Full Vectorial 3-D Sensitivity Analysis and Design Optimization Using BPM

We present a novel approach to the sensitivity analysis of 3D structures using the full vectorial beam propagation method (FVBPM). Using no extra simulations, the sensitivities of the response with respect to all design parameters are obtained regardless of their number. Our approach is exploited to calculate the sensitivities of the propagation constants of multimode waveguides. It is also applied to the 3D imaginary distance FVBPM (ID-FVBPM) and utilized to extract the sensitivities of the mode parameters. The calculated sensitivities are then utilized within a gradient-based optimization algorithm to illustrate the application of the obtained sensitivities. The accuracy of our approach is verified through a comparison with the expensive central finite difference applied directly at the response level.     

Directly performance-constrained template-based layout retargeting and optimization for analog integrated circuits

Due to intrinsic intricacy, layout parasitics exhibit a significant impact on the performance of analog integrated circuits. In this paper a directly performance-constrained parasitic-aware automatic layout retargeting and optimization algorithm is presented. Unlike the conventional sensitivity analysis, a general central-difference based scheme using any simulator for sensitivity computation is deployed. We propose a piecewise sensitivity model to enforce more accurate sensitivity computation during parasitic optimization. Moreover, mixed-integer performance constraints due to parasitics are included in the formulated mixed integer nonlinear programming problem rather than through either indirect parasitic-bound constraints or inaccurate worst-case sensitivities. A graph technique and mixed-integer nonlinear programming are effectively combined to solve the formulated parasitic optimization problem. The automatically generated target layouts can satisfy performance constraints to ensure the desired specifications. The experimental results show that the proposed algorithm can achieve effective retargeting of analog circuits with less layout area and significant reduction in execution time.     

Design of multiplierless elliptic IIR filters with a smallquantization error

We present a new technique for the design of multiplierless IIR elliptic filters. The multiplierless filter has all multiplication constants implemented with a small number of shifters and adders. The proposed technique is based on sensitivity analysis. An analytical expression for amplitude response sensitivity is derived for the filter structures consisting of two allpass subfilters in parallel. It is shown that the amplitude response sensitivity to some constant x can be expressed as a product of the filter reflectance function and the phase sensitivity of the allpass section that implements the constant. The closed-form expressions for the phase sensitivities of the first- and second-order allpass sections are also developed. It is shown in the paper that the (n+1)/2 most sensitive constants can be directly controlled by the transfer function parameters if the transfer function is derived by the bilinear transformation from an elliptic minimal Q-factors (EMQF) analog prototype. This way, (n+1)/2 multiplication constants can be implemented without quantization, leaving the filter characteristic strictly elliptic. This is achieved for a class of low-noise allpass sections and for the wave lattice digital filter as well. The quantization of the remaining (n-1)/2 less-sensitive constants is performed using the phase-tolerance scheme and phase-sensitivity functions. The proposed design technique is straight-forward and, consequently, very fast. The application is demonstrated on the examples of narrowband, wideband, and halfband filters     

基于节点法求解线性网络灵敏度的系统方法

把矩阵的张量运算引入到电路的灵敏度计算中,并通过电路分析的节点法的增量方程,导出了计算电路灵敏度矩阵一般公式,提出了求解线性网络灵敏度的一种系统方法。该方法用于电路灵敏度计算,只需要进行一系列矩阵变换与运算,即可得到电路中节点电压和支路电压对电路参数的灵敏度矩阵,其运算过程规则便于用计算机编程实现,有较大的实用价值。     

Spectral and nonlinear analyses of MEG background activity in patients with Alzheimer's disease.

The aim of the present study is to analyze the magnetoencephalogram (MEG) background activity from patients with Alzheimer's disease (AD) and elderly control subjects. MEG recordings from 20 AD patients and 21 controls were analyzed by means of two spectral [median frequency (MF) and spectral entropy (SpecEn)] and two nonlinear parameters [approximate entropy (ApEn) and Lempel-Ziv complexity (LZC)]. In the AD diagnosis, the highest accuracy of 75.6% (80% sensitivity, 71.4% specificity) was obtained with the MF according to a linear discriminant analysis (LDA) with a leave-one-out cross-validation procedure. Moreover, we wanted to assess whether these spectral and nonlinear analyses could provide complementary information to improve the AD diagnosis. After a forward stepwise LDA with a leave-one-out cross-validation procedure, one spectral (MF) and one nonlinear parameter (ApEn) were automatically selected. In this model, an accuracy of 80.5% (80.0% sensitivity, 81.0% specificity) was achieved. We conclude that spectral and nonlinear analyses from spontaneous MEG activity could be complementary methods to help in AD detection.     

