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Materials for Nanosensors
Published in Vinod Kumar Khanna, Nanosensors, 2021
Surface plasmon resonance sensors are usually constructed by using prism coupling of incident light onto an optical substrate that is coated with a semitransparent (partially transparent: not perfectly or completely transparent) noble metal under conditions of total internal reflection (complete reflection of a ray of light at the boundary between two transparent media, which occurs if the angle of incidence is greater than a certain limiting angle, called the critical angle). Therefore, a condition of total internal reflection (Figure 2.3a) must exist at the interface. Total internal reflection will exist for incident angles greater than the critical angle θc; at this angle, some of the light is refracted across the interface. At the point of reflection at the interface, an evanescent field (standing wave) penetrates the exit medium to a depth of the order of one-quarter of the incident light wavelength. A standing wave, also known as a stationary wave, is a wave that remains in a constant position; standing waves are produced wherever two waves of identical frequency interfere with one another while traveling in opposite directions along the same medium. (a) Total internal reflection at an interface. (b) Use of a prism coupling configuration for SPR.
Superposition of Waves
Published in Myeongkyu Lee, Optics for Materials Scientists, 2019
This represents a standing wave, as opposed to a traveling wave. Unlike traveling waves, standing waves do not move through space. Consequently, there is no net transfer of energy. Equation 3.14 can be regarded as either a sine wave with time-varying amplitude or a cosine wave with space-dependent amplitude. Figure 3.7 shows the spatial variations of E at various times. There are x values for which the disturbance is zero for all t. These values (x = 0, λ/2, λ, 3λ/2….etc.) are called the nodes of the standing wave. The amplitude is maximized at t = 0, τ/2, τ, 3τ/2….etc., where τ is the temporal period of the constituent waves. The disturbance E will be zero at all x whenever cos ωt = 0, that is, when t = τ/4, 3τ/4;….etc.
Monitors, headphones, and your room
Published in Rick Snoman, Dance Music Manual, 2019
A subwoofer is an additional mono speaker designed to handle all the low frequencies. The subwoofer will deliver all frequencies typically ranging from 20 Hz to 120 Hz leaving the main studio monitors to reproduce the rest of the frequency spectrum. While this can provide a great solution – particularly if the monitors do not have an extended frequency response – in a small, untreated room, the low frequencies produced by a subwoofer result in standing waves and interference. Standing waves are a result of two waves of the same frequency, amplitude, and wavelength meeting one another from opposite directions. This occurs because the waveform leaving the subwoofer meets the previous waveform reflected from another surface.
Numerical modelling of microwave heating of a porous catalyst bed
Published in Journal of Microwave Power and Electromagnetic Energy, 2019
P. D. Muley, K. Nandakumar, D. Boldor
We also studied the effect on temperature profile when the catalyst bed is moved slightly off centre (0.01 m and 0.02 m off centre) (Figure 6). For position z = 0.01 m off centre, the highest temperature noted was 600 °C (Figure 6c). This temperature dropped significantly to only 260 °C when the catalyst was moved 0.02 m off centre (to a range of 100–260 °C). We also observed that the temperature gradient greatly reduces when the catalyst bed position is 0.02 m off from the centre (Figure 6d). These observations could be attributed to the smaller sample size which causes arbitrary wave reflection resulting in multimode of field pattern (Cha-um et al. 2009). For a closed microwave cavity like the one studied here, the occurrence of standing waves creates uneven heating. Some methods to cancel or minimize the effect of standing waves pattern is to move the sample continuously, change the size of cavity or change the size and/or position of sample within the cavity. Placing the sample 0.02 m off centre might have minimized this effect, resulting in lower temperature gradient.
Transverse surface waves in steady uniform and non-uniform flows through an array of emergent and slightly submerged square cylinders
Published in Journal of Hydraulic Research, 2020
Meriem Chetibi, Sebastien Proust, Saadia Benmamar
Transverse standing waves are characterized by nodes and antinodes, at which the free surface oscillation amplitude is minimum and maximum and the transverse velocity fluctuation is maximum and minimum, respectively. Water motion is entirely horizontal at nodes and entirely vertical at antinodes (Rabinovich, 2009). It should be noted that two antinodes are always observed at the channel sidewalls owing to the zero-flow condition. The transverse wavelength is defined (e.g. Dean & Dalrymple, 1991) by: where n is the oscillation mode, i.e. the number of nodes.