Saranraj Karuppuswami

Demonstration of RF and Microwave Passive Circuits Through 3-D Printing and Selective Metalization

The ultimate goal of this paper is to print radio frequency (RF) and microwave structures using a 3-D platform and to pattern metal films on nonplanar structures. To overcome substrate losses, air core substrates that can readily be printed are utilized. To meet the challenge of patterning conductive layers on complex or nonplanar printed structures, two novel self-aligning patterning processes are demonstrated. One is a simple damascene-like process, and the other is a lift-off process using a 3-D printed lift-off mask layer. A range of microwave and RF circuits are designed and demonstrated between 1 and 8 GHz utilizing these processes. Designs are created and simulated using Keysight Advanced Design System and ANSYS High Frequency Structure Simulator. Circuit designs include a simple microstrip transmission line (T-line), coupled-line bandpass filter, circular ring resonator, T-line resonator, resonant cavity structure, and patch antenna. A commercially available 3-D printer and metal sputtering system are used to realize the designs. Both simulated and measured results of these structures are presented.

RFID Compatible Sensor Tags for Remote Liquid Sample Interrogation

In this paper, a passive harmonic generator based wireless sensor for long range interrogation of small liquid samples is demonstrated. A step by step method for development of the harmonic doubler based sensor is presented. Two different sensor designs are evaluated for liquid sensing. The first sensor is a T-line resonator coupled to patch antennas and harmonic doubler. The second sensor is a compact design in which a split ring resonator is directly coupled to a dipole antennas based diode doubler. The resonators are loaded by the liquid samples that in turn induce changes in reflected power from the tag. The sensors are evaluated for their remote interrogation capabilities of sensing different liquids under test. Liquid samples measured include mixtures of isopropyl alcohol-water, methanol-water and glucose-water samples. These mixtures provide a range of dielectric properties for the evaluation of the long range sensor. This sensor holds good for potential application in food safety, bio sensing and hazardous chemicals monitoring and detection.

A Hybrid Magnetoelastic Wireless Sensor for Detection of Food Adulteration

This paper investigates a step by step design procedure of a hybrid passive wireless sensor. The hybrid sensor measures both the electrical (dielectric constant) and the mechanical (viscosity) properties of liquid, providing a two-factor quality control. The hybrid sensor is based on an inductor-capacitor resonant tank coupled with a magnetoelastic strip. The mechanical and the electrical resonances change as a function of viscosity and dielectric constant, respectively. Two different hybrid sensor designs are investigated: 1) a parallel plate capacitor coupled with a separate amorphous ferromagnetic magnetoelastic strip (Metglas) and 2) a capacitor made using two parallel mounted magnetoelastic strips. The sensors are integrated as part of the “smart vial” making it field operable for food quality monitoring and control. Here, detection of adulteration in extra virgin olive oil is achieved by measuring the change in viscosity and dielectric constant for different adulteration levels. The real part of the dielectric constant for different liquid samples is measured in the frequency range of 3–24 MHz. The hybrid sensor is able to detect adulteration levels below 10% in volume. These sensors can be integrated with passive RFIDs for simultaneous measurement of multiple samples in an array format.

A Hybrid Electrical-Mechanical Wireless Magnetoelastic Sensor for Liquid Sample Measurements

This paper presents a hybrid passive wireless resonant electrical and mechanical sensor for enhanced sensitivity and specificity. Mechanical resonance measures the viscosity and electrical resonance measures the dielectric properties of liquid samples. The sensor is composed of two magnetoelastic (amorphous ferromagnetic ribbons) strips placed in parallel that are separated with a dielectric spacer forming a capacitor. An inductive coil is attached in parallel to this capacitor leading to an electrical resonant inductive-capacitive (L-C) tank. Both mechanical and electrical resonance frequencies are wirelessly measured using a single pickup coil hooked to an impedance analyzer. Several liquid samples, including food items, having different viscosity and dielectric properties are measured and key advantages of this sensor are demonstrated. This sensor can be used in food quality monitoring and can be integrated with passive RFIDs.

