1. Severaldifferent types of bi-morph valves have beenexploredto dateandhavebeenavailablecommercially in thepast.Hewlett-Packard'*"andIC Sensors8*11912 in the US andRobertBoschGmbH13in Germanyhaveconducted work with this valvetype. The Hewlett-Packardconceptis shownin Fig. 3 to illustratetheconcept.Figure3 is adapted from Ref. 10This valve conceptwasdevelopedby Barm0022. It featuresa nickel-silicon bi-morph membraneactuator. Nickel andsilicon membranethicknessesareboth between 25 - 50 pm. As can be seen,by inspectingFig. 3 more ' closely,themembraneisbendoutwardslightly in theclosed position throughthe useof a centralboss that is slightly higherthanthesealingring alongtheperimeterof the valve body, thus providing spring forces aiding in sealing the valve. The valveappearsto havebeenfabricatedthrough a seriesof anisotropicetches,combinedwith silicon fusion bondingstepsandmetaldepositionsequences.
2. The'ICSensorsvalvehasbeenoperatedatpressures up to 50 psig0022. Reported leak rates are somewhat ambiguous.At 30 psi inlet pressure,leakratesof 3 x 10m4 scclsechavebeenreported0022,while at 5 psi inlet pressures thereportedleakratewas5 x 10m4scc/sec0022,i.e. largerthan for thehigherpressurevalue. Maximum flow ratesof up to 150 seemwere reported0022. Valve responsetimes range between100to 300msto fully openthe valve0022, depending onthepowerlevel. Additionaltime is requiredto closethe valveby cooling,leadingtototalvalvecycletimesof about 250- 450ms0022. Powerrequirementsfor this valve aregiven as0.5W8.Totalpackageweight of theIC Sensorsvalveis 5.8grams8.
3. Hewlett-Packard IC Sensors Robert Bosch GmbH Pressure(psi) 5-200 l-50 0.15- 15 Power(W) 1 0.5 1 Weight(gr) 5.8 5.8 Size(cm3) 2.3xi .7x0.6 2.7x2.3x1.1 1x0.6x0.13 ResponseTime(ms) 100 100-300 50 Stroke(micron) 50-100 25 8 Flow Rate 0.1- 1000 upto 150 5 Reference
4. Shape-memoryalloycanbe deformedplasticallyat low temperatures,asaccomplishedby the spring actionin thevalveshownin Fig. 5.Uponheatingaboveits so called transitiontemperature,thealloy "remembers"its original,or parent,stateandreturnsto this state.The parentstateis establishedthrougha previoushigh-temperatureannealof thematerialduringfabrication15.Accordingto Ref. 15, the shape-memoryactuatorisformedby sputter-depositionfrom a nickel-titaniumtarget.The resulting film then behaves like thebulk shapememory-alloymaterial.Heatingof the Ti/Ni actuatorisaccomplishedby passingaresistivecurrent throughit. Actuatorfilm thicknessesrangebetween4 - 10 pm accordingto Ref. 15. The silicon spring returnsthe valve to its closedposition afterthe currentthrough the Ti/Ni membranehasbeenswitchedoff.