Hiroki Wakatsuchi

Hiroki Wakatsuchi
Nagoya Institute of Technology · Center for Fostering Young and Innovative Researchers

About

44
Publications
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630
Citations

Publications

Publications (44)
Article
Full-text available
Anisotropic impedance surfaces have been used to control surface wave propagation, which has benefited applications across a variety of fields including radio-frequency (RF) and optical devices, sensing, electromagnetic compatibility, wireless power transfer, and communications. However, the responses of these surfaces are fixed once they are fabri...
Preprint
Full-text available
This Roadmap takes the reader on a journey through the research in electromagnetic wave propagation control via reconfigurable intelligent surfaces. Meta-surface modelling and design methods are reviewed along with physical realisation techniques. Several wireless applications are discussed, including beam-forming, focusing, imaging, localisation,...
Article
In recent years, metasurfaces composed of lumped circuit components, including nonlinear Schottky diodes, have been reported to be capable of sensing particular electromagnetic waves even at the same frequency depending on their waveforms, or more specifically, their pulse widths. In this study, analogous waveform‐selective phenomena using only lin...
Article
Full-text available
We numerically demonstrate two types of metasurface absorbers to efficiently absorb digital signals. First, we show that the digital waveforms used in this study contain not only a fundamental wave but also nonnegligible harmonic waves, which limits the absorption performance of a conventional metasurface absorber operating in only a single, finite...
Preprint
In recent years, metasurfaces composed of lumped circuit components, including nonlinear Schottky diodes, have been reported to be capable of sensing particular electromagnetic waves even at the same frequency depending on their waveforms, or more specifically, their pulse widths. In this study, we report analogous waveform-selective phenomena usin...
Preprint
We numerically demonstrate two types of metasurface absorbers to efficiently absorb digital signals. First, we show that the digital waveforms used in this study contain not only a fundamental wave but also nonnegligible harmonic waves, which limits the absorption performance of a conventional metasurface absorber operating in only a single, finite...
Article
Full-text available
We numerically demonstrate a new type of waveform-selective metasurface that senses the difference in incoming waveforms or pulse widths at the same frequency. Importantly, the proposed structure contains precise rectifier circuits that, compared to ordinary schottky diodes used within old types of structures, rectify induced electric charges at a...
Preprint
We numerically demonstrate a new type of waveform-selective metasurface that senses the difference in incoming waveforms or pulse widths at the same frequency. Importantly, the proposed structure contains precise rectifier circuits that, compared to ordinary schottky diodes used within old types of structures, rectify induced electric charges at a...
Preprint
In this study, we demonstrate simplified equivalent circuit models to effectively approximate responses of recently reported waveform-selective metasurfaces that distinguish different electromagnetic waves even at the same frequency depending on their waveforms or pulse widths. Compared to conventional equivalent circuit models that represent behav...
Preprint
Full-text available
We report a waveform-selective metasurface that operates at 2.4 GHz band, i.e. one of ISM (Industrial, Scientific and Medical) bands. This structure gives us an additional degree of freedom to control electromagnetic waves and absorbs a particular waveform or pulse width of an incident wave at the same frequency band, while transmitting others. Thi...
Article
Full-text available
In this study, we demonstrate simplified equivalent circuit models to effectively approximate responses of recently reported waveform-selective metasurfaces that distinguish different electromagnetic waves even at the same frequency depending on their waveforms or pulse widths. Compared to conventional equivalent circuit models that represent behav...
Article
Full-text available
The role of frequency is very important in electromagnetics since it may significantly change how a material interacts with an incident wave if the frequency spectrum varies. Here, a new kind of microwave window is demonstrated that has the unique property of controlling transmission and reflection based on not only the frequency of an incoming wav...
Article
The authors demonstrate two types of non-reciprocal waveform-selective metasurfaces that control the level of reflectance, depending not only on the direction of the incident wave but also on the waveform, namely, on the pulse width. A capacitor-based waveform-selective metasurface exhibits strong reflectance for a short pulse compared to that for...
Article
Full-text available
We demonstrate a series of nonlinear, active, and tunable metasurfaces for a variety of electromagnetic applications. The metasurfaces have achieved a range of exotic properties by populating nonlinear or active circuit components on a periodically patterned metallic surface. The circuit components such as diodes, varactors, transistors, and other...
Article
Full-text available
Conventional materials vary their electromagnetic properties in response to the frequency of an incoming wave, but these responses generally remain unchanged at the same frequency unless nonlinearity is involved. Waveform-selective metasurfaces, recently developed by integrating several circuit elements with planar subwavelength periodic structures...
Article
We demonstrate a concept of a nonlinear metamaterial that provides power dependent absorption of incident surface waves. The metasurface includes nonlinear circuits which transform it from a low loss to high loss state when illuminated with high power waves. The proposed surface allows low power signals to propagate but strongly absorbs high power...
Article
Full-text available
Absorbers play an important role in protecting sensitive electronic devices from electromagnetic interference by absorbing the energy of incoming waves and reducing unnecessary reflection or transmission. In this paper we introduce new types of absorbers based on periodic structures, or the so-called metamaterials, which give us additional degrees...
Article
Full-text available
In general electromagnetic response of each material to a continuous wave does not vary in time domain if the frequency component remains the same. Recently, it turned out that integrating several circuit elements including schottky diodes with periodically metallised surfaces, or the so-called metasurfaces, leads to selectively absorbing specific...
Article
Full-text available
