电磁逆散射无相位检测的相位复原

利用入射场作为约束条件,用最优化泛函的方法由总场幅度信息重建散射场幅度和相位.分析了散射场自由度和噪声对重建结果的影响.讨论了成功实施相位复原和避免局部极小值的条件.首次用实验结果验证电磁逆散射无相位检测相位复原的可行性,证明了方法的有效性、高度稳定性和较强的抗噪声能力.该方法的计算成本低,实用性较强.研究结果是实施无相位检测电磁逆散射的基础.     

Phase shifter with high amplitude accuracy

A phase shifter for the audio and subaudio range has been built that keeps the amplitude deviation within ±0.4%. The phase angle can be varied between 0 and approximately 180°, with infinite resolution.     

Phase difference between linear components of ellipticallypolarized waves from amplitude only measurements

An amplitude-only measurement setup can measure the axial ratio and tilt angle of an elliptically polarized wave. During design, both the amplitude and phase of the linear components are needed. The equipment measures the amplitudes directly. A nomograph, using the well-known relationships between polarization components determines the phase of the vertical component relative to the horizontal. The value of the nomograph goes beyond the stated objective, because it shows the relationships between the variables. The nomograph gives both the requirements for good circularity, and the sensitivity of the various parameters     

屏蔽对阻抗测量的影响

屏蔽对抑制电磁场耦合干扰起着重要的作用.为了研究屏蔽在阻抗测量中的影响,通过屏蔽原理以及实现等电位屏蔽,了解屏蔽对电容、电感、电阻测量值影响的重要性,进而保证测量值的可靠性.     

A probe for organ impedance measurement

In this paper, we describe the theory and practical implementation of an electrical impedance probe for making in vivo measurements of the electrical admittance of living tissue. The probe uses concentric annular electrodes and is shown to sample a more localized, yet greater, volume of tissue than the standard four-electrode probe. We have developed a mathematical model for the conduction of current between the probe electrodes assuming that we are investigating a uniform, isotropic, semi-infinite region and taking into account the contact impedance between the electrodes and the organ. The electric fields produced by the probe have been calculated by solving a weakly singular Fredholm integral equation of the second kind. The size and position of the probe electrodes have been optimized to maximize both the accuracy in the admittance measurement and insensitivity to contact impedance. A probe and driving hardware have been constructed and experimental results are provided showing the accuracy of admittance measurements at 50 and 640 KHz.     

Phase and amplitude uncertainties in heterodyne detection

The quantum limits on simultaneous phase and squared-amplitude measurements made via optical heterodyne detection on a single-mode radiation field are established. The analysis proceeds from a fully quantum mechanical treatment of heterodyning with ideal photon detectors. A high mean field uncertainty principle is proven for simultaneous phase and squared-amplitude observations under the condition that the signal and image band states are independent, and the image band has zero mean. Operator representations are developed which show that no such principle applies when arbitrary signal/image band dependence is permitted, although the mean observations are no longer functions of the signal field alone. A multimode two-photon coherent state illustrating this behavior at finite energy is exhibited. Potential applications for the resulting improved accuracy measurements are briefly described.     

New measurement method of Gunn-diode impedance

Using a suitably designed cavity, the negative conductance of X band Gunn diodes is derived from oscillation buildup characteristics when a steep bias voltage step is applied. By this method, a quick assessment of the diode negative conductance as a function of r.f. voltage amplitudes can be made.     

Optical fiber sensor for vibration amplitude measurement

An optical fiber vibration sensor capable of measuring vibration amplitudes ranging from 1 mm down to 0.1 μm with a wide range of frequencies form 0.5 Hz to 100 kHz is described. The proposed method can be used to calibrate accelerometers. In this method the light from a tungsten halogen lamp is made to pass through an optical fiber whose exit end is mounted on the object under test. The emergent light is detected by a lock-in amplifier and then measured by a digital panel meter which can be made to give direct reading of the vibration amplitude. The main advantages of this method are wide dynamic range, wide frequency range, linearity, noise reduction, ruggedness, and light weight. The ultimate detectability can be as much as 0.5 Å/√Hz at 1 kHz     

Phase retrieval near-field metrology of unknown apertures

The complex aperture and far fields of a millimetre wave reflector are determined by phase retrieval from the near-field intensity and a partial constraint. The data scans are close together and provide comprehensive metrology suitable for near-field facilities.<>     

Phase and amplitude fluctuations in a mode-locked laser

Comparisons are made of the phase and amplitude fluctuations of a laser when it operates single mode and when it is mode locked with the same total average power. Despite the much lower signal-to- (spontaneous emission) noise ratio of the mode-locked laser, the linewidth of each of the locked modes is the same as that of the single mode. The fluctuation of the total intensity of the mode-locked laser, and the linewidth enhancement factor due to intensity fluctuation as recently analyzed by Henry, are the same in both cases.     

Electrical impedance measurement of urinary bladder fullness

A tetrapolar 75-kHz, 0.2-mA constant-current electrical impedance measuring system was used to monitor urinary volume change over 12 four-hour sessions in 20 male and 20 female normal human subjects. Two spot voltage electrodes (E) and two spot current electrodes (I) were applied 5 cm above the symphysis pubis at 15 cm interelectrode distances, 7.5 cm bilaterally from the midline. Five measurements of impedance and skin temperature were made at 15-minute intervals over 4 hours. Specific gravity, impedance change, and volume were recorded with each voided specimen. Suprailiac and infrascapular skinfolds, and circumference at iliac crests were measured. The subjects drank 175 ml of fluids per hour during the testing session. Subjects remained in the supine position during measurements. They walked to the lavatory to void. Bladder fullness is defined as the urge to void. Results include: (1) a poor negative correlation between specific gravity of urine and impedance (r2 = 0.1240, p less than or equal to 0.01); (2) baseline impedance was dependent upon individual subject characteristics: in males skin area, skinfold thickness, and suprailiac circumference; in females skinfold thicknesses and time since last menstrual period; (3) impedance decreased with urinary bladder filling and increased upon voiding (p less than or equal to 10(-10)); (4) the cumulative sum test (CUSUM) predicted time to void in 78.9% of voids (p less than or equal to 0.05) and no void (when voiding did not occur) in 66.8% of no voids (p less than or equal to 0.05). Overall accuracy of the CUSUM test was 74.6% (p less than or equal to 0.05).     

