Lithium tetraborate transducers

Lithium tetraborate is a tetragonal material of considerable promise for frequency control and signal processing applications. It exhibits piezoelectric coupling values that fall between those of lithium niobate and quartz, but possesses orientations for which the temperature coefficient of frequency and delay time is zero for bulk and surface acoustic waves. The properties of two doubly rotated bulk wave resonator orientations having first- and second-order temperature coefficients equal to zero are discussed. These are suitable for shear and compressional wave transducers in applications where very low temperature sensitivity is required simultaneously with moderately strong piezocoupling coefficients.     

Flexible ultrasonic transducers

Flexible ultrasonic transducers (UTs) consisting of a metal foil, a piezoelectric ceramic film, and a top electrode have been developed. The flexibility is realized owing to the porosity of piezoelectric film and the thinness of metal foil. In this paper, the stainless steel (SS), lead-zirconate-titanate (PZT)/PZT composite and silver paste were chosen as metal foil, piezoelectric film, and top electrode materials, respectively. The SS foil serves as both substrate and bottom electrode. The PZT/PZT piezoelectric composite film is made by the sol-gel spray technique. PZT/PZT films of thicknesses from 40 to 70 microm were fabricated onto SS foils. The capability of these flexible sensors operated in the pulse-echo mode for nondestructive testing on flat and curved surfaces of different materials at room temperature and 160 degrees C has been demonstrated. Numerical simulations of the effects of the metal foil thickness on the ultrasonic performance of flexible UTs also were carried out, and the results are in reasonable agreement with experimental data. In addition, a PZT/PZT flexible transducer showed a signal strength comparable with that obtained by a commercial room temperature broad bandwidth transducer.     

Materials and transducers for ultrasonic flowmeters

The construction and operation of a lead zirconate-titanate (TsTS-19) piezoelectric transducer as a component of the model UZR-V ultrasonic flowmeter with an Akustron counter is analyzed. Techniques are proposed for enhancing the operating efficiency of ultrasonic flowmeters. The study has resulted in the development of the UZD-1 and UZD-3 transducers, which utilize the new materials and have parameters superior to those of a standard transducer using TsTS-19 ceramic. The new transducers are recommended for systems designed to monitor cold and hot water flow in conduits from 30 mm to 1000 mm in diameter.Translated from Izmeritel'naya Tekhnika, No. 7, pp. 57–58, July, 1993.     

Self-focused ZnO transducers for ultrasonic biomicroscopy

A simple fabrication technique was developed to produce high frequency (100 MHz) self-focused single element transducers with sputtered zinc oxide (ZnO) crystal films. This technique requires the sputtering of a ZnO film directly onto a curved backing substrate. Transducers were fabricated by sputtering an 18 μm thick ZnO layer on 2 mm diameter aluminum rods with ends shaped and polished to produce a 2 mm focus or f-number equal to one. The aluminum rod served a dual purpose as the backing layer and positive electrode for the resultant transducers. A 4 μm Parylene matching layer was deposited on the transducers after housing and interconnect. This matching layer was used to protect the substrate and condition the transfer of acoustic energy between the ZnO film and the load medium. The pulse-echo response for a representative transducer was centered at 101 MHz with a -6 dB bandwidth of 49%. The measured two way insertion loss was 44 dB. A tungsten wire phantom and an adult zebrafish eye were imaged to show the capability of these transducers.     

New transducers for high-resolution ultrasonic testing

High resolution NDT requires ultrasonic transducers which can produce very short pulses with well-defined constant shape throughout the field. The theory, construction and applications of such transducers are discussed.     

Reproducibility of properties of niobate ferro-piezoelectric ceramic for mechanical-loading transducers

The reproducibility of the properties of niobate ferro-piezoelectric ceramics of various compositions is studied. It is shown that its parameters and metrological properties make SPK-1 a promising materal for highly sensitive high-frequency mechanical-loading transducers. Translated from Izmeritel'naya Tekhnika, No. 7, pp. 56–60, July, 2000.     

Choosing ultrasonic flow transducers

We consider flowmeters using piezoelectric transducers attached to pipes; these devices are characterized by high error and low sensitivity. Translated from Izmeritel'naya Tekhnika, No. 10, pp. 18–20, October, 1997.     

