Jeremy Hawkes - Academia.edu (original) (raw)

Papers by Jeremy Hawkes

Plasma preparation from whole blood using ultrasound

Ultrasound in Medicine & Biology, 2000

A technique to efficiently separate plasma from human whole blood is described. Essentially, 3-mL... more A technique to efficiently separate plasma from human whole blood is described. Essentially, 3-mL samples are held on the axis of a tubular transducer and exposed for 5.7 min to an ultrasonic standing wave. The cells concentrate into clumps at radial separations of half wavelength. The clumps grow in size and sediment under gravity. A distinct plasma/cell interface forms as the cells sediment. The volume of clarified plasma increases with time. The separation efficiencies of transducers of 29-mm and 23-mm internal diameters driven, by test equipment, at radial resonances of 3.4 and 1.5 MHz, respectively, were compared. The average efficiency of separation was 99.6% at 1.5 MHz and 99.4% with the 3.4-MHz system. The cleared plasma constituted 30% of the sample volume at 1.5 MHz and 25% at 3. 4 MHz. There was no measurable release of haemoglobin or potassium into the suspending phase, indicating that there was no mechanical damage to cells at either frequency. A total of 114 samples from volunteers and patients were subsequently clarified in a 1.5-MHz system driven by an integrated generator. The average efficiency of clarification of blood was 99.76% for the latter samples. The clarification achieved is a significant improvement on that previously reported (98.5%) for whole blood exposed to a planar ultrasonic standing wave field (Peterson et al. 1986). We have, therefore, now achieved a six-fold reduction of cells in plasma compared to previous results.

Three modelling approaches; empirical formulae, Matrix models (Disperse ©) and FE (Abaqus ©) have... more Three modelling approaches; empirical formulae, Matrix models (Disperse ©) and FE (Abaqus ©) have been combined to create a design process for producing desired vibration modes in discs. The precision of this approach is demonstrated experimentally by the movement of particles or liquids, which form into the expected shapes at frequencies within 2% of those predicted. The experiments also showed that liquids move in the opposite direction to solid particles and when a reflector is placed one-half wavelength above these discs, some particles rise to the nodal plane and form clumps. The clarity of the vibration in these well-defined modes allowed us to observe that airborne clumps formed at the wall displacement anti-nodes and that streaming was a maximum at the wall displacement nodes.

Ultrasound standing wave radiation acts on suspensions, emulsions, and colloids to drive the disp... more Ultrasound standing wave radiation acts on suspensions, emulsions, and colloids to drive the dispersed particles (solid particles, bubbles, or oil droplets) towards either nodal or anti-nodal positions in the sound field. Using narrow chambers which contain only one nodal plane we have been able to position this pressure node at: 1) The reflector side wall of a chamber, this has been used to d raw cells to a surface for detection by a biosensor. 2) The centre of the chamber, this has been combined with manipulation by laminar flow to produce a filter to remove contaminating particles. These systems have been developed using a one-dimensional transfer matrix model to predict the node positions and the acoustic energy density in the fluid. The model has been further used to predict chamber designs in which pressure nodes are at 1) the transducer side wall of the chamber and 2) both walls of the chamber.

Aggregation of suspended yeast cells in a small-scale ultrasonic standing wave field has been mon... more Aggregation of suspended yeast cells in a small-scale ultrasonic standing wave field has been monitored and quan- tified. The aggregation effect is based on the acoustic radiation force, which concentrates the cells in clumps. The ultrasonic chamber employed (1.9 MHz, one wavelength pathlength) had a sonication volume of 60 µl. The aggreg- ation process was observed from above the transducer

This work presents the use of natural frequencies and mode shapes to produce longitudinal and fle... more This work presents the use of natural frequencies and mode shapes to produce longitudinal and flexural vibrations in a stepped horn and in a plate, respectively, to generate acoustic streaming on the plate for controlling the motion of particles. The design procedure for producing the desired vibration modes and particle movement involved formulae, Global Matrix model (Disperse) and FE model

Ultrasound standing wave radiation force and laminar flow have been used to transfer yeast cells ... more Ultrasound standing wave radiation force and laminar flow have been used to transfer yeast cells from one liquid medium to another (washing) by a continuous field-flow fractionation (FFF) approach. Two co-flowing streams, a cell-free suspending phase (flow rate w 50% of the total flow-through volume) and a yeast suspension, were introduced parallel to the nodal plane of a 3 MHz

Resonant ultrasonic particle manipulators and their applications in sensor systems

Proceedings of IEEE Sensors, 2004., 2004

Page 1. Resonant Ultrasonic Particle Manipulators and their Applications in Sensor Systems Martyn... more Page 1. Resonant Ultrasonic Particle Manipulators and their Applications in Sensor Systems Martyn Hill1, Jeremy J Hawkes2, Nicholas R Harris3, Martin B McDonnell4. 1School of Engineering Sciences, University of Southampton ...

