压电复合材料宽带横波换能器的实验研究

本文用实验方法研究了２－２压电复合材料的厚度切变特性，定性地给出了２－２压电复合材料的性能与ＰＺＴ相体积百分比，以及与共振频率牟关系。并用这种材料作为换能元件，制作出高灵敏度窄脉冲横波换能器。     

1-3型压电复合材料非均匀振动换能器的研究

通过调整1－3型压电复合材料换能器中压电相的分布，可以控制换能器辐射面上振动幅度和相位的分布，从而获得具有特殊性能的声场．作为辐射源表面振动速度等相位不等幅和等幅不等相位的两种典型情况，本文对边线高斯型换能器和Wesnel聚焦换能器进行了实验研究，讨论了其声场特性．     

压电复合材料换能器

压电复合材料是将压电陶瓷与聚合物材料按一定的连通方式、一定的体积百分比和一定的空间分布复合而成的。它可以提高材料的某些压电性能,并具有常用压电陶瓷材料所没有的某些优良性能。在过去的十几年中材料研究者们做了大量工作并取得实用性进展。     

1-3型压电复合材料非均匀振动换能器的研究

通过调整１－３型压电复合材料换能器中压电相的分布，可以控制换能器辐射面上振动幅度和相位的分布，从而获得具有特殊性能的声场。     

面切变压电复合材料及其换能器

本文通过控制压电相在压复合材料中的分布工，把四块完全相同的等腰直角三角形２－２型压电复合拼材料拼接起来，四个直角顶点位于晶片的中心，     

高频宽带嵌套式复合材料换能器

研制了一种嵌套式高频宽带复合材料换能器,利用1-3型压电复合材料Q值较低、频带较宽的特点,采用组合式的结构拓展换能器的工作带宽。通过切割框型压电陶瓷、灌注环氧树脂得到压电复合材料框型敏感元件,再将不同厚度的框型敏感元件沿轴向嵌套从而制成多层嵌套的压电复合材料敏感元件。建立1-3型压电复合材料中压电小柱的等效电路,根据等效电路计算出压电小柱的谐振频率,并与1-3型压电复合材料的谐振频率理论计算结果进行对比。通过ANSYS软件对敏感元件结构进行仿真,并根据仿真结果确定了敏感元件的最佳设计方案。最终制作出的换能器进行水下测试,该换能器的谐振频率为310 kHz,最大发送电压响应为188.5 dB,-3 d B带宽可达130 kHz,接收灵敏度最大可达-186.8 dB,-3 dB带宽可达90 kHz,谐振频率处-3 d B的指向性开角约为2.4°。该嵌套式敏感元件可实现换能器宽带发射与接收声波的目标。     

一种高灵敏压电平面水声换能器

设计并制作了一种高灵敏压电平面水声换能器。该换能器敏感元件是对1-3-2型压电复合材料结构的改进,即在带基底的压电陶瓷小柱阵列间不注入聚合物,并在其上表面直接覆盖金属板,构成“带基底的压电小柱阵列+金属盖板”结构敏感元件(称为“空气填充型”敏感元件)。对“空气填充型”敏感元件的谐振频率进行了理论计算和有限元仿真,与实测结果较吻合。为便于对比性能,同时制作了同尺寸“1-3-2型压电复合材料+金属盖板”结构敏感元件(称为“聚合物填充型”敏感元件)换能器。分别对“空气填充型”和“聚合物填充型”敏感元件换能器的有效机电耦合系数、发送电压响应和接收灵敏度进行有限元仿真和实测,结果均显示,“空气填充型”敏感元件换能器具有较高的接收灵敏度,相较于“聚合物填充型”敏感元件换能器可提高21 dB。该敏感元件换能器能有效提高灵敏度,可为研制高灵敏换能器提供参考。     

检测超声换能器用1-3型压电PZT/环氧复合材料及换能器的研究

本文介绍了一种制做1—3型压电 PZT/环氧复合材料的新方法.此方法采用了PZT小柱非周期性均匀分布,有效地消除了由于PZT小柱周期性分布而产生的有害横向结构共振模式,获得了振动模式较单纯的1—3型压电复合材料晶片,研制出宽带(低Q)换能器及高斯型换能器.     

