| Active noise cancellation with WaveGuard |
| By means of the shielded electrodes you are able to record quality EEG in conditions where conventional electrode systems will not work. For instance, when you are doing EEG/ERP research 'in the field' using a portable ERP system, you will not have your special shielded room with you. In these cases the active shielding of your electrode leads will still give you good quality recordings. Active shielding of the electrodes works only when the EEG amplifier and the cap are shielded. The ASA-Lab amplifier and WaveGuard cap system are the only products available that follow this innovative concept! |
Example The images on the right show a comparison between the power spectra of the EEG measured with a conventional cap (electro-cap, ECI) and that measured with the cap using the shielded electrodes. This recording was carried out in the USA in a normal EEG lab. No filtering was applied to the data. As you can see, the power spectrum of the conventional cap (shown on the left) shows a clear peak around the 60 Hz. Spectrum comparison and time-frequency plots of the signal at electrode CZ: using the Electro-cap (left), and the WaveGuard cap (right). Environmental noise is clearly reduced in case shielded electrodes are used! |  |
How does it work? The Waveguard caps are equipped with individual shielded micro-coax leads for each EEG channel that connect with the micro-coax inputs on the headbox. Only the combination of both micro-coax leads in the cap and the amp makes the active shielding function. In case we put 'normal' leads on the caps their would be no shield around the signal cable making it much more sensitive to electromagnetic noise. This electromagnetic or environment noise can be caused by e.g. a power wire of electrical equipment, a USB cable that is connected with a computer, lighting in the ceiling or an air-conditioning installation. The biggest source of interference in measured EEG signals results from the capacitive coupling of the cables with the mains (50 / 60 Hz)*. In the asa-lab amplifiers, the shields of the micro-coax cables are driven with the measured signal from the inner wire. We call this technique active shielding. Active shielding reduces the capacitive coupling effect extremely. For optimal results active shielding is applied for each channel separately. |  |
Key benefits of active shielding | ||||
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