Historically, piezoelectric vibration energy harvesters have been limited to operation at a single, structurally resonant
frequency. A piezoceramic energy harvester, such as a bimorph beam, operating at structural resonance exchanges
energy between dynamic and strain regimes. This energy exchange increases the coupling between piezoceramic
deformation and electrical charge generation. Two BVEH mechanisms are presented that exploit strain energy
management to reduce inertial forces needed to deform the piezoceramic, thus increasing the coupling between structural
and electrical energy conversion over a broadband vibration spectrum.
Broadband vibration excitation produces a non-sinusoidal electrical wave form from the BVEH device. An adaptive
energy conversion circuit was developed that exploits a buck converter to capture the complex waveform energy in a
form easily used by standard electrical components.
A mathematical model was developed to represent the behavior of circular piezoelectric bimorphs in a synthetic jet
actuator. Synthetic jet actuators are popular active flow control devices whose application is being widely explored in
aerodynamics. The material properties were matched to those of PZT-5A mounted on a substrate. The actuator’s
geometry consisted of a cylindrical cavity of low height to diameter aspect ratio. A bimorph formed one of the cylinder’s
bases. The ingestion/expulsion orifice for the synthetic jet actuator was placed in the edge of the cavity so as to allow for
either the present single bimorph or future dual bimorph configurations. Simply supported and rigidly supported
boundary conditions were assessed around the circumference of the bimorph. The potential of alternate mode shapes
occurring in the bimorphs during operation of the synthetic jet was evaluated. A limited parametric study was conducted
varying the thickness of the piezoelectric wafers used in the bimorphs and the geometry of the cavity and orifice. Results
were obtained for the displacement of the center of the bimorph’s surface and the peak velocity of the air being ingested
and expulsed through the orifice. These results were compared to values obtained through a mathematical model.
Experimental data present in literature were also compared. The mathematical model was seen to have considerable
potential for predicting the performance of synthetic jet actuators and their resonant frequencies but failed to capture the
effects of acoustic coupling with the cavity, which is a topic of future research.
Piezoelectric materials have long been used for active flow control purposes in aerospace applications to increase the
effectiveness of aerodynamic surfaces on aircraft, wind turbines, and more. Piezoelectric actuators are an appropriate
choice due to their low mass, small dimensions, simplistic design, and frequency response. This investigation involves
the development of piezoceramic-based actuators with two bimorphs placed in series. Here, the main desired
characteristic was the achievable displacement amplitude at specific driving voltages and frequencies. A parametric
study was performed, in which actuators with varying dimensions were fabricated and tested. These devices were
actuated with a sinusoidal waveform, resulting in an oscillating platform on which to mount active flow control devices,
such as dynamic vortex generators. The main quantification method consisted of driving these devices with different
voltages and frequencies to determine their free displacement, blocking force, and frequency response. It was found that
resonance frequency increased with shorter and thicker actuators, while free displacement increased with longer and
thinner actuators. Integration of the devices into active flow control test modules is noted. In addition to physical testing,
a quasi-static analytical model was developed and compared with experimental data, which showed close correlation for
both free displacement and blocking force.
Direct structural deformation to achieve aerodynamic benefit is difficult because large actuators must supply energy for structural strain and aerodynamic loads. This ppaer presents a mechanism that allows most of the energy required to twist or deform a wing to be stored in descrete springs. When this device is used, only sufficient energy is provided to control the position of the wing. This concept allows lightweight actuators to perform wing twisting and other structural distortions, and it reduces the onboard mass of the wing-twist system. The energy shuttle can be used with any actuator and it has been adapted for used with shape memory alloy, piezoelectric, and electromagnetic actuators.
60-NiTinol (60% Nickel 40% Titanium content by weight) was developed by the US Naval Ordnance Laboratory in the 1950s as a structural form of NiTinol. Due to 60-NiTinol's extreme brittleness the application development was abandoned. Nitinol Technology Inc. successfully produced cutting instruments with this material in the early 90's. Subsequent work demonstrated that with the proper heat treatment the material exhibits a strong, stable, shape memory response. Unlike other Nitinol alloys, 60-Nitinol does not require cold work. Initial testing of this material shows that the transition temperature is a strong function of the heat treatment. Therefore the same ingot of material can produce samples with superelastic and shape memory effect. Samples with different heat treats exhibited transition temperatures varying from -55 C to +60 C. Additionally, appropriate heat treatment allows the material to exhibit extreme hardness (Rc 63) or a two-way shape memory effect. This paper provides the first study of the thermomechanical properties, including stress-strain curves and thermal cycling, of axially loaded slender 60-Nitinol samples. The samples were tested at extremely high stress level greater than 695 MPa (100 ksi) with recoverable strain of 2.5%. In addition, flexures designed with potential for aerospace applications were tested. This initial research shows that 60-Nitinol has some enticing advantages over 55 Nitinol, however further study is required.
