High-frequency ultrasonic imaging with improved spatial resolution has gained increasing attention in the field of biomedical imaging. Sensitivity of transducers plays a pivotal role in determining ultrasonic image quality. Conventional ultrasonic transducers are mostly made from lead-based piezoelectric materials that may be harmful to the human body and the environment. In this study, a new (K,Na)NbO $_{3}$ -KTiNbO $_5$ -BaZrO $_{3}$ -Fe $_{2}$ O $_{3}$ -MgO (KNN-NTK-FM) lead-free piezoelectric ceramic was utilized in developing eco-friendly transducers for high-frequency biomedical ultrasonic imaging applications. A needle transducer with a small active aperture size of 0.45 × 0.55 mm $^2$ was designed and evaluated. The fabricated transducer exhibits great performance with a high center frequency (52.6 MHz), a good electromechanical coupling ( $k$ $_{eff}$ ~ 0.45), a large bandwidth (64.4% at -6 dB), and a very low two-way insertion loss (10.1 dB). Such high sensitivity is superior to those transducers based on other lead-free piezoelectric materials and can even be comparable to the lead-based ones. Imaging performance of the KNN-NTK-FM needle transducer was analyzed by imaging a wire phantom and an agar tissue-mimicking phantom. Imaging capabilities of the transducer were further demonstrated by ex vivo imaging studies on a porcine eyeball and a rabbit aorta. The results suggest that the KNN-NTK-FM piezoceramic has many attractive properties over other lead-free piezoelectric materials in developing eco-friendly highly sensitive transducers for high-frequency biomedical ultrasonic imaging applications.

A concise overview of ferroelectric ceramics and composites, which constitute the backbone of transducer applications such as actuators, sensors, energy harvesting, and storage are provided. For piezoelectric composites based on ferroelectric ceramics, underlying principles are developed using linear equations of state for piezoelectricity and the concepts of crystalline anisotropy, symmetry, composite connectivity, and form factor engineering as unifying themes. Emphasis is given to diphasic piezoelectric composites which have revolutionized transducer engineering in fields such as sonar and medical ultrasound imaging. It is shown that through judicious selection of a ferroelectric ceramic in conjunction with an inactive material such as a polymer or metal, effective material properties exceeding the performance of single-phase ceramics can be achieved. The application of traditional composite strategies and advances in fabrication technologies to rapidly growing fields such as dielectric energy storage and piezoelectric energy harvesting are also discussed.

This paper delves into the enhancement of dynamic performance in Piezoelectric Micromachined Ultrasonic Transducers (PMUTs) under forced vibration in pulse wave mode, with an emphasis on mitigating blind area and enhancing axial resolution. The investigation begins with a theoretical framework that elucidates the relationship between the resonant frequency of the device and various excitation parameters, such as the applied frequency and the burst count. Empirical findings illustrate that the operation of PMUTs under forced vibration conditions significantly curtails the duration of ringdown by 40% compared to their resonant performance. Furthermore, acoustic range evaluations indicate that this methodology substantially reduces the blind area by 37.5% and amplifies the axial resolution of echo signals by approximately 440%. The study concludes that the proposed technique, noted for its universality and straightforwardness, provides a robust solution for enhancing near-range detection capabilities in ultrasonic sensors, thereby heralding considerable progress in the domain of precise acoustic measurements. This paper not only explicates the fundamental mechanisms but also substantiates the feasibility and efficacy of employing forced vibration in PMUT across diverse applications.

The study of piezoelectric composites traces its origins back to the 1970s, when the concept of combining ceramics and polymers to introduce self-connectivity was first proposed [ 1–3]. Creating composites using polymers as the matrix and ferroelectric ceramics as fillers has proven to be an effective approach for improving the electromechanical coupling performance of piezoelectric materials. As flexible electronics have experienced significant advancements in recent years, the demand for high-performance flexible sensors, actuators and energy harvesters based on soft piezoelectric materials has also increased. This necessitates the development of piezoelectric composites that possess enhanced mechanical compliance and high piezoelectric coefficients.

This paper presents a novel piezoelectric micromachined ultrasonic transducer (PMUT) with theoretical simulation, fabrication, and testing. Conventional methods using a PCB or an external horn to adjust the PMUT acoustic field angle are limited by the need for transducer size. To address this limitation, the stepped-tube (expanded tube) backside cavity PMUT has been proposed. The stepped-tube PMUT and the tube PMUT devices have the same membrane structure, and the acoustic impedance matching of the PMUT is optimized by modifying the boundary conditions of the back cavity structure. The acoustic comparison experiments show that the average output sound pressure of the stepped-tube backside cavity PMUT has increased by 17%, the half-power-beam-width (θ_-3db) has been reduced from 55° to 30° with a reduction of 45%, and the side lobe level signal is reduced from 147 mV to 66 mV. In addition, this work is fabricated on an eight-inch wafer. The process is compatible with standard complementary metal oxide semiconductor (CMOS), conditions are stable, and the cost is controllable, plus it facilitates the batch process. These conclusions suggest that the stepped-tube backside cavity PMUT will bring new, effective, and reliable solutions to ranging applications.

The advancement of spatial interaction technology has greatly enriched the domain of consumer electronics. Traditional solutions based on optical technologies suffers high power consumption and significant costs, making them less ideal in lightweight implementations. In contrast, ultrasonic solutions stand out due to their lower power consumption and cost-effectiveness, capturing widespread attention and interest. This paper addresses the challenges associated with the application of ultrasound sensors in spatial localization. Traditional ultrasound systems are hindered by blind spots, large physical dimensions, and constrained measurement ranges, limiting their practical applicability. To overcome these limitations, this paper proposes a miniature ultrasonic spatial localization module employing piezoelectric micromechanical ultrasonic transducers (PMUTs). The module is comprised of three devices each with dimension of 1.2 mm × 1.2 mm × 0.5 mm, operating at a frequency of around 180 kHz. This configuration facilitates a comprehensive distance detection range of 0–800 mm within 80° directivity, devoid of blind spot. The error rate and failure range of measurement as well as their relationship with the SNR (signal-to-noise ratio) are also thoroughly investigated. This work heralds a significant enhancement in hand spatial localization capabilities, propelling advancements in acoustic sensor applications of the meta-universe.