Flat Transducer Research Articles

On the thermal characteristic of a heating flat surface under low frequency ultrasonic waves

This study investigates the heat transfer capability between the near-wall water and a heating flat surface under the low frequency ultrasonic waves. The experiment was conducted at the main stream velocities of 0.12, 0.14, and 0.17 m/s, corresponding with the local Reynolds number between 60,000 and 200,000. The ultrasound, having a frequency of 25, 33, and 40 kHz was released from a 60 W flat transducer in a downward direction to disturb a near-wall flow over the flat surface having a constant heat flux of 1875 W/m2. The temperature decrease due to the disturbance of ultrasound, detected by 7 thin-leaf thermocouples, led to the increase in the Nusselt number by up to 10%, 16.5%, and 20.8%, at the wave frequency of 25, 33, and 40 kHz, respectively. The use of the thermochromic liquid crystals on the heating surface, disturbed by the 40 kHz wave, revealed that the bound of the wave incident region was shaped like a spiky structure that alternately occurs following with time. This incident region moved further downstream when the mainstream velocity increased and caused a retardation of the near wall flow, leading to a worse heat transfer in the upstream region. Therefore, the inclination of the acoustic beam, occurring as a variation of mainstream velocity, must be considered in order to use the ultrasound to enhance the heat transfer. Finally, the predictive formulas for the local Nusselt number under the 25–40 kHz waves are also provided and the mechanism of heat transfer is discussed.

Development of Fuel Debris Inspection Methods using Air-Coupled Ultrasound

Japan has decided to start fuel debris removal on 2021. Therefore, before starting retrieval of the fuel debris, investigation of location, shape, and also properties of fuel debris have to be performed. In this study, air-coupled ultrasound technique had been developed in order to visualize of fuel debris. Firstly, simulated fuel debris was represented by stone and experiment was done in laboratory scale. Flat and focused air-coupled ultrasound were used as a sensor to get echo signals of the target surface. Results showed that both flat and focused sensor successfully reconstructed the flat surface image in good spatial resolution. However, flat air-coupled transducer shown unstructured. On the other hand, focused air-coupled ultrasound shown good performance when target surface was unstructured. Therefore, it was recommended to used focused sensor when target surface was unstructured like simulated fuel debris.

PMN-PT Single Crystal Ultrasonic Transducer With Half-Concave Geometric Design for IVUS Imaging.

As the key component of intravascular ultrasound (IVUS) imaging systems, traditional commercial side-looking IVUS transducers are flat and unfocused, which limits their lateral resolution. We propose a PMN-PT single crystal IVUS transducer with a half-concave geometry. This unique configuration makes it possible to conduct geometric focusing at a desired depth. To compare performances, the proposed and the traditional flat transducer with similar dimensions were fabricated. We determined that the half-concave transducer has a slightly higher center frequency (35MHz), significantly broader -6dB bandwidth (54%) but a higher insertion loss (-22.4dB) compared to the flat transducer (32MHz, 28%, and -19.3dB, respectively). A significant enhancement of the lateral resolution was also confirmed. The experimental results are in agreement with the finite element simulation results. This preliminary investigation suggests that the half-concave geometry design is a promising approach in the development of focused IVUS transducers with broad bandwidth and high lateral resolution.

Frequency domain synthetic aperture focusing technique for variable-diameter cylindrical components.

Ultrasonic non-destructive testing (UNDT) plays an important role in ensuring the quality of cylindrical components of equipment such as pipes and axles. As the acoustic beam width widens along propagation depths, the diffraction of acoustic wave becomes serious and the images of defects will be interfered with. To precisely evaluate the dimensions of defects and flaws concealed in components, the synthetic aperture focusing technique (SAFT) is introduced to enhance the image resolutions. Conventional SAFTs have been successfully implemented for the ultrasonic imaging of normal cylinders, while solutions for complex ones, such as variable-diameter cylinders, are still lacking. To overcome this problem, a frequency-domain SAFT for variable-diameter cylindrical components is proposed. This algorithm is mainly based on acoustic field extrapolation, which is modified from cylindrical phase shift migration with the aid of split-step Fourier. After a series of extrapolations, a high-resolution ultrasound image can be reconstructed using a particular imaging condition. According to the experimental results, the proposed method yields low side lobes and high resolutions for flat transducers. Its attainable angular resolution relies on the transducer diameter D and scanning radius R and approximates D/(2R).

Localization of ultrasound waveform for low intensity ultrasound-induced neuromodulation in a mouse model.

