- Study on the radiation hardness of GaN and ZnO
- Development of ZnO-based biomedical sensors
- A study on the evaluation of the optical properties in transparent ceramics and its laser applications
- A study of electrostatic force microscopy to measure surface potential of insulating materials
- A study on intelligent network systems
- A study on multimedia to support human communications
- A study on advanced multi-hop wireless communications
- Subspace model identification methods and their applications
Study on the radiation hardness of GaN and ZnO
Wide bandgap semiconductors GaN and ZnO are expected to have high degrees of radiation hardness due to their large displacement threshold energies of constituent atoms. We studied the effects of high-energy proton irradiation on GaN and ZnO bulk crystals by comparing with those of GaAs and InP ones.
Figure 1 shows the change of the electrical resistance normalized to the pre-irradiation value with the increase of 8MeV proton fluence. It is clearly understood that the ZnO bulk crystal has the most excellent radiation hardness suitable for such advanced device applications under high radiation exposure as the electronics in space satellites.
Development of ZnO-based biomedical sensors
Biomedical sensors to detect various human health markers from a small droplet of blood are developed. Our sensors consist of a polycrystalline ZnO-based field-effect transistor (FET) on a glass substrate. ZnO has many advantages such as capability of low-temperature synthesis, low toxicity to the human body, and transparency.
Figure 1 shows a schematic diagram of the device structure. The basic device for these biomedical sensors is the ion-sensitive FET shown at the uppermost of the figure. When enzyme (or IgG-aptamer) is immobilized on the gate surface, the device operates as a glucose (or IgG immune) sensor as shown in Figs. 2. Due to the fast response time with a wide detection range of the target concentrations, these FET-type sensors are promising for the application to next-generation health care chips.
A study on the evaluation of the optical properties in transparent ceramics and its laser applications
For transparent ceramic laser gain media, unlike single-crystalline materials, structural control in the macro-, micro-, and nano meter-scale is an important factor that can increase their applicability to a wide variety of lasers. For instance, even with a small gain transparent ceramic medium, high-power laser light can be generated by tuning the structure. To fully exploit ceramic media characteristics, we study the structural dependencies of transparent ceramics for laser applications by evaluating optical properties such as spectral line width, wavelength, and quantum efficiency, as well as thermo-mechanical properties and host/dopant combinations. In addition, we fabricate our own original media that incorporates various structures, and are developing novel techniques to apply these exciting materials for the creation of novel ceramic lasers.
A study of electrostatic force microscopy to measure surface potential of insulating materials
Scanning electron microscopy (SEM) is an indispensable instrument used in current nanotechnologies. However, almost all SEM specimens to be observed are insulators, and the charging phenomenon by the electron beam (EB) irradiation is a serious problem. In our research, using a proprietary electrostatic force microscopy (EFM) that we developed, the surface potential distribution is measured on the irradiated area. The surface potential distribution obtained is shown in the figure as a function of lateral distance from the center of EB position for two working distances (WD). The accelerating voltage of EB is 30 kV, the current is 1 nA, and the bias to the specimen is 0 or +200 V. If the bias is +200 V, electrons flying outward the surface with less than 200 eV are attracted by the field and negative potential distribution is formed at the specimen. The characteristic variations reveal spatial and energy distribution of electrons above the surface.
A study on intelligent network systems
Our lives have become more convenient over the past few years, thanks to various wireless communication systems, but the system itself has become increasingly complex. As a result, most current wireless services are anything but "user-friendly." To help remedy this situation, we are investigating an "intellectual network," a kind of system that has its own "intelligence" and can therefore better adapt to user demands, providing smart and automatic configuration for a more pleasing user experience.
Research theme 1: Radio-on-Fiber technology can transmit radio signals through an optical fiber while preserving formats, and is widely used in areas where radio signals cannot easily reach. Our research explores the technology of combining wireless service with a CATV network, to provide wireless services for areas in the so-called digital divide, where reception of radio signals is problematic.
Research theme 2: An ad-hoc network can form a network using only wireless terminals, and can be robust against the effects of various disasters. However, such networks often have problems in stability and the maintenance of adequate data rates. Our research into routing protocols and control methods aims to solve these problems.
A study on multimedia to support human communications
We study computer information processing technology to discover new ways to help people communicate. Our goal is to make modern human communication secure, easy and fun.
For example, in our research on "An attendance identification system using cellular phones," we studied and developed secure identification systems that professors and students can use to register attendance instantly, thus saving time. Another fascinating area of research is "3D image creation from 2D images," in which we explore new algorithms and mathematical models that can extract 3D coordinates of objects from two or more 2D photos or images. The picture here shows a 3D acoustic system, which we built for an experimental project that explored a variety of 3D acoustic systems. The goal of this research project was to develop a 3D acoustic system that can generate a realistic 3D acoustic field that surrounds an audience.
Our "Study of distributed virtual environments using client-server models" explored virtual worlds, objects, and avatars that enable people around the world to communicate with each other, to make friends and share experiences more easily, using the internet through PCs and cell phones.
A study on advanced multi-hop wireless communications
Multi-hop wireless networks have recently attracted much interest in the wireless communication field. Multi-hop networks offer many advantages in connectivity, robustness, and wide area coverage, so they are especially suitable during emergencies and in areas struck by disasters. We are now pursuing advanced research in this field, to develop state-of-the-art transmission technologies for the next generation of multi-hop wireless networks. The following are but a few of our research themes.
Research theme 1: To improve the transmission efficiency of multi-hop networks, we are studying bi-directional relay technologies using network coding. We have proposed many novel network coding methods and are investigating the effectiveness of the proposed schemes using computer simulations.
Research theme 2: To achieve simultaneously high transmission quality and efficiency for multi-hop networks, we proposed and studied sophisticated bi-directional co-operative relay technologies by combining the technologies of the above research theme with MIMO (multiple-input multiple-output) transmission. We are now doing computer simulations to refine our designs. We also plan to make hardware prototypes of the proposed schemes and carry out hardware transmission experiments.
Subspace model identification methods and their applications
We are engaged in research on control theory and system identification, especially topics that include developing subspace model identification methods for both open- and closed-loop systems, the derivation of online (recursive) algorithms for both open- and closed-loop subspace model identification methods, and their application to the detection of change (or faults). The developed methods and algorithms are used to model real-life systems such as inverted pendulum systems, radio-controlled helicopters, one-dimensional acoustic systems, and other related systems.