2001 IEEE Ultrasonics Symposium. Proceedings. An International Symposium (Cat. No.01CH37263), 2001

The forces on suspended particles in acoustic fields are reviewed briefly and the theoretical mod... more The forces on suspended particles in acoustic fields are reviewed briefly and the theoretical modelling of ultrasonic separators based on piezoelectrically excited layered resonators is described. Two flow-through resonator chamber concepts for ultrasonic particle (bio-cell) separation are investigated: a) the coagulation or sedimentation approach, b) the so-called h-shaped ultrasonic separator. The h-shaped ultrasonic separator is analysed by combining for the first time the mathematical modelling of the laminar flow with the acoustic force based velocity field of the particles relative to the suspension medium. This allows a complete modelling of the resonator's particle separation performance. Examples for separation chamber designs optimized by use of the mathematical model are presented and the calculated particle traces in the h-resonator are shown and compared with experimental results. For direct comparison of different ultrasonic flow through separator concepts a separation performance figure is introduced and its value is given for the two investigated separator concepts for the sample suspensions of polystyrene spheres, yeast and spirulina cells in (salt) water. The presented results are of importance for the state of the art design of acoustic cell filters for perfusion type bioreactors, as recently launched at the biotechnology market, as well as for the ultrasonic separation of plant (algae) cells under low gravity conditions, where the sedimentation concept fails.

Patterns of particles aggregation and streaming in resonating fluids

ABSTRACT Particles suspended in water move to pressure nodes in a standing wave due to the acoust... more ABSTRACT Particles suspended in water move to pressure nodes in a standing wave due to the acoustic radiation force. A current problem is the interaction between direct acoustic forces on particles and viscous drag forces from acoustic streaming. The result is an apparently chaotic picture which changes with time. Here we identify some patterns in the chaos. Our objective is to identify the influence of acoustic streaming on the formation and destruction of particle aggregates in nodal planes.

Microparticle manipulation in millimetre scale ultrasonic standing wave chambers

Ultrasonic standing wave chambers with acoustic pathlengths of 1.1 and 0.62 mm have been construc... more Ultrasonic standing wave chambers with acoustic pathlengths of 1.1 and 0.62 mm have been constructed. The chambers were driven at frequencies over the range 0.66-12.2 MHz. The behaviour of 2 microns diameter latex microparticles and 5 microns diameter yeast in the chambers has been elucidated. One (flow) chamber had a downstream laminar flow expansion section to facilitate observation of concentrated particle bands formed in the ultrasonic field. A second (microscopy) chamber allowed direct observation of band formation in the field and their characterisation by confocal scanning laser microscopy. Clear band formation occurs when the chamber pathlength is a multiple of half wavelengths at the driving frequency, so that the chamber rather than the transducer resonance has the most influence on band formation in this system. Band formation occurred in half-wavelength steps from a position one quarter of a wavelength off the transducer to a band at a similar distance from the reflector. Ordered band formation was preserved by the laminar flow in the expansion chamber, although bands that formed very close to the wall were dissipated downstream. The microscopy chamber provided evidence of significant lateral particle concentration within bands in the pressure nodal planes. The approaches described will be applicable to the manipulation of smaller particles in narrower chambers at higher ultrasonic frequencies.

