AD5934 Datasheet, PDF (26/32 Pages) Analog Devices – 250 kSPS, 12-Bit Impedance Converter, Network Analyzer

AD5934
TYPICAL APPLICATIONS
This section describes typical applications for the AD5934.
BIOMEDICAL: NONINVASIVE BLOOD IMPEDANCE
MEASUREMENT
When a known strain of a virus is added to a blood sample
that already contains a virus, a chemical reaction takes place
whereby the impedance of the blood under certain conditions
changes. By characterizing this effect across different
frequencies it is possible to detect a specific strain of virus.
For example, a strain of the disease exhibits a certain
characteristic impedance at one frequency but not at another,
therefore the requirement to sweep different frequencies to
check for different viruses. The AD5934, with its 27-bit phase
accumulator, allows for sub-Hz frequency tuning.
The AD5934 can be used to inject a stimulus signal through
the blood sample via a probe. The response signal is analyzed
and the effective impedance of the blood is tabulated. The
AD5934 is ideal for this application because it allows the user to
tune to the specific frequency required for each test.
PROBE
1
16
2
15
AD5934
3 _{TOP VIEW} 14
RFB ^{(Not to Scale)}
4
13
5
12
6
11
7
10
8
9
ADuC702x
TOP VIEW
(Not to Scale)
7V
0.1μF 10μF
ADR43x
2
6
4
Figure 35. Measuring a Blood Sample for a Strain of Virus
SENSOR/COMPLEX IMPEDANCE MEASUREMENT
The operational principle of a capacitive proximity sensor is
based on the change of a capacitance in a RLC resonant circuit.
This leads to changes in the resonant frequency of the RLC
circuit, which can be evaluated as shown Figure 36.
It is first required to tune the RLC circuit to the area of
resonance. At the resonant frequency, the impedance of the
RLC circuit is at a maximum. Therefore, a programmable
frequency sweep and tuning capability is required, which is
provided by the AD5934.
RESONANT
FREQUENCY
CHANGE IN
RESONANCE DUE
TO APPROACHING
OBJECT
F_O
FREQUENCY (Hz)
Figure 36. Detecting a Change in Resonant Frequency
An example of the use of this type of sensor is for a train
proximity measurement system. The magnetic fields of the
train approaching on the track change the resonant frequency
to an extent that can be characterized. This information can be
sent back to a mainframe system to show the train location
on the network.
Another application for the AD5934 is in parked vehicle
detection. The AD5934 is placed in an embedded unit
connected to a coil of wire underneath the parking location.
The AD5934 outputs a single frequency within the 80 kHz to
100 kHz frequency range, depending upon the wire
composition. The wire can be modeled as a resonant circuit.
The coil is calibrated with a known impedance value and at a
known frequency. The impedance of the loop is monitored
constantly. If a car is parked over the coil, the impedance of the
coil changes and the AD5934 detects the presence of the car.
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