The anisotropy of the basic characteristics of Lamb waves in a (001)-Bi<Subscript>12</Subscript>SiO<Subscript>20</Subscript> piezoelectric crystal

The orientation dependences of the phase velocity, the effective electromechanical coupling coefficient, and the angle between the wave normal and the energy flux vector are numerically calculated for zeroand first-order Lamb waves propagating in the (001) basal plane of a Bi₁₂SiO₂₀ cubic piezoelectric crystal. It is shown that the anisotropies of these modes are different and depend on the plate thickness h and the wavelength λ. For h/λ < 1, the mode anisotropy can exceed the anisotropy of the corresponding characteristics of surface acoustic waves propagating in the same plane; for h/λ > 1, it approximately coincides with the SAW anisotropy for all the characteristics.     

Application of an acoustoelectronic technique to study ordered microstructured disperse systems with biological objects in a hydrogel

Using acoustoelectronic sensors not containing sensitive coatings, we studied a series of microbiological preparations: yeast cells and bacteria, as well as virus particles, immobilized in hydrogels of different concentration. The obtained measurement data on the acoustic characteristics make it possible to (1) reveal the presence of biological objects in both fluid media and agarose-based hydrogels of various concentration; (2) establish the physical mechanism that results in acoustoelectronic detection; (3) evaluate changes in the concentration of biological objects and their electric conductivity. The data confirm the possibility of applying the acoustoelectronic technique to detect microbiological objects and observe their growth in hydrogel media. We discus the limitations and drawbacks of the acoustoelectronic technique.     

A new type of acoustic modes of vibration of thin piezoelectric plates: Quasi-longitudinal normal modes

Using ST-cut quartz crystal plates as an example, a new type of normal modes of acoustic vibrations is described. The modes propagate along the x axis with a velocity close or equal to that of longitudinal bulk waves propagating in the same direction and have a longitudinal component of elastic displacement no less than two orders of magnitude greater than the two other components (the shear-horizontal and shear-vertical ones) throughout the whole plate thickness. The domain of existence of the quasi-longitudinal modes consists of a set of limited zones that contain the “allowed” values of the plate thickness H/λ (H is the plate thickness and λ is the wavelength) and are separated by “forbidden” zones corresponding to common Lamb modes. The closeness (or coincidence) of the velocities of a quasi-longitudinal mode in the plate and a longitudinal bulk wave in an unbounded crystal is a necessary but not sufficient condition for the existence of the aforementioned type of modes in ST,x quartz.     

Sensing properties of normal oscillatory modes of quartz plates

Acoustical Physics - The responses (relative velocity variations Δv/v of normal (symmetric or asymmetric) Lamb and shear-horizontal modes of ST-cut quartz plates, whose thickness is comparable...     

Integral array of acoustic sensors for micro-liter liquid discrimination

It is shown experimentally that the sensing properties of normal acoustic waves propagating in a piezoelectric plate are sensitive to the mass load and the viscosity and electric conductivity of a liquid deposited on the plate. The sensing properties depend on (a) the direction of propagation, (b) the mode number for each direction, and (c) the plate thickness normalized to the acoustic wavelength for each mode and each direction. Based on these properties, a prototype of an acoustic liquid sensor array with different patterns of selectivity is developed and tested. The sensors are located on a single plane of a piezoelectric plate and do not use any sorbent film for sensing. The array is capable of identifying types and sorts of liquids according to their physical effects on the absorption of normal waves with different numbers. The total number of acoustic responses is presented in the form of histograms that are acoustic images of the analyzed substances’ flavors. Having no sorbent film improves the reliability and long-term consistency of sensing.     

Temperature properties of plate modes in quartz

The shear horizontal modes that occur in a quartz plate are studied both theoretically and experimentally. These modes are shown to possess a wide variety of temperature properties, including the characteristic behavior of the temperature coefficient of delay, which can take on negative, zero and record-breaking high positive values up to 350×10^?6/°C. The dependence of this coefficient on the mode number is explained by the varying partial contributions of three elastic moduli, c ₁₂, c ₁₄, and c ₄₄, to this coefficient.     

Hydrogen detection with surface acoustic transverse waves

Summary A new hydrogen sensor is here presented, based on the use of horizontally polarized surface transverse waves (STW). The use of these waves for application to chemical sensors seems attractive because of the possibility of controlling their penetration depth into the substrate and thus increasing the sensitivity of the device. Preliminary experiments, performed on a ST-cut quartz substrate, have shown how the response of the device strongly increases with the STW energy trapping in the sensitive Pd film.     

Acoustic Wave Propagation Along Piezoelectric Plate Coated with Piezoelectric Films

Acoustical Physics - A novel solid state structure consisting of piezoelectric plate sandwiched between two piezoelectric films is suggested as propagation medium for acoustic waves. Considering,...     

Thermoconductometric detection of gases and gas flows by means of SAW delay lines

Surface acoustic wave (SAW) delay lines without gas-sensitive coatings are used as thermal sensors for the thermoconductometric detection of gases and gas flows. The forced convection of 13 gases is analyzed in the linear approximation without regard for their interaction with the environment. Quartz, LiNbO₃, Bi₁₂GeO₂₀, and Bi₁₂SiO₂₀ delay lines are used to detect H₂, He, Ar, CH₄, NH₃, N₂, and O₂ at frequencies f=21–263 MHz and temperatures T=25–165 °C. The SAW “response” is measured as a function of the gas concentration n, the flow rate U, the temperature coefficient of the SAW velocity (TCV), and the working temperature T _p . The feasibility of controlling the level of the gas “response” and imparting selectivity to the choice of TCV and T _p is demonstrated. The threshold gas concentrations are 0.35% for CH₄ and 0.1% for H₂ and NH₃ in nitrogen. A linear response is obtained in the interval U=20–200 ml/min. Zh. Tekh. Fiz. 67, 119–123 (May 1997)     

New type of an acoustic plate mode: quasi-longitudinal normal wave

A new type of an acoustic wave belonging to the family of the normal plate modes is discovered numerically and verified experimentally in ST, x-quartz plates with free surfaces. It exists within restricted bands of the normalized plate thickness H/λ, where H is the thickness, λ is the wavelength, separated by forbidden H/λ-bands attributed to the common plate modes. Polarization of the wave over the whole plate thickness is almost longitudinal. Velocity of the wave is close to or equal to the velocity of the longitudinal bulk wave, propagating in the same direction. The proximity or/and equality of the velocities is a necessary, but not sufficient condition of the existence of the new wave.