Orientation dependences of the phase velocity vn, coupling coefficient Kn2, and power flow angle Ψn for zero-order and high-order acoustic modes are calculated numerically in ST-quartz and 128°Y-LiNbO3 plates with normalized thickness h/λ = 0.1, 0.25, 0.5, 1.0, 1.25, 1.5, and 1.67 (n is the mode order, θ is the angle between propagation direction and the x-axis, h is the thickness, and λ is the wavelength). Results of the calculations are experimentally verified using 128°Y-LiNbO3 plates with h/λ = 1.0, 1.67 and θ = 0°, 30°, 60°, 90° as examples.

Anisotropy of the acoustic plate modes in ST-Quartz and 128°Y-LiNbo 3

Plate acoustic wave sensor for detection of small amounts of bacterial cells in micro-litre liquid samples

Acoustic Plate Mode sensing in liquids based on free and electrically shorted plate surfaces.

The article studies the spectrum of acoustic oscillations generated by interdigital transducers in a plate made from a LiNbO3 piezocrystal with a thickness on the order of the acoustic wavelength. It is shown that, along with zeroth and higher-order modes, this spectrum also contains odd harmonics of the same modes. Unlike surface waves without dispersion, the harmonic frequencies of normal waves are not exact multiples of their fundamental frequency due to velocity dispersion, and the harmonic amplitudes can differ from the wave amplitudes at fundamental frequencies due to the dispersion of the electromechanical coupling coefficient. The temperature sensitivities of modes and harmonics differ from each other and vary with the fluid loading of the surface.

Features of Normal Higher-Order Acoustic Wave Generation in Thin Piezoelectric Plates

The results from experimental studies of the sensor properties of acoustic modes in LiNbO3 plates with thicknesses h/λ from 0.7 to 5 (where h is thickness and λ is wavelength) are discussed. It is shown that the mode responses are not always equal when liquid is applied to the upper and lower surfaces of a plate. When h/λ ≤ 1, the higher harmonics of lower order modes n are localized near the surface by transducers and interfere with the fundamental harmonics of higher order modes, violating the response symmetry. When h/λ ≥ 1, no such interference is observed, since the higher order modes are localized in the central part of the plate while the lower order modes are localized near the surface with transducer, again violating the response symmetry. The development of sensors for gases and liquids based on higher order modes thus becomes possible only with thin plates at frequencies that exclude interference.

Aspects of using acoustic plate modes of higher orders for acoustoelectronic sensors

Properties of shear horizontal acoustic plate modes (SHAPMs) in BT-cut quartz were calculated and measured. A delay line with a long interdigital transducer, deposited on -50.5°YX90°-oriented quartz plate, was used for the measurements. For one of the SHAPMs, at a frequency of about 100.4 MHz, insertion loss, turnover temperature, and quadratic temperature coefficient of frequency of about 10 dB, 15°C, and -30 ppb/(°C)2 in air, respectively, were obtained. Using water and glycerin solutions, insertion loss changes against dynamic viscosity were measured for this mode. In a viscosity range from about 1 mPa·s to 1000 mPa·s, an insertion loss change of about 14 dB was obtained.

M. Lysakowska

Papers

Properties of shear horizontal acoustic plate modes in BT-Cut quartz