Laser Vibrometer System Research Articles

Acoustoelastic Interaction in Combustion Chambers: Modeling and Experiments

To decrease NOx emissions from combustion systems, lean premixed combustion is used. A disadvantage is the higher sensitivity to combustion instabilities, leading to increased sound pressure levels in the combustor and resulting in an increased excitation of the surrounding structure: the liner. This causes fatigue, which limits the lifetime of the combustor. This paper presents a joint experimental and numerical investigation of this acoustoelastic interaction problem for frequencies up to 1kHz. To study this problem experimentally, a test setup has been built consisting of a single burner, 500kW, 5bar combustion system. The thin structure (liner) is contained in a thick pressure vessel with optical access for a traversing laser vibrometer system to measure the vibration levels of the liner. The acoustic excitation of the liner is measured using pressure sensors measuring the acoustic pressures inside the combustion chamber. For the numerical model, the finite element method with full coupling between structural vibration and acoustics is used. The flame is modeled as an acoustic volume source corresponding to a heat release rate that is frequency independent. The temperature distribution is taken from a Reynolds averaged Navier Stokes (RaNS) computational fluid dynamics (CFD) simulation. Results show very good agreement between predicted and measured acoustic pressure levels. The predicted and measured vibration levels also match fairly well.

Dynamics-based Damage Detection of Composite Laminated Beams using Contact and Noncontact Measurement Systems

A reliable and effective damage detection technique is one of the significant tools to maintain the safety and integrity of structures. A dynamic response offers viable information for the identification of damage in the structures. However, the performance of such dynamics-based damage detection depends on the quality of measured data and the effectiveness of data processing algorithms. In this article, the experimentally measured data of two sensor systems, i.e., a surface-bonded piezoelectric sensor system and a noncontact scanning laser vibrometer (SLV) system, are studied, and their effectiveness in damage identification of composite laminated beams is compared. Three dynamics-based damage detection algorithms are evaluated using the data acquired from these two measurement systems. The curvature mode shape is selected as a parameter to locate damage due to its sensitivity. The piezoelectric sensors directly acquire the curvature mode shapes of the structures, while the SLV measures the displacement mode shapes. The difference in the measurement characteristics of these systems and their influence in the damage identification performance are addressed. The beam specimens are made of E-glass/epoxy composites, and several different types of damages are introduced in the beams (i.e., delaminations, and impact and saw-cut damages). This study provides a thorough assessment of the two sensor systems in damage detection of composite laminated beams and verifies the validity of dynamics-based damage detection methodology in locating the local defects in composite structures.

Heterodyne speckle interferometer for full-field velocity profile measurements of a vibrating membrane by electronic scanning

Dynamic deformation measurements were carried out by combining full-field speckle interferometry and heterodyne interferometry. A digital demodulation technique based on the evaluation of the instantaneous frequency have been implemented in the digital signal processor of a complementary metal-oxide semiconductor (CMOS)-based camera to extract velocity measurements from phase modulated optical carrier signals. The purpose of this experimental investigation was to demonstrate a full-field laser vibrometer system that could replace electro-mechanical scanning with electronic scanning within a programmable stand-alone and relatively low-cost digital camera. Velocity profiles of a vibrating membrane in the order of few microns per second were reconstructed automatically by performing an electronic scanning of the surface over the image sensor.

Acoustics of the mridangam: Study of a new design of a South Indian drum

The acoustical properties of the ancient Carnatic drum, the mridangam, have been studied, including instruments of traditional design as well as instruments with a newly designed mounting method for the drumheads. The mridangam is comprised of three primary parts: The tonal head (valanthalai), the bass head (thoppi), and the central shell (katta), to which the two heads are traditionally fastened by leather rope. The new design is proposed as a convenient and practical way to mount and tune the drumheads. Measurements were made on drums with the drumheads mounted in the traditional way, and then repeated with the heads remounted using the new design. For measurements of the modes and mode frequencies of the drumheads, the modes were excited by a mechanical vibrator and vibration of the drumhead was measured using a laser vibrometer system. The frequencies of the first few modes of the tonal head were found, as expected, to be tuned to be approximately harmonic. Measurements of drumhead vibration and sound spectra were also made when the drumhead was excited by a skilled player using standard strokes. Some effects of coupling between the two drumheads were studied. [Work supported by the Kalamazoo College HHMI Undergraduate Research Program.]

