Piezoelectric and flexoelectric effects of DNA adsorbed films on microcantilevers

DNA-based biosensors have played a huge role in many areas,especially in current global coronavirus outbreak.However,there is a great difficulty in the characterization of piezoelectric and flexoelectric coefficients of the nanoscale DNA film,because the existing experimental methods for hard materials are almost invalid.In addition,the relevant theoretical models for DNA films only consider a single effect without clarifying the difference between the two electromechanical effects on device detection signals.This work aims to present multiscale models for DNA-microcantilever experiments to clarify the competitive mechanism in piezoelectric and flexoelectric effects of DNA films on detection signals.First,a Poisson-Boltzmann(PB)equation is used to predict the potential distribution due to the competition between fixed phosphate groups and mobile salt ions in DNA films.Second,a macroscopic piezoelectric/flexoelectric constitutive equation of the DNA film and a mesoscopic free energy model of the DNA solution are combined to analytically predict the electromechanical coefficients of the DNA film and the relevant microcantilever signals by the deformation equivalent method and Zhang’s two-variable method.Finally,the effects of detection conditions on microscopic interactions,electromechanical coupling coefficients,and deflection signals are studied.Numerical results not only agree well with the experimental observations,but also reveal that the piezoelectric and flexoelectric effects of the DNA film should be equivalently modeled when interpreting microcantilever detection signals.These insights might provide opportunities for the microcantilever biosensor with high sensitivity.

Study of the Isotope Effects of Novel Superconducting LaH₁₀-LaD₁₀and H₃S-D₃S Systems

This paper is directed to study the isotope effects of some superconducting materials that have a strong coupling coefficient λ > 1.5, and focuses on new superconducting materials whose critical temperature is close to room temperature, specifically LaH10-LaD10 and H3S-D3S systems. The Eliashberg-McMillan (EM) model and the recent Gor’kov-Kresin (GK) model for evaluating the isotope effects coefficient α were examined for these systems. The predicted values of α as a function of pressure, as compared to experimental values led to inference that these two models, despite their importance and simplicity, cannot be considered complete. These models can be used to calculate isotope effect of most superconducting materials with strong coupling coefficients but with critical reliability. The significance of studying the isotope effect lies in the possibility of identifying the interatomic forces that control the properties of superconducting materials such as electrons-mediated phonons and Coulomb interactions.

背腔刻蚀型横向激励薄膜体声波谐振器制备技术研究

随着移动通信技术的快速发展,薄膜体声波滤波器逐渐向高频和大带宽方向发展。该文研究了POI(LiNbO_(3)/SiO_(2)/Si)基片上背腔刻蚀型横向激励薄膜体声波谐振器制作工艺,通过研究POI基IDT光刻、背腔硅刻蚀等工艺,确定了IDT层曝光量和背腔刻蚀等关键工艺参数。研制出的背腔刻蚀型横向激励薄膜体声波谐振器,其谐振频率为4565 MHz,反谐振频率为5035 MHz,机电耦合系数为20.86%。此制备工艺对研究高频、大带宽薄膜体声波滤波器具有重要的参考意义。

Effective electromechanical coupling coefficient of high-overtone bulk acoustic resonator

A high-overtone bulk acoustic resonator （HBAR） is composed of a substrate, a piezoelectric film and upper and lower electrodes, the influences of their structure parameter （thickness） and performance parameter （characteristic impedance） on effective electromechani- cal coupling coefficient K^2eff are investigated systematically. The relationship between K^2eff and these parameters is obtained by a lumped parameter equivalent circuit instead of distributed parameter equivalent circuit near the resonant frequency, and K^2eff at the resonance frequency closest to the given frequency is analyzed. The results show that K^2eff declines rapidly and oscillatorily with the continuous increase of the substrate thickness when the piezoelectric film thickness is fixed, and decreases inversely proportion to the thickness when the substrate thick-ness is greater than a certain value. With the ratio of the characteristic impedance of the substrate to the piezoelectric layer increasing, the maximum of K^2eff obtained from the vari- ation curve of K^2eff with the continuous increase of the piezoelectric film thickness decreases rapidly before reaching the minimum value, and later increases slowly. Fused silica with low impedance is appropriate as the substrate of HBAR to get a larger K^2eff. Compared with Al electrode, Au electrode can obtain larger K^2eff when the appropriate electrode thickness is selected. The revealed laws above mentioned provide the theoretical basis for optimizing parameters of HBAR.

