SMT transducers are audible devices which consist of a surface mount housing that encloses a mounted sounder element. SMT transducers do not have any circuitry, so this means the user must apply a square or sine wave at the appropriate rated frequency & appropriate rated peak-to peak voltage (Vpp) as listed on the data sheet.
Both piezoelectric and electromagnetic technology are used in SMT transducers. Piezoelectric SMT transducers will typically have a higher rated sound frequency, require more peak-to-peak voltage, but will draw much less current. Electromagnetic SMT transducers will have a lower rated sound frequency for the size, will produce more sound level at lower voltage levels, but current draw will be much higher. Because electromagnetic SMT transducers can produce high sound levels at lower voltages, this technology is more popular for the SMT package type. Here is a chart comparing two similarly sized SMT transducers with one using piezoelectric technology and the other electromagnetic:
| Part Number | Sound Freq. | Voltage Rating | Current Draw | Typical Sound Level at 10 cm | Size |
|---|---|---|---|---|---|
| AST1027MW-03Q | 2700 Hz | 2.5 to 4.5 Vpp | 80 mA @ 3 Vpp | 87 dB @ 3 Vpp | 10 x 10 x 3.2 mm |
| AST1109MLQ | 4100 Hz | 1 to 20 Vpp | 1 mA @ 5 Vpp | 75 dB @ 5 Vpp | 11 x 9 x 1.7 mm |
So, which is electromagnetic and which is piezoelectric? The frequency, voltage, and current draw all show significant differences between the electromagnetic one (P/N AST1027MW-03Q) and the piezoelectric one (P/N AST1109MLQ). For piezoelectric technology, the more Vpp applied, the louder the sound level will be, so if the user has 20 Vpp available, then applying this voltage to P/N AST1109MLTRQ, a louder sound will be generated. Some users take advantage of this aspect of piezoelectric technology to control the sound level of the audible device by applying more or less Vpp. On the other hand, electromagnetic technology has a much narrower rated voltage window, so applying max voltage (4.5 Vpp) to P/N AST1027MW-03TRQ will not increase the sound level significantly higher than when applying 3 Vpp
While some SMT transducers packages only have two physical SMT terminals, others have four SMT terminals with two of them used only for mounting. These two extra “dummy” terminals do not need the Vpp signal applied to them. You can see this package difference in the two part numbers previously discussed:
Mallory has 11 different piezoelectric SMT transducer part numbers, and 22 different electromagnetic SMT transducer part numbers. All of Mallory’s SMT devices are available in Tape-n-Reel (T&R) packaging, and all SMT devices can also be purchased in smaller quantities by purchasing partial reels (Cut-Tape), or some SMT devices are available in Tube packaging. Mallory SMT devices with the suffix “TRQ” are Tape-n-Reel packaging, while the part numbers without the “TR” are either Cut-Tape or in Tubes, so see the individual data sheet for the packaging information.
Mallory is an ISO 9001:2015 company that has been supplying SMT buzzers and transducers for 25 years. Mallory has the broadest line of audible and visual signaling devices in the industry, and has been the technology leader for over 50 years.