Stephen J. Carey

Toward in-cylinder absorption tomography in a production engine

Design requirements for an 8000 frame/s dual-wavelength ratiometric chemical species tomography system, intended for hydrocarbon vapor imaging in one cylinder of a standard automobile engine, are examined. The design process is guided by spectroscopic measurements on iso-octane and by comprehensive results from laboratory phantoms and research engines, including results on temporal resolution performance. Novel image reconstruction techniques, necessary for this application, are presented. Recent progress toward implementation, including details of the optical access arrangement employed and signal-to-noise issues, is described. We present first cross-cylinder IR absorption measurements from a reduced channel-count (nontomographic) system and discuss the prospects for imaging.

Chemical species tomography by near infra-red absorption

The spatial distribution of chemical species can be a critical determinant of the performance of chemical reactors. One such reactor is the combustion chamber of the Internal Combustion engine. This paper presents a design for the measurement of hydrocarbon concentration distribution within a running engine using near infra-red absorption tomography. The fundamentals of the technique, and design parameters for the equipment are discussed. By utilising micro-optic components, a minimally invasive system is feasible and by utilising advanced laser/photodetector combinations, good temporal performance is anticipated.

A Control System for a Cellular Processor Array

Presented in this paper is a system that controls the SCAMP-3 cellular processor array vision chip, and provides an interface between it and a host system. This system can be used in real-time image processing, or computer vision applications. The system includes a sequencer for issuing instructions to the array processor, a configurable analogue interface and read-out circuitry, a system controller, which enables system operation and communication with the host, and a suite of software components, which include libraries, simulator, compiler and user interface. The presented hardware is a stand-alone vision system, which can be used in the development of PC-based or embedded applications

A high voltage pulser ASIC for driving high frequency ultrasonic arrays

This paper presents a high voltage integrated circuit (IC) that has been designed for connection to a hybrid printed circuit board (PCB) in close proximity to a polyvinyldenefluoride (PVdF) high resolution transducer array. An array of 16 pulser channels has been fabricated on chip; each channel provides an output train of -100 V pulses of 25 ns width, and fall and rise times of 6.3 ns and 13 ns, respectively, with a capacitive load of 2 pF.

Low power high-performance smart camera system based on SCAMP vision sensor

Vision sensors based upon pixel-parallel cellular processor arrays offer the unique opportunity to realise high-performance, flexible, low power image processing systems. By virtue of processing on the focal-plane, the energy-demanding requirement to digitize a captured frames raw pixel data is reduced, with returned data constituting only that which is salient. We describe a stand-alone vision system incorporating a SCAMP-3 vision chip, an FPGA and an ARM Cortex-M3 microcontroller. SCAMP integrated circuits operate as SIMD computers; each pixel incorporating a compact but powerful analogue processor and local memory, with all operations occurring in parallel over the 128x128 array. Algorithms are developed to operate natively upon the focal-plane as far as possible, with additional serial and higher-level operations occurring on the microcontroller. The power consumption of the system is algorithm-dependent. An algorithm developed for loiterer detection at 8fps has been shown to consume an average power of 5.5mW, with a more complex object tracking and counting system consuming 29mW.

PVdF array characterisation for high frequency ultrasonic imaging

Polyvinylidenefluoride (PVdF) has been utilized for a number of years within ultrasonic hydrophones. However, polymeric materials have rarely been incorporated into medical imaging phased arrays due to lower emitted power levels (relative to PZT transducers), and higher transducer element impedance. PVdFs advantages as a transducer material lie in its inherent wide bandwidth and the potential to create high-resolution images whilst maintaining low transducer manufacturing costs. Here we report the fabrication and test of PVdF linear arrays with 28 /spl mu/m PVdF film with elements on a 250 /spl mu/m pitch. These arrays are connected to equipment that has been developed to perform transmit beamforming to a variable focal point, and receive echoes from single transducer elements that are close-coupled to a 48-channel array of amplifiers. A-line data can then be post processed to perform dynamic receive beamforming. Utilizing this equipment, measurements of pressure field distributions are presented, and compared with simulations, to determine the optimum number of pulsed elements. Using the arrays in pulse-echo mode, imaging quality is assessed with biological tissue samples and ultrasound phantoms. A prototype transducer, operated to produce ultrasound with >20MHz centre frequency, realized spatial resolution of <0.4mm laterally and 0.1mm axially, at a distance of 15mm from the transducer.

Near infra-red chemical species tomography of sprays of volatile hydrocarbons

We report an All-Opto-Electronic tomography system that is sensitive to hydrocarbon vapour distribution, or liquid spray distribution, with temporal resolution of over 3000 frames per second. A tomography system comprising 32 channels has been built and tested. For chemical sensitivity to saturated hydrocarbons, we exploit the principle of Near Infra-Red (NIR) absorption at 1700 nm relative to a reference wavelength, using laser diode sources whose technology is based on that of the communications industry. Images are obtained from a laboratory set-up incorporating both gaseous injection and a liquid Gasoline Direct Injection (GDI) system. The performance of a prototype system on a running GDI engine is reported. The difficulty in performing concentration measurements of the gaseous fuel within the liquid spray region is shown, and means to improve this performance are discussed. However, it has been found possible to image the liquid spray cone using attenuation of the reference beam. These images correlate well with other techniques [1].

Scanning Head with 128-Element 20-MHz PVDF Linear Array Transducer

A scanning head has been designed and fabricated that incorporates a 20-MHz, 128-element linear transducer. The scanning head also incorporates -200 V pulsers and a custom 16-channel amplifier. The transducer was constructed with 28 mum PVDF film with an element pitch of 250 mum. The transducer showed an average -20 dB pulse length of 69 ns. The elements of the PVDF array were tested and found to have 7.5 mPa/radicHz equivalent noise pressure. The radiated power level for 32 pulsed elements was ~1 MPa. An imaging test shows that the system achieves axial and lateral resolutions of 40 mum and 0.2 mm, respectively. The entire scanning head dissipates ~1.6 W at a pulse repetition rate of 750 Hz.

Pre-amplifier arrays for intra-oral ultrasound probe receiving electronics

In this paper, we present an array of pre-amplifier (16-channels) used in the receiving electronics of an intra-oral ultrasound probe, that forms part of a portable ultrasound imaging system. In general, this is a 2 stage amplifier, performing the task of minimising noise interference for the received ultrasound echoes and as the impedance converter between the transducer and beamforming stage. At the same time, it provides adequate gain at the centre frequency of 20MHz. The amplifier is capable of providing a -3dB bandwidth of 30MHz whilst driving loads equivalent to coaxial cables. The noise level and crosstalk are less than 10nV//spl radic/Hz and -16dB respectively at 20MHz for proper operation. The IC measures 4mm /spl times/ 2mm and can be connected in series for application with more than 16 channels without affecting the pitch requirement of the transducer array.

High density interconnect for polymer based ultrasound transducers

Electrical interconnect strategy is an essential part of ultrasound transducer array development. Methods available include soldering, conductive adhesive bonding, fine wire welding (wire bond), Z-axis conductive films and, presented for the first time in an ultrasonic transducer, anisotropic conductive adhesive (ACA) pastes and films (ACF). ACA pastes work by trapping a metal coated polymer sphere between conductors. The spheres are then held in place by the supporting heat cured epoxy matrix. Images of the component parts are presented, as is an image from a PVdF transducer array with ACA interconnects and a centre frequency of 25 MHz. This work is of particular use in high frequency ultrasound arrays where interconnect density is high and for 2D array where large element counts are prevalent.