Medium and interface components in impedance microbiology

Classic impedance microbiology (CIM) is based on the measurement of the impedance components that appear between a pair of electrodes submerged in a cell containing inoculated broth. Either a bipolar or a tetrapolar technique can be applied, requiring about 1 x 10(3) to 3 x 10(7) cells/ml to produce detectable changes in the impedance curves. Theoretical analysis of the electrode-electrolyte interface during bacterial growth is lacking, with no generally accepted measuring standards. Besides, there is considerable disagreement. We separated out the interface and medium components using the frequency variation technique (FVT) and also analyzed the interface reactance-resistance diagram, both before and after bacterial growth. Medium resistance Rm, interface reactance Xi, and interface resistance Ri, were quantified as time functions growth curves, from the complex bipolar impedance seen between two electrodes. We took into account the electrical current density, the temperature and the associated circuitry, also explaining the theoretical and experimental bases that justify the proposed dissecting procedure. It was found that, within the working frequency range, Rm, Ri, and Xi percental growth curves are frequency-independent, i.e., neither Rm(f), nor Xi(f) nor Ri(f) changed their slopes before, during and after bacterial growth. Besides, no alpha-dispersion effect in Rm curves was detected. It is concluded that impedance microbiology could become a fertile area for interdisciplinary knowledge; its development might offer new avenues for basic and applied research.     

Electrode and Electrolyte Impedance in the Detection of Bacterial Growth

The growth of bacteria in culture was found to produce impedance changes between two metal electrodes which result from changes both in conductivity and electrode impedance. Predominant changes were found in the imaginary impedance component at low frequency. Linear ac impedance characteristics were found in the relation between real and imaginary impedance components before and during bacterial growth. This linear relation is consistent with characteristics of diffusion and electron exchange (oxidation-reduction) at the electrode. The measurement of impedance in this system was limited below 100 Hz by nonlinearity in the voltage-current relation. Bacterial growth was best detected with stainless steel electrodes at low frequency (100 Hz) and including the imaginary component of impedance.     

Simple architecture low phase noise microwave cryogenic sapphire oscillators

The operation of a low phase noise 10.35 GHz microwave cryogenic sapphire resonator oscillator is demonstrated. Based on a very simple architecture, the oscillator presents phase noise performances of -104 dBrad²/Hz at f=10 Hz off the carrier (slope 1/f ³), lower than -152 dBrad²/Hz at f=1 kHz (slope 1/f), and of -160 dBrad²/Hz at fgsim10 kHz (white)     

Impedance analysis applicable to cardiac muscle and smooth musclebundles

An electrical equivalent circuit was constructed to represent a chain of five myocardial cells in a cardiac muscle bundle with various degrees of cell-to-cell coupling, and an impedance analysis was performed. The impedance across the entire network was measured at frequencies ranging from 10(1) to 10(6) Hz. The Bode plots were nearly superimposable for 1, 10, and 100 tunnels; for 10(3), 10(4), and 10(5) tunnels, the absolute zeta at 10 Hz was lower: e.g., 9.82 M omega for 1 tunnel compared to 6.64 M omega for 10(5) tunnels. The delta zeta 1/2 values were shifted to the left in the well-coupled cases: e.g., for 1 tunnel, f1/2 was 37.8 kHz, and for 10(5) tunnels, f1/2 was 1.2 kHz. For high coupling, the Bode plots contained a double component due to the end membranes. When Ro was increased by eight times, zeta increased by 7.47 fold (for 1 tunnel, 10 Hz), and by 3.72 fold (for 10(5) tunnels, 10 Hz). Raising Ro to x 12, x 100, and x 1000 produced a further and further shift to the left of the Bode plots. The total tissue resistivity (Rt) increased as a function Ro. Thus, in low coupling cases, almost all of the applied current passes through the interstitial space; e.g., at 1 tunnel (10 Hz), 1.0% of the current passes through the cell pathway (Rcell). The ratio of impedances at 10 kHz to 10 Hz (zeta 10kHz/zeta 10Hz) decreased with increasing tunnels (for Ro x 1). The ratio of resistivities at Ro x 8 to Ro x 1 (Rt'/Rt) was 7.47 for 1 tunnel. In contrast, the ratio at 10(5) tunnels was 3.73. It is concluded that it is difficult to determine the degree of cell coupling from such impedance analysis, unless the same tissue can be used for its own control, i.e., before and after a large change in cell coupling is introduced.     

