Piezoelectric Ultrasonic Transducer Research Articles

Characterization of an omnidirectional parametric loudspeaker with exponential sine sweeps

An omnidirectional parametric loudspeaker (OPL) is a sound source that is made of hundreds of ultrasonic piezoelectric transducers set on a sphere. Relying on the parametric acoustic array (PAA) phenomenon, each transducer emits an ultrasonic carrier beam modulated by an audible signal. Thanks to non-linear propagation in air, natural demodulation takes place and focused audible beams are obtained. An OPL thus emits hundreds of audible sound beams in all directions. In this work, the performance of an OPL prototype containing 750 transducers set on a sphere of radius 0.125 cm is examined in free-field conditions. The frequency response, sound pressure level (SPL) and directivity are measured using exponential sine sweeps (ESS). Compared to broad band signals such as white or pink noise, the OPL can produce higher SPLs with ESS because the acoustic power concentrates on a single frequency only. This makes the OPL suitable for room acoustic measurements. A conventional dodechaedral sound source is also measured for comparison. Results show that the OPL produces a better omnidirectional sound field above ∼1 kHz, but it performs worse at lower frequencies. Moreover, it presents a flatter frequency response in all directions, although it generates lower SPL values. The Directivity Index (DI) required by the ISO 3382-2 and ISO 16283-1 standards has also been computed for both sources. The OPL cannot fulfill the requirements of the standard at low frequencies. This paper also demonstrates and discusses DI measurements of high resolution both for the new OPL and the traditional onmidirectional speakers.

Recent Development and Perspectives of Optimization Design Methods for Piezoelectric Ultrasonic Transducers

A piezoelectric ultrasonic transducer (PUT) is widely used in nondestructive testing, medical imaging, and particle manipulation, etc., and the performance of the PUT determines its functional performance and effectiveness in these applications. The optimization design method of a PUT is very important for the fabrication of a high-performance PUT. In this paper, traditional and efficient optimization design methods for a PUT are presented. The traditional optimization design methods are mainly based on an analytical model, an equivalent circuit model, or a finite element model and the design parameters are adjusted by a trial-and-error method, which relies on the experience of experts and has a relatively low efficiency. Recently, by combining intelligent optimization algorithms, efficient optimization design methods for a PUT have been developed based on a traditional model or a data-driven model, which can effectively improve the design efficiency of a PUT and reduce its development cycle and cost. The advantages and disadvantages of the presented methods are compared and discussed. Finally, the optimization design methods for PUT are concluded, and their future perspectives are discussed.

Coupling characteristics analysis of micro-emulsion cutting fluid for thickness on-machine measurement using ultrasonic

Stable and reliable coupling state between piezoelectric ultrasonic transducer and tested workpiece is very important for ultrasonic measurement. Traditional coupling agents need to be smeared manually or recycled separately, which cannot meet the requirement of on-machine thickness measurement by ultrasonic. Herein, a suitable coupling agent is selected for thickness on-machine measurement in industrial application of ultrasonics. The acoustic impedance and the attenuation coefficient are adopted to characterize the coupling effect of coupling agents and appropriate coupled flow field is selected theoretically. The experimental system of ultrasonic on-machine measurement is established with external circulating jet. The coupling characteristics of machining coolant liquid is calculated and analyzed. From experimental comparison with commonly used coupling agents, it is indicated that the micro-emulsion cutting fluid with volume concentration from 8% to 10% could be selected as compatible coupling agent for ultrasonic on-machine measurement, because it can not only meet the ultrasonic measurement requirements, but also perform friendly to industrial environment.

Design of Piezoelectric Ultrasonic Transducer Based on Doped PDMS

The performance of the ultrasonic transducer will directly affect the accuracy of ultrasonic experimental measurement. Therefore, in order to meet the requirements of a wide band, a kind of annular 2-2-2 piezoelectric composite is proposed based on doped PDMS. In this paper, the transducer structure consisted of PZT-5A piezoelectric ceramics and PDMS doped with 3 wt.% Al2O3:SiO2 (1:6) powder, which constituted the piezoelectric composite. MATLAB and COMSOL software were used for simulation. Meanwhile, the electrode materials were selected. Then, the performance of the designed annular 2-2-2 ultrasonic transducer was tested. The simulation results show that when the polymer phase material of the piezoelectric ultrasonic transducer is doped PDMS, the piezoelectric phase and the ceramic substrate account for 70% of the total volume, the polymer phase accounts for 30% of the total volume, and the maximum frequency band width can reach 90 kHz. The experimental results show that the maximum bandwidth of −3 dB can reach 104 kHz when the frequency is 160 kHz. The results of the electrode test show that the use of Cu/Ti electrode improves the electrical conductivity of the single electrode. In this paper, the annular 2-2-2 transducer designed in the case of small volume had the characteristics of a wide frequency band, which was conducive to the miniaturization and integration of the transducer. Therefore, we believe that the annular 2-2-2 piezoelectric composite has broad application prospects.

