Electro-acoustic sounding of the atmosphere

This paper presents the results of measurement of the electrical field generated by a high-power acoustic signal in the atmosphere (electro-acoustic sounding). The radiated acoustic power was about 1 kW. The acoustic-signal frequency varied linearly within the interval 17–21 Hz with a period of 8 min. The electric field was registered by a -shaped antenna. The results of processing of the electric-field records for a part of sessions indicate the presence of an electric response with frequency close to the acoustic-signal frequency. The signal amplitude at the input of the receiving device was 0.1–1 µV.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 48, No. 1, pp. 33–37, January 2005.     

NRD leaky-wave antenna for narrow beams in 94GHz

Theoretical analyses and numerical results of NRD leaky-wave antenna are presented. The results show that the characteristics of frequency scanning and very narrow beam can be implemented by NRD leaky-wave antenna. At the freguency of 94GHz, the half-power beamwidth of 0.14° of the antenna canbe obtained when the length of the antenna is 1.5m. From 90 to 98GHz, frequency scanning is about ±7° relating to the beam angle at 94GHz. The theoretical results are compared with the experimental data.     

Millimeter Wave Antenna with Scanning Beam

The results of theoretical analysis and experimental investigation of the millimeter waves antenna with scanning beam are presented. The operation concept of the antenna is based on the effect of transformation of the surface waves of dielectric waveguide in the volume waves. The smooth space scanning of beam has been made by means of change of wave propagation constant inside of the dielectric waveguide. All experiments were made in the four-millimeter wave range. The angle of scanning was =35° and width of directional diagram was 2° in the scanning plane. The lens and the mirror antennas were designed.     

On the theory of acoustothermometry of waterlike media: Effects of the quasi-static field,strong absorption,and radiation pattern

An integral equation relating the thermal noise’s pressure measured by an acoustothermometer to the one-dimensional temperature profile of a waterlike medium is derived by applying the fluctuation-dissipative theorem to hydrodynamic equations. On the basis of this equation, effects of the quasi-stationary field of thermal radiation, a strong absorption of acoustic waves in the medium, and a finite beam width of the receiving antenna are investigated. Conditions under which the solution to the equation coincides with the result of the transfer theory, which ignores the aforementioned effects, are determined. The role of the effects under study in acoustothermometry of biological media is investigated. A method is proposed for controlling the depth from which the radiation is received. This method allows the retrieval of the temperature profile of the medium from the data of acoustic sounding.     

Degrees of Freedom of a K-User Interference Channel in the Presence of an Instantaneous Relay

In this paper, we study the degrees of freedom (DoF) of a frequency-selective K-user interference channel in the presence of an instantaneous relay (IR) with multiple receiving and transmitting antennas. We investigate two scenarios based on the IR antennas’ cooperation ability. First, we assume that the IR receiving and transmitting antennas can coordinate with each other and that the transmitted signal of each transmitting antenna can depend on the received signals of all receiving antennas, and we derive lower and upper bounds for the sum DoF of this model. In an interference alignment scheme, we divide receivers into two groups called clean and dirty receivers. We design our scheme such that a part of the messages of clean receivers can be de-multiplexed at the IR. Thus, the IR can use these message streams for an interference cancellation at the clean receivers. Next, we consider an IR, the antennas of which do not have coordination with each other and where the transmitted signal of each transmitting antenna depends only on the received signal of its corresponding receiving antenna. We also derive lower and upper bounds for the sum DoF for this model of IR. We show that the achievable sum DoF decreases considerably compared with the coordinated case. In both of these models, our schemes achieve the maximum K sum DoF if the number of transmitting and receiving antennas is more than a finite threshold.     

Sub-THz radiation room temperature sensitivity of long-channel silicon field effect transistors

Room temperature operating n-MOSFETs (n-type metal-oxide silicon field effect transistors) used for registration of sub-THz (sub-terahertz) radiation in the frequency range ν = 53−145 GHz are considered. n-MOSFETs were manufactured by 1-μm Si CMOS technology applied to epitaxial Si-layers (d ≈15 μm) deposited on thick Si substrates (d = 640 μm). It was shown that for transistors with the channel width to length ratio W/L = 20/3 μm without any special antennas used for radiation input, the noise equivalent power (NEP) for radiation frequency ν ≈76 GHz can reach NEP ∼6×10⁻¹⁰ W/Hz^1/2. With estimated frequency dependent antenna effective area S_est for contact wires considered as antennas, the estimated possible noise equivalent power NEP_pos for n-MOSFET structures themselves can be from ∼15 to ∼10³ times better in the specral range of ν ∼55–78 GHz reaching NEP_pos ≈10⁻¹² W/Hz^1/2.     

