Design Of Ultrasound Transducers Research Articles

Miniaturized Preamplifire Integration in Ultrasound Transducer Design for Enhanced Photoacoustic Imaging

Miniaturized Preamplifire Integration in Ultrasound Transducer Design for Enhanced Photoacoustic Imaging

Design and Verification of Sector Vortex Archimedean Spiral Phased Array Transducer for Improving Focus Acoustic Pressure

The emergence of high-intensity focused ultrasound applications brings great potential to establish noninvasive therapeutic treatment in place of conventional surgery. However, the development of ultrasonic technology also poses challenges to the design and manufacture of high-power ultrasound transducers with sufficient acoustic pressure. Here, the design of a sector vortex Archimedean spiral phased array transducer that is able to enhance focal acoustic pressure is proposed by maximizing the filling factor of the piezoelectric array. The transducer design was experimentally verified by hydrophone measurements and matched well with acoustic simulation studies. The focal deflection was shown to be feasible up to ±9 mm laterally and up to ±20 mm axially, where the effective focal acoustic pressure can be maintained above 50% and the level of the grating lobe below 30%. Furthermore, a homogeneous pressure distribution without secondary focus was observed in the pre-focal region of the transducer. The rational design of a high-intensity focused ultrasound transducer indicates promising development in the treatment of deep tissue thermal ablation for clinical applications.

Design and Fabrication of Annular-Array Ultrasound Transducer Based (K, Na) NbO3 Lead-Free 1-3 Piezoelectric Composite.

This article reports the design, fabrication, and performance of an annular-array ultrasound transducer using (K, Na)NbO3 (KNN)-based lead-free 1-3 piezoelectric composite. The 1-3 piezoelectric composite based on lead-free 0.965(K0.45Na0.55)(Nb0.96Sb0.04)O3-0.035 Bi0.5Na0.5Zr0.85Hf0.15O3 (KNNS-BNZH) was first prepared with the dice-and-fill method. Different from previous reported studies, by patterning annular electrodes on this kind of 1-3 composite, a five-element annular-array transducer in diameter of 6 mm was designed and successfully fabricated and its working center frequency was increased from 5 MHz to around 15 MHz. Meanwhile, a -6 dB bandwidth of 50% was achieved for each annular-array element via a pulse-echo response measurement. Moreover, the obtained annular-array transducer exhibits low crosstalk (<-40 dB) and a high electromechanical coupling coefficient of around 0.7. The application of ultrasonic imaging was further demonstrated to show its excellent performance. Both theoretical analysis and experimental results show that the obtained annular-array transducer presented in this work has a competitive capability for ultrasonic application.

An Improved Equivalent Circuit Simulation of High Frequency Ultrasound Transducer

The equivalent circuit simulation plays an important role in the design of ultrasound transducer. However, the existing methods are difficult to achieve the effect of matching and backing layer, and not able to accurately simulate the transducer with cable. Especially in the application of high frequency ultrasound, the long cable has a great influence on the performance of the transducer. To overcome these limitations, this paper proposed an improved equivalent circuit method, which combined Leach model and transmission line model. It can realize the complete simulation of ultrasound transducer with a long cable, matching layer, and backing layer in PSPICE circuit simulation software when the parameters were measured. Its principles were briefly introduced, and ultrasound transducers with different frequencies (12 and 20 MHz), different matching layers, and different cable lengths (0.5–2.5 m) were designed and fabricated to verify the effectiveness of the method, which is also compared with the traditional KLM method using PiezoCAD. The experiment results showed that the long cable, matching layer, and backing layer have a significant impact on the performance of high frequency ultrasound transducers, and this proposed method has good agreement with these results. Moreover, for the simulation of the complete transducer, the effect of this method is better than KLM model. Besides, this method does not need to know the specific equivalent circuit of matching, backing layer, or cable wire, it can accurately predict the impedance and phase of the transducer through the material parameters, which is very helpful for the material selection and optimization of subsequent transducer design and fabrication. The study indicates that this improved equivalent circuit method is suitable to be applied in the general circuit simulation software and provides strong support for the high frequency transducer and system design.

Design and Fabrication of a Novel Dual-Frequency Confocal Ultrasound Transducer for Microvessels Super-Harmonic Imaging.