Current research has shown that aircraft can gain significant aerodynamic performance benefits from active flow control (AFC). AFC seeks to control large scale flows by exploiting natural response triggered by small energy inputs. The principal target application is download alleviation of the V-22 Osprey under the DARPA sponsored Boeing Active Flow Control System program. One method of injecting energy into the flow over the V22 wings is to use an active vibrating surface on the passive seal between the wing and flapperon. The active surface is an oscillating cantilevered beam which injects fluid into the flow, similar to a synthetic jet, and interacts with the flow field. Two types of actuators, or flipperons, are explored. The first is a multilayer piezoelectric polyvinylidene fluoride cantilevered bender. The second is a single crystal piezoelectric (SCP)d<SUB>31</SUB> poled wafer mounted on a cantilevered spring steel substrate. This paper details the development effort including fabrication, mechanical and electrical testing, and modeling for both types of actuators. Both flipperons were mounted on the passive seal between a 1/10th scale V22 wing and flapperon and the aerodynamic performance evaluated in low speed wind tunnel. The SCP flipperon demonstrated significant cruise benefits, with increase of 10 percent lift and 20 percent angle of attack capability. The PVDF flipperon provided a 16 percent drag reduction in the hover mode.
Thermally activated shape memory materials have been employed as actuators fora number of years. They are generally activated by electrical resistance heaters, or sometimes by direct electrical resistance. Thermoelectric modules can also provide activation energy, and they provide several unique advantages over the more conventional heating methods. Antagonistic Shape Memory Actuator systems, the utilization of thermoelectric modules as heaters, and the advantages and practical approaches for utilizing actuators employing thermoelectrics are discussed.
This paper describes the continuing development of Boeing High Power Piezo Drive Amplifiers. Described is the development and testing of a 1500 Vpp, 8 amp switching amplifier. This amplifier is used to drive a piezo stack driven rotor blade trailing edge flap on a full size helicopter. Also discuss is a switching amplifier designed to drive a Piezo Fiber Composite (PFC) active twist rotor blade. This amplifier was designed to drive the PFC material at 2000 Vpp and 0.5 amps. These amplifiers recycle reactive energy, allowing for a power and weight efficient amplifier design. This work was done in conjunction with the DARPA sponsored Phase II Smart Rotor Blade program and the NASA Langley Research Center sponsored Active Twist Rotor (ATR) blade program.
The Shape Memory Alloy (SMA) Consortium (SMAC) has been developing actuators and magnetically actuated SMA materials. This paper will summarize the overall SMAC developments, and concentrate on the development of a SMA torsional actuator. This is being developed for quasi-static twisting the V-22 rotor blades for added performance. The paper provides updated results to the 1999 SPIE paper on this subject, including further and more focused development of the actuator that combines thermoelectric heat control with SMA materials.
This paper describes the development and testing of a 4KVpp, 750 ma piezo drive switching amplifier. This amplifier is used to drive Piezo Fiber Composite material imbedded in a 1/6 scale CH-47 blade. This amplifier will allow higher harmonic control of the blade thus reducing rotor craft vibration and nose. The amplifier recycles reactive energy required to drive piezo material allowing for an efficient amplifier design. A multi level topology is used allowing solid sates switching devices with voltage rating of half the output drive voltage. The amplifier modular design allows easy migration to the power levels required to drive a full size CH-47 blade. This work was done in conjunction with the Smart Structures for Rotor Craft Control in support of DARPA/ONR.
This paper describes the development and testing of a 3KV, 400 ma piezo drive switching amplifier. This amplifier is used to drive Piezo Fiber Composite material embedded in a 1/6 scale CH-47 blade. This amplifier will allow higher harmonic control of the blade thus reducing rotor craft vibration and noise. The amplifier recycles reactive energy required to drive piezo material allowing for an efficient amplifier design. A multi level topology is used allowing solid state switching devices with voltage rating of half the output drive voltage. The amplifier modular design allows easy migration to the power levels required to drive a full size CH-47 blade. This work was done in conjunction with the Smart Structures for Rotor Craft Control in support of DARPA/AFOSR.
This paper describes drive amplifier development for large, high voltage piezo actuators. Piezo actuation's highly capacitive nature and its influence on drive amplifiers is discussed. A switching amplifier driving an inductor in series with the piezo material and controlled by an appropriate control law can drive piezo actuators. Since large piezo actuators tend toward higher voltages, a multi- level topology is described that allows drive amplifiers to provide voltages higher than solid state switching device ratings. High efficiency piezo drive amplifiers must accommodate energy stored in the piezo material. A topology is described that actively stores the capacitative energy, thus reducing the size, weight and power consumption of the electronics system. Test results are presented for a developmental 1.2 KV, piezo drive amplifier that can drive a 0.6 (mu) F piezo actuator at 100 Hz. This work done in conjunction with Smart Structures for Rotor Craft Consortium in support of AFORS/DARPA.