Dispersion characteristics of complex electromechanical parameters of porous piezoceramics

In this paper, the results of experimental study of dispersion characteristics of complex electromechanical parameters of ferroelectrically “hard” porous piezoceramics based on PZT composition were presented. Experimental samples of porous piezoceramics were fabricated using a modified method of burning-out a pore former. The complex constants of porous piezoceramics with relative porosity 16% and their frequency dependences were measured using the piezoelectric resonance analysis method. As a result of experimental studies, regions of elastic, piezoelectric and electromechanical dispersion, characterized by anomalies in the frequency dependences of the imaginary and real parts of the complex constants of porous piezoelectric ceramics were found. It was revealed also that the microstructural features of porous piezoceramics determine the character of frequency dependences of complex electromechanical parameters of porous piezoelectric ceramics. In conclusion, the microstructural and physical mechanisms of electromechanical losses and dispersion in porous piezoceramics were discussed.

Measurement of the absorption coefficient of a periodically poled LiNbO3 crystal at a radiation wavelength of 3 μm

Problem formulating. In the case of nonlinear-optical conversion of high-power laser radiation in nonlinear-optical crystals the optical absorption leads to a nonuniform heating of the crystals, which results in the violation of phase matching conditions, the formation of defects, and optical damage. Goal. Measurements of optical absorption coefficient of the periodically poled lithium niobate (PPLN) crystal at 3 μm radiation wavelength using the piezoelectric resonance laser calorimetry (PRLC). Result. The optical absorption coefficient of PPLN crystal at 3.045 μm radiation wavelength was measured using the piezoelectric resonance laser calorimetry. The value (1.15±0.15) 10⋅ -2cm-1 of absorption coefficient within the measurement error limits was independent of the initial temperature of PPLN and the incident radiation power in the ranges 293–343 K and 0.2–10 W respectively. Practical meaning. The interaction of mid-IR laser radiation with PPLN crystal was studied using the piezoelectric resonance laser calorimetry.

Ultrasonic Transceiver with a Regular/Periodic 1-3 Piezocomposite Based on the SAW Resonance Mode on Damping Backing

A novel effective vibrational mode was discovered in the conventional transducer with an array of orthogonal (square) regular piezoelectric rods in 1-3 piezocomposite, containing the damping backing and front matching layers. The operational resonance in the structure was determined as the Surface Acoustic Wave (SAW) on the backing boundary excited by the adjacent piezo-rods, with its frequency typically near 3 times lower the fundamental half-lambda conventional piezocomposite resonance. Pulse-echo sensitivity and transmitting sound pressure level (SPL) in air showed that the signal strength is roughly comparable to the industrial similar air transducers at the frequency range 100–700 kHz, where at these frequencies the lateral and longitudinal piezoelement dimensions in the conventional transducer design are typically close to each other causing interference with unwanted coupling modes. As was determined theoretically and proved in experiments, the backing SAW resonance effect in the transducer performance is inherent just to the regular periodic 1-3 piezocomposite structure and does occur neither with randomly located/oriented piezo-rods nor in the homogeneous piezo-plate at least with the same lateral cross-section as the connected to it backing. The purpose of the article is to investigate a newly discovered operational vibrational mode of a SAW type in 1-3 regular piezocomposite, other than piezoelectric resonance. The investigated phenomena can improve the transceiver sensitivity and bandwidth, providing lower drive voltage and smaller and lighter weight ultrasonic transducers. Based on the piezocomposites with thickness’ 1–1.5 mm (rod resonance near 2–3 MHz), pillar width 0.2–0.8 mm, kerf width 0.1–0.4 mm, the transceivers with an operating frequency from 140 kHz to 650 kHz were designed and fabricated with a conventional backing of a mixture of high-density tungsten powder and epoxy and a matching layer of a mixture of low-density glass bubbles and epoxy. Experimental evaluation of their acoustical performance showed expected characteristics suitable for practical applications.

Исследование нелинейных процессов в сегнетоэлектрической керамике в слабых электрических полях

The paper proposes a new method for studying nonlinear processes in ferroelectric ceramics under external influences, based on the measurement and analysis of piezoelectric resonance spectra. The method provides high accuracy in determining complex elastic, dielectric and piezoelectric constants of piezoelectric materials, as well as their changes under external influences. To study nonlinear processes, we measured the dependences of complex electromechanical parameters of ferroelectrically «soft» piezoceramics based on PZT system on dc electric field. A physical interpretation of the results is proposed.