Stretchable touch sensitive keypad

AbstractWe present a multifunctional and stretchable capacitive sensor capable of accurately detecting large strains, pressure and human touch. The device is prepared as a plate capacitor with stretchable thin gold film electrodes. Using conventional patterning techniques, a 3x3 array of stretchable sensors is prepared and implemented as a largearea 9-node touch pad. The array can operate when worn around the wrist or subjected to large deformations (>10% strain), measure pressure (up to 160kPa) and register touch applied with a finger, a metallic or plastic stylus

Thick-film piezoelectric slip sensors for automatic grip control in prosthetic hands

INTRODUCTION Piezoelectric sensors produce a charge when mechanically deformed (for example through the action of an applied force). This charge decays with time dependant upon the connected electronics. This makes piezoelectric sensors an ideal candidate for detecting the vibrations (change in surface forces) associated with object slip from a prosthetic hand. Most previous work undertaken with piezoelectric sensors to detect object slip from upper limb prosthetics has used polyvinylidene fluoride strips (PVDF) (Dario 1996) (Howe 1989). This type of sensor has a low sensitivity of around 20-30 pCN-1 and comes in a sheet format so would have to be adhered manually to a hand. Thick-film piezoelectric sensors offer a superior alternative for this application with a much higher sensitivity than PVDF of around 130pCN-1 (Torah et al 2005) and the thick-film fabrication technique allows the sensors to be accurately printed onto the flat surface of a prosthesis finger or fingertip

A new binderless thick-film piezoelectric paste

This paper presents an investigation into a screen printable piezoelectric paste formulated from a blend of PZT-Pz29 powders of different mean particle size mixed in an organic vehicle. In order to enhance d33 properties of the thick-film (a piezoelectric coefficient), no binder material was mixed into the paste. The d33 coefficient and maximum applied electrical field of devices processed at peak temperatures of 150ºC, 200ºC, 750ºC, 850ºC and 1000ºC were measured and the film adhesion assessed using scratch and tape tests. The applications that would benefit from these enhanced properties are also discussed. The thick-films produced at these processing temperatures showed good adhesion to 96% alumina substrates. They also showed the ability to withstand high electrical fields and a significant enhancement in d33 when compared to thick-film materials processed at similar temperatures using polymer or glass binders. A maximum average d33 value of 168pCN-1 was obtained for samples processed at a peak temperature of 1000ºC. This is 28% higher than the reported d33 value for a conventional piezoelectric thick-film processed at the same temperature. All samples withstood electric field strengths of over 14MVm-1 which is between 2.5 to 4.5 times higher than that used for conventional piezoelectric thick-films

Thick-film piezoceramic “slip sensors” for a multifunctional prosthetic hand

The majority of prosthetic hands lack an intelligent feedback control system meaning that the user has to rely on visual feedback to detect whether an object is being crushed or if it is slipping out of the hand. Recently, a new type of fingertip for the Southampton Hand has been developed encompassing an array of thick-film sensors to measure grip force and the onset of object slip. There are three types of sensor used: piezoresistive thick-film sensors to detect the force on a finger, a piezoelectric thick-film sensor to detect the onset of slip and a thick-film thermistor to monitor temperature. Some initial results are presented for the “slip” signals produced from the thick-film piezoelectric sensor. The sensor has already shown its ability to differentiate between the initial contact with an object and the object sliding past the fingertip. It may also be able to determine several variables and parameters such as: object acceleration, the coefficient of friction between the sliding surfaces and the force applied by the fingertip to the sliding object. There characteristics could then be used in a closed loop control system