Olutosin Fawole

Terahertz Near-Field Imaging of Biological Samples With Horn Antenna-Excited Probes

We report terahertz near-field imaging of different biological samples with metallic, Teflon, and quartz (dielectric) probes excited with a horn antenna and using a terahertz vector network analyzer. The terahertz decay length (Ld) of the metallic probe was 445 μm at 0.8375 THz (λfree ~ 375 μm), while the Teflon probe had Ld of 230 μm at 1.0422 THz (λfree ~ 288 μm), and the quartz probe had Ld of 75 μm at 0.8024-0.8424 THz (λfree ~ 288 μm). With these probes, we imaged a slice of mouse brain, a dwarf umbrella tree leaflet section, and a boxelder bug wing section. In the terahertz image of the mouse brain slice, we observed the outline of the different regions of the brain slice. In the terahertz image of the leaflet, the venation in the leaflet (because of its relatively high water content) was clearly observed at terahertz which was not well defined in its optical image. In the terahertz image of the bug wing section, the transition from the thick corium region to the thin membrane region had a profile that was different from its optical image. Finally, we demonstrated the capability of the near-field imaging system for imaging through a dielectric slab with internal structure that was clearly detected at terahertz, while it was completely concealed optically.

Monitoring yeast activation with sugar and zero-calorie sweetener using terahertz waves

We report for the first time the use of terahertz waves (0.75 THz-1.1 THz) to monitor activation of yeast cells in solutions containing normal sugar and artificial sucralose sweetener. We observed that the yeast solution with regular sugar and artificial sweetener each showed 14 dB of variation in the terahertz reflection over 42 minute. The solution with sweetener was in particular very active and generated CO2 bubbles more vigorously than sugar. The control solution containing only yeast and water had a nearly constant terahertz reflection coefficient over time. This finding is quite surprising and we did not expect any activations of yeast with sweetener.

A novel near-field terahertz imaging probe for biological imaging

We report a resonant frequency-domain terahertz (THz) near-field probe setup and its application in imaging a slice of a mouse brain slice and the leaf of a dwarf umbrella tree. In our probe setup, we coupled the waveguide output of a terahertz Vector Network Analyzer (VNA) system to feed a horn antenna and then used the horn antenna to excite a sharp iron or Teflon tip. The tip transforms and concentrates the Transverse Electric (TE) mode waves of the horn to longitudinal electric fields (LE) at the metallic or Teflon tip for stronger interaction with a sample. The spatial resolution of the probe setup (from spread with an iron and a Teflon tip function measurements) were 445 μm (at 0.8375 THz) and 230 μm (at 1.0422 THz), respectively.

A novel circular micro-plasma magnetic field sensor

We report a planar device with two co-axial electrodes for creating an atmospheric glow discharge (micro-plasma) that can easily rotate around an axis when a force is applied to the glow. When the device is placed in an external magnetic field, the glow experiences an accelerating Lorentz force and decelerating frictional and drag forces. Therefore, the glow rotates at an angular velocity proportional to the external magnetic field strength and to glow parameters such as electron/ion mobility. Hence, this device can be used both as a magnetic field sensor and a Hall-effect device, to measure carrier mobilities in micro-plasmas.

A novel geometry for a corona wind electrohydrodynamic pump

We report the flow velocity of a new electrohydrodynamic (EHD) pump configuration fabricated using a 3-D printer. It consisted of an inner conical electrode with an apex angle of 43.6 degrees and an outer conical structure with apex angles of 43.6 degrees, 63.6 degrees, 83.5 degrees, 103.5 degrees, and 180 degrees that were mounted over the inner electrode. A maximum airflow velocity of 2 m/s was measured at 8000 V/cm in the pump with the 103.5 degrees cone. In all the pumps, the velocity peaked and then dropped as the electric field reached the airs breakdown field. In these pumps, the field gradient accelerates the charged air molecules that drag the neutrons. That charged the air molecules in the inlet side of the pump which improved the efficiency.

Remote Microwave and Field-Effect Sensing Techniques for Monitoring Hydrogel Sensor Response

This paper presents two novel techniques for monitoring the response of smart hydrogels composed of synthetic organic materials that can be engineered to respond (swell or shrink, change conductivity and optical properties) to specific chemicals, biomolecules or external stimuli. The first technique uses microwaves both in contact and remote monitoring of the hydrogel as it responds to chemicals. This method is of great interest because it can be used to non-invasively monitor the response of subcutaneously implanted hydrogels to blood chemicals such as oxygen and glucose. The second technique uses a metal-oxide-hydrogel field-effect transistor (MOHFET) and its associated current-voltage characteristics to monitor the hydrogel’s response to different chemicals. MOHFET can be easily integrated with on-board telemetry electronics for applications in implantable biosensors or it can be used as a transistor in an oscillator circuit where the oscillation frequency of the circuit depends on the analyte concentration.

Electromechanically-modulated permanent magnet antennas for wireless communication

High-frequency electromagnetic waves suffer considerable attenuation when propagating through media such as soil, rocks, human body, water, etc. However, low-frequency magnetic waves easily penetrate the aforementioned media. Earlier magnetic field communication systems typically employ current-excited coils to generate modulated magnetic fields for communication. These systems require large currents to produce detectable magnetic fields at long distances. However, the availability of rare-earth magnets with surface magnetic flux densities of 0.1–0.6 T provide current-free sources of magnetic fields that can be electromechanically modulated for long-distance magnetic communication. Here, two designs of electromechanically-modulated permanent magnet antennas are presented. In the first design, the rotational frequency of a rotor magnet was electromechanically modulated to produce modulated magnetic fields that transmit information wirelessly. In the second design, the vibrational frequency of a permanent magnet-loaded piezoelectric beam was electromechanically modulated to produce modulated magnetic fields. These magnet antennas can transmit binary data at rates of up to 8 bits/s.

An Electromechanically Modulated Permanent Magnet Antenna for Wireless Communication in Harsh Electromagnetic Environments

High-frequency electromagnetic waves are greatly scattered and attenuated by soil, rocks, water, and the human body, which impede their propagation across these media. However, low-frequency magnetic waves propagate with low attenuations through these dispersive media as long as these media are nonmagnetic. Unlike static electric fields that can be produced by “free” positive/negative charges, static magnetic fields are divergence-free and thus can be produced only by particles with noninteger spins (i.e., electrons), or permanent magnets, or current loops. Fields produced by these dipoles decay steeply as a third-order function of distance. Hence, magnetic current loops require excessively large currents to produce detectable magnetic field at large distances. However, rare-earth magnets with surface magnetic flux densities of 0.3–0.6 T, provide sufficiently large fields at large distances, thus the fields produced by these magnets that can be modulated by mechanically modulating the magnets for portable wireless magnetic field communication. Here, we present the development of an electromechanically modulated permanent magnet antenna operating at a frequency of 22 Hz, producing a magnetic flux density of

Terahertz quantification of ethanol and sugar concentrations in water and its application for noninvasive real-time monitoring of fermentation

0.6~\mu \text{T}

A terahertz Fabry-Pérot modulator using charge injection-induced insulator-metal transition in vanadium dioxide

amplitude at 1 m. This antenna requires a starting energy of 0.48 J and it is capable of data rate of 8 b/s. This magnet antenna can reliably transmit binary data over a distance of up to 70 cm through obstacles that would severely hamper electromagnetic wave propagation.