Ultrasound probe system

Most chemists working on sonochemistry in the laboratory will either use some form of ultrasonic bath or a commercial probe system. The latter instruments are often equipped with a pulse facility which was originally designed for biological cell disruption where temperature control is important. This pulse facility enables the power ultrasound to be delivered intermittently and thereby allow periods of cool-... 

Rehmann [90] has employed ultrasound to improve the yield of polyphenylene, thought at one time to have a future as a conducting material. Using dibromobenzene and a nickel complex catalyst he investigated both bath and probe systems and found that sonication led to improved yield when compared to the conventional synthesis (i. e. reflux) and also had the advantage of allowing the use of a lower temperature (20 °C). 

In general they found both enhanced reaction rates and polymers with lower poly-dispersities in the presence of ultrasound provided by both bath and probe systems. Higher ultrasonic intensities resulted in narrower molar mass distributions. 

The same workers [84] have also examined the copolymerisation of a-methylstyrene and 4-bromostyrene again with similiar effect using 25 kHz probe system. In the absence of an electrical potential but in the presence of ultrasound, they failed to produce any sonochemically-induced polymerisation of the monomer over a 24 h period. This is an important experiment since ultrasound is well knovm to produce radical species which could themselves influence polymerisation. 

Of the four types of laboratory ultrasonic apparatus commercially available for practising chemists in general (namely, whistle reactors, ultrasonic cleaning baths, probes and cup-horn devices) analytical chemists, except for a few specialists working in (or with) ultrasound detectors, use mainly cleaning baths and probes both of which are usually operated at a fixed frequency dependent on the particular type of transducer, that is usually 20 kHz for common probe systems and 40 kHz for baths. Both types of devices are described below. 

Cavitation, which is the source of the main effects of ultrasound, is also the origin of a common problem with probe systems tip erosion, which occurs despite the fact that most probes are made of a titanium alloy. There are two unwanted side effects associated with erosion, namely (a) metal particles eroded from the tip will contaminate the system and (b) physical shortening of the horn reduces efficiency — eventually, the horn will be too short to be efficiently tuned. The latter problem is avoided by... 

Figure 2.8. Continuous-flow laboratory manifolds for US-assisted processes. (A) One-way system for liquid-liquid extraction, (B) Open, one- or two-way leaching system and (C) Closed, one- or two-way leaching system. C — coil, CR — collection reservoir, IV — injeotion valve, LP — liquid phase, PC — personal computer, PL — propagating liquid, PP — peristaltic pump, SC — sample cell, SL — sample loop, S / — switohing value, UP — ultrasound probe and WB — water bath.

Figure 11. Effect of ultrasound power upon ferrocyanide voltammetry at platinum wire electrode. Insonation from 20-kHz horn probe system for all traces. The power was measured calorimetrically. Scan rate 25 mV sec-1 (taken from ref. 31).

The use of an ultrasonic bath has the advantages of simplicity, low cost, and modest power outputs reducing the likelihood of localized heating effects with ultrasound probe and cuphom systems. The most obvious limitations are that the operating frequency is normally fixed and power densities vary within the bath. Consequently standardization of sample locations is essential for comparative purposes. In our study, the water addition to the bath was as high as 230 mm from the bottom and the sample was fixed at the position of 180 mm from the bottom. The maximum power density with water as medium was obtained in the center and this location was used for all the following reactions. The power densities were 0.21W/ml, 0.28 W/ml, 0.36 W/ml and 0.48 W/ml, respectively, when the power outputs were 40 W, 60 W, 80 W and 100 W, respectively. 

Microelectromechanical systems (MEMS) combine the electronics of microchips with micromechanical features and microfluidics to create unique devices. The multitude of MEMS applications continues to grow including many types of accelerometers, radio frequency (RF) devices, variable capacitors, strain and pressure sensors, deformable micromirrors for image projection systems, vibrating micro-membranes for acoustic devices, ultrasound probes, micro-optical electromechanical systems (MOEMS) and MEMS gyroscopes, to name a few. 

More recently, there has been interest in robotic systems for manipulating ultrasound probes.Figures 29.10 and 29.21 show typical current research efforts in development of such robotic systems. Most of this activity has targeted diagnostic procedures such as systematic examination of carotid arteries for occlusions. However, these systems have the potential to become as ubiquitous as the robotic endoscope holders discussed above. Our research group at Johns Hopkins... 

The microwave-ultrasound combined system has been constructed from a Prolabo Maxidigest 350 single-mode microwave oven, in which a sonotrode is placed at the base for indirect ultrasonic agitation of the sample. The ultrasonic probe is placed at a sufficient distance from the electromagnetic field to avoid interactions and short-circuits. The use of this system has allowed the digestion of C03O4 and olive oil in shorter times than those required by the conventional method (from 3 to 1 h and from 45 to 30 min, respectively). 

Piezoelectric transducers are the most common devices employed for the generation of ultrasound and utilise ceramics containing piezoelectric materials such as barium titanate or lead metaniobate. The piezoceramic element commonly used in ultrasonic cleaners and for probe systems is produced in the form of a disk with a central hole. Ceramic transducers are potentially brittle and so it is normal practice to clamp them between metal blocks. This serves both to protect the delicate crystalline material and to prevent it from overheating by acting as a heat sink. Usually two elements are combined so that their overall mechanical motion is additive (Figure 10.4). Piezoelectric transducers are better than 95% electrically efficient and can operate over the whole ultrasonic range. 

Fig. 28.3. Close-up of biopsy experiment a robot (the IBM/ JHU LARS) holds the ultrasound probe and a second robot is used for positioning a needle guide. On both, an electromagnetic (EM) tracking system (Flock of Birds, model 6D FOB, Ascension Technology, Inc.) interfaces with the robot workstation. [Reprinted with permission from Boctor et al. (2004)]...

Vascular ultrasound has also greatly facilitated the implant process by easing axillary vein localization. Commercially available systems (Site Rite , Bard Access Systems, Salt Lake City, UT) include either a 9 or 7.5 MHz ultrasound probe to localize the axillary artery and vein. Differentiating the vein from artery is easily accomplished by compressing the structures with probe and noting which collapses more easily (Fig. 5.3). In patients with elevated right heart pressures, this same effect can be facilitated by having the patient inspire forcefully. 

Fig. 7.5 Micrographs of (a) apple and (b) potato tissue, untreated (non-US) and sonicated in water using a probe system (US). For sonicated samples, micrographs taken from the surface and at 800 [tm tissue depth are compared. Parameters of the ultrasound treatment with an ultrasonic...

Probe systems have been used to study the influence of ultrasound application on osmotic dehydration, for example the treatment of apples in sugar solutions (Carcel... 

The use of auxiliary energies to accelerate or increase the extraction efficiency of OBPs from OIW has scarcely been explored even though ultrasound and superheated extractants have been found to result in improved extraction. An attempt to extract BPs from alpemjo was made by using the continuous ultrasound-assisted method based on the approach illustrated in Figure 4.11, where the sample, held in the extraction chamber, was subjected to the action of an ultrasound probe meanwhile, the extractant (1 3 methanol-water) was recirculated in a closed circuit to ensure adequate mass transfer to the liquid phase under optimal working conditions. The direction of the extractant was changed at 40 s intervals to minimize dilution of the extract and compaction in the extraction cell, which could result in overpressure in the dynamic system [268]. 

Efficient dispersion of nanoparticles was achieved by sonicating with an ultrasound probe the PDMS and the appropriate amount of clay for 6 min, at room temperature. The crosslinking system was then added and dispersed into the mixture and the samples were cast into molds for subsequent cure at room temperature for 12 hours. 

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