IEEE Consumer Electronics Magazine - November/December 2019 - 16

Disease Detection Using Wearable Device

Table 1. Proposed optimized values of the key design
specifications.
Parameter

Value

Transducer type

Linear array

Number of elements

128

Scan dimension per artery

4 cm × 4 cm

Transducer frequency

7.5 MHz

Element pitch

0.3 mm

Depth of focus

4 cm

Dynamic range

> 60 dB

Optimal frame rate

25 Hz

and energy efficiency. The carotid artery has a
depth of only $4 cm, and a linear array is good
enough to measure up to this depth without any
dynamic focusing. The other proposed design
parameters are described as follows:
Frequency: A transducer frequency of 7.5 MHz
will provide the desired image resolution of 1 mm.
Given a tissue attenuation rate of 1 dB/cm/MHz,
> 60 dB dynamic range enables imaging of most
object up to a depth of 4 cm at this frequency. A
frame rate of 25 Hz is enough for obtaining
decent-quality images that allow edge detection
during subsequent analysis.
Element pattern: Capacitive micromachined
ultrasound transducers (CMUTs) are a good
choice since they can be fabricated in large arrays
and have wider fields of view than equivalent piezoelectric transducer arrays. For our application,
two individual 128-element linear CMUT arrays are
considered in order to obtain the desired resolution at a reasonable manufacturing cost.12
Scan dimension for a single array: For monitoring the carotids individually, the transducer
arrays need to capture an area of at least 4 cm ×
4 cm with a depth of focus of 4 cm (from the skin
surface to the center of the artery), as shown in
Figure 1.
Transmit (Tx) Circuitry: This consists of a Tx
beamformer, a high-voltage (HV) Tx amplifier
(pulser), and a digital-to-analog converter. The
circuitry is placed on the back part of the neck
brace (see Figure 2(c)).
Receive (Rx) Circuitry: This includes an Rx
beamformer, a low-noise amplifier (LNA), an

analog-to-digital converter (ADC), a variablegain amplifier (VGA), and an image processor.
This circuitry is also located toward the back
(see Figure 2(c)).
Transducer-circuit interface: A Tx/Rx switch
for protecting RX circuitry from HV transmission
pulses and a (128×1) HV multiplexer/demultiplexer (mux/demux) for hardware complexity
reduction are housed near the Tx and Rx circuitry.
Power module: A rechargeable battery
placed on the back will be used as the power
source. The associated charging and power management unit will also be integrated.
Storage: This includes both volatile and nonvolatile memory for storing user-specific information, present and previous measurements,
assessment reports, etc.
Nozzle: Two electrically controlled nozzles
and a flow controller are used for automatic gel
application on the target area.
For the CMUT array, the estimated total capacitance of the array is around $203 pF (considering a
per-element capacitance of $1.6 pF). The excitation
voltage chosen is 30 V. At 7.5 MHz, this will result in
a peak current of $2.3 mA per element. Therefore,
the total peak power level will be $72 mW for individual elements and $9 W for the entire array.

Operation Cycle
The proposed device mainly measures lumen
diameter in the common carotid artery (CCA)
area since studies show the best results from
this region.13 The goal is to perform CCA imaging
from three angles: 1) anterior, 2) lateral, and
3) posterior.
Operation: The working principle of the proposed device is explained using the flow chart in
Figure 4. First, it is put on the neck as a neck brace.
Next, the nozzles release some ultrasound gel and
prepare the area for efficient ultrasound transmission. Then, the nozzles are moved forward to make
room for the transducer arrays. Once the array
location is adjusted, a scan is performed and an
image of the carotid artery is collected. Next, a
novel lumen-diameter-based anomaly detection
algorithm is applied to the collected images. The
algorithm estimates the lumen diameter and verifies whether it is within the normal range (e.g., 4.3-
7.7 mm14) for the population. If the diameter is
below this range or has decreased significantly

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