基于X-LiNbO_(3)/SiO_(2)/Si低温漂、大机电耦合SH-SAW谐振器的设计

铌酸锂(LN)单晶薄膜具有较高的机电耦合系数(k_(eff)^(2)>30%),其水平剪切(SH)声学模式常被应用于开发具有大机电耦合系数的薄膜声学谐振器和超宽带滤波器。但LN的频率温度系数较大(TCF>-50×10^(-6)/℃),这不仅会降低滤波器的可用有效带宽,同时也会限制器件的功率处理能力。采用3D周期有限元模型对基于X切LN/SiO2/Si结构SH声表面波(SH-SAW)谐振器进行了优化研究。研究结果表明,当SH-SAW传播角ψ=-10°~-20°、LN和SiO2膜厚分别为hLN=0.1λ和hSiO_(2)=0.2λ(λ为叉指换能器周期)、铝电极金属化率η=0.4、电极相对厚度hAl/λ=5%~10%时,SH-SAW谐振器的k_(eff)^(2)约为30%,且其TCF<-20×10^(-6)/℃,有望用于开发新一代的低温漂、超宽带5G SAW滤波器。

基于氮化铝薄膜的二维模态谐振器双模结构设计与仿真

基于氮化铝(aluminum nitride,AlN)压电薄膜的二维模态谐振器(two-dimensional-mode resonators,2DMR)由于其较高的有效机电耦合系数k^(2)_(eff)及其与集成电路工艺兼容等优势,引起了业内广泛的关注。然而,传统的2DMR只研究单谐振模态,难以满足多模无线通信系统的需求。针对该问题,提出一种应用于5G new radio(5GNR)频段为2.6~3.4 GHz的二维模态(2DM)双模谐振器,通过合理设计电极宽度和电极周期,使得2个模态的品质因数Q和k^(2)_(eff)相当,实现了S1模态和高阶S1模态的有效激励。通过有限元方法研究分析了压电材料厚度及梳齿电极结构对2DMR双模谐振频率和k^(2)_(eff)的影响,S1模态谐振频率主要受压电材料厚度影响,高阶S1模态谐振频率在受压电材料厚度影响的同时还易受金属电极宽度影响。基于Al N压电薄膜中d_(33)和d_(31)压电系数的共同作用,所设计的2DMR中2个模态的k^(2)_(eff)分别达到3.1%和3.6%。随后,基于S1模态和高阶S1模态谐振处无杂散和高机电耦合性能,设计了含有50Ω阻抗匹配网络的双频带通滤波器,通过增加阶数提高器件的带外抑制。滤波器的2个传输频带相邻,无带内波纹且陡峭滚降,中心频率分别位于2.852和3.082 GHz,插入损耗分别为2.0和1.9 dB,分数带宽分别为29和39 MHz。研究结果说明了这种2DMR双模结构设计在射频前端极具应用潜力。

一种改进型1-3-2压电复合材料的研究

高质量的压电换能器需要具备较高的机电耦合系数和灵敏度。该文在传统型1-3-2压电复合材料的基础上提出了一种改进型1-3-2压电材料,提高了压电换能器的机电耦合系数和换能器的接收灵敏度。通过有限元仿真分析了不同间距对改进型1-3-2压电材料敏感元件的谐振频率、反谐振频率及机电耦合系数的影响,并与传统1-3-2型压电复合材料进行了对比。结果表明,与传统型1-3-2压电复合材料相比,在相同间距条件下,改进型压电材料的机电耦合系数约大0.03。制做的3种不同间距改进型压电材料表明,间距为1 mm的改进型压电材料的机电耦合系数较大,约为0.68。

