HT_c SQUID磁强计阵列研究

高温超导量子干涉器(HTcSQUID)已有20多年研究历史。目前,HTcSQUID磁强计以它对磁场高的分辨率、低磁通白噪声和低的1/f噪声起始频率,相对成熟、便宜的制冷技术,被认为是开发无线电频谱低端应用和微弱磁场测量领域有竞争力的新技术。但是,囿于高温超导体的材料特性和高温超导约瑟夫森结的研究水平,当前HTcSQUID磁强计的磁场灵敏度比传统LTcSQUID磁强计仍然要低一个数量级,因而导致它在低频无线电电子学系统和相关领域中的应用还存在一些困难。为在现有条件下积极开展HTcSQUID磁强计技术的应用研究,拓展HTcSQUID磁强计技术的应用范围,作者主要通过试验,在HTcSQUID磁强计当前内禀磁通噪声限制下,使用多HTcSQUID磁强计对待测场的相干检测可能是提高SQUID检测接收系统输出信噪比的有效方法进行了研究。已经获得的初步实验结果表明,在电磁干扰不太大的环境中,多HTcSQUID磁强计技术可以在现有HTcSQUID磁强计的磁场灵敏度指标限制下,使系统的接收信噪比得到提高。     

Multichannel fetal magnetocardiography using SQUID bootstrap circuit

Fetal magnetocardiography （MCG） is a sophisticated non-invasive technique for the fetal heart diagnosis. We constructed a multichannel fetal MCG system based on a novel superconducting quantum interference device （SQUID） direct readout scheme called SQUID bootstrap circuit （SBC）. The system incorporates four SBC gradiometers for the signal detection and three SBC magnetometers as the references. The fetal MCG signal at a 28-weeks’ gestation was measured. By the fetal MCG signal separation and average, the P-wave and QRS complex can be clearly identified. These results indicate that the SBC is one of the most promising techniques for the fetal MCG recordings.     

Baseline optimization for scalar magnetometer array and its application in magnetic target localization

Generally, a magnetic target can be described with six parameters, three describing the position and three describing the magnetic moment. Due to a lack of sufficient components from one magnetometer, we need more than one magnetometer when locating the magnetic target. Thus, a magnetometer array should be designed. The baseline of the array is an important factor that affects the localization accuracy of the target. In this paper, we focus on the localization of a static target by using a scalar magnetometer array. We present the scalar magnetometer array with a cross-shaped structure.We propose a method of determining the optimal baseline according to the parameters of the magnetometer and detection requirements. In the method, we use the traditional signal-to-noise ratio(SNR) as a performance index, and obtain the optimal baseline of the array by using the Monte Carlo method. The proposed method of determining the optimal baseline is verified in simulation. The arrays with different baselines are used to locate a static magnetic target. The results show that the location performance is better when using the array with the optimal baseline determined by the proposed method.     

小波变换在心磁信号处理中的应用

噪声的消除一直是微弱信号检测和处理中尤为重要的一个环节.从小波变换的角度出发，利用了小波变换在时、频两域都具有表征信号局部特征的能力，对心磁信号这种典型的微弱信号进行了消噪处理.实验中的心磁数据是单通道高温超导量子干涉磁强计测得.理论分析和实验结果表明，这种方法能有效地提高输出信噪比，同时也适合于其他非平稳信号的消噪. 关键词： 小波变换 心磁 消噪     

应用在相控阵雷达上的光学实时延迟线

相控阵天线是雷达技术的重要发展方向之一。电子相控阵雷达所遇到的问题是天线阵列孔径效应限制了雷达信号的瞬时带宽,使其不能满足通信和雷达技术的发展需要。光学实时延迟技术,可以解决这一问题。介绍了相控阵天线光实时延迟控制原理。并对几种典型的光实时延迟线的工作原理和技术特点作了简要的分析。     

丝阵负载Z箍缩可见光图像诊断系统

主要介绍了为“强光一号”加速器丝阵负载Z箍缩实验设计的可见光图像诊断系统,系统时间分辨约为5 ns,空间分辨约为6.5 lp/mm,光谱响应范围365~750 nm。系统能够满足从早期单丝电离到等离子体柱飞散整个Z箍缩过程的诊断要求, 给出了系统在Z箍缩实验中获得的丝阵负载内爆图像序列,并对其反映的内爆现象进行了初步的唯象分析。     

Optical beam forming techniques for phased array antennas

Three optical beam forming techniques are identified as applicable to large spaceborne phased array antennas. They are 1) the fiber replacement of conventional RF phased array distribution and control components, 2) spatial beam forming, and 3) optical beam splitting techniques. Two novel optical beam forming approaches, i.e., the spatial beam forming with a smart pixel spatial light modulator (SLM) and the optical beam splitting approaches are conceived with integrated quasi-optical components. Also presented are the transmit and receive array architectures with the new SLM.     