Whole blood clarification in an ultrasonic standing wave

Particle filtration by a combination of ultrasound standing waves and laminar flow

A continuous¯ow microparticle ®lter that combines megahertz frequency ultrasonic standing waves a... more A continuous¯ow microparticle ®lter that combines megahertz frequency ultrasonic standing waves and laminar¯ow is described. The ®lter has a 0.25 mm, single half wavelength, acoustic pathlength at right angles to the¯ow. Standing wave radiation pressure on suspended particles drives them towards the centre of the acoustic pathlength. Clari®ed suspending phase from the region closest to the ®lter wall is drawn away through a downstream outlet. Experimental tests achieved >1000-fold clearance of 5 mm yeast cells, at a sample¯ow rate of 6 ml min À1 , from which the clari®ed aliquot is 1 ml min À1 . At this¯ow rate the average residence time in the sound ®eld was <1 s. Latex particles of 25, 9, 5.7, 2.8 and 1.5 mm diameter were also tested. The temperature increase during an operating period >1 h was less than 1 K. The design criteria considered in the fabrication of this high performance device are discussed. A theoretical model of the ®lter's ef®ciency, which considers the action of primary radiation force and the particle distribution across a laminar¯ow pro®le is presented here. The model predicts that totally clari®ed ®ltrate (i.e. zero suspended particles) may be drawn from the downstream outlet. The system described offers a generic approach to automated ®ltration in some applications. It is continuous¯ow thereby solving many of the problems of automation presented by batch ®lter methods and centrifuges. It could be developed for both larger scale and micro¯uidic applications. # (J.J. Hawkes). 0925-4005/01/$ ± see front matter # 2001 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 5 -4 0 0 5 ( 0 1 ) 0 0 5 5 3 -6

Modelling of layered resonators for ultrasonic separation

The potential of ultrasonic techniques for the separation and concentration of particles within a... more The potential of ultrasonic techniques for the separation and concentration of particles within a fluid has been investigated in some detail in recent years. Devices for effecting such separation typically consist of a piezoceramic transducer driving into a matching layer, fluid layer and reflector layer. This paper uses an equivalent-circuit transducer model, coupled with acoustic impedance transfer relationships to model such cells with regards to both their electrical characteristics and the strength of the resonance produced under different conditions. The model is compared with experimental results from two different cells and is shown to match experimental values well in terms of electrical characteristics and separator performance. The effects of matching layer thickness are also examined using the model. The importance of the adhesive bonding layer is demonstrated, and it is shown that the model can predict the effects of such a layer. The model is also used to demonstrate the effects of coincident resonances in cell layers and to examine the pressure distribution across cells at key frequencies.

Ultrasonics, 2000

There has been interest for a number of years in the possibility of separating blood into cells a... more There has been interest for a number of years in the possibility of separating blood into cells and plasma by methods other than centrifugation, so that the plasma can be analysed on-line. Cells in whole blood normally occupy about 45% of the suspension volume. It has been shown with a number of different cell types, such as yeast and bacteria, that for concentrations of this order the cells are not as efficiently harvested by ultrasound as those for lower concentrations. In this study, removal of cells from 3-4 ml whole blood volumes has been examined in ultrasonic standing wave fields from tubular transducers driven at a frequency of 1.6 MHz. Samples of whole human blood (n=11) from two volunteers have been processed by three tubular transducers where high levels of cell removal, 99.7% on average, have been demonstrated with high reproducibility between samples as well as for different transducers.

Analytical scale ultrasonic standing wave manipulation of cells and microparticles

Ultrasonics, 2000

The ultrasonic standing-wave manipulation of suspended eukaryotic cells, bacteria and submicron l... more The ultrasonic standing-wave manipulation of suspended eukaryotic cells, bacteria and submicron latex or silica particles has been examined here. The different systems, involving plane or tubular ultrasonic transducers and a range of acoustic pathlengths, have been designed to treat suspension volumes of analytical scale i.e. 5ml to 50μl for both sample batch and ‘on-line’ situations. Frequencies range from 1 to

Modelling of layered resonators for ultrasonic separation

Ultrasonics, 2002

The potential of ultrasonic techniques for the separation and concentration of particles within a... more The potential of ultrasonic techniques for the separation and concentration of particles within a fluid has been investigated in some detail in recent years. Devices for effecting such separation typically consist of a piezoceramic transducer driving into a matching layer, fluid layer and reflector layer. This paper uses an equivalent-circuit transducer model, coupled with acoustic impedance transfer relationships to model such cells with regards to both their electrical characteristics and the strength of the resonance produced under different conditions. The model is compared with experimental results from two different cells and is shown to match experimental values well in terms of electrical characteristics and separator performance. The effects of matching layer thickness are also examined using the model. The importance of the adhesive bonding layer is demonstrated, and it is shown that the model can predict the effects of such a layer. The model is also used to demonstrate the effects of coincident resonances in cell layers and to examine the pressure distribution across cells at key frequencies.