Spectral and Nonlinear Analyses of MEG Background Activity in Patients With Alzheimer's Disease

The aim of the present study is to analyze the magnetoencephalogram (MEG) background activity from patients with Alzheimer's disease (AD) and elderly control subjects. MEG recordings from 20 AD patients and 21 controls were analyzed by means of two spectral [median frequency (MF) and spectral entropy (SpecEn)] and two nonlinear parameters [approximate entropy (ApEn) and Lempel-Ziv complexity (LZC)]. In the AD diagnosis, the highest accuracy of 75.6% (80% sensitivity, 71.4% specificity) was obtained with the MF according to a linear discriminant analysis (LDA) with a leave-one-out cross-validation procedure. Moreover, we wanted to assess whether these spectral and nonlinear analyses could provide complementary information to improve the AD diagnosis. After a forward stepwise LDA with a leave-one-out cross-validation procedure, one spectral (MF) and one nonlinear parameter (ApEn) were automatically selected. In this model, an accuracy of 80.5% (80.0% sensitivity, 81.0% specificity) was achieved. We conclude that spectral and nonlinear analyses from spontaneous MEG activity could be complementary methods to help in AD detection.     

Advanced types of the sensitivity analysis in frequency and time domains

The majority of standard tools for computer-aided design can perform only limited types of the sensitivity analysis: Spice determines operating-point sensitivities, and SpectreRF contains a parametric sensitivity analysis that can be used for determining the phase noise, for example. In the paper, some new types of the sensitivity analysis in frequency and time domains are described. These types of the analysis are not implemented in the standard circuit simulators.In the frequency domain, a procedure for determining the sensitivities of the noise figure is suggested. First, an improvement of the method for computing the noise figure is presented, which incorporates necessary circuit matching and eliminates the subtraction of output noise from the load at each frequency. Second, a simple formula is derived for computing the sensitivities of the noise figure. The sensitivity analysis in the frequency domain is generally demonstrated by means of a distributed microwave amplifier. The application of the sensitivity analysis of the noise figure for improving the noise properties of a monolithic microwave amplifier is described.In the time domain, a new recurrent formula is derived for the sensitivity analysis that efficiently uses high-order expressions of the algorithm for implicit numerical integration. Since the chosen integration algorithm is more flexible than the more frequently used Gear's one, the suggested formula leads to more efficient procedure. The sensitivity analysis in the time domain is important for analyzing symmetrical microwave circuits, because their operating-point sensitivities are zero in principle. For this reason, the significance of the proposed method is demonstrated by an analysis of a symmetrical radio-frequency CMOS multiplier. As an unusual example of exploiting the method, a temperature sensitivity analysis of a power operational amplifier is described.     

Internal stress compensation and scaling in ultrasensitive siliconpressure sensors

The pressure sensitivity of boron-doped silicon membranes has been characterized as a function of diaphragm dimensions and internal membrane stress. Using an electrostatic technique based on silicon microbridges, the internal stress for p⁺⁺ silicon (on glass), LPCVD silicon dioxide, and LPCVD silicon nitride was measured; typical values are 40, -300, and 950 MPa, respectively. Silicon membranes with several different edge lengths and deposited oxide and/or nitride coatings were characterized for sensitivity. While the pressure sensitivity can be reduced by more than a factor of twenty in the membranes due to boron-induced internal stress, the use of stress-compensating dielectrics can improve this sensitivity by a factor of six or more. Based on this theory and the measured material parameters, scaled experimental devices show typical sensitivities within 10-20% of the theoretical design targets. Pressure sensitivities as high as 2900 ppm/Pa have been achieved     

Optical preamplifier using optical modulation of amplified spontaneous emission in saturated semiconductor optical amplifier

