Acoustic Separation Research Articles

A Novel Separation Technique of Flexural Loading-Induced Acoustic Emission Sources in Railway Prestressed Concrete Sleepers

This study determines the effectiveness and suitability of acoustic emission in order to monitor the structural health condition of railway pre-stressed concrete sleepers since the acoustic emission sensing provides effective means for detecting cracking events and quantifying the crack density. The aim of this study is two-fold. First, we establish a novel acoustic emission source separation that offers the possibility for analyzing the content of each source separately. This study is thus the first to demonstrate that these sources can be separated from each other by employing a classification algorithm based on decision trees. Hence, a technically sound decision can be made regarding the severity of the damage and appropriate measures can be taken. Second, the paper presents a new method for compressing the essential acoustic emission information of the loaded structure for further post-processing. Data compression of 70 % with respect to the full set of features is achieved through the elimination of those acoustic emission signatures that yield the largest mutual correlation with other signatures. The reduced set of acoustic emission signatures (only two uncorrelated features) still possesses the essential information of structural health of the structure of interest at a cost of a relatively small drop in classification accuracy from around 96% to 84%. The proposed method is validated experimentally on full-scale pre-stressed concrete sleepers under positive and negative bending moment configurations under static three-point bending tests, which correspond to anticipated failure modes at rail seats by industry.

Insights into agglomeration and separation of fly-ash particles in a sound wave field.

The efficiency of fine particle removal by using traditional devices is relatively low. Acoustic agglomeration is an effective pretreatment method that agglomerates particles before they enter a particulate control device so that they can be easily removed. The movements of particles exposed in a sound wave field were captured using a high-speed camera in this study. Agglomeration and separation of two particles were directly observed. Photographs were analyzed frame by frame to obtain motion information. A model was constructed, and COMSOL Multiphysics software was employed to simulate their relative motions. The simulation results matched the experimental results well. The conditions under which an aggregate consisting of two particles will be separated by a sound wave were calculated. The calculated results revealed that a non-breakable region exists: when sizes of primary particles are within this region, agglomerates will not be separated into smaller particles, but outside this region, agglomerates can be separated. The observation of particle motion deepens understanding of acoustic agglomeration and separation processes taking place in the agglomeration chamber. The calculation of separation of agglomerates can guide enhancement of acoustic agglomeration processes.

Acoustic emission signal source separation for a flank wear estimation of drilling tools

The knowledge of the tool wear condition is essential for the dimensional accuracy of the workpiece. Commonly used systems for wear monitoring are usually based on the piezoelectric force measurement. However, in industry these systems are difficult to integrate. A suitable to integrate sensor type is the acoustic emission (AE) sensor. In this paper the main focus will be on the flank wear of drilling tools. For the investigation of the emitted frequency of the flank wear different analogy experiments needs to be realized. With the help of machine learning algorithms the recorded data will be classified.

Acoustic Signal Separation and Noise Reduction of a Contra-Rotating Fan

How to reduce fan noise has always been a significant research topic in equipment ranging from small-scale devices, such as computer cooling fans and building ventilation fans, to large high bypass ratio turbo engines. In recent years, in order to produce higher pressure rise or larger flow rate with lower noise level in the fan stage, interest in the contra-rotating fan (CRF) configuration has been rekindled. The Vold-Kalman order tracking filter technique was employed to separate tonal and broadband noise components from CRF acoustic data to study the characteristics of the noise spectrum. Based on the spectrum peaks, noise reduction solution with casing treatment is proposed according to acoustic performance prediction by finite element simulation. In the simulation, the CRF is modelled at one end of a duct, which is surrounded by a semi-spherical space with perfect match layer to simulate the free field condition. The other end of the duct is modelled with non-reflecting boundary condition to simulate the anechoic termination. The simulated and experimental results show that casing treatment by micro-perforated panels can significantly reduce the CRF noise.

