A harmonic oscillator with low harmonic distortion and stable amplitude

A generator of the harmonic signal is described for frequencies in the acoustic region with the reference stabilized amplitude, linear frequency scale and total harmonic distortion below 2 × 10^?3. The signal is produced as the solution of the corresponding differential equation where the constant amplitude is maintained by periodic control of the first derivative value [xdot](t) at the moments when x(t) crosses zero and has a positive slope.     

Modulated Lapped Transform Domain Acoustic Echo Canceller with Double Talk Detector

A complete acoustic echo cancellation system with double talk detection capability is presented in this paper. The proposed system includes a new acoustic echo canceller (AEC) based on the modulated lapped transform (MLT) domain adaptive structure and a robust two-stage double talk detector (DTD) to cope with MLT domain AEC. The proposed AEC achieves better signal decorrelation via orthogonal MLT of size 2N× N rather than N× N square orthogonal transform such as DCT, DFT, etc. Both the input signal and the desired response are modulated lapped transformed in order to reduce the adaptation error between them so that the signal adaptation is purely operated in MLT domain. As a complementary of this, a two-stage DTD is developed to stabilize the operation of the AEC. The proposed DTD has robust algorithm structure and it allows faster switching according to the talker state change.Several simulation results with a synthetic and real speech are presented to demonstrate the performance of the proposed AEC and DTD. The proposed MLT based AEC proven to be very useful for the echo cancellation applications requiring high convergence speed and good echo attenuation. It can achieves faster convergence rate by more than twice over those of traditional DCT based AEC with an additional advantage of 10–15 dB ERLE improvement. On the other hand, a proposed two-stage DTD is shown to react quickly to both the onset and the end of the double-talk with reasonable high accuracy.     

声透镜指向性换能器研究

该文利用声学透镜使声波能量聚焦,实现小尺寸换能器窄波束声辐射。利用有限元方法分别建立了单凹面声透镜及双凹面声透镜仿真模型,优化了声透镜结构参数,设计并制作了双凹面声透镜指向性换能器,并在消声水池内对换能器样机和声透镜进行了性能测试。换能器样机辐射面积直径?120 mm,设置声透镜后,提高发送电压响应级4 dB,发射指向性-3 dB波束开角由76°变为约30°(@10 kHz),与仿真计算结果相符。实验结果表明,声透镜有效减小了换能器发射波束宽度,提高了换能器主瓣发送电压响应,验证了双凹面声透镜对优化换能器指向性的效果。     

Nondestructive evaluation of the semiconductor interface states' density using the transverse acoustoelectric voltage

Nondestructive determination of the interface states' density (D_it) is presented. The measurement technique, utilizing the surface acoustic waves, is applied to silicon/thermal oxide structure. The detected signal is the transverse acoustoelectric voltage amplitude (TAV) which is monitored as a function of the applied bias voltage (TAV-V). D_it is measured by comparing the theoretical and experimental TAV-V curves. The calculation procedure of the D_it and the experimental example are presented.     

Frequency Selectivity via Inner Boundary Conditions for A Self-Powered Multiresonant Acoustic Sensing Array with Broad Bandwidth

This study investigates and proposes innovative approaches to achieve frequency selectivity within a limited space. Traditional multiresonant acoustic devices use individual sensing elements of varying sizes to achieve resonance frequency (f_r), leading to an inability to sense focused acoustic waves, unlike the human ear. A miniaturized, self-powered artificial basilar membrane that incorporates multiresonant features is introduced. Multiple f_r of the diaphragms are developed using inner boundary conditions (iBCs) defined by an adjustable micropatterned elastomeric support (µ-support) and a porous nanofiber (NF) mat. This new approach offers the advantage of all-in-one fabrication, eliminating the need for device area variation or an additional rigid frame typically required in conventional multiresonant acoustic devices. The efficacy of the iBCs in shifting f_r within the vocal frequency ranges is verified via a laser Doppler vibrometer, simulation, and triboelectric output. With its self-powering capabilities based on triboelectric principles, this artificial basilar membrane holds promise for accurately recognizing musical and vocal signals with specific frequency characteristics. With four different iBCs in a total device area of 23 × 23 mm², a tunable four-channel system with f_r ranging from 400 to 3000 Hz is achieved. This advancement enables the sensing of focused acoustic waves, simulating the functionality of an artificial human ear model.     

