Sine-wave modulation technique

S. Brukenstein et al. proposed in 1973 [5] this technique as an alternative to the sine-wave modulation technique. Their approach was based on the Benton s analysis of fluid flow near an impulsively started disk from rest [61]. They assumed that the... 

A comprehensive overview of frequency-domain DOT techniques is given in [88]. Particular instraments are described in [166, 347, 410]. It is commonly believed that modulation techniques are less expensive and achieve shorter acquisition times, whereas TCSPC delivers a better absolute accuracy of optical tissue properties. It must be doubted that this general statement is correct for any particular instrument. Certainly, relatively inexpensive frequency-domain instruments can be built by using sine-wave-modulated LEDs, standard avalanche photodiodes, and radio or cellphone receiver chips. Instruments of this type usually have a considerable amplitude-phase crosstalk". Amplitude-phase crosstalk is a dependence of the measured phase on the amplitude of the signal. It results from nonlinearity in the detectors, amplifiers, and mixers, and from synchronous signal pickup [6]. This makes it difficult to obtain absolute optical tissue properties. A carefully designed system [382] reached a systematic phase error of 0.5° at 100 MHz. A system that compensates the amplitude-phase crosstalk via a reference channel reached an RMS phase error of 0.2° at 100 MHz [370]. These phase errors correspond to a time shift of 14 ps and 5.5 ps RMS, respectively. 

An alternate approach, developed in a speech coding context [McAulay and Quatieri, 1986a, McAulay and Quatieri, 1992], uses a harmonically-dependent set of sine waves with a random phase modulation. Yet another related technique [Marques and Almeida, 1988], represents the signal by a sum of adjacent narrowband sines of uniformly-spaced center frequency, with random amplitude and frequency modulation. 

Modulated Temperature DSC. This is a relatively new technique with tremendous application to thermosets (4). By superimposing a sine wave on the... 

Temperature Oscillation Calorimetry A more elegant way to estimate online the overall heat transfer coefficient without any additional measurement was developed by Carloff [ 11] by the technique known as temperature oscillation calorimetry, TOC. In this approach, the unknown product UA is computed from the analysis of the sine-shaped oscillations, which are superposed on either the reactor temperature or jacket temperature. The objective is to decouple the slow dynamic of the chemical heat production from the fast dynamic variable heat transfer during the reaction. The oscillations can be achieved either by adding a calibration heater to the system or by adding a sine signal to the set point of either T or Ty Figure 7.2 shows the evolution of the reactor and jacket temperatures in a reaction calorimeter where a sine wave temperature modulation was superimposed on the reactor jacket temperature. 

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