Joan Carletta

A Micromachined High Throughput Coulter Counter for Bioparticle Detection and Counting

We describe a micromachined Coulter counter with multiple sensing microchannels for quantitative measurement of polymethacrylate particles and pollen. A unique design with sensing microelectrodes in the center of the microchannels is demonstrated. This design creates isolation resistances among channels, and thus circumvents the crosstalk caused by automatic electrical connection among microchannels. When implemented using microfluidic channels, this design is appropriate for the sensing of microscale particles in deionized water or in dilute electrolyte solution. Our design has multiple channels operating in parallel, but integrated with just one sample reservoir and one power source. The results with a four-channel device show that this device is capable of differentiating and counting micro polymethacrylate particles and Juniper pollen rapidly. Moreover, the device throughput is improved significantly in comparison to a single-channel device. The concept can be extended to a large number of sensing channels in a single chip for significant improvement in throughput.

Detection and counting of micro-scale particles and pollen using a multi-aperture Coulter counter

We demonstrate a high throughput, all-electronic Coulter-type sensor with four sensing microapertures to detect and count micro-scale particles. Four particle samples are utilized for this study: polymethacrylate particles 40 µm and 20 µm in diameter, Juniper Scopulorum (Rocky Mountain Juniper) pollen and Cottonwood pollen particles. The two types of pollen particles are roughly 20 µm in diameter. The particles are mixed with deionized water and forced to pass through the microapertures. Voltage pulses across all four apertures are recorded and analysed. Results demonstrate that the sensor can detect and count particles through its four sensing apertures simultaneously. Thus, the counting efficiency of the four-aperture sensor is approximately 300% higher than that of a single-channel Coulter counter, while maintaining the same accuracy, sensitivity and reliability. The counting efficiency can be improved further by integrating more sensing channels on a single micromachined chip. Results also demonstrate that the device can be used to differentiate between pollen and polymethacrylate particles; differentiation is based on a difference in surface charge for the two types of particles.

An efficient architecture for lifting-based two-dimensional discrete wavelet transforms

An architecture for the lifting-based two-dimensional discrete wavelet transform is presented. The architecture is easily scaled to accommodate different numbers of lifting steps. The architecture has regular data flow and low control complexity, and achieves 100% hardware utilization. Symmetric extension of the image to be transformed is handled in a way that does not require additional computations or clock cycles. The architecture is investigated in terms of hardware parameters such as memory size and number of ports, number of memory accesses, latency, and throughput. The proposed architecture achieves higher throughput and uses less embedded memory than architectures based on convolutional filter banks.

A methodology for FPGA-based control implementation

When used for digital compensator implementation, field-programmable gate arrays (FPGAs) allow the use of a short sampling period, and of a customized fixed-point hardware definition wherein each coefficient and each state variable may be represented using a different number of bits. A methodology is presented based on the control system L/sub 1/ or l/sub 1/ norms for computing the appropriate number of bits to represent each quantity. The methodology is shown to be effective for designing hardware for both traditional shift-form and delta-form representations of the compensator. The methodology is applied to the implementation of a magnetic bearing control system. In this example, a delta-form realization requires less hardware than a shift-form realization, and provides a closer approximation to the original analog compensator. The results show that the methodology is useful for the comparison of competing digital compensator structures.

A microfluidic multichannel resistive pulse sensor using frequency division multiplexing for high throughput counting of micro particles

In this work we demonstrate an on-chip multiplexed multichannel resistive pulse sensor (Coulter counter) for high throughput counting of microscale particles. The design, fabrication and testing of this device are presented. The high throughput counting is a result of using multiple parallel microfluidic channels to analyze the sample. Detection is achieved by using frequency division multiplexing; each microchannel is modulated with its own known and unique frequency, a combined measurement is made across a single pair of electrodes, and the measured signal is demodulated to determine the signal across each individual channel. Testing results using 30 µm polystyrene particles demonstrate that the throughput of the multiplexed device gets improved 300% over a single-channel device; this is achieved by simultaneously detecting particles through the devices four parallel channels. In addition, the ac modulation method used in this paper reduces the polarization effect on the microelectrodes, and thereby allows for measurement of the particle sizes with significantly reduced error. The multiplexed detection principle can be extended to a larger number of channels to further improve the throughput, without increasing the external detection electronics.

