Rectangular Transducer Research Articles

Theory of acoustooptical filtration of light beams in the inhomogeneous acoustic field

The theory of acoustooptical (AO) interaction between light beams in the longitudinally inhomogeneous acoustic field is constructed with allowance for conditions typical of AO filtration. In the case of smooth acoustic inhomogeneities, analytical expressions for the spatially spectral characteristic relating the spatial spectra of incident and diffracted light beams are derived. The situation where a Gaussian light beam undergoes filtration in the acoustic field excited by a rectangular transducer is discussed in detail. The narrowband quasi-collinear AO filter based on a paratellurite crystal is simulated. It is demonstrated that the maximum diffraction efficiency and transmission-function shape distortion (with respect to the plane-wave model) of the given device depend to the greatest extent on the misalignment between the directions of the group velocities of interacting light beams.

Effects of sidelobes on acousto-optic tunable filter imaging

An acousto-optic tunable filter (AOTF) is used in the development of hyperspectral imagers from the ultraviolet to the longwave infrared. The spectral response of the transmitted intensity from an AOTF with a rectangular transducer has a sinc2(x) distribution and so far the light leakage from the sidelobes is ignored in hyperspectral imagers. When unpolarized white light is incident on an AOTF, two orthogonally polarized diffracted beams at a specific wavelength with a narrow bandpass filter are transmitted for an applied radio frequency (RF), and an image cube is obtained by tuning the applied RF. We carried out a detailed study of light transmitted through the sidelobes of a TeO2 AOTF operating in the shortwave infrared region from 0.9 to 1.7 μm to image a scene containing a laser. The AOTF imaging system used telecentric confocal optics that compensate for AOTF aberrations. We used a 16-channel RF driver with independent amplitude and frequency control. By switching off specific RF signals applied to the AOTF, the detailed sidelobe structure for the transmitted intensity was measured and compared with theory. We found that close to 10% of the transmitted light is leaked through the sidelobes. Here, we present our experiment and analysis of the results.

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 Fast Method to Calculate the Spatial Impulse Response for 1-D Linear Ultrasonic Phased Array Transducers.

A method is developed to accurately determine the spatial impulse response at the specifically discretized observation points in the radiated field of 1-D linear ultrasonic phased array transducers with great efficiency. In contrast, the previously adopted solutions only optimize the calculation procedure for a single rectangular transducer and required approximation considerations or nonlinear calculation. In this research, an algorithm that follows an alternative approach to expedite the calculation of the spatial impulse response of a rectangular linear array is presented. The key assumption for this algorithm is that the transducer apertures are identical and linearly distributed on an infinite rigid plane baffled with the same pitch. Two points in the observation field, which have the same position relative to two transducer apertures, share the same spatial impulse response that contributed from corresponding transducer, respectively. The observation field is discretized specifically to meet the relationship of equality. The analytical expressions of the proposed algorithm, based on the specific selection of the observation points, are derived to remove redundant calculations. In order to measure the proposed methodology, the simulation results obtained from the proposed method and the classical summation method are compared. The outcomes demonstrate that the proposed strategy can speed up the calculation procedure since it accelerates the speed-up ratio which relies upon the number of discrete points and the number of the array transducers. This development will be valuable in the development of advanced and faster linear ultrasonic phased array systems.

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.

Feasibility study for removing calcified material using a planar rectangular ultrasound transducer.

The aim of the proposed study was to conduct a feasibility study using a flat rectangular (3mm×10mm) MRI compatible transducer operating at 5.3MHz for destroying calcified material in an in vitro model. The proposed method can be used in the future for treating atherosclerosis plaques of the coronary, carotid or peripheral arteries. The system was tested initially on calcium rods. Another test was performed in a hydroxyapatite-polylactide model. A parametric study was performed where the mass of calcified material removed was studied as a function of intensity, pulse repetition frequency (PRF), duty factor (DF) and presence of bubbles. The amount of calcified material removed is directly related to the intensity, PRF and DF. It was found that the presence of bubbles accelerates the removal of calcified material. In order to ensure that pure mechanical mode ultrasound was used, the protocols were designed so that the temperature does not exceed 1°C.