A collimator design was investigated to localize ultrasound stimulation using a flat ultrasound transducer for ultrasound-induced neuromodulation in a mouse model. In brain stimulation, the specific location of stimulation must be specified, as the region responsible for motor or sensory function is clustered in a narrow brain area. To localize ultrasound stimulation, three types of collimator design were simulated to determine the optimal collimator design. The performance of the simulated optimal collimator was compared to that of an unmounted collimator in a transducer in both in vivo and in vitro experiments. Throughout the experiments, the localized ultrasound waveform was shaped using the optimized collimator, which elicited neural spike activity in the targeted motor cortex. The optimized collimator shows potential for controlling a localized ultrasound waveform for ultrasound-induced neuromodulation in a small animal model.

The research of compression and generation of high-precision dynamic focusing delay data for ultrasound beamformer

In an ultrasound imaging system, dynamic focusing is crucial in improving the spatial resolution and signal-to-noise ratio. However, the generation of focusing delay data (FDD) requires complex calculations and a large amount of memory. The dynamic focusing system may become extremely complex as the number of focusing channels and the focal depth increase. This paper presents a simplified scheme of a high-precision generator for the FDD in Field-programmable Gate Array (FPGA). First, the original FDD are pre-calculated, quantized, decomposed, and compressed by exploiting the recursive characteristics between focusing channels. Then, the initial value and changing locations of each channel are stored as a reference data set. Finally, the FDD are generated in real time by decompressing the preloaded reference data set during the focusing process. The results indicate that the proposed approach consumes less than l% of the memory space of the original method, which may provide significant resource savings and low hardware power consumption. The proposed method can also be applied to convex or flat transducers array in compact beamformers. Moreover, the focusing accuracy and compression ratio can be flexibly adjusted, and the compression ratio can be further improved when the proposed approach is combined with the dynamic aperture. The proposed approach is contribute to the solution of the problem of the complex and large amount of data in ultrasonic imaging system. It is suitable for designing a specific compact focusing beamformer, particularly for a portable ultrasound imaging system.

Microbubble-Based Sonothrombolysis Using a Planar Rectangular Ultrasonic Transducer

The aim of the proposed study was to evaluate in an in vitro flow model the ability of small planar rectangular (2 × 10 mm2) ultrasonic transducer to enhance thrombolysis induced by the thrombolytic agent tenecteplase (TNK-tPA). To provide a more realistic clinical environment of stroke, the study was conducted under realistic flow conditions and TNK-tPA concentrations. Fully retracted porcine blood clots were used to determine the thrombolytic efficacy of ultrasound (US) waves as an adjunct to TNK-tPA or in combination with microbubbles (MBs). Two ultrasonic flat rectangular transducers were used in the experiments, operating at 3.7 and 5.2 MHz respectively. A pulsed US protocol that maintained temperature elevation at the target of 1°C was applied. Thrombolysis efficacy was measured in milligrams of mass clot removed. The effect of experimental parameters, such as power, frequency, and MBs administration, on thrombolysis efficacy was explored. The results revealed that thrombolysis efficacy decreases at higher frequency, and therefore, the possibility of using lower frequency to improve efficacy should be further investigated. Additionally, study findings demonstrated that the combination of 3.7 MHz with MBs as an adjunct to TNK-tPA strongly enhanced thrombolysis efficacy, because with 30 minutes of treatment, 700 mg of clot was removed through nonthermal mechanisms. As a final point, this study has shown that MBs dose influences thrombolysis enhancement, because higher thrombolytic efficacy was observed with higher doses of MBs.

A High Frequency Geometric Focusing Transducer Based on 1-3 Piezocomposite for Intravascular Ultrasound Imaging.

Due to the small aperture of blood vessel, a considerable disadvantage to current intravascular ultrasound (IVUS) imaging transducers is that their lateral imaging resolution is much lower than their axial resolution. To solve this problem, a single-element, 50 MHz, 0.6 mm diameter IVUS transducer with a geometric focus at 3 mm was proposed in this paper. The focusing transducer was based on a geometric-shaped 1-3 piezocomposite. The impedance/phase, pulse echo, acoustic intensity field, and imaging resolution of the focusing transducer were tested. For comparison, a flat IVUS transducer with the same diameter and 1-3 piezocomposite was made and tested too. Compared with their results, the fabricated focusing transducer exhibits broad bandwidth (107.21%), high sensitivity (404 mV), high axial imaging resolution (80 μm), and lateral imaging resolution (100 μm). The experimental results demonstrated that the high frequency geometric focusing piezocomposite transducer is capable of visualizing high axial and lateral resolution structure and improving the imaging quality of related interventional ultrasound imaging.

