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handbook of modern sensors

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7.7 Radar Sensors 289<br />

(A)<br />

(B)<br />

Fig. 7.40. Piezoelectric ultrasonic transducer: (A) input voltage flexes the element and transmits<br />

ultrasonic waves, whereas incoming waves produce output voltage; (B) open-aperture type <strong>of</strong><br />

ultrasonic transducer for operation in air. (Courtesy <strong>of</strong> Nippon Ceramic, Japan.)<br />

(A)<br />

(B)<br />

Fig. 7.41. (A) ultrasonic transducer for air. (B) directional diagram.<br />

and receiver. A typical design <strong>of</strong> an air-operating sensor is shown in Figs. 7.40B and<br />

7.41A. A directional sensitivity diagram (Fig. 7.41B) is important for a particular<br />

application. The narrower the diagram, the more sensitive the transducer is.<br />

7.7 Radar Sensors<br />

7.7.1 Micropower Impulse Radar<br />

In 1993, Lawrence Livermore National Laboratory had developed a micropower<br />

impulse radar (MIR), which is a low-cost noncontact ranging sensor. The operating<br />

principle <strong>of</strong> the MIR is fundamentally the same as that <strong>of</strong> a conventional pulse radar<br />

system, but with several significant differences. The MIR (Fig. 7.42) consists <strong>of</strong><br />

a white-noise generator whose output signal triggers a pulse generator. The pulse<br />

generator produces very short pulses with an average rate <strong>of</strong> 2 MHz ±20%. Each pulse

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