Investigation of the Performance of a Piezoelectric Ultrasonic Transducer by Finite Element Modeling

Investigation of the Performance of a Piezoelectric Ultrasonic Transducer by Finite Element Modeling

Piezoelectric Single Crystal Ultrasonic Transducer for Endoscopic Drug Release in Gastric Mucosa.

Modern advanced minimally invasive surgery has been implemented for most of the significant gastrointestinal diseases. However, patients with coagulopathy or unresectable tumors cannot be cured by current treatment methods. Moreover, other existing medical devices for targeted drug release are too large to be applied in gastric endoscope because the diameter of the biopsy channel is smaller than 3 mm. To address it, in this work, we developed a piezoelectric single crystal ultrasonic transducer (the diameter was only 2.2 mm and the mass was 0.076 g) to produce acoustic waves, which could promote the drug release in the designed position of the digestive tract through an endoscope. It exhibited the electromechanical coupling coefficient of 0.36 and the center frequency of 6.9 MHz with the -6-dB bandwidth of 23%. In in vitro sonophoresis experiment, the gastric mucosa permeability to Bovine Serum Albumin increased about 5.6 times when the ultrasonic transducer was activated at 40 [Formula: see text] and 60% duty ratio, proving that employment of this transducer could facilitate drug penetration in the gastric mucosa. Meanwhile, the permeability could be adjusted by tuning the duty ratio of the ultrasonic transducer. The corresponding sonophoresis mechanism was related to the acoustic streaming and the thermal effect produced by the transducer. In addition, the measured maximum power density was 128 mW/cm2 and the mechanical index of the ultrasonic transducer was 0.02. The results held a great implication for applications of the transducer for targeted drug release in the gastrointestinal tract.

Intelligent Optimization of Matching Layers for Piezoelectric Ultrasonic Transducer

The performance of piezoelectric ultrasonic transducer (PUT) is obviously affected by its matching layer. An intelligent optimization method for matching layer of PUT is proposed to fabricate PUT with high performance. The original data, including matching layer and performance parameters of PUT, is obtained by PiezoCAD software. Then the neural network models are established to mathematically characterize the effect of matching layer on the performance of PUT. The optimization criteria for PUT is constructed according to its performance requirements, such as center frequency (CF), bandwidth (BW) and pulse width (PW). In order to decrease the material cost, the thicknesses of matching layers are also considered in the optimization criteria. The modified particle swarm optimization algorithm is used to optimize the thicknesses of matching layers (Ag-epoxy and Parylene C). According to the designed performance, the optimized thicknesses of Ag-epoxy and Parylene C are about $54~\mu \text{m}$ and $21~\mu \text{m}$ , respectively. Based on the optimized thicknesses of matching layers, the simulated and experimental performances of PUT well agree with the designed ones. In addition, compared to the traditional quarter-wavelength theory, the proposed method can effectively decrease the materials cost. The −6dB BW and PW of PUT fabricated according to the optimized parameters are about 68.5% and $0.123~\mu \text{s}$ , which are better than that fabricated according to the quarter-wavelength theory (about 50% and $0.147~\mu \text{s}$ ).

Analytical and Numerical Study of Pre-Stress Effect in Piezoelectric Sandwich Type Ultrasonic Transducer

In this paper, the effect of pre-stress condition on the resonance frequency of the transducer is studied by using numerical and analytical methods. To compare the obtained results, two sandwich-type transducers with nominal frequency of 25 kHz and 30 kHz are considered. Experimental determination of pre-stress value in transducer is described and measured. Then resonance frequency of transducers in the presence of pre-stress is determined by impedance analyser. Numerical analysis is conducted by modelling three-dimensional transducer in details at ABAQUS software. The resonance frequency is determined with and without pre-stress. The FE results show that by applying pre-stress on the transducers, the resonance frequency of transducers decreased. Furthermore, the FE results are very close to experimental results. Furthermore, a systematic analytical solution is presented based on one-dimensional wave propagation. The resultant displacement for each sub-section of the transducer is calculated and then all of them are assembled and solved by considering the continuity conditions of displacement and force components. It is found that pre-load condition that is produced by central bolt reduces resonance frequency of the transducer. The obtained analytical results provide fast and reliable model for predicting resonance frequency of transducer.