The Hyper-Angular Cube Concept for Improving the Spatial and Acoustic Resolution of MBES Backscatter Angular Response Analysis

This study presents a novel approach, based on high-dimensionality hydro-acoustic data, for improving the performance of angular response analysis (ARA) on multibeam backscatter data in terms of acoustic class separation and spatial resolution. This approach is based on the hyper-angular cube (HAC) data structure which offers the possibility to extract one angular response from each cell of the cube. The HAC consists of a finite number of backscatter layers, each representing backscatter values corresponding to single-incidence angle ensonifications. The construction of the HAC layers can be achieved either by interpolating dense soundings from highly overlapping multibeam echo-sounder (MBES) surveys (interpolated HAC, iHAC) or by producing several backscatter mosaics, each being normalized at a different incidence angle (synthetic HAC, sHAC). The latter approach can be applied to multibeam data with standard overlap, thus minimizing the cost for data acquisition. The sHAC is as efficient as the iHAC produced by actual soundings, providing distinct angular responses for each seafloor type. The HAC data structure increases acoustic class separability between different acoustic features. Moreover, the results of angular response analysis are applied on a fine spatial scale (cell dimensions) offering more detailed acoustic maps of the seafloor. Considering that angular information is expressed through high-dimensional backscatter layers, we further applied three machine learning algorithms (random forest, support vector machine, and artificial neural network) and one pattern recognition method (sum of absolute differences) for supervised classification of the HAC, using a limited amount of ground truth data (one sample per seafloor type). Results from supervised classification were compared with results from an unsupervised method for inter-comparison of the supervised algorithms. It was found that all algorithms (regarding both the iHAC and the sHAC) produced very similar results with good agreement (>0.5 kappa) with the unsupervised classification. Only the artificial neural network required the total amount of ground truth data for producing comparable results with the remaining algorithms.

Simulation and optimization of a sheathless size-based acoustic particle separator

Standing surface acoustic waves (SSAW) have been widely used for sorting of particles and cells. However, the challenge with the acoustic driven separation process is the need for an optimized setup to achieve effective separation and the range of particles that can be separated. In this study, we present out findings on a custom simulation model to investigate and optimize the separation of varying size particles in a sheathless acoustic separation platform that was developed in our research lab. Specifically, we investigate the effect of flowrate, pressure amplitude, wavelength and interdigitated transducers physical parameters on the separation efficiency. We also explored the critical particle size for acoustic particle separation with 3 µm particles and demonstrated, successful 3 µm and 6 µm particles for the first time for this sheathless separation platform. The ANSYS® FLUENT was used to numerically simulate acoustic radiation force on the particles for separation. With the increase in the pressure amplitude in the first and second stage to 80 kPa and 110 kPa respectively, the optimization studies presented have shown to improve the separation efficiency of the model over 96% for both 10 and 3 µm particles. Findings of the present study will aid in increasing the efficiency of particle separation and in designing the SSAW driven microfluidic devices.

Abstract A027: A novel two-step tumor cell isolation system, combining acoustophoresis and negative selection of white blood cells using CD45-conjugated elastomeric particles