Embedded Passive RF Tags towards Intrinsically Locatable Buried Plastic Materials

This paper demonstrates the use of passive harmonic tags (transponder) as markers for buried plastic pipes. The tag design is based on a double slot antenna that can be buried in the plastic pipes during manufacturing. Design and measurement results are presented for two tag designs: one with a metal backing and one without. The tags are embedded in a plastic casing representing the walls of the plastic pipes. The tag operates at a fundamental frequency (fo) of 2.5 GHz with a return signal (2fo) of 5 GHz. Use of harmonic tags eliminates the clutter from the surface of the ground and thus enhances signal to noise (S/N) ratio of the return signal without the use of filters. The antenna is linearly polarized and polarization can be used as a marker for the direction of the buried pipes. The tag design is compact and can also readily be interrogated using simple hand-held radar units.

A Triaxial Applicator for the Measurement of the Electromagnetic Properties of Materials.

The design, analysis, and fabrication of a prototype triaxial applicator is described. The applicator provides both reflected and transmitted signals that can be used to characterize the electromagnetic properties of materials in situ. A method for calibrating the probe is outlined and validated using simulated data. Fabrication of the probe is discussed, and measured data for typical absorbing materials and for the probe situated in air are presented. The simulations and measurements suggest that the probe should be useful for measuring the properties of common radar absorbing materials under usual in situ conditions.

Capillary Condensation Based Wireless Volatile Molecular Sensor

In this paper, a LC (inductor capacitor) wireless gas sensor is demonstrated for the identification of volatile organic compounds (VOCs) in the air environment. A near-field LC resonant tank consisting of an interdigitated capacitor fabricated on a porous flexible substrate coupled with an inductor coil is used as a sensor and its resonance is interrogated using an external pick up coil. The porous substrate enables capillary condensation of volatiles leading to a change in effective dielectric constant of the substrate which in turn shifts the resonance frequency. The designed sensor has multiple reuse capability and is applicable for continuous monitoring of volatiles such as methanol, iso-propyl alcohol, acetone and n-octane. The proposed sensor can wirelessly detect a 0.15 cc volume of volatiles in air making it highly sensitive. These sensors can be integrated with passive RFIDs in an array format for simultaneous detection of multiple volatile gases similar to an electronic nose. It can also be integrated with food packages to detect volatiles from food along the supply chain for quality control applications.

AuNP-RF sensor: An innovative application of RF technology for sensing pathogens electrically in liquids (SPEL) within the food supply chain

Rapid detection techniques of pathogenic bacteria in the liquid food supply chain are of significant research interest due to their pivotal role in preventing foodborne outbreaks, and in maintaining high standards of public health and safety. Milk and dairy products are of particular interest due to their widespread consumption across the globe. In this paper, a biosensor for detecting pathogenic bacteria in milk using dextrin-capped gold nanoparticles (d-AuNP) as labels decoded at microwave frequencies is presented. The SPEL (sensing pathogens electrically in liquids) biosensor consists of a 3D printed vial and uses an RF reader and an RFID (radio-frequency identification) compatible Split Ring Resonator (SRR) based tag. The SPEL biosensor is capable of detecting bacteria at 5 log CFU/mL within 75 min, with the possibility of testing multiple concurrent samples. Detection is based on impedance loading of SRR by d-AuNP bound to pathogenic bacteria. Spectrophotometry, along with carbohydrate-functionalized magnetic nanoparticle (MNP) cell capture, is used to verify the sensitivity of the SPEL biosensor with respect to d-AuNP presence. The proof-of-concept device, along with challenges and opportunities for commercialization, are also outlined.

3D Printed Out-of-Plane Antennas for Use on High Density Boards

This paper presents out-of-plane antenna designs for use on high density boards. These antennas are fabricated using 3D plastic printing (additive manufacturing) and subsequent metallization. Various out-of-plane microwave structures including a transmission line, vertical mount microstrip patch antenna, elevated patch antenna, air-lifted patch antenna, and a monopole antenna are demonstrated. These antennas can be integrated directly on packaged chips or mounted vertically on high density electrical boards. Metal patterning on these non-planar structures is carried out using a damascene like process. Details of simulation, fabrication, and measurements are presented.

A Nonlinear Transmission Line Based Harmonic RF Tag

This paper describes the design and development of a nonlinear transmission line based passive RFID tag. When the tag receives a signal from the interrogator, it generates harmonics which are transmitted back to interrogator. The reflected signal is distorted in time domain due to the harmonic contents. Hence, a change in the rise time would be observed in the received signal. Experimentally, a decrease in rise time by 14% is demonstrated using the wireless tag at a distance of 100mm from the interrogator. The tag was designed to operate in the range of 100 MHz to 500 MHz with Braggs cutoff frequency of 1.2 GHz. This circuit will find applications in tagging, tracking and sensing.