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This paper reports our work on the design, microfabrication and testing of a novel bistable electromagnetically actuated microvalve that is fully fabricated by surface micromachining on a single silicon wafer with a potentially CMOS compatible process. The microvalve has an overall diameter of 1600 µm and an overall height of 600 µm that includes the thickness of the silicon wafer. The microvalve consists of four main components: a soft magnetic (NiFe) base, an Au microcoil, a CoNiMnP permanent magnet and a soft magnetic (NiFe) membrane with supported legs. The latching and unlatching mechanism of the microvalve governs the bistable positions of the membrane. The microvalve was tested for its performance to open/unlatch and close/latch a flow of deionized water at flow rates of 10-50 µl min?1. The microvalve operates at a current of 0.43 A, and its power and energy consumption are of the order of 1.6 W and 16 mJ, respectively. The microvalve has a response time of 10 ms and a burst pressure of 7.8 kPa.

AbstractThe article synthesises the lessons drawn from Unity and Diversity in Development Ideas: Perspectives from the UN Regional Commissions.Confronted with the different realities of their regions, the UN Regional Commissions gave different answers to similar issues such as regional cohesion, development, and regionalisation versus globalisation. Their analyses and policies often had an impact beyond the limits of the region where they were elaborated and, conversely, the Commissions also acted as the regional arm of the United Nations, adapting some UN principles and agreements to regional circumstances. The regret is expressed that the wealth of analyses and policies accumulated in the UN regionally and globally has not been used to elaborate an alternative development paradigm that would restore intellectual leadership to the UN.

Ultrasonic Lamb waves are generated in 90 m thin copy paper with a Q-switched low-power Nd:YAG laser and detected with an Ar+laser Doppler interferometer. This noncontact method enables one to determine two elastic constants (C44or C55) that are related to the compressive strength of the paper by matching the measured high frequency limit of the phase velocity of the a0mode with that predicted by orthotropic plate theory. The method is also used to measure the phase velocity of the nondispersive fast mode and infer the corresponding elastic constants (C11and C22), which are directly related to the tensile strength of the paper. Although excellent agreement is obtained with orthotropic plate theory and also with independent measurements made with contact transducers, the results must be taken cautiously because interferometric measurements made simultaneously on the opposite side of the sample showed clearly the unexpected antisymmetric nature of the fast mode, thus showing the limitation of the orthotropic model when applied to paper. © 1997 Society of Photo-Optical Instrumentation Engineers.

A differential laser Doppler velocimeter (LDV) has been used to measure in‐plane motion associated with waves propagating on a thin cylindrical shell excited radially at a single frequency by a shaker. It has been established that (1) the laser probe can be used to detect shear waves even in the presence of flexural waves; and (2) that wave‐vector analysis of the recorded in‐plane motion of the shell allows one to separate very clearly the types of waves propagating on the shell. The fiber optic technology used in the LDV system allows the optical probe head, located at a distance of about 30 cm from the shell, to be scanned over the entire surface of the shell. Data were recorded along an array of 32 points circumferentially and 16 points axially, enough to sample spatially both extensional (fast waves, low wave numbers) and flexural waves (slow waves, high wave numbers). The data were analyzed with both a two‐dimensional spatial Fourier transform and a Prony spectral method. The analysis clearly reveals both type of waves separately. Experimentally measured mode shape and dispersion curves are in good agreement with theoretical predictions based on Donnell’s thin shell equations.

Some aspects of the generation and detection of ultrasound with laser beams are presented. The objective of the study is (1) to present some experimental results on the generation of ultrasound with an array of optical fibers, (2) to discuss the possibility of generating directional surface waves with acousto-optic scanning in a very narrow frequency band, thus increasing the signal-to-noise ratio, and (3) to discuss the feasibility of the directional detection of ultrasound by using an array of optical fibers as a receiver, also with the goal of increasing the signal-to-noise ratio.