Intense Signal Modulation of Nonlinear Optical Scattering and Multiphoton Fluorescence by Ultrasound Irradiation

Tagging linear fluorescence signals by ultrasound has been proposed to achieve improved spatial resolution at known imaging depths. An alternative way to enhance imaging resolution is the use of nonlinear optical methods such as second-harmonic imaging microscopy and two-photon excitation fluorescence. Extending further along these lines, we have studied the fundamental aspects of the effect of ultrasound irradiation on two nonlinear optical effects. In contrast to the focused transducers that are traditionally used in the study of ultrasound -mediated fluorescence that cause a small fluorescence modulation, we have made use of a simple, flat disc-shaped transducer to generate standing waves in the sample cell. Upon ultrasound irradiation, a prompt increase of the hyper-Rayleigh scattering signal with 35% was observed. The signal enhancement shows a clear correlation with the standing wave pattern, as characterized by laser beam deflection scanning measurements. The viability of different possible mechani...

Evaluation of a small flat rectangular therapeutic ultrasonic transducer intended for intravascular use

BackgroundThe aim of the proposed study was to evaluate the performance of a flat rectangular (2×10mm2) transducer operating at 4MHz. The intended application of this transducer is intravascular treatment of thrombosis and atherosclerosis. MethodsThe transducer’s thermal capabilities were tested in two different gel phantoms. MR thermometry was used to demonstrate the thermal capabilities of this type of transducer. ResultsTemperature measurements demonstrated that this simple and small transducer adequately produced high temperatures, which can be utilized for therapeutic purposes. These high temperatures were confirmed using thermocouple and MR measurements. Pulsed ultrasound in combination with thrombolytic drugs and microbubbles was utilized to eliminate porcine thrombi. ConclusionsThe proposed transducer has the potentials to treat atherosclerotic lesions using the thermal properties of ultrasound, since high temperatures can be achieved in less than 5s. The results revealed that the destruction of thrombi using pulsed ultrasound requires long exposure time and high microbubble dosage.

Reflection Modeling Based Broadband Matching Network Design

Abstract In this paper, a new broadband matching network design approach based on reflection modeling is proposed, which has two parts: impedance data generation and modeling. In the approach, firstly the output impedance data of the matching network is obtained to get the desired flat transducer power gain in the passband. Next the output reflection data are calculated using the obtained impedance data, then they are modeled as a bounded real function. Then this function is synthesized and the desired lossless matching network with initial element values is obtained. A double matching example is solved to illustrate the use of the proposed approach. It is seen that proposed approach provides suitable initials for CAD tools for final trimming.

Acoustic field measurement of high-intensity ultrasound source system using acoustic waveguide for calibration of hydrophone

In recent years, high-intensity ultrasound equipments have been used. It is expected that nonlinear calibration and evaluation will be needed more often. It is necessary to develop a high-intensity ultrasound source that transmit a plane wave in far-field for calibration of hydrophone in order to evaluate high intensity acoustic field. We proposed an ultrasound source system using a cylindrical type acoustic waveguide and a concave type piezoelectric transducer. The focused ultrasound wave is emitted from the concave type transducer, propagated through the acoustic waveguide, and the output from that forms high-intensity acoustic beam. We simulated the output acoustic pressure of the proposed source system using axisymmetric 3D acoustic field simulation based finite element method, compared with that of a flat disk type transducer with the same aperture size as the acoustic waveguide, and the simulated data showed the acoustic pressure of our proposed system was higher than that of the flat disk type transducer with the same main beam width. We fabricated the experimental source system using the concave type piezoelectric transducer and the acoustic waveguide using closed cell sponge, and measured acoustic pressure distribution. The obtained results were nearly coincident with the simulated data

Nearfield and farfield measurements of dolphin echolocation beam patterns: No evidence of focusing.

The potential for bottlenose dolphins to actively focus their biosonar transmissions was examined by measuring emitted clicks in four dolphins using horizontal, planar hydrophone arrays. Two hydrophone configurations were used: a rectangular array with hydrophones 0.2 to 2 m from the dolphins and a polar array with hydrophones 0.5 to 5 m from the dolphins. The biosonar task was a target change detection utilizing physical targets at ranges from 1.3 to 6.3 m with all subjects and "phantom" targets at simulated ranges from 2.5 to 20 m with two subjects. To provide a basis for evaluating the experimental data, sound fields radiated from flat and focused circular pistons were mathematically simulated using transient excitation functions similar to dolphin clicks. The array measurements showed no evidence that the dolphins adaptively focused their click emissions; axial amplitudes and iso-amplitude contours matched the pattern of the simulation results for flat transducers and showed a single region of maximum amplitude, beyond which spherical spreading loss was approximated.

