Underwater Thermoacoustic Generation by a Hierarchical Tetrapodal Carbon Nanotube Network.

Solid-state fabricated carbon nanotube (CNT) sheets have shown promise as thermoacoustic (TA) sound generators, emitting tunable sound waves across a broad frequency spectrum (1-105 Hz) due to their ultralow specific heat capacity. However, their applications as underwater TA sound generators are limited by the reduced mechanical strength of CNT sheets in aqueous environments. In this study, we present a mechanically robust underwater TA device constructed from a three-dimensional (3D) tetrapodal assembly of carbon nanotubes (t-CNTs). These structures feature a high porosity (>99.9%) and a double-hollowed network of well-interconnected CNTs. We systematically explore the impact of different dimensions of t-CNTs and various annealing procedures on sound generation performance. Furnace-annealed t-CNTs, in contrast to directly resistive Joule heating annealing, provide superior, continuous, and homogeneous hydrophobicity across the surface of bulk t-CNTs. As a result, the t-CNTs-based underwater TA device demonstrates stable, smooth, and broad-spectrum sound generation within the frequency range of 1 × 102 to 1 × 104 Hz, along with a weak resonance response. Furthermore, these devices exhibit enhanced and more stable sound generation performance at nonresonance frequencies compared to regular CNT-based devices. This study contributes to advancing the development of underwater TA devices with characteristics such as being nonresonant, high-performing, flexible, elastically compressible, and reliable, enabling operation across a broad frequency range.

A Comprehensive Study on Magnetoelectric Transducers for Wireless Power Transfer Using Low-Frequency Magnetic Fields.

Magnetoelectric (ME) transducers, comprising of layered magnetostrictive and piezoelectric materials, are more efficient than inductive coils in converting low-frequency magnetic fields into electric fields, particularly in applications that require miniaturized devices such as biomedical implants. Therefore, ME transducers are an attractive candidate for wireless power transfer (WPT) using low-frequency magnetic fields, which are less harmful to the human body and can penetrate easily through different lossy media. The literature lacks a comprehensive study on the ME transducer as a power receiver in a WPT link. This paper studies the impact of different ME design parameters on the WPT link performance. An accurate analytical model of the ME transducer, operating in the longitudinal-transverse mode, is presented, describing both temporal and spatial deformations. Nine ME transducers with different sizes (ME volume: 5-150 mm3) were fabricated with Galfenol and PZT-5A as magnetostrictive and piezoelectric layers, respectively. Through the modeling and measurement of these ME transducers, the effects of the ME transducer dimension, DC bias magnetic field, loading (RL), and operation frequency on the resonance frequency, quality factor, and received power (PL) of the ME transducer are determined. In measurements, a 150 mm3 ME transducer achieved > 10-fold higher PL for a wide RL range of 500 Ω to 1 MΩ at 95.5 kHz, compared to an optimized coil with comparable size and operation frequency.

A New Method for Evaluation of the Complex Material Coefficients of Piezoelectric Ceramics in the Radial Vibration Modes.

The determination of complex elastic, piezoelectric, and dielectric coefficients of piezoelectric ceramics is important for precision engineering devices. Here, a novel method for determining the optimal material coefficients is presented. This method minimizes the average relative error in the values of conductance, susceptance, resistance, and reactance obtained from the 1-D model in the IEEE Standard (ANSI/IEEE Std 176-1987) and the experimental measurements of the first and second radial modes. Poisson's ratio is assumed to be a complex number in addition to the elastic, piezoelectric, and dielectric coefficients in the present method. The global minimum of the average relative error is found by searching the minimum among all local minima of the average relative error, which are obtained with the Levenberg-Marquardt modification of Newton's method from randomly chosen initial conditions. The optimal material coefficients of an APC 850 disk and an APC 855 disk are calculated with this method. The uncertainties in the optimal material coefficients are evaluated by calculating the minimum average relative error when the real or imaginary part of each coefficient is prescribed.

Universal Multienergy Harvester Architecture.

The energy available in the ambient vibrations, magnetic fields, and sunlight can be simultaneously or independently harvested using universal architecture. The universal harvester design is shown to effectively convert ambient magnetic fields, vibration, and light into electricity. The architecture is composed of a perovskite solar cell integrated onto a magnetoelectric composite cantilever beam. The efficiency of the large-area perovskite solar cell is shown to reach 15.74% (cell area is >1100% larger than traditional perovskite solar cells) by selecting glass/indium tin oxide (ITO) as the cathode that reduces the charge recombination. The magnetoelectric composite beam is designed to include the effect of the mass and volume of the solar cell on power generation. Results demonstrate that universal energy harvester can simultaneously capture vibration, magnetic fields, and solar irradiation to provide an ultrahigh-power density of 18.6 mW/cm3. The total power generated by the multienergy harvester, including vibration, magnetic field, and solar stimuli, is 23.52 mW from a total surface area of 9.6 cm2 and a total volume of 1.26 cm3. These results will have a tremendous impact on the design of the power sources for Internet of Things sensors and wireless devices.

3D printed graphene-based self-powered strain sensors for smart tires in autonomous vehicles.

The transition of autonomous vehicles into fleets requires an advanced control system design that relies on continuous feedback from the tires. Smart tires enable continuous monitoring of dynamic parameters by combining strain sensing with traditional tire functions. Here, we provide breakthrough in this direction by demonstrating tire-integrated system that combines direct mask-less 3D printed strain gauges, flexible piezoelectric energy harvester for powering the sensors and secure wireless data transfer electronics, and machine learning for predictive data analysis. Ink of graphene based material was designed to directly print strain sensor for measuring tire-road interactions under varying driving speeds, normal load, and tire pressure. A secure wireless data transfer hardware powered by a piezoelectric patch is implemented to demonstrate self-powered sensing and wireless communication capability. Combined, this study significantly advances the design and fabrication of cost-effective smart tires by demonstrating practical self-powered wireless strain sensing capability.

Crumpled sheets of reduced graphene oxide as a highly sensitive, robust and versatile strain/pressure sensor.

Sensing of mechanical stimuli forms an important communication pathway between humans/environment and machines. The progress in such sensing technology has possible impacts on the functioning of automated systems, human machine interfacing, health-care monitoring, prosthetics and safety systems. The challenges in this field range from attaining high sensitivity to extreme robustness. In this article, sensing of complex mechanical stimuli with a patch of taped crumpled reduced graphene oxide (rGO) has been reported which can typically be assembled under household conditions. The ability of this sensor to detect a wide variety of pressures and strains in conventional day-to-day applications has been demonstrated. An extremely high gauge factor (∼103) at ultralow strains (∼10-4) with fast response times (<20.4 ms) could be achieved with such sensors. Pressure resulting from a gentle touch to over human body weight could be sensed successfully. The capability of the sensor to respond in a variety of environments could be exploited in the detection of water and air pressures both below and above atmospheric, with a single device.