The problem of obtaining low loss ultrasonic delay lines for switching, computer, and certain radar applications is discussed. An analysis is made of structures using half‐wavelength and quarter‐wavelength bonds between the transducer and the acoustic medium to widen the pass‐band; results are listed for both quartz crystal and barium titanate transducers.For barium titanate transducers (80 percentBaTiO3, 12 percentPbTiO3, 8 percentCaTiO3), it is shown that a theoretical flat band width of approximately 30 percent with less than 1 db midband loss can be obtained with a bond of negligible thickness. This band width can be increased to approximately 46 percent without additional loss if a properly designed bond is used, (i.e.,14λbond for radiating into water,12λfor use with a fused silica delay medium). A 70 percent band width can be obtained with only 4 db loss per transducer.Confirming experimental results are described for delay lines using quartz crystals and one‐half wavelength plastic seals or one‐quarter wavelength solder seals. For the latter, band widths of 85 percent of midband frequency have been obtained. An efficient delay line usingBaTiO3transducers is also described.