속도 분포 기반 단층촬영을 위한 최적의 트랜스듀서의 조합

The type of ultrasound transducer used influences the quality of a reconstructed ultrasound image. This study analyzed the effect of transducer type on ultrasound computed tomography (UCT) image quality. The UCT was modeled in an ultrasound simulator by using a 5 cm anatomy model and a ring-shape 5 MHz 128 transducer array, which considered attenuation, refraction, and reflection. Speed-of-sound images were reconstructed by the Radon transform as the UCT image modality. Acoustic impedance images were also reconstructed by the delay-and-sum (DAS) method, which considered the speed of sound information. To determine the optimal combination of transducers in observation, point-source, flat, and focused transducers were tested in combination as trasmitters and receivers; UCT images were constructed from each combination. The combination of point-source/flat transducer as transmitting and receiving devices presented the best reconstructed image quality. In UCT implementation, the combination of a flat transducer for transmitting and a point transducer for receiving permitted acceptable image quality.

5-Aminolevulinic acid-mediated sonosensitization of rat RG2 glioma cells in vitro.

Sonodynamic therapy (SDT) is a promising technique based on the ability of certain substances, called sonosensitizers, to sensitize cancer cells to non-thermal effects of low-energy ultrasound waves, allowing their destruction. Sonosensitization is thought to induce cell death by direct physical effects such as cavitation and acoustical streaming as well as by complementary chemical reactions generating oxygen free radicals. One of the promising sonosensitizers is 5-aminolevulinic acid (ALA) which upon selective uptake by cancer cells is metabolized and accumulated as protoporphyrin IX. The objective of the study was to describe ALA-mediated sonodynamic effects in vitro on a rat RG2 glioma cell line. Glioma cells, seeded at the bottom of 96-well plates and incubated with ALA (10 µg/ml) for 6 h, were exposed to the sinusoidal US pulses with a resonance frequency of 1 MHz, 1000 µs duration, 0.4 duty-cycle, and average acoustic power varying from 2 W to 6 W. Ultrasound waves were generated by a flat circular piezoelectric transducer with a diameter of 25 mm. Cell viability was determined by MTT assay. Structural cellular changes were visualized with a fluorescence microscope. Signs of cytotoxicity such as a decrease in cell viability, chromatin condensation and apoptosis were found. ALA-mediated SDT evokes cytotoxic effects of low intensity US on rat RG2 glioma cells in vitro. This cell line is indicated for further preclinical assessment of SDT in in vivo conditions.

Modified transfer function with a phase rotation parameter for ultrasound longitudinal waves in cancelous bone

The through-transmission ultrasound signal in cancelous bone consists of two longitudinal waves, called the fast and slow waves. The conventional propagation model assumes that the wavefront of an ultrasound wave passing through a bone specimen is flat and that each wave arrives simultaneously at all the points on a transducer surface. To compensate for the waveform change caused by the effect of the uneven wavefront received at a flat transducer, we propose a new transfer function modified with a phase rotation parameter. We also propose a fast decomposition method that requires only 5 seconds using a laptop personal computer. The proposed decomposition method using the modified transfer function succeeded to separate the two waves and characterize each of them accurately, where the normalized residual intensity power was less than −20 dB in the experimental study when the bone specimen thickness was from 6 to 15 mm. In the simulation study, the normalized residual power was less than −20 dB when the specimen thickness was from 3 to 8 mm. These results show that the transfer function with a phase rotation parameter is valid and that the proposed decomposition method has a great potential to provide good indicators of osteoporosis in real-time.

