Paper reports a resistive type humidity sensing studies
of ZnO-SnO<sub>2</sub> nanocomposite powder pellets prepared
through solid-state reaction route. When exposed to
humidity, resistance of pellets decreases with increase
in relative humidity from 10 to 90%. Sensing element
with 25 weight% of SnO<sub>2</sub> in ZnO shows best results
with maximum sensitivity of 1.25 MΩ/%RH in 10-
90% relative humidity range. This sensing element
manifests smallest crystallite size of 60 nm as
measured from XRD and lowest grain size of 92 nm
calculated from SEM micrograph. This sensing
element manifests low hysteresis, less effect of ageing
and good reproducibility. The response and recovery
time of sensing element SZ-25 is found to be 92 and
480 seconds respectively.
The presence of a residual sphericity in a reference beam causes magnification in the reconstructed image in
digital holography. We discuss a method to estimate the relative sphericities in a multi-perspective multi-camera
digital hologram recording unit. The digital holograms can then be compensated with numerical quadratic phase
factors so that the object appears with the same magnification in all the reconstructions.
We discuss some common sources of noise which affect the quality of reconstruction in digital holography. We show
that by using holograms obtained with independent illumination patterns, we can suppress these noise sources in a
unified manner and improve the image quality while reducing the memory usage.
We examine some fundamental theoretical limits on the ability of practical digital holography (DH) systems to resolve detail in an image. Unlike conventional diffraction-limited imaging systems, where a projected image of the limiting aperture is used to define the system performance, there are at least three major effects that determine the performance of a DH system: (i) The spacing between adjacent pixels on the CCD, (ii) an averaging effect introduced by the finite size of these pixels, and (iii) the finite extent of the camera face itself. Using a theoretical model, we define a single expression that accounts for all these physical effects. With this model, we explore several different DH recording techniques: off-axis and inline, considering both the dc terms, as well as the real and twin images that are features of the holographic recording process. Our analysis shows that the imaging operation is shift variant and we demonstrate this using a simple example. We examine how our theoretical model can be used to optimize CCD design for lensless DH capture. We present a series of experimental results to confirm the validity of our theoretical model, demonstrating recovery of super-Nyquist frequencies for the first time.
We show how the reconstruction of digital holograms can be speeded up on ordinary computers by precomputing
the chirp factor in the Fresnel transform for a given detector array size. The
speedup in time is shown for various hologram sizes. We also run the same algorithm on a Nvidia GPU. The
speedup and the error introduced due to quantizing to different levels is investigated. Additionally a variance based