Reversible transducer

The testing concepts described so far make explicit use of the fact that additional drive electrodes, together with those used to capacitively sense a primary sensor input signal, may be used for built-in tests. Design for test concepts therefore appear to be limited to the class of sensors employing reversible transducer mechanisms (i.e., capacitance or piezoelectricity) and to their processing sequences. 

Reversible transducers In case the relations of a TF or GY are linear, the operator is a constant matrix that is anti- or skew-symmetric due to power continuity. In case the inputs are independent functions of time (externally modulated MTF or MGY) the anti-symmetric matrix is time variant. In both cases the transduction is reversible in the sense that the sign of the power of each of the ports is always unconstrained, in other words power can flow in both directions. In case of two-ports the matrix is a 2 x 2-dimensional anti-synometric matrix that has only one independent parameternfor the TF or r for the GY ... 

Note that junctions fall into the category of non-mixing, reversible transducers. They may be seen as a TF or MTF with a constitutive matrix that contains only 1,-1, and 0 as matrix elements and modulation consists of changing the absolute values of this matrix. Furthermore, the same holds for multiport substructures that only contain junctions. The transpose of this matrix relates the independent voltages to the dependent ones and thus corresponds to those columns of the reduced incidence matrix of an electrical circuit that relate the link voltages to the branch voltages. 

An ideal sensor recognizes analytes in a sensitive, selective, and reversible manner. This recognition is in turn reported as a clear response. In recent years, conducting polymers have emerged as practical and viable transducers for translating analyte-receptor and nonspecific interactions into observable signals. Transduction schemes include electronic sensors using conductometric and potentiometric methods and optical sensors based on colorimetric and fluorescence methods [1]. 

In broad terms, a flow-through sensor is an analytical device consisting of an active microzone where one or more chemical or biochemical reactions, in addition to a separation process, can take place. The microzone is connected to or incorporated into an optical, electric, thermal or mass transducer and must respond in a direct, reversible, continuous, expeditious and accurate manner to changes in the concentrations of chemical or biochemical species in the liquid or gaseous sample that is passed over it, whether forcefully (by aspiration or injection) or otherwise (gases). 

A sensor is a device able to respond to the presence of one or many given substances in a more-or-less selective way, by means of a reversible chemical interaction it may be employed for qualitative or quantitative determinations (Cattrall, 1997). All sensors are composed of two parts the responsive region and the transducer. The responsive region is responsible for sensitivity and selectivity of the sensor, while the transducer converts energy from one to another form, providing a signal which is informative about the system analyzed. Usually, basic signalprocessing electronics, and control and display units complete the device. 

Closely related to ferroelectricity is piezoelectricity in which polarization is induced and an electric field is established across a specimen by the application of external force (see Figure 6.28a,b). Reversing the direction of the external force, as from tension to compression, reverses the direction of the field. Alternatively, the application of an external electric field alters the net dipole length and causes a dimensional change, as in Figure 6.28c. Piezoelectric materials can be used as transducers—devices that... 

The practical application of ultrasonics requires effective transducers to change electrical energy into mechanical vibrations and vice versa. Transducers are usually piezoelectric, ferroelectric, or magnetostrictive. The application of a voltage across a piezoelectric crystal causes it to deform with an amplitude of deformation proportional to the voltage. Reversal of the voltage causes reversal of the mechanical strain. Quartz and synthetic ceramic materials are used. 

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