Two transducer topologies are available: monostatic or bistatic. Topology must be based on the short range requirement.

Monostatic topology is when a single transducer both transmits an echo and listens for returning echoes. This is the lower-cost method preferred in most applications. The drawback of the monostatic transducer topology is that the excitation ringing-decay of the sensor creates a blind zone that limits the minimum detection range. In a monostatic configuration, this blind zone can be reduced by adding a damping resistor. More information can be found in Section 2.6.

To eliminate this ringing decay, a bistatic topology must be used where there are two separate transducers — one for transmitting and one for receiving. The drawback to using the bistatic approach is that additional calibration required, as the designer must consider the angle of the incoming echo at the receiver when computing the time-of-flight calculation.

Figure 2-7 Monostatic vs Bistatic Configuration