Patent GB-1084860-A (GB)
Title: Improvements in or relating to devices for investigating the chemical and/or physical nature of substance
IPC: G01N22/00
Filed: 1965-08-24
Abstract: 1,084,860. Measuring chemical and physical properties electrically. N. KAISER. Aug. 24, 1965, No. 36213/65. Heading G1N. Apparatus for investigating the chemical and physical nature of substances by measuring the attenuation and phase shift of microwave energy on reflection from or transmission through a sample substance comprises a klystron oscillator 1 the output of which passes through a frequency meter 4 to a measuring bridge 9 comprising in one branch a calibrated phase shifter 12 and sample vessel 14 and in the other branch calibrated attenuators 10, 11. The bridge output passes through an attenuator 18 and a modulator 19, fed from a 100 kc/s crystal oscillator 32, to a magic T 23 where the energy is split equally between path 25 containing differential demodulator diodes 27 and path 24 comprising a 90‹ phase shifter 28 and differential demodulator diodes 26. 10% of the klystron output is fed via phase shifter 12a and magic T 29 to the demodulator diodes. The outputs of the diodes, related to the attenuation and phase change components of the measuring bridge output respectively, are fed through twin amplifier 30 to an oscilloscope 31 where they are displayed. Oscillator 32 also feeds a brightness control device 33 of the oscilloscope to ensure that the Lissajous figure, normally an ellipse, is only reproduced at one end of its major axis. The scale can be calibrated in decibels and degrees. A line recorder may be provided. The klystron may be crystal controlled stabilized and its frequency is selected to fall within the range of absorption, dispersion, or any molecular resonance, frequencies of the sample. The apparatus may be used for chemical analysis and measurement of rates of reaction; recording hardening processes in polymerizing reactions, e. g. in artificial silk production; measurement of moisture content; recording changes in bacterial or tissue cultures and digestion of albumens by fermentation; and investigation of gases and plasmas. The sample is contained in, or passed through, the sample vessel and the measuring bridge is initially balanced by adjusting attenuators 10, 11 and phase shifter 12, subsequent departures from balance denoting changes in the sample. In modifications (not shown), each branch of the measuring bridge may contain a sample vessel, e.g. to allow for effects due to solvents. For investigation of reactions, a common sample vessel may be used with two or more sets of apparatus operating at different frequencies typical of the initial reagents, intermediate and/or end products. A sample cell for a citrate blood coagulation test is described with reference to Fig. 2 (not shown). The cell (35) is of the same crosssection as the waveguides used and has inlet and outlet drillings (37, 38). Reflection-free windows (39, 40) and tuning pins (not shown) are provided. Inner and outer heating jackets (41, 44) enable the sample vessel to be brought to the correct temperature before introduction of the sample which is also pre-heated. Cooling coils (47, 48) are provided for the waveguides.