Methoden zur Minimierung des Rauscheinflusses durch Hitzeflimmern bei einem heterodynen Laser-Doppler-Vibrometer

Schewe, Marvin; Kohlmann, Dhyan; Wulfmeier, Hendrik; Fritze, Holger; Rembe, Christian

doi:10.1515/teme-2020-0023

Cited by 6 publications

(3 citation statements)

References 9 publications

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“…Therefore, there is a need to reduce the noise level. One possibility for decreasing the noise level involves utilising a differential LDV (DLDV) [7] . To highlight the capability of noise reduction with a DLDV, a reflector and a mirror are attached to a larger drone (the DJI Mavic 2 Pro) with the rotors set to idle mode (1900 r/min).…”

Section: Methodsmentioning

confidence: 99%

Towards airborne laser Doppler vibrometry for structural health monitoring of large and curved structures

Schewe¹,

Ismail²,

Rembe³

2021

insight

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Laser Doppler vibrometry is an important sensing technology for many structural health monitoring (SHM) methods, such as modal analysis. However, when it comes to large civil structures, for example historic structures and bridges, the applicability of laser Doppler vibrometry is significantly constrained by inaccessible remote surfaces. Some of these surfaces are fully inaccessible to a ground-mounted laser Doppler vibrometer (LDV), while others are partially inaccessible, and measurements are only possible for low incident angles. Consequently, LDV measurements are either impossible or have a weak signal strength. In this study, the concept of constructing an airborne LDV for SHM is explored, including the examination of a recently developed mechanism, the partially airborne LDV, comprising a reflective mirror attached to a drone. Preliminary proof of concept laboratory tests have been successfully conducted using two different set-ups and drone models.

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Section: Methodsmentioning

confidence: 99%

Towards airborne laser Doppler vibrometry for structural health monitoring of large and curved structures

Schewe¹,

Ismail²,

Rembe³

2021

insight

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“…One possibility is differential laser Doppler vibrometry (D-LDV). Such measurements are taken on the ceria sample using a differential laser Doppler vibrometer conceived and realized by the authors [39,40]. It employs a Koheras Basik X15 fiber laser (NKT Photonics, Denmark) with 1550 nm wavelength.…”

Section: Experimental Setup: Sp-ldv and D-ldvmentioning

confidence: 99%

Chemical expansion of CeO2−δ and Ce0.8Zr0.2O2−δ thin films determined by laser Doppler vibrometry at high temperatures and different oxygen partial pressures

et al. 2023

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The chemical expansion of ceria (CeO2−δ) and ceria-zirconia (Ce0.8Zr0.2O2−δ, CZO80) thin films is investigated by high-temperature laser Doppler vibrometry (LDV) at temperatures from 600 to 950 °C. The films are deposited on single-crystalline 8 mol-% yttria-stabilized zirconia substrates, which act as pumping cells to adjust oxygen non-stoichiometry in the thin films. Oxygen deficiency causes film expansion, leading to mechanical strain that bends the sample. The total displacement, i.e., the sum of bending and film-thickness change, is determined contact-less by LDV. A differential laser Doppler vibrometer (D-LDV) is realized to enable measurements on a very long time scale, which is necessary due to the long equilibrium times of the ceramic films. These displacements are compared to those acquired with a commercial single-point laser Doppler vibrometer (SP-LDV) for motions above 1 Hz. Here, both devices yield similar results. CZO80 films are found to bend a substrate much more than ceria films under similar experimental conditions. A model describing the displacement of the sample is derived from the Stoney model and applied to calculate deflections using literature data. The displacements at the center of the CZO80 sample measured with the SP-LDV increase from 0.18 nm at 10 Hz and 600 °C to 32.7 nm at 0.1 Hz and 800 °C. For ceria, the displacements range from 1.6 nm (10 Hz, 800 °C) to 79.4 nm (0.1 Hz, 900 °C). The D-LDV enables the detection of quasi-static displacements at very low frequencies. The ceria sample exhibits 218 nm at 0.001 Hz and 800 °C.

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“…With the advancement of laser-Doppler vibrometers (LDVs), various additional applications are continuously made available in which contactless vibration measurement is possible [1][2][3]. These applications are difficult to implement with conventional methods of vibration measurement, impossible in the case of rotating or hot parts [4], or unwanted in medical applications [5].…”

Section: Introductionmentioning

confidence: 99%

Signal Diversity for Laser-Doppler Vibrometers with Raw-Signal Combination

Schewe

Rembe

2021

Sensors

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The intensity of the reflected measuring beam is greatly reduced for laser-Doppler vibrometer (LDV) measurements on rough surfaces since a considerable part of the light is scattered and cannot reach the photodetector (laser speckle effect). The low intensity of the reflected laser beam leads to a so-called signal dropout, which manifests as noise peaks in the demodulated velocity signal. In such cases, no light reaches the detector at a specific time and, therefore, no signal can be detected. Consequently, the overall quality of the signal decreases significantly. In the literature, first attempts and a practical implementation to reduce this effect by signal diversity can be found. In this article, a practical implementation with four measuring heads of a Multipoint Vibrometer (MPV) and an evaluation and optimization of an algorithm from the literature is presented. The limitations of the algorithm, which combines velocity signals, are shown by evaluating our measurements. We present a modified algorithm, which generates a combined detector signal from the raw signals of the individual channels, reducing the mean noise level in our measurement by more than 10 dB. By comparing the results of our new algorithm with the algorithms of the state-of-the-art, we can show an improvement of the noise reduction with our approach.

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Methoden zur Minimierung des Rauscheinflusses durch Hitzeflimmern bei einem heterodynen Laser-Doppler-Vibrometer

Cited by 6 publications

References 9 publications

Towards airborne laser Doppler vibrometry for structural health monitoring of large and curved structures

Towards airborne laser Doppler vibrometry for structural health monitoring of large and curved structures

Chemical expansion of CeO2−δ and Ce0.8Zr0.2O2−δ thin films determined by laser Doppler vibrometry at high temperatures and different oxygen partial pressures

Signal Diversity for Laser-Doppler Vibrometers with Raw-Signal Combination

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