Frequency-Azimuth-Elevation Determination with a Single Acoustic Vector-Sensor Involved in a Reflecting Boundary

The temporally regularized multiresolution ESPRIT (Estimation of Signal Parameters via Rotational Invariance Techniques) algorithm is proposed to exploit the second-order information present in the superposition of incidence of direct and reflected monochromatic acoustic waves for uni-vector-sensor direction finding in the presence of a reflecting boundary. The data are organized such that the phase shifts for frequency estimation of each signal corresponding to two distinct sampling rates are separately embedded in the modulus and argument of the ESPRIT eigenvalue, whereas the direction cosines for azimuth-elevation direction-of-arrival (DOA) estimation dwell in the associated ESPRIT eigenvector, and thus the matching procedure for aligning the output of multidimensional and multi-invariant data manipulation is avoided. The temporal multiresolution herein realized is iteration free and needs merely one lower-dimensional eigendecomposition. The simplified version of the presented method offers a similar performance while requiring only two time-delayed data sets and thus has a comparable computational complexity with the traditional single resolution ESPRIT. This ESPRIT-type method is also blind to the reflection coefficient which generally depends on the boundary nature, medium property, and signal parameters still to be estimated, viz. DOAs and signal frequencies. Simulation results are included to validate the proposed algorithm.     

Acquirement and enhancement of remote speech signals

To address the challenges of non-cooperative and remote acoustic detection, an all-fiber laser Doppler vibrometer (LDV) is established. The all-fiber LDV system can offer the advantages of smaller size, lightweight design and robust structure, hence it is a better fit for remote speech detection. In order to improve the performance and the efficiency of LDV for long-range hearing, the speech enhancement technology based on optimally modified log-spectral amplitude (OM-LSA) algorithm is used. The experimental results show that the comprehensible speech signals within the range of 150 m can be obtained by the proposed LDV. The signal-to-noise ratio (SNR) and mean opinion score (MOS) of the LDV speech signal can be increased by 100% and 27%, respectively, by using the speech enhancement technology. This all-fiber LDV, which combines the speech enhancement technology, can meet the practical demand in engineering.     

Are transverse phonons important for Γ - X-intervalley scattering?

We employ the rigid pseudo-ion method to calculate the q-dependence of intervalley deformation potentials for GaP from the Γ-point to the X-valley. We find that the fast transverse acoustic phonon (which cannot couple to the symmetry point X) becomes as important along the XW-direction as the longitudinal acoustic phonon (which is allowed at X). We have measured the temperature dependence of the lifetime broadenings of the E₀-gap of GaP with spectroellipsometry in order to obtain an effective intervalley phonon energy from which the relative contributions of the different phonon branches can be determined, but difficulties arise as intervalley and intravalley (Fröhlich) exciton-phonon interaction both contribute to the broadenings.     

Saw minimum peak sidelobe filter for 15-bitM-sequence phase code signals

This paper presents computation results of the minimum peak sidelobe filter (LP filter) for the 15-bitM-sequence phase coded signal with feedback connection [4,3,0] and initial condition 1001. The design of the filter resorts to the linear programming method. The peak sidelobe level is reduced to −21.47 dB by the LP filter of length 15, and is 7.49 dB lower than that by the matched filter. The LP filter can suppress the peak sidelobe even more by increasing its length. The minimum peak sidelobe filter for the 15-bitM-sequence phase coded signal (initial condition 1001) has been implemented with a surface acoustic wave (SAW) device. Experiments show that the peak sidelobe level of the manufactured filter is −19 dB and, thus, only differs from the theoretical value of −21.47 dB by 2.47 dB.     

Time-critical underwater sensor diffusion with no proactive exchanges and negligible reactive floods

In this paper we study multi-hop ad hoc routing in a scalable underwater sensor network (UWSN), which is a novel network paradigm for ad hoc investigation of the world below the water surface. Unlike existing underwater acoustic networks (UAN), the new UWSN paradigm dispatches large number (in the thousands) of unmanned low-cost sensor nodes to locally monitor and report otherwise not easily accessible underwater events in a time-critical manner. Due to the large propagation latency and very low bandwidth of the acoustic channel, a new protocol stack and corresponding models are required as conventional approaches fail. In particular, we show that neither proactive routing message exchange nor reactive/on-demand flooding is adequate in the challenging new underwater environment. Unlike the terrestrial scenarios, on-demand flooding cannot be both reliable and efficient due to widespread collisions caused by the large propagation delay. On the other hand, as in terrestrial scenarios, proactive routing is more expensive and less efficient than on-demand routing in typical underwater environments. We propose a “conservative” communications architecture that minimizes the number of all packet transmissions to avoid possible acoustic collisions. This is implemented in the non-intrusive underwater diffusion (UWD), which is a multi-hop ad hoc routing and in-network processing protocol with no proactive routing message exchange and negligible amount of on-demand floods. To achieve its design goal, UWD does not rely on GPS or power hungry motors to control currents. Instead, UWD is designed in a minimalist’s framework, which assumes homogeneous GPS-free nodes and random node mobility. Our simulation study verifies the effectiveness and efficiency of our design.     

