On-Body Long-Range Wireless Backscattering Sensing System Using Inkjet-/3-D-Printed Flexible Ambient RF Energy Harvesters Capable of Simultaneous DC and Harmonics Generation

A novel wearable and flexible energy autonomous on-body sensing network is proposed featuring full operability through energy harvesting from a hand-held 464.5-MHz UHF two-way talk radio. Three different functions are provided utilizing the hand-held two-way talk radio as the only energy source for our proposed system. There are two types of energy harvesters (EHs) proposed for the presented system. The first EH that is mounted on the sensing capable backscattering RFID tags harvests the 464.5-MHz signal energy to drive the tags; the second EH that can be worn on hands harvests the same 464.5-MHz signal to produce both the dc power and the carrier signal. The second EH is more efficient than conventional ambient RF energy harvesting architectures because for the first time, both the dc and the second harmonics generated by the rectifier are utilized to enable two additional functions. The generated second harmonic is used to interrogate backscattering RFID tags for on-body sensing, while the dc power is used to power an RF amplifier in order to enhance the second harmonic to effectively extend the sensing and communication range. For the proof-of-concept demonstration, the measured dc and the second harmonic, 929 MHz, output power from the proposed EH are 17.5 and 1.43 dBm, respectively, while a two-way talk radio is 9 cm away. The measured second harmonic output power is increased to 13 dBm utilizing the harvester-powered RF amplifier, and the reading range of the custom backscattering sensor tag is extended to more than 70 m. Also, the interrogation of multiple sensor tags and the wireless detection of ammonia gas utilizing an inkjet printed flexible ammonia sensor are demonstrated showing the wide range of applications of the proposed approach.