Study of a Microwave Radar Signal Backscattered at Small Incidence Angles: In-Situ Measurements

We present the results of data processing of the field experiment devoted to a study of a microwave signal backscattered by a rough water surface and compare them with the theoretical estimates. The measurements were conducted sequentially using a radar with parabolic and knife-beam antennas. The radar was mounted on the Molitovsky bridge at a height of 40 m across the Oka river in Nizhny Novgorod, Russia. For the radar with knife-shaped antenna pattern, we examined the reflected-signal power and the shift and width of the Doppler spectrum as functions of the azimuthal angle for the nadir sounding. For the parabolic antenna, we studied the reflected-signal power as a function of the incidence angle. Comparison with the experimental data shows that the developed theoretical model of a Doppler spectrum is in good agreement with the observations. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 48, No. 8, pp. 661–673, August 2005.     

Radio-acoustic sounding of the ionosphere

We present the results of first experiments on radio-acoustic sounding of ionosphere at the altitudes from 70 to 85 km. The sounding was performed in autumn 2006, using a horn acoustic emitter and a radar on the basis of the “Sura” facility. The emitter had an acoustic power of about 1 kW and operated in the chirp-modulation regime with frequency variation from 15.9 to 18.4 Hz. The radar transmitter operated in the pulse regime at a frequency of 9 MHz and had an average power of 30 kW. The power of the radio signal scattered from a sound wave in the ionosphere did not exceed 10⁻¹⁶ W, and the measured values of the temperature in the scattering region ranged from 190 to 225 K. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 52, No. 2, pp. 128–133, February 2009.     

Active Frequency-Tune Beam-Scanning Leaky-Wave Antenna Arrays

X-band active beam-scanning leaky-wave antenna arrays, including 1 × 1,1 × 2 and 1 × 4 prototypes, have been demonstrated. These antennas integrated one or several microstrip leaky-wave antenna elements with a single varactor-tuned HEMT VCO as an active source. Measured results on experimental antennas indicate that the beam scanning angle of the 1 × 1 antenna close to 40° can be achieved and the scanning range of 1 × 2 and 1 × 4 antenna arrays are both close to 32°. Furthermore, reflected wave due to the open end of each leaky-wave antenna element has been suppressed by the symmetric configuration of this antenna array and the antenna efficiency increases. When comparing with the measured radiation pattern of the single element antenna, we found that the 1 × 2 and 1 × 4 antenna arrays can effectively suppress the reflected power by more than 5.5 dB and 10.5 dB, respectively, at 10.2GHz. The power gain are more than 2 dB and 3.16 dB higher than the single element antenna with a measured EIRP of 18.67 dBm.     

Precise Underwater Distance Measurement by Dual Acoustic Frequency Combs

Underwater acoustics is of fundamental importance for marine science and technology. However, acoustic waves transmitted by state‐of‐the‐art underwater acoustic systems are not inherently phase locked, which hinders the development of underwater acoustic technology. For example, the precision of underwater distance measurement can only achieve centimeter level. As a versatile tool, optical frequency combs have enabled revolutionary progress in optical metrology and precision measurement. In parallel with optical frequency combs, here, the generation of fully stabilized, underwater acoustic frequency combs is reported, in which equidistant acoustic modes are produced via a hydroacoustic transducer. The precision of each individual acoustic mode is measured to be 10^?9 at 1 s and 10^?12 at 1000 s averaging times. Underwater distance measurements are carried out in an anechoic pool using a dual‐comb scheme. Comparison with reference values shows consistency within 50 µm (7 × 10^?6 in relative). The relatively long‐duration experiments at 7 m distance yield an Allan deviation of 1.8 µm (2.6 × 10^?7 in relative) at 1 s and further 480 nm (6.8 × 10^?8 in relative) at 40 s averaging times. The approach to acoustic frequency comb generation offers a promising and powerful platform for future underwater distance measurement, positioning, and navigation.     

