In some cases, the source and receiver transducers are separate devices but are located next to each other in what is called a collocated arrangement (Figure 4). Another option is to have them separated by a substantial distance and also have different orientations if the object being sensed is at an angle. This is called a bistatic configuration. In this case, the object deflects the impinging energy rather than reflecting it back to the source. Separate devices also allow for flexibility in their selection to match the application. It also allows for flexibility in the power of the transmitter’s drive circuit as it’s no longer proximal to the sensitive analog circuitry of the receiver. For these situations, a pairing such as the 40 kHz UT-1640K- TT-2-R ultrasonic transmitter and UR-1640K-TT-2-R ultrasonic receiver may be a good choice. The transmitter measures 12 mm high and has a diameter of 16 mm. It requires just 20 VRMS drive, and it produces an SPL of 115 dB while presenting a nominal capacitance of 2100 pF and 80° beamwidth directivity. The complementary receiver has the same appearance, dimensions, directivity, and capacitance as the transmitter (Figure 5).
Figure 4: In a collocated arrangement, the ultrasonic source and receiver are located adjacent to each other. (Image source: Science and Education Publishing Co.)
Figure 5: The UT-1640K-TT-2-R ultrasonic transmitter and the UR-1640K-TT-2-R ultrasonic receiver provide different, complementary functions, but have the same form factor and dimensions. (Image source: PUI Audio)
Sensing fluid flow Beyond basic object detection, ultrasonic transducers are used for non-invasive, non-contact measurement of liquid and gas
flow rates. For these applications, the transducers operate at higher frequencies, typically above 200 kHz, to provide the needed measurement resolution.
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