Smart uses of QTC

10 SSERC Bulletin 235 Spring 2011

Quantum Tunnelling Composite (QTC) wasfirst produced in 1996 and has proved tobe a very versatile pressure sensor as itsresistance changes from the order of 1012Ω to 1 Ω when pressure is applied. It canbe directly interfaced to electrical andelectronic devices. Carbon compositeshave been known about for many years.Traditionally their resistance changes withpressure but only by a factor of about ahundred. The deformation required tocause a factor of ten change in resistanceis significantly greater than for QTC. QTCis therefore more sensitive to changes inpressure. Unlike QTC, composites cannotbe regarded as insulators when nopressure is applied, so they cannot be usedas switches. These unique properties haveenabled QTC to be used as a sensor in awide variety of applications e.g. electronicblood pressure and respiration ratemonitors. Interactive whiteboards aresensitive to pressure and make use of QTC.A variable speed drill makes use of thedecrease in resistance of QTC withpressure applied to it. The tighter thehandle is gripped the faster the drill turns.Prosthetic hands that are sensitive totouch have a sensing skin of QTC.

This novel material is used in sportswearto monitor foot pressure distributionwhile running and to register a scoringhit when an opponent’s sword hastouched the jacket of a fencer. In termsof Curriculum for Excellence theseactivities are of relevance to the LearningOutcome - Novel materials & theirproperties SCN 4-16a

Here we illustrate the use of QTC tocontrol the motion of an MFA buggyusing simple QTC switches, as well as adesign for buzzing flip-flops that cansense pressure on the soles of the feet.

Using QTC switches to controlthe motion of an MFA buggy■ pellets of QTC, 2x■ flexible plastic sheet (3x6 cm)■ sheet of craft foam (3x6 cm)■ aluminium piece (3x6 cm)■ 1.5 V batteries, 4x■ battery holder for 4x AA batteries■ battery connector.

Buzzing shoesUsing a pair of flip flops, a buzzing shoecan be very easily assembled at low cost.

All you need is:■ pair of flip flops with the strapsremoved■ buzzer, 3 V dc x2■ aluminium squares, 4 x (3 x 3 cm) ■ battery holder x2 for 2 x AA batteriesand 4 x AA batteries■ 4 pellets of QTC■ Corriflute ■ Velcro 20 cm width, 140 cm length■ sheet of craft foam■ pair of pointed scissors and a craft knife■ Elastic 0.5 cm width, length 48 cm

Place the flip flop on top of the one of thepieces of Corriflute and with a felt tip penmark the position of the battery holder,the position of the two holes in the flipflop that the straps went through at theheel end of the flip flop and the singlehole at the toe end on the Corriflute. Usethe scissors to cut away the top layer ofthe Corriflute where the battery is to be(see Figure 5), this indent will keep thebattery holder in position.

This piece of Corriflute forms the sole ofthe shoe. Cut 2 cm slits starting at theposition of the holes in the flip flop at theheal end and going towards the toe endand either side of the single hole 2 cmfrom the edge of the Corriflute at the toeend as indicated in figure 5. Cut slits inthe same position in the flip flop and inthe top layer of Corriflute. These slits arefor the Velcro to be threaded through.

Figure 1 - Cut a 3x 6 cm piece of foamand mark on 3 x 3 mm squares for theQTC pellets 1.5 cm from each end andfrom each side. Using a sharp pair ofscissors cut out the squares in the foamsheet. Insert one QTC pellet into each ofthe square holes.

Figure 2 - Lay the plastic sheet on top ofthe foam sheet and mark the position ofthe holes for the connecting wires so thatthe wires are centrally located either side ofeach of the QTC pellets.

Figure 3 - Make a hole in the aluminiumsheet 0.5 cm from one side and 3 cmfrom each end (a) and thread the barewire from the battery connector throughit. Fold the wire back and twist the wireround itself, or solder, to make a goodelectrical connection. Make holes in theplastic at the positions indicated so theyare just large enough for the wire to passthrough. Take one wire from each of themotors and strip 1.5 cm of wire from theend of each. Thread one of the wires fromeach of the motors through the holes inthe plastic as shown in (c).

Figure 4 - Place the plastic sheet over thefoam sheet, ensuring the QTC pellets arelocated under each wire, put the 3 x 6 cmstrip of aluminium under the foam andwrap Sellotape round them to hold thelayers in position. Connect the other wirefrom the battery connector to the other wirecoming from each of the motors by twistingall three wires together or soldering themtogether. Connect the battery holder to a 6 Vsupply. On pressing the plastic above eachof the QTC pellets, the motors can beturned on and off and their speed controlledso the buggy can be steered around a course.

