by Gustavo C. Martins
Sensor networks are used in many application areas, such as biomedical sensors, predictive maintenance and RFID tags, which generally needs a long lifetime and small sizes . For these systems emerges the necessity to develop energy harvesting integrated circuits. With no batteries we can develop sensors that has a longer lifetime, are smaller and, possibly, cheaper.
This project consists in a temperature sensor tag powered by an RF signal emitted by a reader. The readerreceives the reflected signal from the tag, which contains information on the temperature measured. The Figure 1 shows a block diagram of the system containing the blocks to be implemented.
The blocks are listed below:
- Impedance Matching: matches the input impedance of the rectifier to the antenna impedance. It assures the maximum power is transmitted to the rectifier ;
- Rectifier (RF-DC): converts a high frequency AC signal to DC ;
- Voltage Limiter: limits the output voltage of the rectifier, so that it remains in a safe level ;
- Voltage Regulator: regulates the voltage that will be used to power the sensor. This voltage isn’t dependent of temperature ;
- Oscillator: is the temperature sensing element. The output signal frequency varies with temperature ;
- Backscattering modulation: modulates the reflected signal by modulating the input impedance .
 R. Vullers, R. Schaijk, H. Visser, J. Penders, and C. Hoof, “Energy Harvesting for Autonomous Wireless Sensor Networks,” IEEE Solid-State Circuits Magazine, vol. 2, no. 2, pp. 29-38, 2010.
 J. W. M. Rogers and C. Plett, Radio Frequency Integrated Circuit Design. Artech House Publishers, 2010, p. 513.
 A. J. Cardoso, L. G. de Carli, C. Galup-Montoro, and M. C. Schneider, “Analysis of the Rectifier Circuit Valid Down to Its Low-Voltage Limit,” IEEE Transactions on Circuits and Systems I: Regular Papers, vol. 59, no. 1, pp. 106-112, 2011.
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