Number Of Bandpass Filters Research Articles

Spectroscopic imaging ellipsometry for two-dimensional thin film thickness measurement using a digital light processing projector

An improved version of spectroscopic imaging ellipsometry is described for accurate reconstruction of two-dimensional thin film thickness. A digital light processing projector enables a selected area of the back focal plane of the objective lens to be illuminated so that the angle of incidence and the polarization state of the light source vary depending on the area of the back focal plane being illuminated. By combining multiple images of the object plane obtained at different polarization states, every pixel in the field of view has its own ellipsometric parameters; therefore a reconstruction of two-dimensional thin film thickness is possible. Because the proposed ellipsometry system has a co-axial optical structure in which the objective lens is arranged in the normal direction to the measurement target, the spatial resolution is improved due to the application of a high-magnitude objective lens. In addition, spectroscopic analysis can be conducted using a number of band-pass filters which each have a central wavelength. The effect of the proposed method on thin film thickness measurement was evaluated by comparing the experimental results with a topographic profile obtained using a commercial atomic force microscope.

New Technique for Segmenting RFID Bandwidth for IoT Applications

This article proposes a new technique to extend the use of the UHF RFID technology in IoT applications. The technique is based on segmenting the bandwidth of the UHF RFID into smaller segments with the use of band-pass filters and circulators. The number of band-pass filters ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${N}$ </tex-math></inline-formula> ) used are equal to the number of segments needed, while the number of circulators are equal to ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${N}$ </tex-math></inline-formula> -1). Subsequently, each of these bandwidth segments is assigned to a specific geographical location/area/zone within a given larger space where an antenna is located. Using the reader, identifying the frequency where the maximum RSSI is received will hence identify its preassigned location/area where tagged object is located. As a proof of concept, in this article the available used-reader band is divided into two segments using two filters and one circulator. The system analysis performed using CST simulations and signal flow graph derived equations. Verification of the technique was done experimentally and location of the tag between the two segments was clearly identified.

Narrowband interference mitigation in an ultra-wideband receiver

Ultra-wideband (UWB) links are inherently subject to interference from other narrowband communication links. The paper proposes a solution for suppressing these narrowband interference sources that is based on using an analogue filter bank (AFB) for pre-processing the received signal. The AFB outputs are subsequently processed by a combination of maximum ratio combining (MRC) and generalised matched filter (GMF) processing. This receiver architecture requires significantly less processing than the optimum GMF processing while achieving a comparable performance in the context of narrow band interference (NBI). Furthermore, because the AFB consists of low-order bandpass filters of modest selectivity, monolithic integration is practical. Hence, the AFB is potentially a low-cost manufacturable implementation of the UWB receiver. Analysis and simulated performance of the AFB architecture are presented in this paper. The metrics used are the overall theoretical capacity and signal-to-noise ratio of the receiver decision variable. These results are presented as a function of the overall receiver complexity for different compositions of narrow and wide bandwidth channel noise. It is also shown that AFB forms a signal space of dimension equal to the number of bandpass filters and that the processing can effectively cancel multiple tones up to this dimensionality.

Starch Index Determination of Apple Fruit by Means of a Hyperspectral near Infrared Reflectance Imaging System

A new technique, based on hyperspectral near infrared reflectance imaging, was developed to determine the maturity stage of pre-climacteric apple fruit. The technique is advantageous with respect to existing machine vision techniques as it avoids the use of toxic iodine solution. It was shown that the starch concentration obtained in each position of the fruit was continuously measured compared with the discrete values (stained/not stained) obtained with the traditional technique. The difference between the starch area and non-starch area was classified using a threshold value of the first principle component score image. The technique may be simplified in the future, using a number of bandpass filters, which will speed up the application while the purchase costs will decrease considerably. It can be considered as a model system to map quality attributes of apple fruit.

Imaging system using frequency modulation/time division multiplexing hybrid reticle

A new frequency modulation/time division multiplexing (FM/ TDM) hybrid reticle for an imaging system is proposed. The spinning reticle modulates the pixels contained in one column of scanned image to different frequencies according to their location. An imaging system using the proposed reticle can reconstruct a high-resolution 2-D image with the same number of bandpass filters as a FM reticle system. An optical experiment shows that the proposed FM/TDM hybrid reticle can be used as a low-cost imaging system. © 1998 Society of Photo-Optical Instru- mentation Engineers. (S0091-3286(98)01907-2)

Recording and preliminary analysis of respiratory sounds from tuberculosis patients.

Respiratory sounds having a pulmonary origin from both normal subjects and tuberculosis patients were recorded and a preliminary analysis was made with a number of bandpass filters. These investigations indicate a distinct difference in wave shapes between sound signals recorded from normal and diseased subjects.