传输型耦合介质振荡器的计算机辅助设计

介绍了一种HEMT管介质振荡器的计算机辅助设计方法。电路采用传输型耦合的介质谐振器作为稳频元件,确定振荡器的谐振频率。通过理论分析和计算机辅助优化设计,可以获得性能较好的介质振荡器。所设计介质振荡器的基本性能为:谐振频率f0=12 GHz,输出功率P0=8.6 dBm,在偏离载频100 kHz处相位噪声小于-140 dBc/Hz。     

Comparison of impedance at the microelectrode-saline andmicroelectrode-culture medium interface

The impedance characteristics of gold-plated indium-tin-oxide microelectrodes immersed in culture medium (MEM) are described and compared with the impedance characteristics observed when those microelectrodes are immersed in isotonic saline. For microelectrode areas of approximately 100 microns2, applied voltage levels of 5, 50, and 100 mV, and for frequencies of from 100 Hz to 10 kHz the resistance, capacitance, capacitive reactance, and total impedance are given as a function of frequency both in culture medium and in saline. The results, which hold for current densities ranging from 0.45 to 700 pA/microns2, are compared. Also given are the alpha and K values determining the frequency characteristics of the interface resistance and capacitance in medium and in saline.     

Low phase noise heterojunction bipolar transistor oscillator

A low phase noise, heterojunction bipolar transistor (HBT) oscillator has been designed and fabricated for operation at X-band. The common emitter oscillator employs a high-Q dielectric resonator as the parallel feedback element between the base and collector terminals. Series capacitive feedback is used in the emitter to enhance the oscillator's negative output impedance. Single-sideband FM noise levels of -76 dBc/Hz and -102 dBc/Hz have been achieved at 1 kHz and 10 kHz frequency offsets, respectively, for an 11.06 GHz carrier frequency. This is one of the lowest phase noise levels ever reported for an X-band solid-state transistor oscillator.<>     

多频声频率成分与感知倒谱距离的初步研究

通过理论计算和主观实验,研究了多频声频率成分在不同频响曲线下与感知倒谱距离和主观评价之间的关系.针对所选定的9种频响曲线和7种节目信号,当频率范围为1～10 kHz之间时,感知倒谱距离与主观评价的相关系数最高仅为0.93,最低为0.80,7种信号中只有3种的主客观相关系数高于0.90.而当频率范围为50～15 000 Hz时,感知倒谱距离与主观评价的相关系数最大达到了0.96,最低为0.85,7种信号中有5种的主客观相关系数都高于0.90.从而得出了在频率成分个数较少的情况下,频率范围比频率间隔需要更优先考虑的结论.     

A 250 Hz spectral linewidth 1.5 mu m MQW-DFB laser diode with negative-electrical-feedback

A 1.5 mu m corrugation-pitch-modulated MQW-DFB laser diode (LD) with multielectrodes was frequency stabilized using the negative electrical feedback technique. The FM response of the LD was precisely measured and used for the feedback loop design. The FM noise of the LD was reduced and reached 10 Hz/sup 2//Hz at 1 kHz>     

Frequency-modulation sensitivity of Gunn oscillators

It is shown that, when Gunn oscillators are frequency-modulated by means of a small a.c. component superimposed on the bias supply, the resulting microwave-frequency deviation and the impedance presented by the diode to the modulation supply are dependent on the modulation frequency. The magnitudes of the frequency-modulation sensitivity and diode terminal impedance have been measured for modulation frequencies in the range 100Hz?100kHz.     