We present the design and experimental demonstration of a programmable subwavelength coil array, which can manipulate the evanescent magnetic field leading to a precisely controlled electric-field pattern at an image plane in the near-field zone. A synthesis methodology is outlined for 2-D near-field manipulations. Simulation based on a full-wave e...
Article
Waveform-selective metasurfaces, reported by Wakatsuchi et al. in 2014, have enabled us to distinguish different surface waves even at the same frequency in accordance with their waveforms or pulse widths. In this study we demonstrate that such new characteristics are applicable to controlling not only surface waves but also free-space waves normal...
Article
Full-text available
We demonstrate numerical simulations of recently reported waveform-selective metasurfaces by developing a new electromagnetic (EM) simulation method based on the Transmission Line Modeling (TLM) method. As opposed to a conventional method integrating an EM simulator with a circuit simulator, this simulation method allows us to fully visualize elect...
Article
Full-text available
Electromagnetic properties depend on the composition of materials, i.e. either angstrom scales of molecules or, for metamaterials, subwavelength periodic structures. Each material behaves differently in accordance with the frequency of an incoming electromagnetic wave due to the frequency dispersion or the resonance of the periodic structures. This...
Conference Paper
We present a new concept of metasurfaces that vary the electromagnetic responses depending not only on the frequency of an incoming surface wave but also on the waveform. Such waveform selectivity is achieved by integrating the rectification of schottky diodes with time domain responses of capacitors and inductors. This new characteristic enables u...
Article
Full-text available
We present the first use of a waveform-dependent absorbing metasurface for high-power pulsed surface currents. The new type of nonlinear metasurface, composed of circuit elements including diodes, is capable of storing high-power pulse energy to dissipate it between pulses, while allowing propagation of small signals. Interestingly, the absorbing p...
Article
Full-text available
The absorbing performance of a nonlinear waveform-dependent metasurface with pulsed signals is demonstrated. The metasurface is a periodic structure containing diodes, capacitors and resistors. These enable us to first rectify a high-power incoming signal to a static field, then store the energy during the illumination and dissipate it before the n...
Conference Paper
Full-text available
Surface currents due to high power microwaves can damage or interfere with sensitive antennas and electronic devices. Absorbers tend to be thick and heavy, and reactive coatings such as high impedance surfaces alter the scattering properties of a surface, thereby affecting the radiation pattern of nearly antennas. In this paper, a novel metamateria...
Article
Full-text available
We demonstrate a concept of circuit-based nonlinear metasurface absorbers that absorb high power surface currents but not small signals. The nonlinear absorbing behavior is achieved through the use of diodes integrated into the metasurface. The diodes rectify high power signals to produce a static field, whose energy is stored in capacitors and the...
Article
Full-text available
Performance of customizable cut-wire-based (CW-based) metamaterial absorbers is studied both numerically and experimentally. In the first part of the paper the fundamental absorbing performance of the CW-based metamaterial absorbers is numerically investigated. In this paper two simple geometrical modifications are proposed to easily enhance the ab...
Article
Full-text available
Most of fundamental biological tissues and organs, such as skin, muscle, and brain, are wet and solid. Water evaporation on the sample surfaces generally deteriorates the measurement of complex permittivities, especially in quasi-millimeter wave and millimeter wave bands. This letter, therefore, introduces a new sample preparation procedure for avo...
Article
Full-text available
Effective equivalent circuits are used for the prediction of resonant and absorbing behavior of cut-wire-based (CW-based) metamaterials. Firstly, an equivalent circuit applicable to electric resonance frequencies of single CW metamaterial arrays is considered. Secondly, the equivalent circuit is extended for prediction of magnetic resonance frequen...
Article
In this thesis computational studies on electromagnetic properties of metamaterials and applications are introduced. The studies include an introduction to the time-domain transmission line modelling (TLM) method and the fundamental scattering properties of metamaterials. The first major objective of the thesis is directed to predicting the resonan...
Article
Full-text available
We numerically show how multiple band scattering parameters for arbitrary polarization can be easily designed by using cut-wire-based (CW-based) metamaterials, which enable us to control six fundamental scattering properties, i.e., reflection, transmission, absorption, and polarization independence, dependence and change. The structure shown here i...
Conference Paper
Full-text available
In this paper, a practical and simple approach for the damping of enclosure resonances using antenna elements is described. The efficiency of the proposed damping strategy is investigated using measurements and simulations of the shielding effectiveness of a rectangular enclosure. Dipole and loop antennas having lumped and distributed resistive loa...
Article
Full-text available
This paper shows that customised broadband absorption of electromagnetic waves having arbitrary polarisation is possible by use of lossy cut-wire (CW) metamaterials. These useful features are confirmed by numerical simulations in which different lengths of CW pairs are combined as one periodic metamaterial unit and placed near to a perfect electric...
Article
Full-text available
This paper demonstrates an efficient modelling method for artificial materials using digital filtering (DF) techniques. To demonstrate the efficiency of the DF technique it is applied to an electromagnetic bandgap (EBG) structure and a capacitively-loaded loop the so-called, CLL-based metamaterial. Firstly, this paper describes fine mesh simulation...
Article
Full-text available
We measured the complex permittivities of whole blood and blood plasma in quasi millimeter and millimeter wave bands using a coaxial probe method. The validity of these measurements was confirmed by comparing with those of a different measurement method, i.e., a dielectric tube method. It is shown that the complex permittivities of the blood sample...
Article
The purpose of this research is to present efficient models of novel materials and surfaces based on metamaterials (MTM) and/or electromagnetic band-gap structures (EBG) suitable for large scale simulation in electromagnetic compatibility (EMC) problems. It is shown that the employment of digital filter (DF) techniques provides an efficient means o...

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