Although the sensors are inexpensive, fast, and have a large operating range, ultrasonic

sensors have many shortcomings and limitations which should be aware of such as

specular reflection foreshortening and cross-talk. Ultrasonic sensors rely on reflection,

and so are susceptible to specular reflection. Figure 2.18 (b) shows the specular

reflection occurs when the wave form hits a surface at an acute angle and the wave

bounces away from the transducer. Ideally all objects would have a flat surface

perpendicular to the transducer. The other side, if the sonar has a 30 degree field of

view, it means that sound is being broadcast in 30 degree wide cone. The foreshortening

problem occurs when the surface is not perpendicular to the transducer. Figure 2.18 (a)

shows one side of the cone will reach the object first and return a range first. Another

problem is the receiving sonar is unable to tell the difference between sound generated

by itself or its peers. Figure 2.18 (c) shows the problem where it is called cross-talk,

because the sound waves are getting crossed and then procures a wrong reading [3].

2.3.2.2Infrared Sensor

Figure 2.19: Infrared Sensor [22].

Infra red sensor is one of the proximity sensors. In an infra red sensing system, there are

two important components which are emitters and receivers. Figure 2.18 shows the

emitter is used to emit infrared light to an object and the receiver is used to pickup the

reflection from the reflective object. Infrared radiation exists in the electromagnetic

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