This a mathematical technique intermediate between direct and reciprocal (Fourier-transform) space for exploring images with well-defined periodicities, like electron microscope lattice-fringe images. As with analog dark-field imaging in a transmission electron microscope, it allows one to "light up" those objects in the field of view where periodicities of interest reside. Unlike analog dark-field imaging it may also allow one to map the Fourier-phase of periodicities, and hence phase gradients, which provide quantitative information on vector lattice strain.

Dark field vs bright fieldmicroscopy reddit

When deciding which type of antenna to purchase for your RFID system, understanding the how these antennas work as well as how the RFID tags should be oriented with respect to the antennas is key.

The interpretation of dark-field images must be done with great care, as common dark features of bright-field microscopy images may be invisible, and vice versa. In general the dark-field image lacks the low spatial frequencies associated with the bright-field image, making the image a high-passed version of the underlying structure.

While the dark-field image may first appear to be a negative of the bright-field image, different effects are visible in each. In bright-field microscopy, features are visible where either a shadow is cast on the surface by the incident light or a part of the surface is less reflective, possibly by the presence of pits or scratches. Raised features that are too smooth to cast shadows will not appear in bright-field images, but the light that reflects off the sides of the feature will be visible in the dark-field images.

In optical microscopes a darkfield condenser lens must be used, which directs a cone of light away from the objective lens. To maximize the scattered light-gathering power of the objective lens, oil immersion is used and the numerical aperture (NA) of the objective lens must be less than 1.0. Objective lenses with a higher NA can be used but only if they have an adjustable diaphragm, which reduces the NA. Often these objective lenses have a NA that is variable from 0.7 to 1.25.[1]

Bright fieldanddark fieldmicroscopy PDF

Weak-beam imaging involves optics similar to conventional dark-field, but uses a diffracted beam harmonic rather than the diffracted beam itself. In this way, much higher resolution of strained regions around defects can be obtained.

Briefly, imaging[5] involves tilting the incident illumination until a diffracted, rather than the incident, beam passes through a small objective aperture in the objective lens back focal plane. Dark-field images, under these conditions, allow one to map the diffracted intensity coming from a single collection of diffracting planes as a function of projected position on the specimen and as a function of specimen tilt.

If all the tags you need to read will be on the same plane and aligned with the plane of the antenna, then you should consider a linear polarized antenna.  If your tag orientation is not something that will be reliable or consistent, then you will likely need to use a circular polarized antenna.

Dark fieldillumination

In single-crystal specimens, single-reflection dark-field images of a specimen tilted just off the Bragg condition allow one to "light up" only those lattice defects, like dislocations or precipitates, that bend a single set of lattice planes in their neighborhood. Analysis of intensities in such images may then be used to estimate the amount of that bending. In polycrystalline specimens, on the other hand, dark-field images serve to light up only that subset of crystals that are Bragg-reflecting at a given orientation.

Dark-field studies in transmission electron microscopy play a powerful role in the study of crystals and crystal defects, as well as in the imaging of individual atoms.

Dark-field microscopy (also called dark-ground microscopy) describes microscopy methods, in both light and electron microscopy, which exclude the unscattered beam from the image. Consequently, the field around the specimen (i.e., where there is no specimen to scatter the beam) is generally dark.

Bright field vs dark field vsphase contrast

One limitation of dark-field microscopy is the low light levels seen in the final image. This means that the sample must be very strongly illuminated, which can cause damage to the sample.

Dark-field microscopy has recently been applied in computer mouse pointing devices to allow the mouse to work on transparent glass by imaging microscopic flaws and dust on the glass's surface.

Bright fieldmicroscope

Dark field vs bright fieldmicroscope

The choice between circular polarization antennas and linear polarization antennas can make a significant difference in an RFID system.

Dark-field microscopy is a very simple yet effective technique and well suited for uses involving live and unstained biological samples, such as a smear from a tissue culture or individual, water-borne, single-celled organisms. Considering the simplicity of the setup, the quality of images obtained from this technique is impressive.

Compared to linear polarized antennas of the same gain, circular polarized antennas will have a shorter read range because they lose about 3 dB splitting their power across two separate planes.

Bright fieldlighting

Due to the concentrated emission, linear polarized antennas typically have greater read range than circular polarized antennas of the same gain.

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Dark field vs bright fieldreddit

In optical microscopy, dark-field describes an illumination technique used to enhance the contrast in unstained samples. It works by illuminating the sample with light that will not be collected by the objective lens and thus will not form part of the image. This produces the classic appearance of a dark, almost black, background with bright objects on it. Optical dark fields usually done with an condenser that features a central light-stop in front of the light source to prevent direct illumination of the focal plane, and at higher numerical apertures may require oil or water between the condenser and the specimen slide to provide an optimal refractive index.[2][3]

Linear polarization occurs when electromagnetic waves broadcast on a single plane (either vertical or horizontal).  Linear polarized antennas must have a known RFID tag orientation and the RFID tag must be fixed upon the same plane as the antenna in order to get a consistent read. Some examples of linear polarized antennas are the MTI MT-263003 Outdoor Antenna, and the Times-7 A5531 Indoor Antenna.

When coupled to hyperspectral imaging, dark-field microscopy becomes a powerful tool for the characterization of nanomaterials embedded in cells. In a recent publication, Patskovsky et al. used this technique to study the attachment of gold nanoparticles (AuNPs) targeting CD44+ cancer cells.[4]

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Annular dark-field imaging requires one to form images with electrons diffracted into an annular aperture centered on, but not including, the unscattered beam. For large scattering angles in a scanning transmission electron microscope, this is sometimes called Z-contrast imaging because of the enhanced scattering from high-atomic-number atoms.

Circular polarized antennas, such as the  Laird S9028PCR Indoor RFID Antenna and the MTI MT-242043 Outdoor RFID Antenna, emit electromagnetic fields in a corkscrew-like fashion.  Technically speaking, they are broadcasting electromagnetic waves on two planes making one complete revolution in a single wavelength.

Dark-field microscopy techniques are almost entirely free of halo or relief-style artifacts typical of differential interference contrast microscopy. This comes at the expense of sensitivity to phase information.