Precise experimental determination of electrical equivalent circuit parameters for ultrasonic piezoelectric ceramic transducers from their measured characteristics

The letter is devoted to a method for determining electric equivalent circuit parameters of piezoelectric ceramic transducers from their resonance characteristics. These parameters represent equivalents of mechanical damping, effective weight of the oscillating element, compliance of the mechanical element and static capacitance associated with the transducer material. This method is considered cost efficient, focuses on transducers commonly available on the market and is presented on a specific transducer – transmitter. The acquired parameters are important for performing subsequent simulations and defining their suitability for a particular application. However, these parameters are not included in the usual technical documentation of the commercially available piezoelectric ceramic transducers. The key part of this letter is an iterative process of finding the parameters. Before starting the iteration process, it is very important to set default values of these parameters. Then, a linearized system of equations, based on expressing a real part of the impedance, is used to determine these parameters. The advantage of this method is its simplicity to measure only the two above-mentioned characteristics, from which the required parameters can be then calculated. Thus, there is no need for expensive circuit analyzers, which are able to determine these parameters directly. Although the iterative process includes a large number of steps, and therefore can be relatively time consuming, it can be performed on a commercially available computer technology.

Use of piezoelement in ultrasound generation

At present, ultrasonic (piezoelectric) transducers are the most promising electromechanical transducers for use in miniature electronic devices. However, the calculation of the piezoelectric element for an ultrasonic environment poses certain problems due to the large number of problems to be solved and its nonlinearity. The article describes the principles of operation of the piezoelectric element, analyzes their advantages and disadvantages, gives the characteristics of the piezoelectric elements, as well as proposes an algorithm for calculating the frequency characteristics of the piezoelectric element based on the electrical model of the piezoelectric element.

Compact Laser Driver for Ultrasonic Arbitrary Position and Width Pulse Sequences Generation

Laser ultrasound offers several benefits in comparison to immersion or air-coupled ultrasound: it directly generates stress on the sample surface; it has a wide bandwidth and a small acoustic source can be produced. Conventionally, high-power pulsed lasers are required therefore equipment is bulky and expensive. Here we propose to use mid-power laser diodes, which are small and low cost. To solve the low signal amplitude problem with lower power lasers, the use of spread spectrum signal, arbitrary position, and width binary pulse sets is proposed. To date, a laser driver for this task has not been available. This article describes the development of such a compact driver, where the essential electronics occupy an area of $10\,\,\times20$ mm. The whole system with a fixture for kinematic mount is comparable in size to a conventional piezoelectric ultrasonic transducer. The driver can supply pulse sets of up to 40 A. Individual pulse duration can vary between 20 and 1000 ns (0.5–25-MHz ultrasound range) and the total pulse train duration is limited by the laser type used. Experiments show that up to 10- $\mu \text{s}$ long pulse sets can be used at 10-A current, without laser degradation. Current waveforms, beam profile, and optical response signals were measured for three rectified topologies. It was concluded that the GaN-based constant current switch topology has the best performance, but a power MOSFET in a source current feedback topology can also be used to generate pulses down to 20 ns. Photoacoustic response signals from chirp and phase shift keying modulation have been demonstrated.

Laser-Excited Acoustics for Contact-Free Inspection of Aerospace Composites

Ultrasonic testing (UT) is widely used for the nondestructive testing (NDT) of composite materials in the aerospace industry. Liquid-coupled piezoelectric ultrasonic transducers are the most common technology used in this field; however, liquid coupling agents are not always practical, economical, or compatible with materials that cannot get wet. Alternative couplant-free technologies such as air-coupled ultrasound or laser ultrasound (LUS) are available, but either lack the required sensitivity and resolution, or are very costly, large, and sensitive to surface condition and properties. In this paper, we introduce a new couplant-free approach using laser excitation and a commercially available optical micro-phone. This technique is termed laser-excited acoustics (LEA) NDT, which combines the advantages of a contact-free ultrasound technology with the potential for improved sensitivity and resolution required for NDT in industrial environments. We will demonstrate the capabilities of LEA on aerospace composite parts made of carbon and glass fiber–reinforced polymer (CFRP/GFRP) under realistic conditions.