This paper demonstrates a novel optical preamplifier using optical modulation of amplified spontaneous emission (ASE) emitted from a saturated semiconductor optical amplifier (SOA). Requirements on optical alignments and antireflection coating for SOAs can be relaxed and the elimination of an optical filter gives us a large tolerance of an input light wavelength in the proposed optical preamplifier. A small-signal gain of a fabricated preamplifier was over 13.5 dB for an input power of below -20 dBm. An optical gain bandwidth was over 60 nm. We measured the small-signal response of the optically modulated ASE. The 3 dB bandwidths at SOA bias currents of 200, 300, and 400 mA were 5.8, 12.6, and 16.5 GHz, respectively. We also investigated improvements in receiver sensitivities with the proposed optical preamplifier. Our calculation shows a possibility of 10 dB improvement in receiver sensitivities by using the optical preamplifier at 10 Gb/s. The measured receiver sensitivity was -22.7 dBm at 10 Gb/s with the optical preamplifier, which is corresponding to an improvement of 2.5 dB in the receiver sensitivity. Further improvements of the receiver sensitivity can be expected by optimizing the structure of SOAs for saturating ASE.     

A Sensitivity Analysis of Frequency Selective Surfaces at Millimeter Wave Band

This work presents a sensitivity analysis for the resonant frequency and bandwidth of frequency selective surfaces (FSS) as a function of the structural parameters. The frequency selective surface structure considered here is composed by crossed dipole conductive patches deposited on an anisotropic dielectric layer. Firstly, the moment method is used in combination with the immittance technique in the spectral domain to determine the frequency response of the analyzed structure. Secondly, numerical techniques are used to obtain the resonant frequency and bandwidth sensitivities as a function of the considered FSS structural parameters.     

An adjoint variable method for time-domain transmission-line modeling with fixed structured grids

We present a novel algorithm for efficient estimation of objective function sensitivities for time-domain transmission-line modeling (TLM) with nondispersive boundaries. The original electromagnetic structure is simulated using TLM. An adjoint TLM simulation that runs backward in time is derived and solved. The sensitivities of the objective function with respect to all designable parameters are estimated using only the original and adjoint simulations. Our approach is illustrated through the estimation of the sensitivities of objective functions with respect to the dimensions of waveguide discontinuities. A very good match is obtained between our sensitivity estimates and those obtained through the accurate and time-intensive central difference approximation.     

An adjoint variable method for sensitivity calculations of multiport devices

Recently, an adjoint variable method (AVM) for sensitivity calculations has been proposed for use with the method of moments solvers. In this paper, we extend this method to be suitable for application to multiport devices. The target objective function is usually represented in terms of the device's S-parameters. Our AVM obtains the sensitivities of the S-parameters with respect to all design variables using only one full simulation with additional overhead. This overhead is usually less than the computation time of a full simulation. An analytical expression for the adjoint excitation is derived, leading to stable sensitivities. The potential of the proposed technique is demonstrated by analyzing low-pass and bandpass filters. The results show very good agreement between the proposed AVM and the conventional finite-difference approach (FDA). Moreover, the AVM is always faster than the FDA. The speed-up factor increases as the size of the problem increases.     

Gradient-based adjoint-variable optimization of broadband microstrip antennas with mixed-order prism macroelements

This paper describes a new finite element method (FEM)-based adjoint-variable approach to design and optimization of planar microwave circuits using sensitivity analysis, with respect to small variations of their design parameters. The implementation is based on a specially developed class of mixed-order prismatic macroelements, suitable for an efficient analysis of planar microwave structures. Their use, combined with a simple probe feed model, not only reduces the overall computational effort but also facilitates a straightforward derivation of port parameter sensitivities. Explicit expressions are given for the adjoint solution and S-parameter sensitivity and the process is verified through the design and optimization of two slotted broadband microstrip patch antennas.     

Tunnel-Diode Low-Level Detection

An analysis of tunnel-diode low-level detection is presented for the purpose of explaining some of the unusual detection characteristics that occur under certain bias conditions. For example, in the vicinity of its inflection bias point, a tunnel diode exhibits a discriminator-like rectification behavior with two sensitivity peaks. When biased at one of these peaks, the diode is capable of unusually high sensitivities, at least an order of magnitude better than the sensitivity of any other known diode. It is shown that these high sensitivities are proportional to (1 - /spl Gamma//sup 2/),where /spl Gamma//sup 2/ is the RF power gain of the detector viewed as a reflection-type amplifier. The resultant gain bandwidth (or sensitivity bandwidth) limitations of the detector are discussed. Unusually high sensitivities are also possible at the lower microwave frequencies when the tunnel diode is biased at its peak current point. A knowledge of the diode static characteristics, the reflection coefficient, and the video circuit permits an accurate analytical evaluation of the sensitivity performance of any tunnel diode, and calculations are carried out for an example diode and compared against measured data. The paper also contains a specific comparison of the relative sensitivity performance of the example tunnel diode versus a hot carrier diode.     

