Acceleration sensors are tools for detecting acceleration and serve purposes like fault monitoring and behavior recognition. It is extensively employed in a variety of industries, including aerospace, artificial intelligence, biology, and many more. Among these, one of the major research hotspots and challenges is the development of low-energy, self-powered, miniature, mass-produced sensors. Due to its capacity to perceive human behavior and identify errors, the flexible acceleration sensor offers a distinct advantage in the use of flexible and miniaturized sensing systems. This review analyzes the current state of piezoelectric flexible acceleration sensors’ applications in the areas of sensitive materials, processing technology, and device structure and briefly summarizes the fundamental properties of these sensors. Additionally, it ends with a prognosis for the future growth of flexible piezoelectric acceleration sensors.

The nanocomposite metal–organic framework (MOF) derivative CoFe₂O₃@C with a double core–shell structure and the nanocomposite MOF derivative CoFe₂O₄@Fe₃C@NiO with a three-layered core–shell structure have been prepared.

Ultrasonic power transfer (UPT) is gaining traction for wireless energy delivery to implants and wearables because it combines centimeter-scale penetration with compact receivers. This review takes a transducer-centric view of UPT and organizes the field across bulk piezoelectrics (including lead-free options), piezoelectric micromachined ultrasonic transducers (PMUTs), capacitive micromachined ultrasonic transducers (CMUTs), flexible polymer platforms and magnetostrictive transducers. We connect working mechanisms and structural configurations to practical performance—operating frequency ranges, bandwidth, link efficiency and output power, and miniaturization trade-offs—and summarize representative demonstrations in biomedical systems. System-level considerations for integration (acoustic/electrical matching and rectification) and bidirectional links (including backscatter and active telemetry) are highlighted to show how a single acoustic carrier can deliver power and data through tissue. We conclude with challenges (attenuation and misalignment, materials reliability and packaging, and scaling to millimeter/sub-millimeter form factors) and opportunities that draw on materials innovations (metamaterials, lead-free ceramics, flexible polymers) and machine-learning-assisted co-design for robust, efficient through-tissue operation. Together, this transducer-focused synthesis provides a practical map from device physics and fabrication choices to system performance and emerging applications.

Precise and time-efficient sensing of tremor dynamics is essential for developing personalized, adaptive stimulation strategies for movement disorders such as Parkinson’s Disease (PD) and Essential Tremor (ET). Existing modalities—such as inertial measurement units (IMUs) and surface electromyography (EMG)—lack muscle specificity and are prone to stimulation artifacts. To address these limitations, we fabricated and applied a Wearable Ultrasound Sensing (WUS) system, featuring dual flexible 64- element transducer arrays with center frequency of 6 MHz conformed over the flexor carpi radialis (FCR) and extensor carpi radialis (ECR) muscles for simultaneous antagonist muscle monitoring. A machine learning (ML) pipeline was introduced to estimate tissue displacement (TD) from raw ultrasound signals. Across three participants and multiple trials, the WUS system achieved tremor frequency detection within 10 %variation relative to commercial B-mode and IMU sensors, and met statistical equivalence thresholds based on two one-sided test (TOST) analysis. The TD estimation models demonstrated high predictive accuracy, with overall Pearson correlation coefficients between predicted and actual values ranging from 0.88 to 0.97, normalized RMSE values below 10 %, and offline model building times under 800 seconds. Compared to classical B-mode speckle tracking, the proposed WUS-ML pipeline reduced offline model building time by 75 % (from 3095 sec to 792 sec). In real-time performance tests, it reduced frame-level latency from 3700 ms to 17 ms and achieved effective processing rates exceeding 50 Hz, well above the Nyquist threshold for tremor analysis. These results demonstrate the feasibility of dual-array wearable ultrasound for accurate, low-latency tremor tracking and lay the groundwork for future closed-loop afferent stimulation systems in both clinical and at-home environments.

Alternating current poling (ACP) has been investigated showing dramatic enhancement of the piezoelectric and dielectric properties of PMN-PT and PIN-PMN-PT single crystals. However, reported studies have been mainly focused on material or simulation study. In this work, we investigated ultrasound transducers with alternating current poling (ACP) Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT) single crystals and compared the key specifications of ACP single crystal transducers with those of conventional direct current poling (DCP) single crystal prototypes. Based on the measured material properties, single layer ultrasound transducers were first designed with a center frequency of 10 MHz with the KLM (Krimholtz, Leedom and Matthae) model. Then, the prototypes were fabricated using ACP and DCP single crystals. After that, the performances of two different kinds of transducers were characterized by comparison of sensitivity, pressure output, bandwidth and imaging quality. At last, the ACP transducer durability was tested with long working hours, which showed a low and recoverable decrease with the transducer’s performance. With an aperture size of 2×2 mm², ACP transducers showed a better electrical impedance, 14% improvement in loop sensitivity and 66% improvement in pressure output compared with DCP transducers . For the imaging test, although the ACP transducers showed comparable resolution with the DCP transducers for the in-vitro wire phantom imaging, the ACP transducers showed 3 dB signal to noise ratio improvement under the same input. These findings suggest that ACP single crystal transducers are promising for diagnostic and therapeutic applications.