Spectra of Auditory Brainstem Responses and Spontaneous EEG

Human auditory brainstem responses (ABR's) are sensory evoked potentials that can be recorded within a few milliseconds following a transient acoustic stimulus. This paper describes results of a simulation study that evaluated alternative techniques for estimating the spectrum of the ABR signal and of the background EEG. The effects of residual noise in the average signal, the number of responses in the average, and the use of smoothing windows were considered. Spectra of human ABR's were also obtained. The spectral energy decreases with frequency to 2 kHz and seems to flatten above 2 kHz. The ABR signal spectrum is limited to below approximately 1.5 kHz. There are three main components: a low-frequency component around 100 Hz, a midfrequency component around 500 Hz, and a high-frequency component at 1000 Hz. Narrow-band filtering suggests that the midfrequency component is primarily associated with Jewett wave V, while the high-frequency component is primarily associated with the early Jewett waves. These two components are probably the most important for determining the latencies of waves. The low-frequency component appears to correspond to a slow wave on which the Jewett waves are superimposed.     

Harmonics terminated L-band frequency quadrupler using composite right/ left-handed transmission line

A design method for an L-band frequency quadrupler with composite right/left-handed transmission line is proposed. The left-handed transmission line in the proposed frequency quadrupler suppresses the fundamental component (f0), while the composite right/left-handed λ/4 open stub reduces unwanted higher-order harmonics. From the experimental results, unwanted harmonics are suppressed to achieve harmonic distortion of 51 dBc minimum with output phase noise of -94.34 dBc/Hz at 10 kHz offset.     

Temporal resolution of the skin impedance measurement in frequency-domain method

The temporal-resolution of the frequency-domain method for the identification of the impedance locus depends on the basis frequency used in the current waveform construction, i.e., the higher basis frequency provides the better temporal resolution. The impedance locus can be characterized by the impedance parameters Z0, beta, and taum. The frequency distribution of limited number of data in the impedance locus would affect the accuracy of the estimated impedance parameters. Therefore, we investigated the relationship between the estimation accuracy of the impedance parameters and the frequency coverage of the impedance locus in relatively low to high impedance conditions (dc impedance Z0= 51 k ohms - 45 M ohms). As the basis frequency, 100 Hz was enough for the usual impedance with Z0 less than 203 k ohms. On the other hand, 10 Hz and 1 Hz were required for the medium-level (Z0 = 517 k ohms), and high-level (Z0 = 45 M ohms) impedance, respectively. The required basis frequency, accordingly the temporal resolution, depended much on the central relaxation time taum which affects the frequency distribution on the impedance locus. The results of this study are expected to serve as the reference of the frequency selection in the frequency-domain analysis of the skin impedance.     

1/f voltage noise in silicon planar bipolar transistors

Measurements on silicon planar transistors in the frequency range 1 Hz?1 kHz have shown conclusively that 1/f noise is present on the equivalent input noise-voltage generator. In some samples of transistors, correlation between the 1/f components of voltage and current noise was detected. In one sample, an estimate of the correlation coefficient was made, the result being a coefficient of approximately ?0.1.     

调制转移光谱稳频的研究

532nm激光的碘吸收谱线的频率被国际计量委员会(CIPM)推荐用于频率计量标准．激光频率标准对长度和时间的计量是很重要的。碘分子在532nm附近有丰富的强吸收谱线．可以作为频率稳定的绝对参考谱线。使用532nm单块固体激光器，在375kHz新的调制频率下．利用调制转移技术，将激光频率调谐到^127I2的R(56)32—0跃迁的吸收谱线，并观察到该吸收谱线相应的15条超精细结构分量。通过展宽的调制谱线可以看出375kHz的调制频率得到比312kHz调制频率更高的鉴频敏感度．并在实验上成功地将激光频率稳定在碘的超精细吸收谱线的α10，分量上长达10h，估计稳定度在10^-13量级。准确的频率稳定性正在两台激光器上用拍频的方法进行测量。     

A low-phase-noise digitally controlled crystal oscillator for DVB TV tuners

This paper presents a 25-MHz fully-integrated digitally controlled crystal oscillator(DCXO) with automatic amplitude control(AAC).The DCXO is based on Colpitts topology for one-pin solution.The AAC circuit is introduced to optimize the phase noise performance.The automatic frequency control is realized by a 10-bit thermometer-code segmental tapered MOS capacitor array,ensuring a～35 ppm tuning range and～0.04 ppm frequency step.The measured phase noise results are-139 dBc/Hz at 1 kHz and-151 dBc/Hz at 10 k...     