A laminar flow expansion chamber facilitating downstream manipulation of particles concentrated using an ultrasonic standing wave

Ultrasonics, 1998

Microparticles (yeast cells) in flowing suspensions have been concentrated in bands in pressure n... more Microparticles (yeast cells) in flowing suspensions have been concentrated in bands in pressure nodal planes of a standing wave chamber driven at resonant frequencies ranging from its thickness fundamental of 0.66 MHz to its 15th harmonic. An outlet laminar flow expansion chamber preserves particle order for many centimeters downstream from the transducer. The 10 mm outlet width has the potential

Lab on a Chip, 2011

[

Lab on a Chip, 2004

Ultrasound standing wave radiation force and laminar flow have been used to transfer yeast cells ... more Ultrasound standing wave radiation force and laminar flow have been used to transfer yeast cells from one liquid medium to another (washing) by a continuous field-flow fractionation (FFF) approach. Two co-flowing streams, a cell-free suspending phase (flow rate w 50% of the total flow-through volume) and a yeast suspension, were introduced parallel to the nodal plane of a 3 MHz standing wave resonator. The resonator was fabricated to have a single pressure nodal plane at the centre line of the chamber. Laminar flow ensured a stable interface was maintained as the two suspending phases flowed through the sound field. Initiation of the ultrasound transferred cells to the cell-free phase within 0.5 s. This particle transfer procedure circumvents the pellet formation and re-suspension steps of centrifuge based washing procedures. In addition, fluid mixing was demonstrated in the same chamber at higher sound pressures. The channel operates under negligible backpressure (cross-section, 0.25 6 10 mm) and with only one flow convergence and one flow division step, the channel cannot be easily blocked. The force acting on the cells is small; less than that experienced in a centrifuge generating 100g. The acoustically-driven cell transfer and mixing procedures described may be particularly appropriate for the increasingly complex operations required in molecular biology and microbiology and especially for their conversion to continuous flow processes. { Electronic supplementary information (ESI) available: movie of cell washing showing experimental visualisation of cell transfer, pdf showing CFD predictions of sodium fluorescein diffusion across the channel at a high and low flow rate. See http://www.rsc.org/suppdata/ lc/b4/b408045a/ { The contents of this paper include material subject to Crown

Plasma preparation from whole blood using ultrasound

Ultrasound in Medicine & Biology, 2000

A technique to efficiently separate plasma from human whole blood is described. Essentially, 3-mL... more A technique to efficiently separate plasma from human whole blood is described. Essentially, 3-mL samples are held on the axis of a tubular transducer and exposed for 5.7 min to an ultrasonic standing wave. The cells concentrate into clumps at radial separations of half wavelength. The clumps grow in size and sediment under gravity. A distinct plasma/cell interface forms as the cells sediment. The volume of clarified plasma increases with time. The separation efficiencies of transducers of 29-mm and 23-mm internal diameters driven, by test equipment, at radial resonances of 3.4 and 1.5 MHz, respectively, were compared. The average efficiency of separation was 99.6% at 1.5 MHz and 99.4% with the 3.4-MHz system. The cleared plasma constituted 30% of the sample volume at 1.5 MHz and 25% at 3. 4 MHz. There was no measurable release of haemoglobin or potassium into the suspending phase, indicating that there was no mechanical damage to cells at either frequency. A total of 114 samples from volunteers and patients were subsequently clarified in a 1.5-MHz system driven by an integrated generator. The average efficiency of clarification of blood was 99.76% for the latter samples. The clarification achieved is a significant improvement on that previously reported (98.5%) for whole blood exposed to a planar ultrasonic standing wave field (Peterson et al. 1986). We have, therefore, now achieved a six-fold reduction of cells in plasma compared to previous results.

Three modelling approaches; empirical formulae, Matrix models (Disperse ©) and FE (Abaqus ©) have... more Three modelling approaches; empirical formulae, Matrix models (Disperse ©) and FE (Abaqus ©) have been combined to create a design process for producing desired vibration modes in discs. The precision of this approach is demonstrated experimentally by the movement of particles or liquids, which form into the expected shapes at frequencies within 2% of those predicted. The experiments also showed that liquids move in the opposite direction to solid particles and when a reflector is placed one-half wavelength above these discs, some particles rise to the nodal plane and form clumps. The clarity of the vibration in these well-defined modes allowed us to observe that airborne clumps formed at the wall displacement anti-nodes and that streaming was a maximum at the wall displacement nodes.

