Hiroyasu Ota

M-type ferrite composite as a microwave absorber with wide bandwidth in the GHz range

The electromagnetic wave absorption properties of Ba M-type (BaFe/sub 12-x/(Ti/sub 0.5/Mn/sub 0.5/)/sub x/O/sub 19/) ferrite-epoxy resin composites were investigated. After measuring the complex permittivities of the samples, the regions of complex permeabilities in which the reflection loss (R.L.) becomes less than -20 dB (-20 dB Regions), were calculated. Altering the conditions such as sintering temperature, particle size and the ratio of ferrite powder in the composite samples, resulted in frequency dependencies of permeabilities that agree well with the calculated -20 dB regions, and which lead to an expansion in bandwidth (frequency range (/spl Delta/f) of R.L. <-20 dB). The BaFe/sub 9/(Ti/sub 0.5/Mn/sub 0.5/)/sub 3/O/sub 19/ ferrite-resin composite, which was produced by sintering at 1573 K for 20 h, crushing into powder (150-300 /spl mu/m) and mixing with epoxy resin at a ratio of 70 mass%, exhibited a wide bandwidth (/spl Delta/f=7.2 GHz) from 13.75 GHz to 20.95 GHz. /spl Delta/f values of 1.4-5.4 GHz in the frequency range 6.35-15.65 GHz, were obtained by changing the composition of the BaFe/sub 12-x/(Ti/sub 0.5/Mn/sub 0.5/)/sub x/O/sub 19//epoxy resin composite from x=3.5 to 4.5.

Visualization of Poynting Vectors by Using Electro-Optic Probes for Electromagnetic Fields

We visualized electromagnetic-energy flows by using newly developed electro-optic probes, which cause little interference with the surrounding electromagnetic fields. Amplitudes and phases of all electric- and magnetic-field components were measured near a coupled line and a patch antenna by the probes. The time-varying Poynting vectors near the objects were evaluated with the data and were visualized. The energy flows that are caused by crosstalk of the coupled line and that are radiated from the antenna are presented. This is the first visualization of Poynting vectors that are evaluated with only experimental data in near-field regions.

Optical magnetic field probe with a loop antenna element doubly loaded with electrooptic crystals

We propose a new type of optical probe designed to detect magnetic near-fields with high accuracy up to the gigahertz range. Its probe head consists of a loop antenna element doubly loaded with electrooptic crystals. Using optical technology, it realizes hybrid operation of a conventional double-loaded loop probe and requires no metallic cables or electrical hybrid junction. We examined probe characteristics for magnetic field detection up to 10 GHz. We confirmed that the probe can measure magnetic fields near a microstrip line with high accuracy in the gigahertz range and can suppress influence of electric fields.

Optical magnetic field sensing with a loop antenna element doubly-loaded with electro-optic crystals

We performed magnetic field sensing near a microstrip line with a new type of optical probe. Its probe head consists of a loop antenna element doubly-loaded with electro-optic crystals. It optically realizes operation of a conventional double loaded loop probe and requires no metallic cables or electrical hybrid junction. We examined probe characteristics for magnetic field detection up to 10 GHz. We confirmed that the probe can detect magnetic fields near a microstrip line with high accuracy up to the gigahertz range and can suppress influence of electric fields.

High speed system for measuring electromagnetic field distribution

An optically scanning electromagnetic field probe system consisting of an electro-optic or magneto-optic crystal and a galvano scanner is proposed for high-speed electromagnetic field distribution measurements. We used this technique to measure electromagnetic field distributions near printed circuit boards or ICs to address electromagnetic compatibility problems or in designing electronic devices. With our scanning system, we can measure the electric field intensities of about 40,000 points with an area of 40 x 40 mm in about 3 minutes (4 ms per point) up to 2.7 GHz. We measured the electric near-field distribution above a five-split transmission line using a cadmium telluride (CdTe) electro-optic crystal. The measurement results showed that the spatial resolution of the system was less than 400 μm in the case of a common current with a crystal thickness of 1 mm. The electric near-field distribution above a microstrip line filter was measured using LiNbΟ 3 electro-optic crystal. Changes in the distribution according to the frequency were observed. The experimental results obtained using this system were compared with simulation results obtained using a finite-difference time-domain method. The overall results indicated that the measurement system is capable of accurately measuring electric near-fields. We also discuss the invasiveness of the measurement system, due to the electro-optic crystals, in terms of both the experimental and simulated results.

