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Preconcentrating particulate and cellular matter for their isolation or detection is often a necessary and critical sample preparation or purification step in many lab-on-a-chip diagnostic devices. While surface acoustic wave (SAW) microcentrifugation has been demonstrated as a powerful means to drive efficient particle concentration, this has primarily been limited to micron dimension particles. When the particle size is around 1 μm or below, studies on SAW microcentrifugation to date have shown that particle ring-like aggregates can only be obtained in contrast to the localized concentrated clusters that are obtained with larger particles. Considering the importance of submicron particles and bioparticles that are common in many real-world samples, we elucidate why previous studies have not been able to achieve the concentration of these smaller particles to completion, and we present a practical solution involving a novel closed chamber configuration that minimizes sample heating and eliminates evaporation to show that it is indeed possible to drive submicron particle and cell concentration down to 200 nm diameters with SAW microcentrifugation over longer durations.

Diamond nitrogen-vacancy (NV) centers constitute a promising class of quantum nanosensors owing to the unique magneto-optic properties associated with their spin states. The large surface area and photostability of diamond nanoparticles, together with their relatively low synthesis costs, make them a suitable platform for the detection of biologically relevant quantities such as paramagnetic ions and molecules in solution. Nevertheless, their sensing performance in solution is often hampered by poor signal-to-noise ratios and long acquisition times due to distribution inhomogeneities throughout the analyte sample. By concentrating the diamond nanoparticles through an intense microcentrifugation effect in an acoustomicrofluidic device, we show that the resultant dense NV ensembles within the diamond nanoparticles give rise to an order-of-magnitude improvement in the measured acquisition time. The ability to concentrate nanoparticles under surface acoustic wave (SAW) microcentrifugation in a sessile droplet is, in itself, surprising given the well-documented challenge of achieving such an effect for particles below 1 μm in dimension. In addition to a demonstration of their sensing performance, we thus reveal in this work that the reason why the diamond nanoparticles readily concentrate under the SAW-driven recirculatory flow can be attributed to their considerably higher density and hence larger acoustic contrast compared to those for typical particles and cells for which the SAW microcentrifugation flow has been shown to date.

The increasing demand for portable, wearable, miniaturized and flexible consumer electronic devices requests the development of flexible and renewable energy storage devices. This paper reports a flexible and renewable electrode material for supercapacitor. The electrode material is made by preparing a porous structured cellulose/graphene oxide (GO) nanocomposite. The morphology of the nanocomposite is shown to be porous structure with a pore size about 10 μm. The Fourier transform infrared spectroscopy of the nanocomposites exhibits that the cellulose and GOs are successfully grafted by a grafting agent, which results in uniform dispersion of GOs in the cellulose matrix. The electrical performance of the nanocomposite is evaluated by measuring cyclic voltammograms and galvanostatic charge-discharge curves. Low cost and sustainability of the cellulose and graphene oxide nanocomposite encourage its possible use for electrode material of flexible energy storage devices.

Tactile haptic feedback is an important consideration in the design of advanced human–machine interfaces, particularly in an age of increasing reliance on automation and artificial intelligence. In this work, we show that the typical nanometer-order surface displacement amplitudes of piezoelectric transducers—which are too small to be detectable by the human touch, and constitute a significant constraint in their use for tactile haptic surface actuation—can be circumvented by coupling the vibration into a liquid to drive the deflection of a thermoplastic membrane. In particular, transmission of the sound energy from the standing wave vibration generated along a piezoelectric transducer into a microfluidic chamber atop which the membrane is attached is observed to amplify the mechanical vibration signalling through both the acoustic radiation pressure and the viscous normal stress acting on the membrane—the latter arising due to the acoustic streaming generated as the sound wave propagates through the liquid—to produce 100 μm-order static deflections of the membrane, upon which approximately 0.5 μm dynamic vibrations at frequencies around 1 kHz are superimposed; both these static and dynamic responses are within the perception range for human finger sensation. The large static deformation, the relatively fast response time, and the ability to incorporate a dynamic vibrotactile response together with the small size and potential for integration of the device into large scale arrays make this mechanism well suited for driving actuation in devices which require tactile haptic responses.