对2-2型压电复合材料横波换能器产生的纵波特性的研究

在固体测量中，横波换能器所产生的波列中常伴随有纵波，认识纵波产生的原因可以解释横波测试中出现的现象，以及抑制纵波提供有效的方法，本文利用实验研究的方法，用一对纵波偶极子换能器的对比实验，分析了２－２型压电复合材料厚度切变换能器产生纵波的机理，发现这是一种伴随着晶片厚度切变振动而产生的“偶极子”纵波，并由此解释了这种纵波的伴随性，频率特性及其首波与横波首波位相相反等问题。     

一种用于线阵换能器的三相压电复合材料

本文介绍了一种具有２－２结构特征的三相压电复合材料的结构及其制备方法，并与一种二相压电复合材料的类似结构对对比，进行了横向耦合，频率特性，声阻抗和介电性能等方面的测试和讨论，同时介绍了这种三相复合成功地应用于线阵换能器的结果。     

Nonlinear characterization with burst excitation of 1-3 piezocomposite transducers

Ultrasonic transducers made with 1-3 connectivity piezocomposites are frequently used in Medical applications and nondestructive testing. When the transducer is used for special applications as, for instance air-coupled transmission, it is necessary to compensate for the high difference of acoustic impedance between transducer and medium using high amplitude pulses to generate high acoustic signal. Thus, the nonlinear behavior of the transducer must be taken into account in similar application conditions. The newly developed method, which performs the nonlinear characterization with burst signal excitation near the thickness resonance frequency, is based on the measure of the current as well as the vibration velocity of the piezocomposite transducer. The current of the stationary response is measured before the end of the burst signal excitation. Burst excitation enables us to measure the nonlinear characterization without producing overheating in the transducers. The amplitude level dependence of mechanical losses tandelta(m) and the stiffness increases |Deltac/c(0)| have been studied, as well as the velocity dependence of a point of the transducer, measured with a laser vibrometer. In this method, the power level applied to the transducers can be higher than other nonlinear measurement methods, providing measurements of high accuracy.     

Investigation of dental samples using a 35MHz focussed ultrasound piezocomposite transducer

Dental erosion and decay are increasingly prevalent but as yet there is no quantitative monitoring tool. Such a tool would allow earlier diagnosis and treatment and ultimately the prevention of more serious disease and pain. Despite ultrasound having been demonstrated as a method of probing the internal structures of teeth more than 40 years ago, development of a clinical tool has been slow. The aim of the study reported here was to investigate the use of a novel high frequency ultrasound transducer and validate it using a known dental technique.A tooth extracted for clinical reasons was sectioned to provide a sample that contained an enamel and dentine layer such that the enamel-dentine junction (EDJ) was of a varying depth. The sample was then submerged in water and a B-scan recorded using a custom-designed piezocomposite ultrasound transducer with a centre frequency of 35 MHz and a −6 dB bandwidth of 24 MHz.The transducer has an axial resolution of 180 μm and a spatial resolution of 110 μm, a significant advance on previous work using lower frequencies. The depth of the EDJ was measured from the resulting data set and compared to measurements from the sequential grinding and imaging (SGI) method.The B-scan showed that the EDJ was of varying depth. Subsequently, the EDJ measurements were found to have a correlation of 0.89 (p < 0.01) against the SGI measurements. The results indicate that high frequency ultrasound is capable of measuring enamel thickness to an accuracy of within 10% of the total enamel thickness, whereas currently there is no clinical tool available to measure enamel thickness.     

Computational and experimental investigation of the fields generated by a 1-3 piezocomposite transducer

Large-scale three-dimensional numerical simulations using the finite-difference time domain technique are used to compute the continuous wave fields associated with a composite transducer. The interior of the transducer is made of a periodic array of square rods. This lattice causes elastic wave Bragg diffraction similar to electrons in a periodic lattice. A low frequency mode shape is assumed for the rods. This prescribed motion includes longitudinal and transverse components. It is shown that the transverse motion in the rod gives rise to shear waves causing standing waves (lateral resonances) in the polymer regions. This is also confirmed by experimental results presented here and other independent analytical and experimental work. The full-scale numerical simulation is performed on a large parallel supercomputer and permits modeling of not only the composite transducer but the radiated pressure from near to far field. In addition, cover plates and edge effects are included, unlike analytical treatments. Although only mechanical effects are included, the wave propagation approach captures many essential features.     

Modeling of a high frequency ultrasonic transducer using periodic structures

Solidly mounted integrated transducers with a Bragg cell inserted between the piezoelectric film and the substrate are investigated for high frequency ultrasonic applications. A numerically stable recursive one dimensional transmission/reflection model was used to analyze the behavior of the periodic structure. This theoretical analysis includes the study of the influence of the acoustic properties of the constitutive layer, the effect of the number of cells and their arrangement. A 35 MHz integrated transducer consisting in a PZT ceramic laid down on a Au/PZT Bragg cell deposited on a porous substrate was fabricated and characterized. Both theoretical and experimental results highlight the interest of using a periodic structure for high frequency ultrasonic applications.     

