Vol.3 No.3 2010
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Research paper : Development of a sensor system for animal watching to keep human health and food safety (T. Itoh et al.)−228−Synthesiology - English edition Vol.3 No.3 (2010) beforehand, even for the Yamaguchi strain where no significant temperature increase could be seen. The activity level can be counted with low power if a generating piezoelectric sensor is used. To realize such a device at a small size and low cost, piezoelectric MEMS technology that combines the MEMS and piezoelectric thin film formation technologies is necessary.As shown in Fig. 6, it is necessary to use the digital MEMS sensor that matches the event-driven type to achieve the ULP node, and also customize the semiconductor elements such as the microcontroller and the radio frequency integrated circuit (RF-IC). As mentioned before, the event-driven node that we developed in this research is a device “where the sensor directly sends out the digital signals, then the node wakes up from the sleep mode and transmits the digital signals wirelessly”. Therefore, the node does not require any high-grade arithmetic processing, and a RF-IC with simple processing function such as a sensor interface and a message writing function is sufficient. Conversely, if one is to install an over-spec universal microcontroller, realization of the chicken node is impossible in terms of power and cost. While the new technological development for semiconductor element technology is not necessary for the introduction of such custom-made RF-IC, there is no example anywhere in the world of RF-IC specialized for event-driven nodes, and it is a key device that must be designed and developed by us on our own. Of course, the increased flexibility of the substrate and downsizing and flexibility of the antenna are also important for practical use.4 Image of the animal watch sensor The specifications of the wireless sensor node scheduled for realization by the end of this research project (end of FY 2011) are as follows.Size/weight of node: substrate (flexible) size 6 × 30 × 0.1 mm3, weight (including batteries) about 1 gAttachment method: Wing bandSensor: digital bimetal thermosensor, digital piezoelectric accelerometer (activity level sensor)Wireless transmission: frequency 315 MHz band (310~320 MHz), modulation GFSK, line-of-sight communication distance of 10 m or moreStandby power consumption: 0.5 W or lessPower source: silver oxide battery (1.55 V)This wireless sensor node transmits data but does not receive. The primary reason is because the reception standby power is large and it cannot fulfill the necessary specs for size and cost, but it is also because the node does not have to receive. The node must be able to receive if there is a need for communication between the nodes or for receiving the re-transmission request in case of a bad reception. For this system, since the frequency of data transmission is once every 30 minutes to 1 hour with short transmitted messages of 10 bits or less, there is hardly any chance of collision of the transmission signals even if there are over 10,000 nodes. However, in the event-driven system, high communication reliability is demanded because one data transmission is extremely important. In this research, the basic concept is to employ an advanced receiver in order to simplify the node system that is subjected to harsh boundary conditions.With this way of thinking, we employed and are developing the direct conversion method as the reception method of this research. This method is also called the software-defined radio, where the frequency spectrum in the range 310~320 MHz as discussed above is received, stored on the memory, and then analyzed to read the message. We are developing the receiver system by fabricating the prototype of the simultaneous multi-channel receiver. Using this method, it will be possible to identify the nodes by frequency and transmission data rate, and Fig. 4 Digital bimetal thermosensorFig. 5 Digital piezoelectric accelerometer BimetaldigitalthermosensorHigh temperatureBimetal cantileverASICGNDPower supply control signal to condenserPower supply control signal to condenserPower supply control signal to condenserSRAMRESETOUTSETF/FVCCVCCGNDSRAMRESETOUTSETF/FVCCGNDControllerSRAMRESETOUTSETF/FGNDMedium temperatureLow temperatureControllerController Piezoelectricthin filmDigital piezoelectric accelerometerHigh Acc.Mid. Acc.Low Acc.F/FMPUSRAMRESETOUTASICMOS‐Tr will be usedEndRecord Time IntervalStart> 0.8 G> 0.6 G> 0.4 GTimeTimeHiLoTimeSETMassHiLoHiLoF/FMPUSRAMRESETOUTSETF/FMPUSRAMRESETOUTSET

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