| Abstract: | A communication device for receiving an interrogation signal at a first
carrier frequency and for transmitting a response signal at a second
carrier frequency is disclosed. The interrogation signal comprises the
first carrier frequency modulated at the second carrier frequency. The
communication device includes a sensor coupled to a demodulator. The
sensor receives a low frequency input used to further modulate the
interrogation signal. The demodulator demodulates the low frequency input
from the first carrier frequency to thereby generate the response signal
comprising the second carrier frequency and the low frequency input. The
demodulator preferably includes a pyroelectric demodulator, a
piezoelectric demodulator, or a detector diode. The demodulator
preferably has a frequency response less than the first carrier frequency
but greater than the second carrier frequency. |