This paper presents an approach to define an optimal piezoactuator length to actively control structural vibration. The
optimal ratio of the piezoactuator length against beam length when a pair of piezoceramic actuator and accelerometer is
used to suppress unwanted vibration with direct velocity feedback (DVFB) control strategy is not clearly defined so far.
It is well known that direct velocity feedback (DVFB) control can be very useful when a pair of sensor and actuator is
collocated on structures with a high gain and excellent stability. It is considered that three different collocated pairs of
piezoelectric actuators (20, 50 and 100 mm) and accelerometers installed on three identical clamped-clamped beams (300
* 20 * 1 mm). The response of each sensor-actuator pair requires strictly positive real (SPR) property to apply a high
feedback gain. However the length of the piezoactuator affects SPR property of the sensor-actuator response. Intensive
simulation and experiment shows the effect of the actuator length variation is strongly related with the frequency range of
SPR property. A shorter actuator gave a wider SPR frequency range as a longer one had a narrower range. The shorter
actuator showed limited control performance in spite of a higher gain was applied because the actuation force was
relatively small. Thus an optimal length ratio (actuator length/beam length) was suggested to obtain relevant performance
with good stability with DVFB strategy. The result of this investigation could give important information in the design of
active control system to suppress unwanted vibration of smart structures with piezoelectric actuators and accelerometers.
The problem considered in this paper is about the collocation strategies of sensor and actuator for the active control of sound and vibration. It is well-known that a point collocated sensor-actuator pair offers an unconditional stability with very high performance when it is used with a direct velocity feedback (DVFB) control, because the pair has strictly positive real (SPR) property. In order to utilize this SPR characteristics, a matched piezoelectric sensor and actuator pair is considered, but this pair suffers from the in-plane motion coupling problem with the out-of-plane motion due to the piezo sensor and actuator interaction. This coupling phenomenon limits the stability and performance of the matched pair with DVFB control. As a new alternative, a point sensor and distributed piezoelectric actuator pair is also considered, which provides SPR property in all frequency range when the pair is implemented on a clamped-clamped beam. The use of this sensor-actuator pair is highly expected for the applications to more practical active control of sound and vibration systems with the DVFB control strategy.
This paper presents the theory, design, and evaluation of a smart device for the enhanced separation of particles mixed in fluid. The smart device takes advantage of the ultrasonic standing wave, which was generated by the operation of a piezoceramic PZT patch installed in the smart device. The details of the device design including the electro-acoustical modelling for separation and PZT transducer are described at first. Based on this design, the separation device was fabricated and evaluated. In the experiments, an optical camera with a zoom lense was used to monitor the position of interested particles within the separation channel layer in the device. The electric impedance of the PZT patch bonded on the separation device was measured. The device shows a strong levitation force against 50μm diameter sand particles mixed with water at the separation channel in the device. Experimetal results also showed that the device can levitate both <i>heavy</i> and <i>light</i> settled sand particles clouds on the bottom to the nodal lines of the generated standing wave field in the separation channel.
This paper presents a study of a distributed arrangement of double PVDF actuator/sensor pairs bonded on a cantilever beam for the control of vibration at the tip. The arrangement of a single PVDF actuator/sensor pair, in practice, is known to be non-minimum phase due to coupling between in-plane motion and out-of-plane motion. This means that a single pair arrangement does not have the conventional driving-point collocated system property. The stability and performance of the arrangement are limited by finite feedback gains, which can be used with direct velocity feedback control. A double pair arrangement using four layers of PVDF has thus been suggested to overcome this problem. Theoretically, when both the actuator pair and the sensor pair are working out-of-phase, then the response becomes minimum phase since in-plane motion cannot be excited or detected. A smart beam with double PVDF actuator/sensor pairs has been implemented. A triangular shaped actuator/sensor pair was bonded on each side of the beam. The initial experimental measurements with individual pairs of transducers showed a good reciprocity and a strong coupling between out-of-plane and in-plane responses. All the four layers have then been used as out-of-phase actuators and sensors to attempt to measure only the out-of-plane response. However, in practice, this compensation method was found not to discriminate against the in-plane response, due to the direct coupling between the actuation and sensing transducers due to their finite thickness and compliance. Therefore, the four layers smart beam does not have a minimum phase property. A new arrangement of actuator/sensor pair for in-plane compensation is then suggested and discussed.