Laser-Excited Acoustics for Contact-Free Inspection of Aerospace Composites

Ultrasonic testing (UT) is widely used for the nondestructive testing (NDT) of composite materials in the aerospace industry. Liquid-coupled piezoelectric ultrasonic transducers are the most common technology used in this field; however, liquid coupling agents are not always practical, economical, or compatible with materials that cannot get wet. Alternative couplant-free technologies such as air-coupled ultrasound or laser ultrasound (LUS) are available, but either lack the required sensitivity and resolution, or are very costly, large, and sensitive to surface condition and properties. In this paper, we introduce a new couplant-free approach using laser excitation and a commercially available optical micro-phone. This technique is termed laser-excited acoustics (LEA) NDT, which combines the advantages of a contact-free ultrasound technology with the potential for improved sensitivity and resolution required for NDT in industrial environments. We will demonstrate the capabilities of LEA on aerospace composite parts made of carbon and glass fiber–reinforced polymer (CFRP/GFRP) under realistic conditions.

Flexible piezoelectric micro ultrasonic transducer array integrated on various flexible substrates

Flexible ultrasonic transducers have attracted much attention in industrial and biomedical applications. However, most of them are fabricated based on a single substrate by complex micromachining techniques. In this paper, a bending mode based flexible piezoelectric micro ultrasonic transducer (PMUT) array has been designed and fabricated through an improved simple and robust adhesive bonding fabrication process. The developed flexible PMUT array consists of 3 × 3 elements and its resonant frequency is about 161 kHz. Our device can be fabricated on various flexible substrates and pasted on concave, convex, and undulant surfaces, reaching an output signal of 75 mVpp under 100 Vpp excitation. The characterizations of the device were performed to verify its excellent flexibility, mechanical stability, and lifespan. Its acoustic performance was also evaluated using diverse time of flight (TOF) tests in air ambient, demonstrating its potential use in flexible acoustic devices or wearable range finder.

An ultrasonic flowmeter for liquid flow measurement in small pipes using AlN piezoelectric micromachined ultrasonic transducer arrays

This paper firstly proposes an ultrasonic liquid flowmeter based on AlN piezoelectric micromachined ultrasonic transducer arrays. By detecting the transit time of ultrasonic wave, the flowmeter can measure liquid flow in small pipes (8 mm), which is difficult for traditional bulk piezoelectric ultrasonic transducers. In the flowmeter, the acoustic path and flow path are overlapped, which greatly improves sensitivity compared with the typical structure. The cross-correlation method is used to determine the ultrasonic transit time, which can effectively reduce the influence of signal noise and amplitude change. The maximum measurement error of the flowmeter is less than 5% in the flow range of 0–3.36 l min−1.

Analytical model and optimal focal position selection for oblique point-focusing shear horizontal guided wave EMAT

As an important application in nondestructive testing (NDT) technology, ultrasonic guided wave testing is widely used in the detection of defects in metal plates, pipes, and bridges. In the detection of defects in metal plates, electromagnetic acoustic transducers (EMATs) can easily excite shear horizontal (SH) guided waves, and a couplant is not required, in contrast to piezoelectric ultrasonic transducers. However, the low energy conversion efficiency of an EMAT has always been its main drawback. Therefore, in this work, we propose a new oblique point-focusing SH (OPFSH) EMAT configuration and obtain two analytical models for both continuous sine pulses and burst signals. The proposed transducer can achieve high-sensitivity detection of defects in the focal area. Moreover, the influence of the focal position on the signal intensity is also studied, and an optimal focal position selection method is demonstrated through simulation and experimental methods. By performing finite element calculations of the wave fields at different focal positions, we find that the optimal focal points are approximately distributed along a line. Therefore, the optimal focal position should be selected carefully to achieve the best OPFSH-EMAT focusing performance.

Optimization design of a new type of high-frequency piezoelectric ultrasonic transducer with the compliant hinge-based mounting clamp

Piezoceramic-based ultrasonic transducers are widely used in the fabrication and packaging of the microelectronic device and their performance largely depends on the ultrasonic energy delivery efficiency (UEDE) which can be reflected by the tip vibration amplitude output (TVAO) of the transducer indirectly. Recently, it was reported that a new type of flexure hinge-based mounting clamp could enhance the TVAO of the transducer significantly. To get the best effect, this research aimed at developing an optimization method for this newly proposed mounting clamp. For the purpose, a series of researches were performed against a self-developed transducer equipped with a pair of circular notched hinge-based mounting clamps. Firstly, the influential rules of several key geometric parameters of the flexure hinge on the TVAO of the ultrasonic transducer were explored. Then, an optimization objective function together with a group of constraints was constructed. Next, the Particle Swarm Optimization (PSO) algorithm was used to optimize the geometric parameters of the circular hinge-based mounting clamp. Finally, the performance of the optimized mounting clamp was tested based on a measurement and evaluation system. The results show the optimized mounting clamp can enhance the TVAO of the transducer greatly, presenting a good improvement effect of the UEDE, and manifesting the feasibility and effectiveness of the developed method.

