Research

Microwave Sensors for Biomedical Applications

One of the actively ongoing research focuses at MEAS lab is the development of novel microwave resonator sensors for microbial monitoring for biomedical applications. We developed real time, nano-invasive sensor devices to monitor bacterial growth in both liquid and solid media. These sensors were successful in determining bacterial growth by measuring variations in resonant amplitude and frequencies aligned with established bacterial growth models. Determining bacterial growth on solid agar using a microwave sensor was first of its kind. The findings of these studies were published in highly reputed journals like Nature Scientific Reports, IEEE Transactions on Biomedical Circuits and System and IEEE Microwave and Wireless Components Letters. We also aim to expand microwave application to investigate bacterial growth response at different nutrient levels, monitor sub-surface growth to assess bacterial penetration during pathogenic infections and further to measure bacterial responses to various concentrations of antibiotics. These biosensors are aimed towards emerging automated complex workflows for rapid and accurate monitoring of bacteria for clinical and food industry applications.

Passive Planar Microwave Resonator for Oil Sand Applications

Development of a novel non-contact interface sensor, based on the electromagnetic planar ring resonator is reported. The reported device is operating at 5.22GHz with initial quality factor of 180. The sensing is carried out using the frequency shift and Q-factor variation as an indication to determine the location of the interface between the different liquid samples in a sample holder. The proposed sensor demonstrates 70 % difference in the quality factor of the device in between water and olive oil interface, and 50 % variation between water and alcohol liquid. Theoretical analysis, along with numerical simulations using HFSS shows good agreement with the experimental results. The proposed sensor has the advantages of being inexpensive and small size. In addition, it is highly compatible with integrated circuit technology, which results in small form factors. In addition, the sensor does not require any pretreatment of the samples under test.

NanoTube Integrarted Passive Planar Microwave Resonator

Steady-state (SRMC) and time-resolved microwave photoconductivity (TRMC) are key techniques used to perform the contact-less determination of carrier density, transport, trapping, and recombination parameters in charge transport materials such as organic semiconductors and dyes, inorganic semiconductors, and metal–insulator composites, which find use in conductive inks, thin film transistors, light-emitting diodes, photocatalysts, and photovoltaics. We present the theory, design, simulation, and fabrication of a planar microwave ring resonator operating at 5.25 GHz with a quality factor of 224, to perform SRMC and TRMC measurements. Our method consists of measuring the resonance frequency (f0) and Q-factor of the microwave resonator with the sample to be probed placed in a defined sensitive region of the resonator where the microwave field is highly concentrated. We also provide proof of concept measurements of the time-resolved microwave photoresponse of anatase-phase TiO2 nanotube array membranes (TNTAMs) using the planar microstrip resonator.

Bulk Mode Resonators

This work reports the design and fabrication of bulk mode micromechanical disc resonators operating in radial and wine-glass modes of excitation. The reported structures are fabricated utilizing a single crystal SOI wafer through micromachining processes. Both resonators are fabricated on a device layer with a thickness of 20 µm and a gap size of 1.75 µm between the resonant beam and surrounding electrodes. Four anchors support the resonant disc using a T-shaped connection stem. The designed structures resonate at 2.87 MHz and 3.99 MHz, in wine glass and radial modes respectively, and are electrostatically actuated by a DC voltage of 110 V between the disc and electrodes. The designed resonators show high quality factors while operating in air, 11876.2 for wine-glass and 7380 for radial. In addition, the resonators are used for distributed and point mass measurements of a sputtered gold metal layer.

Integrated Circuit for Implantable Biomedical Applications

Monitoring the electrical activities of a large number of neurons in vertebrates’ central nervous system in vivo through hundreds of parallel channels without interferring in their natural functions is a neuroscientist’s interest. Value of this information in both scientific and clinical contexts, especially in expansion of brain–computer interfaces, is extremely significant. Therefore, low-noise amplifiers are needed with filtering capability on the front end to amplify the desired signals and eliminate direct current baseline shifts. Hence, size and power consumption need to be minimized to reduce trauma and heat dissipation, which can result in tissue damage for human applications and the system needs to be implantable and wireless. The practical solution for developing such systems is system-on-a-chip, based on ultra-low-power mixed-mode and wideband RFIC designs. They, however, impose a number of challenges that may require nontraditional solutions. In this paper, we present a fully differential low-power low-noise preamplifier suitable for recording biological signals, from a few mHz up to 10 kHz. This amplifier has a bandpass filter that is tunable between 10 mHz and 10 kHz, and has been designed and simulated in a standard 90-nm CMOS process. The circuit consumes 10 µW from a 1.2 V supply and provides a gain of 40 dB and an output swing of ±0.5 V with a total harmonic distortion of less than 0.5%. The total input-referred noise level is 4.6 µV integrating the noise over 0.01 Hz to 10 kHz.