Recently, super-harmonic ultrasound imaging technology has caused much attention due to its capability of distinguishing microvessels from the tissues surrounding them. However, the fabrication of a dual-frequency confocal transducer is still a challenge. In this work, 270- [Formula: see text] PMN-PT single crystal 1-3 composite and 28- [Formula: see text] PVDF thick film, acting as transmission layer and receiving layer, respectively, are integrated in a novel co-focusing structure. To realize delicate wave propagation control, microwave transmission line theory is introduced to design such structure. Two acoustic filter layers, 13- [Formula: see text] copper layer and 39- [Formula: see text] Epoxy 301 layer, are indispensable and should be added between two piezoelectric layers. Therefore, an acoustic issue can be overcome via an electrical method and the successful achievement of a dual-frequency (5 MHz/30 MHz) ultrasound transducer with a confocal distance of 8 mm can be realized. The super-harmonic ultrasound imaging experiment is conducted using this kind of device. The 3-D image of 110- [Formula: see text]-diameter phantom tube injected with microbubbles can be obtained. These promising results demonstrate that this novel dual-frequency (5 MHz/30 MHz) confocal ultrasound transducer is potentially usable for microvascular medical imaging application in the future.

Validation of an ultrasound transducer's generation and receiving function on one single-mode fiber

This paper presents the design, fabrication and testing of a single-mode fiber optic ultrasound transducer. This transducer can work as an ultrasound generator and a receiver, based on principles of photoacoustic (PA) effect and Fabry–Pérot (FP) interference. PA effect is a process in which ultrasound waves are generated from optical energy by a PA material, and an FP structure is used for ultrasound receiving. The transducer was manufactured by coating a material called gold nanocomposite directly onto a single-mode optical fiber tip. The gold nanocomposite acted as the PA material and formed the FP structure as well. The transducer had the same size as the single-mode fiber, whose diameter was only 125 μm. It demonstrated its ability to generate ultrasound signals with a bandwidth of 5.6 MHz at an efficiency of 3.2 × 10−5 and function as an ultrasound receiver with a sensitivity of 2.81 mV/MPa. The generator and receiver built together can currently only work separately. This new transducer has substantial potential to work in restricted space and harsh environments for non-destructive testing.

Design and Fabrication of a High-Frequency Single-Directional Planar Underwater Ultrasound Transducer.

This paper describes the fabrication of 1-3 piezoelectric composites by using PZT5-A pure piezoelectric ceramics and the preparation of a high-frequency single-directional planar underwater ultrasound transducer by using the developed composites. First, three material models of the same size were designed and simulated by ANSYS finite element simulation software. Next, based on the simulation results, the 1-3 piezoelectric composites were developed. Finally, a high-frequency single-directional planar underwater ultrasound transducer was fabricated by encapsulating and gluing the 1-3 piezoelectric composites. The performance of the transducer was tested, and results showed that the device was characterized by single-mode operation in the working frequency band, a high transmitting voltage response, and single directivity.

Resonating Shell: A Spherical-Omnidirectional Ultrasound Transducer for Underwater Sensor Networks.

This paper presents the design and fabrication process of a spherical-omnidirectional ultrasound transducer for underwater sensor network applications. The transducer is based on the vibration of two hemispheres with a thickness of 1 mm and an outer diameter of 10 mm, which are actuated by two piezoelectric ring elements. Since the ultrasound wave is generated by the vibration of the two hemispheres, a matching layer is not required. Silicon Carbide (SiC) is used as the material of the hemispherical shells of the transducer. The shells were fabricated by laser sintering as an additive manufacturing method, in which the hemispheres were built layer by layer from a powder bed. All manufactured transducers with an outer dimension of mm and a center frequency of 155 kHz were measured in a water tank by a hydrophone or in mutual communication. The circumferential source level was measured to vary less than 5dB. The power consumption and the insertion loss of the transducer, ranging from 100 W to 2.4 mW and 21.2 dB, respectively, along with all other measurements, prove that the transducer can transmit and receive ultrasound waves omnidirectionally at tens of centimeters intervals with a decent power consumption and low actuation voltage.

Acoustic field simulation method for arbitrarily shaped transducer with dynamically refined sub-elements.

