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A semisolid human-body phantom for simulating the steady-state temperature elevation at the skin surface due to exposure to millimeter waves (MMWs) and quasi-MMWs was developed in this article. The phantom was designed by optimizing the electric constants of a mixed material consisting mainly of water and glycerin. First, the empirical equation of the complex permittivity of the phantom with respect to the composition and frequency was derived from dielectric measurements of phantoms. Then, the phantom composition used to obtain the temperature elevation equivalent to skin exposure were optimized using a computational approach. Here, the phantom composition was optimized at frequencies ranging from 10 to 100 GHz. In addition, we found that a single composition can be used for frequencies from 20 to 100 GHz. This phantom can simulate the temperature elevation due to skin exposure within the variation of the temperature elevation due to the individual differences in human tissue thickness. The developed phantom was validated by thermographic measurement using a horn antenna and an array antenna at 28 and 60 GHz, respectively. The developed phantoms are applicable to the thermal assessment of skin exposure to electromagnetic fields at MMW and quasi-MMW frequencies.

It is known that millimeter waves (MMW) are absorbed by surface tissue such as skin and the cornea. We previously demonstrated that MMW damages the eye by heat accumulation and transfer. To examine the influence of humidity on such damage, we investigated the difference in MMW-induced ocular tissue temperature increase under high (70%) and low (30%) relative humidity. Eyes of pigmented rabbits (Dutch, 11–15-week old) were exposed unilaterally to 40-GHz 200 mW/cm2 MMW for 5 or 30 min at the center of the pupillary area with a spot-focus type lens antenna. Infrared thermography was used to measure corneal surface temperature during exposure. Temperature of corneal stroma and lens nucleus were measured using a fluoroptic thermometer during 0–30-min exposure. To visualize the dynamic change of temperature and its distribution in the anterior chamber, saline containing 0.2% microencapsulated thermochromic liquid crystal (MTLC) was injected into the eye anterior chamber. All three temperature measurements were much higher under high than low humidity at 24 °C room temperature and MTLC results showed the same trend during MMW exposure. These findings indicate that humidity affects MMW-induced ocular temperature elevation. We showed that low humidity during MMW exposure decreased heat accumulation and transfer, whereas high humidity increased the thermal effect. The present data demonstrated that controlling the environmental humidity might have an impact on ocular damage in eyes exposed to MMW.

The dielectric constant of the normal corneal tissue of a rabbit eye was obtained in vitro in the range from approximately 0.1 to 1 THz, and the drying process on the eye surface exposed to high-power terahertz waves was investigated by in vivo reflectance measurement using terahertz time-domain spectroscopy. When the rabbit eye was exposed to terahertz waves at 162 GHz for 6 min with an irradiation power of 360 or 480 mW/cm2, the reflectance temporally increased and then decreased with a temperature increase. Based on multiple-reflection calculation using the dielectric constant and anterior segment optical coherence tomography images, those changes in reflectance were attributed to drying of the tear and epithelium of the cornea, respectively. Furthermore, the drying progressed over a temperature increase of around 5°C under our exposure conditions. These findings suggest that the possibility of eye damage increases with the progress of drying and that the setting of the eye surface conditions can be a cause of disagreement between computational and experimental data of absorbed energy under high-level irradiation because reflectance is related to terahertz wave penetration in the eye tissue. The time-domain spectroscopic measurements were useful for the acquisition of the dielectric constant as well as for the real-time monitoring of the eye conditions during exposure measurement.

Permanent magnet synchronous machines (PMSMs) performance is highly dependent on the Permanent Magnets (PMs) temperature. Knowledge of the PMs temperature is therefore of great importance both for control and monitoring purposes. An increase in the PM temperature during motor operation, decreases PMs magnetic flux strength and consequently the PMSM torque production capability, eventually causing irreversible demagnetization of the PMs; for the case of variable leakage flux PMSMs (VLF- PMSMs), it will affect the variable leakage property of the machine, which will place additional concerns on the machine control. This paper proposes a PM temperature estimation method for VLF-PMSMs from the PM flux linkage. PM flux linkage is obtained from the response of the machine to a small-amplitude, low frequency, square-wave signal (either voltage or current). The signal is injected on top of the fundamental excitation, allowing on-line temperature estimation without interfering with the operation of the machine

