Much progress had been made during the last two decades in acoustic and optical methods for measuring charge distributions in dielectrics. A review on this topic is given, which mainly covers the past research activities associated with that at our laboratory. For acoustic methods, we will discuss andoompare the pulsed electroacoustic (PEA) and pressure wave propagation (pwP) methods and present some of the results that enabled us to gain physical insights into the charge dynamics within solid plate samples and coaxial cables. For optical methods, we will discuss the Pockels effect technique that is used for the dynamic measurement of surface charge distributions, and the Kerr effect technique that is developed for measuring electric field distributions within liquid dielectrics.

Acoustic and optical methods for measuring electric charge distributions in dielectrics

Microwave heating has been extensively explored in various fields of materials processing. This technology exhibits unique characteristics including volumetric and selective heating, which eventually lead to many exceptional advantages over conventional processing methods including both energy and cost savings, improved product quality, faster processing and greater eco-friendliness, making microwave heating appropriate for applications in metallurgy. This paper presents a critical review on the use of microwave energy in metallurgy, with emphasis on both fundamentals of microwave heating and recent experimental efforts on extractive metallurgy via pyrometallurgical and/or hydrometallurgical routes. Applications to metallurgical processes for extraction of various metals, including heavy metals (Fe, Ni, Co, Cu, Pb and Zn), light metals (Al and Mg), rare metals (Ti, Mo, W and Re) and precious metals (Au, Ag and Pt), are reviewed and discussed.

Microwave-assisted metallurgy

The real and imaginary parts of the relative complex permittivity (er' and er") were measured in the ranges of X-band frequencies (8.2 to 12.4 GHz) and between 1 and 10 GHz for graphite, carbon black and coal powders at room temperature so as to clarify the relation between the complex permittivities of carbonaceous materials and their characteristics, i.e., graphitization, porosity (i.e., specific surface area) and ash contained in coals. It is found that the complex permittivities increase with increasing crystallite size and specific surface area. It is also found that the dependency of the permittivities on the ash content seems be negligible within the range of the ash content in the present study.

Complex Permittivity of Graphite, Carbon Black and Coal Powders in the Ranges of X-band Frequencies (8.2 to 12.4 GHz) and between 1 and 10 GHz

The human hearing range is from 20 Hz to 20 kHz. However, many animals can hear much higher sound frequencies. Dolphins, especially, have a hearing range up to 300 kHz. To our knowledge, there is no data of a reported wide-band sound frequency earphone to satisfy both humans and animals. Here, we show that graphene earphones, packaged into commercial earphone casings can play sounds ranging from 100 Hz to 50 kHz. By using a one-step laser scribing technology, wafer-scale flexible graphene earphones can be obtained in 25 min. Compared with a normal commercial earphone, the graphene earphone has a wider frequency response (100 Hz to 50 kHz) and a three times lower fluctuation (±10 dB). A nonlinear effect exists in the graphene-generated sound frequency spectrum. This effect could be explained by the DC bias added to the input sine waves which may induce higher harmonics. Our numerical calculations show that the sound frequency emitted by graphene could reach up to 1 MHz. In addition, we have demonstrated that a dog wearing a graphene earphone could also be trained and controlled by 35 kHz sound waves. Our results show that graphene could be widely used to produce earphones for both humans and animals.

Graphene earphones: entertainment for both humans and animals.

The use of tablet PCs is spreading rapidly, and accordingly users browsing and inputting personal information in public spaces can often be seen by third parties. Unlike conventional mobile phones and notebook PCs equipped with distinct input devices (e.g., keyboards), tablet PCs have touchscreen keyboards for data input. Such integration of display and input device increases the potential for harm when the display is captured by malicious attackers. This paper presents the description of reconstructing tablet PC displays via measurement of electromagnetic (EM) emanation. In conventional studies, such EM display capture has been achieved by using non-portable setups. Those studies also assumed that a large amount of time was available in advance of capture to obtain the electrical parameters of the target display. In contrast, this paper demonstrates that such EM display capture is feasible in real time by a setup that fits in an attache case. The screen image reconstruction is achieved by performing a prior course profiling and a complemental signal processing instead of the conventional fine parameter tuning. Such complemental processing can eliminate the differences of leakage parameters among individuals and therefore correct the distortions of images. The attack distance, 2 m, makes this method a practical threat to general tablet PCs in public places. This paper discusses possible attack scenarios based on the setup described above. In addition, we describe a mechanism of EM emanation from tablet PCs and a countermeasure against such EM display capture.

https://dl.acm.org/doi/pdf/10.1145/2660267.2660292

A Threat for Tablet PCs in Public Space: Remote Visualization of Screen Images Using EM Emanation