Ultrasound standing wave radiation acts on suspensions, emulsions, and colloids to drive the disp... more Ultrasound standing wave radiation acts on suspensions, emulsions, and colloids to drive the dispersed particles (solid particles, bubbles, or oil droplets) towards either nodal or anti-nodal positions in the sound field. Using narrow chambers which contain only one nodal plane we have been able to position this pressure node at: 1) The reflector side wall of a chamber, this has been used to d raw cells to a surface for detection by a biosensor. 2) The centre of the chamber, this has been combined with manipulation by laminar flow to produce a filter to remove contaminating particles. These systems have been developed using a one-dimensional transfer matrix model to predict the node positions and the acoustic energy density in the fluid. The model has been further used to predict chamber designs in which pressure nodes are at 1) the transducer side wall of the chamber and 2) both walls of the chamber.

Aggregation of suspended yeast cells in a small-scale ultrasonic standing wave field has been mon... more Aggregation of suspended yeast cells in a small-scale ultrasonic standing wave field has been monitored and quan- tified. The aggregation effect is based on the acoustic radiation force, which concentrates the cells in clumps. The ultrasonic chamber employed (1.9 MHz, one wavelength pathlength) had a sonication volume of 60 µl. The aggreg- ation process was observed from above the transducer

This work presents the use of natural frequencies and mode shapes to produce longitudinal and fle... more This work presents the use of natural frequencies and mode shapes to produce longitudinal and flexural vibrations in a stepped horn and in a plate, respectively, to generate acoustic streaming on the plate for controlling the motion of particles. The design procedure for producing the desired vibration modes and particle movement involved formulae, Global Matrix model (Disperse) and FE model

Ultrasound standing wave radiation force and laminar flow have been used to transfer yeast cells ... more Ultrasound standing wave radiation force and laminar flow have been used to transfer yeast cells from one liquid medium to another (washing) by a continuous field-flow fractionation (FFF) approach. Two co-flowing streams, a cell-free suspending phase (flow rate w 50% of the total flow-through volume) and a yeast suspension, were introduced parallel to the nodal plane of a 3 MHz

Resonant ultrasonic particle manipulators and their applications in sensor systems

Proceedings of IEEE Sensors, 2004., 2004

Page 1. Resonant Ultrasonic Particle Manipulators and their Applications in Sensor Systems Martyn... more Page 1. Resonant Ultrasonic Particle Manipulators and their Applications in Sensor Systems Martyn Hill1, Jeremy J Hawkes2, Nicholas R Harris3, Martin B McDonnell4. 1School of Engineering Sciences, University of Southampton ...

2001 IEEE Ultrasonics Symposium. Proceedings. An International Symposium (Cat. No.01CH37263), 2001

The forces on suspended particles in acoustic fields are reviewed briefly and the theoretical mod... more The forces on suspended particles in acoustic fields are reviewed briefly and the theoretical modelling of ultrasonic separators based on piezoelectrically excited layered resonators is described. Two flow-through resonator chamber concepts for ultrasonic particle (bio-cell) separation are investigated: a) the coagulation or sedimentation approach, b) the so-called h-shaped ultrasonic separator. The h-shaped ultrasonic separator is analysed by combining for the first time the mathematical modelling of the laminar flow with the acoustic force based velocity field of the particles relative to the suspension medium. This allows a complete modelling of the resonator's particle separation performance. Examples for separation chamber designs optimized by use of the mathematical model are presented and the calculated particle traces in the h-resonator are shown and compared with experimental results. For direct comparison of different ultrasonic flow through separator concepts a separation performance figure is introduced and its value is given for the two investigated separator concepts for the sample suspensions of polystyrene spheres, yeast and spirulina cells in (salt) water. The presented results are of importance for the state of the art design of acoustic cell filters for perfusion type bioreactors, as recently launched at the biotechnology market, as well as for the ultrasonic separation of plant (algae) cells under low gravity conditions, where the sedimentation concept fails.

Patterns of particles aggregation and streaming in resonating fluids

ABSTRACT Particles suspended in water move to pressure nodes in a standing wave due to the acoust... more ABSTRACT Particles suspended in water move to pressure nodes in a standing wave due to the acoustic radiation force. A current problem is the interaction between direct acoustic forces on particles and viscous drag forces from acoustic streaming. The result is an apparently chaotic picture which changes with time. Here we identify some patterns in the chaos. Our objective is to identify the influence of acoustic streaming on the formation and destruction of particle aggregates in nodal planes.

