Frequency demodulation of magneto-inductive vehicle signatures for vehicle detection and speed and acceleration estimation using a software defined radio

Victor Aboh, Purdue University

Abstract

A vehicle moving over a magneto-inductive sensor buried underneath the road creates a frequency modulated signal by changing the apparent inductance of a resonant circuit resulting in a signal whose instantaneous frequency varies in time. The oscillators in use energize the sensors in bursts. Three demodulation techniques were evaluated in MATLAB. The first method uses a Fast Fourier Transform (FFT) to compute the frequency spectrum of each burst and then detects the frequency of the burst as the frequency at which the FFT magnitude is maximum. In addition, zero-crossing and phase detector demodulators were also implemented with each demodulator providing a frequency estimate per burst. Experiments were conducted for microloop sensors, which were set up in a speed-trap configuration (two sensors placed in line at a known distance). The vehicles used for this experiment were fitted with Global Positioning System units in order to accurately detect the speed and acceleration of the vehicles for latter comparison. The oscillator’s signal was recorded using a Universal Serial Radio Peripheral and stored on a computer during the vehicles’ passage over the speed-traps. It was found that the FFT demodulator performed better than any of the other methods.

Degree

M.S.E.C.E.

Advisors

Krogmeier, Purdue University.

Subject Area

Electrical engineering

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