Optical probe for absolute measurement of surface-acoustic-wave amplitude

A simple method is proposed for absolute measurement of s.a.w. mechanical deformation normal to the surface of propagation. Experimental results are given with an error smaller than 5%.     

点源离焦图像位相复原方法

为了实现利用点源传递函数测试仪器在测量可见光镜头光学传递函数的同时测出镜头出瞳的波前,采用了一种基于点源目标离焦图像的位相复原算法.该方法无需改变点源传递函数测试仪器的硬件设置,直接利用在传递函数测试过程中,通过改变位于镜头后焦面附近的显微镜与CCD的位置所采集的多幅离焦图像及改进的GS算法实现离焦面与镜头出瞳面光场的...     

Phase and amplitude measurements for high bandwidth optical signals

In this paper a novel technique for obtaining the amplitude and phase of optical pulses with time extents as short as tens of ps is presented. The method which is based on the transport-of-intensity equation only requires, for a practical realization, of passive fiber optic devices. It employs as the main component a dispersive element with a known second order dispersion coefficient. Two different setup implementations are considered, for which simulations are carried out in order to test the method performance taking into account both, realizable models of the involved devices and typical pulses found in optical transmission systems. The characterization of optical pulses affected by dispersion and nonlinear effects, such as self-phase modulation, is used to evaluate the performance of the method and show the practical feasibility of the future implementation.     

Phase and amplitude phase restoration in synthetic aperture radarimaging

Methods for addressing two types of multiplicative noise in synthetic aperture radar (SAR) imaging are presented. The authors consider a multiplicative noise with a real phase (i.e. the SAR signal's phase is contaminated but its amplitude is uncorrupted) that possesses unknown functional characteristics with respect to the radar signal's temporal frequencies. A perturbation solution for phase reconstruction from amplitude is developed from a wave equation governing the SAR signal and a Riccati equation that relates the amplitude and phase functions of the SAR signal. This solution is converted into a noniterative analytical solution in terms of the moments and powers of the log amplitude function. Next, the authors consider a multiplicative noise with a complex phase (i.e. both the amplitude and phase of the SAR signal are contaminated) that varies linearly with respect to the radar signal's temporal frequencies. The two wave equations governing the SAR signal at two temporal frequencies of the radar signal are combined to derive a method to reconstruct the complex phase error function.     

基于MSP430单片机的便携式阻抗测量系统

为了克服现有阻抗测量仪功耗大,体积大,价格高的问题,基于AD5934与MSP430F169设计了一种具有低功耗特性的便携式阻抗测量系统。采用超低功耗的MSP430F169作为主控芯片,通过I2C总线控制基于AD5934的阻抗测量模块完成阻抗的测量,并通过LCD液晶屏显示测量结果。RLC串联回路和R||C电路测量实验表明:该系统能精确测量待测物的阻抗值,并可测其共振频率,相对误差低至0.04%。该系统在功耗和便携性方面实现了创新,与传统的阻抗测试仪相比具有体积小、功耗低、精度高、成本低等优点,可广泛应用于普通电阻电容、水电导率、生物复阻抗等测量。     

Phase and amplitude pre-emphasis techniques for low-power serial links

A novel approach to equalization of high-speed serial links combines both amplitude pre-emphasis to correct for intersymbol interference and phase pre-emphasis to compensate for deterministic jitter, in particular, data-dependent jitter. Phase pre-emphasis augments the performance of low power transmitters in bandwidth-limited channels. The transmitter circuit is implemented in a 90-nm bulk CMOS process and reduces power consumption by pushing CMOS static logic to the output stage, a 4:1 output multiplexer. The received signal jitter over a cable is reduced from 16.15 ps to 10.29 ps with only phase pre-emphasis at the transmitter. The jitter is reduced by 3.6 ps over an FR-4 backplane interconnect. A transmitter without phase pre-emphasis consumes 18 mW of power at 6Gb/s and 600mVpp output swing, a power budget of 3mW/Gb/s, while a transmitter with phase pre-emphasis consumes 24mW, a budget of 4 mW/Gb/s.     

An impedance measurement method for double-gap klystron cavity

A new method has been developed for measuring the impedance of a two-gap cavity used in high-power klystrons. The principle is based on network analysis. The cavity under test is considered as a microwave network. The two gaps of the cavity and its output terminal are referred to as three ports. We then can use an impedance matrix to characterize this system, and the six independent impedance parameters can be found by measuring the input impedance seen from the output waveguide when the gaps are in different conditions; viz., either open, shorted, or perturbed. The gap impedance then can be deduced therefrom. It is shown that there are three impedances for a double-gap cavity instead of one for a single-gap cavity. Another problem dealt with here is how to evaluate the capacitance introduced by the perturbation. A few typical experimental results are presented.     

基于阻抗测量的孤岛检测方案

本文对单相光伏并网发电系统的孤岛检测方案进行了研究.结合goertzel算法,采用注入谐波电流法进行电网基波阻抗估计,并详细给出了推导过程和结论.