The objective of this study was to develop a model of ocular damage induced by 40, 75, and 95 GHz continuous millimeter waves (MMW), thereby allowing assessment of the clinical course of ocular damage resulting from exposure to thermal damage-inducing MMW. This study also examined the dependence of ocular damage on incident power density. Pigmented rabbit eyes were exposed to 40, 75, and 95 GHz MMW from a spot-focus-type lens antenna. Slight ocular damage was observed 10 min after MMW exposure, including reduced cornea thickness and reduced transparency. Diffuse fluorescein staining around the pupillary area indicated corneal epithelial injury. Slit-lamp examination 1 day after MMW exposure revealed a round area of opacity, accompanied by fluorescence staining, in the central pupillary zone. Corneal edema, indicative of corneal stromal damage, peaked 1 day after MMW exposure, with thickness gradually subsiding to normal. Three days after exposure, ocular conditions had almost normalized, though corneal thickness was slightly greater than that before exposure. The 50% probability of ocular damage (DD50) was in the order 40 > 95 ≈ 75 GHz at the same incident power densities.

Use of Millimeter wave (MMW) frequencies in 5G and WiGig wireless devices will increase the public concerns on human safety for electromagnetic fields exposure. Major health effects due to MMW exposure are the local temperature elevation on the skin surface. To evaluate the heating effects caused by wireless devices employing MMW frequencies, it is essential to develop a human-skin equivalent phantom to represent the required surface temperature elevation on a multi-layer skin model.

This study aims to develop an experimental approach to estimate the transmitted power density inside human body for dosimetry study of millimeter wave exposure. We developed a temperature measurement system comprised of a millimeter wave generation apparatus at 60 GHz, a semi-solid glycerin phantom and an infrared camera. Based on this system, an estimation method of transmitted power densities was proposed by analyzing the temporal trend of temperature elevation on phantom surface. The validity of the proposed method was confirmed for the case of using a standard horn, and some results of using multi-element patch array antennas were demonstrated.

Biological tissue has its own complex permittivity. Measurement of the complex permittivity of biological tissue has been conducted in many studies, however it is a macroscopic level study. On the other hand, when evaluating electromagnetic field exposure for the cell scale, data on the complex permittivity for the molecular level is required. The purpose of this study is to establish the scheme to estimate macroscopic complex permittivity of bio-molecules from microscopic molecular simulations. If the complex permittivity is obtained from theoretical simulation, induced electromagnetic fields within biological-cells will be predicted, and it helps to discuss possible effects of electromagnetic field on the biological systems.

The purpose of this study is to develop a novel in vitro millimeter-wave (MMW) applicator for an exposure apparatus that allows high power efficiency with reasonably good homogeneity over a sufficient exposure area, as well as the capability of temperature control in biological samples. The applicator is made of a printed circuit board and has a large and circular (90-mm diameter) exposure area that is fed with MMWs using post-wall waveguide technology. The applicator is designed for the exposure of cells to MMWs at 60 GHz. The proposed applicator has an absorption efficiency of 54%, where the absorption efficiency is defined as the ratio of the total power absorbed in the culture medium to the input power. Its efficiency is higher than those of other apparatuses operating at 60 GHz reported in the literature. Most of the cells (89%) are located within the $\pm {\hbox{5-dB}}$ region relative to the average specific absorption rate, which shows reasonably good homogeneity compared with previously reported literature data. The applicator enables efficient temperature control for in vitro experiments to explore unknown and possible nonthermal effects of MMW exposures.

Measurement of the dielectric properties of ocular tissues up to 110 GHz was performed by the coaxial probe method. A coaxial sensor was fabricated to allow the measurement of small amounts of biological tissues. Four-standard calibration was applied in the dielectric property measurement to obtain more accurate data than that obtained with conventional three-standard calibration, especially at high frequencies. Novel data of the dielectric properties of several ocular tissues are presented and compared with data from the de facto database.

SUMMARY Nowadays, trials to use even higher frequencies are pursued to realize high-speed wireless communications. In order to respond to such a trend, dielectric properties of insulating polymers at high frequencies have to be clarified, although the importance of clarifying low-frequency properties is still very high, especially for use as high-voltage insulators. In this regard, complex permittivity spectra from 10 mHz to 4.0 THz were obtained for various insulating polymers. The spectra obtained in the very wide frequency range are important, because they can be a valuable database and they provide various pieces of important information on dielectric characteristics.

