Radio chip harvests energy from RFID readers

Spanish firm Farsens has an RFID chip which is powered by harvesting radio frequency energy from commercial UHF RFID readers and communicates with them using EPC C1G2 standard commands.

The device also has an SPI interface to drive sensors in a battery-free design.

Because the RFID device, called ANDY100, works under standard EPC C1G2 commands any commercial UHF RFID reader can be used just by programing with the correct standard commands.

The ANDY100 IC includes a RF frontend for UHF RFID power harvesting and communication, a power supply module to generate the required voltage levels, an EPC C1G2/ISO18000-6C digital processor including a trimmed clock oscillator, a non-volatile memory and a SPI master module. The SPI master module can be controlled via EPC C1G2 standard memory access commands.

The San Sebastián-based company has designed an RF energy harvesting development platform based on the chip.

Called Medusa, the development platform for UHF RFID battery-free devices, combines the RFID IC with an MSPG2233IPW20 microcontroller from Texas Instruments for interfacing with the rest of the system under development.

"Users can now develop their own wireless sensors or actuators without requiring batteries on the tag," said the company. "The development platform harvests energy from the RF field created by the RFID reader to power up the ANDY100 IC, the microcontroller and the circuitry and devices attached to it."

Farsens says the chip can be used for asset tracking, via a unique ID and monitoring, via the attached sensor.

There is also an evaluation board for testing the energy harvesting chip with RFID EPC C1G2 wireless communication and SPI master. Called Spider, the board includes the ANDY100 chip and a start-up circuit to allow developers to work directly with SPI sensors or connect a microcontroller of their choice for further processing.

The Spider evaluation board comes with a wideband dipole antenna (pictured).

A diode is used to isolate the supply of the RFID tag from the supply of the rest of the system. A capacitor acts as an energy storage unit to support current peaks of the system during active operation, such as initialisation and active operation.

A voltage monitor is included to connect external loads only after the energy storage capacitor has been charged.

The voltage monitor connects the external load when the voltage in the capacitor is over 2.4V and disconnects it when the voltage falls below 1.8V. This architecture avoids oscillation of the system during the start-up.

The SPI communication lines of the ANDY100 and the isolated power signals are available at an external connector to evaluate the ANDY100 IC with external components.

One of the application specific RFID devices Farsens has designed the energy-harvesting technology into is a voltage level monitoring tag, called Vmeter.

The tag, which works without a battery, transmits a unique identifier and the associated voltage level measurement data to a commercial EPC C1G2 reader without the need of a battery on the sensor tag. This device can measure voltages in a range from 0V to 1.5V with an adjustable gain of 1-1000.

The VMETER-DCLV10 has a 96 bits EPC number, a 32 bit TID and a password protected Kill command. The tag comes in a number of different antenna designs and sizes for applications in the 860-960MHz band.

The reading distance for the battery-free thermistor tag is around 1.5 metres (5 feet) and it can be embedded in a wide variety of materials such as plastics or concrete.

It can also be encapsulated in an IP67 or IP68 casing for usage in harsh environments. Evaluation kits are available.

There is also a pressure monitoring tag which has a MS5803-05BA sensor from Measurement Specialties to monitor pressures up to 6 bar.