Hypodermic needle electrode

In electrostatic atomization, an electrical potential is applied between a liquid to be atomized and an electrode placed in the spray at a certain distance from liquid discharge nozzle. As a result of the mutual repulsion of like charges accumulated on the liquid surface, the surface becomes unstable and disrupts when the pressure due to the electrostatic forces exceeds the surface tension forces of the liquid. Droplets will be generated continuously if the electrical potential is maintained above a critical value consistent with liquid flow rate. Both DC and AC systems have been employed to provide high electrical potentials for generating fine droplets. Many configurations of electrode have been developed, such as hypodermic needles, sintered bronze filters, and cones. 

The most important use of iridium is as an alloying metal for platinum and palladium. Such alloys are used for jewelry, decorative purposes, electrical contacts, thermocouples, crucibles, electrodes, hypodermic needles, and medical accessories. Iridium enhances resistance of platinum to chemical attack and corrosion. It also enhances hardness and tensile strength. The radioisotope Ir-192 is used in examination of ferrous welds and in other radiographic applications. 

Iridium oxide, Ir02, is used in the fabrication of thin films for stable electrochromic materials and as an electrode material. Iridium metal is used in the manufacture of fountain pen points, airplane spark plugs, and hypodermic needles, see also Inorganic Chemistry. 

Figure 1 Equipment used for measuring dissolved oxygen and pH profiles from the soil surface. On the left is shown, the specially-designed steel probe (with white markings for each 5 cm), with the inner rod which has the measuring sensor attached. The middle image shows the dissolved oxygen micro-sensor with protective hypodermic needle. The image to the right shows the pH electrode...

FIGURE 25.6 Needle electrodes for subcutaneous EMG recordings. For the single fiber and concentric electrodes, the cannula of the hypodermic needle acts as reference electrode. The monopolar electrode is used with a remote reference electrode. 

Fine wires can also be introduced into tissue using a hypodermic needle, which is then withdrawn. This wire can remain in tissue for acute or chronic measurements. Caldwell and Reswick [6] and Knutson et al. [7] have used fine coiled wire electrodes that were placed through the skin into the skeletal muscle for several years without adverse effects. The advantage of the coil is that it makes the electrode very flexible and compliant. This helps it and the lead wire to endure the frequent flexing and stretching that occurs in the body without breaking. 

In FIA, chemical-sensing field-effect transistors (Chem. FETs) and ion-selective field-effect transistors (ISFETs) (see sections 2.1.3 and 2.1.4) can be used with notable advantages over the more familiar membrane electrodes - namely miniaturization capability, high signal-to-noise ratio, faster response, decreased contribution of the detector to the creation of sample dispersion, etc. [346]. These types of potentiometric detectors can be reduced in size, enabling their incorporation into a hypodermic needle or other suitable probe, for making in vivo measurements [347]. 

For emergency use when chronic implantation is contraindicated, a single coaxial bipolar electrode is useful. This scheme requires the use of one needle instead of two. The electrode is shown schematically in Figure 1.1. The unit is a No. 18 standard hypodermic needle to which has been added an external insulating sheath and an insulated internal central electrode. It is used in cases of temporary heart block or until corrective procedures can be instituted in the case of permanent block (Ferris and Cowley, 1968). 

The Caldwell-Reswick electrode is a helix of nichrome resistance wire filled internally with a silicone rubber core. A retaining hook is located on the distal end The electrode is placed by means of a 23-gauge hypodermic needle in the same manner as the cardiac electrode shown in Figure 8.1. This electrode can be placed directly into a muscle. The silastic core and the helical assembly minimize electrode breakage. Placement and removal of the electrode is quick and easy. 

The spear-type glass pH microelectrode can be made with a long shank which can be inserted into a hypodermic needle having an inside diameter as small as 100 microns. We have made such electrodes with the sensing part of the electrode resting in the bevel of the needle. These are difficult to clean. Foreign materials have a tendency to accumulate in the bevel. 

A typical apparatus for electrospinning of polymers consists of a nozzle, a high-voltage power supply, a container for polymer fluid, and an electrode collector of an injection pump with a hypodermic syringe (Fig. 1.2]. The solution is pumped through the needle/ nozzle, a grounded collector that can be either stationary or rotating. Experiments can also be carried out in a box in order to precisely control environmental conditions such as temperature and relative humidity. 

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