COUNCIL FOR THE CENTRAL LABORATORY OF THE RESEARCH COUNCILS Dimples Day Meeting – 25 April 2006 Graham Arthur Central Microstructure Facility Rutherford Appleton Laboratory Chilton, Didcot Oxon OX11 0QX

COUNCIL FOR THE CENTRAL LABORATORY OF THE RESEARCH COUNCILS Outline 1.Dimples Fabrication 2.Pressure Sensor Design 3.Other items i.SPIE Smart Structures and Materials Symposium Two new mechanisms for dimple actuators ii.Asymmetric dimple

COUNCIL FOR THE CENTRAL LABORATORY OF THE RESEARCH COUNCILS Dimple Fabrication

COUNCIL FOR THE CENTRAL LABORATORY OF THE RESEARCH COUNCILS Characterisation of elastomers As supplied, MED-4905 and Sylgard 186 are highly viscous (up to 600,000cP). They must be diluted to allow spin- coating onto wafers at the required thicknesses (10-50um). Dilutions ranging from 25 – 60% solids are being tested. Results (see following slides) All spin-coating was at 1500rpm for one minute. Elastomer 20  m film40  m film MED % solids, w/w58 % solids, w/w Sylgard % solids, w/wn/a

COUNCIL FOR THE CENTRAL LABORATORY OF THE RESEARCH COUNCILS Characterisation of elastomers (left) MED-4905 Dilution vs. Coating Thickness (right) MED-4905 Dilution vs. Ln Coating Thickness

COUNCIL FOR THE CENTRAL LABORATORY OF THE RESEARCH COUNCILS Characterisation of elastomers (left) Sylgard 186 Dilution vs. Coating Thickness (right) Sylgard 186 Dilution vs. Ln Coating Thickness

COUNCIL FOR THE CENTRAL LABORATORY OF THE RESEARCH COUNCILS Characterisation of elastomers Data for Sylgard 186 shows that increasing viscosity gives poorer uniformity of coating – multi-layer coatings should lead to improvements.

COUNCIL FOR THE CENTRAL LABORATORY OF THE RESEARCH COUNCILS Inspection of Carbon Powder The carbon powder used at Imperial for the dimple electrodes has been inspected using an scanning electron microscope (SEM) at RAL. This reveals (see next slide) that there is a vast range of particle sizes (~50  m to <250nm) Is this a problem? An alternative (finer) “carbon nano-powder” material is available from Sigma Aldrich and a small quantity have been obtained by Stella. Particle size is stated as <30nm. Cost is £75 for 25g

COUNCIL FOR THE CENTRAL LABORATORY OF THE RESEARCH COUNCILS Inspection of Carbon Powder

COUNCIL FOR THE CENTRAL LABORATORY OF THE RESEARCH COUNCILS New Dimple Design Following input from Stella, a new dimple wafer has been designed. Key points are: Top edge of substrate has been rounded to avoid high strain at edge causing elastomer failure. Carbon powder electrodes will be used (and sealed to surface if necessary) 4 dimples - diameter is 10mm and separation is 10mm Design layout is shown on next slide. Full process is shown in an accompanying Powerpoint file.

COUNCIL FOR THE CENTRAL LABORATORY OF THE RESEARCH COUNCILS New Dimple Design

COUNCIL FOR THE CENTRAL LABORATORY OF THE RESEARCH COUNCILS Pressure Sensor Design

COUNCIL FOR THE CENTRAL LABORATORY OF THE RESEARCH COUNCILS New Pressure Sensor Design Existing sensor: Silicon Nitride membrane (typically 0.5  m thick) Four strain gauges – two sensing and two reference Low sensitivity New sensor: Elastomer membrane (10-50  m thick) Improved sensitivity (>2 orders of magnitude possible) Possibly too much strain – but tuneable via film thickness……will dynamic range be a problem? New strain gauge arrangement (via Lorenzo) – four sensing (two radial strain, two tangential strain)

COUNCIL FOR THE CENTRAL LABORATORY OF THE RESEARCH COUNCILS New Pressure Sensor Design

COUNCIL FOR THE CENTRAL LABORATORY OF THE RESEARCH COUNCILS New Pressure Sensor Design

COUNCIL FOR THE CENTRAL LABORATORY OF THE RESEARCH COUNCILS Other Items

COUNCIL FOR THE CENTRAL LABORATORY OF THE RESEARCH COUNCILS SPIE SS&M Symposium SPIE’s Smart Structures and Materials symposium consisted of 15 conferences. Two had double sessions making 17 sessions in all, with running in parallel – lots of running between sessions and still missed some! Topics covered included: Electroactive polymers (EAPs) and devices, Smart wings, (Bio)mimetics, Nastic structures, Active control, Non- destructive evaluation (NDE), Energy harvesting, Ferroelectrics, Magneto-rheological fluids, Nanostructures, Sensors, BioMEMS, Shaped memory materials,…….

