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。     

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电复合材料中的分布形式，把四块完全相同的等腰直角王角形2－2型压电复合材料拼接起来，四个直角顶点位于晶片的中心，相邻块压电相的极化方向相对．这种新型材料可产生面切变振动，其换能器可辐射面切变波．波列中的纵波具有伴随性且其首波位相与面切变波首波位相相反     

切变模换能器暂态效应的初步分析

本文从压电介质的基本方程出发,用拉氏变换推导了厚度切变模横波换能器暂态效应的响应公式,得出了适用于计算换能器初始响应的雷德伍德等效电路。     

横波换能器的研制

本文从压电介质的基本方程出发,推导了厚度切变模横波换能器的梅森等效电路。进一步得出了适于工程应用的等效电路。介绍了有关晶片电弹常数的测量原理和换能器的研制工艺。     

扭转压电复合材料及其应用

本文描述了轴向－切向连通的圆柱２－２型压电复合材料。用ＰＺＴ／环氧树脂制作的普通２－２型压电复合材料可拼接成一种具有扭转振动的压电复合材料。这种压电复合材料和为圆柱２－２型压电复合材料的近似。本文还给出两组这种拼接型压电材料晶片的参数，用这种压电材料制作了产生扭转振动的换能器，测试了换能器的波形，频谱特性和偏振特性，指出了使用适当的高通滤波器可以抑制横波中的径向模，分析了接收波列中纵波抑制较强的原     

同时发射和接收纵波和横波的压电复合材料换能器

通过控制压电复合材料中压电相的分布形式，本文具有在百度模振动的１－３型压电复合材料和具有扭转模振动的拼接２－２型压电复合材料组合在一起，构成一种混俣模式压电材料，并测试了这种压电材料晶片的性能参数，使用这种晶片作的换能器可以根据使用者的要求，单独产生纵波或横波，也可同时产生这两种波。     

孔隙地层井壁上的声波首波及其诱导电磁场的原因

声波测井时孔隙地层中的声波首波平行于井轴沿井壁传播，它既有轴向位移分量，又有垂直于井壁的位移分量.这种以快纵波速度传播的波, 不仅含有由快、慢纵波势给出的梯度场,而且还含有由横波势给出的旋度场.慢纵波势的梯度是渗流位移首波的主要构成成分, 也是声电效应测井响应中存在伴随声波首波电场的主要原因.首波包含有旋度位移场，是存在伴随声波首波磁场的原因. 关键词： 孔隙介质 声波首波 诱导电磁场 测井     

横波远探测测井换能器研究

为提高偶极子横波远探测反射波的信噪比和增加其探测距离,根据偶极子井孔模式波的激发特性及反射波传播特征分析,研制了基于三叠片的低频大功率偶极子的横波远探测换能器,以降低模式波的相对能量和增加反射波的相对能量。为了得到满足要求的低频大功率偶极换能器,采用有限元方法对现有三叠片进行了优化改进,得到一种符合设计要求的换能器结构,最后制作了样机并对其进行了测试。样机测试结果跟仿真吻合得很好,低频性能得到了极大改善：换能器在谐振频率1.2 kHz附近具有极好的偶极子指向性,谐振频率处的响应比X-MAC同频率段大19 dB。该换能器的研发成功将为偶极子远探测测井仪器性能及成像质量的提高奠定了坚实的基础。     

光弹法测量超声换能器声场

超声换能器声场的测试对于超声检测具有基础性作用,而传统的超声换能器声场测试方法具有一些局限性。本文介绍了搭建的动态激光光弹实验平台,并利用动态光弹法测量了纵波换能器和横波换能器辐射声场的特征,由瞬态声场图像获得了传声介质的声波速度及超声换能器的中心频率;由稳态声场图像获得了声场的近场长度、指向性和扩散角等参数;分析了光弹实验系统和测量方法可能引起测量误差。本文结果表明动态光弹法是一种有效的定量测量超声换能器声场的方法。     

弯曲模式波测井的多极子换能器

本文根据井孔中弯曲等模式声波的速度频散特性,利用压电晶片的弯曲振动模式,提出并设计了一种用于直接横波测井的偶极子和四极子换能器.对设计制作的多极子换能器的振动和电声性能进行了测试。在快地层人工模拟井孔中的一发一收的试验表明,这种换能器能较好地在充液井孔中激发出弯曲等模式的声波,为实现快慢地层井孔中的直接横波测井提供了一种发射和接收换能器。     

Observation of intermittent states and nonlinear wave–wave interaction in neon glow discharges

In the plasma of a neon glow discharge under certain conditions two waves (s- and p-wave) are known to exist simultaneously. The transition region between these two kinds of waves is experimentally investigated in the space of plasma parameters. An intermittent behaviour of s- and p-waves dynamics is proved by the analysis of the recorded spatio-temporal patterns of light emitted by plasma. The experimental data are analyzed with the biorthogonal decomposition (BOD) and the empirical mode decomposition (EMD), respectively. The wave states can be described by means of a coupled system of amplitude equations resulting from a hydrodynamic plasma model. Comparison of experimental data and theoretical predictions shows satisfactory agreement. The discrepancies are discussed.     

