Multiple Bandpass Filters Research Articles

A robust SEM auto-focus algorithm using multiple band-pass filters

An auto-focus algorithm using multiple band-pass filters for a scanning electron microscope (SEM) is proposed. To acquire sharp images of various kinds of defects by SEM defect observation in semiconductor manufacturing, the auto-focus process must be robust. A method for designing a band-pass filter for calculating the ‘focus measure’ (a key parameter of the auto-focus process) is proposed. To achieve an optimal specific frequency response for various images, multiple band-pass filters are introduced. As for the proposed method, two series of focus measures are calculated by using multiple band-pass filters independently, and it is selected according to reliability of the series of focus measures. The signal-to-noise ratio of an image for acceptable auto-focus precision is determined by simulation using pseudo images. In an experiment using the proposed method with real images, the success rate of auto focus is improved from 79.4% to 95.6%.

Human-inspired modulation frequency features for noise-robust ASR

This paper investigates a computational model that combines a frontend based on an auditory model with an exemplar-based sparse coding procedure for estimating the posterior probabilities of sub-word units when processing noisified speech. Envelope modulation spectrogram (EMS) features are extracted using an auditory model which decomposes the envelopes of the outputs of a bank of gammatone filters into one lowpass and multiple bandpass components. Through a systematic analysis of the configuration of the modulation filterbank, we investigate how and why different configurations affect the posterior probabilities of sub-word units by measuring the recognition accuracy on a semantics-free speech recognition task. Our main finding is that representing speech signal dynamics by means of multiple bandpass filters typically improves recognition accuracy. This effect is particularly noticeable in very noisy conditions. In addition we find that to have maximum noise robustness, the bandpass filters should focus on low modulation frequencies. This reenforces our intuition that noise robustness can be increased by exploiting redundancy in those frequency channels which have long enough integration time not to suffer from envelope modulations that are solely due to noise. The ASR system we design based on these findings behaves more similar to human recognition of noisified digit strings than conventional ASR systems. Thanks to the relation between the modulation filterbank and procedures for computing dynamic acoustic features in conventional ASR systems, the finding can be used for improving the frontends in those systems.

Fast calculation algorithm for discrete resonance-based band-pass filter

A discrete resonant band-pass filter with a fast calculation algorithm, which can be used to perform discrete frequency transformations, is presented. The algorithm has low memory consumption requirements. It implements a numerical integration method, simulating a harmonic resonator element modeled by the under-damped driven oscillator equations, expressed in a discrete form. The output from the presented filter is a discrete function with an amplitude of the steady-solution that closely matches the theoretical steady-solution amplitude of the continuous band-pass filter output. Multiple discrete resonant band-pass filters can be used to build a filter bank, which in turn can be used to perform a time-to-frequency transformation of discrete signals. The filter achieves a frequency and a time localization without utilizing the time windowing method. The presented stand-alone calculation algorithm related to this filter produces its output with a delay of just one sampling period. The algorithm’s calculation cost is only 3 multiplications and 3 additions per sample, and does not require long memory buffers. The presented transformation does not surpass the precision of the Discrete Fourier and Discrete Wavelet Transformations. However, it may prove essential when the noise-artifacts of the near-real-world simulation are necessary in order to produce some specific auditory-perception phenomena.

Quantitative phase imaging using transport of intensity equation with multiple bandpass filters.

A phase imaging based on the transport of intensity equation using multiple bandpass filters is proposed. The proposed method enables us to measure a phase distribution quantitatively from through-focus intensity images obtained by using a white light source and multiple bandpass filters. The technique improves the accuracy of a phase measurement by increasing the number of intensity images obtained at different defocused positions. The feasibility of the phase measurement and the improvement in the accuracy with the increasing the through-focus images are confirmed by numerical simulations and optical experiments.

Tailoring of the Brillouin gain for on-chip widely tunable and reconfigurable broadband microwave photonic filters.

An unprecedented Brillouin gain of 44 dB in a photonic chip enables the realization of broadly tunable and reconfigurable integrated microwave photonic filters. More than a decade bandwidth reconfigurability from 30 up to 440 MHz, with a passband ripple <1.9 dB is achieved by tailoring the Brillouin pump. The filter central frequency is continuously tuned up to 30 GHz with no degradation of the passband response, which is a major improvement over electronic filters. Furthermore, we demonstrate pump tailoring to realize multiple bandpass filters with different bandwidths and central frequencies, paving the way for multiple on-chip microwave filters and channelizers.

