Multi-channel Amplifier System Research Articles

Design of a wideband multi-channel system for time reversal hyperthermia

Purpose: To design and test a wideband multi-channel amplifier system for time reversal (TR) microwave hyperthermia, operating in the frequency range 300 MHz–1 GHz, enabling operation in both pulsed and continuous wave regimes. This is to experimentally verify that adaptation of the heating pattern with respect to tumour size can be realised by varying the operating frequency of the antennas and potentially by using Ultra-wideband (UWB) pulse sequences instead of pure harmonic signals.Materials and methods: The proposed system consists of 12 identical channels driven by a common reference signal. The power and phase settings are applied with resolutions of 0.1 W and 0.1°, respectively. Using a calibration procedure, the measured output characteristics of each channel are interpolated using polynomial functions, which are then implemented into a system software algorithm driving the system feedback loop.Results: The maximum output power capability of the system varies with frequency, between 90 and 135 W with a relative power error of ±6%. A phase error in the order of ±4° has been achieved within the entire frequency band.Conclusions: The developed amplifier system prototype is capable of accurate power and phase delivery, over the entire frequency band of the system. The output power of the present system allows for an experimental verification of a recently developed TR-method on phantoms or animals. The system is suitable for further development for head and neck tumours, breast or extremity applications.

Design and test of a 434 MHz multi-channel amplifier system for targeted hyperthermia applicators

Purpose: For our head-and-neck hyperthermia (HT) applicator, an amplifier system with full amplitude and phase-control to deliver the radio-frequency signals, was not available. We therefore designed and tested a 433.92 MHz multi-channel amplifier system.System description: The design consists of a direct digital synthesizer (DDS) system that generates 12 phase-controlled coherent 433.92 MHz signals, which are amplified to maximum 200 W output per channel. Directional couplers are placed at the amplifiers to couple a small portion of both forward and reflected signals to gain-and-phase detectors. The power setting is applied with a resolution of 2 W and for the phase it is 0.1°. The channels are sequentially sampled at 100 Hz per channel.Methods: We tested the performance of the designed amplifier system by measuring the RF spectrum, power and phase accuracy, and by characterising the feedback control by using highly accurate power and phase meters.Results: The spurious emission is less than 60 dBc and the first two harmonic frequencies are suppressed more than 45 dB. The measurement accuracy for the power (±5%) is valid for at least 20 days after calibration and for the phase (±5°) it is valid for at least 2 months.Conclusions: The amplifier system operates according to our design criteria to support targeted HT. It can be used for both our in-house developed superficial and head-and-neck HT applicators or any other HT applicator that works on the same frequency of 433.92 MHz.

Pacemaker phase shift in the absence of neural activity in guinea‐pig stomach: a microelectrode array study

Gastrointestinal (GI) motility is well organized. GI muscles act as a functional syncytium to achieve physiological functions under the control of neurones and pacemaker cells, which generate basal spontaneous pacemaker electrical activity. To date, it is unclear how spontaneous electrical activities are coupled, especially within a micrometre range. Here, using a microelectrode array, we show a spatio-temporal analysis of GI spontaneous electrical activity. The muscle preparations were isolated from guinea-pig stomach, and fixed in a chamber with an array of 8 x 8 planar multielectrodes (with 300 microm in interpolar distance). The electrical activities (field potentials) were simultaneously recorded through a multichannel amplifier system after high-pass filtering at 0.1 Hz. Dihydropyridine Ca(2+) channel antagonists are known to differentiate the electrical pacemaker activity of interstitial cells of Cajal (ICCs) by suppressing smooth muscle activity. In the presence of nifedipine, we observed spontaneous electrical activities that were well synchronized over the array area, but had a clear phase shift depending on the distance. The additional application of tetrodotoxin (TTX) had little effect on the properties of the electrical activity. Furthermore, by constructing field potential images, we visualized the synchronization of pacemaker electrical activities resolving phase shifts that were measurable over several hundred micrometres. The results imply a phase modulation mechanism other than neural activity, and we postulate that this mechanism enables smooth GI motility. In addition, some preparations clearly showed plasticity of the pacemaker phase shift.

Time synchronized measurement of multi-bridge force transducers

This report describes the analysis and evaluation of a multi-bridge force transducer with a newly developed multi-channel amplifier system, which is able to measure the different individual strain gauge full bridges with up to eight high-precision amplifiers in an absolutely simultaneous way and with small measurement uncertainty. With the suitable evaluation software, it is then possible to calculate the sums and differences of the different output signals and with those, perform an analysis of the force transducer’s measurement behavior. It is also possible to gain results of the behavior of the materials testing machines in the presence of side forces, moments as well of swinging of the masses of dead weight force standard machines.

Multichannel system for high precision static and fast dynamic measurements

This paper describes a multichannel system which is equally well suited for high-speed dynamic measurements as well as precise high-resolution static measurements, fulfilling both tasks simultaneously. The system is based on a new ADC principle which is able to convert analogue signals into fast digital data streams without loss of information in resolution or bandwidth. All signal conditioning can thus be carried out digitally and therefore without errors. All items of interest in the analogue input signals — e g, mean values, fast peak levels or alternating signals — are also included in the digital data streams and can be extracted simultaneously by parallel working computer algorithms. The complete system consists of three well adapted parts, the Digital Multichannel Amplifier System DMC9012A, a Macintosh Computer and a software package called ‘BEAM’, which provides a very user-friendly graphic interface and all the important data processing functions. It is a ‘turnkey’ solution which relieves the user of many tedious installation and setting tasks.

Multi-channel amplifier system for computerized topographic EEG analysis

Topographic analysis of EEG and evoked potentials requires the computer processing of data from multi-lead recording. The use of 20 or more channels is now quite common, straining the resources of the usual EEG machine. We present a design for a high gain, low noise, 32-channel amplifier matched to computer data acquisition requirements. Low cost and small size are additional benefits to the design.