadriceps and closed. Injured and contralateral uninjured hind limbs were collected and fixed for SUSI imaging. Imaging was performed with a VisualSonics VEVO770 high resolution small animal ultrasound imaging system, using a 30 MHz center frequency single element transducer. Injured muscles were imaged at the crush injury and the corresponding place on the contralateral limb. Analysis of radiofrequency data was done as previously described in literature and SUSI parameters were calculated using the average acoustic concentration (AAC) of the fibrotic region and the corresponding region in the contralateral muscle. AAC values were grouped by time point and tissue type for statistical comparison using unpaired t tests. Results: In our rodent model, SUSI identified muscle fibrosis as early as 7 days post injury. The average AAC of injured fibrotic versus uninjured muscle was significantly increased at post injury day 7 (36.33 vs 18.36 db/mm3, injured versus uninjured, p = 0.003) and day 28 (54.64 vs 28.29 db/mm3, injured versus uninjured, p<0.0001). Though not statistically significant at day 14 (38.69 vs 27.61 db/mm3, injured vs uninjured, p=0.14) the fibrotic muscle did trend toward a higher AAC value. These results indicate that at day 7 and 28, the SUSI measurement AAC can be used to distinguish injured fibrotic muscle from uninjured muscle. Conclusions: SUSI offers a portable, non-invasive, and safe diagnostic modality to detect muscle fibrosis, making it an ideal modality for post traumatic injuries. Here, we show SUSI distinguishes muscle fibrosis from healthy tissue at day 7 and 28 post injury in our model allowing for early treatment. Unlike qualitative grayscale imaging, SUSI determines unique parameters of the tissue based on a calibrated spectrum related to the inherent properties of the tissue, making it less user-dependent and more reproducible.

Underwater single crystal piezocomposite transducer with extended usable frequency band

A single crystal/epoxy 1–3 composite plate transducer with air backing and two acoustic matching layers was modelled, fabricated and compared to a similar PZT transducer. For the relevant underwater applications, the usable frequency band is restricted by reactive electrical power. The design goal was to provide an underwater transmitter that could be operated over a wide range of frequencies, but not necessarily create a single pulse spanning the entire frequency band. The thicknesses and the characteristic acoustic impedances of the matching layers were therefore optimized for a wide passband rather than a maximally flat passband. The resulting single crystal transducer had reactive power below 50 % in a frequency band 132 % wide relative to the center frequency.

Scattering-coded architectured boundary for computational sensing of elastic waves

Object localization through active elastic waves is a crucial technology but generally requires a transducer array with complex hardware. Although computational sensing can overcome the shortcomings of transducer array by merging artificially designed structures into the sensing process, coding spatial elastic waves for active object sensing is still a knowledge gap. Here, we propose a scattering-coded architectured boundary composed of randomly distributed scatterers for computational sensing of objects with a single transducer. The multiple scattering effects of the architectured boundary introduce complexity into scattered fields to achieve a highly uncorrelated scattering coding of Lamb waves, thereby eliminating the ambiguity of the object location information. We demonstrate that the object locations can be uniquely identified by using the scattering-coded architectured boundary. The proposed strategy opens avenues for artificially designed boundaries with the capability of information coding and identification, providing important applications in wave sensing such as human-machine interactions and structural monitoring. • An architectured boundary is proposed for object localization with a single transducer • Complex disturbances caused by multiple scattering enable spatial scattering coding • Object locations are identified by using a computational sensing algorithm • A type of touchscreen with an architectured boundary is designed for interactive input Jiang et al. propose a scattering-coded architectured boundary composed of randomly distributed scatterers for computational sensing of objects with a single transducer. This strategy provides avenues for artificially designed boundaries with the capability of information coding, boosting wave-sensing applications such as structural monitoring and human-machine interactions.

A Multiple-Echo Calibration Technique for Guided Wave Testing

Guided wave testing has become an established technology for screening long lengths of pipe for safety-critical defects from a single transducer position. The location of any defect is accurately determined and a rough idea of defect severity is obtained. However, it would be very beneficial to obtain a more accurate severity estimate from the guided wave data, especially in cases where follow-up inspection is expensive. This requires a more reliable calibration technique than the conventional approach, which relies on assumptions about the amplitudes of weld reflections. A multiple-echo calibration technique using data collected with standard test protocols but processed to extract the amplitude of reverberations between two features on either side of the sensor ring is presented, which removes the need for assumptions about the weld reflection amplitudes that reduce the accuracy of the conventional method of calibration. This novel technique is less dependent on operator judgement, and field examples presented show that it gives more accurate measures of cross-section loss than the conventional calibration technique. The improvement is particularly marked in cases where the weld geometry is not known or is nonuniform.

The Imaging Performance of Preclinical Ultrasound Scanners Using the Edinburgh Pipe Phantom

The greyscale imaging performance of a total of 17 preclinical transducer/scanner combinations were measured over a period of 10 years. These comprised nine single element transducers and eight array transducers with nominal central frequencies ranging between 15 and 55 MHz, and were from four commercially-available preclinical ultrasound scanners. Performance was assessed using a single figure of merit, the resolution integral, using measurements acquired from images of a test-object, the Edinburgh Pipe Phantom. Two further parameters were derived from the resolution integral: characteristic resolution and depth-of-field. Our results demonstrate that 1) resolution integral values of the array transducers were greater than single-element transducers, and 2) the array transducers demonstrated greater depths of field than the single-element transducers of the same nominal frequency. Moreover we demonstrate that use of this single figure-of-merit enabled identification and quantification of changes in imaging performance of preclinical transducers over a 10-years period.