基于扫频检测的微机械陀螺耦合误差系数辨识

为减小微机械陀螺阻尼耦合、刚度耦合、力耦合误差的影响,提出一种基于扫频检测的微机械陀螺耦合误差系数辨识方法。首先,拓展了微机械陀螺动力学方程并建立误差模型,表明耦合误差造成陀螺输出不稳定且难以消除。其次,推导了耦合误差系数辨识方法,通过数值仿真分析了幅值、相位检测误差对辨识精度的影响,并给出不同误差系数下辨识结果的理论相对误差分布。结果表明,所提方法对耦合误差系数的辨识范围存在局限性;测量误差对辨识结果的影响不可忽略。最后,对某陀螺进行耦合误差系数辨识实验验证,结果表明:该陀螺力耦合系数、阻尼耦合系数、刚度耦合系数的辨识误差分别为0.542 ppm、6.09%、0.205 ppm;辨识曲线的拟合优度为0.99。

建筑火灾与人员疏散耦合模拟研究

为研究火灾环境下烟气对人员的影响,将火灾发展与人员疏散过程进行耦合。以某商场为研究对象,引入当量速度系数和有效剂量分数模型对商场火灾场景下的人员疏散速度进行修正,利用Pyrosim与Pathfinder建立更贴近真实火场的商场火灾与人员疏散耦合模型,得到火灾发展过程中的烟气浓度、温度、能见度与人员疏散过程的耦合时空分布图和烟气毒性对人员伤害的累积作用。模拟结果表明:通过对火灾发展与人员疏散的时空动态分析,在火灾发生380s后,商场剩余77人由于能见度下降不能完成疏散。相比于比较建筑内人员可用安全疏散时间(ASET)和必需安全疏散时间(RSET)的大小的传统判定方式,耦合模型更能直观准确地表现建筑物内火灾烟气对被疏散人员的实时影响。

PROPAGATION OF SURFACE ACOUSTIC WAVES IN PRESTRESSED ANISOTROPIC LAYERED PIEZOELECTRIC STRUCTURES

The propagation of surface acoustic waves in layered piezoelectric structureswith initial stresses is investigated. The phase velocity equations are obtained for electricallyfree and shorted cases, respectively. Effects of the initial stresses on the phase velocity and theelectromechanical coupling coefficient for the fundamental mode of the layered piezoelectricstructures are discussed. Numerical results for the c-axis oriented film of LiNbO_3 on a sapphiresubstrate are given. It is found that the fractional change in phase velocity is a linear functionwith the initial stresses, and the electromechanical coupling factor increases with an increase ofthe absolute values of the compressive initial stresses. The results are useful for the design ofsurface acoustic wave devices.

Propagations of Rayleigh and Love waves in ZnO films/glass substrates analyzed by three-dimensional finite element method

Propagation characteristics of surface acoustic waves（SAWs） in ZnO films/glass substrates are theoretically investigated by the three-dimensional（3D） finite element method. At first, for（11ˉ20） ZnO films/glass substrates, the simulation results confirm that the Rayleigh waves along the [0001] direction and Love waves along the [1ˉ100] direction are successfully excited in the multilayered structures. Next, the crystal orientations of the ZnO films are rotated, and the influences of ZnO films with different crystal orientations on SAW characterizations, including the phase velocity, electromechanical coupling coefficient, and temperature coefficient of frequency, are investigated. The results show that at appropriate h/λ, Rayleigh wave has a maximum k^2 of 2.4% in（90°, 56.5°, 0°） ZnO film/glass substrate structure; Love wave has a maximum k^2 of 3.81% in（56°, 90°, 0°） ZnO film/glass substrate structure. Meantime, for Rayleigh wave and Love wave devices, zero temperature coefficient of frequency（TCF） can be achieved at appropriate ratio of film thickness to SAW wavelength. These results show that SAW devices with higher k^2 or lower TCF can be fabricated by flexibly selecting the crystal orientations of ZnO films on glass substrates.

Influence of air pressure on mechanical effect of laser plasma shock wave

The influence of air pressure on mechanical effect of laser plasma shock wave in a vacuum chamber produced by a Nd：YAG laser has been studied. The laser pulses with pulse width of 10ns and pulse energy of about 320mJ at 1.06μm wavelength is focused on the aluminium target mounted on a ballistic pendulum, and the air pressure in the chamber changes from 2.8 × 10^ 3 to 1.01 × 10^5pa. The experimental results show that the impulse coupling coefficient changes as the air pressure and the distance of the target from focus change. The mechanical effects of the plasma shock wave on the target are analysed at different distances from focus and the air pressure.