基于高次谐波体声波谐振器的微波振荡器设计

基于高次谐波体声波谐振器(HBAR)的高品质因数(Q)值和多模谐振特性,设计了Colpitts和Pierce两种形式的微波振荡器。采用HBAR与LC元件组成谐振回路的方法,与放大电路构成反馈环路直接基频输出微波频段信号。Colpitts振荡器输出信号频率为980 MHz,信号输出功率为-4.92dBm,信号相位噪声达-119.64dBc/Hz@10kHz;Pierce振荡电路输出信号频率达到2.962GHz,信号输出功率为-9.77dBm,信号相位噪声达-112.30dBc/Hz@10kHz。     

Circuit Models and Simulation Analysis of Electromyographic Signal Sources?I: The Impedance of EMG Electrodes

The impedance of surface and intramuscular biopotential electrodes was measured during rest and muscle contraction in humans. A frequency-dependent parallel RC circuit model of the skin-electrode interface that captures the dependence of this impedance on the size and geometry of electrode placement was developed and its components were estimated. The model could explain between 86-97 percent of the variations in impedance (Z), 72-92 percent of the variations in resistance (R), and 34-93 percent of the variations in capacitance (C). The impedance and resistance of these electrodes decrease by about tenfold for a 20-fold increase in frequency, while the capacitance decreases by about twofold for the same change in frequency (f). Thus, the overall FRC factor of this parallel RC circuit model remains nearly unchanged over the range of frequencies studied (50-2000 Hz). A significant difference was found between the impedances of the electrodes comprising the differential electrode pair. This imbalance in impedance was between 8-14 percent for surface electrodes and 6-19 percent for wire electrodes. These data provide essential design criteria for the development and simulation of a system for the measurement of electromyographic activity.     

A fully integrated 5.8 GHz U-NII band 0.18-/spl mu/m CMOS VCO

A fully integrated 5.8 GHz CMOS L-C tank voltage-controlled oscillator (VCO) using a 0.18-/spl mu/m 1P6M standard CMOS process for 5 GHz U-NII band WLAN application is presented. The VCO core circuit uses only PMOS to pursue a better phase noise performance since it has less 1/f noise than NMOS. The measurement is performed by using a FR-4 PCB test fixture. The output frequency of the VCO is from 5860 to 6026 MHz with a 166 MHz tuning range and the phase noise is -96.9 dBc/Hz at 300 kHz (or -110 dBc/Hz at 1 MHz) with V ctrl = 0 V. The power consumption of the VCO excluding buffer amplifiers is 8.1 mW at V/sub DD/ = 1.8 V and the output power is -4 dBm.     

穿孔机械阻抗板的吸声特性研究

为提高低频吸声性能,在机械阻抗板(MIP)上穿少量微孔形成穿孔机械阻抗板(MIPMP)吸声结构。对MIPMP结构吸声性能进行初步研究,建立计算模型,用驻波管测量吸声系数。结果表明,MIPMP结构的吸声为机械阻抗和微穿孔的共同作用。吸声曲线出现两个吸声峰:一个在200~300 Hz,由机械阻抗引起,吸声系数可达0.95;一个出现在300~600Hz,由微穿孔引起。计算模型与实验结果所示趋势一致:随穿孔率的增大,机械阻抗单元吸声峰值先增大后减小,向高频移动,微穿孔单元吸声峰值逐渐减小,带宽增大,向高频移动;随背腔的增厚,机械阻抗单元吸声峰值变大,频率基本不变,微穿孔单元吸声峰值略减小,向低频移动。MIPMP与微穿孔板(MPP)构成的复合吸声结构在200~1 600Hz有好的吸声性能。