V. Ivchenko

Sub-threshold sampling in a correlation-based ultrasonic spectrometer

A pseudo-random code/correlation-based ultrasonic spectrometer can detect signals whose amplitudes are significantly less than both the input noise floor and the voltage increment equivalent to the least significant bit of the analogue to digital converter. The phenomenon is explained on the basis of classical information theory, which also provides the basis for the design of such systems. An overall noise model is developed, and experimental results are presented that demonstrate its validity.

Compensation for temperature variation in ultrasonic chemical process monitoring

Chemical processes often involve heat exchange that causes changes in the temperature of the reactor. These temperature changes could affect ultrasonic monitoring of the processes to the same extent as changes in chemical composition. Discrimination between these two factors requires separate monitoring of the temperature. An ultrasonic reflector for pulse-echo monitoring of aqueous solutions with integrated temperature sensing was developed, implemented and experimentally tested. It contains a water filled cavity isolated from the test medium that is used as a reference. A compact 3 mm wide cavity provides changes in propagation delay of about 1 sample per 0.05 o C at a sampling frequency of 2430 MHz. The possibility of achieving even finer resolution is demonstrated.

VLSI architecture for repetitive waveform measurement with zero overhead averaging

The architecture and performance of a digital waveform acquisition instrument with built in averaging is discussed. The substantial time required for averaging in software was eliminated in the developed architecture by using hardware averaging at the speed of waveform occurrence, due to a fully pipelined operation of constituent units. This architecture was implemented using an FPGA development board, and was tested at a number of averages above 10,000 that should theoretically provide a reduction of the additive noise by more than 100 times. The effect of the noise reduction was clear from experiment. However, lower than predicted improvements were achieved when the level of the input noise before averaging was low. This occurred due to the quantization of the input signal, and should not be attributed to the averaging. Therefore, averaging of digitized data can impose particular limits on the achievable noise reduction but this only occurs when the noise level is very low and does not require much reduction per se.

Super-resolution in situ ultrasonic monitoring of chemical reactions

This paper describes experiments to compare the sensitivity and robustness of ultrasound measurements with pH measurements when monitoring chemical reactions under laboratory conditions, the aim being to determine the relative suitability of the two techniques for process monitoring and control. It is shown that ultrasonic time-of-flight measurements, based on the centre of the area of an ultrasonic pulse, provides for super-resolution with respect to the sampling frequency. In comparison to reaction monitoring based on pH measurements, ultrasound was found to be superior in terms of its response time and resolution.

A field programmable gate array-based ultrasonic spectrometer

This paper describes a novel architecture for a low-voltage ultrasonic data acquisition system intended for process monitoring of liquid chemicals in an industrial context. The system is appropriate for operations in hazardous environments where limits are imposed on the working voltage levels of equipment, due to potential fire or explosion hazards. High SNRs in the captured signal records were achieved using 1 V Golay complementary sequences combined with cross-correlation for signal detection, all of which were implemented on a single-field programmable gate array chip. The system has an operating bandwidth of 40 MHz and a dynamic range at the receiver of 2 Vp-p with a resolution of 14 bits. Theoretical and practical design criteria are examined to optimize received signal SNR and data acquisition rate whilst minimizing hardware complexity. The system was implemented using a reconfigurable hardware platform of relatively low cost, providing a basis for developing more powerful and robust systems in future. Experiments show that the performance of the system is equivalent to that of a conventional high-voltage pulse-transmission system.

Ultrasonic monitoring of foamed polymeric tissue scaffold fabrication

Polymeric tissue scaffolds are central to many regenerative medicine therapies offering a new approach to medicine. As the number of these regenerative therapies increases there is a pressing need for an improved understanding of the methods of scaffold fabrication. Of the many approaches to processing scaffolds, supercritical fluid fabrication methods have a distinct advantage over other techniques as they do not require the use of organic solvents, elevated processing temperatures or leaching processes. The work presented here is centred on the development of a new approach to monitoring supercritical scaffold fabrication based on determination of the scaffold acoustic impedance to inform protocols for scaffold fabrication. The approach taken uses an ultrasonic pulse-echo reflectometer enabling non-invasive monitoring of the supercritical environment on-line. The feasibility of this approach was investigated for two scaffolds of different molecular weight. Acoustic results demonstrate that differences in the physical properties of the two scaffolds could be resolved, particularly during the foaming process which correlated with findings from time-lapsed imaging and micro X-ray computed tomography (μ X-ray CT) images. Thus, this work demonstrates the feasibility of ultrasonic pulse-echo reflectometry to non-invasively study supercritical scaffold fabrication on-line providing a greater understanding of the scaffold fabrication process.

Resolving Complex Chemical Processes: Comparison of Monitoring by Ultrasound with Other Measurement Methods

A weak acid-strong base time-resolved titration has been monitored by ultrasonic and pH measurements. Various treatments have been applied to the acquired data, and the results obtained are presented and discussed. It has been found that the group velocity of ultrasound is the most robust parameter after enhancement of the time resolution of the ultrasonic hardware by signal processing. Application of temperature correction transformed the ultrasonic titration curves into two nearly straight lines that intersect at the equivalence point of the titration at the maximum point on the curve. The ultrasonic instrument exhibited much lower stabilisation times after titrant addition compared to the conventional pH-meter making ultrasonic spectroscopy potentially very useful for monitoring/controlling fast chemical processes including acid-base reactions

AN INTEGRATED ULTRASONIC CORRELATION SPECTROMETER

A novel architecture for a low voltage ultrasonic data acquisition system is described. The system is appropriate for process monitoring in hazardous environments with potential fire or explosion hazards, where limits are imposed on the working voltage levels of equipment. High SNR is achieved using 1V Golay complementary sequences combined with cross‐correlation for signal detection, all of which were implemented on a single FPGA chip.

Development of Electronic Components for an Integrated Ultrasonic Front End ASIC

The development of an ASIC for ultrasonic front end is described. The ASIC contains a high speed binary driver and broadband amplifier optimised for a conventional piezoelectric transducer. Experimental results that agree well with simulations are presented and discussed.

Self-Calibrating Scalable Research Platform for Ultrasonic Measurements in Chemical and Biological Reactors

A research platform that integrates high accuracy FPGA waveform acquisition architectures and MATLAB graphical user interface is described. The platform provides self-calibrating measurements and frame jitter free operation. The FPGA architectures were tested on two different chips using the same user interface successfully. Examples of the platform utilization for monitoring of chemical and biological reactors are presented.