Abstract Introduction: Circulating tumor cells (CTCs) are a promising tool for disease monitoring and for better-targeted therapies for patients with disseminating tumors. However, isolation of CTCs is challenging, due to their scarcity, heterogeneous size, and lack of universal expression markers. We employ a novel ultrasonic standing wave-based microfluidic technique (acoustophoresis) to enable unbiased, label-free isolation of circulating tumor cells (CTCs). The cell separation is based on intrinsic cell properties, such as size, morphology, density, and compressibility. During acoustophoresis cells/particles get positioned to nodes or antinodes depending on their acoustic contrast factor. The contrast factor depends on the density and compressibility ratios between the particles and the surrounding medium. Both cancer cells and subpopulations of white blood cells (WBCs) partly possess positive acoustic factors and are therefore positioned to pressure nodes during acoustophoresis. By employing negative contrast CD45-conjugated elastomeric particles (EPs) to capture the contaminating WBCs, a negative acoustic complex can be formed that positions the remaining WBCs to the antinodes. This cell separation technique is gentle towards the target cells and tunable to fit various situations, depending on whether throughput, cancer cell recovery, or purity is of major importance. Both paraformaldehyde (PFA) fixed cells and fresh blood can be processed through acoustophoresis. However, acoustophoretic cancer cell separation from fresh blood generates higher WBC contamination than processing of PFA fixed cells, due to overlapping acoustic properties. Therefore, an additional purification step is needed to remove excess contaminating WBCs. Hence, we have added an additional purging step after acoustophoresis, employing CD45-conjugated negative selection of WBCs using negative acoustic contrast EPs. Material and Methods: The acoustic separation device is a glass/silicon microchip connected to a pressure-driven system. For optimal separation performance, the system is temperature controlled and a prefocusing step is included before the main separation in the first cell separation step. The setup can process samples up to 10 mL, with a processing speed of 1 mL sample in 13 minutes without compromising the cell separation capacity. To evaluate the system performance, 1 mL model samples were processed, consisting of 10,000 DU145 prostate cancer cells spiked in 0.5 mL red blood cell (RBC) lysed blood from healthy donors. Results and Discussion: In the primary acoustic separation step, an average of 93% of the DU145 cancer cells were collected at the central outlet, whereas 7% were found in the side fraction. A 20-fold WBC depletion was achieved after the primary acoustophoresis-based tumor cell separation step. The central fraction output was subjected to a subsequent one-hour incubation with CD45-conjugated EPs in room temperature. The incubated samples were processed by acoustophoresis to negatively select EP/WBC complexes from cancer cells into separate outlet fractions, with subsequent flow cytometry analysis. Result showed a 98% cancer cell separation efficiency and a total 250-fold WBC depletion from the starting WBC concentration. Although the separation efficiency in the two steps was high, there was some cell loss in the total system, which needs to be further addressed. We propose a two-step acoustic-based microfluidic technology, consisting of an upstream primary label-free acoustophoretic separation of cancer cells from blood and a subsequent negative WBC depletion. This may lay the foundation for future analytical and clinical studies aimed to validate novel biomarkers for effective treatment management of cancer patients. Citation Format: Cecilia Magnusson, Eva Undvall, Thomas Laurell, Hans Lilja. A novel two-step tumor cell isolation system, combining acoustophoresis and negative selection of white blood cells using CD45-conjugated elastomeric particles [abstract]. In: Proceedings of the AACR Special Conference: Prostate Cancer: Advances in Basic, Translational, and Clinical Research; 2017 Dec 2-5; Orlando, Florida. Philadelphia (PA): AACR; Cancer Res 2018;78(16 Suppl):Abstract nr A027.

Circulating Tumor Cell Phenotyping via High-Throughput Acoustic Separation.

The study of circulating tumor cells (CTCs) offers pathways to develop new diagnostic and prognostic biomarkers that benefit cancer treatments. In order to fully exploit and interpret the information provided by CTCs, the development of a platform is reported that integrates acoustics and microfluidics to isolate rare CTCs from peripheral blood in high throughput while preserving their structural, biological, and functional integrity. Cancer cells are first isolated from leukocytes with a throughput of 7.5 mL h-1 , achieving a recovery rate of at least 86% while maintaining the cells' ability to proliferate. High-throughput acoustic separation enables statistical analysis of isolated CTCs from prostate cancer patients to be performed to determine their size distribution and phenotypic heterogeneity for a range of biomarkers, including the visualization of CTCs with a loss of expression for the prostate specific membrane antigen. The method also enables the isolation of even rarer, but clinically important, CTC clusters.

Size-amplified acoustofluidic separation of circulating tumor cells with removable microbeads

Isolation and analysis of rare circulating tumor cells (CTCs) is of great interest in cancer diagnosis, prognosis, and treatment efficacy evaluation. Acoustofluidic cell separation becomes an attractive method due to its contactless, noninvasive, simple, and versatile features. However, the indistinctive physical difference between CTCs and normal blood cells limits the purity of CTCs using current acoustic methods. Herein, we demonstrate a size-amplified acoustic separation and release of CTCs with removable microbeads. CTCs selectively bound to size-amplifiers (40 μm-diameter anti-EpCAM/gelatin-coated SiO2 microbeads) have significant physical differences (size and mechanics) compared to normal blood cells, resulting in an amplification of acoustic radiation force approximately a hundredfold over that of bare CTCs or normal blood cells. Therefore, CTCs can be efficiently sorted out with size-amplifiers in a traveling surface acoustic wave microfluidic device and released from size-amplifiers by enzymatic degradation for further purification or downstream analysis. We demonstrate a cell separation from blood samples with a total efficiency (Etotal) of ∼ 77%, purity (P) of ∼ 96%, and viability (V) of ∼83% after releasing cells from size-amplifiers. Our method substantially improves the emerging application of rare cell purification for translational medicine.

