Sensor piezo

The truly wearable sensing inter ces must be easy to use and customised for patient requirements of age, body size and posture, state of mobility etc. The mechanical processing of integrating sensors must be done using industrially viable techniques which neither affects the durability nor the function of smart fabrics. Many sensors can be used to measure the strain and deformation in materials such as piezoelectric sensors, piezo-resitive sensors, and fibre optic sensors. 

Biosensors may provide the basis for in-field analyses and real-time process analysis. However, biosensors are generally limited to the determination of a limited range of analytes in defined matrices. Enzyme-based biosensors, principally acetylcholinesterase (AChE) inhibition, have been successfully used in environmental analysis for residues of dichlorvos and paraoxon, " carbaryl " and carbofuran. " Immunochemically based biosensors may be the basis for the determination of pesticide residues in liquid samples, principally water and environmental samples, but also fruit juices. The sensors can be linked to transducers, for example based on a piezo-... 

Fig. 5.59 shows a section through a Piezo-resistive silicon pressure sensor. The ambient pressure is applied from above, while the pressure being measured is applied from below. A silicon membrane that deforms under the pressure is applied to a silicon carrier structure. Piezo-resistive structures are fitted in the membrane, which then change their resistance accordingly when the membrane deforms. A bridge circuit generates an electrical output signal which is proportional to the difference in pressure. 

Piezoresistive sensors, 20 655-656 Piezo technology, in commercial printing, 14 327... 

In addition, the reduction of infection risks by a controlled overpressure is advantageous. During sterilization, pressure is of paramount interest for safety reasons. A variety of sterilizable sensors exists, e.g. piezo-resistive, capacitive or resistance strain gauge sensors (Fig. 6), but not all of them are sufficiently temperature compensated. 

Fig. 6. Schematic design of a pressure sensor. A flexible stainless steel membrane interfaces the pressure-sensitive elements (bridged piezo-resistors) from the measuring liquid. Some products contain the amplifier electronics in the housing and are (somehow) temperature compensated. The shown 2-strand cabling mode resulting in a current signal is very convenient...

With the aid of a particular class of materials (thin-film piezoelectrics), incorporation of AW devices and conventional integrated circuit components on the same silicon substrate is in fact possible. Under the proper conditions, a number of piezoelectric materials can be deposited in thin-film form, typically by RF sputtering, and retain their piezoelectric nature. For this to occur, the crystallites that grow during deposition must be predominantly oriented in a single, piezo-electrically active crystallographic direction. Two such materials are 2 0 and AIN the former has been used as an overlayer on Si wafers to fabricate all of the FPW devices studied for sensor applications to date, and also for SAW resonators. Because extremely thin piezoelectric films are readily fabricated, both ZnO and AIN have been used to make bulk resonators that operate at much higher... 

For power sources with reduced size, increased flexibility, longer lifetime, and increased reliability, there are also some approaches concerning the hybridization of the Li microbatteries with energy conversion devices (i.e. solar cells and piezo-electric generator) [11, 12], This is claimed to be particularly feasible for autonomous sensors that do not have a direct connection to a host for either power or communication. 

Two key issues in SECM are speed and resolution. These are tied to the nature of the available tips and the techniques used to move them in the vicinity of the sample. One approach to greater speed is the use of multiple tips. There are a number of approaches to the fabrication of an array of tips. A problem with these arrays is alignment of the array with the sample so that all of the tips are at the same or a known distance from the sample. This can be accomplished by having each tip on its own controllable positioning device, such as an array of cantilevers with individual piezoelectric control (32,33). For example, 50 cantilevers with a 200-/xm period (to cover a span of 1 cm) were fabricated with integrated piezo sensors and zinc oxide actuators. Such an array provided 35 A resolution and a 20 kHz bandwidth. A difficulty with such arrays is the complexity of the instrumentation needed to use them. Each sensor in the array essentially needs its own driver and potentiostat. An alternative would be an array of individually addressable tips on a single chip that all move in the x, y, and z directions in unison. This would require some additional means to orient and align the array chip... 

Especially in rnicromachined sensors, these parasitics are often comparable to or larger than the sense capacitance and can significantly reduce the sensor performance. The relatively small variation of the relative permeability compared with the range of conductance of different materials is the reason why parasitics tend to be much more important in sensors with capacitive rather than (piezo)-resistive interfaces. 

Fig. 2. Measuring set-up (A) photograph of the piezoelectric device and flow system, the inset shows the cell holding the quartz sensor (B) sample QCM sensor with 10 MHz base frequency (as used throughout the described experiments) (C) cross-section through the piezo-cell showing the two rubber O-rings holding the quartz plate, only one side of the sensor is in contact with the fluid (D) cross-section of the cell used for combined piezoelectric and amperometric measurements, the lid also hold a titanium wire electrode and the Ag/AgCI reference electrode.

Campbell, G. A., Mutharasan, R. Monitoring of the self-assembled monolayer of 1-hexa-decanethiol on a gold surface at nanomolar concentration using a piezo-excited millimeter-sized cantilever sensor. Langmuir 2005, 21 (25), 11568-11573... 

Electret materials are meanwhile used in a large number of modern high-tech applications including microphones, acoustic sensors, transducers, radiation and pollution dosimeters, power generators, filters, and many more. Additionally, electret technology is of great interest in the field of biomaterials, for instance in callus formation and wound healing [10, 11], When used in cellular or in multilayer sandwich structures, polymer electrets can exhibit piezoelectricity. Such materials are ferroelectrets, as they show typical features of ferroelectric materials such as piezo-and pyroelectricity [12-17],... 

The components of a TS system are shown in Figure 11.39 (130). A resonance stethoscope is used to transmit crystalline vibrations in the sample to the audio frequency range where they are converted to electrical signals by use of a piezo-electric crystal. The stethoscope is constructed of quartz, which, because of its high Q value, operates mechanically both as a tuned pick-up sensor and as a self-exciting resonator. The unit incorporates a sample-holder head shaped as an acoustic transformer and fitted with a transmitter rod that mechanically matches the piezo-electric cell fixed on a heavy recoil... 

---