A scanning laser Doppler vibrometer acoustic array

Experiments confirm that a laser Doppler vibrometer can be used to detect acoustic particle velocity on a fluid-loaded acoustically compliant, optically reflective surface. In these experiments, which were completed at the Acoustic Test Facility of the Naval Undersea Warfare Center, Scotchgard™ reflective tape was affixed to the interior surface of a standard acoustic window. The polyurethane array window had a thickness of 0.9525cm (0.375in.) and a material density of 1000kg∕m3. The surface velocity measured, using a commercial scanning laser vibrometer system (SLVS), was beamformed conventionally and flawlessly detected and localized acoustic signals. However, the laser Doppler vibrometer used in the experiments had relatively poor acoustic sensitivity, presumably due to high electronic noise in the photodetector, speckle noise, standoff distance, and drifting laser focus. An improved laser Doppler vibrometer, the simplified Michelson interferometer laser vibrometer sensor (SMIV), is described in brief. The SMIV achieves sensitivity of 61dB∕μPa in a 1-Hz band at 11.2kHz, which represents a 39-dB acoustic sensitivity improvement.

Fabrication and electromechanical properties of a self-actuating Pb(Zr0.52Ti0.48)O3 microcantilever using a direct patternable sol-gel method

The use of direct-patternable lead zirconate titanate (PZT) films produced using photosensitive stock solutions with ortho-nitrobenzaldehyde and UV (365 nm) irradiation has reached an advanced stage of application in microdetection systems. Electromechanical properties of direct patterned PZT microcantilevers on SiNx∕Ta∕Pt∕PZT∕Pt∕SiO2 structure were measured by a laser vibrometer system as a function of cantilever length. The gravimetric sensitivity of cantilevers in air was characterized by Au deposition, and the mass detecting resolution was 38Hz∕ng. These results suggested a possibility that microelectromechanical systems may be fabricated relatively easily and without high cost processes, for example, by PZT dry etching.

A study on the performance of bending mode piezoelectric accelerometers

The method of eigenfunction expansion is proposed for obtaining an analytical expression for the frequency response of a bending mode piezoelectric accelerometer system. A set of approximate formulae derived relating the sensitivity with system parameters such as length, width, thickness and the seismic to beam mass ratio. Furthermore, the proposed model was experimentally validated using a laser vibrometer system configured for linear displacement measurements.

The Load Capability of Piezoelectric Single Crystal Actuators

ABSTRACTPiezoelectric lead magnesium niobate-lead titanate (PMN-PT) single crystal is one of the most promising materials for electromechanical device applications due to its high electrical field induced strain and high electromechanical coupling factor. PMN-PT single crystal-based multilayer stack actuators and multilayer stack-based flextensional actuators have exhibited high stroke and high displacement-voltage ratios. The actuation capabilities of these two actuators were evaluated using a newly developed method based upon a laser vibrometer system under various loading conditions. The measured displacements as a function of mechanical loads at different driving voltages indicate that the displacement response of the actuators is approximately constant under broad ranges of mechanical load. The load capabilities of these PMN-PT single crystal-based actuators and the advantages of the capability for applications will be discussed.

Vibratory response of diamond-like amorphous carbon cantilevers under different temperatures

Diamond-like amorphous carbon films were deposited using filtered cathodic vacuum arc (FCVA) with the plasma ion immersion implantation (PIII) system. A unique multilayer film, comprising of alternating high-sp 3 content (90%), high-stress (9 GPa) films, low-sp 3 content (50%), and low-stress films (<0.5 GPa), was fabricated. By alternating these layers, a 1.5-μm-thick film was subsequently deposited. Free-standing microcantilevers measuring 150×50 μm had been subsequently fabricated by using standard lithography and wet etching. The resonance frequency of the microcantilevers was measured by a vacuum laser vibrometer system to be 109.5 kHz. After gradual heating to 240 °C, the resonance frequency was observed to increase to a high of 111.5 kHz.

Acoustical studies of the American reed organ

The reed organ enjoyed a period of great popularity in North America which reached a peak in the late 19th century, when thousands of instruments per year were manufactured and sold in the United States and Canada. Displaced by the emergence of the upright piano, the reed organ had very much fallen out of favor by 1929. In the past decade a number of acoustical investigations have been undertaken on the instrument known as the American reed organ. Observations of reed motion and velocity have been made with electronic proximity sensors and a laser vibrometer system. The variation of the frequency and amplitude of reed vibration as a function of blowing pressure has been explored in some detail and the results compared with predictions of a simple theoretical model. Measurements have been made of the spectrum of the near-field sound including the effects of changes in dimensions of the reed cell. While most treatments of free reed oscillation approximate the reed vibration as a sinusoidal oscillation of a cantilever beam in the fundamental transverse mode, recently some evidence of higher transverse modes and torsional modes of vibration have been observed.