Time difference of arrival-based acoustic source localization and separation technique for sparse arrays

An acoustic source localization and separation technique intended for sparse arrays is suggested in this paper. Unlike conventional beamforming approaches, the proposed technique is based on time difference of arrival (TDOA) information. This effectively eliminates the spatial aliasing problem due to overly large inter-element spacing of sensors. This method begins with estimation of the TDOAs between at least 4 sensors for 3-dimensional sound fields, with the aid of the generalized crosscorrelation-phase transformation (GCC-PHAT) algorithm and the subspace-based time delay estimation algorithm. Next, a constrained least squares (CLS) algorithm is applied to locate the source based on the above-estimated TDOAs. Once the source location is found, the source signal is extracted by using the Tikhonov regularization (TIKR) algorithm and minimum variance distortionless response (MVDR) beamformer. Regularization parameter is selected with a special search procedure to best preserve the audio quality in the inverse solution process. Experiments and listening tests are undertaken to validate the proposed TDOA-based localization and separation technique.

Investigating the status of a rare cross-linguistic contrast: The case of Romanian palatalized postalveolars.

This study examines a rare cross-linguistic contrast, that between plain and secondarily palatalized postalveolar fricatives, through (i) an acoustic analysis of the production of 31 Romanian speakers, and (ii) a perception experiment with a different group of 31 native speakers. Evidence of acoustic separation between plain and palatalized forms was found for 27 of the subjects, suggesting that the contrast is produced by the majority. This is consistent with previous reports of native speakers collected in 1961. These findings were supported by the results of the perceptual experiment, which showed that native speakers exhibit moderate sensitivity to this contrast. An examination of each of the two genders' production separately suggests that a process of neutralization may be in progress, more strongly realized by males compared to females. Aside from documenting this phenomenon in Romanian, an explanation is sought for its longevity, and it is proposed that grammatical restructuring offers the best account for the observed facts.

Object-based attention modulates the discrimination of level increments in stop-consonant noise bursts.

This study tested the hypothesis that object-based attention modulates the discrimination of level increments in stop-consonant noise bursts. With consonant-vowel-consonant (CvC) words consisting of an ≈80-dB vowel (v), a pre-vocalic (Cv) and a post-vocalic (vC) stop-consonant noise burst (≈60-dB SPL), we measured discrimination thresholds (LDTs) for level increments (ΔL) in the noise bursts presented either in CvC context or in isolation. In the 2-interval 2-alternative forced-choice task, each observation interval presented a CvC word (e.g., /pæk/ /pæk/), and normal-hearing participants had to discern ΔL in the Cv or vC burst. Based on the linguistic word labels, the auditory events of each trial were perceived as two auditory objects (Cv-v-vC and Cv-v-vC) that group together the bursts and vowels, hindering selective attention to ΔL. To discern ΔL in Cv or vC, the events must be reorganized into three auditory objects: the to-be-attended pre-vocalic (Cv–Cv) or post-vocalic burst pair (vC–vC), and the to-be-ignored vowel pair (v–v). Our results suggest that instead of being automatic this reorganization requires training, in spite of using familiar CvC words. Relative to bursts in isolation, bursts in context always produced inferior ΔL discrimination accuracy (a context effect), which depended strongly on the acoustic separation between the bursts and the vowel, being much keener for the object apart from (post-vocalic) than for the object adjoining (pre-vocalic) the vowel (a temporal-position effect). Variability in CvC dimensions that did not alter the noise-burst perceptual grouping had minor effects on discrimination accuracy. In addition to being robust and persistent, these effects are relatively general, evincing in forced-choice tasks with one or two observation intervals, with or without variability in the temporal position of ΔL, and with either fixed or roving CvC standards. The results lend support to the hypothesis.

Purification of Lymphocytes by Acoustic Separation in Plastic Microchannels.

