Conversion efficiency of vibrational energy harvester is defined primarily by the ratio between the mechanical power incoming to the system and the electrical output power. Measuring the output power is straightforward but how is the incoming power measured? Such a physical quantity is known only when the force acting on the power generator is measured by using a force sensor virtually inserted between the vibration source and the energy harvester, which does not look practical. In this article, we look into an analytical model for a vibrational energy harvester or so-called velocity-damped resonant generator (VDRG) and discuss indices alternative to the efficiency of power conversion.

We developed a MEMS ultrasonic array sensor that is capable of detecting 1 MHz airborne ultrasonic waves for use in devices for inspecting the interior of objects. The sensor is an array of vibrating membranes, each consisting of a metal lower electrode, a platinum upper electrode, and a polymer ferroelectric layer between them. In this study, two kinds of electrode materials, aluminum or gold, were used for the lower electrode to investigate how they affect the characteristics of such high resonant-frequency sensors. The sensor using aluminum showed about four times better sensitivity than that using gold.

To develop a visual prosthesis, it is necessary to understand the changes in the electrochemical properties of stimulating electrodes implanted in the body. To evaluate these properties, we examined three types of equivalent circuit models that represented the electrode interface 23 weeks after the stimulation began. The results indicated that the Randles circuit model with Warburg impedance exhibited the difference in the electrochemical properties of the active and inactive electrodes, which might have been caused by the desorption of adsorbed protein from the electrode surface owing to the stimulation current. This model can be used to characterize the changes in the properties of porous stimulating electrodes.

Plant-parasitic nematodes cause the significant damage to agricultural crops all over the world. To establish an environmental-friendly method for managing the plant-parasitic nematodes, understanding the infection process is important. In this paper, we present a new method for analyzing an effect of external stimulation on the infection process of plant-parasitic nematodes, Meloidogyne incognita or root-knot nematode, by using a microfluidic device integrated with micropillar array. We estimated the applied mechanical stresses, which act as the external stimulation, on the gall (or root knot) by using the contact analysis based on finite elemental method. By using the developed analytical system, we clearly observed the growth behavior of the growing roots infected with the plant-parasitic nematodes. The experimental results suggest that the mechanical stress might effectively inhibit the growth of the gall formed by the infection of root-knot nematodes.