Daniel D. Shin

Development of a SMA-based actuator for compact kinetic energy missile

In this paper, a prototype SMA-based actuator for a compact kinetic energy missile was fabricated. Thin film nickel-titanium was selected as an actuating mechanism because it exhibited high power density compared to other smart materials. This study represents a proof of concept that high drive frequency and high power density can be both achieved with thin film SMA. The thin film reached a drive frequency of 80Hz while achieving a power density of 27900 Watts/kg. As for the pump, the power density was 2.93 Watts/kg, but obtaining higher value can certainly be achieved by reducing the chamber weight through optimization. In any case, CFD analysis revealed that the pump chamber had to be redesigned to change the flow profile because the present design created non-circulating dead zones immediately adjacent to the diaphragm. Therefore by redirecting the liquid flow to directly cool the SMA diaphragm improved the heat transfer and thus improved performance of the actuator can be achieved.

STRESS INDUCED PHASE CHANGING MATERIAL FOR THERMOACOUSTIC REFRIGERATION

ABSTRACT A novel concept to use a stress induced phase transformation in NiMnGa for solid state refrigeration is investigated. The stress needed to induce a phase transformation was measured at temperatures from 24 to 60°C. The stresses were sufficiently low enough such that an acoustic wave can in theory induce the phase transformation. DSC measurements were done on the NiMnGa material to measure the latent heat that can be absorbed and release. Theoretical calculations of the coefficient of performance for a heat pump using this stress induced thermal phenomena showed a possible efficiency of 67%. A solid state heat pump using a piezoelectric or magnetostrictive transducer to generate the acoustic pressure wave and a fluid medium suspended with NiMnGa nanoparticles is suggested as a possible implementation of the concept.

Miniature actuator using thin-film shape-memory alloy

In this paper, a thin film nickel-titanium (NiTi) shape memory alloy (SMA) was used to develop a prototype compact hybrid actuator. SMA was selected as an actuating mechanism because it had the highest work density among active materials. Combining this attribute with high frequency response of thin films resulted in large power output. High drive frequency was also possible in part from manipulating the liquid flow to directly cool the SMA membranes. The actuator reached a drive frequency of 100Hz while producing 2.6Watts. The results indicated that power output is linearly related to the drive frequency since the volume flow rate increased proportional to frequency.

High Performance Microvalve Array

The fabrication, analysis, and testing of a large flow rate and high frequency microvalve array are presented in this paper. The array consists of 88-microvalves fabricated on a silicon-on-insulator (SOI) substrate. The SOI wafer simplifies the fabrication process and eliminates the need for multi-layer surface micromachining process and bulk wafer-bonding procedures. The analytical resonant frequency of the valve is up to 50 kHz and operates at high delta pressures (i.e. 0.14 MPa). The microvalves are fabricated with various flap widths ranging from 300 to 400 μm and flap thickness ranging from 10 to 13 μm. The results indicate that flap displacement and flow rate are strongly dependent on flap thicknesses and to a lesser degree on flap widths increases. The resonance frequency with valve flap thickness increases and width decreases. Comparison between predicted and measured flow rate shows good agreement. A flow rate up to 35 cc/sec was measured. A failure criterion is also presented using the fracture stress analysis and shows good agreement with experimental result.Copyright

Microvalve for SMA-based CHAD

This paper describes the development of a micro-machined passive check valve for an SMA-based compact hybrid actuator device (CHAD). The overall diameter of the valve is 12 mm and the thickness is 1 mm. The structure houses an array of 56 micro check valves. Each micro valve has a 250 μm diameter orifice covered by 10 mm thick nickel flap. Stoppers on each micro valves limit the displacement of the flaps during an opening. This design allows the Ni flaps to withstand high-pressure gradient created by the actuator while achieving high flow rate. A finite element analysis is used to characterize the static and dynamic behaviors of the valve flap for the prediction on flow rate. The prediction is found to be in good agreement with the experiment on static flow rate. The test results indicate that the flaps are able to withstand pressure difference of 0.28 MPa while achieving flow rate of 20 cc/sec. The valve also has low cracking pressure and reverse leakage.

Compact Hybrid Actuator Device (CHAD) for ultracompact, navigation, guidance and control

The objective of our Compact Hybrid Actuator Device (CHAD) program is to produce a novel, ultra-compact, high force actuator to meet the aggressive requirements for navigation, guidance and control of a compact missile as well as other military and commercial applications confronted with tight volume constraints. Our approach to this challenge uses the high power density of thin film shape memory alloys coupled with fluid rectification and commercial power electronics. Phase One of our program demonstrated the performance of critical technical elements in a non-compact form factor. NiTi films were reproducibly deposited and then fabricated into bubble actuators that demonstrated ≥ 100 Hz performance when forced convection heat transfer to a liquid was optimized. Increased efficiency in thermal activation was achieved through high Joule heating rates for short duty cycles; this allowed simplification of the power electronics. These technical elements were combined to produce a thin film SMA pump which ultimately demonstrated force outputs on the order of 250 N and average power densities on the order of 50 W/kg when operated at 100 Hz. The demonstrated performance shows great promise for applications requiring ultracompact form factors with high output force.