F. Bastien

Lamb wave and plate mode in ZnO/silicon and AlN/silicon membrane: Application to sensors able to operate in contact with liquid

Abstract Lamb waves, especially the A 0 mode, can be used to build sensors able to operate in contact with liquid. Nevertheless, some difficulties remain for practical devices. First, we discuss the relevance of the electromechanical coefficient. We present the element of choice of the device characteristics and the piezoelectric material. We compare two kinds of devices, the first is a classical delay line device and the second a resonant device. The behavior of these devices has been controlled using optical visualization of vibration modes. Furthermore, the performance of the devices is experimentally tested and advantages of the resonant device are shown.

A large scale X-Y positioning and localisation system of liquid droplet using SAW on LiNbO/sub 3/

Recently published works have demonstrated the interest of surface acoustic waves (SAW) for guiding and positioning small liquid droplet atop a flat surface. The application fields of such device mainly concern biochemical tools for well-controlled interaction of given bodies and small volume experimentation. In the proposed paper, the fabrication of a SAW-based X-Y stage on LiNbO/sub 3/ for positioning small liquid droplet is described. An actuation strategy to accurately control the motion and detect the position of the droplet have been developed.

Detection and High-Precision Positioning of Liquid Droplets Using SAW Systems

The capability to accurately handle liquids in small volumes is a key point for the development of lab-on-chip devices. In this paper, we investigate an application of surface acoustic waves (SAW) for positioning micro-droplets. A SAW device based on a 2 times 2 matrix of inter-digital transducers (IDTs) has been fabricated on a (YXl)/128deg LiNbO3 substrate, which implies displacement and detection in two dimensions of droplets atop a flat surface. Each IDT operates at a given frequency, allowing for an easy addressing of the active channel. Furthermore, very low cross-talk effects were observed as no frequency mixing arose in our device. Continuous as well as pulsed excitations of the IDTs have been studied, yielding, respectively, continuous and step-by-step droplet displacement modes. In addition, we also have used these two excitation types to control the velocity and the position of the droplets. We also have developed a theoretical analysis of the detection mode, which has been validated by experimental assessment.

Displacement of droplets and deformation of thin liquid layers using flexural vibrations of structures. Influence of acoustic radiation pressure.

In this paper observations concerning some effects of vibrating structures on fluids are presented, followed by a tentative theoretical analysis. First, a brief description of a caterpillar-like structure is made. This structure is almost equivalent to an infinite beam which allows the choice of positions of the nodal lines of a vibrating mode. Displacement of liquid droplets using switching between two modes of this structure is then presented. This phenomenon is supposed to be induced by acoustic radiation pressure. Possible extensions of this principle are then discussed. After this, results are reported concerning deformations of thin liquid layers.

Investigations on excitation and detection methods for Lamb wave sensors

Due to a high potential sensitivity, Lamb wave acoustic sensors have been studied for biochemical applications. Usually, Lamb waves are generated and detected using piezoelectric transducers. This technology involves bilayers structures and causes some problem of induced strain and temperature compensation. In this paper, we have investigated optical and electrostatic excitation methods. The optical excitation of Lamb waves is studied, and the main limitations of such an excitation method are pointed out. Theoretical as well as experimental studies are reported on electrostatic excitation of Lamb waves, and it is shown that this technique can be suitable for biosensors.

On the generation and identification of traveling waves in non-circular structures - application to innovative piezoelectric motors

We have been developing new concepts of linear and circular ultrasonic actuators using traveling waves in rectangular or square structures, which are adapted to batch micro-machining of silicon. The first prototypes we built were all clamped and used a simple combination of modes allowing movement transmission through one contact point. Yet, in order to increase the efficiency of our motors, we consider using new combinations of modes with higher ranks (and then more contact points) and also other boundary conditions. As it is not easy to predict if an accurate quasi-traveling wave can be generated in a given structure and with a given contribution of modes, we have developed a simulation program using MAPLE software. This program uses successive criteria to select the zones where the traveling wave can be found, according to computer parameters. In this paper, we present the different steps used to check the possibility of realizing an actuator with a given configuration in any type of structure. We illustrate this with simple theoretical examples using several structures with different boundary conditions and finally we give some experimental results obtained with a circular motor using a more complex combination of modes.