Simulation of the emitted acoustic field is crucial to the design of ultrasound transducers. The method based on the spatial impulse response (SIR) and aperture discretization provides a powerful tool to study the acoustic field emitted by a transducer with complex aperture geometry and sophisticated apodization/excitation pattern. In this work, a new method based on the dynamically refined sub-elements (SE) is employed to discrete the aperture and generate the SIR. Then, these SIRs are convoluted with the excitation pulse to get the acoustic pressure (AP) signal. When calculating the SIR with this method, the slowly changed time flight from a SE to a field point (FP) is approximated with a step function, and the fast changed length of intersection between a SE and a spherical wave centered at a FP is accurately estimated with the areas of the sub-parts (SP) which are given by the dynamically refined SE. Simulations of the acoustic field created by a focusing transducer array and a hollow structured point focusing transducer indicate that the proposed new method can give similar data accuracy with a sampling frequency 16 times lower than the conventional time tracing SE (TTSE) based method. The computational cost is also reduced by nearly one order of magnitude. A new method is proposed to simulate the acoustic field emitted by transducers with complex geometrical structure and sophisticated apodization/excitation patterns. The required sampling frequency with the new algorithm is greatly reduced compared to that of the conventional TTSE-based method; thus, the efficiency of the acoustic field calculation is improved significantly.

Design and fabrication of ultrasound linear array transducer based on polarization inversion technique

It has been well known that fabrication of the ultrasound array transducer is very difficult mainly due to the thin piezoelectric layer. Since the center frequency of the ultrasound array transducer is inversely proportional to the thickness of the piezoelectric layer, as the center frequency is increased, fabrication of the array transducer becomes more difficult. To solve this problem, in this paper, the polarization inversion technique (PIT) was employed to increase the center frequency of the array transducer without making the piezoelectric layer thin. Additionally, the PIT can increase the frequency bandwidth of the transducer by using its multiple-resonance feature. According to the finite element analysis (FEA) simulation, when the total thickness of the piezoelectric layer was fixed at 311 μm, the conventional transducer had a center frequency of 4.5 MHz and −6 dB bandwidth of 71.4%, while the proposed transducer with PIT had a center frequency of 8.1 MHz and −6 dB bandwidth of 83.2%. In the case of conventional transducer with about 8 MHz center frequency, the thickness of the piezoelectric layer was 155 μm, and −6 dB bandwidth was 72.3%. Subsequently, we fabricated a prototype transducer with PIT and verified that the center frequency and −6 dB bandwidth were 7.8 MHz and 81.3%, respectively. Therefore, the PIT can be a useful method for manufacturing the ultrasound array transducer with high frequency and broad bandwidth.

Effect of ultrasound transducer design on the acoustically-assisted supercritical fluid extraction of antioxidants from oregano

Power ultrasound is applied in food technology to intensify extraction processes, due to the phenomena ultrasonic energy induces in the medium, enhancing mass transfer. The purpose of this work was the acoustic characterization of four transducers of different geometries and the evaluation of their performance in the ultrasonically assisted supercritical fluid extraction of antioxidants from oregano. The transducers differed in the amount of energy transmitted into the medium. Designs varied from the base model (T1), a larger cylindrical headmass (T2), a stepped circular section sonotrode (T3) and a multiplate configuration (T4). The highest nominal power density provided according to the calorimetric method was for T4 (151.6 ± 7.1 W/L). The T2 produced a more uniform acoustic field and a higher acoustic pressure (150.6 ± 20.5 kPa). Both parameters had an impact on total phenolics and antioxidants extraction with CO2 under supercritical conditions (35 MPa, 35 °C, 2.3% ethanol as co-solvent). T4 and T2 were equally efficient (4.0 ± 0.2 and 4.2 ± 0.2 mg GA/g) for phenolic extraction, and with respect to antioxidant capacity, the best performance was that of T4 (26.4 ± 1.1 μmol TE/g). Of the antioxidant compounds extracted, flavones and flavanones were identified. Therefore, transducer geometry influenced the amount and distribution of energy transmitted into the medium, thus determining the efficiency of the extraction process.

Effects of Non-Elevation-Focalized Linear Array Transducer on Ultrasound Plane-Wave Imaging.

