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Sensitivity of the tag of radio frequency identification (RFID) system is one of the most important factors to evaluate the tag performance. The sensitivity is usually degraded when the tags are located very closely or when they are attached on the surface of high dielectric objects because the power transmission ratio between chip and antenna of the tag is decreased due to the impedance mismatching...
A two-dimensional communication sheet is used as a receiving antenna of a smart-shelf system. Radio frequency identification (RFID) is the protocol used in this system to read the tag that includes information of the goods on the smart-shelf system. In this report, the diversity reception where the termination condition is switched between open and short circuits is proposed to improve the diversity...
Invention and development of the Yagi-Uda antenna, and self-complementary antennas in Tohoku University, Japan are described. Analysis methods of large loop antennas is also presented.
A battery-free wireless monitoring system of vibration waveform for rotary motion is proposed. The sensor node is composed of a replicated-mass type piezoelectric generator, a 10 bit resolution ADC, a controller for quadrature phase shift keying (QPSK) data transmission and a cavity-backed slot antennas for the modulated back scattering communications. Consumption power of the sensor node is 60 microwatt...
A novel wireless ECG sensor tag using 2.4 GHz band for an ultra low power consumption and a long reading range is proposed. Consumption power of the proposed ECG sensor tag is 340 μW by using a 2 V battery and 300 sps continuous data transmitting operation. Experimental study of the wireless ECG monitoring system using −20 dBm (10μW) RF output power of tag reader is described, where 4.5 m reading...
A cooling water-wall room is developed and the forward-nulling passive millimeter-wave (PMMW) imaging is performed using developed room. It is shown experimentally that high-quality of PMMW images is obtained by the presence of the cooling water-wall room which works as a nulling source and a shielding wall.
Reflectarray is used as a passive reflector for improving outdoor radio channel in none-line-of-sight (NLOS) environment. The proposed reflectarray is designed with a 58-degree scattering angle and installed on the roof of a high building to eliminate blind spots and enhance MIMO performance. The performance and effectiveness in improvement of the receiving signal noise ratio (SNR) and channel quality...
A design method of reflectarray by the induced electromotive force method is proposed. The effect of oblique incidence from a primary source to a reflectarray element is included in the design process of the reflectarray by the proposed method. The CPU time for design of the reflectarray by the proposed method is small because mutual coupling between reflectarray elements are ignored. The reflectarray...
Numerical analysis of the near-field power transfer for multi-user is performed by using the multi-port scattering parameters. The transfer power efficiency is derived by using the multi-port scattering parameters. Since the multi-port scattering parameters are easily measured by a vector network analyzer and calculated by a full-wave numerical analysis, it is convenient to investigate the relation...
Some research activities on antennas are reviewed from the author's point of view. The academic organizations are described first, and the recent developments of researches on antennas and the relative topics in Japan are briefly described with emphasis on the Japanese contributions to this field.
A novel semi-passive sensor RF-tags using 5 GHz band for a low power consumption and a long reading range are proposed. Multi-subcarrier back scattering communications are employed for the data transmission and the distance measurement of 1 mm resolution over 30 m range. Current requirements of 3 V battery in the distance measurement tag and monitoring tag of sensing data are 30 μA and 600 μA with...
Dipole antenna in the vicinity of dielectric object is analyzed by characteristic basis function method (CBFM). Accuracy of numerical analysis is investigated by using different block division for the antenna and dielectric object. It is shown that all antenna segments should be allocated in the same block for calculating input reactance accurately. In addition, it is demonstrated that polarization...
In order to improve the quality of object recognition characteristics in passive millimeter-wave (PMMW) imaging, a new method to form a null in the direction of human body and objects is proposed. The forward-nulling passive millimeter-wave imaging using a dielectric tube occupied by cooling water placed on focus line of a parabolic cylinder are performed. It is shown experimentally that the contrast...
A planar dual-antenna system (DAS), composed of series-fed microstrip antenna and planar Yagi-Uda antenna, is proposed for blind spots elimination in mobile communication system. The planar DAS is developed as a reflector in a non-line-of-sight (NLOS) environment. Broad-angle scattering and polarization transition can be realized. Equivalent bi-static radar cross section (BRCS) is used to demonstrate...
A 42 × 44-element reflectarray using interdigital gap loading structure element is used as a passive reflector for elimination blindness propagation channel. The proposed reflectarray is designed with a 58-degree scattering angle and fabricated to experimentally investigate the performance and effectiveness in improvement of the receiving signal noise ratio (SNR) and channel quality. It was found...
A concept of modulated scattering antenna array (MSAA) is proposed based on the modulated scattering technique. The antenna array is composed of one regular antenna element and several modulated scattering elements (MSE). The regular antenna has its RF front-end circuit, but the MSA has not. The configuration of the array antenna is very simple because only one branch of the front-end circuit is required...
In mobile communication system, it is a serious problem that radio wave signal from base stations is blocked by the high and dense buildings in a downtown, high-building district, especially in narrow streets, which will result in a weak signal level and poor communication qualities, and this kind of areas are typically called blind spots. Many efforts were made in order to eliminate blind spots which...
A frequency-tunable and switched beam antenna is proposed. Variable capacitances are loaded to monopole antenna elements and switch the radiation beam as well as the frequency band. Numerical results of the frequency band and beam pattern of the proposed antenna are shown with varying the value of variable capacitances.
In order to improve the detection performance of concealed objects in clothes by using the passive millimeter wave imaging technique, a forward-nulling passive millimeter wave (FN-PMMW) imaging method forwarding a null in the direction of human body and objects has been proposed by the authors [1]. The contrast between human body and conducting objects is improved using a developed nulling source...
Method of Moments (MoM) is one of the powerful method for numerical analysis of antennas or scatterers [1]. Recently, many fast MoM for large scale problems has been proposed and various large scattering problems have been analyzed [2], [3]. In general, there is trade-off between the accuracy of solution and CPU time in the fast MoM. Nevertheless, in practice, the pattern of the large scattering problems...
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