Mirrored Modified Howland Circuit for Bioimpedance Applications: Analytical Analysis

Bertemes-Filho, Pedro; Negri, Lucas Hermann; Felipe, Alexandre; Vincence, V. C.

doi:10.1088/1742-6596/407/1/012030

Cited by 14 publications

(7 citation statements)

References 11 publications

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“…We note that the value obtained is consistent with values reported for modelled current sources without multiplexers (e.g. Bertemes-Filho et al, 2012). An improvement in the output impedance of the current generator at the higher frequencies can be achieved by using resistors of tolerance better than 1% and higher frequency opamps (Bertemes-Filho et at., 2012;Bertemes-Filho et al, 2016).…”

Section: Discussionsupporting

confidence: 89%

“…Bertemes-Filho et al, 2012). An improvement in the output impedance of the current generator at the higher frequencies can be achieved by using resistors of tolerance better than 1% and higher frequency opamps (Bertemes-Filho et at., 2012;Bertemes-Filho et al, 2016). Additionally, measurement of injected current amplitude can increase the impedance measurement accuracy and that may be implemented in future designs.…”

Section: Discussionmentioning

confidence: 99%

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A Multi-Frequency Focused Impedance Measurement System Based on Analogue Synchronous Peak Detection

2021

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Monitoring of anatomical structures and physiological processes by electrical impedance has attracted scientists as it is noninvasive, nonionizing and the instrumentation is relatively simple. Focused Impedance Method (FIM) is attractive in this context, as it has enhanced sensitivity at the central region directly beneath the electrode configuration minimizing contribution from neighboring regions. FIM essentially adds or averages two concentric and orthogonal combinations of conventional Tetrapolar Impedance Measurements (TPIM) and has three versions with 4, 6, and 8 electrodes. This paper describes the design and testing of a multi-frequency FIM (MFFIM) system capable of measuring all three versions of FIM at 8 frequencies in the range 10 kHz—1 MHz. A microcontroller based multi-frequency signal generator and a balanced Howland current source with high output impedance (476 kΩ at 10 kHz and 58.3 kΩ at 1 MHz) were implemented for driving currents into biological tissues with an error <1%. The measurements were carried out at each frequency sequentially. The peak values of the amplified voltage signals were measured using a novel analogue synchronous peak detection technique from which the transfer impedances were obtained. The developed system was tested using TPIM measurements on a passive RC Cole network placed between two RC networks, the latter representing skin-electrode contact impedances. Overall accuracy of the measurement was very good (error <4% at all frequencies except 1 MHz, with error 6%) and the resolution was 0.1 Ω. The designed MFFIM system had a sampling rate of >45 frames per second which was deemed adequate for noninvasive real-time impedance measurements on biological tissues.

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Section: Discussionsupporting

confidence: 89%

Section: Discussionmentioning

confidence: 99%

A Multi-Frequency Focused Impedance Measurement System Based on Analogue Synchronous Peak Detection

2021

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Section: Development Of Feedback Systemmentioning

confidence: 99%

“…The current has a constant value regardless of the DUT using OPA655 operational amplifiers. These op-amps were chosen as they outperformed three others in a study by Bertemes-Filho et al [15]. In addition, a B&K Precision model 4053 Function Generator (B&K Precision Corp, Yorba Linda, CA, USA) is used to generate the 50 kHz 1 Vpp sinusoidal wave that is used as the reference signal.…”

Section: Development Of Feedback Systemmentioning

confidence: 99%

Design of an Impedance-Controlled Hot Snare Polypectomy Device

Thornton

Choi

2019

Sensors

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This paper goes through the process of first designing a feedback system that allows for the measuring of impedance while using the hot snare polypectomy method. The electrosurgical unit used in this study was the Olympus PSD-30. After the impedance-controlled feedback system was completed, the device was tested under a range of power settings from 10 W–50 W. The test was performed ex vivo using porcine colon samples. Using the information gathered from these tests, a technique of determining the threshold of perforation and implementing a system to automatically stop the applied current from the PSD-30 was developed. The data showed that after an increase in impedance of 25% from that of the initially measured impedance, perforation ensued in the tissue samples. Using this information, the device was programmed to interrupt the PSD-30 at this threshold point. This final design was tested and proved able to automatically prevent the event of perforation from occurring, resulting in the ability to prevent serious complications.

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“…In order to improve the stability of the circuit, two single-ended Howland circuits can be set together in order to have a differential output rrent, which is also called cu Figure 6 [17]. This type of current source uses two equal input voltages with 180 degrees phase shift from each other but also has a unique reference for both sides of the circuit, which, in turns, reduce the feed-through capacitance between output and input.…”

Section: Mirrored Howland Current Source: Modelingmentioning

confidence: 99%

High Accurate Howland Current Source: Output Constraints Analysis

Bertemes-Filho¹,

Felipe²,

Vincence³

2013

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Howland circuits have been widely used as powerful source for exciting tissue over a wide frequency range. When a Howland source is designed, the components are chosen so that the designed source has the desired characteristics. However, the operational amplifier limitations and resistor tolerances cause undesired behaviors. This work proposes to take into account the influence of the random distribution of the resistors in the modified Howland circuit over the frequency range of 10 Hz to 10 MHz. Both output current and impedance of the circuit are deduced either considering or the operational amplifiers parameters. The probability density function due to small changes in the resistors of the circuit was calculated by using the analytical modeling. Results showed that both output current and impedance are very sensitive to the resistors variations. In order to get higher output impedances, high operational amplifier gains are required. The operational amplifier open-loop gain increases as increasing the sensitivity of the output impedance. The analysis done in this work can be used as a powerful co-adjuvant tool when projecting this type of circuit in Spice simulators. This might improve the implementations of practical current sources used in electrical bioimpedance.

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Mirrored Modified Howland Circuit for Bioimpedance Applications: Analytical Analysis

Cited by 14 publications

References 11 publications

A Multi-Frequency Focused Impedance Measurement System Based on Analogue Synchronous Peak Detection

A Multi-Frequency Focused Impedance Measurement System Based on Analogue Synchronous Peak Detection

Design of an Impedance-Controlled Hot Snare Polypectomy Device

High Accurate Howland Current Source: Output Constraints Analysis

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