The real and imaginary parts of relative complex permittivity (e′ and e″) and relative complex permeability (μ′ and μ″) were measured for powder and bulk SiO2 and Fe3O4 in the frequency range of 200 MHz–13.5 GHz. The e′ and e″ values of SiO2 powder samples are in good agreement with the previous data. The e′ values of powder SiO2 and Fe3O4 samples with the relative density below 1 are smaller than the values estimated using the linear relation between e′ and the relative density, and larger than those estimated using the Lichtenecker's logarithm mixed law. The μ″ values of powder Fe3O4 samples show the peaks in the frequency range of 706 MHz to 3.21 GHz. The frequency at the peak of the μ″ vs. frequency curve decreases with an increase in the particle size of Fe3O4 sample. All the powder samples with an identical relative density have almost the same μ″ values around 2 to 3 GHz irrespective of the particle size. Above ca. 3 GHz, the μ″ values of all samples become smaller as the measurement frequencies become higher. These results suggest that 2.45 GHz, the frequency of the most commercially prevailing microwave generators, may be the most suitable one for microwave heating of iron ores.

/pdf/complex-permittivity-and-permeability-of-sio2-and-fe3o4-4bi3retqcg.pdf

Complex Permittivity and Permeability of SiO2 and Fe3O4 Powders in Microwave Frequency Range between 0.2 and 13.5 GHz

We measured leaked electromagnetic radiation that came from a laser printer. Using the measured data, we were able to easily reconstruct the printed image. To avoid unwanted monitoring, we have to prevent the printed image data from being reconstructed. In this paper, we first measured the magnetic field at a near field point and then reconstructed the image. Then, using the Sommerfeld integration model, we calculated the magnetic field shielding required to reduce the emitted radiation to a level where the image could not be constructed. From the calculation results, we found that we can easily attenuate the electromagnetic wave by using a thin shielding sheet and we can not remake the image if the distance from the noise source to observation point is more than 30 mm.

Feasibility study for reconstruction of information from near field observations of the magnetic field of laser printer

Various chemical reactions occur simultaneously in barrels during the fermentation processes of alcoholic beverages. Chemical analyses are employed to monitor the change in chemical components, such as glucose and ethyl alcohol. The tests are carried out with extracted specimens, are costly and require time. We have developed a permittivity measurement system for liquid specimens in the frequency range from 2.6 to 50 GHz, and applied the system to fermentation monitoring. Experimental results proved that the observed change in complex permittivity suggests a decrease in the amount of glucose and an increase in alcohol content, which are the key chemical components during the fermentation process.

http://iopscience.iop.org/article/10.1088/0022-3727/40/1/S09/pdf

Complex permittivity measurement at millimetre-wave frequencies during the fermentation process of Japanese sake

Two-Dimensional Lock-in Amplifier System: A New Technique for Improving the Depth Resolution in Microscopic Imaging

Coaxial sensors are effective for measurement of dielectric properties of biological tissues Several measurement methods used to derive dielectric properties have been investigated for the measurement with a coaxial sensor at microwave frequencies While the measurement accuracy depends on the method used, there has been insufficient intercomparison of these methods and their model approximation errors On the other hand, we have developed a coaxial sensor for the measurement of complex permittivity at millimeter-wave (MMW) frequencies of up to 100 GHz However, the scarcity of reference data at MMW frequencies makes the validation of the measurement system difficult Thus, it is essential to clarify the model approximation error of the method used in the measurement system, particularly at MMW frequencies This study aims to clarify the model approximation errors of methods for dielectric property measurement using a coaxial sensor at MMW frequencies The model approximation errors were assessed by comparing results obtained by the methods with those based on the theoretical formula of the full-wave modal expression of Maxwell's equations The measurement uncertainty for the theoretical formula was estimated for a standard liquid sample to clarify the contribution of the model approximation errors to the uncertainty Furthermore, the methods were applied to the measurement of porcine tissues at body temperature, and the measurement accuracy and usability for measurement at MMW frequencies are discussed

Atsuhiro Nishikata

Papers

Complex Permittivity and Permeability of SiO2 and Fe3O4 Powders in Microwave Frequency Range between 0.2 and 13.5 GHz

Feasibility study for reconstruction of information from near field observations of the magnetic field of laser printer

Complex permittivity measurement at millimetre-wave frequencies during the fermentation process of Japanese sake

Two-Dimensional Lock-in Amplifier System: A New Technique for Improving the Depth Resolution in Microscopic Imaging

Intercomparison of methods for measurement of dielectric properties of biological tissues with a coaxial sensor at millimeter-wave frequencies.