Vibrometer

Fig. 1 shows the block diagram of the vibrometer, in which the most sensible to small phase variations interferometric scheme is employed. It consists of the microwave and the display units. The display unit consists of the power supply 1, controller 2 of the phase modulator 3, microprocessor unit 9 and low-frequency amplifier 10. The microwave unit contains the electromechanical phase modulator 3, a solid-state microwave oscillator 4, an attenuator 5, a bidirectional coupler 6, a horn antenna 7 and a microwave detector 11. The horn antenna is used for transmitting the microwave and receiving the reflected signal, which is mixed with the reference signal in the bidirectional coupler. In the reference channel the electromechanical phase modulator is used to provide automatic calibration of the instrument. To adjust the antenna beam to the object under test, the microwave unit is placed on the platform which can be shifted in vertical and horizontal planes. 

The brief history, operation principle, and applications of the above-mentioned techniques are described in this chapter. There are several other measuring techniques, such as the fluorometry technique. Scanning Acoustic Microscopy, Laser Doppler Vibrometer, and Time-of-flight Secondary Ion Mass Spectroscopy, which are successfully applied in micro/nanotribology, are introduced in this chapter, too. 

Equations (33) and (34) demonstrate that the motion quantities 5 (displacement) and v (velocity) are encoded in phase and frequency modulation of the detector output signal, purely referenced to the laser wavelength A. Tobeableto recover the time histories s(t) and v t) from the modulated detector signal, adequate phase and frequency demodulation techniques, or both, are utilized in the signal decoder blocks of a laser vibrometer. 

Lawton, R., "MEMS Characterization Using Scanning Laser Vibrometer, Reliability, Testing, and Characterization of MEMS/MOEMS II, R. Ramesham and D. M. Tanner, Eds., Proceedings ofSPIE, Vol. 4980,2003, pp. 51-62. 

In laser Doppler vibrometry (SLDV), surfaces are slightly vibrated by mechanical activation while the vibrometer scans the object producing 2- or 3D maps of velocity, amplitude, and phase, which allow the detection and mapping of structural defects [15]. 

The specimen used for ITS testing can be any section of the composite, provided that after mounting and polishing, fibers normal to the polished surface can be found. A section of composite approximately 1 cm x 1 cm was cut from the laminates previously prepared. The sections were embedded in 1 in. diameter phenolic ring mounts with room temperature-cured epoxy mounting media. The sections were oriented so that the fiber ends were normal to the face of mount to be polished. The initial steps of the polishing were accomplished on a Struers Abramin polisher and the final step was a on Beuhler Vibromet I vibrating lap polisher. The steps used are listed in Table 2. 

Xiang and Sabatier [149] used a scanning laser Doppler vibrometer (LDV) to detect acoustic-to-seismic surface motion. This technique exploits airborne acoustic waves penetrating the ground and causing seismic motion. When an anti-personnel landmine... 

Vibrometer 366 Vieille Test 179 366 Virial equation 120 viscosity of nitrocellulose 224 Visol Visol-1 -4 -6 = vinylethylether and mixtures with isopropylalcohol and vinylbutylether liquid rocket fuel (german)... 

The following vibrometers are developed, produced and distributed by WASAGCHEMIE Sythen, Haltern, Federal Republic of Germany ... 

Vibrometer ZEB/SM 3 and. ZEBI/SM 6 DIN 45669 Indication of the maximum values in alphanumeric display. Registration of the complete recording with the aid of an UV (ultraviolet) recorder. 

Noise and vibration measurements are made with microphones and accelerometers. Sometimes, sophisticated instruments like laser vibrometers are used for NVH work. Common noise fixes include cutting slots and/or chamfers on the brake pads and linings, the application of constrained layer damping noise insulators to the back of the brake pad shoe plates, and detuning the resonant frequency of mechanical brake corner components. 

Sohn H, Dutta D, Yang JY, DeSimio M, Olson S, Swenson E. Automated detection of delamination and disbond from wavefield images obtained using a scanning laser vibrometer. Smart Mater Struct 2011 20(4) 045017. http //dx.doi.org/10.1088/0964-... 

Tissue Vibration. Noncontact methods are preferred for measuring the surface motion of tissues. Laser vibrometers are commercially available with sufficient bandwidth and resolution for most studies. A direct mass load on the skin, together with the skin s elasticity, forms a mechanical low-pass filter (see Simple Lumped Models in Sec. 10.3.1). If a device is to be mounted directly on the skin, it must be of low weight (e.g., <3 g) and possess a comparatively large attachment area (e.g., >S cm ), in order for vibration to be recorded without attenuation of the motion at 80 Hz. An upper frequency limit of 200 Hz is theoretically achievable (—3dB) with a transducer and skin mount weighing 3 g and an attachment area of 1.8 cm. ... 

In Fig. 3.11, velocity motion detected by the laser vibrometer is shown at the middle and that of Lamb s solution is shown at the bottom. Remaika-ble agreement is confirmed except the latter reflections in the detected wave. Because a concrete block was employed in the experiment, these reflected motions are observed. At the top, frequency spectrum of the detected wave is shown as a solid curve and is compared with that of Lamb s solution denoted by a broken curve. Reasonable agreement is again confirmed. This result suggests an application of the laser vibrometer for the absolute calibration instead of the capacitive transducer. 

Hatano and Moro [1976] suggested the use of a reciprocity method, where sensors are coupled onto a steel plate. This approach uses Rayleigh waves. Other methods described in the literature suggest using a laser-vibrometer to measure the displacement of the free surface of the sensor, or a network analyzer (Weiler and Grosse 1995 Grosse 1996). 

Fig. 5.5. (top) Example of frequency response functions of a resonant and a so-called broadband transducer. The frequency response function was measured using a laser-vibrometer (middle) and a face-to-face method (bottom). Amplitudes are on a linear scale. 

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