Disposable PVDF ultrasonic transducers for nondestructive testingapplications

Disposable ultrasonic contact transducers have been constructed with inexpensive PVDF films for nondestructive testing (NDT) applications. This paper reports the temperature-dependent ultrasonic performance of commercial polyvinylidene fluoride (PVDF) films and PVDF sensors. PVDF film was evaluated for its material properties of interest for ultrasonic transducer performance including the relative dielectric constant ε_r, dielectric loss tangent tan δ_e , electromechanical coupling constant k_t, mechanical quality factor Q_m, and acoustic impedance Z. Disposable PVDF transducers were then coupled to both low and high acoustic impedance test panels and their ultrasonic insertion loss/sensitivity and frequency bandwidth measured as a function of temperature in both the pulse-echo and pitch-catch modes. The results yielded center frequencies in the 3.5-16 MHz range, with -6-dB fractional bandwidths for some of the transducers exceeding 100%. The temperature dependence of the transducers' performance is reported for the -40 to 80°C range and shows an approximate linear decrease in center frequency and increase in fractional bandwidth with increasing temperature. These measured results are compared with predictions from computer simulations based on Mason's model. These tests showed that the same disposable transducers can be used for both ultrasonic and acoustic emission sensing NDT applications. This paper summarizes the quantitative ultrasonic and vibration sensing performance for all of the disposable PVDF film transducers which were tested     

Broadband EMFi-based transducers for ultrasonic air applications

In this work, we explore the possibilities of electromechanical film (EMFi) as a new material for developing broadband transducers for ultrasonic air applications. The advantages of the EMFi film are its wide usable frequency range and easiness to use, making it highly suitable for self made, customizable ultrasonic sensors. This paper presents theoretical and experimental information focused on the needs of the sensor's end user, namely, frequency response, actual dynamic mass and Young's modulus, bandwidth, sensitivity, electromechanical dynamical model, acoustic response, and directivity. It is found empirically that the behavior of the film as an almost ideal piston-like acoustic source permits accurate prediction of the characteristics of transducers built on a developable surface. The results obtained represent the first step to more complex geometries, and, ultimately, to completely customizable field ultrasonic transducers.     

Micromachined ultrasonic capacitance transducers for immersion applications

Investigations into the characteristics of water-coupled ultrasonic capacitance transducers have been undertaken for a range of transducer configurations. The radiated fields have been scanned in water using a miniature hydrophone detector, and the results compared to theory based on a plane piston approach. Micromachined backplates in conjunction with thin Mylar and mica membranes have been investigated, together with aperture modifications such as an annulus and Fresnel zone plate. The measured results agree well with theory, thus demonstrating that wideband predictable performance (>8 MHz) is obtainable with such transducers. Additionally, pulse-echo C-scans of a Plexiglas plate containing an artificial defect have been undertaken with the capacitance transducer, in order to demonstrate that the capacitance transducer has sufficient sensitivity to allow routine nondestructive testing within immersion applications.     

用于超声清洗复合振动换能器的研究

本文研究了一种由纵向振动夹心式压电超声换能器与弯曲圆盘组成的用于液体中超声处理的复合振动辐射器。推出了恢复合振动系统的共振频率设计方程，分析了各个振动模式的机电转换特性及其声波辐射特性，测量了振动系统的共振频率及其有效机电耦合系数。从实验及理论结果可以看出，振动系统的频率测试值与设计值基本符合。在一定的共振频率上，该振动系统具有最大的有效机电耦合系数，是一种很有前途的功率超声辐射器。     

Piezo-polymer transducers for ultrasonic imaging in air

Airborne polyvinylidenefluoride transducers have been designed for robotic applications in air. Characteristics of transducer prototypes are: working frequencies from 61 kHz to 86 kHz, quality factor Q from 4 to 6, and two-way insertion loss of about 90 dB. The small dimension, the lightness, and the low-cost fabrication technology allow the development of arrays or matrices for ultrasonic imaging systems in air. In this work two different image reconstruction algorithms are proposed: the first carries out a combined spectral and aperture synthesis for detecting isolated scatterers with a spatial resolution of about 2 mm; the second is based on an accurate ranging algorithm with sub-millimeter resolution at distances up to 50 cm. Finally, this work's application to the reconstruction of three-dimensional object profiles is discussed.     

