Power Ultrasonic Transducer Research Articles

Ultrasonic system for continuous washing of textiles in liquid layers

The use of ultrasonic energy for washing of textiles has been tried several times without achieving practical development. In fact, the softness of the fibres makes the cavitation to produce small erosion effect and the reticulate structure of the fabric favours the formation of air bubble layers which obstruct wave penetration. In addition, a high proportion of water with respect to the wash load and a certain water degassing is required to assure efficiency and homogeneity in the wash performance. Such requirements have hindered the commercial development of the ultrasonic washing machines for domestic purposes. For specific industrial applications, a great part of these limitations may be overcome. This article deals with a new process in which the fabric is exposed to the ultrasonic field in a flat format. Such process has been implemented at laboratory and at semi-industrial stage by using specially designed power ultrasonic transducers with rectangular plate radiators. The cleaning effect is produced by the intense cavitation field generated by the plate radiator within a thin layer of liquid where the fabric is introduced. The homogeneity of such effect is achieved by the successive exposure of all the fabric areas to the intense acoustic field. In this paper the structure and performance of the developed system are shown.

An approach to design a high power piezoelectric ultrasonic transducer

Application of ultrasonic waves has been considerably progressed during the last decade and piezoelectric ceramics have had a common use as the driving source of such waves. However, there is not enough documented information on design and technology of manufacturing a high power ultrasonic transducer. In this paper, an attempt has been made to analyze the stress produced along the oscillating PZT employed ultrasonic head by applying the principles of acoustic wave propagation. Then, based on such analysis, general principles of PZT transducer design, excited by a DC-biased alternating electrical source, has been derived and finally a typical such transducer has been designed, manufactured and tested. By employing finite element modal analysis, the resonance frequency of the transducer was determined and compared with the experimental results. It was concluded that, the constitutive piezoelectric equations referred to in most sources and books are not valid for analyzing the acoustical dynamic stress in ultrasonic transducers. Instead, the analysis should be done with considering the dynamic behavior (elastic, damping and Inertia factors) of the problem.

Correct Prediction of the Vibration Behavior of a High Power Ultrasonic Transducer by FEM Simulation

This paper presents a study on three types of finite element analyses of high power ultrasonic transducer by using the finite element commercial software called ANSYS. The transducer geometry was treated as a 2D axi- symmetric model, 3D quart and full 3D model. For all of the simulations the modeled transducer was used in modal analysis and harmonic solutions to understand its mechanical behavior and its natural frequency. A comparison was made between each type of modeling and experimental results. This comparison allows the parameters of FEM models to be iteratively adjusted and optimized and also leads to selection of the best modeling type. The achieved FEM results exhibited a remarkably high predictive potential of ANSYS in modeling and simulation and allowed control on the design and on the vibration behavior of the high power ultrasonic transducer.

Ultrasonic enhancement of the supercritical extraction from ginger

This work examines the concurrent use of power ultrasound during the extraction of pungent compounds from a typical herb (ginger) with supercritical CO 2. A power ultrasonic transducer with an operating frequency of 20 kHz is connected to an extraction vessel and the extraction of gingerols from freeze-dried ginger particles (4–8 mm) is monitored. In the presence of ultrasound, we find that both the extraction rate and the yield increase. The higher extraction rate is attributed to disruption of the cell structures and an increase in the accessibility of the solvent to the internal particle structure, which enhances the intra-particle diffusivity. While cavitation would readily account for such enhancement in ambient processes, the absence of phase boundaries should exclude such phenomena above the critical point. Possible alternate mechanisms for the cell structure damage are discussed.

High power ultrasonic transducer with broadband frequency characteristics at all overtones and harmonics

A transducer assembly for receiving a stimulating signal and producing ultrasound therefrom at one or more frequencies, over an ultrabroad bandwidth at each frequency, includes a front mass disposed about a central axis, and a back mass disposed about the central axis, laterally offset from the front mass. The transducer assembly also includes one or more resonators disposed about the central axis and between the front mass and the back mass, including at least one electrical contact for receiving the stimulating signal. The back mass consists of a low-density material, such as aluminum, aluminum alloy, magnesium, or magnesium alloy, or any of various low-density materials known in the art. In general, the back mass is characterized by a density of less than 6.0 g/cc. In one embodiment, the front mass and the back mass are made from different materials, and the front mass includes a deviation from symmetrical symmetry.