An experimental technique is proposed to analyze and control laser-generated Lamb waves propagating in aluminum plates. The technique consists in forming on the surface of the specimen an array of concentric arc sources by passing the laser beam through a Fresnel lens. The spacing between the illuminated arcs produces a “forcing wavelength” for which only a few specific frequencies (those which satisfy the dispersion relation) can propagate in the sample. Dispersion curves can be obtained by measuring the frequency content of the received signals for a range of wavenumbers. The technique offers a relatively high signal-to-noise ratio because of the narrow-band nature of the method and because of the confocal geometry of the source distribution. Reasonably good agreement is obtained between theoretical and experimental dispersion curves especially for the lower modes, thus showing that the proposed technique may have some potential for some specific applications in laser ultrasonic nondestructive evaluation.

Experiments have been conducted to study the propagation of sound over a rigid surface with a step discontinuity. The Biot–Tolstoy–Medwin (BTM) model of a rigid wedge [J. Acoust. Soc. Am. 69, 1060–1064 (1981)] is used to predict the acoustic field directly in the time domain. Experiments carried out with a transient acoustic spark source confirm that: (1) in the region where there are no direct reflected waves, diffracted waves combine with diffracted/reflected waves to produce a smooth transition; (2) the acoustic field around the step discontinuity can be highly directional due to the interference of the direct, the reflected, the diffracted, and the diffracted/reflected waves; and (3) the acoustic field is essentially unchanged if the step discontinuity is replaced with a smooth step whose radius of curvature is less than the characteristic wavelength of the incident sound.

The forced vibrations of thin shells of finite length are analyzed from a structural wave viewpoint. The proposed theory is restricted to in‐vacuo vibrations and to radial harmonic excitation at a surface point on the shell. The theory is based on Donnell’s equations of motion for thin shells. The solution to the forced problem is obtained by solving a boundary value problem that involves a 16×16 system. The 16 equations that are necessary to solve the system are: 4 boundary conditions at each end of the shell, 7 continuity conditions at the excitation point, and 1 discontinuity condition at the excitation point. The method is based in part on Forsberg’s original paper [AIAA J. 2 (12), 2150–2156 (1964)] on the free vibrations of shells of finite length, and, in part, on a general technique for solving one‐dimensional forced vibration problems. The theory can be easily implemented on a microcomputer. Some sample axial mode shapes are calculated. To gain physical insight, all the waves that combine into the given mode shape are presented. The theory is also used to perform a wave‐vector analysis of the predicted vibration field on the shell surface to separate the contributions from flexural, shear, and longitudinal waves. It is found that a Prony decomposition algorithm in the axial direction of the shell is more useful than the standard fast Fourier transform because it yields a much finer resolution of the helical wave spectrum. The algorithm developed in this study does not include internal losses in the shell. It appears that, with no internal losses, the amplitude of the helical wave spectrum is very sensitive to the physical parameters of the shell, in particular to its thickness, when the excitation frequency is very close to a natural frequency of the shell.

Experiments on ultrasonic propagation in thick annular structures show that one can simplify the modal structure of the received signals by carefully controlling the wedge angles of the generation and detection transducers. This is important if one is to detect cracks along the path between source and receiver. In particular, one should excite and detect only those modes whose energy is concentrated where the cracks are expected to form. To do so, the following methodology is used: First, experimental signals are obtained for various source–receiver configurations with a standard pulser/receiver; a wavelet transform is then applied to the signals to localize precisely in time the arrival of a given mode packet at a given frequency and to determine the corresponding group velocity. These modes are then identified by comparing the results with predictions from theoretical dispersion curves. One can then predict the energy distribution within the structure by using the method of normal mode expansion for transients. [Work supported by the ONR, Code 332.]

Scale model experiments have been conducted to study the diffraction of sound by a curved surface of finite impedance. The theory of matched asymptotic expansions (MAE) offers an alternative to Berry and Daigle’s generalized creeping wave series. [J. Acoust. Soc. Am. 83, 2047–2058 (1988)] Experimental results are in excellent agreement (less than 1 dB) with predictions from the MAE theory both in the deep shadow zone and in the penumbra along the line of sight.