Stoney formula for piezoelectric film/elastic substrate system

With the trends in miniaturization, and particularly the introduction of micro- and nano-electro-mechanical system, piezoelectric materials used in microelectronic devices are deposited usually in the form of thin film on elastic substrates. In this work, the bending of a bilayer comprising a piezoelectric film deposited on an elastic substrate, due to the mismatch, is investigated. An analytic formula relating the curvature of the bilayer to the mismatch, the electroelastic constants and the film thickness is obtained, and from this formula, a transverse piezoelectric constant d31 can be estimated. Meanwhile the influence of electrornechanical coupling coefficient on the curvature is discussed.

Theoretical analysis and experimental validation of radial cascaded composite ultrasonic transducer

A radial cascaded composite ultrasonic transducer is analyzed.The transducer consists of three short metal tubes and two radially polarized piezoelectric ceramic short tubes arranged alternately along the radial direction.The short metal tubes and the piezoelectric ceramic short tubes are connected in parallel electrically and in series mechanically,which can multiply the input sound power and sound intensity.Based on the theory of plane stress,the electro-mechanical equivalent circuit of radial vibration of the transducer is derived firstly.The resonance/anti-resonance frequency equation and the expression of the effective electromechanical coupling coefficient are obtained.Excellent electromechanical characteristics are determined by changing the radial geometric dimensions.Two prototypes of the transducers are designed and manufactured to support the analytical theory.It is concluded that the theoretical resonance/anti-resonance frequencies are consistent with the numerical and experimental results.When R_(2) is at certain values,both the anti-resonance frequency and effective electromechanical coupling coefficient corresponding to the second mode have maximal values.The radial cascaded composite ultrasonic transducer is expected to be used in the fields of ultrasonic water treatment and underwater acoustics.

High Quality of Piezoelectric Response of Nano Ni Doped Pb1-xNixTiO3 Ceramic

A series of Pb1-xNixTiO3 (x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5) were prepared by the general ceramic and co-precipitation method. The grain size decreased with increasing Ni contents. The piezoelectric modulus d33 increased with increasing Ni contents. It was observed also the d33 of the nanocomposite Pb1-xNixTiO3 prepared by co-precipitation method is higher than those of the prepared by general ceramic method. The coupling factor kp increased by the more doping of Ni. The ultrasonic wave velocity decreased also with increasing Ni contents. The polarized nano-sample of composition Pb0.5Ni0.5TiO3 is suitable for improving application of useful piezoelectric technology.

摆式摩擦发电机非线性机电耦合建模研究

面向摆式摩擦发电机结构优化设计需求,开展非线性机电耦合建模与参数敏感性分析,以推动其向工程实用化方向发展.在摩擦发电机理分析的基础上,构建等效电容拟合函数;结合能量原理和等效电路法,建立了考虑摆角非线性变化的机电耦合模型.利用谐波平衡法,解析求解摆式摩擦发电机的周期稳态输出,并判断结果稳定性.结合数值积分和动态测试两种手段,验证谐波平衡分析的准确性.与线性模型结果进行深入对比,并考察了不同设计参数对摆式摩擦发电机输出特性的影响.考虑非线性效应,模型预估的工作带宽显著增加(相对增量83%).文章提出的机电耦合模型能够有效避免线性模型对工作带宽的低估问题,显著提升输出性能估计的准确性;增加激励幅值、降低系统阻尼或减小电极夹角,均有助于提升摆式摩擦发电机的输出表现;在实际设计时,需综合考虑间隙长度和摩擦力幅值,以使摆式摩擦发电机输出表现处于较优状态;构建多种拟合模型用于表征设计参数与输出性能的关系,可作为摆式摩擦发电机输出性能设计的依据.

接触压力下CFRP板-钢界面摩擦系数试验研究

CFRP板-钢界面摩擦系数是预应力CFRP锚具锚固性能的关键参数,为增大摩擦系数以提高锚固效率,首先采用抛光处理、化学腐蚀和滚花等得到不同粗糙度的钢夹片表面,然后对CFRP板-钢夹片界面在20~100MPa的接触压应力下的摩擦行为进行静力张拉试验,分析不同CFRP板厚、钢表面粗糙度和接触压力的CFRP板-钢夹片的摩擦力-滑移曲线和界面磨损情况,得到CFRP板-钢界面的静、滑动摩擦系数。结果表明,短期力学试验条件下静摩擦系数实测值范围为0.11~0.33,滑动摩擦系数较小,范围为0.04~0.31。接触压力作用下钢夹片表面粗糙颗粒对CFRP表面产生的犁沟效应是摩擦力的来源,而随着CFRP板-钢界面磨损量增加,滑移后产生自润滑效应,导致滑动摩擦系数减小。摩擦系数主要取决于CFRP板厚、接触面粗糙度和接触压力的相互匹配,较厚CFRP板具有较大的摩擦系数。

