Hideo Iizuka

Left-Handed Dipole Antennas and Their Implementations

A new type of dipole antenna using a left-handed transmission line is proposed. The antenna is composed of a transmission line loaded periodically with shunt inductors and series capacitors. The placement of capacitors into one side only of the line leads to currents of different amplitude on the two sides. Because out-of-phase currents have different amplitudes, they do not completely cancel in the far field, and as a result radiate. Numerical investigation of a wire model shows a unique feature of left-handed transmission lines, which is a reduced wavelength with decreasing frequency. Measured results of two antennas are presented. One is a short dipole antenna working at n=-1, based on conventional resonance numbering. The antenna of 0.18 wavelengths in free space has a gain of -3.9 dBi and bandwidth of 1.7% for |S11 |<-10 dB. The other is a meandered dipole antenna working at n=-9. Polarization orthogonal to a right-handed one is achieved by the induced current of |-9| half wavelengths on the meander having 0.77 wavelengths in free space

Rectification of evanescent heat transfer between dielectric-coated and uncoated silicon carbide plates

Here, we show analytically that the thermal rectification via evanescent waves is obtained in the parallel semi-infinite bodies of the dielectric-coated silicon carbide and uncoated silicon carbide. The permittivity and the thickness of the dielectric coating are derived for maximizing the thermal rectification. In the nonequilibrium situation holding temperatures of 500 K for one body and 300 K for the other, either a coating with a high permittivity of 14 and a thickness of 1 nm or a coating with a low permittivity of 2 and a thickness exceeding 10 nm, results in rectifying coefficients of 0.4 to 0.44.

Omnidirectional Loop Antenna With Left-Handed Loading

This letter presents an omnidirectional horizontally polarized planar printed loop-antenna using left-handed CL loading with 50-Omega input impedance. The antenna has a one wavelength circumference and gives an omnidirectional pattern in the plane of the loop, whilst working in an n = 0 mode. In contrast, a conventional right-handed loop, with the same dimensions, has a figure of eight pattern in the plane of the loop. The antenna is compared with other right-handed periodically loading loop antennas and shown to have the best efficiency and is much easier to match. Design details and simulated results are presented. The concept significantly extends the design degrees of freedom for loop antennas.

Experimental investigation of radiative thermal rectifier using vanadium dioxide

Vanadium dioxide (VO2) exhibits a phase-change behavior from the insulating state to the metallic state around 340 K. By using this effect, we experimentally demonstrate a radiative thermal rectifier in the far-field regime with a thin film VO2 deposited on the silicon wafer. A rectification contrast ratio as large as two is accurately obtained by utilizing a one-dimensional steady-state heat flux measurement system. We develop a theoretical model of the thermal rectifier with optical responses of the materials retrieved from the measured mid-infrared reflection spectra, which is cross-checked with experimentally measured heat flux. Furthermore, we tune the operating temperatures by doping the VO2 film with tungsten (W). These results open up prospects in the fields of thermal management and thermal information processing.

Modified H-shaped antenna for automotive digital terrestrial reception

A modified H-shaped antenna is proposed for automotive digital terrestrial reception. The antenna is analyzed by the method of moments. The antenna has the feature that a figure-8 radiation pattern is rotated with increasing frequency. Four symmetrically mounted antennas at the top of the front and rear windows of a car have gain to the sides of the car as well as to the front and rear directions. The VSWR is less than 3 from 470 to 710 MHz since the antenna has three resonant modes. Measurement results for a single prototype antenna agree with the calculation results. The reception system adopts an adaptive array based on the maximal ratio combining (MRC) method. A near omnidirectional pattern was obtained in a plotted pattern of steered beam in the horizontal plane with the mounted prototype antennas.

Parallel-plate submicron gap formed by micromachined low-density pillars for near-field radiative heat transfer

Near-field radiative heat transfer has been a subject of great interest due to the applicability to thermal management and energy conversion. In this letter, a submicron gap between a pair of diced fused quartz substrates is formed by using micromachined low-density pillars to obtain both the parallelism and small parasitic heat conduction. The gap uniformity is validated by the optical interferometry at four corners of the substrates. The heat flux across the gap is measured in a steady-state and is no greater than twice of theoretically predicted radiative heat flux, which indicates that the parasitic heat conduction is suppressed to the level of the radiative heat transfer or less. The heat conduction through the pillars is modeled, and it is found to be limited by the thermal contact resistance between the pillar top and the opposing substrate surface. The methodology to form and evaluate the gap promotes the near-field radiative heat transfer to various applications such as thermal rectification, thermal modulation, and thermophotovoltaics.

Reactively Steered Ring Antenna Array for Automotive Application

A novel type of smart antenna, called a reactively steered ring antenna array (RSRAA), is proposed. The antenna features a conformal configuration with three overlapping one-wavelength ring elements. Directivity can be controlled by changing the values of variable reactance circuits that are embedded in the antenna. The antenna can be mounted on the windshield of an automobile without interfering with the view of the driver. An equivalent model of six dipole elements is derived from the original antenna configuration to enable simple calculation of directivity when a set of reactance values is given. The validity of the proposed equivalent model is confirmed by comparing simulation results calculated by the equivalent model and by the method of moments. Another simulation shows that the conventional reactance domain multiple signal classification algorithm can be applied to the proposed antenna while keeping the estimated direction-of-arrival number equal to the number of reactance circuits. In addition, the characteristics of an RSRAA, which is optimized at 2.4 GHz and is mounted on an automobile, are measured in an anechoic chamber, and directivity control is found to be implemented effectively.

Multilevel radiative thermal memory realized by the hysteretic metal-insulator transition of vanadium dioxide

Thermal information processing is attracting much interest as an analog of electronic computing. We experimentally demonstrated a radiative thermal memory utilizing a phase change material. The hysteretic metal-insulator transition of vanadium dioxide (VO2) allows us to obtain a multilevel memory. We developed a Preisach model to explain the hysteretic radiative heat transfer between a VO2 film and a fused quartz substrate. The transient response of our memory predicted by the Preisach model agrees well with the measured response. Our multilevel thermal memory paves the way for thermal information processing as well as contactless thermal management.

Millimeter-Wave Transition From Waveguide to Two Microstrip Lines Using Rectangular Patch Element

A millimeter-wave transition from a waveguide to two microstrip lines and the design methodology are proposed. A rectangular patch element in a short-terminated waveguide is analyzed by the cavity model of a patch antenna and the dyadic Greens function of the waveguide. The analysis points out that the rectangular patch element has an optimum width for wideband, which only has the function of the broad wall width of the waveguide. The transition also works as a divider. A numerical investigation of a transition having two microstrip lines validates the analytical model in terms of wideband, and indicates that the distance between the two microstrip lines has an optimum length for suppressing higher order modes. A prototype transition exhibits an insertion loss of 0.5 dB from 76 to 77 GHz, and a bandwidth of 6.9% (5.29 GHz) for the reflection coefficient below -15 dB for the waveguide port

Dipole Antenna With Left-Handed Loading

A new small antenna consisting of a dipole with left-handed loading is proposed. The antenna is composed of a ladder network periodic structure of unit cells having series capacitors and shunt inductors. Placing capacitors into one side of the network leads to out of phase currents with different amplitudes that allow strong radiation. The numerical analysis show that the antenna has a length of 0.15 wavelengths in free space, input impedance close to 50 Omega and well-behaved radiation patterns, but that losses in the loading components reduce efficiency to 16%. The antenna is compared with other right-handed periodically loading dipoles and shown to less efficient than inductive loading, but much easier to match