A differential laser Doppler velocimeter (LDV) has been assembled and tested to provide noninvasive absolute measurements of acoustic particle displacements of standing waves generated in a water‐filled tube. The principle of the technique [see K. J. Taylor, J. Acoust. Soc. Am. 59, 691–694 (1976)] is to measure the Doppler shift of laser light scattered from colloidal microparticles oscillating under the action of an acoustic field. The system tested is capable of detecting particle displacements of the order of a few nanometers with a bandwidth of several kilohertz. The performances and limitations of the system are discussed. In particular, the effect of Brownian motion is shown to produce only negligible broadening of the spectral density of the signal of interest. The sensitivity of the present LDV system is estimated to be very close to the shot noise limit of the photomultiplier tube used to detect the Doppler shift of the scattered light. Experimental results are obtained under controlled laboratory situations with calibrated microparticles of radii 10, 1, 0.1, and 0.01 μm in suspension in very pure (reverse osmosis) water.

The differential equation that governs the motion of microparticles in suspension in an insonified fluid is derived. Two forces are included in the model: the viscous drag force on the microparticle and the force imparted by the acoustic pressure gradient around the microparticle. This model is useful within the context of the laser detection of sound [see J. Acoust. Soc. Am. 90, 1275–1286 (1991)]. Standard models of particle motion in fluid mechanics with laser Doppler velocimetry usually do not consider the force imparted by the pressure gradient around the microparticle. It is shown that, at low frequencies, the viscous drag force dominates; but at high frequencies, the presure gradient term dominates. The transition frequency is given by 3aη/m, where a is the particle radius, η is the kinematic viscosity of the fluid, and m is the mass of the particle.

It appears that a slight modification of the definition of source–receiver distance in the creeping wave series of Berry and Daigle [J. Acoust. Soc. Am. 83, 2047–2058 (1988)] yields consistently better agreement with experimental data at several points in the shadow zone, for several frequencies, and for several impedance surfaces. It is also in better agreement with predictions from matched asymptotic expansions and the data of Berthelot and Zhou [J. Acoust. Soc. Am. 93, 605–608 (1993)]. © 1996 Acoustical Society of America.

In a laser Doppler vibrometry, the characterization of the measured surface plays an important role in both in‐plane and out‐of‐plane surface motion measurements. Experimental data is presented for the in‐plane optical probe configuration, where the vibrating surface is illuminated symmetrically by two laser beams. However, some of the conclusions of the present study apply also to out‐of‐plane vibration measurements. It is found that certain surfaces perform better than others. How the surface character affects the in‐plane surface motion measurement (in particular, the signal‐to‐noise ratio and the probe alignment) is studied. The surfaces studied are lathe‐finished, polished aluminum and steel surfaces and two types of retroreflecting tapes from 3M company. Also, the profiles of the metallic surfaces are obtained with a profilometer. A simple model is used to relate the surface characteristics to the performance of in‐plane motion measurement. The effect of polarization of the two laser beams is also studied, including the depolarization of the light by the surface. [Work supported by ONR.]

Scale model experiments have been conducted to study the propagation of sound over a curved surface partially covered with rigid random roughness elements in the high‐frequency diffraction/low‐frequency scattering regime. The effects of roughness are found by comparing the sound field with that obtained with a fully smooth curved surface. Experiments indicate that roughness in the shadow zone acts to tunnel more sound into the shadow zone of the partially rough surface, relative to the curved smooth surface, via a ‘‘creeping boundary wave.’’ This wave qualitatively follows the trends of both creeping waves due to diffraction and Tolstoy‐type ‘‘boundary waves’’ due to coherent scattering. However, roughness in the bright zone causes less sound to propagate into the shadow zone of the partially rough surface, relative to the curved smooth surface, because of incoherent scattering. [This work is supported by a Fannie and John Hertz Fellowship.] a)Current address: National Center for Physical Acoustics, University, MS 38677.