Mass transfer enhancement in supercritical fluids extraction by means of power ultrasound

The use of high-intensity ultrasound represents an efficient manner of producing small scale agitation, enhancing mass transfer on supercritical fluids (SF) extraction processes. In this way, a supercritical CO 2 extraction of oil from particulate almonds using power ultrasound was studied. To examine the effect of the acoustic waves all experiments were performed with and without ultrasound. A power ultrasonic transducer for a working frequency of about 20 kHz was constructed and installed inside a high-pressure 5 l SF extractor. The experimental tests were carried out with CO 2 at 280 bar and 55 °C. Grounded almonds with an oil content of about 55%, in an amount of 1500 g were deposited inside the SF reactor where the solvent was introduced at a flow rate of 20 kg/h. The results show that the kinetics and the extraction yield of the oil were enhanced by 30% and 20% respectively, when a power of about 50 W was applied to the transducer. The average time of each extraction process was of about 8 h and 30 min. In addition, the transducer was also used as a sensitive probe capable to detect the phase behavior of supercritical fluids when it was driven with low power signals.

Self-demodulation acoustic signatures for nonlinear propagation in glass beads

The present Note describes some experimental work related to the nonlinear propagation of acoustic waves in granular media such as unconsolidated glass beads. The studied nonlinear effect is a self-demodulation process performed with the operation of the so-called parametric transmitting antenna. The pump (or carrier) wave is generated by a high power ultrasonic broad-band transducer (100 kHz central frequency) which is LF (low frequency, i.e., a few kHz) amplitude modulated. As the attenuation of acoustic waves increases with frequency, only the LF demodulated wave can be transmitted. A parametric study is performed where the HF central frequency is monitored between 60 and 300 kHz. The LF demodulation profile versus the HF frequency is modified, its shape being temporally derived almost twice. A numerical analysis of the order of temporal derivation is done in the Fourier domain, its value varying from 1.25 to 2.7. Qualitative agreement with current theoretical models is described, and an advanced theoretical analysis by the same authors [Phys. Rev. E 66 (2002) 041303], taking into account absorption, nonlinearity, dispersion and scattering, is briefly discussed. To cite this article: V. Tournat et al., C. R. Mecanique 331 (2003).

Measurement of ultrasonic power and electro-acoustic efficiency of high power transducers

In this paper, an improved method for the measurement of acoustic power and electro-acoustic efficiency of high power ultrasonic transducers is presented. The measuring principle is described, the experimental results are given. In comparison with traditional methods, the method presented in this paper has the advantages of simplicity, economy and practicality. The most important is that it can measure the output acoustic power and the electro-acoustic efficiency of the transducer under the condition of high power and practical applications, such as ultrasonic cleaning and soldering.

Mechanical and electrical properties of PZT ceramics (Zr:Ti=0.40:0.60) related to Nd 3+ Addition

Single phase lead zirconate titanate (PZT) of tetragonal structure (Zr:Ti=0.40:0.60) was modified using a trivalent rare earth additive Nd 2O 3. The samples having composition Pb 1-(3x/2)Nd x(Zr 0.40Ti 0.60)O 3 was prepared by solid state route. The Nd content in the samples was varied from 0–4 mol %. The effect of Nd 3+ additive on mechanical and electrical properties of PZT ceramics has been studied. It was observed that Nd addition results in enhancement of fracture toughness ( K IC) and Vicker’s hardness ( H v) in the samples. Nd addition also results in substantial increase in dielectric constant and d 33 piezo coefficient of PZT ceramics. The maximum value of K IC obtained is 2.05 Mpam 1/2. Also the peak value of 680 for dielectric constant and a d 33 of 240 pCN −1 is obtained for the same composition. Both the mechanical and electrical properties seem to peak at 2% Nd 3+ addition, which makes this composition attractive for actuator and other high power ultrasonic transducer applications. The increase in mechanical properties has been attributed the increased tetragonality (c/a ratio) and increase in sintered density with Nd addition. It seems that the ferroelastic domain switching is the main contributor to toughening in these ceramics. The increased tetragonality with Nd addition results in more work done in domain switching and, hence, enhanced toughness. The increase in electrical properties with Nd addition has been attributed to reduction in oxygen vacancies in the samples. The X-ray and the sintered density results also suggest that at 2 mol % Nd addition, Nd is reaching its solubility limit in PZT system.