High-frequency laser sonar system

A set of measurements recently completed at the Naval Undersea Warfare Center (NUWC) demonstrated that a laser-based sonar system can be used to detect acoustic particle velocity on the surface of a thin acoustically-compliant plate embedded beneath a standard acoustic window. The theoretical acoustic and measured surface particle velocity varied by less than 1 dB (reference m/s) over a wide frequency band (10 kHz to 100 kHz). However, the Polytec Model PSV-100 Scanning Laser Vibrometer System (SLVS) used in the experiments had relatively poor acoustic sensitivity, presumably due to high electronic noise, speckle noise, stand-off distance, and drifting laser focus. The laser’s acoustic sensitivity appears to be inversely proportional to the backscatter signal level. The existing SLVS can sample a grid of 512 by 512 points, with each grid point having a spot size of approximately 10 mm (0.0004 in.). Such fine sampling may be used to create essentially a continuous aperture, eliminating acoustic grating lobes at all frequencies of practical sonar interest.

Laboratory measurements on free reeds from the reed organ, accordion, and khaen

Several series of experimental measurements have been made on the motion of air-driven free reeds. These include individual reed organ reeds mounted on a laboratory wind chamber, accordion reeds mounted on the accordion reed block, and khaen reeds in individual bamboo pipes, in which the symmetric free reed is coupled to the pipe resonator. Measurements of reed displacement and velocity as a function of time have been made using a variable impedance transducer and a laser vibrometer system. Additional measurements made for each type of reed include sound pressure and air flow waveforms, as well as variation of sounding frequency and amplitude of vibration with blowing pressure. In comparing the sound pressure and air flow waveforms among the various types of reeds or for the same reed at different blowing pressures, differences can be understood in terms of the configuration of the reed and reed frame system and the amplitude of reed vibration. Some of the results can be interpreted in terms of simple theoretical models.

Fabrication and Resonant Behavior of PZT Thick Film Cantilever for BioChip

PZT(52/48) thick films with an Pb-based complex oxide (PCW) additive were prepared on Pt/TiO 2 /YSZ/SiO 2 /Si substrate by new hybrid method based on the screen printing. It is found that solinfiltration for thick films fabrication process significantly improves the electrical properties due to the improved structural compactness. By applying these high quality piezoelectric thick films on micro cantilever devices, a highly sensitive thick film cantilever for mass(ng- ¯ ) detection devices is successfully fabricated. Resonant frequency and displacement of PZT-0.12PCW thick film cantilever for biochip are measured by laser vibrometer system as a function of cantilever size (width, length). We change the added mass from 4ng to 5 ¯ through Au deposition. The shorter cantilever is more sensitive for mass change and it is found that the sensitivity of cantilever decreases due to viscous damping effect in liquid. Finally, the application of these PZT-0.12PCW thick film cantilever devices to a protein detector i...

Characterization of Resonant Behavior and Sensitivity Using Micromachined PZT Cantilever

Micromachined piezoelectric cantilevers have been fabricated using PZT (52/58) films. Electromechanical characteristics of micromachined PZT cantilever were measured by laser vibrometer system as a function of cantilever length for the cantilever with two different supported layer thickness respectively. The 1 st version unimorph cantilever consists of a 0.6 -thick PZT layer on 1.5 -thick SiN x elastic supported layer. In order to increase Q-factor in air and liquid, from calculated spring constant as a function of variable supporting layer thickness, 2 nd version cantilever was designed to have a 0.8 -thick PZT layer on 4.5 -thick SiN x /Si elastic supported layer. The gravimetric sensitivities of cantilever in air were characterized by Au deposition on the backside of cantilever. The gravimetric sensitivity of 100 2 200 -dimension cantilever was 300 cm 2 /g and the mass of 5 ng was detectable.

Characterization of Resonant Behavior and Sensitivity Using Micromachined PZT Cantilever

Micromachined piezoelectric cantilevers have been fabricated using PZT (52/58) films. Electromechanical characteristics of micromachined PZT cantilever were measured by laser vibrometer system as a function of cantilever length for the cantilever with two different supported layer thickness respectively. The 1 st version unimorph cantilever consists of a 0.6 -thick PZT layer on 1.5 -thick SiN x elastic supported layer. In order to increase Q-factor in air and liquid, from calculated spring constant as a function of variable supporting layer thickness, 2 nd version cantilever was designed to have a 0.8 -thick PZT layer on 4.5 -thick SiN x /Si elastic supported layer. The gravimetric sensitivities of cantilever in air were characterized by Au deposition on the backside of cantilever. The gravimetric sensitivity of 100 2 200 -dimension cantilever was 300 cm 2 /g and the mass of 5 ng was detectable.