Emerging cell therapies have created new demands for instruments that will increase processing efficiency. Purification of lymphocytes prior to downstream steps of gene transfer currently relies on centrifugal separation, which has drawbacks in output sample purity and process automation. Here, we present an alternative approach to blood cell purification using acoustic forces in plastic microchannels. We provide details regarding the system's ability to purify lymphocytes relative to other blood cell types while maintaining a high overall recovery, testing performance starting from leukapheresis product, buffy coat, and whole blood. Depending on settings, the device achieves for lymphocytes up to 97% purity and up to 68% recovery, and depletes 98% of monocytes while also reducing red cells and platelets. We expect that future scale-up of our system for increased throughput will enable its incorporation in the cell therapy workflow, and that it could ultimately reduce costs and expand access for patients.

Acoustic separation in plastic microfluidics for rapid detection of bacteria in blood using engineered bacteriophage.

A more effective treatment of bacteremia requires a diagnostic platform that is both sensitive, accurate and rapid. Currently, clinical laboratory techniques require growth of bacteria prior to diagnosis, take days to complete, and leave empiric therapy and broad spectrum antibiotics as the only option at the onset of treatment. In order to bypass this growth requirement, we engineered a system that purifies bacteria from blood to improve performance in a bacteriophage-based luminescence assay. To perform the purification, we used acoustophoresis in plastic microfluidic chips, enabling future development into a low cost point-of-care system. Acoustophoresis achieves differential separation on the basis of size differences between bacteria and blood cells. We show isolation of three known pathogen species, including members of both Gram-negative and positive-bacteria from blood, and show isolation at clinically relevant concentrations. Using the device as a preparation step prior to the bacteriophage-based luminescence assay, we demonstrate a 33-fold improvement in limit of detection, compared with the unpurified sample, achieving a limit of detection of 6 bacteria.

Rapid and effective enrichment of mononuclear cells from blood using acoustophoresis

Effective separation methods for fractionating blood components are needed for numerous diagnostic and research applications. This paper presents the use of acoustophoresis, an ultrasound based microfluidic separation technology, for label-free, gentle and continuous separation of mononuclear cells (MNCs) from diluted whole blood. Red blood cells (RBCs) and MNCs behave similar in an acoustic standing wave field, compromising acoustic separation of MNC from RBC in standard buffer systems. However, by optimizing the buffer conditions and thereby changing the acoustophoretic mobility of the cells, we were able to enrich MNCs relative to RBCs by a factor of 2,800 with MNC recoveries up to 88%. The acoustophoretic microchip can perform cell separation at a processing rate of more than 1 × 105 cells/s, corresponding to 5 µl/min undiluted whole blood equivalent. Thus, acoustophoresis can be easily integrated with further down-stream applications such as flow cytometry, making it a superior alternative to existing MNC isolation techniques.

Acoustofluidic hematocrit determination

Hematocrit (HCT) measurements of blood from patients, blood donors and athletes are routinely performed on a daily basis. These measurements are often performed in centralized hospital labs by whole blood analyzers, which leads to long time-to-result. On site measurements, based on centrifugation can be done, but these assays require manual handling, are slow and can just measure HCT in contrast to the central lab whole blood analyzers. In this work, we present a microfluidic based method to measure HCT in blood samples by acoustic separation of whole blood into discrete regions of plasma and red blood cells. Comparison of the areas of the red blood cell and plasma regions gives an accurate HCT value, with a linear correlation to the centrifugation-based reference method. A readout can be performed within 2 s of acoustic actuation providing a readout accuracy of approximately 3% points (pp) HCT. Additional accuracy can be achieved by extending the acoustic actuation to 20 s, yielding an error of less than 1 pp HCT. This acoustic tool is optimal for integration into a lab-on-a-chip device with in-line measurements of different clinical parameters.

