Multiple-frequency ultrasonic imaging by transmitting pulsed waves of two frequencies

An Enhanced Multi-Frequency Distorted Born Iterative Method for Ultrasound Tomography Based on Fundamental Tone and Overtones

Conventional Distorted Born Iterative Method (DBIM) using single frequency has low resolution and is prone to creating images with high-contrast subjects. We propose a productive frequency combination method to better result in tomographic ultrasound imaging based on the multi-frequency technique. This study uses the natural mechanism of emitting oscillators' frequencies and uses these frequencies for imaging in iterations. We use a fundamental tone (i.e., the starting frequency f0) for the first iteration in DBIM, then consecutively use its overtones for the next ones. The digital simulation scenarios are tested with other multi-frequency approaches to prove our method's feasibility. We performed 57 different simulation scenarios on the use of multi-frequency information for the DBIM method. As a result, the proposed method for the smallest normalization error (RRE = 0.757). The proposed method's imaging time is not significantly longer than the way of using single frequency information.

Frequency Representation: Visualization and Clustering of Acoustic Data Using Self-Organizing Maps

Extraction and display of frequency information in three-dimensional (3D) acoustic data are important steps to analyze object characteristics, because the characteristics, such as profiles, sizes, surface structures, and material properties, may show frequency dependence. In this study, frequency representation (FR) based on phase information in multispectral acoustic imaging (MSAI) is proposed to overcome the limit of intensity or amplitude information in image display. Experiments are performed on 3D acoustic data collected from a rigid surface engraved with five different letters. The results show that the proposed FR technique can not only identify the depth of the five letters by the colors representing frequency characteristics but also demonstrate the 3D image of the five letters, providing more detailed characteristics that are unavailable by conventional acoustic imaging.

Switching 70Pb(Mg1/3Nb2/3)O3-0.30PbTiO3 single crystal by 3 MHz bipolar field

Polarization switching and associated electromechanical property changes at 3.0 MHz were investigated with and without a direct current (dc) bias for [001]c poled 0.70Pb(Mg1/3Nb2/3)O3-0.30PbTiO3 single crystal. The results showed that the coercive field under a bipolar pulse at 3.0 MHz is 2.75 times as large as conventional defined Ec (2.58 kV/cm at 0.1 Hz), and a dc bias can further enlarge the driving field. Our results point to an innovative transducer operating mechanism at high frequencies since one could drive the crystal under much larger fields at high frequencies to produce much stronger signals from a small array element for deeper penetration imaging.

PMN-PT single crystal focusing transducer fabricated using a mechanical dimpling technique

A ∼5MHz focusing PMN-PT single crystal ultrasound transducer has been fabricated utilizing a mechanical dimpling technique, where the dimpled crystal wafer was used as an active element of the focusing transducer. For the dimpled focusing transducer, the effective electromechanical coupling coefficient was enhanced significantly from 0.42 to 0.56. The dimpled transducer also yields a -6dB bandwidth of 63.5% which is almost double the bandwidth of the plane transducer. An insertion loss of the dimpled transducer (-18.1dB) is much lower than that of the plane transducer. Finite element simulation also reveals specific focused beam from concave crystal surface. These promising results show that the dimpling technique can be used to develop high-resolution focusing single crystal transducers.