A customer has an Electronic Spin Resonance (ESR) experiment. ESR is based on the fact that the magnetic moment of an electron precesses in an applied magnetic field, not unlike a child's top in a gravitational field, at a well-defined frequency called the Larmor frequency. Electromagnetic radiation at the Larmor frequency, when impinging on such an electron, will be preferentially absorbed. This principle is identical to that employed in Nuclear Magnetic Resonance (NMR), where the atomic nucleus precesses. In NMR, Larmor frequencies are of order 100 MHz. Because the electron is 2000 times lighter than the proton, however, ESR Larmor frequencies are of order 100 GHz, and microwave cavity systems are required. In NMR, shifts in Larmor frequencies may arise from changes in the electron density about a resonating nucleus. By contrast, ESR directly probes the resonating electron and is therefore a powerful tool to study the electronic properties and chemical bonds in solids.
In the customer's ESR experiment, the sample sits in a microwave cavity surrounded by an electromagnet. The cavity is excited by broadband microwave radiation that is abruptly switched off. The subsequent microwave radiation emitted by the sample is monitored as it decays over about one second. The different frequency components observed in this radiation indicate different electronic environments or chemical bonds within the sample.
The ~100 GHz microwave signal is put through mixer circuits to shift the central frequency down to ~100 kHz. The customer wants to sample this mixed-down signal at 10 MS/s in order to capture as many harmonics as possible. He also wants 12-bit resolution to permit the detection of small amounts of a given frequency. Finally, the customer needs to sample continuously for 10 seconds, which will give a fine frequency resolution of 1/10 s = 0.1 Hz, or one part per million.
The GaGe solution is a CompuScope1012/PCI A/D board and a 256 MB MMD 5400 PCI memory board in a GaGePC 586 computer. The experimental setup is illustrated below. The CS1012/PCI provides the 10 MS/s sampling and 12-bit resolution that the customer requires. (In single-channel mode, the card can actually sample at rates up to 20 MS/s.)
Since there are 2 bytes per 12-bit sample, the continuous data creation rate is 20 MB/s. This is well below the 100 MB/s continuous throughput achievable using PCI Real Time Transfer in the GaGePC 586.
Using PCI Real Time Transfer, the CS1012/PCI does not store incoming data in on-board memory, but puts it directly on the PCI bus. The CS1012/PCI becomes the PCI Initiator and streams data directly to the PCI Target without CPU mediation. A 2kS FIFO buffer onboard the CS1012/PCI ensures no data loss due to occasional PCI bus latencies. The PCI Target device, often PC RAM, is in this case the 256 MB MMD5400 PCI memory board.
With a data storage rate of 20 MB/s for 10 s, the total amount of data is 200 MB. The customer has consequently chosen the 256 MB MMD 5400 board. If in future the customer wants to sample faster or for a longer time, an MMD board with up to 2 GB of memory can be purchased.
Once all the captured data is in the MMD board, it may be PCI transferred to PC RAM, to storage media or to a PCI Digital Signal Processing (DSP) board for processing and later display. This GaGePC-based solution will replace the outdated, inflexible and expensive dedicated acquisition system that the customer previously used.
We encourage you to contact us and discuss your research & development application in more detail with our engineering team. GaGe can provide tailored custom data acquisition hardware and software solutions to meet specific application requirements.