Interference (wave propagation)

About: Interference (wave propagation) is a research topic. Over the lifetime, 26086 publications have been published within this topic receiving 321110 citations.

Phase shifting interferometer and method for surface topography measurement

Abstract: A system for measuring surface topography with notably decreased sensitivity to errors in phase and phase interval calibration and to the presence of low-frequency vibration during data acquisition includes an optical interferometer for developing interference data from the surface to be profiled, an electronic imaging system or camera for receiving the interference data, an arrangement for variably adjusting the reference phase of the interferometer illumination, and a digital signal processing device or computer for determining surface height from the interference data. A sequence of seven intensity images are detected by the imaging system and stored electronically. The intensity images correspond to interference patterns for seven different reference phase values spaced at intervals of approximately π/2. The images are processed by the computer so as to recover the surface topography. The invention differs substantially from the prior art in that the phase shifts need not be perfectly exact or repeatable, and neither is it necessary to completely eliminate low-frequency mechanical vibrations from the optical system during data acquisition. An alternative embodiment of the invention includes a laser diode-based illumination source that is operatively tuned in wavelength to effect the required phase shifts.

Effects of reader interference on the RFID interrogation range

Abstract: In this paper, the effects of radio frequency identification (RFID) reader interference are investigated in terms of the interrogation range. In order to evaluate RFID interference quantitatively, the signal-to-interference ratio (SIR) equation is initially derived, and the interrogation-reduction range ratio (IRRR) defined. IRRR is a function of the distance between a desired reader and an interfering reader. Co-channel interference (CCI) and adjacent-channel interference (ACI) instances of IRRR are simulated. Simulation results show that reader-reader distances achieving 0 % IRRR, indicating no interference between the two readers, are 1200 m and 35 m for the CCI and ACI cases, respectively. The IRRR factor is inversely proportional to the reader-reader distance in both cases. The simulation results were also verified by measurement results using an ETRI UHF RFID system. Measurement results were found to be in good agreement with the simulation results. It can be concluded that the present simulation results are reliable and applicable in analyses of more complex interfering problems in actual RFID system deployment instances.

Determination of the phase change on reflection from two-beam interference

Abstract: Light reflected by a nondielectric material experiences a phase change on reflection that differs from light reflected by a dielectric material and other nondielectric materials. The complex degree of coherence for small optical path differences is derived for two-beam interference when the illumination source is extended, incoherent, and quasi-monochromatic. An analysis of the two-beam interference pattern reveals a simple relationship between the phase of the interference pattern at the point of maximum fringe visibility and the material-dependent phase change on reflection.

Single beam grating coupled interferometry: high resolution miniaturized label-free sensor for plate based parallel screening.

Abstract: Grating Coupled Interferometry (GCI) using high quality waveguides with two incoupling and one outcoupling grating areas is introduced to increase and precisely control the sensing length of the device; and to make the sensor design suitable for plate-based multiplexing. In contrast to other interferometric arrangements, the sensor chips are interrogated with a single expanded laser beam illuminating both incoupling gratings simultaneously. In order to obtain the interference signal, only half of the beam is phase modulated using a laterally divided two-cell liquid crystal modulator. The developed highly symmetrical arrangement of the interferometric arms increases the stability and at the same time offers straightforward integration of parallel sensing channels. The device characteristics are demonstrated for both TE and TM polarized modes.

Apparatus and method for dynamically allocating resources in a communication system using an orthogonal frequency division multiple access scheme

Abstract: An orthogonal frequency division multiple access (OFDMA) communication system. The system has a plurality of cells, divides an entire frequency band into a plurality of subcarrier bands in each cell, and has subchannels that are a set of a preset number of subcarrier bands, respectively. Interference from neighbor cells of the plurality of cells is predicted. A time interval in which interference is absent and a time interval in which the interference is present are classified according to the interference predicted from the neighbor cells. Transmit power is equally distributed and allocated to subchannels capable of being allocated in the time interval in which the interference is absent. Transmit power is adjusted and allocated for the subchannels capable of being allocated such that inference to the neighbor cells does not occur in the time interval in which the interference is present.