Sonar Tracking SP2011

Progress Report, February 11, 2011.

• I am currently working on determining the feasibility of this project. To do this, I have done the following:
  • Determine the maximum velocity of the mobile platforms.
    • I found the maximum forward radial velocity was 7 rad/s. The max backwards radial velocity was 8 rad/s.
    • This translates to a maximum forwards and backwards velocity of 0.35 m/s and 0.4 m/s respectively.
    • Image of .vi used to find radial velocity.
    • This result is lower than hoped. We were expecting a velocity of around 1.0 m/s.
  • Set-up of Ultrasonic Transmitter and Receiver
    • Setting up the transmitter and receiver proved harder than expected. With help from Ed Richter, I got a .vi working that could run both the transmitter and receiver on the same Elvis board. However, there was an issue of the signals being mixed somewhere between the board and the computer; even if I had the transmitter unplugged, the receiver would still show a strong peak at the frequency the transmitter was programmed to transmit (40khz). So, my temporary solution is to run the receiver and transmitter on different Elvis boards (each of which is connected to a different computer). This works, but is not the most practical solution, so work will have to be done in that regard.
  • Analyze the Fourier Transform
    • Analysis is being done with the following settings:
      • Fs of 250k, taking 250k samples over 1 second. Emitting a sine wave of frequency 40khz.
      • Default Amplitude of sine wave was set at 3. Found setting higher created a more notable peak. Max setting is 10.
    • Moving transmitter by hand comparable to that of a mobile platform creates a noticeable shift in the peak of the receiver's FFT graph. Not sure of said peak's consistency over repeated experiments.
  • Analysis of the Spectogram
    • This is my first time working with a spectogram (or hearing of a spectograph). While I am not entierly familiar with it yet, I have made some progress with it.
      • Initially, I had settings that created a notable band of frequency around 40hz.
      • I am currently using a Hanning filter. The filter's setting has a very big effect on the output of the spectogram, and will probably have to be experimented with to a fair extent later on.
      • Increasing the frequency bins leads to a higher frequency band on the output of the spectogram.
      • This behavior is not what I expect. Will ask Phani about it next week.
• End Progress Report

Progress Report, February 18, 2011.

• We figured out how to properly use the spectogram. Yay!
• I am now trying to find the sampling criteria we need to have in order to detect a change in the mobile platform's velocity.
• The sampling frequency, Fs, is 250,000hz. We also know the robot can move at a maximum of 0.4 m/s.
• To calculate this, I have combined several equations to come up with this:
  • N = Fs/[f0*(vr-vs)/(v+vs)] , where:
    • N: number of samples
    • Fs: sampling frequency
    • f0: input signal frequency
    • vr: velocity of receiver
    • vs: velocity of transmitter
    • v: velocity of ultrasonic wave in air
• Which for my purposes, would look like:
  • N = 250k/[40k*(vrobot/340)]=2125/vrobot
    • where vrobot is the minimum change in velocity measurable
  • So, assuming I want a resolution of 0.01m/s, I would need to sample for 0.85 seconds.
    • Window Length: 212,500
    • Frequency Bins: 131,072
    • Time steps is variable. Preferably: (212,500/n)+1, where n is the number of time windows wanted.
• I tested to see how the receiver will deal with receiving both the original signal from the receiver and the reflected signal from the mobile platform. This was done by combining two sine waves.
  • I assumed the signal sent by the receiver would be at 40,000 hz with an amplitude of 10 (the previously measured max).
  • The first wave is at 40,000hz with an amplitude of (10/(1.05)), which assumes the receiver is 5cm away from the transmitter.
  • The second wave is at 40,035hz. This assumes a speed of around 0.3 m/s. The amplitude of the second wave is an approximation, based on the assumption that the amplitude of the wave decreases proportionally with distance. The calculations I ran assumed the mobile platform was 2 meters away from the receiver at t=0, and was moving away from it. So, the amplitude was: (10/(1+.05))