Microparticle manipulation in millimetre scale ultrasonic standing wave chambers

Ultrasonic standing wave chambers with acoustic pathlengths of 1.1 and 0.62 mm have been construc... more Ultrasonic standing wave chambers with acoustic pathlengths of 1.1 and 0.62 mm have been constructed. The chambers were driven at frequencies over the range 0.66-12.2 MHz. The behaviour of 2 microns diameter latex microparticles and 5 microns diameter yeast in the chambers has been elucidated. One (flow) chamber had a downstream laminar flow expansion section to facilitate observation of concentrated particle bands formed in the ultrasonic field. A second (microscopy) chamber allowed direct observation of band formation in the field and their characterisation by confocal scanning laser microscopy. Clear band formation occurs when the chamber pathlength is a multiple of half wavelengths at the driving frequency, so that the chamber rather than the transducer resonance has the most influence on band formation in this system. Band formation occurred in half-wavelength steps from a position one quarter of a wavelength off the transducer to a band at a similar distance from the reflector. Ordered band formation was preserved by the laminar flow in the expansion chamber, although bands that formed very close to the wall were dissipated downstream. The microscopy chamber provided evidence of significant lateral particle concentration within bands in the pressure nodal planes. The approaches described will be applicable to the manipulation of smaller particles in narrower chambers at higher ultrasonic frequencies.

Whole blood clarification in an ultrasonic standing wave

Particle filtration by a combination of ultrasound standing waves and laminar flow

A continuous¯ow microparticle ®lter that combines megahertz frequency ultrasonic standing waves a... more A continuous¯ow microparticle ®lter that combines megahertz frequency ultrasonic standing waves and laminar¯ow is described. The ®lter has a 0.25 mm, single half wavelength, acoustic pathlength at right angles to the¯ow. Standing wave radiation pressure on suspended particles drives them towards the centre of the acoustic pathlength. Clari®ed suspending phase from the region closest to the ®lter wall is drawn away through a downstream outlet. Experimental tests achieved >1000-fold clearance of 5 mm yeast cells, at a sample¯ow rate of 6 ml min À1 , from which the clari®ed aliquot is 1 ml min À1 . At this¯ow rate the average residence time in the sound ®eld was <1 s. Latex particles of 25, 9, 5.7, 2.8 and 1.5 mm diameter were also tested. The temperature increase during an operating period >1 h was less than 1 K. The design criteria considered in the fabrication of this high performance device are discussed. A theoretical model of the ®lter's ef®ciency, which considers the action of primary radiation force and the particle distribution across a laminar¯ow pro®le is presented here. The model predicts that totally clari®ed ®ltrate (i.e. zero suspended particles) may be drawn from the downstream outlet. The system described offers a generic approach to automated ®ltration in some applications. It is continuous¯ow thereby solving many of the problems of automation presented by batch ®lter methods and centrifuges. It could be developed for both larger scale and micro¯uidic applications. # (J.J. Hawkes). 0925-4005/01/$ ± see front matter # 2001 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 5 -4 0 0 5 ( 0 1 ) 0 0 5 5 3 -6

Modelling of layered resonators for ultrasonic separation

The potential of ultrasonic techniques for the separation and concentration of particles within a... more The potential of ultrasonic techniques for the separation and concentration of particles within a fluid has been investigated in some detail in recent years. Devices for effecting such separation typically consist of a piezoceramic transducer driving into a matching layer, fluid layer and reflector layer. This paper uses an equivalent-circuit transducer model, coupled with acoustic impedance transfer relationships to model such cells with regards to both their electrical characteristics and the strength of the resonance produced under different conditions. The model is compared with experimental results from two different cells and is shown to match experimental values well in terms of electrical characteristics and separator performance. The effects of matching layer thickness are also examined using the model. The importance of the adhesive bonding layer is demonstrated, and it is shown that the model can predict the effects of such a layer. The model is also used to demonstrate the effects of coincident resonances in cell layers and to examine the pressure distribution across cells at key frequencies.

