A small mutti-layer piezoelectric actuator, which contains a stack of piezoelectric crystals in a thin-layered Compact Structure, was evaluated for its suitability as a stimulator in middle ear hearing implants. Using laser Doppler vibrometry for non-contact vibration measurement, the actuator was found to have a useful bandwidth spanning the range of audio frequencies. During simulated surgical implantation on human temporal bones, one side of the actuator was cemented to the medial wall of the attic of the middle ear and the other side was cemented to the body of the incus. Stapes displacement from actuator excitation at 3.5V(rms) was equivalent to that from acoustic stimulation at 90 dB SPL below 1 kHz, increasing to 120 dB at 8 kHz, which is more than adequate stimulation of the ossicular chain. The total harmonic distortion (THD) was less than 2.5%, over the audio frequency range. The corresponding power consumption was 0.7 mW per volt of excitation at I kHz, which is low enough for the actuator to be used in a partially implantable hearing implant. The surgical implantation and positioning of this type of actuator are straightforward due to the simple linear motion it provides. (C) 2001 Elsevier Science Ltd. All rights reserved.