Multi-filter transport of intensity equation solver with equalized noise sensitivity.

Phase retrieval based on the Transport of Intensity Equation (TIE) has shown to be a powerful tool to obtain the phase of complex fields. Recently, it has been proven that the performance of TIE techniques can be improved when using unequally spaced measurement planes. In this paper, an algorithm is presented that recovers accurately the phase of a complex objects from a set of intensity measurements obtained at unequal plane separations. This technique employs multiple band-pass filters in the frequency domain of the axial derivative and uses these specific frequency bands for the calculation of the final phase. This provides highest accuracy for TIE based phase recovery giving minimal phase error for a given set of measurement planes. Moreover, because each of these band-pass filters has a distinct sensitivity to noise, a new plane selection strategy is derived that equalizes the error contribution of all frequency bands. It is shown that this new separation strategy allows controlling the final error of the retrieved phase without using a priori information of the object. This is an advantage compared to previous optimum phase retrieval techniques. In order to show the stability and robustness of this new technique, we present the numerical simulations.

High-Q filters with complete transmission by quasi-periodic dielectric multilayers

A multiple narrow bandpass filter with both high Q factor and complete transmission using quasi-periodic Thue-Morse dielectric multilayers is proposed. The Q factor of the system increases exponentially with the generation order. Even though the Q factor of resonances increases as the generation order of the multilayers increases, these resonances are still complete resonances. The number of resonance peaks for the bandpass filter of the system also increases as the generation order increases. These resonance peaks have a multifractal distribution throughout the frequency range, which is different from that in traditional periodical multilayers.

A Reconfigurable Compact Coupled Line Multiple-Band Bandpass Filter

This study proposes a circuit structure with reconfigurable multiple bands bandpass filter. This circuit can provide a triple-band or dual-band bandpass facility by adjusting two open stubs (L6 and L7) location. The circuit design used three sections of transmission line in series, the two sets of the coupled lines connected to the gap in each transmission line, and two open stubs in the appropriate locations. The design and manufacturing of the circuit structure is innovative and simple. The center frequencies of the triple-band bandpass filter are set at 2.4, 4.2, and 6.5 GHz, respectively, while the center frequencies of the dual-band bandpass filter are the two lower pass band of the triple-band bandpass filter at 2.4 and 4.2GHz. The filters were simulated using the full-wave electromagnetic simulator, IE3D, and measured by Anritsu-37269D. The simulated and measured results show good agreement in the frequency of interest.

Integrated detection of intrinsic fluorophores in live microbial cells using an array of thin film amorphous silicon photodetectors

Two-dimensional fluorescence spectroscopy (2D FS) provides a non-invasive means to assess cell condition without the introduction of changes to the cell environment. The method relies on the measurement of the excitation–emission fluorescence intensity matrix of key intrinsic fluorophores, like aromatic amino acids, enzyme cofactors, and vitamins. Commonly used detection systems are complex, with multiple bandpass filters, and are hard to miniaturize. Here, an amorphous silicon photodetector array system integrated with amorphous silicon–carbon alloy filters designed to detect three key fluorophores – tryptophan (Trp), reduced nicotine adenine dinucleotide (NADH) and flavin adenine dinucleotide (FAD) – is demonstrated. These intrinsic fluorophores were detected in pure solutions and also in suspended yeast cells. The array system was used to monitor changes in intrinsic fluorophore concentration when a yeast cell solution was subject to a thermal shock stress.

Narrow-line-width 131-μm wavelength tunable quantum dot laser using sandwiched sub-nano separator growth technique

A wide wavelength tunable quantum dot (QD) external cavity laser operating in the 1.31-μm waveband with a narrow line-width is successfully demonstrated. A high-density, high-quality InAs/InGaAs QD optical gain medium for the 1.31-μm waveband was obtained using a sandwiched sub-nano separator growth technique. A wide wavelength tunability of 1.265-1.321 μm and a narrow line-width of 210 kHz were successfully achieved using a compact and robust external cavity system constructed with multiple optical band-pass and etalon filters for active optical mode selection. The laser also achieved an error-free 10-Gb/s photonic data transmission over an 11.4-km-long holey fiber.