Ultrasonics, 2000

There has been interest for a number of years in the possibility of separating blood into cells a... more There has been interest for a number of years in the possibility of separating blood into cells and plasma by methods other than centrifugation, so that the plasma can be analysed on-line. Cells in whole blood normally occupy about 45% of the suspension volume. It has been shown with a number of different cell types, such as yeast and bacteria, that for concentrations of this order the cells are not as efficiently harvested by ultrasound as those for lower concentrations. In this study, removal of cells from 3-4 ml whole blood volumes has been examined in ultrasonic standing wave fields from tubular transducers driven at a frequency of 1.6 MHz. Samples of whole human blood (n=11) from two volunteers have been processed by three tubular transducers where high levels of cell removal, 99.7% on average, have been demonstrated with high reproducibility between samples as well as for different transducers.

Analytical scale ultrasonic standing wave manipulation of cells and microparticles

Ultrasonics, 2000

The ultrasonic standing-wave manipulation of suspended eukaryotic cells, bacteria and submicron l... more The ultrasonic standing-wave manipulation of suspended eukaryotic cells, bacteria and submicron latex or silica particles has been examined here. The different systems, involving plane or tubular ultrasonic transducers and a range of acoustic pathlengths, have been designed to treat suspension volumes of analytical scale i.e. 5ml to 50μl for both sample batch and ‘on-line’ situations. Frequencies range from 1 to

Modelling of layered resonators for ultrasonic separation

Ultrasonics, 2002

The potential of ultrasonic techniques for the separation and concentration of particles within a... more The potential of ultrasonic techniques for the separation and concentration of particles within a fluid has been investigated in some detail in recent years. Devices for effecting such separation typically consist of a piezoceramic transducer driving into a matching layer, fluid layer and reflector layer. This paper uses an equivalent-circuit transducer model, coupled with acoustic impedance transfer relationships to model such cells with regards to both their electrical characteristics and the strength of the resonance produced under different conditions. The model is compared with experimental results from two different cells and is shown to match experimental values well in terms of electrical characteristics and separator performance. The effects of matching layer thickness are also examined using the model. The importance of the adhesive bonding layer is demonstrated, and it is shown that the model can predict the effects of such a layer. The model is also used to demonstrate the effects of coincident resonances in cell layers and to examine the pressure distribution across cells at key frequencies.

A laminar flow expansion chamber facilitating downstream manipulation of particles concentrated using an ultrasonic standing wave

Ultrasonics, 1998

Microparticles (yeast cells) in flowing suspensions have been concentrated in bands in pressure n... more Microparticles (yeast cells) in flowing suspensions have been concentrated in bands in pressure nodal planes of a standing wave chamber driven at resonant frequencies ranging from its thickness fundamental of 0.66 MHz to its 15th harmonic. An outlet laminar flow expansion chamber preserves particle order for many centimeters downstream from the transducer. The 10 mm outlet width has the potential

Lab on a Chip, 2011

[

Lab on a Chip, 2004

Ultrasound standing wave radiation force and laminar flow have been used to transfer yeast cells ... more Ultrasound standing wave radiation force and laminar flow have been used to transfer yeast cells from one liquid medium to another (washing) by a continuous field-flow fractionation (FFF) approach. Two co-flowing streams, a cell-free suspending phase (flow rate w 50% of the total flow-through volume) and a yeast suspension, were introduced parallel to the nodal plane of a 3 MHz standing wave resonator. The resonator was fabricated to have a single pressure nodal plane at the centre line of the chamber. Laminar flow ensured a stable interface was maintained as the two suspending phases flowed through the sound field. Initiation of the ultrasound transferred cells to the cell-free phase within 0.5 s. This particle transfer procedure circumvents the pellet formation and re-suspension steps of centrifuge based washing procedures. In addition, fluid mixing was demonstrated in the same chamber at higher sound pressures. The channel operates under negligible backpressure (cross-section, 0.25 6 10 mm) and with only one flow convergence and one flow division step, the channel cannot be easily blocked. The force acting on the cells is small; less than that experienced in a centrifuge generating 100g. The acoustically-driven cell transfer and mixing procedures described may be particularly appropriate for the increasingly complex operations required in molecular biology and microbiology and especially for their conversion to continuous flow processes. { Electronic supplementary information (ESI) available: movie of cell washing showing experimental visualisation of cell transfer, pdf showing CFD predictions of sodium fluorescein diffusion across the channel at a high and low flow rate. See http://www.rsc.org/suppdata/ lc/b4/b408045a/ { The contents of this paper include material subject to Crown