The Wilcoxon Research model F4/F7, a dual piezoelectric and electromagnetic vibration (shaker) system, provides wide-frequency-range structural excitation. It simulates a multitude of external forces, determines structural resonance frequencies, and provides structural characterizations under excitation. Its unique design combines a high-frequency piezoelectric vibration exciter (model F7) encircled by a low-frequency electromagnetic vibration exciter (model F4). Units employ a transducer base containing a force gauge for test structure force monitoring and an accelerometer for measuring resultant motion. The model F4 electromagnetic vibration generator provides low frequency excitation from 10 Hz to 7,500 Hz while the model F7 piezoelectric vibration generator produces vibration forces over a range of 500 Hz to more than 20 kHz. MEGGITT SENSING SYSTEMS, San Juan Capistrano, CA. (949) 493-8181.