AC susceptometry give information on how fast magnetization is building up in a material. Different types of magnetization processes can be detected with AC susceptometry such as magnetization reversal in magnetic single domains (Néel relaxation), random rotation of particles containing thermally blocked single-domains (Brownian relaxation) and domain-wall motion that occur in poly-domain materials. All of these magnetization processes create a specific response in the AC susceptibility measurement. In the field of magnetic nanoparticles and AC susceptometry we have a large collaborate international network. The DynoMag system is a portable easy to use AC susceptometer for measuring the dynamic magnetic properties of liquids, powders and solids. The excitation frequency range is from 1 Hz up to 500 kHz with a resolution in volume susceptibility 1·10-5 (SI units) at 1 kHz and field amplitude 0.5 mT. The DynoMag system has been developed at Swedish ICT Acreo – Sensor Systems since 2000 internally and in a EU FP6 project, Biodiagnostics.

The Biodiagnostics project was a large collaborative project regarding using MNP and different types of magnetic detection principles. At Acreo we used changes in the dynamic magnetic response in order to sense binding activities of biomolecules. Today we have sold internationally DynoMag systems to both academia and industry for mostly magnetic characterization of magnetic nanoparticles. We are also involved in a Vinnova financed project with the Ångström Laboratory in Uppsala in the field of bio-detection using magnetic nanoparticles and AC susceptometry. The HF AC susceptometer system is a AC susceptometer for measuring the dynamic magnetic properties of liquids, powders and solids. The excitation frequency range is from 25 kHz up to 10 MHz with a resolution in volume susceptibility 4.10-5 (SI units) at 100 kHz and field amplitude 30 µT. The HF AC susceptometer system was developed at Swedish ICT Acreo – Sensor Systems since 2008 internally and in a EU FP7 project Nano3T.

The Nano3T project was focused on studying and optimizing MNPs for magnetic hyperthermia. Together with the DynoMag system we are able to detect the dynamic magnetic properties of magnetic material in the frequency range from 1 Hz to 10 MHz, thus we cover mostly all of the interesting magnetic relaxations of magnetic nanoparticle systems.ac unit how many tons Peter Björkholm, Sensor systemspeter.bjorkholm [at] acreo.seac window unit alternativesLeaf Wetness Sensors / 237-Lac unit 6 ton Sensitive yet DurableCompatible with most Campbell Scientific dataloggers The 237 measures leaf wetness by determining the electrical resistance on the surface of the sensor (a wet surface is less resistant). It is primarily used to determine the percentage of time that a leaf surface is wet, versus the time it is dry.

Note: The 237 is designed for short duration ac excitation; dc excitation or continuous ac excitation may damage the sensing grid. Sensor is shipped unpainted so customer can choose appropriate surface finish that best fits their application Imitates characteristics of a leaf Compatible with all Campbell Scientific dataloggers (including the CR200(X) series) The "-L" on a product model indicates that the cable length is specified at the time of order. The 237 consists of a circuit board with interlacing gold-plated fingers. Condensation on the sensor lowers the resistance between the fingers, which is measured by the datalogger. Droplets must touch two fingers simultaneously to change the sensor resistance. For this reason, the 237 is typically coated with flat latex paint, which spreads water droplets. The color and type of paint affect sensor performance. Campbell Scientific supplies the sensor unpainted allowing customers to determine the appropriate paint to apply to the sensor's surface.

The appropriate pigmentation should closely emulate the properties of a typical leaf. The resistance of the sensor at the wet/dry transition point should be determined. A sharp change in resistance occurs in the wet-dry transition on the uncoated sensor; normally the transition is between 50 and 200 kohms. Coated sensors have a poorly defined transition which normally occurs from 20 kohms to above 1,000 kohms. For best results, the leaf wetness sensor should be field calibrated since the transition point will vary for different areas and vegetation. Resistance at Wet/Dry Transition Normally 50 and 200 kohm (uncoated sensor) Normally 20 to 1000 kohm (coated sensor) Short-Term Survivability Temperature Range -40° to +150°C Sensor may crack when temperature drops below -40°C. 7.6 x 7.1 x 0.64 cm (3.0 x 2.75 x 0.25 in.) 91 g (3 oz) with 3.05-m (10-ft) cable The 237 requires one single-ended analog input and one switched excitation channel for measurement.

237 Leaf Wetness Sensor 237-L Leaf Wetness Sensor Number of FAQs related to 237-L: 13 What type of paint should be used on the surface of the 237-L? Paint only with a flat latex paint. Usually, a high-quality, white, flat latex paint is used with a tiny amount of pigment. What is the distance between the two electrodes in the 237-L? What are the power requirements of the 237-L? Variable, but always negligible. The theoretical maximum for each measurement is 5000 mV at 5 µA for less than 3 ms. Can the 237-L generate a specific moisture content?The sensor signal can only be interpreted as either wet or dry. Is there a difference in the wetness duration between the 237-L and the leaf because of the difference in thermal conductivity?The thermal characteristics of the 237-L are probably different from those of any surrounding objects, including leaves. Consequently, the 237-L will dry at a rate different from surrounding objects, including leaves.

How should the 237-L be mounted? The mounting method used depends on the application. In plant canopies, consider mounting the 237-L so that it receives the least amount of solar radiation at noon. This means tipping the sensor, electrodes up, so that its sensing surface is parallel to the plane of the ecliptic. Tipping the sensor also minimizes the chance of water puddling on its surface. On non-living surfaces, such as a man-made structure, consider mounting the 237-L flat against a flat surface on the shady side. This will cause the 237-L’s thermal characteristics to be more similar to those of the surface being studied. Can the 237-L be used as a conductivity sensor? The 237-L is not designed to be used as a conductivity sensor. To our knowledge, a few people have tried this but have been unsuccessful. Is the 237-L really a sensor? Only in the most basic sense. The signal output from the 237-L can only be interpreted as an indication of the presence of a conductive material bridging the two electrodes on its surface.

If the circuit is open (infinite resistance or zero conductance), there is no conductive material.  If the circuit is closed, there is conductive material. The primary use of the 237-L is to indicate the presence of free water on the surface of surrounding objects. Consequently, the 237-L will dry at a rate different from surrounding objects, including leaves. Data from the 237-L are only interchangeable from measurement site to measurement site if the following are true: Each 237-L is prepared and maintained in the same way. Each 237-L is mounted in nearly identical environments. Plant disease researchers found that if a 237-L sensor was placed in a plant canopy at a consistent position, with a consistent coating of a spreading material on its surface (that is, paint), they could estimate when free water was in the plant canopy. From this discovery, they were able to formulate disease emergence models. The resulting models tolerate significant deviation in moisture-presence data.