handbook of modern sensors

3.14 Dynamic Models of Sensor Elements 113
(A)
(B)
(C)
Fig. 3.48. (A) Traveling electromagnetic wave has electric and magnetic field vectors; (B)
unpolarized electric field viewed along the x axis (magnetic vectors are not shown but they are
always there); (C) vertically polarized electric field.
liquid-crystal displays (LCDs) and in many optical sensors that are described in the
corresponding chapters of this book.
3.14 Dynamic Models of Sensor Elements
To determine a sensor’s dynamic response, a variable stimulus should be applied to its
input while observing the output values. Generally, a test stimulus may have any shape
or form, which should be selected depending on a practical need. For instance, for
determining a natural frequency of an accelerometer, sinusoidal vibrations of different
frequencies are the best. On the other hand, for a thermistor probe, a step function of
temperature would be preferable. In many other cases, a step or square-pulse input
stimulus is often employed. The reason for that is the theoretically infinite frequency
spectrum of a step function; that is, the sensor can be tested simultaneously at all
frequencies.
Mathematically, a sensor can be described by a differential equation whose order
depends on the sensor’s physical nature and design. There are three general types of
relationship between the input s and the output S: a zero-order, a first-order and a
second-order response.