圆形巷道围岩破坏机制解析及静动耦合响应力学行为

非等压圆形巷道围岩塑性区相关问题是影响围岩破坏失稳的重要因素。首先,基于Mohr-Coulomb破坏准则,分析非等压圆形巷道围岩塑性区边界条件,探究侧压系数对塑性区形成的影响机制。此外,利用ANSYS/LS-DYNA仿真平台对不同侧压系数下的巷道围岩力学行为进行静动载荷耦合响应数值模拟。结果表明:侧压系数的增大显著改变围岩有效应力的分布特征。有效应力场的分布特性与塑性区边界理论解具有一定的吻合性。不同侧压系数的应力场作用时,巷道围岩的变形具有显著的差异性,随着侧压系数的增大,围岩发生较大的非均匀性变形。静动耦合作用下顶板和底板的围岩破坏区域显著增加,但两帮围岩的破坏面积有减小的趋势。

双不确定参数作用下双稳态能量采集系统的随机响应分析

非线性多稳态能量采集系统模型复杂、结构参数较多,由于测量、加工、装配过程中不可避免的存在误差,这些结构参数都存在一定的不确定性.而关键参数的微小变化都可能对系统输出电压产生显著影响,特别当多不确定参数同时存在时,可能会对系统能量采集性能产生更加复杂的影响.因此,研究多不确定参数作用下非线性能量采集系统的随机行为十分必要.本文针对具有双不确定参数的双稳态能量采集系统,首先,利用Routh-Hurwitz定理分析了确定性双稳态系统平衡点的稳定性及其静态分岔特性;继而,借助正交多项式逼近法,将具有两个相互独立的不确定机电耦合系数的随机双稳态系统转化为等价确定性扩阶系统,使系统的随机响应问题转换为等价系统的响应问题;之后,从全局和局部两个角度出发,通过等价系统与确定性系统吸引子、吸引域、相轨、均方电压以及能量转化率的对比,揭示了不确定参数对系统动力学行为和发电性能的影响.结果表明,在一些敏感的参数区间内,两机电耦合系数的不确定性均会导致系统运动状态发生变化,且不确定参数强度越大,系统会越早通过倍周期分岔级联进入混沌状态;此外,在两机电耦合系数的不确定性作用下,系统均方电压均会出现一定程度的降低;且与电方程中机电耦合系数相比,机械方程中机电耦合系数对系统的影响更显著,当两不确定参数共同作用时,系统的能量采集性能变化更显著.

考虑多因素耦合效应的冻结兰州黄土动力学参数研究

为了探究多因素耦合效应对冻结兰州黄土动力参数的影响,以分布在我国西部季节冻土区的兰州黄土为研究对象,通过动三轴试验研究了不同围压(0.1、0.2、0.3 MPa)、温度(−1、−3、−5℃)、含水率(14%、16%、18%)及加载频率(1、2、4 Hz)影响下冻结兰州黄土的动力参数变化特征。基于试验结果,分析了冻结兰州黄土最大动弹性模量、等效黏滞阻尼系数、参考应变幅值在温度、围压、含水率、加载频率等多因素耦合影响下的变化规律。结果表明,温度、含水率、加载频率和围压等耦合因素对冻结兰州黄土动弹性模量、参考应变幅值和等效黏滞阻尼系数的影响程度有差异。可以发现,冻结兰州黄土动弹性模量和参考应变幅值随温度变化的影响最显著,等效黏滞阻尼系数随加载频率变化表现最敏感。基于试验数据,对影响冻结兰州黄土的4种因素进行归一化和无量纲化处理,采用多元回归分析方法提出了冻结兰州黄土动力学参数的预测公式,有助于快速预测冻结兰州黄土在多因素耦合效应影响下的动力学参数变化特征。