Capacitive Coulter Counting: Detection of Metal Wear Particles in Lubricant Using a Microfluidic Device

A microfluidic device based on the capacitance Coulter counting principle to detect metal debris particles in lubricant oil is presented. The device scans each individual metal debris particle as they pass through a microfluidic channel by monitoring the capacitance change. We first proved the feasibility of using the capacitance Coulter counting principle for detecting metal particles in a fluidic channel. Next, we tested the microfluidic device with aluminum abrasive particles ranging from 10 to 25 µm; the testing results show the microfluidic device is capable of detecting metal wear particles in low-conductive lubricant oil. The design concept demonstrated here can be extended to a device with multiple microchannels for rapid detection of metal wear particles in a large volume of lubricant oil.

Determining appropriate precisions for signals in fixed-point IIR filters

This paper presents an analytical framework for the implementation of digital infinite impulse response filters in fixed-point hardware on field programmable gate arrays. This analysis is necessary because FPGAs, unlike fixed register size digital signal processors, allow custom bit widths. Within the framework, the designer determines the number of bits necessary for representing the constant coefficients and the internal signals in the filter. The coefficient bit widths are determined by accounting for the sensitivity of the filters pole and zero locations with respect to the coefficient perturbations. The internal signal bit widths are determined by calculating theoretical bounds on the ranges of the signals, and on the errors introduced by truncation in the fixed-point hardware. The bounds tell how many bits are required at any point in the computation in order to avoid overflow and guarantee a prescribed degree of accuracy in the filter output. The bounds form the basis for a methodology for the fixed-point digital filter implementation. The methodology is applied to the implementation of a second-order filter used as a compensator in a magnetic bearing control system.

A direct mapping FPGA architecture for industrial process control applications

Industrial process control is an untapped market for field programmable gate arrays (FPGAs). Programs used for industrial process control are traditionally written in a graphical language called relay ladder logic, and implemented on programmable logic controllers (PLCs). The mapping of ladder logic onto typical FPGAs is a lengthy process, and results are hard to verify. We propose an FPGA architecture implementing relay ladder logic directly. Conversion to Boolean algebra is eliminated. Technology mapping is simple and direct. Placement and routing are also considerably simpler than in the general FPGA case. The architecture scales to devices of differing sizes and resources. This paper describes the FPGA architecture, and its role in high performance industrial process control.

A microfluidic Coulter counting device for metal wear detection in lubrication oil

We present the design, fabrication, and testing of a microfluidic device for metal wear detection in lubrication oils. The detection is based on the capacitance Coulter counting principle, that is, on the change in a microchannels capacitance caused by the presence of a metal particle in the microchannel. The testing of the microfluidic device using 10-25 microm aluminum particles has demonstrated the feasibility for detection and counting of microscale metal particles in low-conductive lubrication oils. This microfluidic device is promising for online oil debris detection by the use of multiple detection microfluidic channels.

A real-time implementation of gradient domain high dynamic range compression using a local Poisson solver

This paper presents a real-time hardware implementation of a gradient domain dynamic range compression algorithm for high dynamic range (HDR) images. This technique works by calculating the gradients of the HDR image, manipulating those gradients, and reconstructing an output low dynamic range image that corresponds to the manipulated gradients. Reconstruction involves solving the Poisson equation. We propose a Poisson solver that utilizes only local information around each pixel along with special boundary conditions, and requires a small and fixed amount of hardware for any image size, with no need to buffer the entire image. The hardware implementation is described in VHDL and synthesized for a field programmable gate array (FPGA) device. The maximum operating frequency achieved is fast enough to process high dynamic range videos with one megapixel per frame at a rate of about 100 frames per second. The hardware is tested on standard HDR images from the Debevec library. The output images produced have good visual quality.