This battery-less pressure sensor is an UHF RFID sensor transponder with an integrated proprietary temperature sensor (prototype) that has been designed for healthcare applications such as remote patient monitoring systems and a commercial pressure sensor. The temperature sensor has a very low power consumption and the communication is proprietary too as it is fully integrated in the ASIC. The pressure sensor is a MPL115A1 from Freescale, one of the sensors with lowest power consumption on the market.

The IC and the sensor communicate via the generic SPI connection that our product integrates and the pressure sensor is supplied from the 2.5V output integrated on chip.   

The tag is completed with an appropriate antenna. For this simple prototype, a dipole antenna has been printed on a PCB. The antenna PCB dimensions are 128x20 mm and it is directly matched to the IC impedance.

The full system requires a reader to obtain the ID and the sensor data into a display. We have used the Motorola MC9090R1 commercial UHF RFID reader, which is compliant with the EPC C1G2 standard. In order to prepare it for sensor data reception, we developed a simple software to request data from a specific sensor register. Note that we still use the EPC C1G2 protocol in our RF communication.

Measurements with this system have reported communication distances of up to 2.2 meters in outdoor tests.

Additionally, the IC is prepared for the implementation of external batteries if needed. This is extremely suitable when the power requirements of the selected external sensors are high. This would increase the communication distance up to the system's sensitivity limitation.

You can find technical details on the following table:

For an easy understanding of the system operation, check the following video: