A sensor network consisting of a number of palm-sized nodes with small electric and magnetic sensors has been proposed to monitor local electromagnetic activities in space plasmas. In the present study, a compact loop antenna system is designed and fabricated for use in sensor nodes that can capture magnetic vector fields from ELF to MF frequencies. The performance of the developed system is shown to be sufficient to allow measurement of the magnetic field activity around artificial structures in addition to intense natural plasma waves in geospace.

We propose a half-swing clocking scheme that allows us to reduce power consumption of clocking circuitry by as much as 75%, because all the clock signal swings are reduced to half of the LSI supply voltage. The new clocking scheme causes quite small speed degradation, because the random logic circuits in the critical path are still supplied by the full supply voltage. We also propose a clock driver which supplies half-swing clock and generates half VDD by itself. We confirmed that the half-swing clocking scheme provided 67% power saving in a test chip fabricated with 0.5 µm CMOS device, ideally 75%, in the clocking circuitry, and that the degradation in speed was only 0.5 ns by circuit simulation. The key to the proposed clocking scheme is the concept that the voltage swing is reduced only for clocking circuitry, but is retained for all other circuits in the chip. This results in significant power reduction with minimal speed degradation.

High level power estimation model is indispensable to optimize architecture and programs in terms of power consumption systematically. This paper describes power analysis results of a general purpose programmable DSP using switch level and cell based power simulation. The analysis results help to know characteristics of the DSP components and to establish a power estimation model. A compensation method for the lack of intra-cell capacitance in a cell based simulation is proposed to improve the simulation accuracy within -20% of error against the measured power. We considered that the error is caused by ignoring short circuit current and is accurate enough for this level of simulation. Through a result of the power breakdown by modules of the DSP obtained by the simulation, it was found that bus power is much less than generally expected (the simulated power is less than 5% of the total), and that the data operation power dominates the chip power (up to 33%) and is strongly data dependent. The reason that the bus power is low is because both of the load capacitance and the activity are low. Some correlation between the number of input signal transitions and the power consumption is found in each of an ALU, register file, and multiplier through further investigation on the data operation modules. The correlation is worthwhile to establish a power estimation model and is eventually useful to optimize a DSP architecture and DSP programs. The importance of power estimation model is demonstrated by showing an example in which we optimize an FIR filter program based upon the analysis results and proposed a direction of architecture optimization.

Radiation properties of magnetic noise from the harness wires of a spacecraft (GEOTAIL) have been studied experimentally and theoretically. A simulation experiment on the noise radiation using a minimum set of subsystems of the spacecraft has shown that the intensity and the directional patterns of the noise radiation from the wires were largely changed by the existence of a conductive plate near the harness wires. The change in the noise characteristics is explained by eddy currents induced in the conductive plate by the signal current flowing in the wires. The eddy currents distributed in the conductive plate were calculated by the Finite Element analysis Method (FEM). The magnetic flux densities calculated from both the source signal current and its induced eddy currents for the wiring configuration of the simulation experiment have shown to be consistent with the values obtained in the experiment. The results in the present study have provided us an important information on a wiring method to diminish noise radiation from harness wires.