Multifunctional ZnO-Based Thin-Film Bulk Acoustic Resonator for Biosensors

Zinc oxide (ZnO) and its ternary alloy magnesium zinc oxide (Mg _x Zn_1−x O) are piezoelectric materials that can be used for high-quality-factor bulk acoustic wave (BAW) resonators operating at GHz frequencies. Thin-film bulk acoustic resonators (TFBARs) are attractive for applications in advanced communication and in various sensors as they offer the capability of monolithic integration of BAW resonators with radio-frequency integrated circuits (RF ICs). In this paper we report Mg _x Zn_1−x O-based TFBAR biosensors. The devices are built on Si substrates with an acoustic mirror consisting of alternating quarter-wavelength silicon dioxide (SiO₂) and tungsten (W) layers to isolate the TFBAR from the Si substrate. High-quality ZnO and Mg _x Zn_1−x O thin films are achieved through a radio-frequency (RF) sputtering technique. Tuning of the device operating frequency is realized by varying the Mg composition in the piezoelectric Mg _x Zn_1−x O layer. Simulation results based on a transmission-line model of the TFBAR show close agreement with the experimental results. ZnO nanostructures are grown on the TFBAR’s top surface using metal- organic chemical vapor deposition (MOCVD) to form the nano-TFBAR sensor, which offers giant sensing area, faster response, and higher sensitivity over the planar sensor configuration. Mass sensitivity higher than 10³ Hz cm²/ng is achieved. In order to study the feasibility of the nano-TFBAR for biosensing, the nanostructured ZnO surfaces were functionalized to selectively immobilize␣DNA, as verified by hybridization with its fluorescence-tagged DNA complement.     

Three-dimensional integral imaging display system based on negative lens array

An integral imaging display system based on negative lens array in real mode is proposed in this letter. Compared with the conventional integral imaging system with positive lens array, the negative one has a huge advantage on viewing angle. The minimum viewing angle of the imaging display system based on negative lens array is the maximum viewing angle of the positive one with the same parameters. And the imaging display system based on negative lens array can enhance the viewing angle to 180° with special parameters. Other parameters, such as resolution and depth-of-field, are the same in both systems. Another advantage is that the proposed imaging display system based on negative lens array can fill the image area gap between 0 and 2f. The feasibility of our proposed method is experimentally proved. This work has been supported by the National Natural Science Foundation of China (No.11474169) and the Hebei Provincial Science Foundation for Youths (No.F2016402115). E-mail:XXJiao@hebeu.edu.cn      

Thermal lens study of the Tris(2,2’-bipyridyl)iron(Ⅱ) tetrafluoroborate

Experimental results of thermal lens measurements for Tris(2,2’-bipyridyl)iron(II) tetrafluoroborate solution are reported using the dual beam technique. The temporal evaluation of thermal lens was observed at input pump power of I=47 mW. The thermal lens effect was observed with increasing the pump power intensity as well. The evolution time of thermal lens and the fitting of the experimental transient curve were useful to evaluate the parameters of the Tris(2,2’-bipyridyl)iron(Ⅱ) tetrafluoroborate solution.     

Wavelength‐Dependent Photosensitivity in a Germanium‐Doped Sol–Gel Hybrid Material for Direct Photopatterning

Photosensitivity, as evident in permanent changes in refractive index and volume upon light exposure, is observed in a germanium‐doped methacrylate hybrid material (hybrimer) and found to depend on the wavelength of the UV light. Exposure to short‐wavelength UV illumination (220–260 nm) results in very high photosensitivity with changes in refractive index (Δn ≈ 0.0164) and film thickness (Δt ≈ –40 %) that are mainly a result of photopolymerization and Ge‐related densification. In contrast, the hybrimer is hardly photosensitive to light in the long UV‐wavelength range (350–390 nm). Direct photopatterning of a single circle on the hybrimer film creates a concave lens‐like topography upon illumination with UV light of short wavelength and a convex lens‐like one upon illumination with UV light of long wavelength.     

多层压电结构中声表面波特性的计算

The propagation properties of the surface acoustic waves(SAWs) in a ZnO-SiO2-Si multilayered piezoelectric structure are calculated by using the recursive asymptotic method.The phase velocities and the electromechanical coupling coefficients for the Rayleigh wave and the Love wave in the different ZnO-SiO2-Si structures are calculated and analyzed.The Love mode wave is found to be predominantly generated since the c-axis of the ZnO film is generally perpendicular to the substrate.In order to prove the calculated results,a Love mode SAW device based on the ZnO-SiO2-Si multilayered structure is fabricated by micromachining,and its frequency responses are detected.The experimental results are found to be mainly consistent with the calculated ones,except for the slightly larger velocities induced by the residual stresses produced in the fabrication process of the films.The deviation of the experimental results from the calculated ones is reduced by thermal annealing.     

