Objective: Muscle contractions are commonly detected by performing EMG measurements. The major disadvantage of this technique is that mechanical disturbances to the electrodes are in the same frequency and magnitude range as the desired signal. In this work we propose an approach and a realized measurement system to combine EMG and bioimpedance measurements for higher reliabilities of muscle contraction detections. Methods: We propose the development of a modular four-channel measurement system, whereat each channel is capable of acquiring EMG, the bioimpedance magnitude and phase, simultaneously. The modules are synchronized by an additional interface board, which communicates with a PC. A graphical user interface enables to control the bioimpedance excitation current in a range from 100 µA to 1 mA in a frequency range from 50 kHz to 333 kHz. Results: A system characterization demonstrated that bioimpedance magnitude changes of less than 250 ppm and phase changes below 0.05° can be detected reliably. Measurements from a subject have shown the timing relationship between EMG and bioimpedance signals as well as their robustness against mechanical disturbances. A measurement of five exemplary hand gestures has demonstrated the increase of usable information for detecting muscle contractions. Conclusion:Bioimpedance measurements of muscles provide useful information about contractions. Furthermore, the usage of a known high-frequency excitation current enables a reliable differentiation between the actual information and disturbances. Significance: By combining EMG and bioimpedance measurements, muscle contractions can be detected much more reliably. This setup can be adopted to prostheses and many other human-computer interfaces.

Objective: Bioimpedance measurements are mostly performed utilizing gel electrodes to decrease the occurring electrode-skin impedance. Since in many measurement environments this kind of electrode is not appropriate, the usability of dry electrodes is analysed. Approach: The development of five different kinds of dry electrodes, including gold, stainless steel, carbon rubber and metallized textile as contact materials are proposed. All test electrodes are based on a circular printed circuit board as carrier and have the same contact surface dimensions. To compare the electrodes' characteristics, the occurring electrode-skin impedances are measured under variation of signal frequency, contact duration, contact pressure, placement position and subjects. Additionally, all measurements are performed with silver/silver chloride (Ag/AgCl) dry gel electrodes for comparison purposes. Main results: The analysed parameters play a significant role regarding the electrode-skin impedance. Choosing a wise setup of these parameters can decrease the electrode-skin impedance of dry electrodes down to ranges of dry gel electrodes and even below. Significance: The usage of dry electrodes is one of the most difficult challenges when transferring scientific measurement techniques to clinical environments or commercial products but it is indispensable for many applications like body composition measurements or prosthesis control.

Pulse wave analysis is an important method used to gather information about the cardiovascular system. Instead of detecting the pulse wave via pressure sensors, bioimpedance measurements can be performed to acquire minuscule changes in the conductivity of the tissue, caused by the pulse wave. This work presents a microcontroller-based bioimpedance measurement system, which has the capability to acquire impedance measurements from up to four independent channels simultaneously. By combining a problem-specific analog measurement circuit with a 24 bits analog-to-digital converter, the system is capable of acquiring 1000 impedances per second with a signal-to-noise ratio in a range from 92 to 96 dB. For data storage and analysis, the digitized data are sent via universal serial bus to a host PC. A graphical user interface filters and plots the data of all channels in real-time. The performance of the system regarding measuring constant impedances, as well as impedance changes over time is demonstrated. Two different applications for pulse wave analysis via multichannel bioimpedance measurements are presented. Additionally, first measurement results from a human subject are shown to demonstrate the system's applicability of analyzing the pulse wave morphology as well as the aortic pulse wave velocity.

Electrical impedance tomography (EIT) is an imaging method that is able to estimate the electrical conductivity distribution of living tissue. This work presents a field programmable gate array (FPGA)-based multi-frequency EIT system for complex, time-resolved bioimpedance measurements. The system has the capability to work with measurement setups with up to 16 current electrodes and 16 voltage electrodes. The excitation current has a range of about 10 µA to 5 mA, whereas the sinusoidal signal used for excitation can have a frequency of up to 500 kHz. Additionally, the usage of a chirp or rectangular signal excitation is possible. Furthermore, the described system has a sample rate of up to 3480 impedance spectra per second (ISPS). The performance of the EIT system is demonstrated with a resistor-based phantom and tank phantoms. Additionally, first measurements taken from the human thorax during a breathing cycle are presented. OPEN ACCESSElectronics 2015, 4 508