Stochastic resonance is a phenomenon where a weak signal is enhanced by adding an adequate amount of noise in a nonlinear system, such as a quartic potential system. In order to detect the high-speed bit rate and the weak signal with high precision, we studied the system parameters for the optimum performance of a quartic potential system using theoretical calculations, numerical analysis, and experimental evaluation. The results show that the response speed is proportional to a positive feedback factor and is inversely proportional to a damping factor. In particular, the results of the experimental evaluation show the effectiveness of increasing the response speed factor, which is defined as the value of the positive feedback factor divided by the damping factor, for improving the signal detection performance for high-speed bit rate (100 kb/s) signals.

We are conducting the advanced development of a sintering Cu paste (with/without pressure type) for use in power devices. For this report, we carried out a power cycle test and its Weibull analysis using sintering Cu as a bonding material and compared the results to the power cycle lives of Sintering Ag and high-lead solder. The characteristic life for sintering Cu without pressure was about 14 times higher than that of high lead solder when the power cycle condition was T _{j max} = 175°C and ΔT _j = 100°C, and about 40 times higher for sintering Cu with pressure. Therefore, the sintering Cu has a superior bonding reliability compared with sintering Ag and high lead solder.

To develop a textile-based wetness detection system that operates without batteries, we created a wetness sensor with an energy storage structure that generates electric power when water comes into contact with electrodes having different redox potentials. Electrodes were prepared by coating a silver current collector layer and an active material layer of silver oxide or zinc on a non-woven fabric and then sewing on a cloth substrate in a comb-like shape using a conductive thread. The output characteristic values of the textile-based sensor were higher than one with the same structure produced by printing on a plastic substrate. A wireless communication IC could be operated by connecting three sensors in series. Thus, we realized a "battery-less textile-based wetness detection system" that can detect a wet fabric, such as, for example, a wet seat.

The relationship between the weld strength, crystallographic texture, and grain size in Al-Al ultrasonic welding was investigated in order to develop a parameter optimization method. The weld strength and cross-sectional microstructure of the welded interface were measured on samples of two aluminum plates which had been welded ultrasonically using various amplitudes and times. For the low strength and interface fracture, the crystallographic texture was simple shear texture components, and the grain size was finer than before welding. On the other hand, for the high strength and upper plate fracture, the crystallographic texture was the same as above, but the grain size was coarser than before welding. The relationship between the strength and the microstructure was hardly affected by the combination of amplitude and time. These results suggest that the welding parameters can be optimized using crystallographic texture and grain size.

The objective of this research is to estimate the length of the grass and the condition of the ground when a robotic lawn mower runs using the Random Forest and Neural Network, and to change the running control according to the ground conditions for efficient lawn mowing. The main robotic lawn mowers currently on the market cannot recognize the length of the grass or the condition of the ground other than the lawn, such as bare soil. Therefore, the robotic lawn mower always rotates its blade at the maximum speed while running randomly over the specified area. In order to mow the lawn efficiently, we propose to estimate the length of the grass and the ground condition using sensors and machine learning, and to control the mower appropriately. In this study, we experimentally show that the system achieves a correct answer rate of more than 90% in estimating the ground conditions.

We investigated a high-performance power module mounting technology with high connection reliability for the purpose of making small power supplies for industrial maintenance-free equipment. In particular, we have developed both water-cooled multilayer ceramic substrates and high-reliability mounting technologies for power devices to realize high-performance and high-power modules for practical use. By forming a Cu circuit pattern on the surface layer of the developed board, the mounted bare chip can be effectively cooled. Furthermore, since the heat dissipation effect of the water cooled multilayer ceramic substrate is high, the temperature rise of the bare chip can be dramatically reduced as compared with the air-cooled method. However, since the temperature fluctuations of the bare chip surface due to power ON/OFF are very fast and large, cracks may develop in the Pb-5Sn solder joint, and the power cycle life may be shortened. Therefore, we investigated the effects of the coefficient of thermal expansion of the clip and solder thickness on the power cycle lifetime in the water cooled multilayer ceramic substrate. By changing the linear expansion coefficient of the clip from 16 ppm/K Cu to 8 ppm/K Cu-Mo, the power cycle life of the module can be extended by more than 4 times relative to that of a module using a Cu clip and 100 μm thick solder even if the thickness is as little as 10 μm. We expect that a reliability of 20 years or more can be achieved with the developed module.

This paper presents a novel method for estimating the wire-liftoff lifetime of wire bonds used in power modules; a mechanical fatigue test using 4-point bending is proposed. The paper describes the system and method of the cyclic 4-point-bending fatigue test. After reviewing the formulae for wire-liftoff lifetime and the methodology for estimating wire-liftoff lifetime in the design phase, we propose a methodology for acquiring a design diagram from the experimental data of the 4-point bending fatigue test. The fatigue lifetime (N_f) can be determined from the 4-point-bending fatigue test, and the inelastic strain range (Δε_in) can be calculated from an inelastic finite element analysis. This design diagram, N_f –Δε_in curve, can then be used to estimate the wire-liftoff lifetime in the design phase. It is also shown that the proposed scheme can be certified using thermal cyclic tests.

The joule heat resulting from the conduction current through a bus bar must be figured in when the bus bar is used as a heat conduction path to dissipate the heat of power devices. This paper verifies the temperature distribution in a bus bar stemming from both the heat conduction and the joule heat.