Question

Circuit:Low pass and High Pass

The nature of lake is that there is a giant explosion of what are called “midges” in the mid to late summer. If you haven’t been around and seen these bugs:

Your car gets covered so bad that you can’t see out the windsheild after driving 10 miles! They get everywhere; don’t open your door at night as they flood in! Now althought this is seen as a menace from bug hell, there are some not so obvious advantages which come from this menace. Who see the bugs, catch them and feed them to their young. And Who “see” bugs through sonar,their voices are their “eyes and ears”.

Professor from the Environmental program is trying to get an estimate of the population of bats that are around the lake to quantify the relationship and population dynamics of bats to the severity of the menace. Now bats are night creatures you see, well he can’t see so well as it is night! He is at a conundrum for how to measure the number of bats in a given area. Very difficult to do as you can’t visually (unless you have a light, yet this will probably throw off the count of bats as the bugs are attracted to the light, hence bats also, yet this would lead to an unnatural or not normal distribution of bats!) so he must be away from the street lights further down the road and the lights from cars with that blasting stereo to drowned out the new street performance muffler shouldn’t affect the natural distribution of bats. The second issue is that bats don’t fly in formation, they come from all directions almost randomly. Prof. has come to you for a solution to his bat count problem. Using the knowledge you have gained, come up with a simple design to help Prof. count his bats. Describe your solution and reasons why you chose this solution. Include any calculations and a concluding paragraph of what you have learned in this problem.

Answer 1

Lets Talk about bats

As we know  bats  emit their echolocation calls through their nostrils: there they have basal fleshy horseshoe or leaf-like structures that are well-adapted to function as megaphones.

Echolocation calls are usually ultrasonic--ranging in frequency from 20 to 200 kilohertz (kHz), whereas human hearing normally tops out at around 20 kHz. Sometimes we can hear echolocation clicks from some bats. These noises resemble the sounds made by hitting two round pebbles together. In general, echolocation calls are characterized by their frequency; their intensity in decibels (dB); and their duration in milliseconds (ms).

The professor is keen to estimate the number of bats but

1. He can't opt manual counting due to insufficient light etc .

2. Can't define any mathematical pattern as bats don’t fly in formation, they come from all directions almost randomly

So he can opt a mechnaism for "Echolocation calls " detection using a filter of frequency range from 20 Khz to 200 Khz and a detector . Detectors output can help in estimation of number of bats.For example Heterodyne.

By down-converting the ultrasound into our audible range, we can indirectly detect it . It has been suggested that bats utilize delay times, arrival time differences, and the Doppler effect to interpret echoes. Of course, we can only guess at what bats actually perceive. Perhaps the end result is somewhat analogous to vision, with an image that is refreshed as new information comes in. (Design is given in figure)

The incoming ultrasonic signal is mixed with a locally generated signal that is close to the same principal frequency. The mixer output contains a signal which is the difference between these two. So, for example, if the incoming sound is based at 50 kHz and the local oscillator is running at 45 kHz, the output will be around 5 kHz — nicely within the range of human hearing.