In this study, we present an assessment of human-body exposure to an electromagnetic field at frequencies ranging from 10 GHz to 1 THz. The energy absorption and temperature elevation were assessed by solving boundary value problems of the one-dimensional Maxwell equations and a bioheat equation for a multilayer plane model. Dielectric properties were measured [Formula: see text] at frequencies of up to 1 THz at body temperature. A Monte Carlo simulation was conducted to assess variations of the transmittance into a skin surface and temperature elevation inside a body by considering the variation of the tissue thickness due to individual differences among human bodies. Furthermore, the impact of the dielectric properties of adipose tissue on temperature elevation, for which large discrepancies between our present measurement results and those in past works were observed, was also examined. We found that the dielectric properties of adipose tissue do not impact on temperature elevation at frequencies over 30 GHz. The potential risk of skin burn was discussed on the basis of the temperature elevation in millimeter-wave and terahertz-wave exposure. Furthermore, the consistency of the basic restrictions in the international guidelines set by ICNIRP was discussed.

Computed radiography (CR), which is one of the most useful methods for dental imaging and nondestructive testing, uses a phosphor imaging plate (IP) because it is flexible, reusable, and inexpensive. Conventional IP scanners utilize a galvanometer or a polygon mirror as a scanning device and a photomultiplier as an optical sensor. Microelectromechanical systems (MEMS) technology currently provides silicon-based devices and has the potential to replace such discrete devices and sensors. Using these devices, we constructed an ultra-compact IP scanner. Our extremely compact plate scanner utilizes a module that is composed of a one-dimensional MEMS mirror and a long multi-pixel photon counter (MPPC) that is combined with a specially designed wavelength filter and a rod lens. The MEMS mirror, which is a non-resonant electromagnetic type, is 2.6 mm in diameter with a recommended optical scanning angle up to ±15°. The CR’s wide dynamic range is maintained using a newly developed MPPC. The MPPC is a sort of silicon photomultiplier and is a high-sensitivity photon-counting device. To achieve such a wide dynamic range, we developed a long MPPC that has over 10,000 pixels. For size reduction and high optical efficiency, we set the MPPC close to an IP across the rod lens. To prevent the MPPC from detecting excitation light, which is much more intense than photo-stimulated light, we produced a sharp-cut wavelength filter that has a wide angle (±60°) of tolerance. We evaluated our constructed scanner module through gray chart and resolution chart images.

We developed a millimeter-wave (MMW) exposure system for in vivo experiments for operating frequencies ranging from 24.5 to 95 GHz. The MMWs are localized to the rabbit ocular tissue with a spot-focus lens antenna. The MMW energy absorption and consequent temperature elevation are evaluated by numerical simulation using measured antenna distribution and precisely modeled rabbit ocular data. Results suggest that corneal damage occurs at an incident power density of 300 ${\hbox{mW/cm}}^{2}$ with our exposure system at frequencies from 26.5 to 95 GHz.

This study presents an investigation of human skin exposure to obliquely incident electromagnetic waves at frequencies from 6 GHz to 1 THz. We aim to clarify the relationship between the power density and the skin surface temperature elevation under various exposure conditions. A Monte Carlo simulation was conducted to assess the transmittance and surface temperature elevation considering the variation of skin tissue thickness. For the case of TM wave injection, transmittance increases with increasing incidence angle from the normal incidence because of the Brewster effect. The normal incidence is confirmed as the worst-case exposure condition when the incident power density is defined in an area normal to the propagation direction. In addition, we investigated the power density required to obtain the equivalent temperature elevation over the skin surface. The analysis shows that the incident power density defined in the direction normal to the skin surface may underestimate the temperature elevation when TM waves are incident over the normal incidence up to the maximum transmittance angle. Our results also show that the power density inside the skin surface strongly correlates with the surface temperature elevation but less dependent on the frequency and independent of the oblique incidence angle and polarization. The findings of this study are expected to be valuable for discussing how to use the different definitions of power density based on dosimetric characteristics as measures in safety guidelines to protect humans from excessive temperature elevation by millimeter and submillimeter-wave exposure.