Optical magnetic field probe working up to 15 GHz using CdTe electrooptic Crystals

This paper presents a new type of optical magnetic field probe designed to detect magnetic near-fields with high accuracy up to 15 GHz. The probe head consists of a loop antenna element and CdTe electrooptic crystals. The probe using CdTe has a resonant frequency higher than that of a previous probe using LiNbO/sub 3/ because CdTe has a dielectric constant lower than that of LiNbO/sub 3/. Through an optical technique, a probe doubly loaded with CdTe can work as a conventional double-loaded loop probe without metallic cables or an electrical hybrid junction. We examined probe characteristics up to 20 GHz. We confirmed that the probe could measure magnetic fields near a microstrip line with high accuracy in the gigahertz range.

Magnetic Near-Field Distribution Measurements above a Patch Antenna by Using an Optical Waveguide Probe

A magnetic field probe consisting of a LiNbO 3 optical waveguide modulator and a loop antenna element was developed to enable accurate measurement of magnetic near-fields in the gigahertz range. The invasiveness of the probe was assessed by using it to measure the magnetic field distribution above a patch antenna operating at 2.49 GHz. The measurements were compared with those obtained using a shielded loop probe. The experimental results obtained using the probe were also compared with simulation results obtained using a finite-difference time-domain (FDTD) method. The overall results indicated that the optical waveguide probe was capable of accurately measuring magnetic near-fields with low disturbance of the measured fields.

EO probe for simultaneous electric and magnetic near-field measurements using LiNbO/sub 3/ with inverted domain

This paper presents a new type of optical probe for simultaneous measurements of electric and magnetic near fields with high accuracy up to the gigahertz range. Its probe head consists of a loop antenna element that is doubly loaded with LiNbO3 electrooptic crystals. Using optical technology, it can work as a conventional double-loaded loop probe without metallic cables and electrical hybrid junction. We examined probe characteristics for electromagnetic field detection up to 20 GHz. We confirmed that the probe can measure electric and magnetic fields simultaneously with a high accuracy in the gigahertz range

Optically scanning electric field probe system

We present an optically scanning electric field probe system designed to provide high-speed measurements of electric field distributions near PCB or LSI chips with high spatial resolution up to the gigahertz range. The optical probe system uses an electro-optic crystal and a scanned laser beam for high-speed measurements. The probe provides measurement speed of 0.1 seconds per point. We examined probe characteristics of frequency response, linearity, minimum detectable field strength, and spatial resolution up to 10 GHz.

Far-Infrared Ferromagnetic Resonance of Magnetic Garnet for High Frequency Electromagnetic Sensor

For the sensor probe of high frequency magnetic field in GHz region, films were prepared by liquid phase epitaxy technique and ferromagnetic resonances were investigated in high frequency region. Magneto-optical (MO) effect of magnetic garnet was utilized for the imaging sensor of the magnetic field distribution. However, for the application to the characterization of high frequency magnetic field in the GHz frequency region, usual MO measurements are difficult to detect the magnetic filed as the decreasing of the permeability of magnetic garnet. Magnetic resonance is an effective way to induce magnetic moment and enhance the magnetooptical effect in high frequency region of GHz order. In order to understand the possibility of magnetic field sensor of high frequency in detail, far-infrared magnetic resonances were measured at the high frequencies up to 315 GHz in pulsed high magnetic field. Taking account into sensitivity of MO signals and magnetic resonance intensities, magnetooptical method using a garnet film is effective at the frequencies below 100 GHz.