Fabrication and Resonant Behavior of PZT Thick Film Cantilever for BioChip

PZT(52/48) thick films with an Pb-based complex oxide (PCW) additive were prepared on Pt/TiO 2 /YSZ/SiO 2 /Si substrate by new hybrid method based on the screen printing. It is found that solinfiltration for thick films fabrication process significantly improves the electrical properties due to the improved structural compactness. By applying these high quality piezoelectric thick films on micro cantilever devices, a highly sensitive thick film cantilever for mass(ng- ¯ ) detection devices is successfully fabricated. Resonant frequency and displacement of PZT-0.12PCW thick film cantilever for biochip are measured by laser vibrometer system as a function of cantilever size (width, length). We change the added mass from 4ng to 5 ¯ through Au deposition. The shorter cantilever is more sensitive for mass change and it is found that the sensitivity of cantilever decreases due to viscous damping effect in liquid. Finally, the application of these PZT-0.12PCW thick film cantilever devices to a protein detector is discussed.

Frequency analysis of turbulent compressible flows by laser vibrometry

The objective of this work was the application of laser vibrometry as a tool for non-intrusive measurement of frequency spectra in turbulent flows. A laser vibrometer system together with a signal analyser was used to obtain frequency spectra of density fluctuations across a turbulent free jet. Since laser vibrometry is based on interferometric techniques, the derived signals are path integrals along the measurement beam. Frequency spectra recorded in the rotational symmetric flow were then treated using Abel inversion in order to derive information on local density fluctuations. Results for two different flow conditions were compared to spectral data from a constant temperature anemometer and a pitot-mounted pressure sensor.

Studies of accordion reed vibrations—Applications in sound synthesis

The accordion is a free-reed instrument. The two identical reeds associated with one note are driven separately by the airflow created by the inward and outward movements of the bellows. In this present study, attention is focused on understanding the aerodynamic phenomena involved in reed vibration. The acoustical model is deduced from the variation of the flow rate through the slot in the reed plate. A variety of laboratory measurements and observations on different accordion reeds have been made with different blowing pressures. Among them: near-field sound pressure (microphones above and under the reed); displacement and velocity of the reed (capacitive sensor and laser vibrometer system); reed profile, magnified stroboscopic images, flow visualization; etc. From these experimental results, we have extracted the most important phenomena involved, which are to be implemented in a physical model accurate enough to describe the behavior of the reed and to reproduce its characteristic sound. This physical model must be as simple as possible to be computationally efficient and usable in sound synthesis. For example, at IRCAM, it is possible to program the accordion model in Modalys, a synthesizer language based on modal representation formalism. Similarities and differences between simulated and real sounds will be discussed.

Experimental investigation of air-driven free reeds using a laser vibrometer system

Previously reported measurements of free-reed vibration using a variable impedance transducer (VIT) gave a picture of the motion of a point on the reed throughout its cycle [J. P. Cottingham, J. Acoust. Soc. Am. 105, 940 (1999)]. A more detailed picture of the reed motion throughout its vibrational cycle has been obtained by measuring reed velocity using a laser vibrometer system. Unlike the VIT sensor, the laser vibrometer can be scanned along the reed, allowing reed profiles to be obtained. The laser system is also usable on reeds of magnetic material (e.g., steel accordion reeds) as well as reeds too small and inaccessible for the VIT. In this investigation the emphasis has been on comparison of the vibrational motion of accordion reeds with that of the reed organ reeds which had been measured in earlier studies. Some of the differences observed between the two types of reeds can be related to the structure of the reed tongues and frames.

The motion of air-driven free reeds

An earlier study on free reeds from reed organs [P. D. Koopman and J. P. Cottingham, Reed Organ Soc. Bull. 15, No. 3–4, 17–23 (1997)] yielded information about the variation in amplitude of reed vibration with pressure, but few further details on the reed motion. A more thorough set of measurements of the motion of these reeds has been done, including the use of a variable impedance transducer to measure reed displacement and a laser vibrometer system to measure reed velocity. For reeds from reed organs, at low to moderate blowing pressures, the reed motion at each point is nearly sinusoidal and the reed profile at maximum amplitude closely approximates that calculated for a cantilevered beam vibrating in the first mode. At blowing pressures considerably higher than normal playing pressure, strong indications of the presence of the second beam mode are observed. The nearly sinusoidal reed motion at normal pressure contrasts with the sound pressure waveform near the reed which, as a result of the valve action of the reed, roughly resembles a pulse wave. Similar measurements on accordion reeds yield somewhat contrasting results.