Linear motor using a quasi-travelling wave in a rectangular plate

Abstract Usually, ultrasonic motors generate a rotating movement, particularly motors using a travelling wave. Due to axial symmetry, production of this type of wave in a circular shape is easier than in others shapes. In this paper, we show that it is possible to generate a linear movement using a quasi-travelling wave in a rectangular plate. If the dimensions of the plate are well adjusted, the combination of two resonant modes, for example 2-1 and 1–3 modes, which have the same frequency, will, with suitable excitation, produce a quasi-travelling wave. A linear motor using a rectangular plate has been made to demonstrate the principle. This type of actuator will of course present the same advantages as in the usual travelling wave ultrasonic motors. In addition, the use of rectangular shapes is suitable for miniaturisation, for example, in the case of chemically etched silicon membranes.

An electrostatically actuated valve for turbulent boundary layer control

A large displacement electrostatic valve has been designed and realized for a realistic turbulent boundary layer control. This actuator consists of a pair of rigid electrodes and a flexible film having a S-shape providing local high electrostatic forces required for controling rather large pressure differences. The aim is the reattachment of the boundary layer near an aircraft flap trailing edge by transferring momentum energy via high speed pulsated micro air jets. The valve controls the frequency and the speed of the micro jets. An array of fifteen actuators has been manufactured and characterized by particles images velocimetry (PIV) and hot wire anemometry (HWA). The devices are able to control pressure differences up to 27 kPa with a supply voltage of 400 V. For this maximum pressure, the corresponding jet velocity downstream a 45 degree skew micro orifice (0.4 mm diameter) is close to 100 ms-1

Low temperature limitation on the quality factor of quartz resonators

The quality factor (Q) for different resonators driven at several overtones has been determined between 1.5 and 300 K. These measurements give an improved interpretation of the Q-factor limitation. A significant consequence is a better understanding of the relationship between Q and random frequency fluctuations. The curves of 1/Q=F(T) show the usual features between 20 and 300 K. These include the sodium ion peak at 55 K as well as a peak at 20 K. However, the region of principal interest lies between 1.5 and 20 K. At very low temperatures, a plateau is always observed. If for a given resonator, the 1/Q value of this plateau is subtracted from the experimental values, the residual 1/Q is almost a linear function of T/sup 4/. This variation obeys the Landau-Rumer theory of acoustic wave absorption caused by phonon-phonon interaction in the crystal. Thus the authors conclude that between 6 and 20 K the main limitation in Q is due to the crystal itself, but the plateau is not caused by intrinsic crystal properties. Data for different overtones enable the elimination, at least for the seventh overtone, of damping effects of the crystal supports. Measurements have also been carried out on crystals with crystal surfaces with different roughness characteristics. These roughness characteristics have been measured using optical interferometry. With a well polished, good crystal the authors measured, for the seventh overtone at 3 K a loaded Q of 25 million corresponding to an unloaded Q of 33 million. Better control of surface roughness and crystal quality could lead to a Q of about 100 million in the liquid helium region. This value would be for an 11 MHz, seventh overtone crystal having an diameter of 15 mm.<<ETX>>

Temperature compensation of lamb wave sensor by combined antisymmetric mode and symmetric mode

Both thermal sensitivity and mass sensitivity in liquid of the first antisymmetric (A0) mode and the first symmetric (S0) mode of Lamb wave biosensor were investigated. A0 and S0 modes are sensitive to the mass change on the surface of the sensor but A0 mode is also sensitive to the liquid in the region of evanescent wave associated with Lamb wave. By combining A0 mode and S0 mode, the measurement error due to the environmental temperature drift decreased by a large factor, therefore, the environmental temperature was efficiently compensated without changing the structure of Lamb wave sensor.