The present study investigates a film actuator made with dielectric cellulose acetate films separated by narrow spacers as a means of electrostatic actuation for potential haptic application. Fabrication process for the actuator is explained along with experiments conducted over a wide frequency range of actuation frequency. A valid finite element simulation of the actuator is made on the quarter section of the actuator by using full 3D finite elements. Vibration characteristics such as fundamental natural frequency, mode shape and output velocity in the frequency range for haptic feeling generation are obtained from the finite element analysis and compared with the experimental results. Experimental results demonstrate that the finite element model is practical and effective enough in predicting the vibration characteristics of the actuator for haptic application. The film actuator shows many promising properties like high transparency, wide range of actuation frequency and high vibration velocity for instance.

Cellulose nanocrystal/graphene oxide composite was reported as a humidity sensor in this study. The composite film was fabricated using simple blending the materials followed by oven drying. The composite film offers a unique advantages of cellulose combined with functionality of GO. It was capitalized to design renewable, flexible and cheap humidity sensor. Performance of the composite film as a humidity sensor was evaluated on the basis of relative capacitance change at different humidity level. Synthesized composite film was characterized using scanning electron microscope, Fourier transform infrared spectroscope, and X-ray diffraction. Environmental effect such as temperature was taken into account on the sensor performance. The sensing mechanism is explained on the basis of presence of hydrophilic functional groups in the composite. The linear and fast response of the developed sensor is advantageous.

The appeal of portable electronic devices is growing gradually, which increases the demand for flexible and renewable energy storage devices. Hybrid materials can be used as renewable and flexible electrode material for this kind of devices. Organic–inorganic hybrid materials represent a creative substitute to design new materials and composites by accepting advantages of both materials. This paper reports the possibility of renewable cellulose and graphene composite as an electrode material for energy storage device such as supercapacitor. The morphology and structure of the nanocomposite are studied using scanning electron microscope and Energy-dispersive X-ray Spectroscopy. The performance of the composite as supercapacitor electrode material is evaluated by cyclic voltammograms and galvanostatic charge-discharge curves.

Ultrasonic haptics actuator is a device that can create a haptic feedback to user’s hand. The modulation of ultrasonic frequency can give different textures to the users. In this study, a feasibility of the ultrasonic haptic actuator made on a flexible piezoelectric substrate is investigated. As the piezoelectric substrate helps to propagate flexural waves, a pair of interdigital transducer (IDT) with reflectors can produce standing waves, which can increase the vibrational displacement of the actuator. A pair of IDT pattern was fabricated on a piezoelectric polymer substrate. A finite element analysis is at first performed to design the actuator. A sinusoidal excitation voltage is applied on IDT electrodes at ultrasonic frequencies and the displacement waveforms are found. The displacement waveforms clearly represent how ultrasonic waves propagate through the piezoelectric substrate.

Hybrid composites with organic and inorganic materials are drawing interest to researchers by adopting advantages of organic materials and inorganic materials. Cellulose is biocompatible, cheap, environmentally friendly, renewable and lightweight material. Nano crystalline form of cellulose (CNC) is a needle like rigid structure with a very high mechanical strength. Graphene, crystalline forms of carbon, provides basic platform for many electronic and optoelectronic devices. This paper introduces the fabrication process of cellulose nanocrystal/graphene oxide blended nanocomposite film. Cellulose nanocrystal/graphene oxide nanocomposite films are prepared by mixing graphene oxide (GO) into cellulose nanocrystal suspension using ultrasonic homogenizer. Scanning electron microscopy is used to study morphology. Optical properties of the composite was characterized to evaluate the change in transparency after addition of GO in CNC.

This study deals with ultrasonic wave propagation on a piezoelectric polymer substrate for tactile actuator. On the piezoelectric polymer substrate, a pair of interdigital transductor (IDT) electrodes is patterned by lift-off process and a resonator is made by exciting the IDTs. A standing wave is generated between the pair of IDT electrodes, of which the wavelength matches with the distance between two IDTs. The standing ultrasonic waves can give different textures to the users. The wave propagation in this periodic structure on the polymer substrate is studied by harmonic and transient analysis. Vertical displacement and induced voltage at the output IDT electrode are calculated and the ultrasonic wave generation is experimentally verified. The proposed concept of tactile actuator based on ultrasonic wave is explained.