Hoseon Lee

Inkjet Printed, Self Powered, Wireless Sensors for Environmental, Gas, and Authentication-Based Sensing

In this paper, inkjet-printed flexible sensors fabricated on paper substrates are introduced as a system-level solution for ultra-low-cost mass production of UHF Radio Frequency Identification (RFID) Tags and wireless sensor nodes in a “green” approach that could be easily extended to other microwave and wireless applications. The authors briefly touch up the state-of-the-art area of fully integrated wireless sensor modules on paper and show several active and power scavenging platforms to power on wireless sensors that could potentially set the foundation for the truly convergent wireless sensor ad hoc networks of the future.

Monopole Antenna With Inkjet-Printed EBG Array on Paper Substrate for Wearable Applications

In this letter, a novel electromagnetic band-gap structure (EBG) with single-ring resonators is inkjet-printed on the commercially available photo paper using conductive nano-silver ink. The printed EBG array is placed above a copper sheet, forming an artificial magnetic conductor (AMC) reflector at the designed frequency range (2.4 ~ 2.5 GHz). A microstrip monopole antenna is backed with the designed AMC reflector and is tested in free space and in contact with a human phantom. The antenna gain of a conventional microstrip monopole on human phantom is as low as -9 dBi. The gain of the proposed AMC backed monopole, measured on a human phantom is 0.95 dBi. The measurements demonstrate superior performance of the proposed monopole with EBG array compared to a conventional microstrip monopole antenna when they are considered for wearable applications.

Carbon-Nanotube Loaded Antenna-Based Ammonia Gas Sensor

Carbon nanotubes (CNTs) have been researched extensively for gas-sensing applications due to their unique electrical, chemical, and structural properties. Single-walled carbon nanotubes (SWNTs) have been predominantly used due to their superior electrical conductivity and higher sensitivity relative to multiwalled CNTs. This paper presents the design and characterization of a novel planar sensor fabricated on paper substrate to detect small concentrations of ammonia gas, using the shift in resonance frequency of a patch antenna as the discriminator. We have investigated three main design issues in depth. First, functionalization of the SWNTs with a polymer is studied in order to enhance the gas detection sensitivity. Second, a thin film of the functionalized SWNT is characterized to create a surface impedance model for the explanation and prediction of the resonance shift due to different gas concentrations. Finally, as a proof of concept, functionalized SWNTs are integrated into a patch antenna design and the return loss is measured in a closed-system environment to show high sensitivity for low concentrations of ammonia gas. The proposed antenna-based wireless gas sensor can be utilized in several applications, given its small form factor, light weight, and little to no power requirements.

RF Fingerprinting Physical Objects for Anticounterfeiting Applications

Rendering typical RF identification (RFID) tags physically unique and hard to near-exactly replicate by complementing them with unique RF certificates of authenticity (RF-CoAs) can prove a valuable tool against counterfeiting. This paper introduces a new robust RFID system with enhanced hardware-enabled authentication and anticounterfeiting capabilities that relies on the near-field RF effects between a 5 × 5 antenna array and the uniquely modified substrate of the RF-CoAs. A microcontroller-enabled, low-power, and low-cost reader is used to accurately extract the near-field response (“RF fingerprint”) of the certificates meant to complement typical RFID tags in the 5-6-GHz frequency range. The RF characterization of all the readers components, with an emphasis on the accuracy provided, has been performed. The state diagram of the fast and accurate reader operation is outlined. Rigorous performance and security test results are presented and verify the unique features of this technology.

SenSprout: inkjet-printed soil moisture and leaf wetness sensor

In this paper we show a low cost and environmentally friendly fabrication for an agricultural sensing application. An antenna, a soil moisture sensor, and a leaf wetness sensor are inkjet-printed on paper substrate. A microprocessor attached to the paper substrate is capable of detecting the capacitance change on the surface of the sensor, and report the data over the wireless communication interface. This sensing system is useful to optimize irrigation systems.

