Phase sensitive digitized frequency modulated thermal wave imaging and pulse compression for NDE applications
Citations
34 citations
16 citations
6 citations
3 citations
Cites background from "Phase sensitive digitized frequency..."
...1: (a) and (b) shows a linear frequency modulated signal (chirp) and it’s digitized form, respectively [10]...
[...]
...Measurements are made over only one frequency-modulated cycle [10]...
[...]
...overcome some of the traditional limitations of conventional thermal wave imaging techniques (resolution, peak power, depth of penetration), the present work focuses on non-stationary forms of thermal excitation technique: frequency modulated thermal wave imaging [7-14]....
[...]
3 citations
Cites background or methods from "Phase sensitive digitized frequency..."
...However for detection of sub-surface feature of the test sample, especially if they are deep, active thermography is preferred instead of passive techniques [2-5]....
[...]
...T (z, t) = T0 ecos(ωt -z/μ) (1) where T0 is amplitude of the oscillating temperature, z the depth below the surface, ω the angular frequency and μ is the thermal diffusion length [1-5], defined as follows μ = [2α/ω] (2) Where α is thermal diffusivity of the material....
[...]
...Various methods [2-5] and analysis techniques [6-10] have further been developed throughout the world to improve and widen the use of IRT for non-destructive characterization....
[...]
...Since most solids conduct heat, IRT has actual and potential use in detecting subsurface features in a variety of materials (metals, semiconductors and composites) [5]....
[...]
References
1,381 citations
"Phase sensitive digitized frequency..." refers background in this paper
...Such signals are particularly used in seismic, sonar and radar applications, and lead to solutions for combined range-resolution problems [11]....
[...]
...Increasing the band width of the excitation signal not only helps to get fine range (depth) resolution but also improves the S/N ratio [11]....
[...]
404 citations
312 citations
"Phase sensitive digitized frequency..." refers background or methods in this paper
...It is very difficult to reliably measure the depth information of cavity from the captured raw image sequence [2-5] because these are sensitive to non-uniform heating, and surface emisitivity variations on the sample surface too cause misinterpretations....
[...]
...Lock-in thermography (LT) uses periodic sinusoidal thermal excitation in order to derive information of reflected thermal wave phase and magnitude [3,4]....
[...]
...Then, neglecting convection losses, the temperature T, as a function of depth z and time t is given by [1,3,5],...
[...]
75 citations
"Phase sensitive digitized frequency..." refers background in this paper
...Theoretically, the short duration excitation pulse in PPT does launch a large number of frequency components into the test samples, but the higher order components may not have sufficient energy to propagate deep into the sample [6-9]....
[...]
...Both ( ) s t and ( ) h t can be considered to be the same as the incident heat flux except for a delay and a change in amplitude [6-8]....
[...]
...The advantage of using a frequency modulated (chirp) heating [6-9] on the sample surface is that it provides good accuracy for time of flight measurements, as it only correlates well at a single well-defined instant of time of arrival (pulse compression)....
[...]
...As prevalent in RADAR (Radio Detection and Ranging), the pulse compression technique [8,9] allows for the transmission of a low peak-power, long-duration modulated wave....
[...]
...) can be represented in time as follows [7-9]...
[...]
62 citations
"Phase sensitive digitized frequency..." refers background or methods in this paper
...) can be represented in time as follows [7-9]...
[...]
...Theoretically, the short duration excitation pulse in PPT does launch a large number of frequency components into the test samples, but the higher order components may not have sufficient energy to propagate deep into the sample [6-9]....
[...]
...The advantage of using a frequency modulated (chirp) heating [6-9] on the sample surface is that it provides good accuracy for time of flight measurements, as it only correlates well at a single well-defined instant of time of arrival (pulse compression)....
[...]
...Measurements are made over only one frequency-modulated cycle [9]....
[...]
...Figure 4: Schematic description of the mild steel sample with flat bottom hole defects [9]....
[...]