A Novel Algorithm for the Sound Field of Rectangular-Shaped Transducers**Supported by the National Natural Science Foundation of China under Grant Nos 11074038 and 11374051.

An alternative extension to the Gaussian-beam expansion technique is provided to simplify the computation of the Fresnel field integral for rectangular symmetric sources. From a known result that the circle or rectangle function is approximately decomposed into a sum of Gaussian functions, the cosine function is similarly expanded by the Bessel–Fourier transform. Two expansions are together inserted in this field integral, it is then expressible in terms of the simple algebraic functions. As examples, the numerical results for the sound pressure field are presented for the uniform rectangular piston transducer, in a good agreement with those directly evaluated from the Fresnel integral. A wide applicability of this approach is discussed in treatment of the ultrasonic field radiation problem for a large and important group of piston sources in acoustics.

Damage localization in aluminum plate with compact rectangular phased piezoelectric transducer array

In this work, a detection method for the damage in plate-like structure with a compact rectangular phased piezoelectric transducer array of 16 piezoelectric elements was presented. This compact array can not only detect and locate a single defect (through hole) in plate, but also identify multi-defects (through holes and surface defect simulated by an iron pillar glued to the plate). The experiments proved that the compact rectangular phased transducer array could detect the full range of plate structures and implement multiple-defect detection simultaneously. The processing algorithm proposed in this paper contains two parts: signal filtering and damage imaging. The former part was used to remove noise from signals. Continuous wavelet transform was applicable to signal filtering. Continuous wavelet transform can provide a plot of wavelet coefficients and the signal with narrow frequency band can be easily extracted from the plot. The latter part of processing algorithm was to implement damage detection and localization. In order to accurately locate defects and improve the imaging quality, two images were obtained from amplitude and phase information. One image was obtained with the Total Focusing Method (TFM) and another phase image was obtained with the Sign Coherence Factor (SCF). Furthermore, an image compounding technique for compact rectangular phased piezoelectric transducer array was proposed in this paper. With the proposed technique, the compounded image can be obtained by combining TFM image with SCF image, thus greatly improving the resolution and contrast of image.

Two dimensional shear lag solution for stress transfer between rectangular piezoelectric wafer transducer and orthotropic host plate

Abstract An accurate assessment of the local interfacial stress distribution between piezoelectric transducers and the host plate is fundamental to their effective use for actuation and sensing applications. In this paper, a two dimensional shear lag model for the stress transfer between rectangular piezoelectric wafer transducer and orthotropic host plate bonded through an adhesive layer is developed. An accurate iterative analytical solution of the governing equations is presented using the recently developed mixed-field multiterm extended Kantorovich method (MMEKM). Both actuation and sensor modes are accounted for through the appropriate boundary conditions. A convergence study reveals that the MMEKM gives very accurate results even with a single-term solution and the results converge within three iterations. Parametric studies are conducted to illustrate the effects of thicknesses of the adhesive layer, the host plate and the transducer, aspect ratio of transducer, and longitudinal to transverse modulus ratio of host plate on the actuator stresses and interfacial shear stresses induced by actuation potential. The effect of transverse piezoelectric constant d 32 on the interfacial shear stress is also shown.

Methods and applications for modeling of continuous-wave ultrasound fields

Techniques are presented for efficient and accurate computation of three-dimensional, continuous-wave radiated fields from ultrasound transducers of canonical geometries. Fields of flat circular pistons are computed using exact series expressions based on orthogonal function expansions of the Rayleigh integral. Fields of concave circular pistons are computed using analogous series expansions for an integral of effective source contributions over the radiating surface; this approach accurately approximates radiated fields of many focused ultrasound transducers of interest. Fields of flat and focused rectangular transducers are computed using closed-form expressions based on a modified Fresnel approximation; accurate fields are obtained at distances large compared to the radiating aperture dimensions, so that the near field for large transducers can be accurately simulated by subdividing the radiating aperture. Efficient methods for field computation facilitate design optimization for therapy and imaging de...