Multiple narrow bandpass optical filters based on one-dimensional rugate photonic structures of two periodicities

A theoretical analysis of a design of multiple narrow bandpass filters based on one-dimensional (1D) rugate photonic structures with a period jump defect is presented. The optical properties, including transmittance and energy density distributions, are numerically calculated using the propagation matrix method. Our results show that multiple resonance transmission modes are produced when the period jump defect is introduced into the 1D rugate film. Both blueshift and redshift of the stop band of the rugate structure and wavelengths of resonant modes are observed, depending on the change of period jump. The number, the wavelengths, the band intervals, and the intensities of multiple resonance transmission modes are tunable by adjusting structure parameters of the rugate structure. Experimental feasibility of the proposed multiple narrow bandpass optical filters using the technique of glancing angle deposition is also discussed.

Learning Multiple Band-Pass Filters for Sleep Stage Estimation: Towards Care Support for Aged Persons

This paper proposes the sleep stage estimation method that can provide an accurate estimation for each person without connecting any devices to human's body. In particular, our method learns the appropriate multiple band-pass filters to extract the specific wave pattern of heartbeat, which is required to estimate the sleep stage. For an accurate estimation, this paper employs Learning Classifier System (LCS) as the data-mining techniques and extends it to estimate the sleep stage. Extensive experiments on five subjects in mixed health confirm the following implications: (1) the proposed method can provide more accurate sleep stage estimation than the conventional method, and (2) the sleep stage estimation calculated by the proposed method is robust regardless of the physical condition of the subject.

Multispectral imaging using multiple-bandpass filters

We present a method for multispectral imaging. This method uses color CCD cameras with a multiple-bandpass filter, which modifies the spectral response of the cameras used and enables concurrent acquisition of multiple images at defined spectral bands. We experimentally demonstrate methodological feasibility using two color CCD cameras and a polychroic mirror to simultaneously capture eight spectral bands. We discuss how the method developed is well suited for multispectral applications of transient phenomena or for real-time measurements.

Design of UWB pulse radio transceiver using statistical correlation technique in frequency domain

Abstract. In this paper, we propose a new technique to extract low power UWB pulse radio signals, near to noise level, using statistical correlation technique in frequency domain. The receiver consists of many narrow bandpass filters which extract energy either from transmitted UWB signal, interfering channels or noise. Transmitted UWB data can be eliminated by statistical correlation of multiple bandpass filter outputs. Super-regenerative oscillators, tuned within UWB spectrum, are designed as bandpass filters. Summers and comparators perform statistical correlation.

Spectral analysis of the temporal self-imaging phenomenon in fiber dispersive lines

A spectral analysis of the temporal Talbot or self-imaging effect based on the exact computation of the radio frequency spectrum of the intensity of pulse trains after propagation in media with arbitrary first-order (/spl beta//sub 2/) and second-order (/spl beta//sub 3/) dispersion is presented. This allows the investigation of the performance of fiber dispersive lines as Talbot devices, where second-order dispersion is considered as a degradation factor. Conditions for repetition-rate multiplication and pulse compression over trains composed of linearly chirped Gaussian pulses, describing the effect as a filter in the intensity domain, are analyzed. The Talbot filter acts as a multiple bandpass filter that selects intensity harmonics. The filter's rejection capability depends on the train's spectral width normalized by the repetition-rate frequency of the output. The intensity fluctuations and pulse distortions of the output train are described from the spectral point of view. The tolerances of the filter under length and timing variations are also considered, and conditions for optimal filter stability are derived.