COUNCIL FOR THE CENTRAL LABORATORY OF THE RESEARCH COUNCILS SPIE SS&M Symposium With regard to EAPs: AMI is marketing EAP devices (eg “Universal Muscle Actuator, UMA – diameter ~5cm) Most EAP actuators are centimetre-scale – we are millimetre-scale (and smaller) Most actuators are “push-pull” (muscle-type) actuation University of Pisa is making a bump-type structure to use as a fluidic pump and mechanical actuator In comparison with most other researchers we appear to be at a comparable stage but working at a smaller scale

COUNCIL FOR THE CENTRAL LABORATORY OF THE RESEARCH COUNCILS SPIE SS&M Symposium Ideas from conference have inspired two new dimple actuator ideas: 1.Pull-pull dimple using a pre-strained actuation films. - Modification of AMI’s UMA. 2.Multi-layer stack giving a reciprocating action - EAP stack similar to Univ. of Pisa

COUNCIL FOR THE CENTRAL LABORATORY OF THE RESEARCH COUNCILS Basic Principle A voltage is applied to the compliant electrodes either side of the EAP material. The electrostatic pressure compresses the EAP and as it is incompressible ( =0.5) it spreads in X & Y, increasing in area. EAP has low E (typically MPa) EAP Basic Principle P Compliant electrodes EAP V

COUNCIL FOR THE CENTRAL LABORATORY OF THE RESEARCH COUNCILS Universal Muscle Actuator If an EAP film is pre-strained (stretched) across a frame, when the voltage is applied, movement is seen in the plane of the film as the strain is relaxed – the area of the electrodes increases. The UMA consists of two such films, back-to-back and joined at their centres. There are now forces acting out-of-plane.

COUNCIL FOR THE CENTRAL LABORATORY OF THE RESEARCH COUNCILS UMA Operating Principle Switching voltage rapidly between actuation films provides an oscillating action. The DA50 has a diameter of >5cm

COUNCIL FOR THE CENTRAL LABORATORY OF THE RESEARCH COUNCILS New Dimple Actuator #1 Modifying this idea, with only the lower side being active (upper surface has no electrodes) a dimple actuator can be formed:

COUNCIL FOR THE CENTRAL LABORATORY OF THE RESEARCH COUNCILS New Dimple Actuator #2 Dimple design #2 requires a long thin strip of EAP material. Top and bottom are coated with carbon or carbon grease to create the electrodes. The strip is folded back and forth many times to form a stack. When a voltage is applied the stack is squeezed by the electrostatic forces. Some spreading occurs, but the height change is the desired movement:

COUNCIL FOR THE CENTRAL LABORATORY OF THE RESEARCH COUNCILS New Dimple Actuator #2 Voltage “off”Voltage “on”

COUNCIL FOR THE CENTRAL LABORATORY OF THE RESEARCH COUNCILS New Dimple Actuator #2 The actuating mechanism can be incorporated into a piston-style dimple with a downward-only reciprocating motion. Airflow

COUNCIL FOR THE CENTRAL LABORATORY OF THE RESEARCH COUNCILS The actuating mechanism can be incorporated into a piston-style dimple with a downward-only reciprocating motion. New Dimple Actuator #2 Airflow

COUNCIL FOR THE CENTRAL LABORATORY OF THE RESEARCH COUNCILS Other items Following some questions, at an earlier meeting, about the possibility of making dimples with an asymmetric cross section, some simple FEAs were carried out: Square dimple – for simplicity at this stage Elastomer membrane – properties similar to those of MED-4905 Grooves etched into upper surface of membrane (depth = 50% of film thickness)

COUNCIL FOR THE CENTRAL LABORATORY OF THE RESEARCH COUNCILS Other items Grooves etched into upper surface of elastomer membrane Dimple outline

COUNCIL FOR THE CENTRAL LABORATORY OF THE RESEARCH COUNCILS Other items Applying pressure gives the dimple shape shown here