Battery-free RFID-enabled wireless sensors

This paper introduces the realization of batter-free RFID-enable wireless sensors by integrating conformal RFID antennas with inkjet-printed carbon nanotubes (CNT) composites in a chipless RFID fashion for gas detection. The whole module is realized by inkjet printing on a low-cost paper-based substrate and the RFID tag is designed for the European UHF RFID band. The electrical conductivity of the CNT film changes in the presence of very small quantities of gases like ammonia, methanol, ethanol, acetone and nitrogen oxide (NOx), resulting in the variation of the backscattered power level which can be easily detected by the RFID reader to realize reliable wireless toxic gas sensing. The electrical performance characterization of the inkjet-printed CNT film is also reported in the UHF band.

UHF solar powered active oscillator antenna on low cost flexible substrate for wireless identification applications

The design of a 920 MHz active oscillator antenna using low cost flexible substrate materials is presented. Flexible amorphous silicon a-Si solar cells are properly integrated in the available area of the circuit substrate preserving the conformal nature of the circuit and providing operational autonomy by harvesting solar power without affecting the radiation properties of the active antenna. Coplanar waveguide fed monopole and slot antennas are designed using EM simulation and harmonic balance simulation is subsequently used to design the oscillator circuit, including the equivalent circuit of the solar module. Two benchmarking prototypes were fabricated, one by method of laser prototyping on PET, and the other by inkjet-printing on photopaper, demonstrating that it is feasible to come up with a cost effective conformal circuit implementation of a beacon signal generator which can find application in wireless identification and monitoring applications.

A novel “Universal” inkjet-printed EBG-backed flexible RFID for rugged on-body and metal mounted applications

A novel inkjet-printed electromagnetic bandgapbacked (EBG) RFID tag has been designed and tested for wearable and metal mount applications. An array of split-ring resonators and a dipole antenna matched to an RFID chip at 915 MHz were designed and inkjet printed on paper substrate. Measurements of the tag in free space show that the required readers minimum transmit power for successful tag reading decreases by 6 dB compared to the case without EBG, while for on-body and on-metal measurements, the read range increases by nearly a factor of 2. It has to be noted that the proposed RFID tag is flexible since it can be easily fabricated by inkjet printing nano- silver particles on paper or platic substrates. It can find numerous applications ranging from wearable antennas and bio-monitoring to transportation and logiitics for mass shipping.

RFID-CoA: The RFID tags as certificates of authenticity

The inadequacy of the traditional, digitally encoded RFID tags in combating counterfeiting prompts us to investigate new hardware-enabled technologies that can complement the remote identification functionality of typical RFIDs in an effective and very low cost way. In this paper, we present RFID-CoA; a system that aims to render typical RFID tags physically unique and hard to near-exactly replicate by complementing them with random 3D scattering structures, which serve as certificates of authenticity (CoA). The unique near-field response, or “fingerprint”, of the CoAs is extracted as a set of S21 curves by our reader prototype, the design and development details of which are discussed. The results of our performance analysis show that the intersection probability of the false positive and false negative error probability curves is inconceivably small (<10−200). The RFID-CoA tags lifecycle from fabrication site to store is presented, and a strategy to block potential attacks is discussed. Our system bridges the world of RFID with a large array of anti-counterfeiting applications by exploiting “hardware-enabled”, modified-material scattering characteristics in the near-field. Based on our multifaceted analysis, we firmly believe that the demonstrated RFID-CoA technology can prove a valuable tool for the low-cost ubiquitous applicability of RFID technology against counterfeiting.

Integrated antenna with inkjet-printed compact artificial magnetic surface for UHF applications

A low-profile antenna on HIS/AMC/EBG surface was developed for UHF applications. The surface is inkjet-printed on paper which produces a low-cost, light-weight, and environment-friendly solution. More compact unit cells (and thus smaller overall size) and/or wider antenna bandwidth can be realized using alternative unit cells/antenna configurations as discussed in [5–6].