Method of measurement of dielectric permittivity using an impedance meter.

Impedance meters allow the measurement of the impedance of the dielectric permittivity of biological materials over a wide frequency range. In the case of study of biological objects in the liquid phase they are incorporated into the measuring chamber - which is a capacitor - and then attaches it to the impedance meter. Used in the exercise impedance meter TESLA BM 508 allows the measurement of impedance modulus and phase angle between the voltage and current - for frequencies above 0.5 MHz. Electric equivalent circuit of this system can be summarized as follows:

C

The impedance of system is presented in the form of a complex number, and the means hindrance, - the phase angle, e is the base of natural logarithms and "i" is the imaginary unit i =. R and C in the diagram represent the ohmic resistance of the studied biological material and the capacitance of the capacitor filled him. SeriallyconnectedcoilL is theresidualinductance ofwiresconnecting themeasuring chamberwiththe impedance meter.

Inorder to expressthe searchchamber capacitybythe measured values​​of hindranceandphase shift, it is convenient touse thecomplex numbers. For parallel connected resistance and capacitor, the resultant conductivity is:

where = 2f, and f is a frequency of the applied voltage.

The resultant resistanceof thispart of thecircuit isconnected in serieswith the resistance ofthe inductioncoil, giving a total impedance of thecircuit:

After separating the real and imaginary parts, we get:

Hence the hindrance of the whole system is:

The tangent of the phase angle is equal to the ratio of the imaginary part to the real, so:

By solvingequation (4)and(5) can be obtained correspondingexpressionfor the capacitance offilledcapacitor:

Dielectric permittivityis definedas the ratio ofthe capacityof the filled capacitor to the capacity of avacuum capacitor, so:

where Cois the capacity of the vacuum capacitor.

Study of the dispersion of the dielectric permittivity of selected biological objects.

I. Course of the exercise.

1.Connect the meterimpedanceto the current generator(mains).

2.Turn on the power (mains) and leave the meter for 10 minutes turned in order to heat.

3. Connect the filled measuring chamber to the impedance meter and set the appropriate ranges of hindrance(Z) and phase angle ().

4. Measure Z and  at the frequency specified in the following table.

ATTENTION!

After completion of the measurements on the meter, set the range of the hindrance to the value of 100 kW.

Measuringtable

f [MHz] / log f / Z [] /  / C [F] / ’ = C/Co
0.5 / 5.7
0.63 / 5.8
0.79 / 5.9
1 / 6.0
1.26 / 6.1
1.59 / 6.2
2 / 6.3
2.51 / 6.4
3.16 / 6.5
3.98 / 6.6
5.01 / 6.7
6.31 / 6.8
7.94 / 6.9
10 / 7
12.6 / 7.1
15.9 / 7.2
20 / 7.3

II. Computational informations.

1. On the basis of equations (6) and (7) calculate the capacityof the filled capacitor(C) and the dielectric permittivity (') of the studied object for all measured frequency, assuming theresidualinductance ofwiresL = 0.06 H and the capacity of the vacuum capacitorCo = 0.15 pF. The results put in a table.

2. Make a graph of the dielectric permittivity on the frequency in the semi-logarithmic scale. An example of thegraph(without plotted experimental points) is shownbelow.

Study of liquid's absorption spectra with a spectrophotometer SPECTRONIC 20D+.

The aim of the exercise is to determine and analyze the absorption spectra of colored liquids (e.g.hemoglobin solutionandcopper sulfate). We use for this purpose spectrophotometer, which allows the study of dependence of permeability and absorption on the wavelength.

I. Course of the exercise.

  1. Turn on the spectrophotometer with knob < 0%T> and wait 15 minutes.
  2. Perform a nulling of device:

a)check whether theholefor samplesis empty and closed,

b)pressing the <mode> switch ontransmittance measurementmode,

c) with the <0%T> knob zero the value of the transmittance.

  1. Press <mode> and turn on the absorption mode.
  2. Place the solvent in the measuring chamber and close the lid.
  3. Set the wavelength indicated by a teacher.
  4. Set the filter in the correct position for the selected wavelength.
  5. With the <100 %T/0A> knob zero the value of absorption.
  6. Remove the solvent, and in measuring chamber put the tested solution and close the lid.
  7. Read the absorbance A.
  8. Repeat activities 4-9 for another wavelength indicated by the teacher.
  9. Repeat the measurements for another solution.

II. Computational informations.

  1. The results of measurement must be recorded in the table.
  2. Foreachsolution, draw a graph of dependence of absorption on wavelength.
  3. Make the interpretation of graphs and draw conclusions.

Hemoglobin / Coppersulphate
[nm] / A / [nm] / A

Determination of the concentration of solutions using spectrophotometric method.

The purpose of this exercise is to investigate the effect of solution's concentration on the absorption of light; and the use of absorptiometry for determining the concentration of colored solutions .

I. Course of the exercise.

  1. Fill the measuring vessel: first of them with solvent, the second with the solution of hemoglobin contained in a test tube marked as 1.
  2. Place the vesselsin a spectrophotometer.Vessels should be caught for the lateral, unpolished walls. Control translucent glass surfaces and, if necessary, wipe with a cloth.
  3. Set the changer that, so the light passes through the solvent.
  4. Pointer deflectionof the meterset to zeroabsorption.
  5. Move the changer so that the light passed through the solution and read the value of absorption A.
  6. The vessel with the solvent leave as a control.
  7. The second vessel fill successively with solutions of tubes 2-10, reading to themabsorption, after checking whether for the solvent A = 0.
  8. Repeat this with the hemoglobin solutions of unknown concentration indicated by the teacher.
  9. Repeat the measurements for other liquids (chlorophyll).

II. Computational informations.

  1. The results of measurements put in the table:

c / A
1
2
3
4
5
6
7
8
9
10
X1
X2
  1. Plot a graph of the absorption on concentration of the solution.
  2. Make the interpretation of graph and draw conclusions.
  3. From the graph read the values ​​of the unknown concentrations of the solutions.