由M2参数定义的光束传输变换理论

本文推导了任意光束与M2参数有关的光腰和发散角经过薄透镜的变换规律,定义了广义的R(z),导出了广义的ABCD法则.     

Analysis of Cell-averaging Based Detectors for χ2 Fluctuating Targets in Multitarget Environments

The χ^2 family of signal fluctuation distributions represents the main fluctuation models which most radar targets follow it in their reflections. This family can be categorized as fluctuation distribution with two degrees of freedom and those with four degrees of freedom. The first category represents all important class of fluctuation models which when illuminated by a coherent pulse train, return a train of fully correlated pulses （Swerling Ⅰ model） or fully decorrelated pulses （Swerling Ⅱ model）. The detection of this type of fluctuating targets is therefore of great importance. This paper is devoted to the analysis of Cell-Averaging （CA） based detectors for the case where the radar receiver noncoherently integrates M square-law detected pulses and the signal fluctuation obeys 2 statistics with two degrees of freedom. These detectors include the Mean-Of （MO）, the Greatest-Of （GO） and the Smallest-Of（SO） schemes. In these processors, the estimation of the noise power levels from the leading and the trailing reference windows is based on the CA technique. Exact formulas for the detection probabilities are derived, in the absence as well as in the presence of spurious targets. The primary and the secondary interfering targets are assumed to be fluctuating in accordance with the χ^2 fluctuation model with two degrees of freedom （SWI ＆ SWII）. The numerical results show that the MO version has the best homogeneous performance, the SO scheme has the best multiple-target performance, while the GO procedure does not offer any merits, neither in the absence nor in the presence of outlying targets.     

Subspace tracking with adaptive threshold rank estimation

In frequency and direction of arrival (DOA) tracking problems, singular value decomposition (SVD) can be used to track the signal subspace. Typically, for a problem sizen, only a few, sayr dominant eigencomponents need to be tracked, wherern. In this paper we show how to modify the Jacobi-type SVD to track only ther-dimensional signal subspace by forcing the (n-r)-dimensional noise subspace to be spherical. Therby, the computational complexity is brought down fromO(n²) toO(nr) per update. In addition to tracking the subspace itself, we demonstrate how to exploit the structure of the Jacobi-type SVD to estimate the signal subspace dimension via a simple adptive threshold comparison technique. Most available computationally efficient subspace tracking algorithms rely on off-line estimation of the signal subspace dimension, which acts as a bottleneck in real-time parallel implementations. The noise averaged Jacobi-type SVD updating algorithm presented in this paper is capable of simultaneously tracking the signal subspace and its dimension, while preserving both the low computational cost ofO(nr) and the parallel structure of the method, as demonstrated in a systolic implementation. Furthermore, the algorithm tracks all signal singular values. Their squares are estimates of the powers in the orthogonal modes of the signal. Thus, applications of the algorithm are not limited to only DOA and frequency tracking where information about the powers of signal components is not exploited.     

New experimental approach for failure prediction in electronics: Topography and deformation measurement complemented with acoustic microscopy

Topography and Deformation Measurements (T.D.M.) under thermo-mechanical solicitation is a new approach for localising and quantifying deformation of electronic assemblies. Cooling and heating capabilities, with different temperature rate and maximum, following JEDEC thermal profiles for example, have been applied on different components before and after assembly using real time Topography and Deformation Measurements.The interest in being able to perform z and (x, y) deformation measurements for traction /compression and shear stress evaluation will be shown. Using acoustic microscopy before and after thermal stress gives the possibility to detect both the conditions in which elastic limits may have exceeded at interfaces, which interface is concerned and the speed at which delamination occurs.Complementarities of this new technique with acoustic microscopy and simulation will be shown for failure prediction applications.     

New Methods for Making the Qubits of a Solid-State Quantum Computer by Implantation of Single Highly Charged 31P Ions

A step-and-repeat and a simultaneous method are proposed and evaluated for the implantation of single highly charged ³¹P ions into a Si/Si _x Ge_{1 – x} heterostructure with the aim of creating the qubits of a solid-state quantum computer. The capabilities of existing axially symmetric compound electromagnetic objective lenses and ion sources are examined in this context. The advantages of such lenses over electrostatic ones are shown. An electromagnetic objective lens of exceptionally small axial aberrations is designed. An optical system using the lens is proposed for a step-and-repeat implanter. The parameters of the implanter are identified that determine its performance. They are lateral ion-positioning tolerance, the chromatic-aberration coefficient of the objective lens, source brightness, and ion multiplicity. An equation is derived that relates the parameters. Requirements are stated on the ion source. Possible ways are discussed of improving the performance of the ion source and the ion-optical system.