Mapping of cavitational activity in a pilot plant dyeing equipment

A large number of papers of the literature quote dyeing intensification based on the application of ultrasound (US) in the dyeing liquor. Mass transfer mechanisms are described and quantified, nevertheless these experimental results in general refer to small laboratory apparatuses with a capacity of a few hundred millilitres and extremely high volumetric energy intensity. With the strategy of overcoming the scale-up inaccuracy consequent to the technological application of ultrasounds, a dyeing pilot-plant prototype of suitable liquor capacity (about 40L) and properly simulating several liquor to textile hydraulic relationships was designed by including US transducers with different geometries.Optimal dyeing may be obtained by optimising the distance between transducer and textile material, the liquid height being a non-negligible operating parameter. Hence, mapping the cavitation energy in the machinery is expected to provide basic data on the intensity and distribution of the ultrasonic field in the aqueous liquor. A flat ultrasonic transducer (absorbed electrical power of 600W), equipped with eight devices emitting at 25kHz, was mounted horizontally at the equipment bottom.Considering industrial scale dyeing, liquor and textile substrate are reciprocally displaced to achieve a uniform colouration. In this technology a non uniform US field could affect the dyeing evenness to a large extent; hence, mapping the cavitation energy distribution in the machinery is expected to provide fundamental data and define optimal operating conditions. Local values of the cavitation intensity were recorded by using a carefully calibrated Ultrasonic Energy Meter, which is able to measure the power per unit surface generated by the cavitation implosion of bubbles. More than 200 measurements were recorded to define the map at each horizontal plane positioned at a different distance from the US transducer; tap water was heated at the same temperature used for dyeing tests (60°C). Different liquid flow rates were tested to investigate the effect of the hydrodynamics characterising the equipment.The mapping of the cavitation intensity in the pilot-plant machinery was performed to achieve with the following goals: (a) to evaluate the influence of turbulence on the cavitation intensity, and (b) to determine the optimal distance from the ultrasound device at which a fabric should be positioned, this parameter being a compromise between the cavitation intensity (higher next to the transducer) and the US field uniformity (achieved at some distance from this device).By carrying out dyeing tests of wool fabrics in the prototype unit, consistent results were confirmed by comparison with the mapping of cavitation intensity.

Simultaneous in- and out-of-plane Mitral Valve Annular Force Measurements.

Mitral valve repair with annuloplasty is often favoured over total valve replacement. In order to develop and optimize new annuloplasty ring designs, it is important to study the complex biomechanical behaviour of the valve annulus and the subvalvular apparatus with simultaneous in- and out-of-plane restraining force measurements. A new flat D-shaped mitral valve annular force transducer was developed. The transducer was mounted with strain gauges to measure strain and calibrated to provide simultaneous restraining forces in- and out of the mitral annular plane. The force transducer was implanted and evaluated in an 80kg porcine experimental model. Accumulation of out-of-plane restraining forces, creating strain in the anterior segment were 0.7±0.0N (towards apex) and an average force accumulation of 1.5±0.3N, creating strain in the commissural segments (away from apex). The accumulations of in-plane restraining forces, creating strain on the inner side of the ring were 1.7±0.2N (away from ring center). A new mitral annular force transducer was successfully developed and evaluated in vivo. The transducer was able to measure forces simultaneously in different planes. Initial indications point towards overall agreement with previous individual force measurements in- and out-of the mitral annular plane. This can provide more detailed insight into the annular force distribution, and could potentially improve the level of evidence based mitral valve repair and support the development of future mitral annuloplasty devices.

Noninvasive photoacoustic measurement of the composite indicator dilution curve for cardiac output estimation.

Recently, the measurement of indicator dilution curves using a photoacoustic (PA) technology was reported, which showed promising results on the noninvasive estimation of cardiac output (CO) that is an important hemodynamic parameter useful in various clinical situations. However, in clinical practice, measuring PA indicator dilution curves from an arterial blood vessel requires an ultrasound transducer array capable of focusing on the targeted artery. This causes several challenges on the clinical translation of the PA indicator dilution method, such as high sensor cost and complexity. In this paper, we theoretically derived that a composite PA indicator dilution curve simultaneously measured from both arterial and venous blood vessels can be used to estimate CO correctly. The ex-vivo and in-vivo experimental results with a flat ultrasound transducer verified the developed theory. We believe this new concept would overcome the main challenges on the clinical translation of the noninvasive PA indicator dilution technology.

Evaluation of Bone Tissue Formation in a Flat Surface Attachment of a Bone Conduction Implant: A Pilot Study in a Sheep Model

The bone conduction implant (BCI) is a new bone conduction hearing device implanted under intact skin. The transducer has a flat direct contact with the mastoid part of the temporal bone, and no screws are used. The sound signal is transmitted from the external audio processor to the implant by means of magnetic induction. In this study, osseointegration of a flat passive BCI transducer dummy in sheep skulls was assessed using quantitative and qualitative histology as well as cone beam computed tomography (CBCT) and computed tomography (CT). The histology results were also related to the mechanical properties of the bone-to-implant interface. Eight months after the surgical implantation, histology sections of the bone close to the implant showed bone remodeling, compact bone and osseointegration. The histological findings corresponded well to the mechanical measurements indicating stiffer bone close to the implant and unaffected skull vibration transmission. Neither CBCT nor CT had enough resolution to visualize the bone-to-implant interface in detail. In this study, using an animal model, it is shown that a flat implant in contact with bone can be a feasible method for efficient vibration transmission to the skull bone.