New type of matching layer for air-coupled ultrasonic transducers

In this paper, Berenger’s Perfectly Matching Layer (PML) and Bettess’ Infinite Element (IE) scheme are combined to create a new type of element for unbounded acoustic wave problems. An assessment of this new element formulation is made through its use in the calculation of the acoustic modal response of a spherical radiator in the frequency domain. The performance of the PML+IE approach is contrasted with the IE only methodology by comparing them to the exact solution of this test problem in terms of the surface inertia and resistance in the near field. The results are encouraging and the PML+IE approach shows a marked improvement in performance, particularly at lower frequencies.

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

Acoustics ◽

10.3390/acoustics2010008 ◽

2020 ◽

Vol 2 (1) ◽

pp. 110-127

Author(s):

Alex Mezheritsky

Keyword(s):

Sound Pressure ◽

Vibrational Mode ◽

Tungsten Powder ◽

Resonance Effect ◽

Ultrasonic Transducers ◽

Practical Applications ◽

Piezoelectric Resonance ◽

Matching Layer ◽

Transducer Design ◽

Pulse Echo

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.

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