New design of matching layers for high power and wide band ultrasonic transducers

Application fields of ultrasonic transducers can be divided into two categories, a high resolution required field and a high power required field. This paper's aim is to determine optimal properties of the matching layers of the transducer for each of the applications. Furthermore, its goal is to optimize the properties of the matching layers that show satisfactory performance for both of the application fields. Through the direct time domain analysis of the transmission and reflection behavior of the ultrasonic wave, apart from the conventional equivalent circuit analysis, and Fourier transformation of its results, we find the optimum acoustic impedance of the matching layers. The newly determined layers provide much better transducer performance—up to 57% more—than those obtained with conventional design methods. For the optimization, we have developed a new transducer performance evaluation parameter that can be applied to any type of ultrasonic transducers.

Considerations and guides of the wattmeter method for measuring output acoustical power of Langevin-type transducer systems — II: experiment

Experiments have been carried out on a clamped transducer system with electrical resistance loads and a transducer-horn system with water loads. The results show that the distributions of the vibration velocity amplitude of a Langevin-type vibration system change with loads and the wattmeter method implies certain theoretical errors. However, under light load conditions (< ϱVS) the error is small and the ratios of the amplitudes of two anti-nodes are almost equal under the condition of loads and without loads. The results also gave out the characteristics of power ultrasonic transducer systems, including frequency, load and power dependent characteristics of electric input impedance and electric-acoustic efficiencies. The results agree well with general linear acoustic theories. They may serve as guidelines on the wattmeter method even for applications of high-power ultrasonics, especially in sonochemistry.

Study of vibrational characteristics for piezoelectric sandwich ultrasonic transducers

Electro-acoustic efficiency is an important parameter for high power ultrasonic transducers. When a transducer is acoustically matched into its load, the electro-acoustic efficiency reaches the potential efficiency, which depends only on the transducer's unloaded parameters, not on the acoustic load. The relation between the potential efficiency and the contacting loss caused by bonding at interfaces and the relation between the potential efficiency and the dimensions of the end sections of the sandwich transducer are examined. The effects of the loss at the contacting surfaces on the transducer's resonant frequency and the potential efficiency are studied. The results show that there is an optimum design of the sandwich transducer which maximizes the potential efficiency and minimizes the effect of the contacting loss on the transducer's resonant frequency.

Fatigue strength of spot welded joints on Al-Mg alloy sheets for auto bodies: Mizukoshi, H., Namba, K. and Sano, H. Sumitomo Light Metal Tech Rep33 1 pp 22–27 (Jan 1992) (in Japanese)

In all ultrasonic processes, the power ultrasonic transducer is the essential starting point, with an understanding of this device being critical to the many applications that can follow. This chapter provides an introduction to the power transducer, including the basic vibration theory that underlies its operation, the elements of piezoelectric materials and transducer construction, the means by which transducers are controlled and characterized, and an introduction to modeling of transducer vibrations. The coverage is intended to be complementary to advanced aspects of transducers, materials, and processes treated elsewhere in this book

Power Sonic and Ultrasonic Transducers Design

<i>Power Sonic and Ultrasonic Transducers Design</i>

Sources of high intensity ultrasound—vols 1 and 2

PZT8 and PZT4 are the common “hard” piezoceramic materials used in power ultrasonic transducers (e.g., welding, cutting, sonar, etc.). PZT8 is perceived as the better choice for resonant devices, primarily due to its higher mechanical quality factor Qm. PZT8 is also considered a “harder” material compared to PZT4, since it has better stability at higher preloads and drive levels. Many transducer designers never consider PZT4 for their applications, even though it has clear advantages such as higher output (i.e., higher d33). Even the perceived advantage of PZT8 regarding Qm may not be significant for most Langevin, bolted stack type transducers if the mechanical joint losses dominate. This research is a case study on the performance of identical ultrasonic transducers used for semiconductor wire bonding, assembled with either PZT8 or PZT4 materials. The main purpose of the study is to establish rule-of-thumb transducer design guidelines for the selection of PZT8 versus PZT4 materials. Several metrics are investigated such as impedance, frequency, capacitance, dielectric loss, Qm, heating, displacement gain, and electro-mechanical coupling factor. The experimental and theoretical research methods include Bode plots, thermal IR camera imaging, scanning laser vibrometry and coupled-field finite element analysis.