DESIGN AND APPLICATIONS OF PIEZOELECTRIC CRYSTALS TRANSDUCER IN DYNAMIC EXPERIMENTS

各种压电器件广泛用于电子工业、信息传输、医学诊断等许多领域,以实现能量转换、传感、驱动、频率控制等功能. 特别地,压电晶体以其高频响的压电效应,在动载实验中用于动态应力的测试. 利用其特有的各向异性特性,通过设计特殊的切型方向,可以实现对不同应力的测试. 本文通过分析各向异性晶体的特性,从压电效应的基本原理出发,导出了利用各向异性晶体作为剪应力量计的设计思想,并给出了两种典型的动态剪应力计:17.705°Y 切石英和165.44°Y 切铌酸锂晶体.     

Inclusion of an arbitrary polygon with graded eigenstrain in an anisotropic piezoelectric half plane

This paper presents an exact closed-form solution for the Eshelby problem of a polygonal inclusion with graded eigenstrains in an anisotropic piezoelectric half plane with traction-free on its surface. Using the line-source Green’s function, the line integral is carried out analytically for the linear eigenstrain case, with the final expression involving only elementary functions. The solutions are applied to the semiconductor quantum wire (QWR) of square, triangular, and rectangular shapes, with results clearly illustrating various influencing factors on the induced fields. The exact closed-form solution should be useful to the analysis of nanoscale QWR structures where large strain and electric fields could be induced by the non-uniform misfit strain.     

Fabrication of broadband poly(vinylidene difluoride-trifluroethylene) line-focus ultrasonic transducers for surface acoustic wave measurements of anisotropy of a (1 0 0) silicon wafer

This paper investigates a new method for fabrication of broadband line-focus ultrasonic transducers by sol–gel spin-coating the poly(vinylidene difluoride-trifluroethylene) [P(VDF-TrFE)] copolymer film on a concave fine-polished beryllium copper backing. The ferroelectric hysteresis loops of the P(VDF-TrFE) films spin-coated from different molar ratios of VDF/TrFE, 77/23 and 55/45, were measured to select the better mixture. Owing to the better acoustic matching to water, compared with lead zirconate titanate (PZT), the fabricated transducers show relatively wide bandwidth of approximately 50 MHz with high central frequency of 60 MHz obtained at the focal plane when a fused-quartz acts as a reflecting target. Each one of the two finished transducers has a focal length of 5 mm and a full aperture angle of 90°. After applying the specially developed digital signal processing algorithm to the defocusing experiment data, which is called V(f,z) analysis method based on two-dimensional fast Fourier transform (2-D FFT), the operating frequency can extend from several MHz to over 90 MHz. Surface acoustic wave (SAW) velocities of a typical (1 0 0) silicon wafer was measured along various directions between [1 0 0] and [0 1 0] to represent the anisotropic features.     

Development of a surface acoustic wave wireless and passive temperature sensor incorporating reflective delay line

based on optimal design on the core element of the sensor,a wireless and passive surface acoustic wave(SAW)temperature sensor integrated with ID Tag was presented.A reflective delay line,which consists of a transducer and eight reflectors on YZ LiNbO3 substrate.Was fabricated as the sensor element,in which,three reflectors were used for temperature sensing,and the other five were for the ID Tag using phase encoding.Single phase unidirectional transducers(SPUDTs)and shorted grating were used to structure the sAW device,leading to excellent signal to noise ratio(SNR).The performance of the SAW device was simulated by the coupling of modes(COM)prior to fabrication.Using the network analyzer,the response in time domain of the fabricated 434 MHz SAW sensor was characterized,the measured S11 agrees well with the simulated one,sharp reflection peaks,high signal/noise,and low spurious noise between the reflection peaks were observed.Using the radar system based on FSCW as the reader unit.the developed SAW temperature sensors were evaluated wirelessly.Excellent1 inearity and good resolution of士1℃ were observed.     

柔性基底红外波段左手材料制备及光学特性

采用平板电极化学电沉积的方法,通过调节实验参量,在柔性ITO导电薄膜基底上制备了尺度与红外波长匹配、结构单元大小不等、排列无序的银树枝状结构.通过调节聚乙二醇-20000浓度可以很好地调控银树枝状结构单元的形貌和尺寸,研究发现,在一定范围内增加电解液中的聚乙二醇-20000浓度,可在基底上形成分布较密、分枝较细、分枝级数较高的银树枝状结构单元.通过在银树枝状结构表面涂覆一定厚度的聚乙烯醇作为绝缘层,组装成了柔性“三明治”结构复合材料,测试得到样品在红外波段的多通带透射谱,平板聚焦实验进一步验证了样品的左手效应.     

Hg2Br2声光器件的换能器带宽和镀层厚度的确定

提出用环氧树脂聚合物作为换能器与Hg2Br2声光介质的缓冲层(粘接层)，设计Hg2Br2声光器件的换能器。根据换能器等效电路网络分析法，就x切LN／Hg2Br2声光器件的电极层各种金属材料和厚度计算了换能器损耗TL随规一化频率f／fo的变化关系。从声光器件的布喇格带宽和工艺条件出发，优化选择了换能器损耗为3dB范围内的换能器结构、电极层材料及其厚度和压电层厚度，并确保了换能器的倍频程带宽。     

Analysis of transient responses in a laminated piezoelectric cylindrical shell

A hybrid numerical method is proposed for analysis of transient responses in a multilayered piezoelectric cylindrical shell.In the present method,the associated equations of the displacement field and the electro-potential field are developed using an analytical-numerical method.The piezoelectric cylindrical shell is discretized into layered annular elements along the wall thickness direction.The governing equations are determined by Hamilton's Principle considering the coupling between the elastic and elec...     

Effect of III‐nitride polarization on VOC in p–i–n and MQW solar cells

We performed detailed studies of the effect of polarization on III‐nitride solar cells. Spontaneous and piezoelectric polarizations were assessed to determine their impacts upon the open circuit voltages (V_OC) in p–i(InGaN)–n and multi‐quantum well (MQW) solar cells. We found that the spontaneous polarization in Ga‐polar p–i–n solar cells strongly modifies energy band structures and corresponding electric fields in a way that degrades V_OC compared to non‐polar p–i–n structures. In contrast, we found that piezoelectric polarization in Ga‐polar MQW structures does not have a large influence on V_OC compared to non‐polar MQW structures. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The predicted compressive strength of a pyramidal lattice made from case hardened steel tubes

A sandwich panel with a core made from solid pyramidal struts is a promising candidate for multifunctional application such as combined structural and heat-exchange function. This study explores the performance enhancement by making use of hollow struts, and examines the elevation in the plastic buckling strength by either strain hardening or case hardening. Finite element simulations are performed to quantify these enhancements. Also, the sensitivity of competing collapse modes to tube geometry and to the depth of case hardening is determined. A comparison with other lattice materials reveals that the pyramidal lattice made from case hardened steel tubes outperforms lattices made from solid struts of aluminium or titanium and has a comparable strength to a core made from carbon fibre reinforced polymers.