Younghwan Choi

ZnO film for application in surface acoustic wave device

High quality, c-axis oriented zinc oxide (ZnO) thin films were grown on silicon substrate using RF magnetron sputtering. Surface acoustic wave (SAW) devices were fabricated with different thickness of ZnO ranging from 1.2 to 5.5 µm and the frequency responses were characterized using a network analyzer. Thick ZnO films produce the strongest transmission and reflection signals from the SAW devices. The SAW propagation velocity is also strongly dependent on ZnO film thickness. The performance of the ZnO SAW devices could be improved with addition of a SiO 2 layer, in name of reflection signal amplitude and phase velocity of Rayleigh wave.

Integrated ZnO Surface Acoustic Wave Microfluidic and Biosensor System

This paper presents the development of a novel portable cancer diagnostic system, based on thin film ZnO surface acoustic wave device, with integrated functions of microfluidic transport, mixing and bio-detection devices. The device is easily integrated with electronic control circuitry and fabricated with low temperature on Si, glass or even polymer substrates. Such a system is targeted at both the consumer market for self-diagnosis and the professional healthcare market for real-time diagnosis in a hospital and clinic environment.

SAW Streaming in ZnO Surface Acoustic Wave Micromixer and Micropump

Surface acoustic wave (SAW) devices were fabricated based on ZnO thin films using magnetron sputtering. When the acoustic wave travels along the surface of the ZnO SAW device with liquid droplet on its path, the momentum of the acoustic wave will be coupled into the liquid. When the applied voltage is below 3V, and the ZnO surface is not treated, the acoustic wave could only induce internal streaming in liquid. The streaming speed is strongly dependent on the applied voltage, which can be used as a micromixer. After the ZnO surface was silanization treated thus realizing a hydrophobic surface, the coupled energy into the liquid from the acoustic wave is efficient to move the droplet from hundred nanoliters to tens of microliters along the wave path. When the voltage is sufficiently high, a mist consisting of small droplets was generated and shot out, which can be explained from SAW heating effect.

Study on coupling of software-defined networking and wireless sensor networks

Typically, wireless sensor networks (WSNs) provide application-specific networking schemes based on restricted resources. For the reasons, WSN-based routing algorithms can be variously designed for applications. Even if two different WSN applications (e.g., target tracking and temperature monitoring) coexist in a network, the two applications can use different routing algorithms, running simultaneously on the same sensor nodes and network. However, the sensor nodes can efficiently spend their restrict resources (e.g., battery power) unless the two algorithms need to run simultaneously. There are a few research tries to deal with this problems by combining sensor networks with basic concepts of software-defined networking (SDN). However, performance of such a combination needs to be fully evaluated because the basic concept of SDN could not always give a positive effects to WSNs. Thus, this paper gives a try to analyze coupling of SDN and WSNs.

Scheme to guarantee IP continuity for NFC-based IoT networking

The key idea of IoT services and technologies is connectivity among all kinds of devices. The devices of the future would include very tiny things. Such a tiny device should support low-powered technology. However, the low-power technology could bring potential problems to device functions. This paper give a solution to overcome one of the problems for IoT devices based on NFC networking. NFC, which is from RFID technology, supports peer-to-peer communication on the link layer. Link addresses of NFC devices are not physically fixed values, so this give negative influences to IP networking; especially, connection continuity. Therefore, this paper gives a scheme to guarantee IP continuity for NFC-based IoT networking.

ZnO film based surface acoustic wave micro-pump

In this study, a micro-pump unit based on surface acoustic wave (SAW) on piezoelectric ZnO film is designed and fabricated as a micro-fluidic device. It employs a mechanical wave, which is generated electrically using an aluminum interdigital transducer (IDT), and propagates on the surface of the ZnO film. The ZnO film was used in this study because it has a high electromechanical coefficient and an excellent bonding with various substrate materials, in particular silicon. The sputtering parameters for ZnO film deposition have been optimized, and the ZnO films with different thickness from 1 micron to 5.5 microns were prepared. The film properties have been characterized using different methods, such as scanning electron microscopy, X-ray diffraction and atomic force microscopy. Aluminum IDT with a finger width and spacing of 8 microns was patterned on the ZnO film using a lift-off process. The frequency generated was measured using a network analyzer, and it varies from 130 MHz to 180 MHz as a function of film thickness. A signal generator was used to generate the frequency with a power amplifier to amplify the signal, which was then applied to aluminum IDT to generate the surface acoustic wave. If a liquid droplet exists on the surface carrying the acoustic wave, the energy and the momentum of the SAW will be coupled into the fluid, causing the liquid to vibrate and move on film surface. The strength of this movement is determined by the applied voltage and frequency. The volume of the liquid drop loaded on the SAW device in this study is of several hundreds of nanoliters. The movement of the liquid inside the droplet and also on the ZnO film surface can be demonstrated. The performance of ZnO SAW device was characterized as a function of film thickness.

Utilizing IP-over-NFC for Secure Data Transmissions: Demo Abstract

Near Field Communication (NFC) is a wireless communication technology using 13.56 MHz to support 2-way communications between two devices within ~10 cm. Such a short communication range may be considered as a shortcoming, but at the same time, this enables a secure data transfer within the connectivity region when compared to Bluetooth Low Energy (BLE) or Wi-Fi. Accordingly, NFC can be optionally utilized when secure data are transmitted in various services and applications focusing on ID validation. This demo presents a proof-of-concept for an alternative packet transmission method for achieving secure data exchange based on IP-over-NFC technology. For realizing this, there are a number of technical challenges. Utmost, the current NFC Linux kernel driver requires updates for supporting network-layer functionalities. Using such implementations, this demo demonstrates the procedures of transmitting secure data using NFC, while normal packet transmissions occur over WiFi simultaneously.

Analysis of design space and use case in IPv6 over NFC for resource-constrained IoT devices

This paper describes the characteristics of link layer technologies that are used at constrained node networks and typical use cases of IPv6 over networks of resource-constrained nodes. In addition to IEEE 802.15.4, various link layer technologies such as BLE, Z-wave, DECT-ULE, MS/TP, and NFC are widely used at constrained node networks for typical services. Based on these link layer technologies, IPv6 over networks of resource-constrained nodes has various and practical use cases. To efficiently implement typical IoT services, a typical use case and consideration of several design spaces in IPv6 over NFC are described.