Design and simulation of a microfluidic device for acoustic cell separation

Experimental acoustic cell separation methods have been widely used to perform separation for different types of blood cells. However, numerical simulation of acoustic cell separation has not gained enough attention and needs further investigation since by using numerical methods, it is possible to optimize different parameters involved in the design of an acoustic device and calculate particle trajectories in a simple and low cost manner before spending time and effort for fabricating these devices. In this study, we present a comprehensive finite element-based simulation of acoustic separation of platelets, red blood cells and white blood cells, using standing surface acoustic waves (SSAWs). A microfluidic channel with three inlets, including the middle inlet for sheath flow and two symmetrical tilted angle inlets for the cells were used to drive the cells through the channel. Two interdigital transducers were also considered in this device and by implementing an alternating voltage to the transducers, an acoustic field was created which can exert the acoustic radiation force to the cells. Since this force is dependent to the size of the cells, the cells are pushed towards the midline of the channel with different path lines. Particle trajectories for different cells were obtained and compared with a theoretical equation. Two types of separations were observed as a result of varying the amplitude of the acoustic field. In the first mode of separation, white blood cells were sorted out through the middle outlet and in the second mode of separation, platelets were sorted out through the side outlets. Depending on the clinical needs and by using the studied microfluidic device, each of these modes can be applied to separate the desired cells.

Particle separation by phase modulated surface acoustic waves.

High efficiency isolation of cells or particles from a heterogeneous mixture is a critical processing step in lab-on-a-chip devices. Acoustic techniques offer contactless and label-free manipulation, preserve viability of biological cells, and provide versatility as the applied electrical signal can be adapted to various scenarios. Conventional acoustic separation methods use time-of-flight and achieve separation up to distances of quarter wavelength with limited separation power due to slow gradients in the force. The method proposed here allows separation by half of the wavelength and can be extended by repeating the modulation pattern and can ensure maximum force acting on the particles. In this work, we propose an optimised phase modulation scheme for particle separation in a surface acoustic wave microfluidic device. An expression for the acoustic radiation force arising from the interaction between acoustic waves in the fluid was derived. We demonstrated, for the first time, that the expression of the acoustic radiation force differs in surface acoustic wave and bulk devices, due to the presence of a geometric scaling factor. Two phase modulation schemes are investigated theoretically and experimentally. Theoretical findings were experimentally validated for different mixtures of polystyrene particles confirming that the method offers high selectivity. A Monte-Carlo simulation enabled us to assess performance in real situations, including the effects of particle size variation and non-uniform acoustic field on sorting efficiency and purity, validating the ability to separate particles with high purity and high resolution.

Separation of Traveling and Standing Waves in a Rigid-Walled Circular Duct Containing an Intermediate Impedance Discontinuity

In this paper, we study the phenomenon of separation of traveling and standing waves in a one-dimensional rigid-walled circular duct. The underlying mechanism for separation, mode complexity, is linear and introduced here by a damped side branch representing an impedance discontinuity. The left end of the duct is driven at a single frequency by a harmonic acoustic source, and the right end is a rigid termination. The position and impedance of the side branch are independent parameters in the analysis. Sufficient conditions for acoustic wave separation in the duct are derived analytically and employed in a three-dimensional finite element analysis to verify the theoretical result. A physical experiment, consisting of a circular duct with a damped side branch, was constructed based on analytical predictions, the physical parameters were measured or identified, and its performance was documented. These experimental parameters were employed in a second three-dimensional finite element analysis to obtain a direct comparison with experimental results. The comparison reveals the extent to which higher-order (unmodeled) effects degrade the separation phenomenon. It is demonstrated that an intermediate damped side branch used as a nonresonant device can be predictively designed to achieve nearly ideal separation of traveling and standing waves in a rigid-walled circular duct in order to direct and control acoustic energy transmission through the duct system.

Wastewater treatment with acoustic separator

Acoustic separation is a filter-free wastewater treatment method based on the forces generated in ultrasonic standing waves. In this report, a batch-system separator based on acoustic separation was demonstrated using a small-scale prototype acoustic separator to remove suspended solids from oil sand process-affected water (OSPW). By applying an acoustic separator to the batch use OSPW treatment, the required settling time, which was the time that the chemical oxygen demand (COD) decreased to the environmental criterion (<200 mg/L), could be shortened from 10 to 1 min. Moreover, for a 10 min settling time, the acoustic separator could reduce the FeCl3 dose as coagulant in OSPW treatment from 500 to 160 mg/L.