Car Bumper Effects in ADAS Sensors at Automotive Radar Frequencies

Abstract

Radars in the W-band are being integrated into car bumpers for functionalities such as adaptive cruise control, collision avoidance, or lane-keeping. These Advanced Driving Assistance Systems (ADAS) enhance traffic security in coordination with Intelligent Transport Systems (ITS). This paper analyzes the attenuation effect that car bumpers cause on the signals passing through them. Using the free-space transmission technique inside an anechoic chamber, we measured the attenuation caused by car bumper samples with different material compositions. The results show level drops lower than 1.25 dB in all the samples analyzed. The signal attenuation triggered by the bumpers decreases with the frequency, with differences ranging from 0.55 dB to 0.86 dB when comparing the end frequencies within the radar band. Among the analyzed bumper samples, those with a thicker varnish layer or with talc in the composition seem to attenuate more. We also provide an estimation of the measurement uncertainty for the validation of the obtained results. Uncertainty analysis yields values below 0.21 dB with a 95% coverage interval in the measured frequency band. When comparing the measured value with its uncertainty, i.e., the relative uncertainty, the lower the frequency in the measured band, the more accurate the measurements seem to be.

Keywords: ADAS technologies; ITS technologies; attenuation measurements; automotive radar; material characterization; radio propagation; wireless.

Figure 1

Layer distribution schema of car bumpers.

Figure 2

Front- and backsides of bumper samples D (down) and E (up).

Figure 3

Diagram of the measurement setup.

Figure 4

Setup inside the anechoic chamber: (a) without sample (view from the transmitter side); (b) with sample (top view).

Figure 5

Sample holder, (a) receiving side, and (b) transmitting side.

Figure 6

Measured attenuation as a function of the frequency for the different bumper samples.

Figure 7

Measured attenuation as a function of the frequency for flat bumper samples.

Figure 8

Results of several measurements of sample D.2.

Figure 9

Uncertainty in dB derived from measurements of sample D.2, with a 95% coverage interval.

Figure 10

Uncertainty in % derived from measurements of sample D.2, with a 95% coverage interval.

Figure 11

Measured attenuation of bumper samples A.2 and D.2. Dotted lines represent attenuation measurements without absorbers covering the multiplier and the back of the antennas, and the solid lines represent the measurements after adding the absorbers.