The Model 18A/40 is a small, very inexpensive ultrasonic transducer that operates in the
40 kHz frequency region, and can be used in applications where larger variations in
electroacoustic performance from unit to unit are acceptable. The transducer is capable
of operating as both a professional transmitter and a receiver. The transmitting response peaks at the
resonant frequency. The receiving response is specified with a 3.9 k OHM resistor across the
transducer and peaks at the anti-resonant frequency.