Batteryless Temperature Sensor

This batteryless temperature 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. The sensor has a very low power consumption and the communication is proprietary too as it is fully integrated in the ASIC.

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 2.8 meters in outdoor tests. For indoor utilization the environment is critical and depending on the application and environment the communication range can vary significantly.

Additionally, the IC is prepared for the implementation of external batteries if needed. This would increase the communication distance up to the system's sensitivity limitation.

You can find technical details on the following table:

Specification	Data	Units
Frequency	868 – 915	MHz
Standard	EPC C1G2	-
Power consumption	23mA@3V	-
Operating temperature	-40 to 85	°C
RX sensitivity	+20 to -5  (battery-less)	dBm (ASK)
Backscattering phase shift	60	degrees (PSK)
Size (die/core)	2.9x1.9 / 1.6x1.3	mm