Lithium niobate guided-wave beam former for steering phased-array antennas

We present the theoretical investigation, design, and simulation of a novel guided-wave optical processor for L-band-transmission beam forming in a linear array of phased active antennas. The proposed configuration includes two contradirectional surface acoustic-wave transducers, and it is based on a Y-cut, X-propagating Ti:LiNbO(3) planar waveguide supporting the lowest-order modes of both polarizations (TE(0) and TM(0)) at the free-space wavelength λ = 0.85 μm. A detailed comparison between the processor we propose and other optical and electronic architectures reported in the literature is carried out, exhibiting a number of significant advantages in terms of weight, total chip size, and power consumption, when the number of antenna elements is greater than 50.     

Surface micromachined capacitive ultrasonic transducers

The current state of novel technology, surface microfabricated ultrasonic transducers, is reported. Experiments demonstrating both air and water transmission are presented. Air-coupled longitudinal wave transmission through aluminum is demonstrated, implying a 110 dB dynamic range for transducers at 2.3 MHz in air. Water transmission experiments from 1 to 20 MHz are performed, with a measured 60 dB SNR at 3 MHz. A theoretical model is proposed that agrees well with observed transducer behavior. Most significantly, the model is used to demonstrate that microfabricated ultrasonic transducers constitute an attractive alternative to piezoelectric transducers in many applications.     

Electroacoustic model for electrostatic ultrasonic transducers withV-grooved backplates

Capacitive ultrasonic transducers are widely used to generate airborne ultrasound. This paper presents an equivalent circuit for an electrostatic transducer with a V-grooved backplate. The comparison between simulation results and measurements on a prototype transducer shows that the model gives reliable results. This model is useful in many applications, for example to simulate sensors in a robot and to design ultrasonic transducer systems     

Triple-beam lens transducers for three-dimensional ultrasonic fluidflow estimation

This paper reports on estimating the 3-D flow velocity vector of blood with ultrasound triple-beam lens transducers. The design, construction, and characterization of experimental lens transducers is described along with the theory of 3-D flow velocity estimation. A triple beam lens transducer consists of three piezoelectric elements mounted on the top surface of a lens. The lens acts to direct and focus the ultrasound from the elements such that three parallel, closely spaced ultrasound beams are generated. Blood cell scatterers are tracked as they move along the beams and from beam to beam using RF correlation techniques. Lenses from fused quartz and aluminum have been designed and fabricated, and the characteristics of the lenses along with lens design considerations and tradeoffs are discussed. The three-dimensional flow velocity vector of fluid in a blood flow phantom has been experimentally measured with an aluminum lens, indicating that the accurate estimation of the 3-D blood flow velocity vector is possible     

An accurate model for capacitive micromachined ultrasonic transducers

Modeling of capacitive micromachined ultrasonic transducers (cMUTs) is based on a two-port network with an electrical and a mechanical side. To obtain a distributed model, a solution of the differential equation of motion of the diaphragm for each element of the transducer has to be found. Previous works omit the mechanical load of the cavity behind the diaphragm, i.e., the effect of the gas inside. In this paper, we propose a distributed model for cMUTs that takes this effect into account. A closed-form solution of the mechanical impedance of the membranes has been obtained, including the effect of the restoring forces because of the stiffness of the membrane and because of the compression of the air in the cavity. Simulation results based on the presented model are compared with the experimental data for two types of cMUTs reported in the recent literature. It is demonstrated that the compression of the air has a significant effect on the fundamental frequency of the air transducer, with a deviation of about 22% from the prediction of a model that does not consider the interaction between the vibrating diaphragm and the air cushion     

MEMS ultrasonic transducers for the testing of solids

Arrays of capacitive diaphragm ultrasonic transducers could potentially be used for non-destructive ultrasonic testing and structural monitoring. In this paper, we consider the efficiency of coupling of these transducers to solid media. We show that efficient coupling can be realized by using a silicone coating as a coupling medium. We present the results of experimental characterization of ultrasonic transducers coupled to solids in this way. We show that these transducers can be used with piezoelectric emitting transducers within the range from 1 to 5 MHz, and we demonstrate the use of several transducers as a phased array to determine the direction and distance of an ultrasonic source.