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Research Papers

A Novel, Needle-Array Dry-Electrode With Stainless Steel Micro-Tips, for Electroencephalography Monitoring

[+] Author and Article Information
J. K. Radhakrishnan

Defence Bioengineering and
Electromedical Laboratory (DEBEL), DRDO,
Bangalore 560093, India
e-mail: jk.radhakrishnan@debel.drdo.in

S. Nithila, S. N. Kartik, U. K. Singh

Defence Bioengineering and
Electromedical Laboratory (DEBEL), DRDO,
Bangalore 560093, India

T. Bhuvana

Indian Institute of Technology Kanpur,
Kanpur 208016, India

G. U. Kulkarni

Jawaharlal Nehru Centre for Advanced Scientific
Research (JNCASR),
Bangalore 560093, India

1Corresponding author.

Manuscript received October 3, 2017; final manuscript received August 16, 2018; published online September 21, 2018. Assoc. Editor: Chris Rylander.

J. Med. Devices 12(4), 041001 (Sep 21, 2018) (7 pages) Paper No: MED-17-1321; doi: 10.1115/1.4041227 History: Received October 03, 2017; Revised August 16, 2018

A novel, needle array dry electrode consisting of 10 × 10 array of stainless steel (SS) Microtips was developed for electroencephalography (EEG) monitoring. The developed dry electrode uses commercially available, inexpensive, SS acupuncture needles certified for invasive use, to collect the EEG signal. The microtips of the acupuncture needles project out of a flat Teflon base by approximately 150 μm. Mechanical failure analysis was carried out, with theoretical calculations for individual needles and experimental measurements with a universal testing machine (UTM). The theoretically calculated critical load for failure for individual needle was 0.88 N, while the UTM measurements show the failure occurring at 0.95 N; this difference is probably due to the simplified assumptions used in calculations. The UTM measurements of the individual needle applied against a Silicone elastomer reveal that the force required for the penetration of the needle of the electrode into skin maybe as low as 0.01 N. Needle array insertion into silicone elastomer sheet and its optical inspection was carried out to assess the ability of the microneedles to penetrate the skin. The impedance of the electrode, measured in three electrode configuration in 0.9% NaCl solution, was approximately 6.8KΩ at 20 Hz, which is sufficiently low to fulfill the requirements of biopotential measurement. The construction and characteristics of the developed needle array dry electrode show that they are suitable for penetrating the stratum corneum of the skin and acquire the EEG signal directly from the interstitial fluidic layer underneath. The construction of the electrode and its mechanical and electrical characteristics show that it is a promising dry electrode for long duration EEG Monitoring.

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Figures

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Fig. 1

Photographs of microneedle array dry-electrode, with 10 × 10 array of SS microtips projecting out of a flat Teflon base. The needle array with Teflon base (a) over a stainless steel stub with a press-button type back contact and (b) over a polymer cup with SS base having a press-button type back contact.

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Fig. 2

Optical micrograph of the acupuncture needle tip used for the needle array electrode fabrication (internal angle at the conical tip is 24 deg)

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Fig. 3

Scanning electron micrograph of a part of the microneedle array dry electrode, showing the microneedles projecting out of the Teflon base

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Fig. 4

Photographs of (a) an individual acupuncture needle and (b) the needle array electrode, mounted in the UTM

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Fig. 5

The plot between critical load for failure versus length, for a SS needle of tapered geometry

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Fig. 6

Displacement versus axial load curve, for a single needle applied against an aluminum block

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Fig. 7

Optical images of a single needle applied against aluminum block in UTM: (a) pre and (b) post UTM measurement

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Fig. 8

(a) Load versus displacement curve for a single needle applied against a Silicone elastomer block and (b) the single needle penetrating into the Silicone elastomer block, upon application of load in UTM

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Fig. 9

Load versus displacement curve for the needle array electrode with 100 microtips, applied against a Silicone elastomer block

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Fig. 10

Optical micrographs (5× magnification) of the Silicone elastomer surface, applied with needle array electrode containing 20 microtips. (a) sites of microtip penetration visible as dark punctured spots and (b) circular white impressions of the circular openings in the Teflon base.

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Fig. 11

Typical (a) impedance and (b) phase characteristics of the needle array electrode

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