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Battery-free temp sensors based on RFID tags

Posted: 28 Jun 2013 ?? ?Print Version ?Bookmark and Share

Keywords:RFID? UHF? sensor? Fenix2? EPC C1G2?

On the sensor side, sensing products and technologies are rewriting future designs in an extensive range of industrial, medical, consumer, communications and automotive applications. The operational specifications of the sensors are quite different depending on the manufacturer, the magnitude to be measured and the final application of the sensor. So, different modes of acquiring and forwarding the data are developed.

Several data-rate options
Periodic sampling can be used for processes that need to be monitored constantly, where power cannot be reduced. If the number of bits transmitted per second is low, the power consumption is also low. Hence the sampling rate is directly correlated to the average power consumption. Implementing a variable data rate, the average power consumption of many sensors can be reduced. From a power consumption point-of-view, one has to look at the average current including the maximum current peak during measurement (or conversion time), instead of simply the quiescent current. The peak current directly shakes the voltage supply and external capacitors must be added to reduce the voltage drop.

The main advantage of the battery-less temperature sensor lies on the possibility of using the sensor without batteries at all. This feature allows for a wide range of opportunities using temperature sensors in applications where the accessibility is restricted, or where the use of batteries is not recommended. Since batteries are not needed, the sensor tags need not to worry about autonomy.

Typical applications for these battery-less temperature sensors are temperature sensitive assets and processes. Each tag has a unique ID and a temperature sensor that is uniquely associated to that ID. It makes the Fenix2 a perfect solution for applications such as cold chain monitoring or fire prevention for high value assets (i.e.: switchgears).

Figure 2: Fenix2 battery free temperature sensor tag (front view).

Figure 3: Farsens' RF IC block diagram.

Farsens' Fenix2 battery free RFID sensor tag as shown in figure 2 is capable of transmitting a unique identifier and the associated temperature data to a commercial EPC C1G2 reader without the need of a battery on the sensor tag. The device, whose RF block diagram is illustrated in figure 3, features a LPS331AP temperature sensor from ST Microelectronics with a temperature range from -30C to +85C.

The tag comes in a variety of antenna designs and sizes to adapt the performance to the required application. The reading distance for the battery free temperature sensor tag is around 1.5m and it can be embedded in a wide variety of materials such as plastics or concrete.

About the author
Mikel Choperena is Business Development Manager at Farsens.

To download the PDF version of this article, click here.


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