阵馈抛物柱面天线合成超宽带高功率微波

在时域推导了超宽带脉冲空间功率合成的条件,得到了多路脉冲信号在极化方向相同,幅度、波形一致的条件下,可实现最大化功率输出的结论。基于此提出了一种阵馈的抛物柱反射面天线。采用10喇叭单元叠状排列形成一维馈源阵列放置于焦线上,照射抛物柱反射面后形成相干脉冲,在主轴方向合成超宽带高功率微波波束。仿真结果表明,该阵馈天线较最优口径的单馈源天线,远场辐射功率密度提高了87倍以上,且波束宽度由66°减为8°,实现了超宽带高功率微波的高效空间功率合成。     

Method for efficient representation of the information on the weighting coefficients of a transmitting beamformer in wireless digital communication systems with multielement adaptive antennas

We consider the problem of transmission of channel state information for a transmitting beamformer in digital communication systems with adaptive transmitting and receiving antennas. It is shown that using the unitary property of the weighting matrices of the transmitting beamformer, we can significantly reduce the amount of transmitted information with the help of the well-known Givens decomposition. We propose a method for determining the optimal bit allocation for quantization of the complex weighting coefficients of the transmitting beamformer. Results of mathematical simulation of a wireless digital communication system with multielement adaptive antenna arrays are shown for a multipath Rayleigh channel. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 51, No. 9, pp. 814–823, September 2008.     

光电导天线辐射阻抗特性模拟分析(英文)

针对连续太赫兹光电导天线辐射功率较低的缺点,利用有限积分方法对三种常用的光电导天线,包括偶极天线、蝶形天线和螺旋天线,进行数值模拟并分析比较其辐射阻抗特性.仿真结果表明,偶极天线的辐射阻抗与偶极长度、宽度、电极间隙以及传输线宽度有关,且在其谐振频率存在峰值阻抗,适用于特定频率的太赫兹波辐射.蝶形天线和螺旋天线在所研究的太赫兹波段具有近似稳定的辐射阻抗,广泛应用于宽带领域.对带有交叉电极的电极间隙进行计算,结果表明由交叉电极引入的附加电容降低了天线的高频阻抗.     

基于2D微电子机械系统(MEMS)镜全向激光雷达光学系统设计

为了满足全向激光探测的需求,提出一种基于2DMEMS镜扫描的激光雷达结构。激光器通过1×6高速光开关分时地给6个扫描子系统提供光信号,6个扫描子系统探测视场叠加起来可实现360°激光探测。每个扫描子系统的扫描范围为60°×30°,其中包含一个扩展MEMS镜扫描角度的发射光学天线和一个大视场有增益的接收光学天线。发射光学天线将MEMS镜±10°的扫描角扩展到±30°,发散度小于0.2mrad;接收视场内的激光波经过接收天线在探测器上所成的半像高小于1mm,接收增益为3.65。通过计算修正后的激光雷达方程可得到发射功率20 W的激光束在工作距离100 m内的回波功率≥1 nW,结果表明该光学系统可适用于激光雷达系统。     

一种基于运动式发射天线的光学接收天线设计

设计一款应用于多发射天线多接收天线自由空间激光通信系统中的折射式光学接收天线。天线焦距120.02 mm,相对孔径1∶1.13,工作波长为850 nm,波长范围覆盖820 nm ~880 nm,在50 lp/mm频率处0视场的MTF为0.5。接收天线可以在发射天线移动48 mm范围内利用光敏面直径为0.5 mm的雪崩光电二极管（APD）接收3 mrad发散角的光信号。该天线由两组、共4片球面透镜组成,结构简单,可实现对运动式发射天线的光信号的接收。     

