Microchip has developed a capacitive contactless identification system that relies on near-field effects around the human body.
A $1 fob or token, carried about a person, sets up a field that extends to the wearers fingertips, allowing them to prove they are the carrier by reaching their hand towards a reader.
Branded BodyCom, no licence fees are payable providing it is implemented with the firm's chips."This is not NFC, which is magnetic near-field communications. It is based more on the e-field. We use conductive pads which form a capacitor," Microchip business development manager Lucio Di Jasio told Electronics Weekly. "The idea is just to carry a BodyCom token. You don't have to push a button. It can be in a shoe, a helmet, a purse or a pocket."
The aim of the development was to transfer a few bytes of identification data with cheap components, with as much cost as possible transferred from the tokens.
As such, the token has only an 8bit microcontroller (a PIC16LF1827 in the evaluation circuit), an RF receiver, and an RF power amplifier (a CMOS inverter) feeding a flat plate aerial through an LC filter. One flat plate on each side of the token means that either can face the body, while the other couples to earth.
The microamp supply current RF receiver chip is an existing Microchip design: the MCP2035/2030 range originally developed for passive keyless car entry systems. Input sensitivity is 1mVp-p and modulation down to 8% can be detected.
"Token battery life is 2-3 years," said Di Jasio. "The system has been in use in Microchip's Milan office for two years."
As the receiver chip is optimised for operation around 125kHz, this has become the de facto frequency for basestation to token communications.
Token to basestation communication is at 8MHz, chosen, according to Di Jasio, because it is the clock frequency generated by the RC clock oscillator built into many PICs. The RC oscillator is sufficiently stable for the system, he added.
The receiver uses a PIC16LF1829 in the demonstrator, with a mixer taking the 8MHz to around 125kHz for a 2035 to provide amplification there as well.
"A basestation cost can be as low as $2, said Di Jasio.
The firm has chosen it existing KeeLoq protocol for identity confirmation.
Around the body, "electromagnetic fields are 80dB below minimum allowed by the FCC", said Di Jasio.
Using a 5x5cm flat plate basestation antenna, the hand of a person will pick up sufficient energy to wake their token at 15cm range, said De Jasio, and to complete the identification transaction at 2cm.
"2cm is deliberately short for security. It is a trade-off between security and convenience," he said.
There is a development kit (DM160213), an application note, and V1.0 of the development framework can be downloaded.
"If you follow our framework specification, we have the patents and you need no other intellectual property," said Di Jasio.