Scale model experiments have been conducted to study the propagation of sound over a curved rough surface with curvature much greater than the wavelength and roughness smaller than the wavelength. The MAE model [J. Acoust. Soc. Am. 92, 605–608 (1993)] is used to determine the sound field in the vicinity of the curved surface. The Tolstoy–Medwin roughness model [J. Acoust. Soc. Am. 79, 657–665 (1986)] is used to model the rough surface. The two models are combined to qualitatively describe the sound field. Experiments indicate that: (1) just above the surface, the roughness causes a boundary wave that is generated by the direct waves in the bright zone and by the creeping waves in the shadow zone; (2) there are two frequency regimes with the transition determined by the curvature and the roughness; (3) along the surface, more sound (compared with diffraction by the curved smooth surface) is tunneled into the shadow zone at low frequencies and less sound is tunneled at higher frequencies. Along the line of sight, the trend is similar but more complicated. [This work is supported by a Fannie and John Hertz Fellowship.]

Experiments have been conducted on the thermoelastic generation of Lamb waves in plates by a Q‐switched ruby laser. Detection was performed both by interferometric laser probe and a miniature piezoelectric pinducer. The long‐term objective of this work is to determine various characteristics of the plate such as material properties, plate thickness, flaws, and inhomogeneities, or even bonding between plates by comparing experimentally determined points with the theoretical dispersion curves. The technique consists in forming on the surface of the specimen an array of confocal arc sources by passing the laser beam through a Fresnel lens. The array spacing produces a ‘‘forcing wavelength’’ for which only a few specific frequencies can propagate. Dispersion curves can be obtained by measuring the frequency content of the received signals for a range of wave numbers. Because of the narrow‐band nature of the technique, and because of the confocal geometry of the source distribution, this technique offers a relatively high signal‐to‐noise ratio. Good agreement is obtained between theoretical and experimental dispersion curves especially for the lower modes, thus showing that the proposed technique has potential for the above‐mentioned applications. [Work supported by the National Science Foundation.]

A differential laser Doppler velocimeter (LDV) [Lee et al., Proceedings of the 3rd International Congress on Intensity Techniques, Senlis, France, pp. 181–188 (1990)] has been used to measure in‐plane motion associated with waves propagating on a thin cylindrical shell excited radially at a single frequency by a shaker. The endcaps of the shell approximate the case of a simply supported shell with axial constraints at both ends. The fiber optic technology used in the LDV system allows the optical probe head, located at a distance of about 30 cm from the shell, to be scanned over the entire surface of the shell. Data were recorded along an array of 32 points circumferentially and 16 points axially, enough to sample spatially both extensional (fast waves, low wave numbers) and flexural (slow waves, high wave numbers) waves. The data were analyzed with both a two‐dimensional spatial FFT algorithm and a Prony algorithm. The analysis clearly reveals both type of waves separately. Theoretical predictions are obtained from the analysis of a point‐driven infinite shell and from Forsberg's original paper [AIAA J. 2 (12), 2150 (1964)]. Both theoretical and experimental results clearly show the presence of shear waves propagating on the structure. [Work supported by ONR.]

An interferometric system consisting of five independent probes cabable of measuring in‐plane or out‐of‐plane surface motion of a vibrating sample at five different points simultaneously has been designed, constructed, and tested. A description of the design, measurement capabilities, and performance specifications will be given. The system utilizes optical fibers and compact probe design (30mm×15mm×9mm) to enable close spacing measurement points. Signal demodulation is performed by phase‐locked loops allowing real‐time measurements. The system is designed to test voided polymer samples excited by a shaker in the 100 Hz to 5 kHz range. It is calibrated for steady state and transient excitation of the sample. Results include measurements of the damping constant of the sample in the time domain for various frequencies of excitation. [Work supported by the Office of Naval Research, Code 334.]

At present, the paper industry lacks an on‐line, noncontact quality control system. Several studies indicate that there are strong correlations between paper strength and elastic stiffness properties. These elastic properties or elastic coefficients can be determined by measuring the velocities of propagation of various ultrasonic waves. Lamb waves, for instance, propagate in paper and appear to be sensitive to paper strength. Experiments have been conducted with a laser‐based system to both generate and detect ultrasonic Lamb waves in copy paper. Results obtained regarding the relationship between the generation laser spot size, power density, and ultrasonic signal strength are presented. Paper damage is assessed at the generation spot. Phase velocity dispersion curves are produced for those modes that have sufficient signal‐to‐noise ratio. These dispersion curves are then compared to those predicted by ortotropic plate theory. [Work supported by OIP‐GT.]