Plane-wave ultrasound imaging (PWUS) has become an important method of ultrasound imaging in recent years as its frame rate has exceeded 10,000 frames per second, allowing ultrasound to be used for two-dimensional shear wave detection and functional brain imaging. However, compared to the traditional focusing and scanning method, PWUS images always suffer from a degradation of lateral resolution and contrast. To improve the image quality of PWUS, many different beamforming algorithms have been proposed and verified. Yet the influence of transducer structure is rarely studied. For this paper, the influence of using an acoustic lens for PWUS was evaluated. Two linear array transducers were fabricated. One was not self-focalized in the elevation direction (non-elevation-focalized transducer, NEFT); the other one was a traditional elevation-focalized transducer (EFT). An initial simulation was conducted to show the influence of elevation focusing. Then the images obtained with NEFT on a standard ultrasound imaging phantom were compared with those obtained with EFT. It was demonstrated that, in a relatively deep region, the contrast of an NEFT image is better than that of an EFT image. These results indicate that a more sophisticated design of ultrasound transducer would further improve the image quality of PWUS.

Design and Fabrication of Double-Focused Ultrasound Transducers to Achieve Tight Focusing.

Beauty treatment for skin requires a high-intensity focused ultrasound (HIFU) transducer to generate coagulative necrosis in a small focal volume (e.g., 1 mm3) placed at a shallow depth (3–4.5 mm from the skin surface). For this, it is desirable to make the F-number as small as possible under the largest possible aperture in order to generate ultrasound energy high enough to induce tissue coagulation in such a small focal volume. However, satisfying both conditions at the same time is demanding. To meet the requirements, this paper, therefore, proposes a double-focusing technique, in which the aperture of an ultrasound transducer is spherically shaped for initial focusing and an acoustic lens is used to finally focus ultrasound on a target depth of treatment; it is possible to achieve the F-number of unity or less while keeping the aperture of a transducer as large as possible. In accordance with the proposed method, we designed and fabricated a 7-MHz double-focused ultrasound transducer. The experimental results demonstrated that the fabricated double-focused transducer had a focal length of 10.2 mm reduced from an initial focal length of 15.2 mm and, thus, the F-number changed from 1.52 to 1.02. Based on the results, we concluded that the proposed double-focusing method is suitable to decrease F-number while maintaining a large aperture size.

Improving the Performance of a 1-D Ultrasound Transducer Array by Subdicing.

In medical ultrasound transducer design, the geometry of the individual elements is crucial since it affects the vibration mode of each element and its radiation impedance. For a fixed frequency, optimal vibration (i.e., uniform surface motion) can be achieved by designing elements with very small width-to-thickness ratios. However, for optimal radiation impedance (i.e., highest radiated power), the width should be as large as possible. This leads to a contradiction that can be solved by subdicing wide elements. To systematically examine the effect of subdicing on the performance of a 1-D ultrasound transducer array, we applied finite-element simulations. We investigated the influence of subdicing on the radiation impedance, on the time and frequency response, and on the directivity of linear arrays with variable element widths. We also studied the effect of varying the depth of the subdicing cut. The results show that, for elements having a width greater than 0.6 times the wavelength, subdicing improves the performance compared with that of nonsubdiced elements: the emitted pressure may be increased up to a factor of three, the ringing time may be reduced by up to 50%, the bandwidth increased by up to 77%, and the sidelobes reduced by up to 13 dB. Moreover, this simulation study shows that all these improvements can already be achieved by subdicing the elements to a depth of 70% of the total element thickness. Thus, subdicing can improve important transducer parameters and, therefore, help in achieving images with improved signal-to-noise ratio and improved resolution.

Design and characterization of a sensitive optical micro-machined ultrasound transducer

Novel 3D intravascular or transesophageal ultrasound approaches require transducer arrays containing many small elements. Conventional piezo-electric techniques face fabrication challenges due to narrow kerfs and dense wiring. Micro-machined alternatives like CMUTs and PMUTs lack either sensitivity or bandwidth to fully compete. Therefore we developed an opto-mechanical ultrasound sensor. The absence of wiring makes it MRI compatible. The developed OMUT contains integrated photonics, which is fabricated using standard silicon-on-insulator technology, providing a small footprint and enabling mass production and ease of integration. The sensor consists of a straight waveguide and a micro-ring resonator integrated on a 124 μm wide, 2.7 μm thick acoustical membrane. Light, passing the waveguide, is partly coupled into the ring resonator. A dip appears in the spectrum of the transmitted light at the resonance wavelength of the micro-ring. If the acoustical membrane and hence the micro-ring is deformed due to an incident ultrasound wave, this is observed as a shift in the resonance wavelength of the ring. This paper presents the construction and characterization of our device. Measurement results of the linearity, frequency response, sensitivity and temperature dependence are compared with a model. The results demonstrate that our OMUT is a promising basis for future ultrasound arrays.

