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Recent developments in telemedicine have caused significant interest in the prolonged monitoring of bioelectric signals. This drives the search for easy-to-use, biocompatible, and environmentally friendly alternatives to conventional resistive wet electrodes. Here we demonstrate the use of Coconut-Oil and Carbon Black based stretchable dry electrodes to monitor electrophysiological signals without the need for conductive gels. The developed material is embedded into an elastomer matrix, exhibits a specific resistance ρ of 33.2 12.3 Ω m, high conformability, and a stretchability up to 1500±%. The realised epidermal electrodes were used to record Electrocardiographic (ECG) signals in a 3-lead configuration and compared to commercial wet electrodes. Even after being elongated by 100 % for 100 stretch/release cycles, a reliable recording of the QRS-complex is demonstrated without the need for any contact enhancing or skin irritating substances, proving its potential use in long term ECG monitoring applications.

Measuring electric potentials using encapsulated flexible probes is advantageous especially when the signal source is comprised of soft and irregular organic tissues, such as the human brain or muscle fibers. However, the capacitive nature of encapsulated probes demands circuits with ultra-high input impedance and low 1/f noise, which are not trivially achieved using flexible transistors. Here, we show an a-IGZO based capacitive bootstrapped cascode buffer where the input impedance is actively controlled to allow capacitive electric potential measurements. By exploring different biasing schemes of the cascode element, we show a relative gain of 55 dB and a bandwidth between 450 Hz and 19 kHz.

Non-contact imaging of electric potentials with micro-metre resolution can provide relevant insights in material characterisation, electrostatic charge imaging and bio-sensing applications. However, scanning electric potential microscopes have been confined to rigid and single-probe devices, making them slow, prone to mechanical damage and complex to fabricate. In this work, we present a novel 5-element flexible array of electric potential probes with spatial resolution down to $20 \mu \mathrm{m}$ which reduces the scanning time by a factor of 5 when compared to a single probe device. This was achieved by combining flexible thin-film probes for active guarding and shielding with state-of-the art discrete conditioning circuits. The potential of this approach is showcased by using the fabricated array to image latent fingerprints deposited on an insulating surface by contact electrification. This is the first example of a micro-scale array of electric potential sensors.

The zero potential technique is an efficient way to selectively condition passive resistive sensor arrays. However, for flexible wearable sensor systems, the currently utilised amplifiers are not desirable as they are normally based on rigid devices. We present a variation of the zero potential approach utilising flexible thin-film transimpedance amplifiers. This integrated amplifier is based on IGZO thin-film transistors (TFTs) and has a measured cut-off frequency of $\approx 4$ kHz, which is sufficient for most sensing applications. To understand the performance when conditioning a grid of sensors, the flexible system was simulated and compared to the results obtained from rigid transimpedance amplifiers. While these rigid devices led to virtually no crosstalk between sensors, the flexible transimpedance amplifier maintained a selectivity factor of nearly 3. At the same time, the fully flexible IGZO amplifier can be seamlessly integrated with a flexible sensor array and has a footprint of only 1.6 mm2. This approach can enable easily manufactureable, fully flexible, and wearable sensor systems with a minimum number of active devices, avoiding active matrix structures and individual sensor conditioning while maintaining a certain level of sensitivity.

Safety requirements and physical constraints often prohibit contacting high voltage terminals. This limits the options for monitoring and maintaining high voltage machinery and power distribution grids. We present a non-contact AC (alternating current) voltage and frequency measurement system with 600 mm of operation range to overcome this issue. The method relies on measuring the electric potential of an AC voltage source using a single capacitive electrometer. Simultaneously, the distance from the AC source is measured using time-of-flight sensors. By combining the data from both sensors, AC voltages can be measured accurately without the need for any galvanic contact. The system is packaged in a handheld battery powered form factor. Measurements of voltages between 25 VRMS and 250 VRMS and distances from 25 mm to 600 mm demonstrated accuracy within 4%. Furthermore, frequencies between 5 Hz to 500 Hz were measured with 10 mHz of resolution. The presented technique can be used as a test and measurement instrument where the source terminals are inaccessible or as a wearable safety device in high-voltage environments.