Development of a compact self-focusing piezoelectric generator using electrical pre-strain piezocomposite material

New clinical concepts in lithotripsy demand small shock heads. Reducing the size of piezoelectric shock heads will only be possible if the pressure generated at the surface of each transducer can be increased so that, the total pressure at the focus remains very high. So, we propose a new method allowing the generation of large surface pressures. It is well known that the piezoelectric rods in piezocomposite material are more fragile in the extension mode than in the compression mode. For this reason, actuators are mechanically pre-stressed between two flasks. This method cannot be used for transducers working at high frequencies, about 0.5 MHz. For this reason, we proposed to electrically pre-strain the piezoelectric material by applying high electric field in the opposite direction of the polarisation. In a first mode we proposed to pre-strain in continuous mode the transducer. Unfortunately we noticed a rapid de-poling and re-poling in the inverse direction. In a second mode to reduce depolarisation, this field was applied only during a short time just before the generation of the pulse which generate the compressive wave and in a third mode, the transducer was re-poled between two successive electrical pulses. Using this last method, it was possible to increase the maximum pressure at the surface of a 20 mm diameter plane piston to 20% and reach 4 MPa. According to this idea a very compact shock wave generator was designed. The generator made of a 1-3 piezocomposite material has a diameter of 120 mm and focused at 120 mm. The maximum pressure and the width of the compressive wave at the focus were, respectively, 60 MPa and 1.5 micros. The focal zone measured at -3 dB is an ellipsoid 6 mm high in the propagating axis and 3 mm width in the perpendicular direction. The efficacy of this generator was measured as the number of shocks necessary to totally disintegrate plaster balls 15 mm in diameter mimicking the kidney stones. At full power the number of shocks was only 150 which is rather the same number as the one obtained using electrohydraulic machine generally considered as the gold standard. This results show that piezoelectric material may be advantageously used for the manufacturing of shock wave generators.     

Transmission characteristics of acousto-optic filter using sectioned transducer

The paper examines operation of a tunable acousto-optic filter applying a sectioned piezoelectric transducer. The analysis was carried out for a tellurium dioxide cell having 1.4-cm long transducer divided into 7 identical sections connected in series. Each section generated acoustic waves with a time delay relatively to adjacent sections. The time delay caused electric and acoustic phase shifts as well as inclination of a resulting acoustic wave front in the crystal. We showed that the inclination of the acoustic front influenced on shape of the filter transmission function causing asymmetry of side lobes. Investigation of the filter was carried out at the driving acoustic frequencies 100–240 MHz. The measurement proved that the electric phase shifts between the adjacent sections increased with the frequency up to 30°. Ratio of intensities of the first two side lobes in the transmission function was varying with the frequency from 0.9 to 0.5. Based on the carried out analysis, we discussed a prototype device using the acoustic beam steering effect. The device applied two sets of transducer sections that simultaneously generated two acoustic wave fronts tilted with respect to each other.     

Measurements of the longitudinal wave speed in thin materials using a wideband PVDF transducer

A flat transducer was constructed, using a 9-microm-thick PVDF (polyvinylidene fluoride) film for generation and detection of high-frequency ultrasonic waves, and used for measurements of the phase velocity of longitudinal waves traveling along the thickness direction in a very thin material. The transducer has a useful wideband frequency characteristic extending from 10 MHz to over 150 MHz. Measurements of the phase velocity of the longitudinal waves are carried out using a 0.212-mm-thick glass slide and a 0.102-mm-thick stainless-steel shim, using water as a coupling medium. The thickness limit for this measurement appears to be approximately 20 microm. The phase velocity of the longitudinal mode is obtained as a function of frequency in the frequency domain by using a modified sampled continuous wave (cw) technique. It can also be measured in the time domain by using a broadband pulse of short duration.     

Resonant-type Smooth Impact Drive Mechanism (SIDM) actuator using a bolt-clamped Langevin transducer

The Smooth Impact Drive Mechanism (SIDM) is a linear piezoelectric actuator that has seen practically applied to camera lens modules. Although previous SIDM actuators are easily miniaturized and enable accurate positioning, these actuators cannot actuate at high speed and cannot provide powerful driving because they are driven at an off-resonant frequency using a soft-type PZT. In the present study, we propose a resonant-type SIDM using a bolt-clamped Langevin transducer (BLT) with a hard-type PZT. The resonant-type SIDM overcomes the above-mentioned problems and high-power operation becomes possible with a very simple structure. As a result, we confirmed the operation of resonant-type SIDM by designing a bolt-clamped Langevin transducer. The properties of no-load maximum speed was 0.28 m/s at driving voltages of 80 V_p-p for 44.9 kHz and 48 V_p-p for 22.45 kHz with a pre-load of 3.1 N     

Evaluation of the piezoelectric behaviour produced by a thick-film transducer using digital speckle pattern interferometry

This paper presents an interferometric measurement of the out-of-plane deflections produced by a piezoelectric transducer, manufactured by thick-film deposition of a ceramic paste over an alumina substrate, when is subjected to a DC electric voltage. It is shown that a digital speckle pattern interferometer with an incorporated phase-shifting facility allows the measurement of nanometer displacements generated by the piezoelectric device. These measurements are used to evaluate the effective piezoelectric charge constant along the polarization direction (d₃₃)_eff that characterizes the thick-film transducer.