Sonar Sensing and its Limitations
You will soon be on a design team about to embark on a project utilizing a mobile robot that uses sonar sensors to detect objects, obstacles, and the world in general. In preparation, you have been asked to write a technical review of sonar sensing and its limitations so that your team can quickly get up to speed on the technology.
Background Information:
You will focus on a specific type of sonar sensor called an ultrasonic range-finder. These devices emit a short burst of sound called a "ping" (actually beyond the range of human hearing, making it "ultrasound"), wait for that ping to bounce off of an object and return, and use the time-of-flight to calculate the distance to the object.
Although these sensors are simple, inexpensive, low-power, and quite accurate in ideal conditions, they suffer from several limitations:
In general:
- Low measurement rate (generally no more than 25 measurements/second)
- Low angular resolution (generally around 20°)
- Difficulty sensing small objects
In specific circumstances:
- Errors when not perpendicular to a flat or sonically-reflective surface
- Errors when facing an inside right-angle corner
What You Should Write About
The goal of the paper is to provide the information necessary to make informed design decisions about sonar sensing.
It should at least include:
- A brief coverage of the theory behind sonar sensing from a functional standpoint. Detailed information about wave shapes, transducer technologies, air pressure, waveform processing, etc. should not be covered.
- A discussion of the limitations of sonar sensing, mainly from a functional standpoint but including the underlying reasons that these limitations exist. The limitations in the previous section are a good starting point.
- A discussion of anticipated problems in provided example situations (more information below).
Note that this is not a ‘checklist' that should be addressed in sequential order. Organize your paper in a logical way.
What Not to Write About
These exclusions are for your benefit in keeping the paper focused.
- Focus only on ultrasonic range-finding. You don't need to discuss any other forms of sonar sensing, or other sensing in general. Do not discuss technologies such as side-scan sonar, sonar imaging, medical ultrasound, echo sounding, or laser, IR, or optical range-finding.
- You don't need to go extremely in-depth about theory. Remember the audience: engineers who are about to use this technology in an already-manufactured, commercial form; not researchers trying to create a new sensor.
- You don't need to justify using sonar sensors. The technology is already chosen; your job is to inform the reader about its use and limitations so that they can make realistic design decisions.
- Do not consider actual implementation. Some examples of what to avoid:
o the specific type of ultrasonic range-finder being used
o how to interface with the sensors, electrically or logically
o anything about software
o specific uses of sonar range-finding: localization, mapping, object recognition, etc.
- Do not discuss anything related to historical development or use of sonar. Consider what the intended audience wants from this paper.
Audience
The intended audience for this document is your peers: engineers who will soon be starting a project using the DE2Bot, and need to understand how sonar works, and how its limitations will affect sensing in certain situations. Although each 2031 student is doing this assignment, in a more realistic situation, one person would do this investigation and use a document like this to disseminate their results to their team.
A DE2Bot will be available in the lab for you to view, and you should assume that your audience is familiar (as you should be) with the general shape and size of it, including a sense of dimensions such as sensor height above the ground.
Required Sections for the Technical Review Paper
The technical review paper will have an executive summary, an introduction, and the body. The body itself will also have two main sections: one for the technical information and one for an application discussion.
Executive Summary.
Even though it comes first, write the summary last. It summarizes the entire document, and it's hard to summarize something that you haven't written. Begin this section with the document purpose and scope, move on to the "big picture" (at most two sentences), and then work to summarize the main points in each section of the report. You're not writing a mystery novel here; let the reader know your findings up front!
Introduction. In the first sentence or two, explicitly state what is being reviewed, and the extent of the paper - the introduction should fully inform the reader whether or not this paper is pertinent to their needs. Define the technology and its use: this section should provide any information that will be necessary to understand the content of the paper but does not belong in the technical body.
Sonar Principles and Limitations. Explain and show how ultrasonic range-finding works and is used. Include visual information wherever possible to most effectively convey the information. This section must be organized using headings and subheadings - consider the most effective layout of information.
Application-Specific Concerns. Considering the situations described below, identify cases where the robot may be unable to provide an accurate measurement, describing the specific reasons for the difficulty.
Notice that there is no conclusion. You are not concluding anything about the technical information nor about your investigation, so there is no reason to have a conclusion section.