By Dr Paul Kamweru (Guest Writer)
We have lost a friend and a respectable colleague. Dr. Abraham Tuwei Kirwa passed on today (9th July 2020) following injuries he sustained on a road accident.
To help me escape the reality of his demise, and the feeling of sadness and sorrow for even the thinnest moment, I choose to take my mind and focus on the good science Dr. Tuwei will forever be remembered for.
For those unfamiliar with his work, allow for a moment to highlight a few of his successes in physics.
Fibre optic sensors
Without doubt, Dr. Tuwei was passionate about physics, and especially the physics of sensors and sensing, utilizing evanescent waves of an optical fibre.
For starters a fibre is a thin cylindrical piece of either glass or plastic, which allows a ray of light to pass through it without loss, due to a principle we call total internal reflection.
What this means, is that the ray of light is not lost, made possible by cladding (coating) a material of a different (lower) refractive index.
Even though the ray is ‘total internally reflected’, there remains a portion of the ray of light (electromagnetic field), that ‘jumps’ into the cladding.
However this ray or wave (a group of rays) normally disappear quickly, that is, it evanescence, such that it is only on a very thin layer of the cladding.
This evanescence wave therefore interacts, and carries with it the information about the cladding (the coating layer). The information about the cladding can therefore be detected.
This is done by analyzing the light signal at other end of the optical fibre, and quantifies any differences in the signal, for different claddings.
This is the principle that Dr. Tuwei utilized to make sensors (i.e. the Evanescent Wave Sensor or EWS) that can detect analyte (chemicals) either in air or in water.
University of Sheffield
For his work that he did at the University of Sheffield, UK, Dr. Tuwei replaced the cladding for a small portion of the fibre with three chemicals i.e. 5,10,15,20-tetrakis[3,4-bis(2-ethylhexyloxy)phenyl]-21H,23H-porphine (EHO), 1-(2-pyridylazo)-2-naphthol(PAN) and zinc 5-(4-carboxyphenyl),10,15,20-triphenyl porphyrin (Zn(P-CO2H-TPP)) that are sensitive to acetic acid vapors, Zinc ions and octylamine respectively.
What happens is that when the newly coated cladding is exposed to the analyte to be detected, it changes its optical properties, and hence the evanescent wave in and from it will behave differently, change, and this is detectable.
Dr. Tuwei’s results that are published a journal articles and a thesis of the same University, proves that the EWS with the sensitive chemicals sprayed as the cladding is efficient to detect the analyte in water, more than in air.
What else can EWS sensors be used for?
Their findings could be stretched further, and explored for sensing other parameters such as temperature, pressure and even noise. The ball is in the court of lovers of Science.
Besides the published thesis work, Dr. Tuwei was working in corroboration of others to make sensors for different purposes, such as detecting electrical signals in plants, monitoring human traffic and movements, among others.
What does this mean for application?
These findings means that we now have, courtesy of the late Dr. Tuwei and others working in a similar discipline, an easy to assemble and sensor that could tell of the presence of harmful compounds and elements in drinking water for example.
With the EWS, fish farmers could be able to follow when toxic compounds are accumulating if fish ponds that may lead to fish deaths. When applied to detect airborne analyte the EWS could be used to detect and monitor air pollution from industries, motor vehicles among others.
Even though gone, his work will remain useful to the scientific community and will be utilized to benefit the human race.
Dr. Tuwei was also a husband, a father, a brother and a friend. He will forever be remembered.
Fare thee well, our Colleague, Dr. Abraham Tuwei Kirwa.