Masato Nakayama

Thermal Behavior of Small Nickel/Metal Hydride Battery during Rapid Charge and Discharge Cycles

To improve a nickel/metal hydride (Ni/MH) batterys rapid charge/discharge performance and enlarge it, a precise understanding of the thermal behavior is required. This report examines numerically and experimentally the thermal behavior of the Ni/MH cell during rapid charge and discharge cycles by considering entropy changes for electrochemical reactions, the exothermic reaction for hydrogen adsorption as MH, the exothermic heat from the side reaction, the heat generation by overpotential, and the heat transfer to ambient air. The overpotential resistance and the current efficiency, the ratio of main reaction current to charge current, have been measured during rapid charge and discharge cycles with constant current. Our proposed model works well to estimate the cell temperatures during charge and discharge cycles not only at smaller currents than the rated one, but also at rapid charge (∼2C) and discharge (∼3C) currents.

Cell Impedance Measurement by Laplace Transformation of Charge or Discharge Current–Voltage

In our previous study overpotential resistances of nickel/metal-hydride and lithium-ion batteries were measured to estimate the battery temperature rises during rapid charge and discharge cycles by using our battery thermal model. However, the cell impedance Z(ω) measured by ac impedance meter did not agree with those induced by charge/discharge characteristics. Therefore, Z(ω) values were again measured by the method of Takano et al. [J. Electrochem. Soc., 147, 922 (2000)], who measured Z(ω) of lithium-ion batteries by Laplace transformation of both signals of the voltage-step input and its current response. This method has been extended here to Laplace transformation of current-step or current-pulse input and its voltage response to measure Z(ω) for any charge/discharge current of nickel/metal-hydride or lithium-ion battery. Nearly the same Z(ω) was obtained by the three different methods (voltage-step, current-step, and current-pulse inputs), and the measured Z(w) did not depend on either the charge/discharge current or the state of charge/charge input. Moreover, the Z(ω) measured by the current-pulse method, which includes the Warburg impedance at low frequency, approaches the overpotential resistance that can provide a good estimate of the battery temoerature rise in our batterv thermal model.

Robust acoustic distance measurement method based on interference in noisy environments

Distance to target is fundamental and very important information in many engineering fields. Many distance measurement methods with sound utilize the time delay of reflected wave which is measured with reference to transmitted one. This method, however, can not measure short distance because the transmitted wave, which has not attenuated enough as of reception of reflected waves, suppresses the reflected waves for short distance. Therefore we proposed acoustic distance measurement method based on interference between transmitted wave and reflected waves, which could measure distance in short range. However, the performance of our method was not discussed in noisy environments. In this paper, we focus discussion on noisy environments with additive noise. We describe our method using real measuring system in noisy environments. In addition, we propose suitable noise reduction for our method by applying an idea of synchronous addition and spectral subtraction in noisy environments. Finally, we confirm the effectiveness of our method using noise reduction through simulation and experiment. As a result, it has been confirmed that the distance can be measured at SNR = 5 or 15 dB by our method without using noise reduction and can be measured at SNR = −5 to 5 dB by our method using noise reduction.

Near Field Sound Source Localization based on Time Delay and Subspace Separation

We study near-field sound source localization, f or which two-dimensional multiple signal classification (2DMUSIC) has already been developed. However, this method requires a lot of elapsed time because it processes in each frequency. A localization method based on crosspower spectrum phase analysis (CSP) in the near field has also been developed. However, its localization accuracy is degraded by noise sources and reverberations. To overcome these problems, we propose a new localization method based on time delay and subspace methods. Experimental results of an evaluation experiment carried out in a conference room demonstrate that the method improves localization accuracy with less elapsed time in a diffused noise environment.

Thermal Behavior of Small Nickel/Metal Hydride Battery during Rapid Charge and Discharge Cycle

In this report the thermal behavior of small Ni/MH battery during rapid charge and discharge cycles has been studied numerically and experimentally. In our previous report, the calculated cell temperature agrees well with the measured below the 1C charge/discharge cycles, but the calculated is larger than the measured above the 1C charge/discharge cycles. Then we have re-measured the cell heat capacity and the cell heat transfer coefficient. By using these data at our thermal model, the calculated cell temperature agrees well with the measured temperature until the 3C charge/discharge cycles.