Dynamics of Electrowetting Droplet Motion in Digital Microfluidics Systems: From Dynamic Saturation to Device Physics

A quantitative description of the dynamics of droplet motion has been a long-standing concern in electrowetting research. Although many static and dynamic models focusing on droplet motion induced by electrowetting-on-dielectric (EWOD) already exist, some dynamic features do not fit these models well, especially the dynamic saturation phenomenon. In this paper, a dynamic saturation model of droplet motion on the single-plate EWOD device is presented. The phenomenon that droplet velocity is limited by a dynamic saturation effect is precisely predicted. Based on this model, the relationship between droplet motion and device physics is extensively discussed. The static saturation phenomenon is treated with a double-layer capacitance electric model, and it is demonstrated as one critical factor determining the dynamics of droplet motion. This work presents the relationship between dynamics of electrowetting induced droplet motion and device physics including device structure, surface material and interface electronics, which helps to better understand electrowetting induced droplet motions and physics of digital microfluidics systems

An Investigation on Efficient Acoustic Energy Reflection of Flexible Film Bulk Acoustic Resonators

ABSTRACT: This paper investigates the issues on acoustic energy reflection of flexible film bulk acoustic resonators (FBARs). The flexible FBAR was fabricated with an air cavity in the polymer substrate, which endowed the resonator with efficient acoustic reflection and high electrical performance. The acoustic wave propagation and reflection in FBAR were first analyzed by Mason model, and then flexible FBARs of 2.66 GHz series resonance in different configurations were fabricated. To validate efficient acoustic reflection of flexible resonators, FBARs were transferred onto different polymer substrates without air cavities. Experimental results indicate that efficient acoustic reflection can be efficiently predicted by Mason model. Flexible FBARs with air cavities exhibit a higher figure of merit (FOM). Our demonstration provides a feasible solution to flexible MEMS devices with highly efficient acoustic reflection (i.e. energy preserving) and free-moving cavities, achieving both high flexibility and high electrical performance. Keywords: Film bulk acoustic resonator, Mason model, Flexible resonator, Acoustic reflectio

Impedance tracking control of magnetostrictive transducer based on variable stiffness tuning

A magnetostrictive transducer (MT) is a highly integrated transducer that enables magneto-mechanical energy conversion when outputting actuation motion or force. To ensure high energy efficiency, an impedance tracking control strategy is proposed based on the variable stiffness tuning mechanism. The transducer's internal impedance is controlled to track the change of the load impedance to obtain the impedance matching for different working conditions, and thus increase the energy efficiency. The developed transducer is driven with magnetostrictive material Terfenol-D. By applying proper magnetic field, the material stiffness is able to be changed and the transducer's internal impedance can be controlled to obtain impedance matching. An impedance network model is built to describe the impedance changing of the transducer. A neural network model is developed to describe the variable stiffness mechanism of Terfenol-D. The impedance tracking is then realized with the feedforward compensation of the inverse neural network model and the inverse impedance network model. The influencing factors of impedance matching have been studied. Simulations and experiments have been conducted to verify the energy efficiency comparisons. Verifications show that the MT efficiency demonstrates big differences with and without the impedance control. The lowest efficiency is 10.8%. With the matching control, the efficiency is 24.7%, and this efficiency is 131% increased

Electrode design for multimode suppression of aluminum nitride tuning fork resonators

This paper is focused on electrode design for piezoelectric tuning fork resonators. The relationship between the performance and electrode pattern of aluminum nitride piezoelectric tuning fork resonators vibrating in the in-plane flexural mode is investigated based on a set of resonators with different electrode lengths, widths, and ratios. Experimental and simulation results show that the electrode design impacts greatly the multimode effect induced from torsional modes but has little influence on other loss mechanisms. Optimizing the electrode design suppresses the torsional mode successfully, thereby increasing the ratio of impedance at parallel and series resonant frequencies (Rp/Rs) by more than 80% and achieving a quality factor (Q) of 7753, an effective electromechanical coupling coefficient (kteff2) of 0.066%, and an impedance at series resonant frequency (Rm) of 23.6 kΩ. The proposed approach shows great potential for high-performance piezoelectric resonators, which are likely to be fundamental building blocks for sensors with high sensitivity and low noise and power consumption

Solid-State Microfluidics with Integrated Thin-Film Acoustic Sensors

For point-of-care applications, integrating sensors into a microfluidic chip is a nontrivial task because conventional detection modules are bulky and microfluidic chips are small in size and their fabrication processes are not compatible. In this work, a solid-state microfluidic chip with on-chip acoustic sensors using standard thin-film technologies is introduced. The integrated chip is essentially a stack of thin films on silicon substrate, featuring compact size, electrical input (fluid control), and electrical output (sensor read-out). These features all contribute to portability. In addition, by virtue of processing discrete microdroplets, the chip provides a solution to the performance degradation bottleneck of acoustic sensors in liquid-phase sensing. Label-free immunoassays in serum are carried out, and the viability of the chip is further demonstrated by result comparison with commercial ELISA in prostate-specific antigen sensing experiments. The solid-state chip is believed to fit specific applications in personalized diagnostics and other relevant clinical settings where instrument portability matters

MEMS ultrasonic transducers for safe, low-power and portable eye-blinking monitoring.

Eye blinking is closely related to human physiology and psychology. It is an effective method of communication among people and can be used in human-machine interactions. Existing blink monitoring methods include video-oculography, electro-oculograms and infrared oculography. However, these methods suffer from uncomfortable use, safety risks, limited reliability in strong light or dark environments, and infringed informational security. In this paper, we propose an ultrasound-based portable approach for eye-blinking activity monitoring. Low-power pulse-echo ultrasound featuring biosafety is transmitted and received by microelectromechanical system (MEMS) ultrasonic transducers seamlessly integrated on glasses. The size, weight and power consumption of the transducers are 2.5 mm by 2.5 mm, 23.3 mg and 71 μW, respectively, which provides better portability than conventional methods using wearable devices. Eye-blinking activities were characterized by open and closed eye states and validated by experiments on different volunteers. Finally, real-time eye-blinking monitoring was successfully demonstrated with a response time less than 1 ms. The proposed solution paves the way for ultrasound-based wearable eye-blinking monitoring and offers miniaturization, light weight, low power consumption, high informational security and biosafety

Dual functionality metamaterial enables ultra-compact, highly sensitive uncooled infrared sensor

International audienceCointegration and coupling a perfect metamaterial absorber (PMA) together with a film bulk acoustic wave resonator (FBAR) in a monolithic fashion is introduced for the purpose of producing ultracompact uncooled infrared sensors of high sensitivity. An optimized ultrathin multilayer stack was implemented to realize the proposed device. It is experimentally demonstrated that the resonance frequency of the FBAR can be used efficiently as a sensor output as it downshifts linearly with the intensity of the incident infrared irradiation. The resulting sensor also achieves a high absorption of 88% for an infrared spectrum centered at a wavelength of 8.2 μm. The structure is compact and can be easily integrated on a CMOS-compatible chip since both the FBAR and PMA utilize and share the same stack of metal and dielectric layers