Rich-Media Tags: Battery-free wireless multichannel digital audio and image transmission with UHF RFID techniques

In this paper we present the first fully passive (battery-free) wireless transmission of multiple digital audio channels and images via modulated backscatter. We leverage a previously reported single chip, passive transponder that can digitize and uplink up to 10 analog input channels sampled at a rate of 26.1 kHz. Given a base station transceiver operating at a frequency of 915 MHz and a transmit power of +36 dBm EIRP, the transponder has a demonstrated operating range of ≈1.4 m. The transponder data uplink uses binary phase-shift key (BPSK) modulated backscatter operating at a total link throughput rate of 5 Mbps, with an uplink energy consumption of only 3.7 pJ/bit. The transponder was initially designed for biomedical telemetry of neural and EMG signals. We present a new application of this tag for multichannel, high fidelity digital audio recording, as well as color image transfer using a slow-scan television (SSTV) modulation (PD290) with a resolution of 640 by 493 pixels. Additionally, we demonstrate fully-passive digital recording of ambient sound using a microphone powered by the chip's harvested energy at an operating range of 0.72 m. The passive, digital microphone is sensitive enough to record human speech within approximately 5 m of the device. We believe these results will serve as a first step toward media-rich battery-free (wirelessly powered) devices that take advantage of the high speed, low power nature of modulated backscatter communication links.