Control Engineering

Paul Grayson

The Five Senses - Sonar
December 10, 2007

2007 DARPA Urban Challenge photo by AIM Team members Linda and Tom Graham.*

HECK BATS DO IT - CAN'T BE HARD TO DO.
While sonar is better known as a navigation tool of bats (10 - 120 kHz) and dolphins (1 - 120 kHz), some people are able to use clicks to image their surroundings and identify the materials that objects are made of.   Early hopes were that machines would be able to navigate using sonar.  It turns out that the application of sonar is more complex than expected.  Sonar beams refused to behave the way engineers wanted them to and apparently, bats and dolphins are doing a lot of signal processing to decode the image they get of their environment.

THINK AGAIN - NEW RESPECT FOR BAT BRAINS
Applications engineers moved away from sonar for a while, in favor of lasers, but they are back now finding ways to make use of acoustics.  Computer processing power has increased a lot recently.  Work on Artificial Intelligence software for processing acoustic and sonar signals has made dramatic progress since the early attempts.  Sonar range finder transducers, for use in air, are now being advertized as plug-and-play.  The production numbers for these transducers is up and the prices are dropping rapidly.  I have been quoted prices as low as $8 for a single transducer and promised lower prices if I buy in quantity.  At those prices, the question becomes "How many would you like to use in your design?"


This sonar transducer is one inch in diameter and has smart software built into it.

SMART BUMPERS FOR SAFER CARS
Typical automotive sonar transducers have a useful detection range of 0 to 50 feet with the most common being 0 to 15 feet. 
Simple transducers that have appeared on rear bumpers of automobiles and small trucks have worked so well at detecting obstructions (bikes and kids) in the 0 to 12 feet range that they are now appearing on front bumpers as well.  These are useful also as part of the fully automatic parking feature available now.  The automobiles being advertized that automatically parallel park themselves use a sonar transducer to profile the size of the parking spot as you pass it getting ready to park.  

SONAR AND MOVING TARGETS
Beyond just detecting the presence of an object in the sensors field, relative motion produces a doppler shift that can provide useful information about the object.  In the echo, frequency shifts up if the object detected is approaching the sensor, frequency shift is down if the object is moving away.  In the case of a bat looking for food the fluttering of insects wings have a dramatic effect on the frequency shift in the returned echo that attracts the bats attention.  Fastest wingbeat -- Midge, at 62,760 beats per minute, Slowest wingbeat -- Swallowtail butterfly -- 300 beats/minute.

HOLLYWOOD'S ILLUSTRATION OF HOW IT WORKS
For those of you seriously interested in sonar, buy a copy of Dare Devil - the Jennifer Garner movie for your acoustical engineering reference collection and note the counter locations of the best acoustical imaging scenes so you can use it to show non-sonar people what it is that you are talking about.

For those of you mildly interested in sonar, rent a copy and fast forward through it to the echo ranging scenes and the rain scenes.  These are some of the best illustrations I have seen of visualizing your surroundings using sound.  We used to use sonar to image our surroundings in the submarine business, but it looks cooler in the movie.

For those of you not much interested in sonar, it has Jennifer Garner in it.

AIM WORKSHOP - TRAINING FACILITY
We have a variety of sonars here at the AIM Team workshop that we are experimenting with, learning about them, trying them.  They range from fish finders to parking aids.  The Massa Products Corporation, Hingham, MA has a very good Introduction To Electroacoustics that covers the subject in just a few pages on-line.

*Top photo: 2007 DARPA URBAN CHALLENGE PHOTO
Here is a great picture of the 2007 DARPA Urban Challenge vehicle "BOSS", first place winner, taken by AIM Team members Linda and Tom Graham.  Team Leader Red Whittaker of CMU explains how the vehicle drove itself 55 miles through city traffic.  That is a very smart car.  I want one.  How about you?




GO ROBOTS !

Posted by Paul Grayson on December 10, 2007 | Comments (0)