Specifications
l)lnstrument generates a current in the range 2P9uA-3mA.
The current introduced intp the human body should be in the range 60OuA-80OuA.
2)Three types of waveform can be generated: square, triangular and sinusoidal.
3)Vpltage amplifier gives gain of 21.,
4)cutoff frequency of low pass filter is 40Hz.
5)The outputJs stored in matlab figure file(.fig) format.

Figures
Figure 1 depicts the complete block diagram of the instrument.
Figure 2 depicts the blocks inside the current generation unit of the instrument.E
Figure 3 depicts the blocks inside the voltage sensing unit of the instrument.0
Field of invention
The field of Invention is biomedical electronics. Research is continuously going on in this field to find new non-invasive diagnostic techniques. Bioimpedance measuring technique is completely a non invasive technique and the results obtained can be accurately Interpreted if extensive and intensive research is carried out in statistical analysis of the impedance values recorded.
Brief description of figures:

Figure 1 is the block diagram.of the. complete instrument. It gives an overview, of the arrangement of various blocks inside the instrument. The current source introduces a sinusoidal current into a section of human body and the voltage across the section is sensed by the voltage sensing unit.

Figure 2 depicts the internal circuitry of the current generation circuit. First a sinusoidal voltage is generated using waveform generator IC 8038 and then this voltage is converted into current using V to I converter..
Figure 3 depicts the internal circuitry of the voltage sensing unit. The sensed voltage is first passed through an instrumentation amplifier which amplifies the low amplitude bioimpedance signal. The amplified signal is then passed through a demodulator to remove the carrier component. The demodulated signal is then passed through a low pass filter to remove the high frequency components.
Detailed Description of the invention

The present invention deals with the design of a low cost bioimpedance measuring instrument. The objective of this invention was to design a low cost bioimpedance measuring instrument so that researchers and scholars can use this instrument to record the bioimpedance signals, process the signals and use it for diagnostic purposes. The instrument designed uses tetra polar method, to record the signals. It takes power from the mains and it records the signal in matiab figure file format so that methods of signal processing can be easily applied on the signal recorded. The instrument designed was tested on patients at a hospital in Ghaziabad. The signal, recorded was used to calculate certain parameters useful for diagnostic purposes.
There are three most popular electrode impedance technologies namely, thoracic electrical impedance cardiography, whole body electrical impedance cardiography and regional impedance cardiography. In this invention we have used the regional electrical impedance cardiography which usually uses the two current electrodes and two sensing electrodes that are placed on a local or a regional position of a limb. Some of the previous studies have indicated that the regional impedance cardiography is as accurate as the thoracic or the. whole body electrical impedance cardiography with advantage of using; peripheral rather than thoracic impedance waves.
Although bioimpedance measurement technique is not a new technique in biomedical diagnostic techniques but research is still going on how to make this technique a standard procedure for diagnosis of a particular diseases. To make this technique a standard procedure it is required that a large amount of data be collected fora particular disease, for a particular community and analysis to be done, correfating the disease with the signal recorded. To enable this we have designed a low cost instrument using common analog signal processing blocks which gives an accurate recording of the bioimpedance signal. The instrument designed measures the impedance of the forearm where the two exterior electrodes are used as currernt etectrodes and and the two inner electrodes are used as the voltage electrodes. This type of arrangement can be used in applications such as measuring heart rate and blood glucose level

The current source as mentioned in figure 2 is used to inject a sinusoidal current of 50kHz frequency and a current of amplitude in the range of 600uA-800uAi A sinusoidal current source is made using a voltage source generator and a V to I converter. A voltage source generator is chosen such that it produces a frequency range of 30kHz tolOOkHz. Integrated circuit 8038 is used as a voltage generator in this instrument. V to I converter is responsible for converting the voltage, produced to the required magnitude.of current. Howland circuit with buffer is used as a V to I converter. The signal recorded from the voltage sensing electrodes is then given to the input of an amplifier. To amplify a biomedical signal a difference amplifier is required which amplifies the voltage drop across the section of human body to which the voltage electrodes have been applied. The signal from the electrodes is given as input to the two terminals of the instrumentation amplifier.The

for the instrumentation amplifier is 27dB. The output of the instrumentation amplifier is connected to the input of the precision demodulator to demodulate the signal received from the amplifiei". The output of the demodulator, is then given to the low pass filter with cutoff frequency of 40Hz to remove the high frequency components. The output signal of the voltage sensing unit as mentioned in figure 3, is giveri as input to the analog pin of arduino. The analog to digital converter in the arduino converts the analog signal to digital signal which is then transmitted to the PC through the USB port. The signal is then interpreted using matlab and the output is displayed in matlab figure file format.

Claims
1) A cost effective bioimpedance measuring instrument has been realized using easily available electronic components. The instrument is capable of providing results with high degree of accuracy and precision under controlled condition.
2)The instrument according to claim 1,.displays voltage measured across a section of human body through which current is passed, on the display of computer. The recorded output signal is time variant. For instance, for a particular patient the recorded bioimpedance output signal may vary after a gap of few minutes. It may be due to motion artifacts or variations in internal dynamics of the human body, any other fault/lapse on the part of patient or technician.
3) The output voltage according to claim 2, is an amplitude modulated signal.
4) The output voltage according to claim 2, is sensitive to contraction and relaxation of muscles.
5) The current source in the instrument according to claim l,injects approximately same current for load impedance values from lOOQ to 5kQ. The impedance of the human body is in the range of IkQ, therefore the output current is independent of the load impedance values of range of interest. _
6)lnstrumentation amplifier is-used as the biopotential amplifier in this instrument according to claim 1. The gain of the amplifier is equal to 27dB over the desired frequency range.
7)Precisi6n enyetope detector' is used in this instrument according to claim 1, to demodulate the signarobtained from human body. The signal from the amplifier contains the low frequency bioimpedance signal amplitude modulated oh the 50kHz carrier.signal injected. The circuit is designed by replacing the diode in the simple envelope detector circuit by the super diode.