Numerical Simulation of Vibration Deflection Effects on the Energy Efficiency of Ultrasonic Transducer for Sonochemistry

The energy efficiency of ultrasound transducers for sonochemistry applications was studied from the point of view of vibration deflection effects of different transducer structures, including the configurations of rectangular plate, cylindrical shell, triangular strip array, rectangular strip array, and pentagonal strip array. It was found that the deflections are not uniform over the transducer surface with the maximum deflection locating at the geometry center of transducers. The simulated maximum deflection of rectangular plate results in the value of2.5×10-16, which is larger than the maximum deflection of cylindrical shell with the value of2×10-16. This finding suggests that the envelope deflection volume of two transducers has significant difference, which has been neglected in the design and selection of ultrasound transducer. For this reason, a quantitative index involving the envelope deflection volume was proposed to compare the efficiency of ultrasound transducers. Based on the simulation results, the triangular strip array transducer structure with higher ultrasound generation efficiency was proposed, which was also theoretically validated by the MATLAB simulation.

集束超音波による生体内精密治療

集束超音波による生体内精密治療

Dual-frequency intravascular ultrasound transducer design for contrast agent imaging

Intravascular ultrasound (IVUS) is a unique diagnostic tool for assessing the composition and degree of stenosis of atheromata in cardiovascular disease. As of yet, contrast enhanced IVUS has not been clinically implemented despite its potential to provide functional information, such as degree of plaque vascularization, in conjunction with standard anatomical mapping. In this study, we demonstrate that nonlinear microbubble signals can be detected with minimal signal processing using an ultra-broadband IVUS transducer composed of a low frequency transmit and a high frequency receive combined element. Raw signals were acquired from a single element transducer (1 × 3 mm, fc = 6.5/35 MHz) after aligning to an acoustically transparent 200 µm inner diameter cellulose tube. Poly-disperse, (1–10 µm diameter) lipid-coated microbubbles were injected at high concentration (4.8 × 108 MBs/mL) and peak negative pressures were varied from −0.3 to −1.8 MPa while transmission cycles were increased from 1to 5. In vitro results indicate signal to noise ratios of 11 dB are attainable at 2nd harmonics and similar SNRs (10–8 dB) at higher harmonics. The results of this study indicate that contrast enhanced IVUS imaging is possible using a single transmit pulsing scheme enabled by using a dual- frequency broadband transducer design.

Variation of Pinch and Grip Force Between Different Size Transducers

Work-related musculoskeletal disorders affect a large percentage of diagnostic medical sonographers. Ultrasound transducer design has been identified as a major contributing factor to hand and wrist strains. The purpose of this study was to determine if the design of the ultrasound transducer affects the amount of pressure exerted by the hands of the sonographer to achieve a quality scan. The study also aimed to determine if the amount of pressure exerted on the transducer relates to the subjective pain level reported by the sonographer. The study found that the average maximum pressure and average force exerted was higher when scanning with a small transducer compared with a large transducer, and the thumb typically exerted a much greater pressure and force. Sonographers reported pain during the scan trials, as well as throughout their typical workdays, leisure pursuits, and daily activities.

Analysis of Ultrasonic Radiation Field Based on Linear MEMS Ultrasonic Transducer Array

The analysis of the acoustic field distribution characteristics for the ultrasonic transducer array plays a very important role in both the optimization of the design parameters of the array and the improvement of image quality. In this paper, the acoustic analysis method based on spatial impulse response is studied for the linear MEMS ultrasonic transducer array. The spatial impulse response for the ultrasonic transducer array and the lateral ultrasonic radiation field for the transducer array are obtained by simulation and calculation, and the simulation results are analyzed, which has important implications on the further optimization of MEMS ultrasound transducer design parameters.