Laser interferometry offers the possibility of measuring in real time instantaneous surface velocities in the μm/s range by noninvasive measurements. It can also be used to measure the three components of the surface vector velocity at several points simultaneously and, therefore, it is a promising way of measuring structural intensity and power flow in arbitrarily complex structures under laboratory conditions. Three different laser interferometric probes are currently being used at Georgia Tech for research in structural acoustics. The advantages and disadvantages of each system will be discussed within the context of structural intensity measurements. [Work supported by the Office of Naval Research, Code 332 SM.]

The thermoelastic generation of surface waves by a Q‐switched ruby laser is investigated both experimentally and analytically. The motivation is to improve the amplitude and to control the frequency content of the ultrasonic signal by taking advantage of the tremendous flexibility that one has in controlling the size and the shape of the thermoelastic source. Waveforms have been recorded for several source geometries at the surface of an aluminum block: spot source, line source, periodic array of spot sources, and periodic array of line sources. Also, focusing effects have been measured with a periodic array of curved line sources obtained with a Fresnel lens. In all cases, the waveforms are reasonably well predicted by a simple and efficient convolution technique. Waveforms have also been generated in a 1‐mm‐thick aluminum plate and recorded over a distance of 50 mm at increments of 0.5 mm. Processing of these waveforms in the frequency–wave‐number domain allows for the extraction of the dispersion curve and the various modes propagating in the plate. [Work supported by NSF.]

A laser Doppler vibrometer has been designed, built, and tested for specific applications to structural acoustics. It is capable of measuring small in‐plane displacements associated with the propagation of fast waves (shear or longitudinal) on the surface of a structure. The probe head is compact, rugged, and can operate underwater. The system has been automated so that extensive data can be collected over the structure and analyzed in the K‐space as is done in acoustical holography. The motion of the probe head is controlled by two stepping motors. The first one controls the focusing action (laser spot size on the structure) and the second one controls the position of the whole probe over the structure. The laser Doppler signal measured by the probe head is detected by a photodiode, demodulated by a phase‐lock loop, digitized, and sent to a computer that acquires the data and controls the stepping motors. Automated focusing action is achieved by an iterative process. Automated scanning over a given structure is also achieved digitally by computer control of the second stepping motor. Results obtained with the system collecting data over a vibrating surface will be presented. [Work supported by ONR.]

Experiments are being conducted to measure directly by laser Doppler interferometry the in‐plane and out‐of‐plane components of the surface motion of a vibrating shell simultaneously at several surface points. The proposed design requires three Bragg cells to generate three coherent optical beams with different carrier frequencies. Three 1×4 fiber optic connectors are used to transmit each beam to four surface points. At each point, both the out‐of‐plane component and one of the in‐plane components of the displacement vector are measured. The light scattered by the vibrating surface is Doppler shifted and collected into a large core multimode fiber situated close to the surface and terminated by a photodiode. The signals are acquired and digitized for direct phase demodulation on a computer by means of Hilbert transforms. [Work supported by ONR.]

The thermalization of water, due to the absorption of laser radiation, offers a way to generate underwater sound from an airborne platform. However, the thermal expansion mechanism that produces sound is notoriously inefficient and the standard technique of amplitude modulation (AM) of the laser intensity is generally inadequate for practical applications such as bathymetry. With the advent of ultra‐high repetition rate pulsed lasers, it is now appropriate to take a fresh look at some alternative schemes for modulating the laser intensity. Computer simulations will be shown for three different modulation techniques in comparison with the standard AM technique. These modulation schemes are, respectively, frequency modulation (FM), pulse density modulation, and pulse amplitude modulation. In each case, the parameters controlling the far‐field acoustic pressure amplitude will be identified in an attempt to optimize the system. [Work supported by NSF.]