J.V. Hatfield

A new generation of integrated electronic noses

Abstract At Eurosensors VII the authors discussed the feasibility of integrating the UMIST artificial electronic nose. A tentative sensor deposition technique was reported along with the development of an application specific integrated circuit (ASIC) to perform the analogue signal processing. The following paper reports further progress in achieving this goal. The integrated nose employs two ASICs; a current multiplexer and a current amplifier. Current-mode signal processing has been utilized where appropriate. Arrays of conducting organic polymers have been successfully fabricated. Results are presented on the dynamics, reproducibility and matching of the sensing elements.

GasFETs incorporating conducting polymers as gate materials

A gas sensitive field effect transistor with a conducting polymer gate is described (polyFET). The devices were fabricated as gateless FETs in an aluminium gate pMOS process. Post-processing steps were performed to provide the gateless devices with polypyrrole gates. On exposing the transistor gates to volatile compounds, the polyFETs experience a change in their threshold voltage which, in an appropriate circuit, manifests itself as a change in drain-source current. A number of results are presented.

An integrated multi-element array transducer for ultrasound imaging

Abstract Much progress has been made towards integrating the electronic circuitry associated with either linear or phased ultrasonic array scanning into the hand-held case of the transducer. The number of wires required to connect the transducer back to the display system has been dramatically reduced and the path length between transducer elements and the driver circuits kept to a few millimetres. To achieve this new construction, polymer transducer arrays have been fabricated and the pulse-control circuitry has been integrated onto custom-designed silicon chips.

A beam-forming transmit ASIC for driving ultrasonic arrays

This paper describes the design of a programmable eight-channel application specific integrated circuit (ASIC) for driving ultrasonic array transducers. The ASIC is capable of generating variable delay lengths of up to 65 μs in steps of 1 ns. Integrated on the same chip is an array of eight high-voltage pulser circuits (up to 100 V). The output pulse width can also be set to match the transducer operating frequency. A minimum width of 20 ns is possible and the rise and fall times are typically 5 and 7 ns. It can also be programmed to give bursts of up to 16 repetitions to facilitate Doppler imaging.

Integrated ultrasound transducers

Piezoelectric polymer materials are of interest for high frequency transducer array applications primarily because the array geometry can be achieved using photolithography. The UMIST research team have fabricated up to 64-element polymer transducer arrays. They have adopted a unique approach whereby the pulse control electronics can be mounted in close physical proximity with the transducer array. In order to accomplish this both transmit and receive circuitry has been integrated onto in-house custom designed silicon chip sets. A notable achievement is the design of a monolithic 16-channel programmable pulse generator chip fabricated in 1.5 μm CMOS technology. By employing novel design techniques time delays with 1 ns time resolution and a dynamic range of 219 have been achieved. A description of the system is provided and preliminary results of beam plotting measurements are given

An integrated array transducer receiver for ultrasound imaging

At Eurosensors VII the authors described an integrated ultrasonic array transducer that featured integrated transmit circuitry. The present paper describes integrated receiving circuitry that the authors have gone on the develop. The motivation for the receiver is the same as for the transmitter: (a) the entire receiver circuitry, along with the transmit circuitry, to be part of a hand-held transducer; (b) a small number of wires to connect the scanner to the base unit. The transducer in question is a one-dimensional polyvinylidene polymer array with a centre frequency of 20 MHz. Novel receiver design concepts have been developed to enable the wide bandwidth to be accommodated.

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.

A programmable multi-channel CMOS pulser chip to drive ultrasonic array transducers

A 16-channel programmable pulse generator ASIC has designed in 1.5¿m CMOS technology. By employing novel design techniques time delays with 1nS time resolution have been achieved with a dynamic range of 219. Currently the chip is being used to drive ultrasonic transducer arrays.

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.

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.