Abstract

1
Ultrasonic Phased Array Imaging System
Kurt Matarese, Professor Michael Ruane
Department of Electrical and Computer
Engineering, Boston University, Boston, MA, 02215
This work was supported in part by CenSSIS, the
Center for Subsurface Sensing and Imaging
Systems, under the Engineering Research Centers
program of the National Science Foundation (Award
Number EEC-9986821)
Abstract
Electronics
LabVIEW
The main menu (Figure 4.1) leads to several
different modes of operation. The first 4 of
these modes are used to create or edit table
files that contain the necessary data stream for
controlling the digital potentiometers. Focal
Control Mode is shown as an example in Figure
4.2. Once created, this file and an XYZ
coordinate file that contains the focal points
are used in the Test and DAQ Mode. This mode
outputs a file of ranges that are considered
valid based on a user input threshold and indexed
in such a way that each range matches up with an
XYZ coordinate. This information is passed to the
Form Image Mode where it is interpreted and made
into an image.

• A PIC16F873 orchestrates the timing of the
  hardware programmatically. All of the 8
  transmitter lines (Figures 1 and 3) are triggered
  at the same time at a rate specified in the PIC
  code.
• On each transmission a trigger in LabVIEW begins
  data acquisition until an echo is received.
• Delay lines are varied by sending different data
  bytes to the MCP41100 digital potentiometers
  (Figure 2) through the parallel port. This
  variation causes the output pulse width from a
  555 timer to change. This pulse width is
  interpreted by the PIC12F683 microcontrollers to
  establish the delays before output.
• The voltage across the transmitters are
  amplified and one side is also inverted to create
  a larger voltage differential.
• The received signal passes through cascaded
  low-pass and high-pass filters with a gain of
  roughly 15000X in the pass band.
• A comparator is used to set a threshold for when
  an echo is considered a detection. The output of
  the comparator is tied to a LabVIEW trigger I/O.

Ultrasonic imaging has many important medical,
testing, and ranging applications. Each system
includes a directed probe beam and a receiver
system that detects and times echoes. Phased
array ultrasonic imaging systems are favored over
mechanical scanning because the beam scan is
controlled by electronics, eliminating expensive
and bulky positioning hardware. Our system uses
an eight-element phased array transmitter and a
single element receiver operating at 40Khz.
Transmission is orchestrated by a PIC16F873
microcontroller that shapes the 40kHz burst and
delivers it to eight identical delay lines. Delay
is varied on each line with a slave PIC12F683
microcontroller and MCP41100 digital
potentiometers controlled through a PC parallel
port. All hardware is on a single PCB. LabVIEW
7.1 controls the beam scan, and acquires range
data to form an image. Our LabVIEW interface
provides several methods of writing data to
depict a beam scan. In the High Tech Tools and
Toys Lab, this project demonstrates to freshmen
applications of signal processing, electronic
filtering, microcontrollers, LabVIEW, data
acquisition, parallel port control, PCB layout,
and project documentation.
Figure 4
Figure 1
Schematic view of a single transmitter/delay line
Challenges

• Timing between LabVIEW 7.1 and phased array
  hardware
• Designing inexpensive yet accurate variable
  delay lines
• Controlling 8 serial inputs through 1 parallel
  port for MCP41100s
• Electronic design, signal processing, and PCB
  layout
• Creating user friendly controls for writing data
  to depict a beam scan

1
2
Significance
Accomplishments

• Educational, K-12 outreach
• Gives students an opportunity to see an
  alternative method of imaging
• Promotes knowledge of LabVIEW, microcontroller
  design and programming, digital and electronic
  signal processing, image analysis, and PCB design
• Designed to promote further testing and
  development

• Learned Assembly language for microcontroller
  programming
• Learned PCB design and layout in Cadence 15.1
• Learned how to control a PC parallel port
• Learned different facets of LabVIEW including
  instrument I/O,
• data acquisition, data logging, signal
  processing, structures,
• menu operation, file I/O, triggers, and various
  user controls

Figure 2
Each digital potentiometer needs 16 bits of
serial data to change its resistance value. The
first 8 bits, called the command byte, are used
to designate that a value of a particular
potentiometer will be changed (there are multiple
potentiometers on other chip models). The last 8
bits, called the data byte, represent values
between 0 and 255 that correspond to resistances
between about 1k and 100K ohms on the MCP41100. A
LabVIEW digital I/O is used to simulate the CS
line, which signals that data is incoming. Pin 17
of LPT1 is used to simulate the SCK line, which
synchronizes the incoming data. Each one of the 8
data pins on LPT1 is used as a separate serial
line to control a digital potentiometer.
Future Plans
Project Setup

• Increase transmitter frequency to effectively
  increase the
• accuracy of the system
• Increase the number of transmitters to create a
  more focused
• beam which also increases accuracy
• Change the method of data transfer
• Make a real-time aiming mode instead of creating
  a data file and then loading it to the Test an
  DAQ mode

Ranges and focal points stored to form image
CB-68LP
Figure 3
CPU LabVIEW 7.1 6023E-DAQ
New delay data sent through parallel port
Acknowledgements
The key component of each transmitter line is the
delay control. Commercial delay lines can be
extremely expensive. In developing a method for
electronically variable delay, cost and accuracy
were two main concerns. Each delay line is
comprised of an MCP41100, an NE555N timer, a
PIC12F683, and a small number of inexpensive
passive components, bringing the total cost of
each line to around 7. The only other necessity
is a means of controlling the potentiometers,
which in this case is a standard PC parallel
port. In short, changing the resistance
proportionally changes the output pulse width
from the 555. The PICs wait for the end of this
pulse to transmit the signal to the amplification
stage.
Hardware

• Professor Michael Ruane and everyone in the
  HTTTL
• Professor Vladimir Kleptsyn
• Andrew Warhole from National Instruments
• CenSSIS and NSF

Data flow
Rec. Signal
Receiver
PCB Triggers, Delay Lines Amps, Filters
CB-68LP
Contact Information
Temperature
Name E-mail Kurt
Matarese Matarese_at_bu.edu Michael
Ruane mfr_at_bu.edu
Transmitters
DAQ Trigger