Record-Breaking Frequency of 44 GHz Based on the Higher Order Mode of Surface Acoustic Waves with LiNbO_(3)/SiO_(2)/SiC Heterostructures

Surface acoustic wave (SAW) technology has been extensively explored for wireless communication, sensors, microfluidics, photonics, and quantum information processing. However, due to fabrication issues, the frequencies of SAW devices are typically limited to within a few gigahertz, which severely restricts their applications in 5G communication, precision sensing, photonics, and quantum control. To solve this critical problem, we propose a hybrid strategy that integrates a nanomanufacturing process (i.e., nanolithography) with a LiNbO_(3)/SiO_(2)/SiC heterostructure and successfully achieve a record-breaking frequency of about 44 GHz for SAW devices, in addition to large electromechanical coupling coefficients of up to 15.7%. We perform a theoretical analysis and identify the guided higher order wave modes generated on these slow-on-fast SAW platforms. To demonstrate the superior sensing performance of the proposed ultra-high-frequency SAW platforms, we perform micro-mass sensing and obtain an extremely high sensitivity of approximately 33151.9 MHz·mm2·μg−1, which is about 1011 times higher than that of a conventional quartz crystal microbalance (QCM) and about 4000 times higher than that of a conventional SAW device with a frequency of 978 MHz.

A new strategy to minimize humidity influences on acoustic wave ultraviolet sensors using ZnO nanowires wrapped with hydrophobic silica nanoparticles

Surface acoustic wave(SAW)technology has been widely developed for ultraviolet(UV)detection due to its advantages of miniaturization,portability,potential to be integrated with microelectronics,and passive/wireless capabilities.To enhance UV sensitivity,nanowires(NWs),such as ZnO,are often applied to enhance SAW-based UV detection due to their highly porous and interconnected 3D network structures and good UV sensitivity.However,ZnO NWs are normally hydrophilic,and thus,changes in environmental parameters such as humidity will significantly influence the detection precision and sensitivity of SAW-based UV sensors.To solve this issue,in this work,we proposed a new strategy using ZnO NWs wrapped with hydrophobic silica nanoparticles as the effective sensing layer.Analysis of the distribution and chemical bonds of these hydrophobic silica nanoparticles showed that numerous C-F bonds(which are hydrophobic)were found on the surface of the sensitive layer,which effectively blocked the adsorption of water molecules onto the ZnO NWs.This new sensing layer design minimizes the influence of humidity on the ZnO NW-based UV sensor within the relative humidity range of 10–70%.The sensor showed a UV sensitivity of 9.53 ppm(mW/cm^(2))^(−1),with high linearity(R^(2) value of 0.99904),small hysteresis(<1.65%)and good repeatability.This work solves the long-term dilemma of ZnO NW-based sensors,which are often sensitive to humidity changes.

Multiscale and hierarchical wrinkle enhanced graphene/Ecoflex sensors integrated with human-machine interfaces and cloud-platform

Current state-of-the-art stretchable/flexible sensors have received stringent demands on sensitivity,flexibility,linearity,and widerange measurement capability.Herein,we report a methodology of strain sensors based on graphene/Ecoflex composites by modulating multiscale/hierarchical wrinkles on flexible substrates.The sensor shows an ultra-high sensitivity with a gauge factor of 1078.1,a stretchability of 650%,a response time of~140 ms,and a superior cycling durability.It can detect wide-range physiological signals including vigorous body motions,pulse monitoring and speech recognition,and be used for monitoring of human respirations in real-time using a cloud platform,showing a great potential for the healthcare internet of things.Complex gestures/sign languages can be precisely detected.Human-machine interface is demonstrated by using a sensor-integrated glove to remotely control an external manipulator to remotely defuse a bomb.This study provides strategies for real-time/long-range medical diagnosis and remote assistance to perform dangerous tasks in industry and military fields.

Strategy to minimize bending strain interference for flexible acoustic wave sensing platform

There are great concerns for sensing using flexible acoustic wave sensors and lab-on-a-chip,as mechanical strains will dramatically change the sensing signals(e.g.,frequency)when they are bent during measurements.These strain-induced signal changes cannot be easily separated from those of real sensing signals(e.g.,humidity,ultraviolet,or gas/biological molecules).Herein,we proposed a new strategy to minimize/eliminate the effects of mechanical bending strains by optimizing off-axis angles between the direction of bending deformation and propagation of acoustic waves on curved surfaces of layered piezoelectric film/flexible glass structure.This strategy has theoretically been proved by optimization of bending designs of off-axis angles and acoustically elastic effect.Proof-of-concept for humidity and ultraviolet-light sensing using flexible SAW devices with negligible interferences are achieved within a wide range of bending strains.This work provides the best solution for achieving high-performance flexible acoustic wave sensors under deformed/bending conditions.