Optical magnetometer with submicron spatial resolution based on Rb vapors

It is shown experimentally that use of fluorescence and transmission spectra obtained from nanocells with the thickness of column of rubidium atomic vapor L = λ/2 and L = λ, respectively (λ = 794 nm is the wavelength of laser radiation close to resonance with D ₁-line transition of Rb atoms), by means of a narrowband diode laser allows spectral separation and study of variations of probabilities of atomic transitions between ground and excited states of hfs of D ₁ lines of ⁸⁵Rb and ⁸⁷Rb atoms in the range of magnetic fields from 10 to 5000 G. Small thickness of atomic vapor column (∼390 nm and ∼794 nm) allows applying permanent magnets simplifying essentially creation of strong magnetic fields. Advantages of this technique are discussed as compared with the technique of saturated absorption. The obtained results show that a nanocell with submicrom thickness of vapor column may serve as a basis for designing a magnetometer with submicron local spatial resolution which is important in case of measuring strongly inhomogeneous magnetic fields. Experimental data are in good agreement with the theoretical results.     

丝阵负载Z箍缩可见光图像诊断系统

 主要介绍了为“强光一号”加速器丝阵负载Z箍缩实验设计的可见光图像诊断系统,系统时间分辨约为5 ns,空间分辨约为6.5 lp/mm,光谱响应范围365~750 nm。系统能够满足从早期单丝电离到等离子体柱飞散整个Z箍缩过程的诊断要求, 给出了系统在Z箍缩实验中获得的丝阵负载内爆图像序列,并对其反映的内爆现象进行了初步的唯象分析。     

Optical film with microstructures array for slim-type backlight applications

A novel optical film with optical microstructures is proposed for enhancing the light control in slim-type backlight modules. The proposed film enables a homogeneous luminance distribution to be obtained though an appropriate adjustment of the filling ratio of the optical microstructures in different regions of the backlight unit. The simulation results show that the luminance provided by a backlight incorporating a filling-ratio-optimized optical film and a pyramid-structured brightness enhancement film is approximately 1.5 times of the luminance obtained from a backlight with conventional optical films. In addition, the proposed film enables a significant reduction in the thickness of the backlight unit. Thus, the novel optical film is suitable for a slim bottom-lit backlight module.     

Optical fiber coupler array for multi-point sound field measurements

A pressure-sensitive device using an optical fiber coupler is proposed, and is integrated into an array system to measure sound field distributions. The optical coupling between two optical fibers is modulated by the applied sound field with the use of a membrane mechanically connected to the coupler. In the array system, a large number of the optical coupler sensors are connected two-dimensionally, and sound pressure at each sensor can be read out by switching the input light sources in turn. A prototype of the basic array system based on this principle was made, and its performance was demonstrated. The signal discrimination between each element was confirmed in a 2x2 array; then, using a four-element linear array, we demonstrated the steering of beam based on the phased array method.     

Optical multilayer detection array for fast ultrasonic field mapping

An optical multilayer detection array for ultrasonic measurements is presented. The probe comprises a dielectric interference filter structure that is evaporated onto a glass plate. An incident acoustic pressure signal deforms the layer system, and the induced modulation of the optical reflectance is determined by a simple optical detection scheme. The principle of measurement is demonstrated by a line scan through the focus of a broadband transducer and can be applied to rapid two-dimensional characterization of ultrasonic fields. The high temporal and spatial resolution of the measurements is combined with high sensitivity and durability of the probe, and, in contrast with fiber-tip multilayer hydrophones, the multilayer detection array provides signals that are not influenced by acoustic resonances and diffraction phenomena.     