Applying ultrasonic fields to separate water contained in medium-gravity crude oil emulsions and determining crude oil adhesion coefficients

Separating produced water is a key part of production processing for most crude oils. It is required for quality reasons, and to avoid unnecessary transportation costs and prevent pipework corrosion rates caused by soluble salts present in the water. A complicating factor is that water is often present in crude oil in the form of emulsions. Experiments were performed to evaluate the performance of ultrasonic fields in demulsifying crude oil emulsions using novel pipe-form equipment. A horn-type piezoelectric ultrasonic transducer with a frequency of 20 kHz and power ranging from 80 W to 1000 W was used for experimental purposes. The influences of the intensity of ultrasonic fields, ultrasonic irradiation time, and the initial water content of crude oils were evaluated to establish the rate of water segregation from oil. The experiments applied ultrasonic-field intensities of 0.25 W/cm3, 0.5 W/cm3, 0.75 W/cm3 and 1 W/cm3 to synthetic emulsions with 10%, 15%, 20%, and 25% of the water in crude oil. Crude oil demulsification occurred for each ultrasonic field intensity tested for all the samples tested. Function β involving adhesion coefficients was expressed in terms of wave-field intensity and initial concentration of water in each of the three crude oil samples tested. The experiments demonstrated that despite the absence of any chemical demulsifier involved, water separation caused by applying ultrasonic fields was effective and occurred rapidly. As the intensity of the ultrasonic field applied increased, the amount of water segregated from crude oil also increased. Subjected to constant field intensity, higher initial water cuts (up to 15% or so) in the crude oil samples and higher ultrasonic irradiation times, resulted in greater segregation of water from crude oil in percentage terms. However, in samples with initial water cuts of 20+% long irradiation times (~5 min), resulted in a decline in water separation compared to 2-min tests. Ultrasonic field treatments offer commercially-viable and environmentally-friendly alternatives to treatments using chemical demulsifiers as they reduce desalination requirements of wastewater.

Electrical tuning for sensitivity enhancement of a piezo-electric ultrasonic transducer: Simulation and fabrication

In this study, two simple electrical impedance tuning methods derived from Krimholtz, Leedom, and Matthaei (KLM) modeling were proposed for increasing the sensitivity of a piezo-electric material-based ultrasonic transducer. In the first method, the reactance components of the ultrasonic transducer were removed, and in the other method, the electrical impedance of an ultrasonic transducer was matched to that of the ultrasonic system. To these ends, electrical circuits composed of inductors and capacitors were de-signed and KLM simulations of the two methods were performed. To verify the simulation results, ultrasonic transducers were fabricated and operated under the same conditions as in the simulations, and the experimental results were compared with the simulated results. In conclusion, the electrical tuning method (elimination of the reactance compo-nents) was more effective and the transducer circuit structure was simpler. The experi-mental results showed good agreement with the KLM simulation results.

Radial Vibration Characteristics of Piezoelectric Ceramic Composite Ultrasonic Transducer

Different from the existing equivalent circuit analysis method of the transducer, based on the vibration theory of the mechanical system and combined with the constitutive equation, this paper analyzes the radial vibration characteristics of the transducer. The piezoelectric ceramic composite ultrasonic transducer is simplified as a mechanical model of a composite thick wall tube composed of a piezoelectric ceramic tube and a metal prestressed tube. The mathematical model of radial vibration of the transducer is established, which consists of the wave equation of radial coupling vibration of the piezoelectric ceramic tube and the metal prestressed tube, the continuity conditions, and the boundary conditions of radial vibration of composite thick wall tube. The characteristic equation and the mode function of radial vibration are derived. The calculated results of natural frequency are in good agreement with the existing experimental results. Based on the analytical method and the difference method, the numerical simulation models of radial vibration are established, and the amplitude-frequency characteristic curves and the displacement responses are given. The simulation results show that the amplitude-frequency characteristic curves and the displacement responses of the two methods are the same, which verifies the correctness of simulation results. Through the simulation analysis, the influence rule of the transducer’s structure sizes on its radial vibration natural frequency is given: when the thickness of the metal prestressed tube and the piezoelectric ceramic tube are constant, the natural frequency decreases with the increase of the inner diameter of the piezoelectric ceramic tube; when the outer diameter of the metal prestressed tube and the inner diameter of the piezoelectric ceramic tube are constant, the natural frequency decreases with the increase of the thickness-to-wall ratio. The calculation method of natural frequency based on elastic vibration theory is clear in concept and simple in calculation, and the simulation models can analyze the mechanical vibration of the transducer.