Application of sensors

Application of microelectronic devices in medicine allows not only to reduce the sizes of devices and devices, but also to create devices and sensors to them, very small sizes. Such small sensors can safely be entered inside of cavities of various bodies, and even to be implanted in a fabric of an organism. In this connection new diagnostic methods have appeared. They is called endoradiometry.

For example, the tiny electric manometer is applied, for measurement of pressure in cavities of heart. It becomes stronger on the end of cordial catheter. Silicone resistance connected to a membrane, perceiving external pressure serves in it as the sensor. The new method endoradiometry is developed for research of a gastroenteric path. Research of temperature, pressure and acidity of environment is made during all paths by means of endoradioprobe, having the form of a pill which the investigated patient swallows. The microradiogenerator is in a pill. It contains the power supply, the transistor, details of contours and on the open end - the sensor influencing frequency of generated fluctuations, radiated in the form of electromagnetic waves.

Semi-conductor sensor serves as the sensor of temperature in endoradioprobe, the sensor of pressure - the coil of inductance of an oscillatory contour of the generator connected with a membrane, the sensor of acidity of environment - two platinum electrodes. The alkaline microaccumulator is the power supply depending on the energy, being a data carrier, distinguishes mechanical, acoustic (sound), temperature, electric, optical and other sensors.

In some cases sensors name on the measured size: so, for example the sensor of pressure.

Sensors are characterized by function of transformation, sensitivity and the time characteristic (inertia).

Function of transformation - functional dependence of target size Y from entrance X, which is described by analytical expression Y= f (Х) or it is represented in the form of the schedule. The most simple and an opportunity is directly proportional dependence Y = kХ. Sensitivity of the sensor shows, in what measure the target size reacts to change entrance size . It is expressed in Ohms on millimeter (Ohm/mm), millivolts on Kelvin in depending on a kind of the sensor.

Sensitivity of consecutive set of sensors is equal to product sensitivity all sensors.

Time characteristics of sensors are essential. The physical processes in sensors do not occur instantly, it leads to delay of change of target size in comparison with change entrance. Analytically such feature, inertness, leads to dependence of sensitivity of the sensor on speed of change of entrance size dx/dt or from frequency at change х under the harmonious law dx/dω. At work with the sensor it is necessary to consider possible errors specific to them. To the reasons of errors can be:

1) temperature dependence of function of transformation;

2) hysteresis - delays Y or X even at slow change of entrance size, as a result of irreversible processes in the sensor;

3) inconstancy of function of transformation in time;

4) return influence of the sensor on the biological system, leading change of indications;

5) inercia the sensor (its neglect time characteristics).

Transfer of a signal. Radiotelemetry.

Communication between the device of removal and the registering device on wires, or by radio is called radiotelemetry. Such measurements concern to telemetry or to biotelemetry. The radiotelemetry is applied also for endoradio researches of digestive tract. The very small capsule with a radio transmitter (endoradio probe) is swallowed by patients.

On change of frequency of the transmitter by the receiver located near to the patient, it is possible to measure pressure, degree of acidities or alkalinity, temperature and other parameters in the location of a capsule (look fig.4).

Fig. 4.

The scheme of endoradio probe for definition of activity of digestive enzymes.

It consists from three basic parts: 1 - the source of a voltage; 2 - a disk pressed from a ferromagnetic powder and particles, dissolved enzyme; 3 - the transistor and other elements of the radioscheme. The disk is located in demountable element. It can be replaced by another after the unitary use. The disk is pressed to the inductance coil 4 and forms with it the closed contour. In process of dissolution of a disk by digestive enzymes inductance L of a circuit decreases and frequency of the generator increases. On perceived frequency it is possible to judge about activity of enzymes.

Analog registering devices

Registering devices are often used in medical electronics. They write down the information on any carrier. It allows to store, reuse, process and analyze the received medical and biologic information.

Displaying and registering devices are subdivided on analog - the continuous, discrete and combined, combining opportunities analog and discrete.

Analog registering devices are most widespread in practice of medical and biologic researches. Some of them are called recorders.

In medicine, biology and physiologies basically are used next ways of registration of the information on the carrier: drawing of a layer substances (dye); change of a condition of substance of the carrier: electrochemical, electrophotographic and magnetic record; removal of a layer of substance from the carrier: the smoked surface, thermal record.

The elementary recorder is kymograph (fig.), working from the got spring, or electrokymograph. Idea of kymograph - uniform rotation or moving of a surface of the carrier. The recording devices used in medical devices transform an electric signal in mechanical displacement. In these devices the current which is passing on coils, cooperates with a magnetic field of a constant magnet. As a result of this interaction the mobile part deviates proportionally to force of a current or an electric signal. The writing element leaving a trace on the moving carrier of record is connected to a mobile part.

Except for the one-coordinate recorders fixing time dependence, in a research practice have was extended two-coordinate recorders.

In a medical practice for fixation of the information the combined devices, for example electron beam tubes are used still.

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