High-sensitivity Ultrasonic Transducers Research Articles

Fabrication and Characterization of High-Sensitivity Ultrasonic Transducers With Functionally Graded Design

In this paper, a PZT/epoxy piezo-composite transducer with functionally graded design was proposed, which facilitated high sensitivity and broad bandwidth. The functionally graded piezocomposite was fabricated using a modified dice and fill method. Finite-element simulation was performed to study the vibration modes of the piezocomposite and to predict the transducer performances. To evaluate the performances experimentally, the proposed and conventional transducer based on monolithic PZT ceramic with similar dimension was fabricated and characterized systematically. We determined that the functionally graded transducer has a slightly higher center frequency (5.37 MHz), broader −6-dB bandwidth (22.5%), and a much lower insertion loss (−13.57 dB) compared to the conventional transducer (5.26 MHz, 18.3%, and −17.72 dB, respectively). The experimental results are in good agreement with the simulation ones. This preliminary investigation suggests that the functionally graded design is a promising approach to enhance the performance of ultrasonic transducers in high-sensitivity applications.

Fabrication of a (K,Na)NbO3-based lead-free 1-3 piezocomposite for high-sensitivity ultrasonic transducers application

Ultrasonic imaging is a well-established powerful medical diagnosis tool at present. However, commercial ultrasonic transducers are commonly made of toxic lead-based piezoelectric materials. Thus, it is vital to develop lead-free alternatives with satisfactory performance. This study presents the development of a phase boundary-engineered (K,Na)NbO3-based lead-free 1-3 piezocomposite and its application on high-sensitivity ultrasonic imaging transducers. A modified dice-and-fill technique was used to manufacture the microscale piezocomposite, by which the ceramic pillars were miniaturized to a width of 55 μm with a kerf of 15 μm. Improved acoustic and electrical properties were obtained in the new piezocomposite, and ultrasonic imaging transducers were further designed and fabricated based on the composite. The fabricated transducers exhibit enhanced performance with a high center frequency (16 MHz), a broad bandwidth (83%), and a very low insertion loss (9.8 dB), outperforming state-of-the-art transducers based on other lead-free materials. Imaging capability of the transducers was evaluated via ex vivo imaging of a porcine eyeball, indicating that this lead-free piezocomposite has many attractive properties in developing environment-friendly high-sensitivity ultrasonic devices for biomedical imaging applications.

Simultaneous dual molecular contrasts provided by the absorbed photons in photoacoustic microscopy

We investigated the feasibility of simultaneously imaging two distinctive molecular contrasts provided by the absorbed photons in biological tissues with a single light source. The molecular contrasts are based on two physical effects induced by the absorbed photons: photoacoustics (PA) and autofluorescence (AF). In an integrated multimodal imaging system, the PA and AF signals were detected by a high-sensitivity ultrasonic transducer and an avalanche photodetector, respectively. The system was tested by imaging ocular tissue samples, including the retinal pigment epithelium and the ciliary body. The acquired images provided information on the spatial distributions of melanin and lipofuscin in these samples.

Development of High-Sensitivity Ultrasonic Transducer in Air with Nanofoam Material

For a high-sensitivity ultrasonic transducer in air, it was considered that nanofoam be applied to its acoustic matching layer. Nanofoam is a porous material that is made by the sol-gel process. Since nanofoam has an extremely low acoustic impedance, it is effective for the acoustic matching layer of an ultrasonic transducer in air. In this study, we have fabricated an ultrasonic transducer that had two acoustic matching layers and estimated its acoustic properties. The two matching layers were made of silica nanofoam and porous ceramic. The sensitivity of the developed ultrasonic transducer was about twenty times higher than that of a conventional ultrasonic transducer in air.