This paper describes a novel phenomenon "liquid needle" produced by the self-focusing acoustic transducer (SFAT). The SFAT is composed of a metal/piezo-material/metal plate (with and without a support layer) which has one side air backed while the other side is liquid backed. The SFAT generates and focuses acoustic waves (through wave interference) at the top surface of the liquid (with acoustic intensity up to 15W/cm2). The focused acoustic beam deforms the free liquid surface through the acoustic streaming effect, and produces a needle-shaped liquid column on the free liquid surface. With various SFATs and different types of liquids, we have obtained liquid needles that are 400-12 000 mum tall. The liquid needle diameter at its tip varies from less than 15 mum to more than 200 mum

http://ieeexplore.ieee.org/iel5/84/4147571/04147609.pdf

Liquid Needle

The Lamb wave and V-groove lenses are distinguished by their high surface wave excitation efficiencies. However, due to the fixed incidence angle, a particular lens can only be used for materials having surface wave velocities within a limited range. Hence, it is desirable to have lenses with adjustable incidence angle. Lamb wave and V-groove lenses constructed as Fresnel lenses are presented. We also discuss the feasibility of Fresnel lenses with air as the coupling medium. It is shown that it is possible to build air coupled Fresnel lenses with a reasonable conversion efficiency into subsurface waves.

/pdf/fresnel-lamb-wave-and-v-groove-lenses-with-tunable-mode-mvzdybbaia.pdf

Fresnel Lamb wave and V-groove lenses with tunable mode selectivity

Acoustic microscopes and acoustic tweezers have great value in the application of microparticle manipulation, biomedical research and non-destructive testing. Ultrahigh frequency (UHF) ultrasonic transducers act as the key component in acoustic microscopes, and acoustic tweezers and acoustic lenses are essential parts of UHF ultrasonic transducers. Therefore, the preparation of acoustic lenses is crucial. Silicon is a suitable material for preparing acoustic lenses because of its high acoustic velocity, low acoustic attenuation and excellent machinability. In previous research, silicon lenses were mainly prepared by etching. However, etching has some drawbacks. The etching of large sizes is complex, time-consuming and expensive. Furthermore, vertical etching is preferred to spherical etching. Thus, a new method of ultra-precision machining was introduced to prepare silicon lenses. In this paper, silicon lenses with an aperture of 892 μm and a depth of 252 μm were prepared. Then, UHF ultrasonic transducers with a center frequency of 157 MHz and a −6-dB bandwidth of 52% were successfully prepared based on silicon lenses. The focal distance of the transducers was 736 μm and the F-number was about 0.82. The transducers had a lateral resolution of 11 μm and could distinguish the 13 μm slots on silicon wafers clearly.

/pdf/ultrahigh-frequency-ultrasonic-transducers-150mhz-based-on-1qbn0vcv.pdf

Ultrahigh Frequency Ultrasonic Transducers (150MHz) Based on Silicon Lenses

In this paper a new lens design is proposed for the characterization of layered materials. A Lamb wave lens employs Lamb waves for this purpose since these waves propagate along interfaces. However, below a cut-off angle, the critical angles of Lamb wave modes are low and the generated V(z) curves have a small number of oscillations, which in turn causes measurement difficulties and accuracy degradation. The bi-angular lens described in this paper, generates an extraobliquely incident wave, instead of a normally incident beam, in order to provide the reference specular reflection. Simulation results as well as experimental results are presented and it is shown that a high sensitivity can be obtained by using this new lens

/pdf/bi-angular-lens-for-material-characterization-1tmlvp7i8t.pdf

Bi-angular lens for material characterization

A new directional acoustic lens is introduced. The geometry is very similar to the line-focus lens except the lens cavity, which is shaped as a groove with flat-bottom V cross section. The slanted planar edges of the groove are inclined in order to generate waves incident on the object surface at a critical angle. Hence, the edges of the groove act like two wedge transducers facing each other. The cross section of the lens is the same as that of the Lamb Wave Lens. Therefore, it enjoys the same sensitivity to surface wave excitations. On the other hand, since the cross section remains the same along one of the lateral directions, it has directional properties very similar to that of the Line Focus Beam Lens. The waves normally incident on the object surface generated from the flat-bottom interfere with those at the critical angle, giving rise to a V(Z) effect. Calculated responses of the lens are presented for silicon (001) surface as a function of crystal orientation. The calculated curves are compared with measurement results. The leaky wave velocities are extracted from the measurement results using the conventional FFT algorithm. A new model based algorithm is proposed for extracting the velocity information from V(Z) data

/pdf/a-new-directional-acoustic-lens-v-groove-lens-44h95o9veg.pdf

G.G. Yarahoglu

Papers

A new directional acoustic lens: V-groove lens

Fresnel Lamb wave and V-groove lenses with tunable mode selectivity