We, the R&D Partnership for Future Power Electronics Technology (FUPET), have reported a forced-air-cooled DC 600 V three-phase AC 400 V inverter built with SiC-JFETs and SiC-SBDs and designed to attain an output power density (OPD) of 40 kW/L with a switching frequency (fSW) of 50 kHz. This paper reports the test results of this inverter attaining an OPD of 40 kW/L in operating a 3-phase motor with fSW = 50 kHz, and an OPD of more than 60 kW/L in operating an equivalent circuit with fSW = 20 kHz by adopting specialized high speed drive circuit boards.

Variable flux permanent magnet synchronous machines (VF-PMSMs) use permanent magnet magnetization as an additional degree-of-freedom to reduce losses based on operating conditions (e.g., at medium to high speeds, losses are reduced by using a lower magnetization). Magnet properties are known to be dependent on temperature; therefore, the magnet temperature effects on magnetization manipulation and maximum torque properties in VF-PMSMs are investigated in this paper with FEA simulations and experiments. Increased magnet temperature changes the available range of attainable magnetization levels and makes demagnetization occur more easily; therefore, a different current angle and magnetization are needed for maximum torque operation. The temperature effects on high speed magnetization manipulation methods, which are needed for driving cycle loss reduction and full power capability, are evaluated with simulation and experiments on a prototype 80 kW traction machine. A closed loop method for magnetization manipulation that mitigates the effect of temperature is proposed.

In this report we describe a rapid and flexible technique for embedding submicrometer-scale polymer structures in the interior of two-dimensional photonic crystals by controlled two-photon induced polymerization. Polymer features were embedded in individual pores with a diameter of 100 nm by controlled photopolymerization under confocal optical microscopy. Spectrum measurements confirm that the photonic stop band limits the light propagation of the emission from the embedded polymer structures.

The dielectric properties of skin layers, which are the epidermis, dermis, and subcutaneous fat, were measured using several measurement systems. Measurements were conducted in vitro from 0.5 GHz to 1 THz. Measurement results indicated good agreement between each measurement system at a tissue temperature of approximately 35 oC.

The absorption spectra of dried porcine dermis were measured under different sample handling conditions in a terahertz band from 0.3 to 12 THz. The spectral shapes and polarization properties depended on the drying and impurity conditions at approximately 3 THz. We inferred that the configuration changes of collagen fibers inside the dermis caused the spectral variations.

Nowadays, trials to use even higher frequencies are pursued to realize high-speed wireless communications. In order to respond to such a trend, dielectric properties of insulating polymers at high frequencies have to be clarified, although the importance of clarifying low-frequency properties is still very high, especially for use as high voltage insulators. In this regard, complex permittivity spectra in an ultrawide frequency range were obtained for various insulating polymers. These spectra are important, because they can be a valuable database that provide important information on dielectric characteristics. Furthermore, by analyzing the temperature dependence of permittivity in a relatively low frequency range, thermal expansion coefficients of polymers were estimated.

Numerous studies have reported the measurements of the dielectric properties of the skin. Clarifying the manner in which the human body interacts with electromagnetic waves is essential for medical research and development, as well as for the safety assessment of electromagnetic wave exposure. The skin comprises several layers: the epidermis, the dermis, and the subcutaneous fat. Each of these skin layers has a different constitution; however, the previous measurements of their dielectric properties were typically conducted on tissue which included all three layers of the skin. This study presents novel dielectric property data for the epidermis and dermis with in vitro measurement at frequencies ranging from 0.5 GHz to 110 GHz. Measured data was compared with literature values; in particular, the findings were compared with Gabriel's widely used data on skin dielectric properties. The experimental results agreed with the data reported by Gabriel for the dermis of up to 20 GHz, which is the upper limit of the range of frequencies at which Gabriel reported measurements. For frequencies of 20-100 GHz, the experimental results indicated larger values than those extrapolated from Gabriel's data using parametric expansion. For frequencies over 20 GHz, the dielectric properties provided by the parametric model tend toward the experimental results for the epidermis with increasing frequency.

The ocular damage caused by MMW exposure is highly depends on the temperature elevation in the anterior part of the ocular tissue with the complicated structure. Especially, aqueous humor in the anterior chamber affects the nature of heat transport under the MMW exposure. In this study, we have originally developed the coupled analysis system on electromagnetic field (EMF) and heat transport (HT) including the fluid convection model. As an example of non-linear HT analysis, distributions of temperature elevation and aqueous humor flow are calculated in the condition of 75GHz, 150mW/cm2 MMW exposure.