Non-leptonic hyperon decays in chiral perturbation theory

The non-leptonic hyperon decays are analyzed up to one-loop order including all counterterms in the framework of heavy baryon chiral perturbation theory. We use the exchange of the spin- decuplet resonances as an indication of which low-energy constants contribute significantly to these investigated processes. We choose four independent decay amplitudes that are not related by isospin relations in order to perform a fit for the pertinent low-energy constants and find a satisfactory fit both for s- and p-waves. The chiral corrections to the lowest order forms for the s-waves are moderate whereas there are significant modifications of the p-wave amplitudes. Received: 16 December 1997 / Revised version: 18 February 1998 / Published online: 15 June 1998     

Optimization of ultrasonic transducers

The so-called KLM-model for ultrasonic transducers is employed to optimize transducer design. Some new performance characteristics are defined which change monotonically with design parameters. These characteristics are based on the area of the envelope of the echo waveform produced by the transducer and of the corresponding amplitude spectrum. The efficiency of the transducer is defined by the round trip energy factor. The performance characteristics are used in a composite performance measure, which is then employed as a criterion in the optimization procedure. Two transducers are investigated: for medical imaging purposes and for spectral analysis of clinical echograms. The influence of electrical matching, backing impedance, matching layer impedance, bond line thickness and series induction on the optimized transducers is investigated.     

压电式摆动圆柱形偶极发射换能器优化研究

为了实现偶极信号有效辐射,获得足够高的信噪比,全面分析弯曲波频散,本文提出了一种新型的频带范围为0.5–5 k Hz的压电式摆动圆柱形偶极声波测井换能器,并采用有限元方法对其进行了模拟和优化设计。此外,论文还对换能器进行了实验样机制作和实验测量,将实验测量与数值模拟结果进行了对比。研究表明,提出的新型偶极声波换能器比传统换能器具有更高的发射灵敏度,尤其是在低频响应范围。本文为新型偶极声波测井换能器的研发工作奠定了基础。     

Strongly resonant p-wave superfluids

We study theoretically a dilute gas of identical fermions interacting via a p-wave resonance. We show that, depending on the microscopic physics, there are two distinct regimes of p-wave resonant superfluids, which we term "weak" and "strong." Although expected naively to form a paired superfluid, a strongly resonant p-wave superfluid is in fact unstable toward the formation of a gas of fermionic trimers. We examine this instability and estimate the lifetime of the p-wave molecules due to the collisional relaxation into trimers. We discuss consequences for the experimental achievement of p-wave superfluids in both weakly and strongly resonant regimes.     

Harmonic analysis of lossy, piezoelectric composite transducers using the plane wave expansion method

Periodic composite ultrasonic transducers offer many advantages but the periodic pillar architecture can give rise to unwanted modes of vibration which interfere with the piston like motion of the fundamental thickness mode. In this paper, viscoelastic loss is incorporated into a three-dimensional plane wave expansion model (PWE) of these transducers. A comparison with experimental and finite element data is conducted and a design to damp out these lateral modes is investigated. Scaling and regularisation techniques are introduced to the PWE method to reduce ill-conditioning in the large matrices which can arise. The identification of the modes of vibration is aided by examining profiles of the displacements, electrical potential and Poynting vector. The dispersive behaviour of a 2-2 composite transducer with high shear attenuation in the passive phase is examined. The model shows that the use of a high shear attenuation filler material improves the frequency band gap surrounding the fundamental thickness mode.     

Anisotropic Fermi superfluid via p-wave Feshbach resonance

We investigate theoretically fermionic superfluidity induced by Feshbach resonance in the orbital p-wave channel and determine the general phase diagram. In contrast with superfluid (3)He, due to the dipole interaction, the pairing is extremely anisotropic. When this dipole interaction is relatively strong, the pairing has symmetry k(z). When it is relatively weak, it is of symmetry k(z) + ibetak(y) (up to a rotation about z;, here beta < 1). A phase transition between these two states can occur under a change in the magnetic field or the density of the gas.     

边界层转捩区声辐射的预报方法研究

对Lighthill剪切应力脉动模型和Liepmann位移厚度脉动模型进行了讨论,在此基础上,本文提出利用Krane偶极子声源模型对Liepmann单极子声源模型进行改进。数值计算结果表明:作为偶极子声源的Lighthill理论剪切应力脉动模型,预报的噪声级偏低;而作为单极子声源的Liepmann模型,预报的噪声级又偏高;本文提出的两种改进模型预报的噪声级则与Lauchle实验值的一致性较好。     

Tunable te-CO2 laser-pumped formaldehyde far-infrared lasers: Offsets, assignment, and superfluorescence

Sixty and three absorption transitions in D₂CO and H₂CO, respectively, have produced a number of far infrared laser lines when they are pumped by an etalon-tuned TE-CO₂ laser. Almost all the absorption transitions pumped previously by a free runing TE-CO₂ laser have been efficiently pumped by the etalon tuned CO₂ laser and found to have offset within ±500 MHz from the line-center of the relevant CO₂ pump lines. 22 (1) absorption and 63 (4) emission lines of D₂CO (H₂CO) are assigned. Some of these lines have generated superfluorescence. In paticular, the D₂CO 319-m line pumped by CO₂-9P(32) delivered an output energy of approximately one half that of the well-known D₂O 66-m. It is shown that a large electric dipole moment and an appreciable amount of fractional population in the lower level of the pump transition of this line are responsible to the superfluorescence.