Amplitude modulation examples

Hellstrand You have shown the coding of the response to PE in terms of frequency of oscillations, but not amplitude modulation. Have you come across any example where the modulation of amplitude also changes the force of contraction, or do you think the amplitude is constant in this system ... 

Even more interesting sounds can be made by more complex usage of the FM formulas. With frequency modulation one might select more than one modulating waveform, or perhaps different waveforms than sinusoids. In addition, a complex amplitude modulation can be imposed. For example, one possibility is revealed in the trigonometric relation... 

Using amplitude or frequency modulation of a carrier at frequency tog, we can achieve exact frequency division if we make sidebands of the carrier to such low frequency that we can force the condition wg-nQ = (n+2) 2-a>g = 2 so that tog/ 2 = n+1. For example, if we examine Fig. 2, we can achieve exact frequency division by any means which locks the phase of the carrier to the phase of the amplitude modulation that is, the undulations of the carrier do not "slip" under the envelope of the amplitude modulation. A divider based on these principles would be quite useful if 2 is in the microwave region (or below) where precise frequency synthesis is possible. Since 2 and n could be freely chosen, any value of uig could be measured in a single device. 

In highly nonisotropic Hartmann-Hahn mixing sequences, the selection of a single magnetization component is a built-in property. Pure amplitude modulation can therefore be obtained in the evolution period using the pulse sequence of Fig. 37A without further modifications. For example. 

The first SMS experiments in 1989 utilized either of two powerful doublemodulation FM absorption techniques, laser frequency-modulation with Stark secondary modulation (FM-Stark) or frequency-modulation with ultrasonic strain secondary modulation (FM-US) [3,26]. The secondary modulation was required in order to remove the effects of residual amplitude modulation produced by the imperfect phase modulator. In contrast to fluorescence methods, Rayleigh and Raman scattering were unimportant. Figure 2.3B (specifically trace d) shows examples of the optical absorption spectrum from a single molecule of pentacene in p-terphenyl using the FM-Stark method. 

It seems intuitively clear that such an achievement is due to the control of quantum dissipative dynamics through the application of a suitably tailored, time-modulated driving field. Indeed, some interesting examples of suppression of quantum decoherence by the modulation of system parameters have been considered in [Viola 1998 Vitali 1999], An improvement of sub-Poissonian statistics of an anharmonic oscillator by the application of amplitude-modulated pump field have been demonstrated in [Kryuchkyan 2002 Kryuch-kyan 2003],... 

Questions of linkage are posed and answered by asking the molecule to satisfy successively two resonance conditions. Schemes which accomplish this include Dispersed Fluorescence Spectroscopy (DF, Section 1.2.2.2 a laser is tuned to excite a single line and the spectrum of the resulting molecular fluorescence is recorded), Modulated Population Spectroscopy (MPS, Section 1.2.2.3) an intense, fixed frequency, amplitude modulated PUMP laser is used to modulate the population in the upper and lower levels connected by the laser excited transition the modulation is then detected by a frequency scanned PROBE laser), which is an example of Optical Optical Double Resonance (OODR, Section 1.2.2.3). 

Finally, the FT-IR system operates by coding the infrared source with an amplitude modulation which is unique to each infrared frequency. The detector is sensitive to the modulated radiation so that unmodulated stray radiation is eliminated from the experiment, permitting the use of the FT-IR as an in-situ detector in many experiments. For example, an FT-IR has been used to monitor the evolution of coal pyrolysis products within a drop tube furnace (24) and within an entrained flow reactor (25). The latter has been operated up to 1200 C. 

In implantable stimulators and electrodes, the stimulation parameters greatly depend on the implantation site. When the electrodes are positioned on or around the target nerve, the stimulation amplitudes are on the order of a few milliamperes or less. Electrodes positioned on the muscle surface (epimysial electrodes) or in the muscle itself (intramuscular electrodes), employ up to ten times higher amplitudes. For muscle force control, implantable stimulators rely either on pulse-width modulation or amplitude modulation. For example, in upper extremity applications, the current amplitude is usually a fixed parameter set to 16 or 20 mA, while the muscle force is modulated with pulse widths within 0-200 p,s. 

Frequency modulation differs from amplitude modulation in that the modulated wave consists of the carrier frequency and numerous sideband components that are generated for each modulating frequency. Recall that AM consists of a carrier and a upper and lower sideband. The bandwidth of an AM signal is determined by the highest frequency of the modulating signal. For example, a carrier is modulated by a audio signal which contains frequencies up to 4000 Hz. The AM bandwidth would therefore be (2) (4000) = 8000 Hz. 

As the Ml increases there are more sidebands produced. As the modulating frequency increases for a given maximum deviation, there will be a smaller number of sidebands spaced at wider intervals. Unlike amplitude modulation, which has a percentage of modulation directly proportional to the carrier power, the percentage of modulation in FM is generally referenced to the maximum allowable occupied bandwidth set by regulation. For example, FM broadcast stations are required to restrict frequency deviation of-F/— 75 kHz from the main carrier. This is referred to as 100% modulation for FM broadcast stations. 

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