SSERC Bulletin No 235 Final2:Layout 1 13/05/2011 11:45 Page 10

Smart uses of QTC

Figure 6 – At the heel end of the flip flopcut out a 2.3 x 1.4 cm shape for thebuzzer to fit in. The buzzer has twomounting sockets, to accommodate thesecut two slots 0.5 cm in length. The slotswill hold the buzzer in place. Onecentimetre from the buzzer opening cutout a rectangle 6.8 x 3.2 cm for thebattery holder.

Figure 7 – Take the second piece ofCorriflute and on the side next to the flipflop 1 cm from the heel end of the batteryholder position, mark out a 3 x 3 cmsquare and cut away the top layer of theCorriflute so that one of the pieces ofaluminium just fits into the cut outsquare. This ensures the QTC switch isbelow the on off switch for the battery.

Figure 8 – Strip 2 cm of wire from theblack wire on the battery connector andthread the wire through the Corriflute asshown. Thread the wire through the holein the aluminium square and twist itaround itself or solder to make a goodelectrical connection.

Figure 9 – Place the aluminium square in the square cut out for it in the top layerof Corriflute.

Figure 10 – Strip 1 cm from the end ofthe red wire attached to the battery and 1cm from the end of the red wire attachedto the buzzer, twist or solder these barewires together to make a good electricalconnection. Strip 2 cm from end of theblack wire connected to the buzzer thenthread it through the hole in the second 3x 3 cm square of aluminium. Twist thewire round itself as described previously orsolder to make a good electricalconnection between the buzzer and thesecond sheet of aluminium.

Figure 11 – Cut a 3 x 3 cm square piece of foam. Cut a 3 x 3 mm squarehole in the centre of the square foam for two pellets of QTC to fit in, one on top of the other. Place the foam square on top of the aluminium square located in the Corriflute.

Figure 12 - Cut a 35 cm length of Velcro.Pull the Velcro apart and rejoin the endsso they stick together. Place the join underthe bottom piece of Corriflute half waybetween two of the slits closest to the heel end.

Figure 13 – Slot the Velcro through theslits cut in the bottom layer of Corriflutethen slot the Velcro through the slots inthe flip flop.

Figure 14 – Thread the Velcro through theslots cut in the flip flop.

Figure 5 – Lay one of the flip flops on topof the Corriflute, draw round it and usinga craft knife cut out the shape of the flipflop in Corriflute. Repeat this so you havetwo identical pieces of Corriflute.

SSERC Bulletin 235 Spring 2011 11

SSERC Bulletin No 235 Final2:Layout 1 13/05/2011 11:45 Page 11

12 SSERC Bulletin 235 Spring 2011

The SSERC Bulletin is published by SSERC, 2 Pitreavie Court, South Pitreavie Business Park, Dunfermline KY11 8UB Managing Editor - Fred YoungTelephone: 01383 626070 Fax: 01383 842793 E-mail: sts@sserc.org.uk

Web: www.sserc.org.uk (existing SSERC site), www.science3-18.org/sserc (new SSERC site - under construction) & www.science3-18.org Copyright is held to be waived only for bona-fide educational uses within current Scottish member EAs, schools & colleges.

Smart uses of QTC

Further readingMore detailed theory http://www.peratech.com/qtcscience.phpApplications of QTC http://www.peratech.com/qtcapplications.php

[1] For advice on safe soldering, see: http://www.sserc.org.uk/members/SafetyNet/bulls/199/3-4.htm

Figure 15 – Push the battery holder intothe space cut out for it in the flip flop andpush the buzzer into its slot at the heelend. Sandwich the pink foam, with thetwo QTC pellets embedded in it, betweenthe two aluminium squares. Ensure thatthe wire connections are on opposite sidesof the square so that no shorting out ispossible. Hold them together usingSellotape. Check the buzzer functions byswitching on the battery and squashingthe aluminium plates together. If nosound is heard, widen the top half of theslits to allow enough space for thevibrations of the buzzer, keeping thebottom of the slits narrow so the buzzer isheld in place.

Figure 16 – Push the aluminium squaresandwich into the square insert cut in thetop piece of Corriflute and Sellotape it inposition. Thread the Velcro through theslits in the top piece of Corriflute and pullit through so the two pieces of Corrifluteand the flip flop are held firmly together.

Figure 17 – Cut a 24 cm piece of elasticand sew each end of the elastic to theVelcro on either side of the shoe at theheel end, 5 cm up from the top layer of Corriflute.

Figure 18 – Lift up the section of Corriflute at the heel end and switch on the battery.

Figure 19 – Attach the shoes to your shoesusing the Velcro fastening. Walk along andevery time pressure is applied to the heel abuzzing sound will be heard. Remember toswitch the battery off after use.

Component Source Product code and price

QTC pellet www.mutr.co.uk QTC 001, £0.15 per pill

Battery holder www.mutr.co.uk EC1035, £0.26

3 V d.c. Buzzer www.mutr.co.uk EW2 002D, £0.62

SSERC Bulletin No 235 Final2:Layout 1 13/05/2011 11:45 Page 12