on the transducers 32 and 34 are made when the transducer assembly 37 is glued together for this it is not necessary to use a conductive glue any suitable adhesive materials or techniques are acceptable it is actually not advisable to use a conductive glue in this case because it would be difficult to avoid unwanted short circuits however an anisotropically conductive glue could possibly be used i e a glue that is significantly more conductive across the thickness of the glue film than along the glue film but this would increase the manufacturing cost because of the more expensive glue before assembling the transducer assembly 37 the surfaces of electrodes 44 48 52 and 54 on the baseplate 38 and on the cover 42 as well as the surfaces of electrodes 46 50 56 and 58 on transducers 32 and 34 are slightly roughened with sand paper the spacer 40 with acoustic transducers 32 and 34 are then glued between baseplate 38 and cover 42 under pressure which makes the glue film so thin that electrical contact is ensured by the roughness of the adjacent surfaces this bonding technique is described in a handbook by the dutch company philips piezoelectric ceramics 2nd ed 1974 appendix b bonding techniques in one embodiment the bonding process is further helped by the fact that the spacer 40 is somewhat thinner than the transducers 32 and 34 which concentrates the pressure on the electrode areas during the gluing a sheet of rubber is pressed against the cover 42 to distribute the contact pressure.