We analyzed temperature increase in the post-wall waveguide type millimeter-wave exposure apparatus in vitro. This results show a similar tendency to the experimental results. The cooling effect in a state of natural cooling was 35–55 % by using heat sink as a basic cooling element. It allows the evaluations for non-thermal effects to expose MMWs of higher intensity than conventional exposure apparatus.

It has been demonstrated that millimeter waves (MMW) are absorbed by surface tissue, such as skin or cornea. It was shown in our laboratory that damage from MMW exposure was related to heat accumulation and transport. To study the relationship between relative humidity and ocular damage, we investigated the effect of relative humidity during MMW exposure. The ocular temperatures of rabbits were measured during exposure to 40 GHz MMW (200 mW/cm2). To visualize the dynamic change of temperature and distribution in the anterior chamber, 0.2% microencapsulated thermochromic liquid crystal (MTLC) was injected into the anterior chamber of rabbit eye. We showed that low humidity during exposure decreased heat accumulation and transfer.

The free space method using a pair of lens antennas was modified for the complex permittivity measurement of biological samples from 20 to 110 GHz. Two methodologies were used to obtain the complex permittivities by the free space method, which were based on the reflection and transmission coefficients. The measurement results obtained with the two methodologies were compared with each other. The measured complex permittivities of the biological samples from the free space method were then compared with those measured using the coaxial probe method. Finally, the measurement data were also compared with those from measurement methods developed in past literatures.

In vivo ocular temperatures in rabbits were measured during 40 GHz millimeter-wave exposure (400–100 mW/cm2). To visualize aqueous humor convection, 0.2% microencapsulated thermochromic liquid crystals (MTLCs) were injected into the anterior chambers of rabbit eyes. Exposure to 40 GHz increased corneal, lens and retrobulbar temperature, with aqueous humor convection having an important role in heat transfer from the cornea to the lens. These findings show that dynamic changes in temperature and distribution in the anterior chamber occur in living rabbit eyes during exposure to 40 GHz millimeter-waves.

A numerical dosimetry was performed for a rabbit ocular exposure by 60-GHz millimeter wave in this study. We compared calculated temperature elevation between localized exposure by a lens antenna and uniformed exposure by plane wave. Here, incident power density was normalized against spacial average of incident power over the surface of cornea according to the previous study. The peak incident power density of the lens antenna was 5.3 times higher than that of the plane wave. Therefore, the maximum temperature elevation by the lens antenna exposure was higher than that by the plane wave exposure. Thus, possibility was shown that threshold incident power density for ocular injury with the lens antenna exposure becomes lower than that with the plane wave exposure.

We report a technique for embedding submicrometer-scale polymer defects in the interior of self-organized two-dimensional photonic crystals by controlled two-photon induced polymerization. They demonstrate a rapid and flexible technique for optical fabrication by creating polymer features in registration with a photonic crystal. Polymer features were embedded in individual pores with a diameter of 100 nm by controlled photopolymerization under confocal optical microscopy. Spectrum measurements confirm that the photonic stop band limits the light propagation of the emission from the embedded polymer structures.

In order to investigate changes in ocular temperature in rabbit eyes exposed to different frequencies (18 to 40 GHz) of quasi-millimeter waves, and millimeter waves (MMW). Pigmented rabbits were anesthetized with both general and topical anesthesia, and thermometer probes (0.5 mm in diameter) were inserted into their cornea (stroma), lens (nucleus) and vitreous (center of vitreous). The eyes were exposed unilaterally to 200 mW/cm2 by horn antenna for 3 min at 18, 22 and 26.5 GHz using a K band exposure system or 26.5, 35 and 40 GHz using a Ka band exposure system. Changes in temperature of the cornea, lens and vitreous were measured with a fluoroptic thermometer. Since the ocular temperatures after exposure to 26.5 GHz generated by the K band and Ka band systems were similar, we assumed that experimental data from these 2 exposure systems were comparable. The highest ocular temperature was induced by 40 GHz MMW, followed by 35 GHz. The 26.5 and 22 GHz corneal temperatures were almost the same. The lowest temperature was recorded at 18 GHz. The elevation in ocular temperature in response to exposure to 200 mW/cm2 MMW is dependent on MMW frequency. MMW exposure induced heat is conveyed not only to the cornea but also the crystalline lens.