Sensitivity points-based self-tuning

Sensitivity points tuning concepts, extension of these concepts to the self-tuning of multiinput/multioutput (MIMO) systems, and implementation issues are discussed. The means of generating the sensitivities needed for tuning is developed in a matrix transfer function form. A block diagram interpretation is presented to illustrate the conceptual clarity of using MIMO sensitivity points. The effectiveness of the self-tuning technique is demonstrated through the application of self-tuning to a magnetic suspension system     

基于微滴腐蚀的微纳光纤Farby-Perot腔的折射率传感特性

为了实现高精度和高灵敏度的折射率测量,采用微米级氢氟酸液滴化学腐蚀的方法制作非对称的微纳光纤Fabry-Perot (FP)腔,具有波导尺寸小、损耗低、双折射率高和腔Q值高等优点。不同正交偏振方向的谐振模式对外界折射率变化具有不同的响应,沿光纤快轴方向的模式折射率灵敏度为133.8 nm/RI-unit,沿光纤慢轴方向的模式折射率灵敏度为117.1 nm/RI-unit,快慢轴方向的温度灵敏度均为11.99 pm/℃,通过光谱仪监测两束偏振光的波长差可实现温度独立的折射率测量。采用不同FP腔参数的光纤传感器进行实验研究,结果表明,光纤FP传感器腔直径越小,腐蚀占腔长比越高,其折射率灵敏度越高。     

Detection of DC and low-frequency AC magnetic fields using an all single-mode fibre magnetometer

A technique for the determination of weak DC and low-frequency AC magnetic fields using a single-mode-fibre magnetometer is described. The technique utilises the dependence between the AC responsitivity and bias field to detect small changes in the bias field. Detection sensitivities in the milli-gauss/metre region have been obtained using a bulk nickel magnetostrictive element with microgauss sensitivities predicted for certain types of metallic glass.     

Comparison of AdaBoost and Support Vector Machines for Detecting Alzheimer's Disease Through Automated Hippocampal Segmentation

We compared four automated methods for hippocampal segmentation using different machine learning algorithms: 1) hierarchical AdaBoost, 2) support vector machines (SVM) with manual feature selection, 3) hierarchical SVM with automated feature selection (Ada-SVM), and 4) a publicly available brain segmentation package (FreeSurfer). We trained our approaches using T1-weighted brain MRIs from 30 subjects [10 normal elderly, 10 mild cognitive impairment (MCI), and 10 Alzheimer's disease (AD)], and tested on an independent set of 40 subjects (20 normal, 20 AD). Manually segmented gold standard hippocampal tracings were available for all subjects (training and testing). We assessed each approach's accuracy relative to manual segmentations, and its power to map AD effects. We then converted the segmentations into parametric surfaces to map disease effects on anatomy. After surface reconstruction, we computed significance maps, and overall corrected $p$-values, for the 3-D profile of shape differences between AD and normal subjects. Our AdaBoost and Ada-SVM segmentations compared favorably with the manual segmentations and detected disease effects as well as FreeSurfer on the data tested. Cumulative $p$-value plots, in conjunction with the false discovery rate method, were used to examine the power of each method to detect correlations with diagnosis and cognitive scores. We also evaluated how segmentation accuracy depended on the size of the training set, providing practical information for future users of this technique.      

Sensitivity of Breath-to-Breath Gas Exchange Measurements to Expiratory Flow Errors

During expiration, fluctuations in gas composition, water vapor, and temperature result in flowmeter errors when the flowmeter is calibrated for a given ambient inspiratory gas. In this paper, we indicate that alternative analytical methods of caleulating breath-to-breath gas exchange exhibit differing sensitivities to this error. A theoretical sensitivity analysis is verified by O2 consumption records from rest to exhausting exercise. We conclude that an error sensitivity of less than one is achieved by a method that incorporates measurements of nitrogen flow into and out of the lung, and includes the analysis of breath-to-breath changes in lung volume.