Abstract
In ultrasound tissue harmonic imaging (THI), it is preferred that the bandwidth of the array transducer covers at least the fundamental frequency f0 for transmission and the second harmonic frequency 2f0 for reception. However, it is challenging to develop an array transducer with a broad bandwidth due to the single resonance characteristics of piezoelectric materials. In this study, we present an improved interleaved array transducer suitable for THI and a dedicated transducer fabrication scheme. The proposed array transducer has a novel structure in which conventional elements exhibiting f0 resonant frequency and polarization-inverted elements exhibiting 2f0 resonant frequency are alternately located, and the thicknesses of all piezoelectric elements are identical. The performance of the proposed method was demonstrated by finite element analysis (FEA) simulations and experiments using a fabricated prototype array transducer. Using the proposed technique, f0 and 2f0 frequency ultrasounds can be efficiently transmitted and received, respectively, resulting in a 90% broad bandwidth feature of the transducer. Thus, the proposed technique can be one of the potential ways to implement high resolution THI.
Highlights
Tissue harmonic imaging (THI) based on nonlinear phenomenon has begun to be widely used in echocardiography because it can provide a high resolution, improved signal-to-noise ratio (SNR), and reduced near-field artifacts [1,2,3,4,5,6,7,8,9]
We propose a novel interleaved array transducer for tissue harmonic imaging (THI) that is capable of overcoming the aforementioned issue
It was verified that the conventional elements can transmit f0 ultrasounds and the polarization inversion technique (PIT) elements can receive reflected 2f0 ultrasounds even though the total thicknesses of the two types of elements were identical
Summary
Tissue harmonic imaging (THI) based on nonlinear phenomenon has begun to be widely used in echocardiography because it can provide a high resolution, improved signal-to-noise ratio (SNR), and reduced near-field artifacts [1,2,3,4,5,6,7,8,9]. With higher frequencies of harmonic signals compared to the fundamental frequency, THI can improve axial resolution. THI transducer uses a narrower bandwidth to filter out frequencies from the fundamental beam, so the axial resolution can be reduced. A composite structure or optimized passive layers can contribute to broadening a bandwidth [13,14,15,16]. Those methods have a limit to increase a bandwidth more than a certain level due to the single resonance feature of the piezoelectric material within the frequency range of interest, which is called an odd-order thickness-extensional vibration [17,18].
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