Brad Lindseth

Chip-scale atomic magnetometer with improved sensitivity by use of the Mx technique

The fabrication and performance of a miniature optically pumped atomic magnetometer constructed with microfabricated components are discussed. This device measures the spin precession frequency of Rb87 atoms to determine the magnetic field by use of the Mx technique. It has a demonstrated sensitivity to magnetic fields of 5pT∕Hz1∕2 for a bandwidth from 1to100Hz, nearly an order of magnitude improvement over our previous chip-scale magnetometer. The 3dB bandwidth has also been increased to 1kHz by reconfiguring the miniature vapor cell heater.

Chip Scale Atomic Magnetometers

An optically pumped magnetometer was drastically miniaturized, by taking advantage of MEMS techniques, producing the chip-scale atomic magnetometers (CSAM) physics package. The key component of the package is an alkali vapor cell. To probe the magnetic field experienced by the atoms, the injection current to the VCSEL was modulated at 3.4 GHz near half the hyperfine frequency of 87Rb. Lock-in detection is used to determine the center of the resonance, and the magnetic field is determined by counting the modulation frequency, which is related to the Larmor precession frequency under these locked conditions. The ITO heaters create a large magnetic field gradient, which broadens the resonance and reduces the sensitivity.

A New Portable 449-MHz Spaced Antenna Wind Profiler Radar

This paper presents the design of a 449-MHz radar for wind profiling, with a focus on modularity and solid-state transmitter design. It is one of the first wind profiler radars to use low-cost Laterally Diffused Metal Oxide Semiconductor (LDMOS) power amplifiers (PAs) combined with spaced antennas. The system is portable and designed for 2-3 month deployments. The transmitter PA consists of three 1-kW peak power modules which feed 54 antenna elements arranged in a hexagonal array, scalable directly to 126 elements. The PA is operated in pulsed mode with a 10% duty cycle at 54% power added efficiency. The antenna array is designed to have low sidelobes, confirmed by measurements. The radar was operated in Boulder, Colorado and Salt Lake City, Utah. Atmospheric wind vertical and horizontal components at altitudes between 200 m and 4 km were calculated from the collected atmospheric return signals.

Non-contact measurement of cardiac electromagnetic field in mice by use of a microfabricated atomic magnetometer

The development of clinical applications of magnetocardiography has been impeded by the large size of the systems used to measure magnetic fields. Here we present the first measurements of the cardiac electromagnetic field with a highly miniaturized (20 mm3), atomic magnetometer constructed by microfabrication techniques. Measurements were performed in two mice. The magnetometer was placed close to the sternum region, approximately 2 mm away from the surface of the skin. QRS complexes were identifiable in the magnetocardiographic signals in all recordings except for those performed when the animal was moved far away (>10 cm) from the sensor. Non-contact recording of cardiac electromagnetic fields with a microfabricated magnetometer is feasible in a shielded environment.

Wind Profiler Radar Antenna Sidelobe Reduction

This paper addresses sidelobe reduction of an antenna array pattern for reducing effects of ground or sea clutter of zenith-looking wind profiler radar. Simulations are performed for various shapes of compact clutter fences for a 915-MHz Doppler radar and a 449-MHz interferometric radar. It is shown that minimal low-cost hardware modifications to existing compact ground planes of the 915-MHz radar allow for reduction of sidelobes of up to 5 dB. The results obtained on a single array are extended to a 449-MHz triple hexagonal array interferometric radar. Cross-correlation, transmit beamwidth, and sidelobe levels are evaluated for various clutter fence configurations and array spacings. The resulting sidelobes are as much as 10 dB below those without a clutter fence and can be easily incorporated into existing and future 915 and 449-MHz wind profiler systems with minimal hardware modifications.

Low-cost 63% efficient 2.5-kW UHF power amplifier for a wind profiler radar

This paper describes a low-cost 449-MHz 2.5-kW peak pulse amplifier for use in a wind profiling radar. New high-power LDMOS transistors are enabling the use of kilowatt level pulse power amplifiers for under US25¢/W in transistor costs. With pulse duty cycles of 10–20%, kilowatt modules with efficiencies greater than 60% can be combined to achieve multi-kilowatt transmitters, allowing higher transmit powers and improved radar signal to noise ratio.

Chip-scale atomic devices at NIST

We provide an overview of our research on chip-scale atomic devices. By miniaturizing optical setups based on precision spectroscopy, we have developed small atomic sensors and atomic references such as atomic clocks, atomic magnetometers, and optical wavelength references. We have integrated microfabricated alkali vapor cells with small low-power lasers, micro-optics, and low-power microwave oscillators. As a result, we anticipate that atomic stability can be achieved with small size, low cost, battery-operated devices. Advances in fabrication methods and performance are presented.

First results from the NCAR 449 MHz, 126-element wind profiler radar

The National Center for Atmospheric Research (NCAR) Earth Observing Laboratory has recently developed a 449-MHz spaced antenna wind profiler radar. The system is divided into 18-element linearly polarized circular patch antenna subarrays that can be reconfigured. Three of the 18-element subarrays were combined and have been deployed to field projects such as the Persistent Cold-Air Pool Study (PCAPS).

Chip-scale atomic magnetometer

We report recent improvements on our microfabricated atom-optical magnetometer. Using a semiconductor laser and 1 mm³ alkali vapor cell, our magnetometer detects a magnetic field at 50 pT / Hz^1/2 sensitivity in a 12 mm³ package.