Optimization of transmitting beam patterns of a conformal transducer array

A method is presented to calculate the driving-voltage weighting vector of a conformal array of underwater acoustic transmitting transducers to obtain a low-sidelobe beam pattern based on the measured receiving array manifold. The relationship among three quantities is given, which are, respectively, the radiated acoustic field, the measured receiving array manifold matrix and the driving-voltage weighting vector of the transducer array. Then, the driving-voltage weighting vector of the array is calculated using the optimization method to obtain a low-sidelobe transmitting beam pattern. At the frequency of 12.5 kHz, the receiving array manifold matrix of a 27-element conformal array is measured in an anechoic water tank. The driving-voltage weighting vector of the array is calculated using the proposed method. In addition, the computer simulation and experiments are carried out. The results agree well and show that the proposed method can obtain a low-sidelobe transmitting beam pattern and at the same time provide the largest amplitude of pressure in the axial direction when the maximum amplitude of the driving voltages of the array elements keeps unchanged.     

Simulation of the Field Emission Arrays with Parallel Wedge Emitter, Gates and Co-Planar Lens

Using the particle-in-cell (PIC) simulation code MAGIC, the wedge emitter, parallel gate and anode with and without co-planar lens have been simulated. The electron beam streamlines and the X-V_x phase space have been evaluated, which show that the co-planar lens focuses the electron. Simulation results are presented for a single FEA's cell with the anode biased at 500V and spaced 100m from the cathode, which indicated that the electron beam width at anode is about 60.2m for without lens FEAs, after add the lens with –70V, the electron beam width will be decrease to 8.1m, meanwhile the maximum transverse velocity will decrease from ±1×10⁶m/s to ±1.46×10⁵m/s.     

A slow gravity compensated atom laser

We report on a slow guided atom laser beam outcoupled from a Bose–Einstein condensate of ⁸⁷Rb atoms in a hybrid trap. The acceleration of the atom laser beam can be controlled by compensating the gravitational acceleration and we reach residual accelerations as low as 0.0027 g. The outcoupling mechanism allows for the production of a constant flux of 4.5×10⁶ atoms per second and due to transverse guiding we obtain an upper limit for the mean beam width of 4.6 μm. The transverse velocity spread is only 0.2 mm/s and thus an upper limit for the beam quality parameter is M ²=2.5. We demonstrate the potential of the long interrogation times available with this atom laser beam by measuring the trap frequency in a single measurement. The small beam width together with the long evolution and interrogation time makes this atom laser beam a promising tool for continuous interferometric measurements.     

基于轴锥镜对的高光能利用率激光通信天线性能分析

提出一种增加轴锥镜对的同轴反射式光学结构激光发射天线方案,通过对入射光束的光强重新排布,降低同轴反射式结构固有的中心遮拦造成的能量损失,提高光能利用率.运用衍射光学原理分析并模拟了单色高斯光束经过轴锥镜对后传播至天线光阑平面处的光场分布,比较了普通同轴反射式天线和高光能利用率天线在不同入射光束腰半径、不同线遮拦比下的发射光能利用率.结果表明:高光能利用率天线在线遮拦比0.1和0.25的情况下,通过合理调整入射光束腰大小,光能利用率分别可达到99%和96%以上,远高于传统的同轴反射式天线.分析了高光能利用率天线发射光束的远场光强分布,发现其进入接收天线口径内的光场可近似为平顶分布.     

The effect of post-annealing on surface acoustic wave devices based on ZnO thin films prepared by magnetron sputtering

Zinc oxide (ZnO) thin films were deposited on unheated silicon substrates via radio frequency (RF) magnetron sputtering, and the post-deposition annealing of the ZnO thin films was performed at 400 °C, 600 °C, 800 °C, and 1000 °C. The characteristics of the thin films were investigated by X-ray diffractometry (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The films were then used to fabricate surface acoustic wave (SAW) resonators. The effects of post-annealing on the SAW devices are discussed in this work. Resulting in the 600 °C is determined as optimal annealing temperature for SAW devices. At 400 °C, the microvoids exit between the grains yield large root mean square (RMS) surface roughness and higher insertion losses in SAW devices. The highest RMS surface roughness, crack and residual stress cause a reduction of surface velocity (about 40 m/s) and increase dramatically insertion loss at 1000 °C. The SAW devices response becomes very weak at this temperature, the electromechanical coupling coefficient (k²) of ZnO film decrease from 3.8% at 600 °C to 1.49% at 1000 °C.