High resolution spectral analysis of visual evoked EEGs for word-recognition “Event-related spectra”

We studied precise spectra of evoked EEGs in the word recognition analyzed with multiple band-pass filters (MBFA). The filter was infinite impulse response in 2nd order. Firstly, a signal swept from 5 to 100 Hz sine wave was tested with MBFA, fast Fourier transform and Wavelet transform. Ten evoked EEGs with word visual stimuli were recorded from three volunteers. The EEGs were sampled at 1 kHz in 14 bits for 1 s, and were analyzed with MBFA to make spectra from 5 to 100 Hz, and the spectra were averaged 10 times for observation. Evoked powers were noted at alpha band over the occipital area and suppressed powers were noted at beta and alpha bands afterward. Gamma bands were noted to be evoked over the posterior central area in the normalized Event-related spectra.

ＴＩＧ溶接におけるプール表面温度の計測−紫外線放射測温法の開発（第１報）−

The problem of emissivity change on metal surface complicates the temperature measurement of molten pools in infrared (IR) radiation thermometry. Therefore, an emissivity correction is one of the most important subjects in IR radiation thermometry. The objective of the present investigation is to develop an ultraviolet (UV) radiation thermometry, which is an emissivity correction free method. According to the Planck's law of radiation, it is evident that the effect of temperature on the spectral radiance is greater at the shorter wavelength, and radiation thermometry in UV range is expected to reduce the error caused by the emissivity change. Generally, the radiation energy in UV range is lower than that in IR range at the same temperature. A measurement system that is sensitive to the UV radiation has been developed in the present work. The system consists of an image intensifier, and multiple optical band-pass filters. In the present paper, two-dimensional temperature distribution on TIG weld pool has been measured by using the developed UV radiation thermometer. It is made clear that the luminance temperature distributions measured by IR and UV range are quite different, and the surface temperature on molten pool is affected by sulfur concentration in the material.

Enhanced Detection of Gas Absorption Using an Erbium-Doped Fiber Ring Laser

We demonstrate gas sensing using a fiber ring laser composed of an erbium-doped fiber as the laser medium and a compact gas cell module. Acetylene absorption at 1.5 µm is enhanced by an intracavity configuration, in which multiple band-pass filters are used to control the wavelength of laser oscillation. A maximum enhancement factor of about 80 is achieved with an 18.3 mm cell under a pressure range below 100 Pa. Experimental results can reasonably be explained by a ring laser theory that describes the influence of acetylene pressure on the threshold and slope efficiency of the laser output characteristics.

Multiple Band-Pass Filtering Method for Improvement on Prediction Accuracy of Linear Multivariate Analysis

An approach coupling signal processing and partial least-squares regression analysis (PLS) is described in which raw spectral data are processed with a multiple band-pass filter and the filtered spectra are used in a PLS to build a calibration model for the analyte of interest. The multiple band-pass filter is specifically designed for a desired analyte based on the Fourier frequency characteristics of the pure spectrum of the desired analyte and the spectra of the interference background. It maximizes the ratio of signal to background. This combined multiple band-pass filtering and PLS method (MFPLS) was evaluated by determining clinically relevant levels of glucose, urea, ethanol, and acetaminophen in simulated human sera, in which triglyceride was simulated with triacetin; bovine serum albumin and globulin were used to model protein molecules in the serum. The results demonstrate that MFPLS produces better accuracy of prediction than PLS in all instances.

MULTIPLE BAND-PASS AUTOREGRESSIVE DEMODULATION FOR ROLLING-ELEMENT BEARING FAULT DIAGNOSIS

This paper presents a novel method to enhance the detection and diagnosis of low-speed rolling-element bearing faults based on discrete wavelet packet analysis (DWPA). The method involves the automatic extraction of wavelet packets containing bearing fault-related features from the discrete wavelet packet analysis representation of machine vibrations. Automated selection of the wavelet packets of interest is achieved via an adaptive network-based fuzzy inference system (ANFIS), which can be implemented on-line. The resultant signal extracted by this technique is essentially an optimal multiple band-pass filter of the high-frequency bearing impact transients. Used in conjunction with the autoregressive (AR) spectrum of the envelope signal, a sensitive diagnosis of the bearing condition can be made. The discrete wavelet packet analysis multiple band-pass filtering of the signal results in a significantly improved signal-to-noise ratio compared to its high-pass counterpart, with an exceptional capacity to exclude contaminating sources of vibration. A more modest increase in the signal-to-noise ratio is achieved when compared to digital band-pass filtering, with the filter range adjusted to obtain the best possible isolation of the bearing transients.