Destruction of atherosclerotic plaque using pulse ultrasound with a planar rectangular transducer

The aim of this paper is to present a feasibility study for using mechanical mode ultrasound for destroying atherosclerotic plaque with MRI monitoring.

Road Performance of Common Piezoelectric Transducer for Asphalt Pavement Energy Harvesting

The discussion in the paper is focused on energy transition efficiency, stiffness and intensity of common piezoelectric transducers in the following aspects. Firstly, we have found out that bridge piezoelectric transducers possess high energy transition efficiency and the similar stiffness to asphalt pavement through comparing and analyzing road performance of several common piezoelectric transducers. Thus, we hold the view that it is applicable for energy collection of asphalt pavement and will be analyzed subsequently. Secondly, we have analyzed energy transition efficiency and stiffness characteristics of arc bridge piezoelectric transducer and rectangular bridge piezoelectric transducer in laboratory test. The results show that, under the same load stress, arc transducers are better than rectangular transducers in terms of energy transition efficiency; but comparing with rectangular transducers, arc transducers are more prone to be destroyed, which is not helpful for bearing traffic load.

Ultrasound Imaging Using Spatial Domain Phase Information

The aim of this paper is to determine the efficacy of the ring-shaped array used for imaging the objects inside the array. Hyperbola algorithm and ellipse algorithm which are conventionally used in the field of guided wave for locating the defects are developed and combined here to extract the image. Meanwhile, much more phase information is added in this process. Fan-shaped ultrasound radiation is generated separately by the 45 rectangular ultrasonic transducers which are circular embedded in the wall of a container. The time of flight data and the attenuation data are obtained and stored in the A-scan wave of each receiving transducer, subsequently, they are applied for reconstructing the image of all tested objects. The validity of the combined measuring method with phase information is demonstrated by imaging the distributed polyurethane objects.

A three-dimensional analysis of natural vibrations of rectangular piezoelectric transducers

A computer program for the three-dimensional analysis of natural vibrations of rectangular piezoelectric transducers of arbitrary dimensions has been developed on the basis of the finite-element method (FEM). The analysis of natural vibrations of transducers was performed for several first modes. The results make it possible to substantiate the choice of the optimal geometric dimensions for a rectangular piezoelectric transducer that operates in the first mode.

Research on Acoustic Field of Ultrasonic Linear Phased Array Based on Spatial Impulse Response of Rectangular Planar Transducer

An analytical method for calculating spatial impulse response of rectangular transducer without far-field or paraxial approximations is presented.According to symmetry of rectangular,the coordinate of observe point is transformed in the fourth quadrant.The solution using only inverse trigonometric functions and simple coordinate transformation,and impulse response of rectangular transducer with different length-width ratios can be calculated.Ultrasonic phased array can freely control the focus point position by exciting each element with independent phase delay,the focus laws of the ultrasonic l-D phased array are derived and the delay time of each element is obtained,then delay time is applied in every transducer element,and the impulse response of phased array transducer is obtained by superposition spatial impulse response of each element.Simulations are carried out for a l-D array transducer in different focusing angles,and the resolution of different distance between the transmitting elements is discussed.Results show that this method can efficiently and accurately predict the radiation field of linear phased array transducer over a wide range of steering angles.

Multi-Gaussian beam model for ultrasonic surface waves with angle beam rectangular transducers

Rayleigh waves propagating in an elastic surface are commonly used for the near surface flaw detection and material characterization. However, unlike the bulk wave case, there are seldom three-dimensional models to be provided for the Rayleigh waves. In the past decade, multi-Gaussian beam models have been gradually developed and perfectly applied to solve many complicated propagation problems of bulk waves. However, up to date they have not been extended to the simulation of the Rayleigh waves. By combining the Rayleigh wave Green function and the multi-Gaussian beam model, a three-dimensional Rayleigh wave model is presented to calculate the beam fields radiated from a rectangular transducer mounted on the Lucite wedge. Furthermore, some simulation results of the provided method are compared to those of a more exacted point source model. It is shown that the multi-Gaussian surface wave model has good capability in both computational accuracy and efficiency.