负二进制编码的光学阵列化复数运算

建立一套新颖的光学负二进制并行算法体系，包括加权－移位加法、列阵乘法等。一切运算无符号位、无进位、无再编码。利用两层阵列可实现高精度的复数运算，三层阵列可实现复数矩阵－矢量运算。该算法体系非常适合于光学执行。相应地，文中给出了两层列阵复数相乘光学系统及实验结果。原理上，该算法是可级联的。     

Baseline optimization of SQUID gradiometer for magnetocardiography

SQUID gradiometer techniques are widely used in noise cancellation for biomagnetic measurements.An appropriate gradiometer baseline is very important for the biomagnetic detection with high performance.By placing several magnetometers at different heights along the vertical direction,we could simultaneously obtain the synthetic gradiometers with different baselines.By using the traditional signal-to-noise ratio(SNR) as a performance index,we successfully obtain an optimal baseline for the magnetocardiography(MCG) measurement in a magnetically shielded room(MSR).Finally,we obtain an optimal baseline of 7 cm and use it for the practical MCG measurement in our MSR.The SNR about 38 dB is obtained in the recorded MCG signal.     

A digital filtering scheme for SQUID based magnetocardiography

Considering the properties of slow change and quasi-periodicity of magnetocardiography (MCG) signal, we use an integrated technique of adaptive and low-pass filtering in dealing with two-channel MCG data measured by high $T_{\rm c}$ SQUIDs. The adaptive filter in the time domain is based on a noise feedback normalized least-mean-square (NLMS) algorithm, and the low-pass filter with a cutoff at 100Hz in the frequency domain characterized by Gaussian functions is combined with a notch at the power line frequency. In this way, both relevant and irrelevant noises in original MCG data are largely eliminated. The method may also be useful for other slowly varying quasi-periodical signals.     

Optical response of a cold-electron bolometer array

A multielement bolometric receiver system has been developed to measure the power and polarization of radiation at a calculated frequency of 345 GHz. Arrays of ten series-parallel connected cold-electron bolometers have been pairwise integrated into orthogonal ports of a cross-slot antenna. Arrays are connected in parallel in the high-frequency input signal and in series in the output signal, which is measured at a low frequency, and in a dc bias. Such an array makes it possible to increase the output resistance by two orders of magnitude as compared to an individual bolometer under the same conditions of high-frequency matching and to optimize the matching with the JFET amplifier impedance up to dozens of megohms. Parallel connection ensures matching of the input signal to the cross-slot antenna with an impedance of 30 Ω on a massive silicon dielectric lens. At a temperature of 100 mK, a response to the thermal radiation of a thermal radiation source with an emissivity of 0.3, which covers the input aperture of the antenna and is heated to 3 K, is 25 μV/K. Taking into account real noise, the optical fluctuation dc sensitivity is 5 mK, the estimated sensitivity corresponding to the noise of the amplifier is about 10⁻⁴ K/Hz^1/2, and the noise-equivalent power is about (1–5) × 10⁻¹⁷ W/Hz^1/2.     

Optical readout method for microcantilever array sensing and its sensitivity analysis

An optical readout platform using a knife-edge filter for detecting the bending of a bimaterial microcantilever array is established, and the influence of stress-induced micromirror deformation on the optical detection sensitivity is discussed. The influence of deformation is modeled theoretically and validated experimentally. Analysis shows that the optical detection sensitivity will decrease by 50% when the mirror has a deformation of lambda/5 (lambda is the wavelength of readout light). Finally, an infrared image is obtained by the platform.     

A synthetic optically pumped gradiometer for magnetocardiography measurements

Magnetocardiography(MCG)measurement is important for investigating the cardiac biological activities.Traditionally,the extremely weak MCG signal was detected by using superconducting quantum interference devices(SQUIDs).As a room-temperature magnetic-field sensor,optically pumped magnetometer(OPM)has shown to have comparable sensitivity to that of SQUIDs,which is very suitable for biomagnetic measurements.In this paper,a synthetic gradiometer was constructed by using two OPMs under spin-exchange relaxation-free(SERF)conditions within a moderate magnetically shielded room(MSR).The magnetic noise of the OPM was measured to less than 70 fT/Hz1/2.Under a baseline of 100 mm,noise cancellation of about 30 dB was achieved.MCG was successfully measured with a signal to noise ratio(SNR)of about 37 dB.The synthetic gradiometer technique was very effective to suppress the residual environmental fields,demonstrating the OPM gradiometer technique for highly cost-effective biomagnetic measurements.     

Optical potential of a disordered array of scatterers

We study the propagation of scalar waves in a disordered array of static scatters. We derive a cluster expansion for the optical potential in analogy to that for the dielectric constant of a polarizable suspension. It is shown that the long range of the free space Green function leads to divergence of the cluster integrals at low energy. The divergences are removed by a resummation procedure analogous to the resummation of Mayer cluster integrals in the theory of electrolytes. We derive expressions for the most important contributions to the optical potential.