On Swatters

 

Long ago, a wisecrack noted that mosquitos fly amidst applause. This must have been before the invention of the electronic fly swatter. 

One of the small joys of life is to hear that sharp, sparky zap of an elusive, pesky mosquito getting caught in a fly swatter. This is especially true in summers when the critters seem to be spoilt for choices with so much of exposed skin, and somehow manage to find the most inaccessible point to dig in for a quick, bloody meal, and slip away at the slightest hint of a being caught out.

After one particularly successful swatting spree I found myself looking with much awe and admiration at my battery operated fly-swatter. Who came up with this brilliant invention? How much voltage does it take to electrocute an insect? What does it cost to make this simple, effective contraption?

The answers to the first two questions were quite easy to find - I leant from Wiki that the patent for this device is held by Taiwanese inventor named Tsao-i Shih. First manufactured in 1996,  the "electronic insect killing swatter" is essentially a scaled down version of a cattle-prod, a taser or stun-gun. Built inside its handle is an electronic oscillator, a step-up transformer and a voltage multiplier. 

Designed to prevent children from getting hurt, the bat's double layer of nets are electrodes that deliver a voltage of 1000 volts of more.  While this might seem like a of using a cannon to kill a mouse, the point to note is that the voltage output is controlled by a capacitor rating less than 45 nanofarads (nF), with a discharge limit of 45 microcolumbs (µC). 

What does this mean? I have not figured this nF - µC thingie yet. All I know so far is that a farad is the unit of electrical capacitance - the ability of a body to store an electrical charge. One farad is defined as the capacitance across which, when charged with one coulomb, there is a potential difference of one volt. A nanofarad is one billionth (10^9) of a farad. 

To put the voltage output of a fly-swatter in perspective, a stun-gun delivers an output between 20,000 V and 150,000 V ! 

It is also interesting to know that the cost of making this device in India (~INR 300+) is nearly double the cost in China. This is mainly because the cost of making the plastic components of the bat is more than double in India, making bulk imports a more viable option for traders. 

-------------------------------------

REFERENCES & LINKS

* How stun-guns work - https://electronics.howstuffworks.com/gadgets/other-gadgets/stun-gun3.htm

* Electronic fly-swatter patent - https://www.freepatentsonline.com/5519963.html

* Teardown - https://tworks.telangana.gov.in/blog/electric-mosquito-racket-teardown

* Wiki - https://en.wikipedia.org/wiki/Fly-killing_device#cite_note-16