The farfield impulse response for a rectangular piston in viscous media

Calculations of the transient radiation pattern in the farfield of rectangular transducers often employ the impulse response of the velocity potential. Analytical expressions for the impulse response are known for lossless media, and similar expressions are needed for propagation in viscous media. Solutions are obtained with two different Green's functions for viscous media. One solution, which is causal, is based on an approximate Green's function for the Stokes wave equation, and the other solution, which is noncausal, is based on an approximate Green's function for the Blackstock wave equation. The impulse response is calculated with these Green's functions using the Rayleigh-Sommerfeld integral, and the results of these calculations are compared to analytical expressions for the impulse response derived for viscous media. Numerical results are obtained for a 1 mm by 1 mm square transducer evaluated in the farfield region, where the Rayleigh-Sommerfeld integral provides the reference calculated with 400 abscissas in each direction. The results show that the causal and noncausal solutions are nearly identical in the farfield region, and the analytical impulse response expressions derived from the causal and noncausal Green's functions are consistently within 1% of the Rayleigh-Sommerfeld reference in the farfield. [Work supported in part by NIH Grant R01 EB012079.]

Simulation of the Thermal and Mechanical Effects of a Planar Rectangular High Intensity Ultrasound Transducer to Be Used for Destroying Atherosclerotic Plaque

The aim of this study is to perform a simulation study of the thermal and mechanical effects of a flat rectangular (3×10 mm2),MRI compatible transducer operating at 5 MHz for the purpose of destroying atherosclerotic plaque. The simulation study focuses on measuring the plaque destruction (due to the thermal of mechanical mode of ultrasound) as a function of power, time, frequency, duty factor and pulse duration. The main goal is to keep the artery temperature at a safe level. The simulation study shows that with the thermal mode the temperature in the artery cannot be kept at a safe level.

The lossy farfield pressure impulse response for a rectangular piston

The impulse response of the velocity potential is useful for computing transient pressures in lossless media, especially for calculations in the nearfield region. Closed form expressions for the lossless impulse response of the velocity potential in the nearfield are available for circular and rectangular transducers and for several other geometries. A closed form lossless farfield expression is also available for rectangular transducers. Typically, when the effects of attenuation are introduced, the numerical calculation is performed in the frequency domain, and the time response is obtained with an inverse fast Fourier transform. To derive an equivalent analytical result directly in the time domain, all path lengths that appear in the denominator scaling term of the lossy diffraction integral are treated as constants, and a binomial expansion is applied to the path length that appears in the time delay term. The resulting analytical expression, which describes the lossy farfield pressure impulse response, is directly expressed in terms of maximally skewed stable probability density functions and cumulative distribution functions. Results are compared with the Rayleigh Sommerfeld integral, and excellent agreement is achieved in the farfield region. [supported in part by NIH Grant R01 EB012079.]

Rectangular to Circular Waveguide Converter for Microwave Devices Characterization

In this paper, a rectangular to circular waveguide converter is investigated numerically and characterized experimentally for microwave devices characterization. The converter is designed as an excitation method of circular waveguide to produce its dominant mode as the problem of circular waveguide in the excitation process. A WR248 type rectangular waveguide transducer with working frequency of 2.60–3.95GHz for TE10 mode is used as the wave exciter to be converted to a WC248 type circular waveguide. Prior to the fabrication, physical parameters of converter including length of rectangular segment, length of transition segment and length of circular segment are analyzed to obtain the optimum design. It shows that the length of transition segment affects to the return loss of converter and its length to produce TE11 mode of circular waveguide smoothly has to be more than twice of waveguide wavelength. From the result, the length of transition segment is chosen to be 275mm as it demonstrates better return loss compared to other lengths almost in the designated working frequency. To verify the design result, the prototype of converter is then realized and characterized experimentally. Furthermore, some discussion related to the results of experimental characterization is also presented.