Kazuhiro Fujimori

The design of mw-class RF-DC conversion circuit using the full-wave rectification

A Rectifying Antenna (Rectenna) is one of the most important components for a wireless power transmission. It has been developed for many applications such as Space Solar Power System (SSPS), and Radio Frequency Identification (RFID) etc. The Rectenna consisting of RF-DC conversion circuits and receiving antennas needs to be designed for high conversion efficiency to achieve efficient power transmission. In this paper, we try to design the mw-Class RF-DC conversion circuit using full-wave rectification.

Ferroelectric Domain Contribution to the Tunability of Ba0.8Sr0.2TiO3 Ceramics

Polarization contributions to the tunable properties of Ba0.8Sr0.2TiO3 ceramics were quantitatively studied by microwave measurements. The width of the ferroelectric domain walls (90° domain walls) decreased with decreasing average grain size. The variation in domain size with grain size for grains smaller than 10 µm was roughly proportional to the square root of the grain size, consistent with previous reports on BaTiO3. The smaller size of the 90° domains (i.e., higher domain-wall density) resulted in greater tunability at an applied DC electric field of 6.7 kV/cm. The tunability of the specimen with a domain size of 161 nm was 26.5%, which was 4.4 times that of the specimen with a domain size of 259 nm (T = 6.0%). Under a relatively low DC field, the density of the domain-wall motion was the dominant factor determining the overall tunable properties, while the contributions of the ionic and electronic polarizations were relatively small in Ba0.8Sr0.2TiO3.

Efficient design approach of mW-class RF-DC conversion rectenna circuits by FDTD analysis

A rectenna is one of the most important components for a wireless power transmission. It has been developed for many applications such as Space Solar Power System (SSPS), and RFID etc. The rectenna consisting of RF-DC conversion circuits and receiving antennas needs to be designed for high conversion efficiency to achieve efficient power transmission. In this paper, the extended FDTD method is proposed as a method for calculating the RF-DC conversion circuit, and the availability of this method is confirmed. Furthermore, the output power from the circuit including the radiation power is investigated.

Negative Refraction and Energy-Transmission Efficiency of Acoustic Waves in Two-Dimensional Phononic Crystal: Numerical and Experimental Study

The negative refraction of acoustic waves in a two-dimensional phononic-crystal slab is studied by numerical simulation based on the finite-difference time-domain (FDTD) method and by ultrasonic measurement. The incident-angle dependences of energy-transmission efficiency in the simulation and experiment are in good agreement in the frequency range of approximately 1.2 MHz. Using the FDTD method, we optimize the efficiency by varying structural parameters such as filling fraction and slab thickness. The effect of deviation from the ideal crystallinity is also evaluated quantitatively via the simulation. These results indicate that an energetically efficient acoustic lens can be fabricated by carefully optimizing the structure of the phononic crystal.

Quasi-millimeter-wave absorption behavior in Y/Yb-stabilized zirconia ceramics

Broadband dielectric spectra from 10 to 1014 Hz were acquired for 8 mol. % Y2O3/Yb2O3-stabilized zirconia (8YSZ and 8YbSZ) ceramics that related the dipole and ionic polarization losses to the absorption efficiency of electromagnetic irradiation. For 24 GHz irradiation, 8YSZ exhibited a higher absorption efficiency than 8YbSZ, resulting in a higher dielectric loss. The difference in the dielectric loss was interpreted as the difference in the loss of the dipoles originating from the fluctuations in the defect associations (Y′ZrVo¨ and Yb′ZrVo¨).

The Fundamental Design Approach of The RF-DC Conversion Circuit for Optimizing Its Characteristics

A Rectifying Antenna (Rectenna) is one of the most important components for a wireless power transmission. It has been developed for many applications such as Space Solar Power System (SSPS), Radio Frequency IDentification (RF-ID), and electric vehicle etc. The Rectenna consisting of RF-DC conversion circuits and receiving antennas needs to be designed for high conversion efficiency to achieve efficient power transmission. In this paper, we investigated the RF-DC conversion circuits by the theoretical analysis. And, we propose the theoretical formula for calculating the output DC voltage in giving the input voltage. The result that is calculated by the formula agreed with the simulators result, so, we confirmed the validity of the formula we derived. The theory and the formula we derived are useful in order to know the basic operation of the RF-DC conversion circuit, and to design the circuit efficiently.

Design of RF-DC conversion circuit composed of chip devices

In this paper, a radio frequency to direct current (RF-DC) conversion circuit composed of chip devices is proposed. This circuit has high conversion efficiency as high as the previously proposed circuit, and the circuit size does not depend on the operating frequency.

Development of high efficiency rectification circuit for mW-class rectenna

For applications of the microwave power transmission technology, it is necessary to realize high efficiency rectennas or rectification circuits. Especially, RF-IDs or ubiquitous power sources demand high RF-DC conversion efficiency for below mW microwave inputs. However, almost all past rectennas or rectification circuits were designed for over 100mW rectifying and the RF-DC conversion efficiencies were less than 20% at 1mW microwave input. In this paper, we investigate rectification circuits for developing mW-class rectennas. Discussing diode mount structures in order to increase the efficiency below 10mW microwave input, we succeeded in developing a rectification circuit whose efficiency is 62.8% for a 10mW microwave input. We also find that approximately 30% of the input microwave power is consumed by the diode in the rectification circuit.

Complex Conductivity Using Wideband Spectroscopy for Yttria/Ytterbia-Stabilized Zirconia Ceramics

Complex conductivity wideband spectra from 10-1 to 1014 Hz (100 THz) were determined for 8 mol % yttria-stabilized zirconia (8YSZ) and 8 mol % ytterbia-stabilized zirconia (8YbSZ) ceramics. The contributions of electrolyte–electrode interfaces, grain boundaries, intragrain ion-hopping, and optical phonons were quantified to relate the microscopic conduction behavior to the overall conductivity. Intrinsic conductivity was mostly governed by ion-hopping. For both 8YSZ and 8YbSZ, ion-hopping followed the universal dielectric response (UDR) for broadband frequencies except for the phonon dispersion frequencies. The higher overall conductivities of the 8YbSZ ceramics compared to the 8YSZ ones were attributed to differences in the UDR contributions. The dominant factor determining the difference in the intrinsic conductivity in broadband frequencies from direct current (DC) to microwave between the 8YSZ and 8YbSZ ceramics was the DC conductivity due to UDR, σdc, where σdc(8YbSZ)>σdc(8YSZ). Other parameters in the UDR and the optical parameters did not greatly influence the intrinsic conductivities.

Selective electroless plating of 3D-printed plastic structures for three-dimensional microwave metamaterials

A technique of selective electroless plating onto PLA-ABS (Polylactic Acid-Acrylonitrile Butadiene Styrene) composite structures fabricated by three-dimensional (3D) printing is demonstrated to construct 3D microwave metamaterials. The reducing activity of the PLA surface is selectively enhanced by the chemical modification involving Sn2+ in a simple wet process, thereby forming a highly conductive Ag-plated membrane only onto the PLA surface. The fabricated metamaterial composed of Ag-plated PLA and non-plated ABS parts is characterized experimentally and numerically to demonstrate the important bi-anisotropic microwave responses arising from the 3D nature of metallodielectric structures. Our approach based on a simple wet chemical process allows for the creation of highly complex 3D metal-insulator structures, thus paving the way toward the sophisticated microwave applications of the 3D printing technology. Published by AIP Publishing.