Manufacturers of UHF (868-950MHz) passive RFID tags often times provide a special tag specifically for mounting on metal. They are normally much thicker than a non-metal mount tag. The main reason for the extra thickness is to provide a non-metallic space between the RFID tag antenna and the metal. Some manufacturers may also create a specially tuned tag to compensate for the shift in frequency due to the close proximity of the metal. The cost of these metal mount tags are substantially more due to the small quantities of tags required in the market place compared to non-metal applications and the extra materials required producing these types of tags.

What consumes the majority of power on a wireless sensor or active RFID tag?

The power budget can be broken up into the following categories:

• Active run time for measuring and computing sensor data (if applicable)
• Time to shutdown the micro-processor to low power mode
• Time spent in shutdown mode
• Time to wake-up the micro-processor from shutdown mode
• Receive time (if applicable)
• Transmit time

If the tag must transmit often or spend a significant amount of time listening for an incoming message, then this normally consumes the majority of the battery capacity. Receive currents are normally in the 12-15 mA range and the transmitters are in the 15-30 mA range. Shutdown currents are normally less than 1 uA which is less than the self discharge current of a lithium cell. If a tag must wake up often, then the time to wake up and the time to shut down are also important. There are many micro-processor companies that brag about their low power requirements. Knowing how to interpret the data sheets and calculate the true power requirement can be a tricky process. Matrix Product Development has the expertise in low power designs to help you achieve the life and reliability for your product.

Go to: www.matrixpd.com or www.RFIDhut.com